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Climate Change 2014

Synthesis Report

Edited by

The Core Writing Team

Synthesis Report

IPCC

Rajendra K. Pachauri

Chairman

IPCC

Leo Meyer

Head, Technical Support Unit

IPCC

Core Writing Team

Rajendra K. Pachauri (Chair), Myles R. Allen (United Kingdom), Vicente R. Barros (Argentina), John Broome (United Kingdom), Wolfgang

Cramer (Germany/France), Renate Christ (Austria/WMO), John A. Church (Australia), Leon Clarke (USA), Qin Dahe (China), Purnamita

Dasgupta (India), Navroz K. Dubash (India), Ottmar Edenhofer (Germany), Ismail Elgizouli (Sudan), Christopher B. Field (USA), Piers

Forster (United Kingdom), Pierre Friedlingstein (United Kingdom/Belgium), Jan Fuglestvedt (Norway), Luis Gomez-Echeverri (Colombia),

Stephane Hallegatte (France/World Bank), Gabriele Hegerl (United Kingdom/Germany), Mark Howden (Australia), Kejun Jiang (China),

Blanca Jimenez Cisneros (Mexico/UNESCO), Vladimir Kattsov (Russian Federation), Hoesung Lee (Republic of Korea), Katharine J. Mach

(USA), Jochem Marotzke (Germany), Michael D. Mastrandrea (USA), Leo Meyer (The Netherlands), Jan Minx (Germany), Yacob Mulugetta

(Ethiopia), Karen O’Brien (Norway), Michael Oppenheimer (USA), Joy J. Pereira (Malaysia), Ramón Pichs-Madruga (Cuba), Gian-Kasper

Plattner (Switzerland), Hans-Otto Pörtner (Germany), Scott B. Power (Australia), Benjamin Preston (USA), N.H. Ravindranath (India), Andy

Reisinger (New Zealand), Keywan Riahi (Austria), Matilde Rusticucci (Argentina), Robert Scholes (South Africa), Kristin Seyboth (USA),

Youba Sokona (Mali), Robert Stavins (USA), Thomas F. Stocker (Switzerland), Petra Tschakert (USA), Detlef van Vuuren (The Netherlands),

Jean-Pascal van Ypersele (Belgium)

Technical Support Unit for the Synthesis Report

Leo Meyer, Sander Brinkman, Line van Kesteren, Noëmie Leprince-Ringuet, Fijke van Boxmeer

Referencing this report

IPCC, 2014: Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the

Intergovernmental Panel on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151 pp.

THE INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE

First published 2015

ISBN 978-92-9169-143-2

This publication is identical to the report that was approved (Summary for Policymakers) and adopted (longer report) at the 40th session of the

Intergovernmental Panel on Climate Change (IPCC) on 1 November 2014 in Copenhagen, Denmark, but with the inclusion of copy-edits and

errata that have been corrected prior to this publication. These pre-publication errata are available at: http://www.ipcc.ch.

The designations employed and the presentation of material on maps do not imply the expression of any opinion whatsoever on the part of the

Intergovernmental Panel on Climate Change concerning the legal status of any country, territory, city or area or of its authorities, or concerning

the delimitation of its frontiers or boundaries.

The mention of speciﬁc companies or products does not imply that they are endorsed or recommended by IPCC in preference to others of a similar

nature, which are not mentioned or advertised.

The right of publication in print, electronic and any other form and in any language is reserved by the IPCC. Short extracts from this publication

may be reproduced without authorization provided that complete source is clearly indicated. Editorial correspondence and requests to publish,

reproduce or translate articles in part or in whole should be addressed to:

IPCC

c/o World Meteorological Organization (WMO)

7bis, avenue de la Paix Tel.: +41 22 730 8208

P.O. Box 2300 Fax: +41 22 730 8025

CH 1211 Geneva 2, Switzerland E-mail: IPCC-Sec@wmo.int

www.ipcc.ch

Cover: Design by Laura Biagioni, IPCC Secretariat, WMO

Photos:

I - Folgefonna glacier on the high plateaus of Sørfjorden, Norway (60°03’ N - 6°20’ E).

II - Planting of mangrove seedlings in Funafala, Funafuti Atoll, Tuvalu. © David J. Wilson

III - China, Shanghai, aerial view. © Ocean/Corbis

Foreword, Preface

and Dedication

/167

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ClimateChange2014SynthesisReportEditedbyTheCoreWritingTeamRajendraK.PachauriLeoMeyerSynthesisReportChairmanHead,TechnicalSupportUnitIPCCIPCCIPCCCoreWritingTeamRajendraK.Pachauri(Chair),MylesR.Allen(UnitedKingdom),VicenteR.Barros(Argentina),JohnBroome(UnitedKingdom),WolfgangCramer(Germany/France),RenateChrist(Austria/WMO),JohnA.Church(Australia),LeonClarke(USA),QinDahe(China),PurnamitaDasgupta(India),NavrozK.Dubash(India),OttmarEdenhofer(Germany),IsmailElgizouli(Sudan),ChristopherB.Field(USA),PiersForster(UnitedKingdom),PierreFriedlingstein(UnitedKingdom/Belgium),JanFuglestvedt(Norway),LuisGomez-Echeverri(Colombia),StephaneHallegatte(France/WorldBank),GabrieleHegerl(UnitedKingdom/Germany),MarkHowden(Australia),KejunJiang(China),BlancaJimenezCisneros(Mexico/UNESCO),VladimirKattsov(RussianFederation),HoesungLee(RepublicofKorea),KatharineJ.Mach(USA),JochemMarotzke(Germany),MichaelD.Mastrandrea(USA),LeoMeyer(TheNetherlands),JanMinx(Germany),YacobMulugetta(Ethiopia),KarenO’Brien(Norway),MichaelOppenheimer(USA),JoyJ.Pereira(Malaysia),RamónPichs-Madruga(Cuba),Gian-KasperPlattner(Switzerland),Hans-OttoPörtner(Germany),ScottB.Power(Australia),BenjaminPreston(USA),N.H.Ravindranath(India),AndyReisinger(NewZealand),KeywanRiahi(Austria),MatildeRusticucci(Argentina),RobertScholes(SouthAfrica),KristinSeyboth(USA),YoubaSokona(Mali),RobertStavins(USA),ThomasF.Stocker(Switzerland),PetraTschakert(USA),DetlefvanVuuren(TheNetherlands),Jean-PascalvanYpersele(Belgium)TechnicalSupportUnitfortheSynthesisReportLeoMeyer,SanderBrinkman,LinevanKesteren,NoëmieLeprince-Ringuet,FijkevanBoxmeerReferencingthisreportIPCC,2014:ClimateChange2014:SynthesisReport.ContributionofWorkingGroupsI,IIandIIItotheFifthAssessmentReportoftheIntergovernmentalPanelonClimateChange[CoreWritingTeam,R.K.PachauriandL.A.Meyer(eds.)].IPCC,Geneva,Switzerland,151pp.THEINTERGOVERNMENTALPANELONCLIMATECHANGE©IntergovernmentalPanelonClimateChange,2015Firstpublished2015ISBN978-92-9169-143-2Thispublicationisidenticaltothereportthatwasapproved(SummaryforPolicymakers)andadopted(longerreport)atthe40thsessionoftheIntergovernmentalPanelonClimateChange(IPCC)on1November2014inCopenhagen,Denmark,butwiththeinclusionofcopy-editsanderratathathavebeencorrectedpriortothispublication.Thesepre-publicationerrataareavailableat:http://www.ipcc.ch.ThedesignationsemployedandthepresentationofmaterialonmapsdonotimplytheexpressionofanyopinionwhatsoeveronthepartoftheIntergovernmentalPanelonClimateChangeconcerningthelegalstatusofanycountry,territory,cityorareaorofitsauthorities,orconcerningthedelimitationofitsfrontiersorboundaries.ThementionofspecificcompaniesorproductsdoesnotimplythattheyareendorsedorrecommendedbyIPCCinpreferencetoothersofasimilarnature,whicharenotmentionedoradvertised.Therightofpublicationinprint,electronicandanyotherformandinanylanguageisreservedbytheIPCC.Shortextractsfromthispublicationmaybereproducedwithoutauthorizationprovidedthatcompletesourceisclearlyindicated.Editorialcorrespondenceandrequeststopublish,reproduceortranslatearticlesinpartorinwholeshouldbeaddressedto:IPCCTel.:+41227308208c/oWorldMeteorologicalOrganization(WMO)Fax:+412273080257bis,avenuedelaPaixE-mail:IPCC-Sec@wmo.intP.O.Box2300CH1211Geneva2,Switzerlandwww.ipcc.chCover:DesignbyLauraBiagioni,IPCCSecretariat,WMOPhotos:I-FolgefonnaglacieronthehighplateausofSørfjorden,Norway(60°03’N-6°20’E).©YannArthus-Bertrand/Altitudewww.yannarthusbertrand.orgwww.goodplanet.orgII-PlantingofmangroveseedlingsinFunafala,FunafutiAtoll,Tuvalu.©DavidJ.WilsonIII-China,Shanghai,aerialview.©Ocean/CorbisForeword,PrefaceandDedicationForewordTheSynthesisReport(SYR)distilsandintegratesthefindingsoftheandobjectivescientificandtechnicalassessmentsinthisfield.Begin-ForewordthreeWorkingGroupcontributionstotheFifthAssessmentReportningin1990,thisseriesofIPCCAssessmentReports,SpecialReports,(AR5)oftheIntergovernmentalPanelonClimateChange(IPCC),theTechnicalPapers,MethodologyReportsandotherproductshavemostcomprehensiveassessmentofclimatechangeundertakenthusbecomestandardworksofreference.farbytheIPCC:ClimateChange2013:ThePhysicalScienceBasis;Cli-mateChange2014:Impacts,Adaptation,andVulnerability;andClima-TheSYRwasmadepossiblethankstothevoluntarywork,dedicationteChange2014:MitigationofClimateChange.TheSYRalsoincorpo-andcommitmentofthousandsofexpertsandscientistsfromaroundratesthefindingsoftwoSpecialReportsonRenewableEnergySourcestheglobe,representingarangeofviewsanddisciplines.WewouldandClimateChangeMitigation(2011)andonManagingtheRisksofliketoexpressourdeepgratitudetoallthemembersoftheCoreWri-ExtremeEventsandDisasterstoAdvanceClimateChangeAdaptationtingTeamoftheSYR,membersoftheExtendedWritingTeam,andthe(2011).ReviewEditors,allofwhomenthusiasticallytookonthehugechal-lengeofproducinganoutstandingSYRontopoftheothertaskstheyTheSYRconfirmsthathumaninfluenceontheclimatesystemisclearhadalreadycommittedtoduringtheAR5cycle.Wewouldalsolikeandgrowing,withimpactsobservedacrossallcontinentsandoceans.tothankthestaffoftheTechnicalSupportUnitoftheSYRandtheManyoftheobservedchangessincethe1950sareunprecedentedoverIPCCSecretariatfortheirdedicationinorganizingtheproductionofdecadestomillennia.TheIPCCisnow95percentcertainthathumansthisIPCCreport.arethemaincauseofcurrentglobalwarming.Inaddition,theSYRfindsthatthemorehumanactivitiesdisrupttheclimate,thegreatertherisksWealsowishtoacknowledgeandthankthegovernmentsoftheIPCCofsevere,pervasiveandirreversibleimpactsforpeopleandecosystems,membercountriesfortheirsupportofscientistsindevelopingthisandlong-lastingchangesinallcomponentsoftheclimatesystem.Thereport,andfortheircontributionstotheIPCCTrustFundtoprovideSYRhighlightsthatwehavethemeanstolimitclimatechangeandtheessentialsforparticipationofexpertsfromdevelopingcountriesitsrisks,withmanysolutionsthatallowforcontinuedeconomicandandcountrieswitheconomiesintransition.Wewouldliketoexpresshumandevelopment.However,stabilizingtemperatureincreasetoourappreciationtothegovernmentofWallonia(Belgium)forhostingbelow2°Crelativetopre-industriallevelswillrequireanurgentandtheScopingMeetingoftheSYR,tothegovernmentsofNorway,thefundamentaldeparturefrombusinessasusual.Moreover,thelongerweNetherlands,GermanyandMalaysiaforhostingdraftingsessionsofthewaittotakeaction,themoreitwillcostandthegreaterthetechnologi-SYR,andtothegovernmentofDenmarkforhostingthe40thSessionofcal,economic,socialandinstitutionalchallengeswewillface.theIPCCwheretheSYRwasapproved.ThegenerousfinancialsupportfromthegovernmentsofNorwayandtheNetherlands,fromtheKoreaTheseandtheotherfindingsoftheSYRhaveundoubtedlyandconsi-EnergyEconomicsInstitute,andthein-kindsupportbytheNetherlandsderablyenhancedourunderstandingofsomeofthemostcriticalissuesEnvironmentalAssessmentAgencyandTheEnergyandResourcesInsti-inrelationtoclimatechange:theroleofgreenhousegasemissions;thetute,NewDelhi(India),enabledthesmoothoperationoftheTechnicalseverityofpotentialrisksandimpacts,especiallyfortheleastdevelo-SupportUnitoftheSYR.Thisisgratefullyacknowledged.pedcountriesandvulnerablecommunities,giventheirlimitedabilitytocope;andtheoptionsavailabletousandtheirunderlyingrequire-WewouldparticularlyliketoexpressourthankstoDrRajendraK.mentstoensurethattheeffectsofclimatechangeremainmanageable.Pachauri,ChairmanoftheIPCC,forhisleadershipandconstantgui-Assuch,theSYRcallsfortheurgentattentionofbothpolicymakersdancethroughouttheproductionofthisreport.andcitizensoftheworldtotacklethischallenge.ThetimingoftheSYR,whichwasreleasedon2ndNovember2014inMichelJarraudCopenhagen,wascrucial.PolicymakersmetinDecember2014inLimaSecretaryGeneralatthe20thConferenceofPartiesundertheUnitedNationsFrameworkWorldMeteorologicalOrganizationConventiononClimateChange(UNFCCC)topreparethegroundworkforthe21stSessionin2015inParis,whentheyhavebeentaskedwithconcludinganewagreementtodealwithclimatechange.ItisourhopethatthescientificfindingsoftheSYRwillbethebasisoftheirmotivationtofindthewaytoaglobalagreementwhichcankeepcli-matechangetoamanageablelevel,astheSYRgivesustheknowledgetomakeinformedchoices,andenhancesourvitalunderstandingoftherationaleforaction–andtheseriousimplicationsofinaction.Ignorancecannolongerbeanexcusefortergiversation.Asanintergovernmentalbodyjointlyestablishedin1988bytheWorldAchimSteinerMeteorologicalOrganization(WMO)andtheUnitedNationsEnviron-ExecutiveDirectormentProgramme(UNEP),theIntergovernmentalPanelonClimateUnitedNationsEnvironmentalProgrammeChange(IPCC)hasprovidedpolicymakerswiththemostauthoritativevPrefaceTheSynthesisReport(SYR),constitutingthefinalproductoftheFifthreport,somespecificissuescoveredundermorethanonetopicofthePrefaceAssessmentReport(AR5)oftheIntergovernmentalPanelonClimatelongerreportaresummarizedinoneparticularsectionoftheSPM.Change(IPCC),ispublishedunderthetitleClimateChange2014.ThisEachparagraphoftheSPMcontainsreferencestotherespectivetextreportdistils,synthesizesandintegratesthekeyfindingsofthethreeinthelongerreport.Inturn,thelattercontainsextensivereferencestoWorkingGroupcontributions–ThePhysicalScienceBasis,Impacts,relevantchaptersoftheunderlyingWorkingGroupReportsorthetwoAdaptation,andVulnerabilityandMitigationofClimateChange–toSpecialReportsmentionedabove.TheSYRisessentiallyself-contained,theAR5inaconcisedocumentforthebenefitofdecisionmakersinanditsSPMincludesthemostpolicyrelevantmaterialdrawnfromthethegovernment,theprivatesectoraswellasthepublicatlarge.ThelongerreportandtheentireAR5.SYRalsodrawsonthefindingsofthetwoSpecialReportsbroughtoutin2011dealingwithRenewableEnergySourcesandClimateChangeAllthethreecontributionstotheAR5includingeachSummaryforMitigation,andManagingtheRisksofExtremeEventsandDisasterstoPolicymakers,eachTechnicalSummary,frequentlyaskedquestionsasAdvanceClimateChangeAdaptation.TheSYR,therefore,isacompre-wellastheSynthesisReportinallofficialUNlanguagesareavailablehensiveup-to-datecompilationofassessmentsdealingwithclimateonlineontheIPCCwebsiteandinelectronicofflineversions.Inthesechange,basedonthemostrecentscientific,technicalandsocio-economicelectronicversions,referencesintheSYRtorelevantpartsoftheunder-literatureinthefield.lyingmaterialareprovidedashyperlinks,therebyenablingthereadertoeasilyfindfurtherscientific,technicalandsocio-economicinformation.ScopeoftheReportAuserguide,glossaryoftermsusedandlistingofacronyms,authors,ReviewEditorsandExpertReviewersareprovidedintheannexestoThisdocumentistheresultofcoordinatedandcarefullyconnectedthisreport.crossWorkingGroupeffortstoensurecoherentandcomprehensiveinformationonvariousaspectsrelatedtoclimatechange.ThisSYRTofacilitateaccesstothefindingsoftheSYRforawidereadershipincludesaconsistentevaluationandassessmentofuncertaintiesandandtoenhancetheirusabilityforstakeholders,eachsectionoftherisks;integratedcostingandeconomicanalysis;regionalaspects;SPMcarrieshighlightedheadlinestatements.Takentogether,thesechanges,impactsandresponsesrelatedtowaterandearthsystems,21headlinestatementsprovideanoverarchingsummaryinsimpleandthecarboncycleincludingoceanacidification,cryosphereandseacompletelynon-technicallanguageforeasyassimilationbyreaderslevelrise;aswellastreatmentofmitigationandadaptationoptionsfromdifferentwalksoflife.Theseheadlinestatementshavebeencraf-withintheframeworkofsustainabledevelopment.ThroughtheentiretedbytheauthorsoftheReport,andapprovedbythemembergover-lengthoftheSYR,informationisalsoprovidedrelevanttoArticle2,nmentsoftheIPCC.theultimateobjectiveoftheUnitedNationsFrameworkConventiononClimateChange(UNFCCC).Thelongerreportisstructuredaroundfourtopicheadingsasmanda-tedbythePanel:OtheraspectsofclimatechangecoveredinthisreportincludedirectObservedchangesandtheircauses(Topic1)integratesnewinformationimpactsofclimatechangeonnaturalsystemsaswellasbothdirectfromthethreeWorkingGroupsonobservedchangesintheclimateandindirectimpactsonhumansystems,suchashumanhealth,foodsystem,includingchangesintheatmosphere,oceans,cryosphereandsecurityandsecurityofsocietalconditions.Byembeddingclimatesealevel;recentandpastdriversandhumaninfluencesaffectingemis-changeriskandissuesofadaptationandmitigationwithintheframe-siondrivers;observedimpacts,includingchangesinextremeweatherworkofsustainabledevelopment,theSYRalsohighlightsthefactthatandclimateevents;andattributionofclimatechangesandimpacts.nearlyallsystemsonthisplanetwouldbeaffectedbytheimpactsofachangingclimate,andthatitisnotpossibletodrawboundariesFutureclimatechanges,risksandimpacts(Topic2)presentsinforma-aroundclimatechange,itsassociatedrisksandimpactsontheonetionaboutfutureclimatechange,risksandimpacts.Itintegratesinfor-handandontheother,developmentwhichmeetstheneedsofthemationaboutkeydriversoffutureclimate,therelationshipbetweenpresentgenerationwithoutcompromisingtheabilityoffuturegene-cumulativeemissionsandtemperaturechange,andprojectedchangesrationstomeettheirownneeds.TheReport,therefore,alsofocusesintheclimatesysteminthe21stcenturyandbeyond.Itassessesfutureonconnectionsbetweentheseaspectsandprovidesinformationonrisksandimpactscausedbyachangingclimateandtheinteractionofhowclimatechangeoverlapswithandmainstreamsintootherdeve-climate-relatedandotherhazards.Itprovidesinformationaboutlong-lopmentalissues.termchangesincludingsea-levelriseandoceanacidification,andtheriskofirreversibleandabruptchanges.StructureFuturePathwaysforAdaptation,MitigationandSustainableDeve-lopment(Topic3)addressesfuturepathwaysforadaptationandTheReportcomprisesaSummaryforPolicymakers(SPM)andalongermitigationascomplementarystrategiesforreducingandmanagingreportfromwhichtheSPMisderived,aswellasannexes.Eventhoughtherisksofclimatechangeandassessestheirinteractionwithsus-theSPMfollowsastructureandsequencesimilartothatinthelongertainabledevelopment.ItdescribesanalyticalapproachesforeffectiveviiPrefacedecision-makinganddifferencesinrisksofclimatechange,adaptationcanprideitselfon.OurthanksgoalsotoallauthorsoftheAR5andandmitigationintermsoftimescale,magnitudeandpersistence.ItthetwoSpecialReportsbecausewithouttheircarefulassessmentofanalysesthecharacteristicsofadaptationandmitigationpathways,thehugebodyofliteratureonvariousaspectsofclimatechangeandandassociatedchallenges,limitsandbenefits,includingfordifferenttheircommentsonthedraftreport,thepreparationoftheSYRwouldlevelsoffuturewarming.nothavebeenpossible.PrefaceAdaptationandMitigation(Topic4)bringstogetherinformationfromThroughouttheAR5,webenefittedgreatlyfromthewisdomandWorkingGroupsIIandIIIonspecificadaptationandmitigationopti-insightofourcolleaguesintheIPCCleadership,especiallyDrThomasons,includingenvironmentallysoundtechnologiesandinfrastructure,StockerandDrQinDahe,WorkingGroupICo-Chairs;DrChrisFieldsustainablelivelihoods,behaviourandlifestylechoices.ItdescribesandDrVicenteBarros,WorkingGroupIICo-Chairs;andDrOttmarcommonenablingfactorsandconstraints,andpolicyapproaches,Edenhofer,DrRamónPichs-MadrugaandDrYoubaSokona,Workingfinanceandtechnologyonwhicheffectiveresponsemeasuresdepend.GroupIIICo-Chairs.TheircooperationonissuesrelatedtoknowledgeItshowsopportunitiesforintegratedresponsesandlinksadaptationfromthereportsofallthreeWorkingGroupswasadefiniteassetforandmitigationwithothersocietalobjectives.theproductionofahigh-qualityfinaldocument.ProcessWealsowishtothankFredolinTangang,DavidWratt,EduardoCalvo,JoseMoreno,JimSkeaandSuzanaKahnRibeiro,whoactedasReviewTheSYRoftheAR5oftheIPCChasbeenpreparedinaccordancewithEditorsduringtheApprovalSessionoftheSYR,ensuringthattheeditstheproceduresoftheIPCCtoensureadequateeffortandrigorbeingmadetotheSPMduringtheSessionwerecorrectlyreflectedintheachievedintheprocess.FortheAR5thepreparationoftheSYRwaslongerreport.TheirimportantworkguaranteedthehighleveloftrusttakeninhandayearearlierthanwasthecasewiththeFourthAssess-betweenthescientistsandthegovernments,enablingthemtoworkmentReport(AR4)–whiletheWorkingGroupReportswerestillsmoothlyinsymbiosis,whichisauniquefeatureoftheIPCCanditsbeingcompleted–withaviewtoenhancingintegrationandensuringcredibility.adequatesynthesis.AscopingmeetingspecificallyforproposingthedetailedoutlineoftheAR5SynthesisReportwasheldinLiège,Weextendourdeepappreciationoftheenthusiasm,dedicationandBelgiuminAugust,2010,andtheoutlineproducedinthatmeetingwasprofessionalcontributionsofGian-KasperPlattner,MelindaTignorandapprovedbythePanelinOctober,2010inBusan,RepublicofKorea.JudithBoschungfromtheTechnicalSupportUnitofWorkingGroupI,InaccordancewithIPCCprocedures,theIPCCChairinconsultationKatieMachandErenBilirfromtheTechnicalSupportUnitofWorkingwiththeCo-ChairsoftheWorkingGroupsnominatedauthorsfortheGroupII,EllieFarahani,JussiSavolainenandSteffenSchlömerfromtheCoreWritingTeam(CWT)oftheSYRandatotalof45CWTmembersTechnicalSupportUnitofWorkingGroupIII,andGerritHansenfromand9ReviewEditorswereselectedandacceptedbytheIPCCBureauthePotsdamInstituteforClimateImpactResearchduringtheApprovalinMarch,2012.Inaddition,14ExtendedWritingTeam(EWT)authorsSessionoftheSYR,workingasateamwiththeTechnicalSupportUnitwereselectedbytheCWTwiththeapprovaloftheChairoftheIPCC,oftheSYR,whichwasindispensableinthesuccessfuloutcomesofandthislattergroupcontributedsubstantiallytothematerialandthetheSession.AspecialthanksgoestoAdrienMichelfromtheTechnicaltextprovidedinthisreport.DuringevolutionofthecontentsoftheSupportUnitofWorkingGroupIforhisworkontheSYRfigures.SYRtheIPCCBureauwasapproachedanditapprovedtheinclusionof6additionalCWTmembersandanadditionalReviewEditor.OurthanksgotoLeoMeyer,HeadoftheTechnicalSupportUnitofThisfurtherenhancedanddeepenedtheexpertiserequiredforthetheSynthesisReport,andthemembersoftheTechnicalSupportUnitpreparationoftheReport.ThefinaldraftreportwhichhasundergoneSanderBrinkman,LinevanKesteren,NoemieLeprince-RinguetandacombinedreviewbyexpertsandgovernmentswassubmittedtotheFijkevanBoxmeerfortheircapacitytoexpandtheirstrengthsandcarry40thSessionoftheIPCC,heldfrom27Octoberto1November2014inoutthemammothtaskofcoordinatingthedevelopmentandpro-Copenhagen,Denmark,wheregovernmentsapprovedtheSPMlinebyductionoftheSYR.Eachoneofthemputintirelessefforts,displayinglineandadoptedthelongerreportsectionbysection.deepcommitmentanddedicationtoensuretheproductionofanout-standingSYR.AcknowledgementsWewouldliketoacknowledgetheworkandinnumerabletasksper-formedinsupportofthepreparation,releaseandpublicationoftheOurprofoundgratitudeanddeepindebtednessgoestothemembersReportbythestaffoftheIPCCSecretariat:GaetanoLeone,CarlosoftheCoreWritingTeamandthesubstantialhelpfromtheExtendedMartin-Novella,JonathanLynn,BrendaAbrar-Milani,JesbinBaidya,WritingTeammembers,fortheirtirelessefforts,expertise,andama-LauraBiagioni,MaryJeanBurer,AnnieCourtin,JudithEwa,JoellezinglevelofdedicationthroughouttheproductionoftheSYR.TheSYRFernandez,NinaPeeva,SophieSchlingemann,AmySmithandWeranicouldnothavebeencompletedsuccessfullywithouttheirinspirationalZabula.ThanksarealsoduetoFrancisHayesandElhousseineGouainicommitmenttoexcellenceandintegrity,andtheirmeticulousattenti-foractingasconferenceofficersattheapprovalSession.ontodetail.WealsowishtothanktheReviewEditorsfortheirinva-luablehelpensuringthattheSYRprovidesabalancedandcompleteWeareappreciativeofthemembergovernmentsoftheIPCCwhoassessmentofcurrentinformationrelevanttoclimatechange.TheirgraciouslyhostedtheSYRscopingmeeting,fourofourCoreWritingrolewascrucialtoensuretransparencyoftheprocesswhichtheIPCCMeetingsandthe40thSessionoftheIPCC:Belgium,Norway,TheNetherlands,Germany,MalaysiaandDenmark.WeexpressourthanksviiiPrefacetothegovernments,WMO,UNEPandtheUNFCCCfortheircontribu-PrefacetionstotheTrustFundwhichsupportedvariouselementsofexpendi-ture.WewishtoparticularlythanktheGovernmentsofNorwayandTheNetherlands,andtheKoreaEnergyEconomicsInstitutefortheirgenerousfinancialsupportoftheSYRTechnicalSupportUnit,andTheNetherlandsEnvironmentalAssessmentAgencyPBLandTheEnergyandResourcesInstitute,NewDelhi,fortheirin-kindsupportoftheSYRTechnicalSupportUnit.WealsoacknowledgethesupportofIPCC’sparentorganizations,UNEPandWMO,andparticularlyWMOforhos-tingtheIPCCSecretariatandourfirstCoreWritingTeammeeting.MayweconveyourdeepgratitudetotheUNFCCCfortheircooperationatvariousstagesofthisenterpriseandfortheprominencetheygivetoourworkinseveralappropriatefora.R.K.PachauriChairmanoftheIPCCRenateChristSecretaryoftheIPCCixDedicationDedicationStephenH.Schneider(11February1945–19July2010)TheSynthesisReportoftheFifthAssessmentReportoftheIntergovernmentalPanelonClimateChange(IPCC)isdedicatedtothememoryofStephenH.Schneider,oneoftheforemostclimatescientistsofourtime.SteveSchneider,borninNewYork,trainedasaplasmaphysicist,embracedscholarshipinthefieldofclimatesciencealmost40yearsagoandcontinuedhisrelentlesseffortscreatingnewknowledgeinthefieldandinformingpolicymakersandthepublicatlargeonthegrowingproblemofclimatechangeandsolutionsfordealingwithit.AtalltimesSteveSchneiderremainedintrepidandforthrightinexpressinghisviews.Hisconvictionsweredrivenbythestrengthofhisoutstandingscientificexpertise.HewashighlyrespectedasFoundingEditoroftheinterdisciplinaryjournalClimaticChangeandauthoredhundredsofbooksandpapers,manyofwhichwereco-authoredwithscientistsfromdiversedisciplines.HisassociationwiththeIPCCbeganwiththeFirstAssessmentReportwhichwaspublishedin1990,andwhichplayedamajorroleinthescientificfoundationoftheUNFrame-workConventiononClimateChange.Subsequently,hewasLeadAuthor,CoordinatingLeadAuthorandExpertReviewerforvariousAssessmentReportsandamemberoftheCoreWritingTeamfortheSynthesisReportoftheFourthAssessmentReport.HislifeandaccomplishmentshaveinspiredandmotivatedmembersoftheCoreWritingTeamofthisReport.SteveSchneider’sknowledgewasararesynthesisofseveraldisciplineswhichareanessentialpartofthediversityinherentinclimatescience.xiContentsFrontmatterForeword...................................................................................................................................................vPreface..................................................................................................................................................viiDedication.................................................................................................................................................xiSPMSummaryforPolicymakers2......................................................................................................................SPM1.ObservedChangesandtheirCauses2.......................................................................................SPM2.FutureClimateChanges,RisksandImpacts8.............................................................................SPM3.FuturePathwaysforAdaptation,MitigationandSustainableDevelopment....................................17SPM4.AdaptationandMitigation..................................................................................................26TopicsIntroduction35..........................................................................................................................................BoxIntroduction.1RiskandtheManagementofanUncertainFuture......................................................36BoxIntroduction.2CommunicatingtheDegreeofCertaintyinAssessmentFindings....................................37Topic1:ObservedChangesandtheirCauses39..............................................................................................1.1Observedchangesintheclimatesystem................................................................................401.1.1Atmosphere.....................................................................................................................401.1.2Ocean.............................................................................................................................401.1.3Cryosphere......................................................................................................................421.1.4Sealevel.........................................................................................................................42Box1.1RecentTemperatureTrendsandtheirImplications....................................................................431.2Pastandrecentdriversofclimatechange...............................................................................441.2.1Naturalandanthropogenicradiativeforcings..........................................................................441.2.2Humanactivitiesaffectingemissiondrivers.............................................................................451.3Attributionofclimatechangesandimpacts............................................................................471.3.1Attributionofclimatechangestohumanandnaturalinfluencesontheclimatesystem....................481.3.2Observedimpactsattributedtoclimatechange.......................................................................491.4Extremeevents.................................................................................................................531.5Exposureandvulnerability..................................................................................................541.6Humanresponsestoclimatechange:adaptationandmitigation.................................................54Topic2:FutureClimateChanges,RiskandImpacts56.....................................................................................2.1Keydriversoffutureclimateandthebasisonwhichprojectionsaremade....................................56Box2.1Advances,ConfidenceandUncertaintyinModellingtheEarth’sClimateSystem.............................56Box2.2TheRepresentativeConcentrationPathways..........................................................................57xiii2.2Projectedchangesintheclimatesystem58..............................................................................................2.2.1Airtemperature................................................................................................................58Box2.3ModelsandMethodsforEstimatingClimateChangeRisks,VulnerabilityandImpacts......................582.2.2Watercycle......................................................................................................................602.2.3Ocean,cryosphereandsealevel...........................................................................................602.2.4Carboncycleandbiogeochemistry........................................................................................622.2.5Climatesystemresponses...................................................................................................622.3Futurerisksandimpactscausedbyachangingclimate.............................................................642.3.1Ecosystemsandtheirservicesintheoceans,alongcoasts,onlandandinfreshwater.......................672.3.2Water,foodandurbansystems,humanhealth,securityandlivelihoods........................................67Box2.4ReasonsForConcernRegardingClimateChange.....................................................................722.4Climatechangebeyond2100,irreversibilityandabruptchanges.................................................73Topic3:FuturePathwaysforAdaption,MitigationandSustainableDevelopment75......................................3.1Foundationsofdecision-makingaboutclimatechange..............................................................763.2Climatechangerisksreducedbyadaptationandmitigation.......................................................773.3Characteristicsofadaptationpathways..................................................................................79Box3.1TheLimitsoftheEconomicAssessmentofClimateChangeRisks.................................................793.4Characteristicsofmitigationpathways..................................................................................81Box3.2GreenhouseGasMetricsandMitigationPathways...................................................................87Box3.3CarbonDioxideRemovalandSolarRadiationManagementGeoengineeringTechnologies—PossibleRoles,Options,RisksandStatus................................................................................893.5Interactionamongmitigation,adaptationandsustainabledevelopment.......................................90Box3.4Co-benefitsandAdverseSideeffects.....................................................................................91Topic4:AdaptationandMitigation93...................................................................................................4.1Commonenablingfactorsandconstraintsforadaptationandmitigationresponses........................944.2Responseoptionsforadaptation..........................................................................................954.3Responseoptionsformitigation...........................................................................................984.4Policyapproachesforadaptationandmitigation,technologyandfinance...................................1024.4.1Internationalandregionalcooperationonadaptationandmitigation.........................................1024.4.2Nationalandsub-nationalpolicies......................................................................................1064.4.3Technologydevelopmentandtransfer.................................................................................1094.4.4Investmentandfinance....................................................................................................1104.5Trade-offs,synergiesandintegratedresponses......................................................................112xivAnnexesAnnexes................................................................................................................................................113I.UserGuide..................................................................................................................................115II.Glossary...................................................................................................................................117III.Acronyms,ChemicalSymbolsandScientificUnits................................................................................131ForewordIV.AuthorsandReviewEditors............................................................................................................135V.ExpertReviewers..........................................................................................................................139VI.PublicationsbytheIntergovernmentalPanelonClimateChange............................................................143Index...............................................................................................................................................147xvSourcescitedinthisSynthesisReportReferencesformaterialcontainedinthisreportaregiveninitalicizedcurlybrackets{}attheendofeachparagraph.IntheSummaryforPolicymakers,thereferencesrefertothenumbersofthesections,figures,tablesandboxesintheunderlyingIntroductionandTopicsofthisSynthesisReport.IntheIntroductionandTopicsofthelongerreport,thereferencesrefertothecontributionsoftheWorkingGroupsI,IIandIII(WGI,WGII,WGIII)totheFifthAssessmentReportandotherIPCCReports(initalicizedcurlybrackets),ortoothersectionsoftheSynthesisReportitself(inroundbrackets).Thefollowingabbreviationshavebeenused:SPM:SummaryforPolicymakersTS:TechnicalSummaryES:ExecutiveSummaryofachapterNumbersdenotespecificchaptersandsectionsofareport.OtherIPCCreportscitedinthisSynthesisReport:SREX:SpecialReportonManagingtheRisksofExtremeEventsandDisasterstoAdvanceClimateChangeAdaptationSRREN:SpecialReportonRenewableEnergySourcesandClimateChangeMitigationAR4:FourthAssessmentReportxviClimateChange2014SynthesisReportCSuhmapmtearryforPolicymakersSummaryforPolicymakersIntroductionThisSynthesisReportisbasedonthereportsofthethreeWorkingGroupsoftheIntergovernmentalPanelonClimateChange(IPCC),includingrelevantSpecialReports.ItprovidesanintegratedviewofclimatechangeasthefinalpartoftheIPCC’sFifthAssessmentReport(AR5).SPMThissummaryfollowsthestructureofthelongerreportwhichaddressesthefollowingtopics:Observedchangesandtheircauses;Futureclimatechange,risksandimpacts;Futurepathwaysforadaptation,mitigationandsustainabledevelopment;Adaptationandmitigation.IntheSynthesisReport,thecertaintyinkeyassessmentfindingsiscommunicatedasintheWorkingGroupReportsandSpecialReports.Itisbasedontheauthorteams’evaluationsofunderlyingscientificunderstandingandisexpressedasaqualitativelevelofconfidence(fromverylowtoveryhigh)and,whenpossible,probabilisticallywithaquantifiedlikelihood(fromexceptionallyunlikelytovirtuallycertain)1.Whereappropriate,findingsarealsoformulatedasstatementsoffactwith-outusinguncertaintyqualifiers.ThisreportincludesinformationrelevanttoArticle2oftheUnitedNationsFrameworkConventiononClimateChange(UNFCCC).SPM1.ObservedChangesandtheirCausesHumaninfluenceontheclimatesystemisclear,andrecentanthropogenicemissionsofgreen-housegasesarethehighestinhistory.Recentclimatechangeshavehadwidespreadimpactsonhumanandnaturalsystems.{1}SPM1.1ObservedchangesintheclimatesystemWarmingoftheclimatesystemisunequivocal,andsincethe1950s,manyoftheobservedchangesareunprecedentedoverdecadestomillennia.Theatmosphereandoceanhavewarmed,theamountsofsnowandicehavediminished,andsealevelhasrisen.{1.1}EachofthelastthreedecadeshasbeensuccessivelywarmerattheEarth’ssurfacethananyprecedingdecadesince1850.Theperiodfrom1983to2012waslikelythewarmest30-yearperiodofthelast1400yearsintheNorthernHemisphere,wheresuchassessmentispossible(mediumconfidence).Thegloballyaveragedcombinedlandandoceansurfacetemperaturedataascalculatedbyalineartrendshowawarmingof0.85[0.65to1.06]°C2overtheperiod1880to2012,whenmultipleindependentlyproduceddatasetsexist(FigureSPM.1a).{1.1.1,Figure1.1}Inadditiontorobustmulti-decadalwarming,thegloballyaveragedsurfacetemperatureexhibitssubstantialdecadalandinterannualvariability(FigureSPM.1a).Duetothisnaturalvariability,trendsbasedonshortrecordsareverysensitivetothebeginningandenddatesanddonotingeneralreflectlong-termclimatetrends.Asoneexample,therateofwarmingover1Eachfindingisgroundedinanevaluationofunderlyingevidenceandagreement.Inmanycases,asynthesisofevidenceandagreementsupportsanassignmentofconfidence.Thesummarytermsforevidenceare:limited,mediumorrobust.Foragreement,theyarelow,mediumorhigh.Alevelofconfidenceisexpressedusingfivequalifiers:verylow,low,medium,highandveryhigh,andtypesetinitalics,e.g.,mediumconfidence.Thefollow-ingtermshavebeenusedtoindicatetheassessedlikelihoodofanoutcomeoraresult:virtuallycertain99–100%probability,verylikely90–100%,likely66–100%,aboutaslikelyasnot33–66%,unlikely0–33%,veryunlikely0–10%,exceptionallyunlikely0–1%.Additionalterms(extremelylikely95–100%,morelikelythannot>50–100%,moreunlikelythanlikely0–<50%,extremelyunlikely0–5%)mayalsobeusedwhenappropriate.Assessedlikelihoodistypesetinitalics,e.g.,verylikely.Seeformoredetails:Mastrandrea,M.D.,C.B.Field,T.F.Stocker,O.Edenhofer,K.L.Ebi,D.J.Frame,H.Held,E.Kriegler,K.J.Mach,P.R.Matschoss,G.-K.Plattner,G.W.YoheandF.W.Zwiers,2010:GuidanceNoteforLeadAuthorsoftheIPCCFifthAssess-mentReportonConsistentTreatmentofUncertainties,IntergovernmentalPanelonClimateChange(IPCC),Geneva,Switzerland,4pp.2Rangesinsquarebracketsorfollowing‘±’areexpectedtohavea90%likelihoodofincludingthevaluethatisbeingestimated,unlessotherwisestated.2(a)GloballyaveragedcombinedlandandoceansurfacetemperatureanomalySummaryforPolicymakersSPM0.40.20(°C)−0.2−0.4−0.6−0.8−11850190019502000Year(b)Globallyaveragedsealevelchange0.10.050(m)−0.05−0.1−0.15−0.21900Year195020001850Globallyaveragedgreenhousegasconcentrations(c)400380CO2(ppm)36018003303401600CH4(ppb)320N2O(ppb)32014003101200300300100029080028028027018501900Year19502000(d)GlobalanthropogenicCO2emissionsCumulativeCO2QuantitativeinformationofCH4andN2Oemissiontimeseriesfrom1850to1970islimitedemissions40200035Fossilfuels,cementandﬂaring150030Forestryandotherlanduse1000(GtCO2/yr)25(GtCO2)5002001517501750––10197020115018501900Year19502000FigureSPM.1Thecomplexrelationshipbetweentheobservations(panelsa,b,c,yellowbackground)andtheemissions(paneld,lightbluebackground)isaddressedinSection1.2andTopic1.Observationsandotherindicatorsofachangingglobalclimatesystem.Observa-tions:(a)Annuallyandgloballyaveragedcombinedlandandoceansurfacetemperatureanomaliesrelativetotheaverageovertheperiod1986to2005.Coloursindicatedifferentdatasets.(b)Annuallyandgloballyaveragedsealevelchangerelativetotheaverageovertheperiod1986to2005inthelongest-runningdataset.Coloursindicatedifferentdatasets.Alldatasetsarealignedtohavethesamevaluein1993,thefirstyearofsatellitealtimetrydata(red).Whereassessed,uncertaintiesareindicatedbycolouredshading.(c)Atmosphericconcentrationsofthegreenhousegasescarbondioxide(CO2,green),methane(CH4,orange)andnitrousoxide(N2O,red)determinedfromicecoredata(dots)andfromdirectatmosphericmeasurements(lines).Indicators:(d)GlobalanthropogenicCO2emissionsfromforestryandotherlanduseaswellasfromburningoffossilfuel,cementproductionandflaring.CumulativeemissionsofCO2fromthesesourcesandtheiruncertaintiesareshownasbarsandwhiskers,respectively,ontherighthandside.TheglobaleffectsoftheaccumulationofCH4andN2Oemissionsareshowninpanelc.Greenhousegasemissiondatafrom1970to2010areshowninFigureSPM.2.{Figures1.1,1.3,1.5}3SummaryforPolicymakersthepast15years(1998–2012;0.05[–0.05to0.15]°Cperdecade),whichbeginswithastrongElNiño,issmallerthantheratecalculatedsince1951(1951–2012;0.12[0.08to0.14]°Cperdecade).{1.1.1,Box1.1}Oceanwarmingdominatestheincreaseinenergystoredintheclimatesystem,accountingformorethan90%oftheenergyaccumulatedbetween1971and2010(highconfidence),withonlyabout1%storedintheatmosphere.Onaglobalscale,theoceanwarmingislargestnearthesurface,andtheupper75mwarmedby0.11[0.09to0.13]°CperdecadeovertheSPMperiod1971to2010.Itisvirtuallycertainthattheupperocean(0−700m)warmedfrom1971to2010,anditlikelywarmedbetweenthe1870sand1971.{1.1.2,Figure1.2}Averagedoverthemid-latitudelandareasoftheNorthernHemisphere,precipitationhasincreasedsince1901(mediumconfidencebeforeandhighconfidenceafter1951).Forotherlatitudes,area-averagedlong-termpositiveornegativetrendshavelowconfidence.Observationsofchangesinoceansurfacesalinityalsoprovideindirectevidenceforchangesintheglobalwatercycleovertheocean(mediumconfidence).Itisverylikelythatregionsofhighsalinity,whereevaporationdom-inates,havebecomemoresaline,whileregionsoflowsalinity,whereprecipitationdominates,havebecomefreshersincethe1950s.{1.1.1,1.1.2}Sincethebeginningoftheindustrialera,oceanicuptakeofCO2hasresultedinacidificationoftheocean;thepHofoceansurfacewaterhasdecreasedby0.1(highconfidence),correspondingtoa26%increaseinacidity,measuredashydrogenionconcentration.{1.1.2}Overtheperiod1992to2011,theGreenlandandAntarcticicesheetshavebeenlosingmass(highconfidence),likelyatalargerrateover2002to2011.Glaciershavecontinuedtoshrinkalmostworldwide(highconfidence).NorthernHemispherespringsnowcoverhascontinuedtodecreaseinextent(highconfidence).Thereishighconfidencethatpermafrosttempera-tureshaveincreasedinmostregionssincetheearly1980sinresponsetoincreasedsurfacetemperatureandchangingsnowcover.{1.1.3}TheannualmeanArcticsea-iceextentdecreasedovertheperiod1979to2012,witharatethatwasverylikelyintherange3.5to4.1%perdecade.Arcticsea-iceextenthasdecreasedineveryseasonandineverysuccessivedecadesince1979,withthemostrapiddecreaseindecadalmeanextentinsummer(highconfidence).ItisverylikelythattheannualmeanAntarcticsea-iceextentincreasedintherangeof1.2to1.8%perdecadebetween1979and2012.However,thereishighconfidencethattherearestrongregionaldifferencesinAntarctica,withextentincreasinginsomeregionsanddecreasinginothers.{1.1.3,Figure1.1}Overtheperiod1901to2010,globalmeansealevelroseby0.19[0.17to0.21]m(FigureSPM.1b).Therateofsealevelrisesincethemid-19thcenturyhasbeenlargerthanthemeanrateduringtheprevioustwomillennia(highconfidence).{1.1.4,Figure1.1}SPM1.2CausesofclimatechangeAnthropogenicgreenhousegasemissionshaveincreasedsincethepre-industrialera,drivenlargelybyeconomicandpopulationgrowth,andarenowhigherthanever.Thishasledtoatmo-sphericconcentrationsofcarbondioxide,methaneandnitrousoxidethatareunprecedentedinatleastthelast800,000years.Theireffects,togetherwiththoseofotheranthropogenicdriv-ers,havebeendetectedthroughouttheclimatesystemandareextremelylikelytohavebeenthedominantcauseoftheobservedwarmingsincethemid-20thcentury.{1.2,1.3.1}Anthropogenicgreenhousegas(GHG)emissionssincethepre-industrialerahavedrivenlargeincreasesintheatmosphericconcentrationsofcarbondioxide(CO2),methane(CH4)andnitrousoxide(N2O)(FigureSPM.1c).Between1750and2011,cumulativeanthropogenicCO2emissionstotheatmospherewere2040±310GtCO2.About40%oftheseemissionshaveremainedintheatmosphere(880±35GtCO2);therestwasremovedfromtheatmosphereandstoredonland(inplantsandsoils)andintheocean.Theoceanhasabsorbedabout30%oftheemittedanthropogenicCO2,causingoceanacidification.AbouthalfoftheanthropogenicCO2emissionsbetween1750and2011haveoccurredinthelast40years(highconfidence)(FigureSPM.1d).{1.2.1,1.2.2}4SummaryforPolicymakersTotalannualanthropogenicGHGemissionsbygases1970–2010+2.2%/yr52Gt2000–20102.2%5.0%5049Gt+1.3%/yr1970–20002.0%6.2%GHGemissions(GtCO2-eq/yr)4038Gt16%20%SPM0.81%3027Gt7.4%11%10%0.44%18%16%Gas65%62%7.9%19%59%F-Gases2017%19901995N2OYearCH410CO2FOLU55%CO2Fossilfuelandindustrialprocesses0197019751980198520002005201020102010(GWP100SAR)(GWP100AR5)FigureSPM.2Totalannualanthropogenicgreenhousegas(GHG)emissions(gigatonneofCO2-equivalentperyear,GtCO2-eq/yr)fortheperiod1970to2010bygases:CO2fromfossilfuelcombustionandindustrialprocesses;CO2fromForestryandOtherLandUse(FOLU);methane(CH4);nitrousoxide(N2O);fluorinatedgasescoveredundertheKyotoProtocol(F-gases).Righthandsideshows2010emissions,usingalternativelyCO2-equivalentemissionweightingsbasedonIPCCSecondAssessmentReport(SAR)andAR5values.Unlessotherwisestated,CO2-equivalentemissionsinthisreportincludethebasketofKyotogases(CO2,CH4,N2OaswellasF-gases)calculatedbasedon100-yearGlobalWarmingPotential(GWP100)valuesfromtheSAR(seeGlos-sary).UsingthemostrecentGWP100valuesfromtheAR5(right-handbars)wouldresultinhighertotalannualGHGemissions(52GtCO2-eq/yr)fromanincreasedcontributionofmethane,butdoesnotchangethelong-termtrendsignificantly.{Figure1.6,Box3.2}TotalanthropogenicGHGemissionshavecontinuedtoincreaseover1970to2010withlargerabsoluteincreasesbetween2000and2010,despiteagrowingnumberofclimatechangemitigationpolicies.AnthropogenicGHGemissionsin2010havereached49±4.5GtCO2-eq/yr3.EmissionsofCO2fromfossilfuelcombustionandindustrialprocessescontributedabout78%ofthetotalGHGemissionsincreasefrom1970to2010,withasimilarpercentagecontributionfortheincreaseduringtheperiod2000to2010(highconfidence)(FigureSPM.2).Globally,economicandpopulationgrowthcontinuedtobethemostimportantdriversofincreasesinCO2emissionsfromfossilfuelcombustion.Thecontributionofpopulationgrowthbetween2000and2010remainedroughlyidenticaltothepreviousthreedecades,whilethecontributionofeconomicgrowthhasrisensharply.Increaseduseofcoalhasreversedthelong-standingtrendofgradualdecarbonization(i.e.,reducingthecarbonintensityofenergy)oftheworld’senergysupply(highconfidence).{1.2.2}TheevidenceforhumaninfluenceontheclimatesystemhasgrownsincetheIPCCFourthAssessmentReport(AR4).Itisextremelylikelythatmorethanhalfoftheobservedincreaseinglobalaveragesurfacetemperaturefrom1951to2010wascausedbytheanthropogenicincreaseinGHGconcentrationsandotheranthropogenicforcingstogether.Thebestestimateofthehuman-inducedcontributiontowarmingissimilartotheobservedwarmingoverthisperiod(FigureSPM.3).Anthro-pogenicforcingshavelikelymadeasubstantialcontributiontosurfacetemperatureincreasessincethemid-20thcenturyovereverycontinentalregionexceptAntarctica4.Anthropogenicinfluenceshavelikelyaffectedtheglobalwatercyclesince1960andcontributedtotheretreatofglacierssincethe1960sandtotheincreasedsurfacemeltingoftheGreenlandicesheetsince1993.AnthropogenicinfluenceshaveverylikelycontributedtoArcticsea-icelosssince1979andhaveverylikelymadeasubstantialcontributiontoincreasesinglobalupperoceanheatcontent(0–700m)andtoglobalmeansealevelriseobservedsincethe1970s.{1.3,Figure1.10}3GreenhousegasemissionsarequantifiedasCO2-equivalent(GtCO2-eq)emissionsusingweightingsbasedonthe100-yearGlobalWarmingPotentials,usingIPCCSecondAssessmentReportvaluesunlessotherwisestated.{Box3.2}4ForAntarctica,largeobservationaluncertaintiesresultinlowconfidencethatanthropogenicforcingshavecontributedtotheobservedwarmingaver-agedoveravailablestations.5SummaryforPolicymakersContributionstoobservedsurfacetemperaturechangeovertheperiod1951–2010OBSERVEDWARMINGSPMGreenhousegasesOtheranthropogenicforcingsCombinedanthropogenicforcingsNaturalforcingsNaturalinternalvariability–0.50.00.51.0(°C)FigureSPM.3Assessedlikelyranges(whiskers)andtheirmid-points(bars)forwarmingtrendsoverthe1951–2010periodfromwell-mixedgreenhousegases,otheranthropogenicforcings(includingthecoolingeffectofaerosolsandtheeffectoflandusechange),combinedanthropogenicforcings,naturalforcingsandnaturalinternalclimatevariability(whichistheelementofclimatevariabilitythatarisesspontaneouslywithintheclimatesystemevenintheabsenceofforcings).Theobservedsurfacetemperaturechangeisshowninblack,withthe5to95%uncertaintyrangeduetoobservationaluncertainty.Theattributedwarmingranges(colours)arebasedonobservationscombinedwithclimatemodelsimulations,inordertoestimatethecontributionofanindividualexternalforcingtotheobservedwarming.Thecontributionfromthecombinedanthropogenicforcingscanbeestimatedwithlessuncertaintythanthecontributionsfromgreenhousegasesandfromotheranthropogenicforcingsseparately.Thisisbecausethesetwocontributionspartiallycompen-sate,resultinginacombinedsignalthatisbetterconstrainedbyobservations.{Figure1.9}SPM1.3ImpactsofclimatechangeInrecentdecades,changesinclimatehavecausedimpactsonnaturalandhumansystemsonallcontinentsandacrosstheoceans.Impactsareduetoobservedclimatechange,irrespec-tiveofitscause,indicatingthesensitivityofnaturalandhumansystemstochangingclimate.{1.3.2}Evidenceofobservedclimatechangeimpactsisstrongestandmostcomprehensivefornaturalsystems.Inmanyregions,changingprecipitationormeltingsnowandicearealteringhydrologicalsystems,affectingwaterresourcesintermsofquantityandquality(mediumconfidence).Manyterrestrial,freshwaterandmarinespecieshaveshiftedtheirgeographicranges,seasonalactivities,migrationpatterns,abundancesandspeciesinteractionsinresponsetoongoingclimatechange(highconfidence).Someimpactsonhumansystemshavealsobeenattributedtoclimatechange,withamajororminorcontributionofclimatechangedistinguishablefromotherinfluences(FigureSPM.4).Assessmentofmanystudiescoveringawiderangeofregionsandcropsshowsthatnegativeimpactsofclimatechangeoncropyieldshavebeenmorecommonthanpositiveimpacts(highconfidence).Someimpactsofoceanacidificationonmarineorganismshavebeenattributedtohumaninfluence(mediumconfidence).{1.3.2}6SummaryforPolicymakersWidespreadimpactsattributedtoclimatechangebasedontheavailablescientiﬁcliteraturesincetheAR4POLARREGIONS(ArcticandAntarctic)NORTHAMERICAEUROPEASIASPMSMALLISLANDS105449329AFRICACENTRALANDSOUTHAMERICA8101AUSTRALASIA198729823255ConﬁdenceinattributionObservedimpactsattributedtoclimatechangefortoclimatechangePhysicalsystemsBiologicalsystemsHumanandmanagedsystemsImpactsidentiﬁedvloewrylowmedhighhveigrhyGlaciers,snow,iceTerrestrialFoodproductionbasedonavailabilityand/orpermafrostecosystemsofstudiesacrossindicatesLivelihoods,healtharegionconﬁdencerangeRivers,lakes,ﬂoodsWildﬁreand/oreconomicsand/ordroughtCoastalerosionMarineecosystemsand/orsealeveleffectsOutlinedsymbols=MinorcontributionofclimatechangeFilledsymbols=MajorcontributionofclimatechangeFigureSPM.4BasedontheavailablescientificliteraturesincetheIPCCFourthAssessmentReport(AR4),therearesubstantiallymoreimpactsinrecentdecadesnowattributedtoclimatechange.Attributionrequiresdefinedscientificevidenceontheroleofclimatechange.Absencefromthemapofaddi-tionalimpactsattributedtoclimatechangedoesnotimplythatsuchimpactshavenotoccurred.Thepublicationssupportingattributedimpactsreflectagrowingknowledgebase,butpublicationsarestilllimitedformanyregions,systemsandprocesses,highlightinggapsindataandstudies.Symbolsindicatecategoriesofattributedimpacts,therelativecontributionofclimatechange(majororminor)totheobservedimpactandconfidenceinattribution.EachsymbolreferstooneormoreentriesinWGIITableSPM.A1,groupingrelatedregional-scaleimpacts.Numbersinovalsindicateregionaltotalsofclimatechangepublicationsfrom2001to2010,basedontheScopusbibliographicdatabaseforpublicationsinEnglishwithindividualcountriesmentionedintitle,abstractorkeywords(asofJuly2011).Thesenumbersprovideanoverallmeasureoftheavailablescientificliteratureonclimatechangeacrossregions;theydonotindicatethenumberofpublicationssupportingattributionofclimatechangeimpactsineachregion.Studiesforpolarregionsandsmallislandsaregroupedwithneighbouringcontinentalregions.TheinclusionofpublicationsforassessmentofattributionfollowedIPCCscientificevidencecriteriadefinedinWGIIChapter18.PublicationsconsideredintheattributionanalysescomefromabroaderrangeofliteratureassessedintheWGIIAR5.SeeWGIITableSPM.A1fordescriptionsoftheattributedimpacts.{Figure1.11}SPM1.4ExtremeeventsChangesinmanyextremeweatherandclimateeventshavebeenobservedsinceabout1950.Someofthesechangeshavebeenlinkedtohumaninfluences,includingadecreaseincoldtem-peratureextremes,anincreaseinwarmtemperatureextremes,anincreaseinextremehighsealevelsandanincreaseinthenumberofheavyprecipitationeventsinanumberofregions.{1.4}Itisverylikelythatthenumberofcolddaysandnightshasdecreasedandthenumberofwarmdaysandnightshasincreasedontheglobalscale.ItislikelythatthefrequencyofheatwaveshasincreasedinlargepartsofEurope,AsiaandAustralia.Itis7SummaryforPolicymakersverylikelythathumaninfluencehascontributedtotheobservedglobalscalechangesinthefrequencyandintensityofdailytemperatureextremessincethemid-20thcentury.Itislikelythathumaninfluencehasmorethandoubledtheprob-abilityofoccurrenceofheatwavesinsomelocations.Thereismediumconfidencethattheobservedwarminghasincreasedheat-relatedhumanmortalityanddecreasedcold-relatedhumanmortalityinsomeregions.{1.4}Therearelikelymorelandregionswherethenumberofheavyprecipitationeventshasincreasedthanwhereithasdecreased.SPMRecentdetectionofincreasingtrendsinextremeprecipitationanddischargeinsomecatchmentsimpliesgreaterrisksoffloodingatregionalscale(mediumconfidence).Itislikelythatextremesealevels(forexample,asexperiencedinstormsurges)haveincreasedsince1970,beingmainlyaresultofrisingmeansealevel.{1.4}Impactsfromrecentclimate-relatedextremes,suchasheatwaves,droughts,floods,cyclonesandwildfires,revealsignificantvulnerabilityandexposureofsomeecosystemsandmanyhumansystemstocurrentclimatevariability(veryhighconfi-dence).{1.4}SPM2.FutureClimateChanges,RisksandImpactsContinuedemissionofgreenhousegaseswillcausefurtherwarmingandlong-lastingchangesinallcomponentsoftheclimatesystem,increasingthelikelihoodofsevere,pervasiveandirreversibleimpactsforpeopleandecosystems.Limitingclimatechangewouldrequiresubstantialandsustainedreductionsingreenhousegasemissionswhich,togetherwithadaptation,canlimitclimatechangerisks.{2}SPM2.1KeydriversoffutureclimateCumulativeemissionsofCO2largelydetermineglobalmeansurfacewarmingbythelate21stcenturyandbeyond.Projectionsofgreenhousegasemissionsvaryoverawiderange,dependingonbothsocio-economicdevelopmentandclimatepolicy.{2.1}AnthropogenicGHGemissionsaremainlydrivenbypopulationsize,economicactivity,lifestyle,energyuse,landusepatterns,technologyandclimatepolicy.TheRepresentativeConcentrationPathways(RCPs),whichareusedformakingprojectionsbasedonthesefactors,describefourdifferent21stcenturypathwaysofGHGemissionsandatmosphericconcentrations,airpollutantemissionsandlanduse.TheRCPsincludeastringentmitigationscenario(RCP2.6),twointermediatescenarios(RCP4.5andRCP6.0)andonescenariowithveryhighGHGemissions(RCP8.5).Scenarioswithoutadditionaleffortstoconstrainemissions(’baselinescenarios’)leadtopathwaysrangingbetweenRCP6.0andRCP8.5(FigureSPM.5a).RCP2.6isrepresentativeofascenariothataimstokeepglobalwarminglikelybelow2°Cabovepre-industrialtemperatures.TheRCPsareconsistentwiththewiderangeofscenariosintheliteratureasassessedbyWGIII5.{2.1,Box2.2,4.3}Multiplelinesofevidenceindicateastrong,consistent,almostlinearrelationshipbetweencumulativeCO2emissionsandprojectedglobaltemperaturechangetotheyear2100inboththeRCPsandthewidersetofmitigationscenariosanalysedinWGIII(FigureSPM.5b).AnygivenlevelofwarmingisassociatedwitharangeofcumulativeCO2emissions6,andtherefore,e.g.,higheremissionsinearlierdecadesimplyloweremissionslater.{2.2.5,Table2.2}5Roughly300baselinescenariosand900mitigationscenariosarecategorizedbyCO2-equivalentconcentration(CO2-eq)by2100.TheCO2-eqincludestheforcingduetoallGHGs(includinghalogenatedgasesandtroposphericozone),aerosolsandalbedochange.6QuantificationofthisrangeofCO2emissionsrequirestakingintoaccountnon-CO2drivers.8SummaryforPolicymakers(a)AnnualanthropogenicCO2emissions200WGIIIscenariocategories:>1000720−1000Annualemissions(GtCO2/yr)580−720FullrangeoftheWGIIIAR5SPMscenariodatabasein2100100530−580480−530430−4800HistoricalRCPscenarios:emissions−100RCP8.51950RCP6.0RCP4.5(b)RCP2.652000205021004YearWarmingversuscumulativeCO2emissionsTemperaturechangerelativeto1861–1880(°C)Totalhuman-inducedwarmingbaselines3720–1000580–7202530–580480–530430–4801observed2000s1000GtC2000GtC00100020003000400050006000700080009000CumulativeanthropogenicCO2emissionsfrom1870(GtCO2)FigureSPM.5(a)Emissionsofcarbondioxide(CO2)aloneintheRepresentativeConcentrationPathways(RCPs)(lines)andtheassociatedscenariocategoriesusedinWGIII(colouredareasshow5to95%range).TheWGIIIscenariocategoriessummarizethewiderangeofemissionscenariospublishedinthescientificliteratureandaredefinedonthebasisofCO2-eqconcentrationlevels(inppm)in2100.ThetimeseriesofothergreenhousegasemissionsareshowninBox2.2,Figure1.(b)GlobalmeansurfacetemperatureincreaseatthetimeglobalCO2emissionsreachagivennetcumulativetotal,plottedasafunctionofthattotal,fromvariouslinesofevidence.Colouredplumeshowsthespreadofpastandfutureprojectionsfromahierarchyofclimate-carboncyclemodelsdrivenbyhistoricalemissionsandthefourRCPsoveralltimesoutto2100,andfadeswiththedecreasingnumberofavailablemodels.Ellipsesshowtotalanthropogenicwarmingin2100versuscumulativeCO2emissionsfrom1870to2100fromasimpleclimatemodel(medianclimateresponse)underthescenariocategoriesusedinWGIII.Thewidthoftheellipsesintermsoftemperatureiscausedbytheimpactofdifferentscenariosfornon-CO2climatedrivers.Thefilledblackellipseshowsobservedemissionsto2005andobservedtemperaturesinthedecade2000–2009withassociateduncertainties.{Box2.2,Figure1;Figure2.3}9SummaryforPolicymakersMulti-modelresultsshowthatlimitingtotalhuman-inducedwarmingtolessthan2°Crelativetotheperiod1861–1880withaprobabilityof>66%7wouldrequirecumulativeCO2emissionsfromallanthropogenicsourcessince1870toremainbelowabout2900GtCO2(witharangeof2550to3150GtCO2dependingonnon-CO2drivers).About1900GtCO8hadalreadybeen2emittedby2011.ForadditionalcontextseeTable2.2.{2.2.5}SPMSPM2.2ProjectedchangesintheclimatesystemSurfacetemperatureisprojectedtoriseoverthe21stcenturyunderallassessedemissionscenarios.Itisverylikelythatheatwaveswilloccurmoreoftenandlastlonger,andthatextremeprecipitationeventswillbecomemoreintenseandfrequentinmanyregions.Theoceanwillcontinuetowarmandacidify,andglobalmeansealeveltorise.{2.2}TheprojectedchangesinSectionSPM2.2arefor2081–2100relativeto1986–2005,unlessotherwiseindicated.Futureclimatewilldependoncommittedwarmingcausedbypastanthropogenicemissions,aswellasfutureanthropogenicemissionsandnaturalclimatevariability.Theglobalmeansurfacetemperaturechangefortheperiod2016–2035relativeto1986–2005issimilarforthefourRCPsandwilllikelybeintherange0.3°Cto0.7°C(mediumconfidence).Thisassumesthattherewillbenomajorvolcaniceruptionsorchangesinsomenaturalsources(e.g.,CH4andN2O),orunexpectedchangesintotalsolarirradiance.Bymid-21stcentury,themagnitudeoftheprojectedclimatechangeissubstantiallyaffectedbythechoiceofemissionsscenario.{2.2.1,Table2.1}Relativeto1850–1900,globalsurfacetemperaturechangefortheendofthe21stcentury(2081–2100)isprojectedtolikelyexceed1.5°CforRCP4.5,RCP6.0andRCP8.5(highconfidence).Warmingislikelytoexceed2°CforRCP6.0andRCP8.5(highconfidence),morelikelythannottoexceed2°CforRCP4.5(mediumconfidence),butunlikelytoexceed2°CforRCP2.6(mediumconfidence).{2.2.1}Theincreaseofglobalmeansurfacetemperaturebytheendofthe21stcentury(2081–2100)relativeto1986–2005islikelytobe0.3°Cto1.7°CunderRCP2.6,1.1°Cto2.6°CunderRCP4.5,1.4°Cto3.1°CunderRCP6.0and2.6°Cto4.8°CunderRCP8.59.TheArcticregionwillcontinuetowarmmorerapidlythantheglobalmean(FigureSPM.6a,FigureSPM.7a).{2.2.1,Figure2.1,Figure2.2,Table2.1}Itisvirtuallycertainthattherewillbemorefrequenthotandfewercoldtemperatureextremesovermostlandareasondailyandseasonaltimescales,asglobalmeansurfacetemperatureincreases.Itisverylikelythatheatwaveswilloccurwithahigherfrequencyandlongerduration.Occasionalcoldwinterextremeswillcontinuetooccur.{2.2.1}7Correspondingfiguresforlimitingwarmingto2°Cwithaprobabilityof>50%and>33%are3000GtCO2(rangeof2900to3200GtCO2)and3300GtCO2(rangeof2950to3800GtCO2)respectively.Higherorlowertemperaturelimitswouldimplylargerorlowercumulativeemissionsrespectively.8Thiscorrespondstoabouttwothirdsofthe2900GtCO2thatwouldlimitwarmingtolessthan2°Cwithaprobabilityof>66%;toabout63%ofthetotalamountof3000GtCO2thatwouldlimitwarmingtolessthan2°Cwithaprobabilityof>50%;andtoabout58%ofthetotalamountof3300GtCO2thatwouldlimitwarmingtolessthan2°Cwithaprobabilityof>33%.9Theperiod1986–2005isapproximately0.61[0.55to0.67]°Cwarmerthan1850–1900.{2.2.1}10SummaryforPolicymakers(a)GlobalaveragesurfacetemperaturechangeMeanover(relativeto1986–2005)2081–210064SPM39(m)RCP2.6(°C)2RCP4.5RCP6.0032RCP8.5–2205021002000YearMeanover(b)Globalmeansealevelrise2081–2100(relativeto1986–2005)10.80.6RCP2.621RCP4.5RCP6.00.4RCP8.50.2210200020502100YearFigureSPM.6Globalaveragesurfacetemperaturechange(a)andglobalmeansealevelrise10(b)from2006to2100asdeterminedbymulti-modelsimulations.Allchangesarerelativeto1986–2005.Timeseriesofprojectionsandameasureofuncertainty(shading)areshownforscenariosRCP2.6(blue)andRCP8.5(red).Themeanandassociateduncertaintiesaveragedover2081–2100aregivenforallRCPscenariosascolouredverticalbarsattherighthandsideofeachpanel.ThenumberofCoupledModelIntercomparisonProjectPhase5(CMIP5)modelsusedtocalculatethemulti-modelmeanisindicated.{2.2,Figure2.1}Changesinprecipitationwillnotbeuniform.ThehighlatitudesandtheequatorialPacificarelikelytoexperienceanincreaseinannualmeanprecipitationundertheRCP8.5scenario.Inmanymid-latitudeandsubtropicaldryregions,meanprecipi-tationwilllikelydecrease,whileinmanymid-latitudewetregions,meanprecipitationwilllikelyincreaseundertheRCP8.5scenario(FigureSPM.7b).Extremeprecipitationeventsovermostofthemid-latitudelandmassesandoverwettropicalregionswillverylikelybecomemoreintenseandmorefrequent.{2.2.2,Figure2.2}Theglobaloceanwillcontinuetowarmduringthe21stcentury,withthestrongestwarmingprojectedforthesurfaceintropicalandNorthernHemispheresubtropicalregions(FigureSPM.7a).{2.2.3,Figure2.2}10Basedoncurrentunderstanding(fromobservations,physicalunderstandingandmodelling),onlythecollapseofmarine-basedsectorsoftheAntarcticicesheet,ifinitiated,couldcauseglobalmeansealeveltorisesubstantiallyabovethelikelyrangeduringthe21stcentury.Thereismediumconfidencethatthisadditionalcontributionwouldnotexceedseveraltenthsofameterofsealevelriseduringthe21stcentury.11SummaryforPolicymakersRCP2.6RCP8.5(a)Changeinaveragesurfacetemperature(1986−2005to2081−2100)SPM3239(°C)−2−1.5−1−0.500.511.523457911(b)Changeinaverageprecipitation(1986−2005to2081−2100)3239(%)−50−40−30−20−1001020304050FigureSPM.7Changeinaveragesurfacetemperature(a)andchangeinaverageprecipitation(b)basedonmulti-modelmeanprojectionsfor2081–2100relativeto1986–2005undertheRCP2.6(left)andRCP8.5(right)scenarios.Thenumberofmodelsusedtocalculatethemulti-modelmeanisindicatedintheupperrightcornerofeachpanel.Stippling(i.e.,dots)showsregionswheretheprojectedchangeislargecomparedtonaturalinternalvariabilityandwhereatleast90%ofmodelsagreeonthesignofchange.Hatching(i.e.,diagonallines)showsregionswheretheprojectedchangeislessthanonestandarddeviationofthenaturalinternalvariability.{2.2,Figure2.2}EarthSystemModelsprojectaglobalincreaseinoceanacidificationforallRCPscenariosbytheendofthe21stcentury,withaslowrecoveryaftermid-centuryunderRCP2.6.ThedecreaseinsurfaceoceanpHisintherangeof0.06to0.07(15to17%increaseinacidity)forRCP2.6,0.14to0.15(38to41%)forRCP4.5,0.20to0.21(58to62%)forRCP6.0and0.30to0.32(100to109%)forRCP8.5.{2.2.4,Figure2.1}Year-roundreductionsinArcticseaiceareprojectedforallRCPscenarios.Anearlyice-free11ArcticOceaninthesummersea-iceminimuminSeptemberbeforemid-centuryislikelyforRCP8.512(mediumconfidence).{2.2.3,Figure2.1}Itisvirtuallycertainthatnear-surfacepermafrostextentathighnorthernlatitudeswillbereducedasglobalmeansurfacetemperatureincreases,withtheareaofpermafrostnearthesurface(upper3.5m)projectedtodecreaseby37%(RCP2.6)to81%(RCP8.5)forthemulti-modelaverage(mediumconfidence).{2.2.3}Theglobalglaciervolume,excludingglaciersontheperipheryofAntarctica(andexcludingtheGreenlandandAntarcticicesheets),isprojectedtodecreaseby15to55%forRCP2.6andby35to85%forRCP8.5(mediumconfidence).{2.2.3}11Whensea-iceextentislessthanonemillionkm2foratleastfiveconsecutiveyears.12Basedonanassessmentofthesubsetofmodelsthatmostcloselyreproducetheclimatologicalmeanstateand1979–2012trendoftheArcticsea-iceextent.12SummaryforPolicymakersTherehasbeensignificantimprovementinunderstandingandprojectionofsealevelchangesincetheAR4.Globalmeansealevelrisewillcontinueduringthe21stcentury,verylikelyatafasterratethanobservedfrom1971to2010.Fortheperiod2081–2100relativeto1986–2005,therisewilllikelybeintherangesof0.26to0.55mforRCP2.6,andof0.45to0.82mforRCP8.5(mediumconfidence)10(FigureSPM.6b).Sealevelrisewillnotbeuniformacrossregions.Bytheendofthe21stcentury,itisverylikelythatsealevelwillriseinmorethanabout95%oftheoceanarea.About70%ofthecoastlinesworldwideareprojectedtoexperienceasealevelchangewithin±20%oftheglobalmean.{2.2.3}SPMSPM2.3FuturerisksandimpactscausedbyachangingclimateClimatechangewillamplifyexistingrisksandcreatenewrisksfornaturalandhumansys-tems.Risksareunevenlydistributedandaregenerallygreaterfordisadvantagedpeopleandcommunitiesincountriesatalllevelsofdevelopment.{2.3}Riskofclimate-relatedimpactsresultsfromtheinteractionofclimate-relatedhazards(includinghazardouseventsandtrends)withthevulnerabilityandexposureofhumanandnaturalsystems,includingtheirabilitytoadapt.Risingratesandmagnitudesofwarmingandotherchangesintheclimatesystem,accompaniedbyoceanacidification,increasetheriskofsevere,pervasiveandinsomecasesirreversibledetrimentalimpacts.Somerisksareparticularlyrelevantforindividualregions(FigureSPM.8),whileothersareglobal.Theoverallrisksoffutureclimatechangeimpactscanbereducedbylimitingtherateandmagnitudeofclimatechange,includingoceanacidification.Thepreciselevelsofclimatechangesufficienttotriggerabruptandirreversiblechangeremainuncertain,buttheriskassociatedwithcrossingsuchthresholdsincreaseswithrisingtemperature(mediumconfidence).Forriskassessment,itisimportanttoevaluatethewidestpossiblerangeofimpacts,includinglow-probabilityoutcomeswithlargeconsequences.{1.5,2.3,2.4,3.3,BoxIntroduction.1,Box2.3,Box2.4}Alargefractionofspeciesfacesincreasedextinctionriskduetoclimatechangeduringandbeyondthe21stcentury,espe-ciallyasclimatechangeinteractswithotherstressors(highconfidence).Mostplantspeciescannotnaturallyshifttheirgeographicalrangessufficientlyfasttokeepupwithcurrentandhighprojectedratesofclimatechangeinmostlandscapes;mostsmallmammalsandfreshwatermolluscswillnotbeabletokeepupattheratesprojectedunderRCP4.5andaboveinflatlandscapesinthiscentury(highconfidence).Futureriskisindicatedtobehighbytheobservationthatnaturalglobalclimatechangeatrateslowerthancurrentanthropogenicclimatechangecausedsignificantecosystemshiftsandspeciesextinctionsduringthepastmillionsofyears.Marineorganismswillfaceprogressivelyloweroxygenlevelsandhighratesandmagnitudesofoceanacidification(highconfidence),withassociatedrisksexacerbatedbyrisingoceantemperatureextremes(mediumconfidence).Coralreefsandpolarecosystemsarehighlyvulnerable.Coastalsystemsandlow-lyingareasareatriskfromsealevelrise,whichwillcontinueforcenturieseveniftheglobalmeantemperatureisstabilized(highconfidence).{2.3,2.4,Figure2.5}Climatechangeisprojectedtounderminefoodsecurity(FigureSPM.9).Duetoprojectedclimatechangebythemid-21stcenturyandbeyond,globalmarinespeciesredistributionandmarinebiodiversityreductioninsensitiveregionswillchallengethesustainedprovisionoffisheriesproductivityandotherecosystemservices(highconfidence).Forwheat,riceandmaizeintropicalandtemper-ateregions,climatechangewithoutadaptationisprojectedtonegativelyimpactproductionforlocaltemperatureincreasesof2°Cormoreabovelate20thcenturylevels,althoughindividuallocationsmaybenefit(mediumconfidence).Globaltem-peratureincreasesof~4°Cormore13abovelate20thcenturylevels,combinedwithincreasingfooddemand,wouldposelargeriskstofoodsecurityglobally(highconfidence).Climatechangeisprojectedtoreducerenewablesurfacewaterandgroundwaterresourcesinmostdrysubtropicalregions(robustevidence,highagreement),intensifyingcompetitionforwateramongsectors(limitedevidence,mediumagreement).{2.3.1,2.3.2}13ProjectedwarmingaveragedoverlandislargerthanglobalaveragewarmingforallRCPscenariosfortheperiod2081–2100relativeto1986–2005.Forregionalprojections,seeFigureSPM.7.{2.2}13SummaryforPolicymakersSPM14RepresentativekeyrisksforeachregionforRegionalkeyrisksandPhysicalsystemsBiologicalsystemsHumanandmanagedsystemspotentialforriskreductionGlaciers,Rivers,lakes,CoastalerosionTerrestrialWildﬁreMarineFoodLivelihoods,healthsnow,iceﬂoodsand/orand/orsealevelecosystemsecosystemsproductionand/oreconomicsand/ordroughteffectspermafrostVeryRisklevelVeryPolarRegions(ArcticandAntarctic)RisksforhealthUnprecedentedchallenges,lowMediumhighRisksforecosystemsandwell-beingespeciallyfromrateofchangePresentNearterm(2030–2040)Longterm2°C(2080–2100)4°CNorthAmericaIncreaseddamagesfromEuropeRisklevelwithPotentialforriverandcoastalﬂoodshighadaptationadditionalRisklevelwithHeat-relatedadaptationtocurrentadaptationhumanmortalityreduceriskIncreaseddamagesIncreaseddamagesAsiafromwildﬁresfromriverandcoastalurbanﬂoodsIncreasedwaterrestrictionsIncreaseddamagesIncreasedﬂooddamagetoIncreaseddrought-fromextremeheatrelatedwaterandeventsandwildﬁresfoodshortageinfrastructure,livelihoodsHeat-relatedandsettlementshumanmortalityTheOceanCentralandSouthAmericaAfricaSmallislandsAustralasiaDistributionalReducedwateravailabilityandCompoundedstressshiftandreducedincreasedﬂoodingandlandslidesonwaterresourcesLossoflivelihoods,Signiﬁcantchangeincompositionﬁsheriescatchsettlements,infrastructure,andstructureofcoralreefsystemspotentialatlowlatitudesReducedfoodproductionandqualityReducedcropproductivityandecosystemservicesandlivelihoodandfoodsecurityeconomicstabilityIncreasedmasscoralSpreadofvector-bornediseasesbleachingandmortalitynotassessedVector-andwater-Risksforlow-lyingIncreasedﬂooddamageIncreasedriskstonotassessedbornediseasescoastalareastoinfrastructureandcoastalinfrastructureCoastalinundationsettlementsandlow-lyingandhabitatlossecosystemsFigureSPM.8Representativekeyrisks14foreachregion,includingthepotentialforriskreductionthroughadaptationandmitigation,aswellaslimitstoadaptation.Eachkeyriskisassessedasverylow,low,medium,highorveryhigh.Risklevelsarepresentedforthreetimeframes:present,nearterm(here,for2030–2040)andlongterm(here,for2080–2100).Inthenearterm,projectedlevelsofglobalmeantemperatureincreasedonotdivergesubstantiallyacrossdifferentemissionscenarios.Forthelongterm,risklevelsarepresentedfortwopossiblefutures(2°Cand4°Cglobalmeantemperatureincreaseabovepre-industriallevels).Foreachtimeframe,risklevelsareindicatedforacontinuationofcurrentadaptationandassuminghighlevelsofcurrentorfutureadaptation.Risklevelsarenotnecessarilycomparable,especiallyacrossregions.{Figure2.4}14Identificationofkeyriskswasbasedonexpertjudgmentusingthefollowingspecificcriteria:largemagnitude,highprobabilityorirreversibilityofimpacts;timingofimpacts;persistentvulnerabilityorexposurecontributingtorisks;orlimitedpotentialtoreducerisksthroughadaptationormitigation.SummaryforPolicymakersClimatechangeposesrisksforfoodproduction(a)Changeinmaximumcatchpotential(2051–2060comparedto2001–2010,SRESA1B)<–50%–21to–50%–6to–20%–1to–5%nodata0to4%5to19%20to49%50to100%>100%SPM(b)100PercentageofyieldprojectionsRangeofyieldchange8050to100%25to50%60increase10to25%inyield5to10%0to5%4020decrease0to–5%inyield–5to–10%–10to–25%–25to–50%–50to–100%02030–20492050–20692070–20892090–21092010–2029FigureSPM.9(a)Projectedglobalredistributionofmaximumcatchpotentialof~1000exploitedmarinefishandinvertebratespecies.Projectionscomparethe10-yearaverages2001–2010and2051–2060usingoceanconditionsbasedonasingleclimatemodelunderamoderatetohighwarmingscenario,withoutanalysisofpotentialimpactsofoverfishingoroceanacidification.(b)Summaryofprojectedchangesincropyields(mostlywheat,maize,riceandsoy),duetoclimatechangeoverthe21stcentury.Dataforeachtimeframesumto100%,indicatingthepercentageofprojectionsshowingyieldincreasesversusdecreases.Thefigureincludesprojections(basedon1090datapoints)fordifferentemissionscenarios,fortropicalandtemperateregionsandforadaptationandno-adaptationcasescombined.Changesincropyieldsarerelativetolate20thcenturylevels.{Figure2.6a,Figure2.7}Untilmid-century,projectedclimatechangewillimpacthumanhealthmainlybyexacerbatinghealthproblemsthatalreadyexist(veryhighconfidence).Throughoutthe21stcentury,climatechangeisexpectedtoleadtoincreasesinill-healthinmanyregionsandespeciallyindevelopingcountrieswithlowincome,ascomparedtoabaselinewithoutclimatechange(highconfidence).By2100forRCP8.5,thecombinationofhightemperatureandhumidityinsomeareasforpartsoftheyearisexpectedtocompromisecommonhumanactivities,includinggrowingfoodandworkingoutdoors(highconfidence).{2.3.2}Inurbanareasclimatechangeisprojectedtoincreaserisksforpeople,assets,economiesandecosystems,includingrisksfromheatstress,stormsandextremeprecipitation,inlandandcoastalflooding,landslides,airpollution,drought,waterscar-city,sealevelriseandstormsurges(veryhighconfidence).Theserisksareamplifiedforthoselackingessentialinfrastructureandservicesorlivinginexposedareas.{2.3.2}15SummaryforPolicymakersRuralareasareexpectedtoexperiencemajorimpactsonwateravailabilityandsupply,foodsecurity,infrastructureandagriculturalincomes,includingshiftsintheproductionareasoffoodandnon-foodcropsaroundtheworld(highconfidence).{2.3.2}Aggregateeconomiclossesacceleratewithincreasingtemperature(limitedevidence,highagreement),butglobaleconomicimpactsfromclimatechangearecurrentlydifficulttoestimate.Fromapovertyperspective,climatechangeimpactsareSPMprojectedtoslowdowneconomicgrowth,makepovertyreductionmoredifficult,furthererodefoodsecurityandprolongexistingandcreatenewpovertytraps,thelatterparticularlyinurbanareasandemerginghotspotsofhunger(mediumconfi-dence).Internationaldimensionssuchastradeandrelationsamongstatesarealsoimportantforunderstandingtherisksofclimatechangeatregionalscales.{2.3.2}Climatechangeisprojectedtoincreasedisplacementofpeople(mediumevidence,highagreement).Populationsthatlacktheresourcesforplannedmigrationexperiencehigherexposuretoextremeweatherevents,particularlyindevelopingcoun-trieswithlowincome.Climatechangecanindirectlyincreaserisksofviolentconflictsbyamplifyingwell-documenteddriversoftheseconflictssuchaspovertyandeconomicshocks(mediumconfidence).{2.3.2}SPM2.4Climatechangebeyond2100,irreversibilityandabruptchangesManyaspectsofclimatechangeandassociatedimpactswillcontinueforcenturies,evenifanthropogenicemissionsofgreenhousegasesarestopped.Therisksofabruptorirreversiblechangesincreaseasthemagnitudeofthewarmingincreases.{2.4}Warmingwillcontinuebeyond2100underallRCPscenariosexceptRCP2.6.SurfacetemperatureswillremainapproximatelyconstantatelevatedlevelsformanycenturiesafteracompletecessationofnetanthropogenicCO2emissions.Alargefrac-tionofanthropogenicclimatechangeresultingfromCO2emissionsisirreversibleonamulti-centurytomillennialtimescale,exceptinthecaseofalargenetremovalofCO2fromtheatmosphereoverasustainedperiod.{2.4,Figure2.8}Stabilizationofglobalaveragesurfacetemperaturedoesnotimplystabilizationforallaspectsoftheclimatesystem.Shiftingbiomes,soilcarbon,icesheets,oceantemperaturesandassociatedsealevelriseallhavetheirownintrinsiclongtimescaleswhichwillresultinchangeslastinghundredstothousandsofyearsafterglobalsurfacetemperatureisstabilized.{2.1,2.4}ThereishighconfidencethatoceanacidificationwillincreaseforcenturiesifCO2emissionscontinue,andwillstronglyaffectmarineecosystems.{2.4}Itisvirtuallycertainthatglobalmeansealevelrisewillcontinueformanycenturiesbeyond2100,withtheamountofrisedependentonfutureemissions.ThethresholdforthelossoftheGreenlandicesheetoveramillenniumormore,andanasso-ciatedsealevelriseofupto7m,isgreaterthanabout1°C(lowconfidence)butlessthanabout4°C(mediumconfidence)ofglobalwarmingwithrespecttopre-industrialtemperatures.AbruptandirreversibleicelossfromtheAntarcticicesheetispossible,butcurrentevidenceandunderstandingisinsufficienttomakeaquantitativeassessment.{2.4}Magnitudesandratesofclimatechangeassociatedwithmedium-tohigh-emissionscenariosposeanincreasedriskofabruptandirreversibleregional-scalechangeinthecomposition,structureandfunctionofmarine,terrestrialandfreshwaterecosystems,includingwetlands(mediumconfidence).Areductioninpermafrostextentisvirtuallycertainwithcontinuedriseinglobaltemperatures.{2.4}16SummaryforPolicymakersSPM3.FuturePathwaysforAdaptation,MitigationandSustainableDevelopmentAdaptationandmitigationarecomplementarystrategiesforreducingandmanagingtherisksofclimatechange.Substantialemissionsreductionsoverthenextfewdecadescanreducecli-materisksinthe21stcenturyandbeyond,increaseprospectsforeffectiveadaptation,reducethecostsandchallengesofmitigationinthelongertermandcontributetoclimate-resilientSPMpathwaysforsustainabledevelopment.{3.2,3.3,3.4}SPM3.1Foundationsofdecision-makingaboutclimatechangeEffectivedecision-makingtolimitclimatechangeanditseffectscanbeinformedbyawiderangeofanalyticalapproachesforevaluatingexpectedrisksandbenefits,recognizingtheimportanceofgovernance,ethicaldimensions,equity,valuejudgments,economicassess-mentsanddiverseperceptionsandresponsestoriskanduncertainty.{3.1}Sustainabledevelopmentandequityprovideabasisforassessingclimatepolicies.Limitingtheeffectsofclimatechangeisnecessarytoachievesustainabledevelopmentandequity,includingpovertyeradication.Countries’pastandfuturecontri-butionstotheaccumulationofGHGsintheatmospherearedifferent,andcountriesalsofacevaryingchallengesandcircum-stancesandhavedifferentcapacitiestoaddressmitigationandadaptation.Mitigationandadaptationraiseissuesofequity,justiceandfairness.ManyofthosemostvulnerabletoclimatechangehavecontributedandcontributelittletoGHGemis-sions.Delayingmitigationshiftsburdensfromthepresenttothefuture,andinsufficientadaptationresponsestoemergingimpactsarealreadyerodingthebasisforsustainabledevelopment.Comprehensivestrategiesinresponsetoclimatechangethatareconsistentwithsustainabledevelopmenttakeintoaccounttheco-benefits,adversesideeffectsandrisksthatmayarisefrombothadaptationandmitigationoptions.{3.1,3.5,Box3.4}Thedesignofclimatepolicyisinfluencedbyhowindividualsandorganizationsperceiverisksanduncertaintiesandtakethemintoaccount.Methodsofvaluationfromeconomic,socialandethicalanalysisareavailabletoassistdecision-making.Thesemethodscantakeaccountofawiderangeofpossibleimpacts,includinglow-probabilityoutcomeswithlargeconse-quences.Buttheycannotidentifyasinglebestbalancebetweenmitigation,adaptationandresidualclimateimpacts.{3.1}Climatechangehasthecharacteristicsofacollectiveactionproblemattheglobalscale,becausemostGHGsaccumulateovertimeandmixglobally,andemissionsbyanyagent(e.g.,individual,community,company,country)affectotheragents.Effectivemitigationwillnotbeachievedifindividualagentsadvancetheirowninterestsindependently.Cooperativeresponses,includinginternationalcooperation,arethereforerequiredtoeffectivelymitigateGHGemissionsandaddressotherclimatechangeissues.Theeffectivenessofadaptationcanbeenhancedthroughcomplementaryactionsacrosslevels,includinginternationalcooperation.Theevidencesuggeststhatoutcomesseenasequitablecanleadtomoreeffectivecooperation.{3.1}SPM3.2ClimatechangerisksreducedbymitigationandadaptationWithoutadditionalmitigationeffortsbeyondthoseinplacetoday,andevenwithadaptation,warmingbytheendofthe21stcenturywillleadtohightoveryhighriskofsevere,wide-spreadandirreversibleimpactsglobally(highconfidence).Mitigationinvolvessomelevelofco-benefitsandofrisksduetoadversesideeffects,buttheserisksdonotinvolvethesamepossibilityofsevere,widespreadandirreversibleimpactsasrisksfromclimatechange,increasingthebenefitsfromnear-termmitigationefforts.{3.2,3.4}Mitigationandadaptationarecomplementaryapproachesforreducingrisksofclimatechangeimpactsoverdifferenttime-scales(highconfidence).Mitigation,intheneartermandthroughthecentury,cansubstantiallyreduceclimatechange17SummaryforPolicymakersimpactsinthelatterdecadesofthe21stcenturyandbeyond.Benefitsfromadaptationcanalreadyberealizedinaddressingcurrentrisks,andcanberealizedinthefutureforaddressingemergingrisks.{3.2,4.5}FiveReasonsForConcern(RFCs)aggregateclimatechangerisksandillustratetheimplicationsofwarmingandofadaptationlimitsforpeople,economiesandecosystemsacrosssectorsandregions.ThefiveRFCsareassociatedwith:(1)Uniqueandthreatenedsystems,(2)Extremeweatherevents,(3)Distributionofimpacts,(4)Globalaggregateimpacts,and(5)Large-SPMscalesingularevents.Inthisreport,theRFCsprovideinformationrelevanttoArticle2ofUNFCCC.{Box2.4}Withoutadditionalmitigationeffortsbeyondthoseinplacetoday,andevenwithadaptation,warmingbytheendofthe21stcenturywillleadtohightoveryhighriskofsevere,widespreadandirreversibleimpactsglobally(highconfidence)(FigureSPM.10).Inmostscenarioswithoutadditionalmitigationefforts(thosewith2100atmosphericconcentrations(a)Risksfromclimatechange...(b)...dependoncumulativeCO2emissions...5Globalmeantemperaturechange(°Crelativetopre-industriallevels)4baselines3720–1000580–7202530–580480–530430–4801observed2000ssystemsreventsimpactspactsevents010002000300040005000600070008000m100CumulativeanthropogenicCO2emissionsfrom1870(GtCO2)atenedweathetionofegateiingular50thretremeistribulaggrcalesChangeinannualGHGemissions&DGlobaarge-sin2050(%relativeto2010levels)0baselinesiqueExUnLemissionemission720–1000reductionsincreaseLevelofadditional580–720riskduetoclimatechange(seeBox2.4)nochangerelativeto2010Veryhigh530–580480–530High−50430–480Moderate−100Undetectable(c)…whichinturndependonannualGHGemissionsoverthenextdecadesFigureSPM.10Therelationshipbetweenrisksfromclimatechange,temperaturechange,cumulativecarbondioxide(CO2)emissionsandchangesinannualgreenhousegas(GHG)emissionsby2050.LimitingrisksacrossReasonsForConcern(a)wouldimplyalimitforcumulativeemissionsofCO2(b)whichwouldconstrainannualGHGemissionsoverthenextfewdecades(c).PanelareproducesthefiveReasonsForConcern{Box2.4}.PanelblinkstemperaturechangestocumulativeCO2emissions(inGtCO2)from1870.TheyarebasedonCoupledModelIntercomparisonProjectPhase5(CMIP5)simulations(pinkplume)andonasimpleclimatemodel(medianclimateresponsein2100),forthebaselinesandfivemitigationscenariocategories(sixellipses).DetailsareprovidedinFigureSPM.5.PanelcshowstherelationshipbetweenthecumulativeCO2emissions(inGtCO2)ofthescenariocatego-riesandtheirassociatedchangeinannualGHGemissionsby2050,expressedinpercentagechange(inpercentGtCO2-eqperyear)relativeto2010.TheellipsescorrespondtothesamescenariocategoriesasinPanelb,andarebuiltwithasimilarmethod(seedetailsinFigureSPM.5).{Figure3.1}18SummaryforPolicymakers>1000ppmCO2-eq),warmingismorelikelythannottoexceed4°Cabovepre-industriallevelsby2100(TableSPM.1).Therisksassociatedwithtemperaturesatorabove4°Cincludesubstantialspeciesextinction,globalandregionalfoodinsecurity,consequentialconstraintsoncommonhumanactivitiesandlimitedpotentialforadaptationinsomecases(highconfidence).Somerisksofclimatechange,suchasriskstouniqueandthreatenedsystemsandrisksassociatedwithextremeweatherevents,aremoderatetohighattemperatures1°Cto2°Cabovepre-industriallevels.{2.3,Figure2.5,3.2,3.4,Box2.4,TableSPM.1}SubstantialcutsinGHGemissionsoverthenextfewdecadescansubstantiallyreducerisksofclimatechangebylimitingSPMwarminginthesecondhalfofthe21stcenturyandbeyond.CumulativeemissionsofCO2largelydetermineglobalmeansurfacewarmingbythelate21stcenturyandbeyond.LimitingrisksacrossRFCswouldimplyalimitforcumulativeemissionsofCO2.SuchalimitwouldrequirethatglobalnetemissionsofCO2eventuallydecreasetozeroandwouldconstrainannualemissionsoverthenextfewdecades(FigureSPM.10)(highconfidence).Butsomerisksfromclimatedamagesareunavoid-able,evenwithmitigationandadaptation.{2.2.5,3.2,3.4}Mitigationinvolvessomelevelofco-benefitsandrisks,buttheserisksdonotinvolvethesamepossibilityofsevere,wide-spreadandirreversibleimpactsasrisksfromclimatechange.Inertiaintheeconomicandclimatesystemandthepossibilityofirreversibleimpactsfromclimatechangeincreasethebenefitsfromnear-termmitigationefforts(highconfidence).Delaysinadditionalmitigationorconstraintsontechnologicaloptionsincreasethelonger-termmitigationcoststoholdclimatechangerisksatagivenlevel(TableSPM.2).{3.2,3.4}SPM3.3CharacteristicsofadaptationpathwaysAdaptationcanreducetherisksofclimatechangeimpacts,buttherearelimitstoitseffec-tiveness,especiallywithgreatermagnitudesandratesofclimatechange.Takingalonger-termperspective,inthecontextofsustainabledevelopment,increasesthelikelihoodthatmoreimmediateadaptationactionswillalsoenhancefutureoptionsandpreparedness.{3.3}Adaptationcancontributetothewell-beingofpopulations,thesecurityofassetsandthemaintenanceofecosystemgoods,functionsandservicesnowandinthefuture.Adaptationisplace-andcontext-specific(highconfidence).Afirststeptowardsadaptationtofutureclimatechangeisreducingvulnerabilityandexposuretopresentclimatevariability(highconfidence).Integrationofadaptationintoplanning,includingpolicydesign,anddecision-makingcanpromotesynergieswithdevelop-mentanddisasterriskreduction.Buildingadaptivecapacityiscrucialforeffectiveselectionandimplementationofadapta-tionoptions(robustevidence,highagreement).{3.3}Adaptationplanningandimplementationcanbeenhancedthroughcomplementaryactionsacrosslevels,fromindividualstogovernments(highconfidence).Nationalgovernmentscancoordinateadaptationeffortsoflocalandsub-nationalgovern-ments,forexamplebyprotectingvulnerablegroups,bysupportingeconomicdiversificationandbyprovidinginformation,policyandlegalframeworksandfinancialsupport(robustevidence,highagreement).Localgovernmentandtheprivatesectorareincreasinglyrecognizedascriticaltoprogressinadaptation,giventheirrolesinscalingupadaptationofcommu-nities,householdsandcivilsocietyandinmanagingriskinformationandfinancing(mediumevidence,highagreement).{3.3}Adaptationplanningandimplementationatalllevelsofgovernancearecontingentonsocietalvalues,objectivesandriskperceptions(highconfidence).Recognitionofdiverseinterests,circumstances,social-culturalcontextsandexpectationscanbenefitdecision-makingprocesses.Indigenous,localandtraditionalknowledgesystemsandpractices,includingindigenouspeoples’holisticviewofcommunityandenvironment,areamajorresourceforadaptingtoclimatechange,butthesehavenotbeenusedconsistentlyinexistingadaptationefforts.Integratingsuchformsofknowledgewithexistingpracticesincreasestheeffectivenessofadaptation.{3.3}Constraintscaninteracttoimpedeadaptationplanningandimplementation(highconfidence).Commonconstraintsonimplementationarisefromthefollowing:limitedfinancialandhumanresources;limitedintegrationorcoordinationofgov-ernance;uncertaintiesaboutprojectedimpacts;differentperceptionsofrisks;competingvalues;absenceofkeyadapta-tionleadersandadvocates;andlimitedtoolstomonitoradaptationeffectiveness.Anotherconstraintincludesinsufficientresearch,monitoring,andobservationandthefinancetomaintainthem.{3.3}19SummaryforPolicymakersGreaterratesandmagnitudeofclimatechangeincreasethelikelihoodofexceedingadaptationlimits(highconfidence).Limitstoadaptationemergefromtheinteractionamongclimatechangeandbiophysicaland/orsocio-economicconstraints.Further,poorplanningorimplementation,overemphasizingshort-termoutcomesorfailingtosufficientlyanticipateconse-quencescanresultinmaladaptation,increasingthevulnerabilityorexposureofthetargetgroupinthefutureorthevulner-abilityofotherpeople,placesorsectors(mediumevidence,highagreement).Underestimatingthecomplexityofadaptationasasocialprocesscancreateunrealisticexpectationsaboutachievingintendedadaptationoutcomes.{3.3}SPMSignificantco-benefits,synergiesandtrade-offsexistbetweenmitigationandadaptationandamongdifferentadap-tationresponses;interactionsoccurbothwithinandacrossregions(veryhighconfidence).Increasingeffortstomitigateandadapttoclimatechangeimplyanincreasingcomplexityofinteractions,particularlyattheintersectionsamongwater,energy,landuseandbiodiversity,buttoolstounderstandandmanagetheseinteractionsremainlimited.Examplesofactionswithco-benefitsinclude(i)improvedenergyefficiencyandcleanerenergysources,leadingtoreducedemissionsofhealth-damaging,climate-alteringairpollutants;(ii)reducedenergyandwaterconsumptioninurbanareasthroughgreeningcitiesandrecyclingwater;(iii)sustainableagricultureandforestry;and(iv)protectionofecosystemsforcarbonstorageandotherecosystemservices.{3.3}Transformationsineconomic,social,technologicalandpoliticaldecisionsandactionscanenhanceadaptationandpromotesustainabledevelopment(highconfidence).Atthenationallevel,transformationisconsideredmosteffectivewhenitreflectsacountry’sownvisionsandapproachestoachievingsustainabledevelopmentinaccordancewithitsnationalcircumstancesandpriorities.Restrictingadaptationresponsestoincrementalchangestoexistingsystemsandstructures,withoutconsider-ingtransformationalchange,mayincreasecostsandlossesandmissopportunities.Planningandimplementationoftrans-formationaladaptationcouldreflectstrengthened,alteredoralignedparadigmsandmayplacenewandincreaseddemandsongovernancestructurestoreconciledifferentgoalsandvisionsforthefutureandtoaddresspossibleequityandethicalimplications.Adaptationpathwaysareenhancedbyiterativelearning,deliberativeprocessesandinnovation.{3.3}SPM3.4CharacteristicsofmitigationpathwaysTherearemultiplemitigationpathwaysthatarelikelytolimitwarmingtobelow2°Crelativetopre-industriallevels.ThesepathwayswouldrequiresubstantialemissionsreductionsoverthenextfewdecadesandnearzeroemissionsofCO2andotherlong-livedgreenhousegasesbytheendofthecentury.Implementingsuchreductionsposessubstantialtechnological,eco-nomic,socialandinstitutionalchallenges,whichincreasewithdelaysinadditionalmitigationandifkeytechnologiesarenotavailable.Limitingwarmingtolowerorhigherlevelsinvolvessimilarchallengesbutondifferenttimescales.{3.4}WithoutadditionaleffortstoreduceGHGemissionsbeyondthoseinplacetoday,globalemissionsgrowthisexpectedtopersist,drivenbygrowthinglobalpopulationandeconomicactivities.Globalmeansurfacetemperatureincreasesin2100inbaselinescenarios—thosewithoutadditionalmitigation—rangefrom3.7°Cto4.8°Cabovetheaveragefor1850–1900foramedianclimateresponse.Theyrangefrom2.5°Cto7.8°Cwhenincludingclimateuncertainty(5thto95thpercentilerange)(highconfidence).{3.4}14EmissionsscenariosleadingtoCO2-equivalentconcentrationsin2100ofabout450ppmorlowerarelikelytomaintainwarmingbelow2°Coverthe21stcenturyrelativetopre-industriallevels15.Thesescenariosarecharacterizedby40to70%globalanthropogenicGHGemissionsreductionsby2050comparedto201016,andemissionslevelsnearzeroorbelowin2100.Mitigationscenariosreachingconcentrationlevelsofabout500ppmCO2-eqby2100aremorelikelythannottolimittemperaturechangetolessthan2°C,unlesstheytemporarilyovershootconcentrationlevelsofroughly530ppmCO2-eq15Forcomparison,theCO2-eqconcentrationin2011isestimatedtobe430ppm(uncertaintyrange340to520ppm)16ThisrangediffersfromtherangeprovidedforasimilarconcentrationcategoryintheAR4(50to85%lowerthan2000forCO2only).ReasonsforthisdifferenceincludethatthisreporthasassessedasubstantiallylargernumberofscenariosthanintheAR4andlooksatallGHGs.Inaddition,alargeproportionofthenewscenariosincludeCarbonDioxideRemoval(CDR)technologies(seebelow).Otherfactorsincludetheuseof2100concentrationlevelsinsteadofstabilizationlevelsandtheshiftinreferenceyearfrom2000to2010.20SummaryforPolicymakersbefore2100,inwhichcasetheyareaboutaslikelyasnottoachievethatgoal.Inthese500ppmCO2-eqscenarios,global2050emissionslevelsare25to55%lowerthanin2010.Scenarioswithhigheremissionsin2050arecharacterizedbyagreaterrelianceonCarbonDioxideRemoval(CDR)technologiesbeyondmid-century(andviceversa).Trajectoriesthatarelikelytolimitwarmingto3°Crelativetopre-industriallevelsreduceemissionslessrapidlythanthoselimitingwarmingto2°C.Alim-itednumberofstudiesprovidescenariosthataremorelikelythannottolimitwarmingto1.5°Cby2100;thesescenariosarecharacterizedbyconcentrationsbelow430ppmCO2-eqby2100and2050emissionreductionbetween70%and95%below2010.Foracomprehensiveoverviewofthecharacteristicsofemissionsscenarios,theirCO2-equivalentconcentrationsandSPMtheirlikelihoodtokeepwarmingtobelowarangeoftemperaturelevels,seeFigureSPM.11andTableSPM.1.{3.4}(a)GHGemissionpathways2000–2100:AllAR5scenarios140AnnualGHGemissions(GtCO2-eq/yr)>1000ppmCO2-eq90thPercentileRCP8.5720–1000ppmCO2-eqMedian120580–720ppmCO2-eq10thPercentileBaseline530–580ppmCO2-eq100480–530ppmCO2-eq430–480ppmCO2-eq80FullAR5databaserange60RCP6.04020RCP4.5RCP2.60–202000202020402060208021002100Year(b)Associatedupscalingoflow-carbonenergysupply100Low-carbonenergyshareofprimaryenergy(%)580–720ppmCO2-eq530–580ppmCO2-eq480–530ppmCO2-eq430–480ppmCO2-eq+95%80+180%Percentile60Max75thMedian25thMin40+135%+275%+135%+145%+185%+310%2020502100203020502100203020502100203020102050210002030FigureSPM.11Globalgreenhousegasemissions(gigatonneofCO2-equivalentperyear,GtCO2-eq/yr)inbaselineandmitigationscenariosfordifferentlong-termconcentrationlevels(a)andassociatedupscalingrequirementsoflow-carbonenergy(%ofprimaryenergy)for2030,2050and2100comparedto2010levelsinmitigationscenarios(b).{Figure3.2}21SummaryforPolicymakersTableSPM.1KeycharacteristicsofthescenarioscollectedandassessedforWGIIIAR5.Forallparametersthe10thto90thpercentileofthescenariosisshowna.{Table3.1}CO2-eqCon-RelativeChangeinCO2-eqLikelihoodofstayingbelowaspecificcentrationsinpositionemissionscomparedtemperatureleveloverthe21stcen-ofthe2100RCPsdto2010(in%)ctury(relativeto1850–1900)d,e(ppmCO2-eq)fCategorylabelSubcategories(conc.range)SPM205021001.5ºC2ºC3ºC4ºC<430450Onlyalimitednumberofindividualmodelstudieshaveexploredlevelsbelow430ppmCO2-eqj(430to480)Totalrangea,gRCP2.6–72to–41–118to–78MoreunlikelyLikely500thanlikely(480to530)Noovershootof–57to–42–107to–73MorelikelyLikely550530ppmCO2-eq–55to–25–114to–90thannot(530to580)–47to–19–81to–59Overshootof530–16to7–183to–86Aboutas(580to650)ppmCO2-eqlikelyasnot(650to720)NoovershootofUnlikelyMoreunlikelyLikely580ppmCO2-eqthanlikelyi(720to1000)bMoreunlikelyOvershootof580thanlikely>1000bppmCO2-eqTotalrangeRCP4.5–38to24–134to–50UnlikelyMorelikelyTotalrangeRCP6.0–11to17–54to–21UnlikelyhthannotTotalrangeRCP8.5MoreunlikelyTotalrange18to54–7to72Unlikelyhthanlikely52to9574to178UnlikelyNotes:aThe‘totalrange’forthe430to480ppmCO2-eqconcentrationsscenarioscorrespondstotherangeofthe10thto90thpercentileofthesubcategoryofthesescenariosshowninTable6.3oftheWorkingGroupIIIReport.bBaselinescenariosfallintothe>1000and720to1000ppmCO2-eqcategories.Thelattercategoryalsoincludesmitigationscenarios.Thebaselinesce-nariosinthelattercategoryreachatemperaturechangeof2.5°Cto5.8°Cabovetheaveragefor1850–1900in2100.Togetherwiththebaselinescenariosinthe>1000ppmCO2-eqcategory,thisleadstoanoverall2100temperaturerangeof2.5°Cto7.8°C(rangebasedonmedianclimateresponse:3.7°Cto4.8°C)forbaselinescenariosacrossbothconcentrationcategories.cTheglobal2010emissionsare31%abovethe1990emissions(consistentwiththehistoricgreenhousegasemissionestimatespresentedinthisreport).CO2-eqemissionsincludethebasketofKyotogases(carbondioxide(CO2),methane(CH4),nitrousoxide(N2O)aswellasfluorinatedgases).dTheassessmenthereinvolvesalargenumberofscenariospublishedinthescientificliteratureandisthusnotlimitedtotheRepresentativeConcentrationPathways(RCPs).ToevaluatetheCO2-eqconcentrationandclimateimplicationsofthesescenarios,theModelfortheAssessmentofGreenhouseGasInducedClimateChange(MAGICC)wasusedinaprobabilisticmode.ForacomparisonbetweenMAGICCmodelresultsandtheoutcomesofthemodelsusedinWGI,seeWGI12.4.1.2,12.4.8andWGIII6.3.2.6.eTheassessmentinthistableisbasedontheprobabilitiescalculatedforthefullensembleofscenariosinWGIIIAR5usingMAGICCandtheassessmentinWGIoftheuncertaintyofthetemperatureprojectionsnotcoveredbyclimatemodels.ThestatementsarethereforeconsistentwiththestatementsinWGI,whicharebasedontheCoupledModelIntercomparisonProjectPhase5(CMIP5)runsoftheRCPsandtheassesseduncertainties.Hence,thelikelihoodstatementsreflectdifferentlinesofevidencefrombothWGs.ThisWGImethodwasalsoappliedforscenarioswithintermediateconcentrationlevelswherenoCMIP5runsareavailable.Thelikelihoodstatementsareindicativeonly{WGIII6.3}andfollowbroadlythetermsusedbytheWGISPMfortemperatureprojections:likely66–100%,morelikelythannot>50–100%,aboutaslikelyasnot33–66%,andunlikely0–33%.Inadditionthetermmoreunlikelythanlikely0–<50%isused.fTheCO2-equivalentconcentration(seeGlossary)iscalculatedonthebasisofthetotalforcingfromasimplecarboncycle/climatemodel,MAGICC.TheCO2-equivalentconcentrationin2011isestimatedtobe430ppm(uncertaintyrange340to520ppm).Thisisbasedontheassessmentoftotalanthropogenicradiativeforcingfor2011relativeto1750inWGI,i.e.,2.3W/m2,uncertaintyrange1.1to3.3W/m2.gThevastmajorityofscenariosinthiscategoryovershootthecategoryboundaryof480ppmCO2-eqconcentration.hForscenariosinthiscategory,noCMIP5runorMAGICCrealizationstaysbelowtherespectivetemperaturelevel.Still,anunlikelyassignmentisgiventoreflectuncertaintiesthatmaynotbereflectedbythecurrentclimatemodels.iScenariosinthe580to650ppmCO2-eqcategoryincludebothovershootscenariosandscenariosthatdonotexceedtheconcentrationlevelatthehighendofthecategory(e.g.,RCP4.5).Thelattertypeofscenarios,ingeneral,haveanassessedprobabilityofmoreunlikelythanlikelytostaybelowthe2°Ctemperaturelevel,whiletheformeraremostlyassessedtohaveanunlikelyprobabilityofstayingbelowthislevel.jInthesescenarios,globalCO2-eqemissionsin2050arebetween70to95%below2010emissions,andtheyarebetween110to120%below2010emissionsin2100.22SummaryforPolicymakersBefore2030After2030Shareofzeroandlow-carbonenergy100AnnualGHGemissionsRateofCO2emissionschangeCancún6PledgesPast1900–20106055380SPM2000–2010500Future2030–2050(GtCO2-eq/yr)(%/yr)4560(%)+90%+240%–3403540–63020–9201025AnnualGHGAR5scenariorange0203020502100203020502100emissionsin2030Interquartilerangeandmedianofmodelcomparisonswith<50GtCO2-eq–122030targets20>55GtCO2-eq200520102015202020252030YearFigureSPM.12Theimplicationsofdifferent2030greenhousegas(GHG)emissionslevelsfortherateofcarbondioxide(CO2)emissionsreductionsandlow-carbonenergyupscalinginmitigationscenariosthatareatleastaboutaslikelyasnottokeepwarmingthroughoutthe21stcenturybelow2°Crelativetopre-industriallevels(2100CO2-equivalentconcentrationsof430to530ppm).Thescenariosaregroupedaccordingtodifferentemissionslevelsby2030(colouredindifferentshadesofgreen).TheleftpanelshowsthepathwaysofGHGemissions(gigatonneofCO2-equivalentperyear,GtCO2-eq/yr)leadingtothese2030levels.TheblackdotwithwhiskersgiveshistoricGHGemissionlevelsandassociateduncertaintiesin2010asreportedinFigureSPM.2.TheblackbarshowstheestimateduncertaintyrangeofGHGemissionsimpliedbytheCancúnPledges.ThemiddlepaneldenotestheaverageannualCO2emissionsreductionratesfortheperiod2030–2050.Itcomparesthemedianandinterquartilerangeacrossscenariosfromrecentinter-modelcomparisonswithexplicit2030interimgoalstotherangeofscenariosintheScenarioDatabaseforWGIIIAR5.Annualratesofhistoricalemissionschange(sustainedoveraperiodof20years)andtheaverageannualCO2emissionchangebetween2000and2010areshownaswell.Thearrowsintherightpanelshowthemagnitudeofzeroandlow-carbonenergysupplyupscalingfrom2030to2050subjecttodifferent2030GHGemissionslevels.Zero-andlow-carbonenergysupplyincludesrenewables,nuclearenergyandfossilenergywithcarbondioxidecaptureandstorage(CCS)orbioenergywithCCS(BECCS).[Note:Onlyscenariosthatapplythefull,unconstrainedmitigationtechnologyportfoliooftheunderlyingmodels(defaulttechnologyassumption)areshown.Scenarioswithlargenetnegativeglobalemissions(>20GtCO2-eq/yr),scenarioswithexogenouscarbonpriceassumptionsandscenarioswith2010emissionssignificantlyoutsidethehistoricalrangeareexcluded.]{Figure3.3}Mitigationscenariosreachingabout450ppmCO2-eqin2100(consistentwithalikelychancetokeepwarmingbelow2°Crelativetopre-industriallevels)typicallyinvolvetemporaryovershoot17ofatmosphericconcentrations,asdomanyscenariosreachingabout500ppmCO2-eqtoabout550ppmCO2-eqin2100(TableSPM.1).Dependingonthelevelofovershoot,overshootscenariostypicallyrelyontheavailabilityandwidespreaddeploymentofbioenergywithcarbondioxidecaptureandstorage(BECCS)andafforestationinthesecondhalfofthecentury.TheavailabilityandscaleoftheseandotherCDRtechnologiesandmethodsareuncertainandCDRtechnologiesare,tovaryingdegrees,associatedwithchallengesandrisks18.CDRisalsoprevalentinmanyscenarioswithoutovershoottocompensateforresidualemissionsfromsectorswheremitigationismoreexpensive(highconfidence).{3.4,Box3.3}Reducingemissionsofnon-CO2agentscanbeanimportantelementofmitigationstrategies.AllcurrentGHGemissionsandotherforcingagentsaffecttherateandmagnitudeofclimatechangeoverthenextfewdecades,althoughlong-termwarmingismainlydrivenbyCO2emissions.Emissionsofnon-CO2forcersareoftenexpressedas‘CO2-equivalentemissions’,butthechoiceofmetrictocalculatetheseemissions,andtheimplicationsfortheemphasisandtimingofabatementofthevariousclimateforcers,dependsonapplicationandpolicycontextandcontainsvaluejudgments.{3.4,Box3.2}17Inconcentration‘overshoot’scenarios,concentrationspeakduringthecenturyandthendecline.18CDRmethodshavebiogeochemicalandtechnologicallimitationstotheirpotentialontheglobalscale.ThereisinsufficientknowledgetoquantifyhowmuchCO2emissionscouldbepartiallyoffsetbyCDRonacenturytimescale.CDRmethodsmaycarrysideeffectsandlong-termconsequencesonaglobalscale.23SummaryforPolicymakersGlobalmitigationcostsandconsumptiongrowthinbaselinescenarios10002100Percentagepointreductioninannualizedconsumptiongrowthrateover21stcentury(%-point)800Consumptionincorrespondingbaseline0.030.040.060.06scenarios(%increasefrom2010)(0.01to0.05)(0.01to0.09)(0.03to0.13)(0.04to0.14)1284thPercentileSPM10600Reductioninconsumptionrelativetobaseline(%)8400203020506210042030Median200205016thPercentile200550(530–580)500(480–530)450(430–480)Corresponding580–650baselinescenariosCO2-eqconcentrationsin2100(ppmCO2-eq)FigureSPM.13Globalmitigationcostsincost-effectivescenariosatdifferentatmosphericconcentrationslevelsin2100.Cost-effectivescenariosassumeimmediatemitigationinallcountriesandasingleglobalcarbonprice,andimposenoadditionallimitationsontechnologyrelativetothemodels’defaulttechnologyassumptions.Consumptionlossesareshownrelativetoabaselinedevelopmentwithoutclimatepolicy(leftpanel).Thetableatthetopshowspercentagepointsofannualizedconsumptiongrowthreductionsrelativetoconsumptiongrowthinthebaselineof1.6to3%peryear(e.g.,ifthereductionis0.06percentagepointsperyearduetomitigation,andbaselinegrowthis2.0%peryear,thenthegrowthratewithmitigationwouldbe1.94%peryear).Costestimatesshowninthistabledonotconsiderthebenefitsofreducedclimatechangeorco-benefitsandadversesideeffectsofmitigation.Estimatesatthehighendofthesecostrangesarefrommodelsthatarerelativelyinflexibletoachievethedeepemissionsreductionsrequiredinthelongruntomeetthesegoalsand/orincludeassumptionsaboutmarketimperfectionsthatwouldraisecosts.{Figure3.4}Delayingadditionalmitigationto2030willsubstantiallyincreasethechallengesassociatedwithlimitingwarmingoverthe21stcenturytobelow2°Crelativetopre-industriallevels.Itwillrequiresubstantiallyhigherratesofemissionsreductionsfrom2030to2050;amuchmorerapidscale-upoflow-carbonenergyoverthisperiod;alargerrelianceonCDRinthelongterm;andhighertransitionalandlong-termeconomicimpacts.Estimatedglobalemissionslevelsin2020basedontheCancúnPledgesarenotconsistentwithcost-effectivemitigationtrajectoriesthatareatleastaboutaslikelyasnottolimitwarmingtobelow2°Crelativetopre-industriallevels,buttheydonotprecludetheoptiontomeetthisgoal(highconfidence)(FigureSPM.12,TableSPM.2).{3.4}Estimatesoftheaggregateeconomiccostsofmitigationvarywidelydependingonmethodologiesandassumptions,butincreasewiththestringencyofmitigation.Scenariosinwhichallcountriesoftheworldbeginmitigationimmediately,inwhichthereisasingleglobalcarbonprice,andinwhichallkeytechnologiesareavailablehavebeenusedasacost-effectivebenchmarkforestimatingmacro-economicmitigationcosts(FigureSPM.13).Undertheseassumptionsmitigationscenariosthatarelikelytolimitwarmingtobelow2°Cthroughthe21stcenturyrelativetopre-industriallevelsentaillossesinglobalconsumption—notincludingbenefitsofreducedclimatechangeaswellasco-benefitsandadversesideeffectsofmitiga-tion—of1to4%(median:1.7%)in2030,2to6%(median:3.4%)in2050and3to11%(median:4.8%)in2100relativetoconsumptioninbaselinescenariosthatgrowsanywherefrom300%tomorethan900%overthecentury(FigureSPM.13).Thesenumberscorrespondtoanannualizedreductionofconsumptiongrowthby0.04to0.14(median:0.06)percentagepointsoverthecenturyrelativetoannualizedconsumptiongrowthinthebaselinethatisbetween1.6and3%peryear(highconfidence).{3.4}Intheabsenceorunderlimitedavailabilityofmitigationtechnologies(suchasbioenergy,CCSandtheircombinationBECCS,nuclear,wind/solar),mitigationcostscanincreasesubstantiallydependingonthetechnologyconsidered.Delayingadditionalmitigationincreasesmitigationcostsinthemediumtolongterm.Manymodelscouldnotlimitlikelywarmingtobelow2°Coverthe21stcenturyrelativetopre-industriallevelsifadditionalmitigationisconsiderablydelayed.Manymodelscouldnotlimitlikelywarmingtobelow2°Cifbioenergy,CCSandtheircombination(BECCS)arelimited(highconfidence)(TableSPM.2).{3.4}24SummaryforPolicymakersTableSPM.2Increaseinglobalmitigationcostsduetoeitherlimitedavailabilityofspecifictechnologiesordelaysinadditionalmitigationarelativetocost-effectivescenariosb.Theincreaseincostsisgivenforthemedianestimateandthe16thto84thpercentilerangeofthescenarios(inparentheses)c.Inaddition,thesamplesizeofeachscenariosetisprovidedinthecolouredsymbols.Thecoloursofthesymbolsindicatethefractionofmodelsfromsystematicmodelcomparisonexercisesthatcouldsuccessfullyreachthetargetedconcentrationlevel.{Table3.2}MitigationcostincreasesinscenarioswithMitigationcostincreaseslimitedavailabilityoftechnologiesdduetodelayedadditional[%increaseintotaldiscountedemitigationcostsmitigationuntil2030(2015–2100)relativetodefaulttechnologyassumptions]SPM[%increaseinmitigationcostsrelativetoimmediatemitigation]2100noCCSnuclearphaseoutlimitedsolar/windlimitedbioenergymediumtermcostslongtermconcentrations(2030–2050)costs(ppmCO2-eq)(2050–2100)450138%7%6%64%}44%37%(430to480)(29to297%)(4to18%)(2to29%)(44to78%)(2to78%)(16to82%)500notavailablen.a.n.a.n.a.(480to530)(n.a.)55039%13%8%18%}15%16%(530to580)(18to78%)(2to23%)(5to15%)(4to66%)(3to32%)(5to24%)580to650n.a.n.a.n.a.n.a.Symbollegend—fractionofmodelssuccessfulinproducingscenarios(numbersindicatethenumberofsuccessfulmodels):allmodelssuccessful:between50and80%ofmodelssuccessful:between80and100%ofmodelssuccessful:lessthan50%ofmodelssuccessfulNotes:aDelayedmitigationscenariosareassociatedwithgreenhousegasemissionofmorethan55GtCO2-eqin2030,andtheincreaseinmitigationcostsismea-suredrelativetocost-effectivemitigationscenariosforthesamelong-termconcentrationlevel.bCost-effectivescenariosassumeimmediatemitigationinallcountriesandasingleglobalcarbonprice,andimposenoadditionallimitationsontechnologyrelativetothemodels’defaulttechnologyassumptions.cTherangeisdeterminedbythecentralscenariosencompassingthe16thto84thpercentilerangeofthescenarioset.Onlyscenarioswithatimehorizonuntil2100areincluded.Somemodelsthatareincludedinthecostrangesforconcentrationlevelsabove530ppmCO2-eqin2100couldnotproduceassoci-atedscenariosforconcentrationlevelsbelow530ppmCO2-eqin2100withassumptionsaboutlimitedavailabilityoftechnologiesand/ordelayedadditionalmitigation.dNoCCS:carbondioxidecaptureandstorageisnotincludedinthesescenarios.Nuclearphaseout:noadditionofnuclearpowerplantsbeyondthoseunderconstruction,andoperationofexistingplantsuntiltheendoftheirlifetime.LimitedSolar/Wind:amaximumof20%globalelectricitygenerationfromsolarandwindpowerinanyyearofthesescenarios.LimitedBioenergy:amaximumof100EJ/yrmodernbioenergysupplyglobally(modernbioenergyusedforheat,power,combinationsandindustrywasaround18EJ/yrin2008).EJ=Exajoule=1018Joule.ePercentageincreaseofnetpresentvalueofconsumptionlossesinpercentofbaselineconsumption(forscenariosfromgeneralequilibriummodels)andabatementcostsinpercentofbaselinegrossdomesticproduct(GDP,forscenariosfrompartialequilibriummodels)fortheperiod2015–2100,discountedat5%peryear.Mitigationscenariosreachingabout450or500ppmCO2-eqby2100showreducedcostsforachievingairqualityandenergysecurityobjectives,withsignificantco-benefitsforhumanhealth,ecosystemimpactsandsufficiencyofresourcesandresilienceoftheenergysystem.{4.4.2.2}Mitigationpolicycoulddevaluefossilfuelassetsandreducerevenuesforfossilfuelexporters,butdifferencesbetweenregionsandfuelsexist(highconfidence).Mostmitigationscenariosareassociatedwithreducedrevenuesfromcoalandoiltradeformajorexporters(highconfidence).TheavailabilityofCCSwouldreducetheadverseeffectsofmitigationonthevalueoffossilfuelassets(mediumconfidence).{4.4.2.2}SolarRadiationManagement(SRM)involveslarge-scalemethodsthatseektoreducetheamountofabsorbedsolarenergyintheclimatesystem.SRMisuntestedandisnotincludedinanyofthemitigationscenarios.Ifitweredeployed,SRMwould25SummaryforPolicymakersentailnumerousuncertainties,sideeffects,risksandshortcomingsandhasparticulargovernanceandethicalimplications.SRMwouldnotreduceoceanacidification.Ifitwereterminated,thereishighconfidencethatsurfacetemperatureswouldriseveryrapidlyimpactingecosystemssusceptibletorapidratesofchange.{Box3.3}SPMSPM4.AdaptationandMitigationManyadaptationandmitigationoptionscanhelpaddressclimatechange,butnosingleoptionissufficientbyitself.Effectiveimplementationdependsonpoliciesandcooperationatallscalesandcanbeenhancedthroughintegratedresponsesthatlinkadaptationandmitiga-tionwithothersocietalobjectives.{4}SPM4.1CommonenablingfactorsandconstraintsforadaptationandmitigationresponsesAdaptationandmitigationresponsesareunderpinnedbycommonenablingfactors.Theseincludeeffectiveinstitutionsandgovernance,innovationandinvestmentsinenvironmentallysoundtechnologiesandinfrastructure,sustainablelivelihoodsandbehaviouralandlifestylechoices.{4.1}Inertiainmanyaspectsofthesocio-economicsystemconstrainsadaptationandmitigationoptions(mediumevidence,highagreement).InnovationandinvestmentsinenvironmentallysoundinfrastructureandtechnologiescanreduceGHGemis-sionsandenhanceresiliencetoclimatechange(veryhighconfidence).{4.1}Vulnerabilitytoclimatechange,GHGemissionsandthecapacityforadaptationandmitigationarestronglyinfluencedbylivelihoods,lifestyles,behaviourandculture(mediumevidence,mediumagreement).Also,thesocialacceptabilityand/oreffectivenessofclimatepoliciesareinfluencedbytheextenttowhichtheyincentivizeordependonregionallyappropriatechangesinlifestylesorbehaviours.{4.1}Formanyregionsandsectors,enhancedcapacitiestomitigateandadaptarepartofthefoundationessentialformanagingclimatechangerisks(highconfidence).Improvinginstitutionsaswellascoordinationandcooperationingovernancecanhelpovercomeregionalconstraintsassociatedwithmitigation,adaptationanddisasterriskreduction(veryhighconfidence).{4.1}SPM4.2ResponseoptionsforadaptationAdaptationoptionsexistinallsectors,buttheircontextforimplementationandpotentialtoreduceclimate-relatedrisksdiffersacrosssectorsandregions.Someadaptationresponsesinvolvesignificantco-benefits,synergiesandtrade-offs.Increasingclimatechangewillincreasechallengesformanyadaptationoptions.{4.2}Adaptationexperienceisaccumulatingacrossregionsinthepublicandprivatesectorsandwithincommunities.Thereisincreasingrecognitionofthevalueofsocial(includinglocalandindigenous),institutional,andecosystem-basedmeasuresandoftheextentofconstraintstoadaptation.Adaptationisbecomingembeddedinsomeplanningprocesses,withmorelimitedimplementationofresponses(highconfidence).{1.6,4.2,4.4.2.1}Theneedforadaptationalongwithassociatedchallengesisexpectedtoincreasewithclimatechange(veryhighconfidence).Adaptationoptionsexistinallsectorsandregions,withdiversepotentialandapproachesdependingontheircontextinvulnerabilityreduction,disasterriskmanagementorproactiveadaptationplanning(TableSPM.3).Effectivestrategiesandactionsconsiderthepotentialforco-benefitsandopportunitieswithinwiderstrategicgoalsanddevelopmentplans.{4.2}26SummaryforPolicymakersTableSPM.3Approachesformanagingtherisksofclimatechangethroughadaptation.Theseapproachesshouldbeconsideredoverlappingratherthandiscrete,andtheyareoftenpursuedsimultaneously.Examplesarepresentedinnospeciﬁcorderandcanberelevanttomorethanonecategory.{Table4.2}OverlappingCategoryExamplesApproachesHumandevelopmentImprovedaccesstoeducation,nutrition,healthfacilities,energy,safehousing&settlementstructures,Vulnerability&ExposureReductionPovertyalleviation&socialsupportstructures;Reducedgenderinequality&marginalizationinotherforms.SPMLivelihoodsecuritythroughdevelopment,planning&practicesincludingmanylow-regretsmeasuresDisasterriskImprovedaccessto&controloflocalresources;Landtenure;Disasterriskreduction;Socialsafetynetsmanagement&socialprotection;Insuranceschemes.AdaptationEcosystemmanagementIncome,asset&livelihooddiversification;Improvedinfrastructure;Accesstotechnology&decision-includingincremental&transformationaladjustmentsSpatialorland-usemakingfora;Increaseddecision-makingpower;Changedcropping,livestock&aquaculturepractices;planningRelianceonsocialnetworks.TransformationStructural/physicalEarlywarningsystems;Hazard&vulnerabilitymapping;Diversifyingwaterresources;Improveddrainage;Flood&cycloneshelters;Buildingcodes&practices;Storm&wastewatermanagement;InstitutionalTransport&roadinfrastructureimprovements.SocialMaintainingwetlands&urbangreenspaces;Coastalafforestation;Watershed&reservoirmanagement;Reductionofotherstressorsonecosystems&ofhabitatfragmentation;MaintenanceSpheresofchangeofgeneticdiversity;Manipulationofdisturbanceregimes;Community-basednaturalresourcemanagement.Provisioningofadequatehousing,infrastructure&services;Managingdevelopmentinfloodprone&otherhighriskareas;Urbanplanning&upgradingprograms;Landzoninglaws;Easements;Protectedareas.Engineered&built-environmentoptions:Seawalls&coastalprotectionstructures;Floodlevees;Waterstorage;Improveddrainage;Flood&cycloneshelters;Buildingcodes&practices;Storm&wastewatermanagement;Transport&roadinfrastructureimprovements;Floatinghouses;Powerplant&electricitygridadjustments.Technologicaloptions:Newcrop&animalvarieties;Indigenous,traditional&localknowledge,technologies&methods;Efficientirrigation;Water-savingtechnologies;Desalinisation;Conservationagriculture;Foodstorage&preservationfacilities;Hazard&vulnerabilitymapping&monitoring;Earlywarningsystems;Buildinginsulation;Mechanical&passivecooling;Technologydevelopment,transfer&diffusion.Ecosystem-basedoptions:Ecologicalrestoration;Soilconservation;Afforestation&reforestation;Mangroveconservation&replanting;Greeninfrastructure(e.g.,shadetrees,greenroofs);Controllingoverfishing;Fisheriesco-management;Assistedspeciesmigration&dispersal;Ecologicalcorridors;Seedbanks,genebanks&otherexsituconservation;Community-basednaturalresourcemanagement.Services:Socialsafetynets&socialprotection;Foodbanks&distributionoffoodsurplus;Municipalservicesincludingwater&sanitation;Vaccinationprograms;Essentialpublichealthservices;Enhancedemergencymedicalservices.Economicoptions:Financialincentives;Insurance;Catastrophebonds;Paymentsforecosystemservices;Pricingwatertoencourageuniversalprovisionandcarefuluse;Microfinance;Disastercontingencyfunds;Cashtransfers;Public-privatepartnerships.Laws&regulations:Landzoninglaws;Buildingstandards&practices;Easements;Waterregulations&agreements;Lawstosupportdisasterriskreduction;Lawstoencourageinsurancepurchasing;Definedpropertyrights&landtenuresecurity;Protectedareas;Fishingquotas;Patentpools&technologytransfer.National&governmentpolicies&programs:National&regionaladaptationplansincludingmainstreaming;Sub-national&localadaptationplans;Economicdiversification;Urbanupgradingprograms;Municipalwatermanagementprograms;Disasterplanning&preparedness;Integratedwaterresourcemanagement;Integratedcoastalzonemanagement;Ecosystem-basedmanagement;Community-basedadaptation.Educationaloptions:Awarenessraising&integratingintoeducation;Genderequityineducation;Extensionservices;Sharingindigenous,traditional&localknowledge;Participatoryactionresearch&sociallearning;Knowledge-sharing&learningplatforms.Informationaloptions:Hazard&vulnerabilitymapping;Earlywarning&responsesystems;Systematicmonitoring&remotesensing;Climateservices;Useofindigenousclimateobservations;Participatoryscenariodevelopment;Integratedassessments.Behaviouraloptions:Householdpreparation&evacuationplanning;Migration;Soil&waterconservation;Stormdrainclearance;Livelihooddiversification;Changedcropping,livestock&aquaculturepractices;Relianceonsocialnetworks.Practical:Social&technicalinnovations,behaviouralshifts,orinstitutional&managerialchangesthatproducesubstantialshiftsinoutcomes.Political:Political,social,cultural&ecologicaldecisions&actionsconsistentwithreducingvulnerability&risk&supportingadaptation,mitigation&sustainabledevelopment.Personal:Individual&collectiveassumptions,beliefs,values&worldviewsinfluencingclimate-changeresponses.27SummaryforPolicymakersSPM4.3ResponseoptionsformitigationMitigationoptionsareavailableineverymajorsector.Mitigationcanbemorecost-effectiveifusinganintegratedapproachthatcombinesmeasurestoreduceenergyuseandthegreen-housegasintensityofend-usesectors,decarbonizeenergysupply,reducenetemissionsandSPMenhancecarbonsinksinland-basedsectors.{4.3}Well-designedsystemicandcross-sectoralmitigationstrategiesaremorecost-effectiveincuttingemissionsthanafocusonindividualtechnologiesandsectors,witheffortsinonesectoraffectingtheneedformitigationinothers(mediumconfi-dence).Mitigationmeasuresintersectwithothersocietalgoals,creatingthepossibilityofco-benefitsoradversesideeffects.Theseintersections,ifwell-managed,canstrengthenthebasisforundertakingclimateaction.{4.3}EmissionsrangesforbaselinescenariosandmitigationscenariosthatlimitCO2-equivalentconcentrationstolowlevels(about450ppmCO2-eq,likelytolimitwarmingto2°Cabovepre-industriallevels)areshownfordifferentsectorsandgasesinFigureSPM.14.Keymeasurestoachievesuchmitigationgoalsincludedecarbonizing(i.e.,reducingthecarbonintensityof)electricitygeneration(mediumevidence,highagreement)aswellasefficiencyenhancementsandbehaviouralchanges,inordertoreduceenergydemandcomparedtobaselinescenarioswithoutcompromisingdevelopment(robustevidence,highagreement).Inscenariosreaching450ppmCO2-eqconcentrationsby2100,globalCO2emissionsfromtheenergysupplysectorareprojectedtodeclineoverthenextdecadeandarecharacterizedbyreductionsof90%ormorebelow2010levelsbetween2040and2070.Inthemajorityoflow‐concentrationstabilizationscenarios(about450toabout500ppmCO2-eq,atleastaboutaslikelyasnottolimitwarmingto2°Cabovepre-industriallevels),theshareoflow‐carbonelectricitysupply(comprisingrenewableenergy(RE),nuclearandcarbondioxidecaptureandstorage(CCS)includingbioenergywithcarbondioxidecaptureandstorage(BECCS))increasesfromthecurrentshareofapproximately30%tomorethan80%by2050,andfossilfuelpowergenerationwithoutCCSisphasedoutalmostentirelyby2100.{4.3}DirectCO2emissionsbymajorsectors,andnon-CO2emissions,forbaselineandmitigationscenarios5080GtCO2/yrCO240Directemissions(GtCO2-eq/yr)30203020201020501021000ScenariosPercentile–10Baselinesmax75th430–480ppmCO2-eqmedian25th–20minTransportBuildingsIndustryElectricityNetAFOLUNon-CO2121121107n=939378808065808065147147127131131118363636292929222222222222363636323232FigureSPM.14Carbondioxide(CO2)emissionsbysectorandtotalnon-CO2greenhousegases(Kyotogases)acrosssectorsinbaseline(fadedbars)andmitigationscenarios(solidcolourbars)thatreachabout450(430to480)ppmCO2-eqconcentrationsin2100(likelytolimitwarmingto2°Cabovepre-industriallevels).Mitigationintheend-usesectorsleadsalsotoindirectemissionsreductionsintheupstreamenergysupplysector.Directemissionsoftheend-usesectorsthusdonotincludetheemissionreductionpotentialatthesupply-sidedueto,forexample,reducedelectricitydemand.Thenumbersatthebottomofthegraphsrefertothenumberofscenariosincludedintherange(upperrow:baselinescenarios;lowerrow:mitigationscenarios),whichdiffersacrosssectorsandtimeduetodifferentsectoralresolutionandtimehorizonofmodels.Emissionsrangesformitigationscenariosincludethefullportfolioofmitigationoptions;manymodelscannotreach450ppmCO2-eqconcentrationby2100intheabsenceofcarbondioxidecaptureandstorage(CCS).Negativeemissionsintheelectricitysectorareduetotheapplicationofbioenergywithcarbondioxidecaptureandstorage(BECCS).‘Net’agriculture,forestryandotherlanduse(AFOLU)emissionsconsiderafforestation,reforestationaswellasdeforestationactivities.{4.3,Figure4.1}28SummaryforPolicymakersNear-termreductionsinenergydemandareanimportantelementofcost-effectivemitigationstrategies,providemoreflexibilityforreducingcarbonintensityintheenergysupplysector,hedgeagainstrelatedsupply-siderisks,avoidlock-intocarbon-intensiveinfrastructures,andareassociatedwithimportantco-benefits.Themostcost-effectivemitigationoptionsinforestryareafforestation,sustainableforestmanagementandreducingdeforestation,withlargedifferencesintheirrelativeimportanceacrossregions;andinagriculture,croplandmanagement,grazinglandmanagementandrestorationoforganicsoils(mediumevidence,highagreement).{4.3,Figures4.1,4.2,Table4.3}SPMBehaviour,lifestyleandculturehaveaconsiderableinfluenceonenergyuseandassociatedemissions,withhighmitigationpotentialinsomesectors,inparticularwhencomplementingtechnologicalandstructuralchange(mediumevidence,mediumagreement).Emissionscanbesubstantiallyloweredthroughchangesinconsumptionpatterns,adoptionofenergysavingsmeasures,dietarychangeandreductioninfoodwastes.{4.1,4.3}SPM4.4Policyapproachesforadaptationandmitigation,technologyandfinanceEffectiveadaptationandmitigationresponseswilldependonpoliciesandmeasuresacrossmultiplescales:international,regional,nationalandsub-national.Policiesacrossallscalessupportingtechnologydevelopment,diffusionandtransfer,aswellasfinanceforresponsestoclimatechange,cancomplementandenhancetheeffectivenessofpoliciesthatdirectlypromoteadaptationandmitigation.{4.4}Internationalcooperationiscriticalforeffectivemitigation,eventhoughmitigationcanalsohavelocalco-benefits.Adapta-tionfocusesprimarilyonlocaltonationalscaleoutcomes,butitseffectivenesscanbeenhancedthroughcoordinationacrossgovernancescales,includinginternationalcooperation:{3.1,4.4.1}•TheUnitedNationsFrameworkConventiononClimateChange(UNFCCC)isthemainmultilateralforumfocusedonaddressingclimatechange,withnearlyuniversalparticipation.Otherinstitutionsorganizedatdifferentlevelsofgover-nancehaveresultedindiversifyinginternationalclimatechangecooperation.{4.4.1}•TheKyotoProtocolofferslessonstowardsachievingtheultimateobjectiveoftheUNFCCC,particularlywithrespecttoparticipation,implementation,flexibilitymechanismsandenvironmentaleffectiveness(mediumevidence,lowagree-ment).{4.4.1}•Policylinkagesamongregional,nationalandsub-nationalclimatepoliciesofferpotentialclimatechangemitigationben-efits(mediumevidence,mediumagreement).Potentialadvantagesincludelowermitigationcosts,decreasedemissionleakageandincreasedmarketliquidity.{4.4.1}•Internationalcooperationforsupportingadaptationplanningandimplementationhasreceivedlessattentionhistori-callythanmitigationbutisincreasingandhasassistedinthecreationofadaptationstrategies,plansandactionsatthenational,sub-nationalandlocallevel(highconfidence).{4.4.1}Therehasbeenaconsiderableincreaseinnationalandsub‐nationalplansandstrategiesonbothadaptationandmitigationsincetheAR4,withanincreasedfocusonpoliciesdesignedtointegratemultipleobjectives,increaseco-benefitsandreduceadversesideeffects(highconfidence):{4.4.2.1,4.4.2.2}•Nationalgovernmentsplaykeyrolesinadaptationplanningandimplementation(robustevidence,highagreement)throughcoordinatingactionsandprovidingframeworksandsupport.Whilelocalgovernmentandtheprivatesectorhavedifferentfunctions,whichvaryregionally,theyareincreasinglyrecognizedascriticaltoprogressinadaptation,giventheirrolesinscalingupadaptationofcommunities,householdsandcivilsocietyandinmanagingriskinformationandfinancing(mediumevidence,highagreement).{4.4.2.1}•Institutionaldimensionsofadaptationgovernance,includingtheintegrationofadaptationintoplanninganddecision-making,playakeyroleinpromotingthetransitionfromplanningtoimplementationofadaptation(robustevidence,29SummaryforPolicymakershighagreement).Examplesofinstitutionalapproachestoadaptationinvolvingmultipleactorsincludeeconomicoptions(e.g.,insurance,public-privatepartnerships),lawsandregulations(e.g.,land-zoninglaws)andnationalandgovernmentpoliciesandprogrammes(e.g.,economicdiversification).{4.2,4.4.2.1,TableSPM.3}•Inprinciple,mechanismsthatsetacarbonprice,includingcapandtradesystemsandcarbontaxes,canachievemitiga-tioninacost-effectivewaybuthavebeenimplementedwithdiverseeffectsdueinparttonationalcircumstancesasSPMwellaspolicydesign.Theshort-runeffectsofcapandtradesystemshavebeenlimitedasaresultofloosecapsorcapsthathavenotprovedtobeconstraining(limitedevidence,mediumagreement).Insomecountries,tax-basedpoliciesspecificallyaimedatreducingGHGemissions—alongsidetechnologyandotherpolicies—havehelpedtoweakenthelinkbetweenGHGemissionsandGDP(highconfidence).Inaddition,inalargegroupofcountries,fueltaxes(althoughnotnecessarilydesignedforthepurposeofmitigation)havehadeffectsthatareakintosectoralcarbontaxes.{4.4.2.2}•Regulatoryapproachesandinformationmeasuresarewidelyusedandareoftenenvironmentallyeffective(mediumevi-dence,mediumagreement).Examplesofregulatoryapproachesincludeenergyefficiencystandards;examplesofinfor-mationprogrammesincludelabellingprogrammesthatcanhelpconsumersmakebetter-informeddecisions.{4.4.2.2}•Sector-specificmitigationpolicieshavebeenmorewidelyusedthaneconomy-widepolicies(mediumevidence,highagreement).Sector-specificpoliciesmaybebettersuitedtoaddresssector-specificbarriersormarketfailuresandmaybebundledinpackagesofcomplementarypolicies.Althoughtheoreticallymorecost-effective,administrativeandpoliticalbarriersmaymakeeconomy-widepolicieshardertoimplement.Interactionsbetweenoramongmitigationpoliciesmaybesynergisticormayhavenoadditiveeffectonreducingemissions.{4.4.2.2}•Economicinstrumentsintheformofsubsidiesmaybeappliedacrosssectors,andincludeavarietyofpolicydesigns,suchastaxrebatesorexemptions,grants,loansandcreditlines.Anincreasingnumberandvarietyofrenewableenergy(RE)policiesincludingsubsidies—motivatedbymanyfactors—havedrivenescalatedgrowthofREtechnologiesinrecentyears.Atthesametime,reducingsubsidiesforGHG-relatedactivitiesinvarioussectorscanachieveemissionreductions,dependingonthesocialandeconomiccontext(highconfidence).{4.4.2.2}Co-benefitsandadversesideeffectsofmitigationcouldaffectachievementofotherobjectivessuchasthoserelatedtohumanhealth,foodsecurity,biodiversity,localenvironmentalquality,energyaccess,livelihoodsandequitablesustainabledevelopment.Thepotentialforco-benefitsforenergyend-usemeasuresoutweighsthepotentialforadversesideeffectswhereastheevidencesuggeststhismaynotbethecaseforallenergysupplyandagriculture,forestryandotherlanduse(AFOLU)measures.Somemitigationpoliciesraisethepricesforsomeenergyservicesandcouldhampertheabilityofsocie-tiestoexpandaccesstomodernenergyservicestounderservedpopulations(lowconfidence).Thesepotentialadversesideeffectsonenergyaccesscanbeavoidedwiththeadoptionofcomplementarypoliciessuchasincometaxrebatesorotherbenefittransfermechanisms(mediumconfidence).Whetherornotsideeffectsmaterialize,andtowhatextentsideeffectsmaterialize,willbecase-andsite-specific,anddependonlocalcircumstancesandthescale,scopeandpaceofimplementa-tion.Manyco-benefitsandadversesideeffectshavenotbeenwell-quantified.{4.3,4.4.2.2,Box3.4}Technologypolicy(development,diffusionandtransfer)complementsothermitigationpoliciesacrossallscales,frominterna-tionaltosub-national;manyadaptationeffortsalsocriticallyrelyondiffusionandtransferoftechnologiesandmanagementpractices(highconfidence).PoliciesexisttoaddressmarketfailuresinR&D,buttheeffectiveuseoftechnologiescanalsodependoncapacitiestoadopttechnologiesappropriatetolocalcircumstances.{4.4.3}Substantialreductionsinemissionswouldrequirelargechangesininvestmentpatterns(highconfidence).Formitigationscenariosthatstabilizeconcentrations(withoutovershoot)intherangeof430to530ppmCO2-eqby210019,annualinvest-mentsinlowcarbonelectricitysupplyandenergyefficiencyinkeysectors(transport,industryandbuildings)areprojectedinthescenariostorisebyseveralhundredbilliondollarsperyearbefore2030.Withinappropriateenablingenvironments,theprivatesector,alongwiththepublicsector,canplayimportantrolesinfinancingmitigationandadaptation(mediumevidence,highagreement).{4.4.4}19Thisrangecomprisesscenariosthatreach430to480ppmCO2-eqby2100(likelytolimitwarmingto2°Cabovepre-industriallevels)andscenariosthatreach480to530ppmCO2-eqby2100(withoutovershoot:morelikelythannottolimitwarmingto2°Cabovepre-industriallevels).30SummaryforPolicymakersFinancialresourcesforadaptationhavebecomeavailablemoreslowlythanformitigationinbothdevelopedanddevelopingcountries.Limitedevidenceindicatesthatthereisagapbetweenglobaladaptationneedsandthefundsavailableforadapta-tion(mediumconfidence).Thereisaneedforbetterassessmentofglobaladaptationcosts,fundingandinvestment.Potentialsynergiesbetweeninternationalfinancefordisasterriskmanagementandadaptationhavenotyetbeenfullyrealized(highconfidence).{4.4.4}SPMSPM4.5Trade-offs,synergiesandinteractionswithsustainabledevelopmentClimatechangeisathreattosustainabledevelopment.Nonetheless,therearemanyopportu-nitiestolinkmitigation,adaptationandthepursuitofothersocietalobjectivesthroughinte-gratedresponses(highconfidence).Successfulimplementationreliesonrelevanttools,suit-ablegovernancestructuresandenhancedcapacitytorespond(mediumconfidence).{3.5,4.5}Climatechangeexacerbatesotherthreatstosocialandnaturalsystems,placingadditionalburdensparticularlyonthepoor(highconfidence).Aligningclimatepolicywithsustainabledevelopmentrequiresattentiontobothadaptationandmitigation(highconfidence).Delayingglobalmitigationactionsmayreduceoptionsforclimate-resilientpathwaysandadaptationinthefuture.Opportunitiestotakeadvantageofpositivesynergiesbetweenadaptationandmitigationmaydecreasewithtime,particularlyiflimitstoadaptationareexceeded.Increasingeffortstomitigateandadapttoclimatechangeimplyanincreas-ingcomplexityofinteractions,encompassingconnectionsamonghumanhealth,water,energy,landuseandbiodiversity(mediumevidence,highagreement).{3.1,3.5,4.5}Strategiesandactionscanbepursuednowwhichwillmovetowardsclimate-resilientpathwaysforsustainabledevelopment,whileatthesametimehelpingtoimprovelivelihoods,socialandeconomicwell-beingandeffectiveenvironmentalmanage-ment.Insomecases,economicdiversificationcanbeanimportantelementofsuchstrategies.Theeffectivenessofintegratedresponsescanbeenhancedbyrelevanttools,suitablegovernancestructuresandadequateinstitutionalandhumancapacity(mediumconfidence).Integratedresponsesareespeciallyrelevanttoenergyplanningandimplementation;interactionsamongwater,food,energyandbiologicalcarbonsequestration;andurbanplanning,whichprovidessubstantialopportu-nitiesforenhancedresilience,reducedemissionsandmoresustainabledevelopment(mediumconfidence).{3.5,4.4,4.5}31IntroductionClimateChange2014SynthesisReportIntroduction1Introduction35IntroductionIntroductionIntroductionTheSynthesisReport(SYR)oftheIPCCFifthAssessmentReport(AR5)assessesprojectionsoffutureclimatechangeandtheresultantpro-providesanoverviewofthestateofknowledgeconcerningthesciencejectedimpactsandrisks.Topic3(FuturePathwaysforAdaptation,Miti-ofclimatechange,emphasizingnewresultssincethepublicationofgationandSustainableDevelopment)considersadaptationandmiti-theIPCCFourthAssessmentReport(AR4)in2007.TheSYRsynthe-gationascomplementarystrategiesforreducingandmanagingthesizesthemainfindingsoftheAR5basedoncontributionsfromWork-risksofclimatechange.Topic4(AdaptationandMitigation)describesingGroupI(ThePhysicalScienceBasis),WorkingGroupII(Impacts,individualadaptationandmitigationoptionsandpolicyapproaches.ItAdaptationandVulnerability)andWorkingGroupIII(Mitigationofalsoaddressesintegratedresponsesthatlinkmitigationandadapta-ClimateChange),plustwoadditionalIPCCreports(SpecialReportontionwithothersocietalobjectives.RenewableEnergySourcesandClimateChangeMitigationandSpe-cialReportonManagingtheRisksofExtremeEventsandDisasterstoThechallengesofunderstandingandmanagingrisksanduncertaintiesAdvanceClimateChangeAdaptation).areimportantthemesinthisreport.SeeBox1(RiskandtheManage-mentofanUncertainFuture)andBox2(CommunicatingtheDegreeTheAR5SYRlongerreportisdividedintofourtopics.Topic1(ObservedofCertaintyinAssessmentFindings).ChangesandtheirCauses)focusesonobservationalevidenceforachangingclimate,theimpactscausedbythischangeandthehumanThisreportincludesinformationrelevanttoArticle2oftheUnitedcontributionstoit.Topic2(FutureClimateChanges,RisksandImpacts)NationsFrameworkConventiononClimateChange(UNFCCC).BoxIntroduction.1RiskandtheManagementofanUncertainFutureClimatechangeexposespeople,societies,economicsectorsandecosystemstorisk.Riskisthepotentialforconsequenceswhensome-thingofvalueisatstakeandtheoutcomeisuncertain,recognizingthediversityofvalues.{WGIISPMBackgroundBoxSPM.2,WGIII2.1,SYRGlossary}Risksfromclimatechangeimpactsarisefromtheinteractionbetweenhazard(triggeredbyaneventortrendrelatedtoclimatechange),vulnerability(susceptibilitytoharm)andexposure(people,assetsorecosystemsatrisk).Hazardsincludeprocessesthatrangefrombriefevents,suchasseverestorms,toslowtrends,suchasmulti-decadedroughtsormulti-centurysealevelrise.Vulnerabilityandexposurearebothsensitivetoawiderangeofsocialandeconomicprocesses,withpossibleincreasesordecreasesdependingondevelopmentpathways.Risksandco-benefitsalsoarisefrompoliciesthataimtomitigateclimatechangeortoadapttoit.(1.5)Riskisoftenrepresentedastheprobabilityofoccurrenceofhazardouseventsortrendsmultipliedbythemagnitudeoftheconse-quencesiftheseeventsoccur.Therefore,highriskcanresultnotonlyfromhighprobabilityoutcomesbutalsofromlowprobabilityout-comeswithverysevereconsequences.Thismakesitimportanttoassessthefullrangeofpossibleoutcomes,fromlowprobabilitytailoutcomestoverylikelyoutcomes.Forexample,itisunlikelythatglobalmeansealevelwillrisebymorethanonemeterinthiscentury,buttheconsequenceofagreaterrisecouldbesoseverethatthispossibilitybecomesasignificantpartofriskassessment.Similarly,lowconfidencebuthighconsequenceoutcomesarealsopolicyrelevant;forinstancethepossibilitythattheresponseofAmazonforestcouldsubstantiallyamplifyclimatechangemeritsconsiderationdespiteourcurrentlyimperfectabilitytoprojecttheoutcome.(2.4,Table2.3){WGITable13.5,WGIISPMA-3,4.4,Box4-3,WGIIIBox3-9,SYRGlossary}Riskcanbeunderstoodeitherqualitativelyorquantitatively.Itcanbereducedandmanagedusingawiderangeofformalorinformaltoolsandapproachesthatareofteniterative.Usefulapproachesformanagingriskdonotnecessarilyrequirethatrisklevelscanbeaccuratelyquantified.Approachesrecognizingdiversequalitativevalues,goalsandpriorities,basedonethical,psychological,culturalorsocialfactors,couldincreasetheeffectivenessofriskmanagement.{WGII1.1.2,2.4,2.5,19.3,WGIII2.4,2.5,3.4}36IntroductionIntroductionBoxIntroduction.2CommunicatingtheDegreeofCertaintyinAssessmentFindingsAnintegralfeatureofIPCCreportsisthecommunicationofthestrengthofanduncertaintiesinscientificunderstandingunderlyingassessmentfindings.Uncertaintycanresultfromawiderangeofsources.Uncertaintiesinthepastandpresentaretheresultoflimita-tionsofavailablemeasurements,especiallyforrareevents,andthechallengesofevaluatingcausationincomplexormulti-componentprocessesthatcanspanphysical,biologicalandhumansystems.Forthefuture,climatechangeinvolveschanginglikelihoodsofdiverseoutcomes.Manyprocessesandmechanismsarewellunderstood,butothersarenot.Complexinteractionsamongmultipleclimaticandnon-climaticinfluenceschangingovertimeleadtopersistentuncertainties,whichinturnleadtothepossibilityofsurprises.ComparedtopastIPCCreports,theAR5assessesasubstantiallylargerknowledgebaseofscientific,technicalandsocio-economicliterature.{WGI1.4,WGIISPMA-3,1.1.2,WGIII2.3}TheIPCCGuidanceNoteonUncertaintyadefinesacommonapproachtoevaluatingandcommunicatingthedegreeofcertaintyinfindingsoftheassessmentprocess.Eachfindingisgroundedinanevaluationofunderlyingevidenceandagreement.Inmanycases,asynthesisofevidenceandagreementsupportsanassignmentofconfidence,especiallyforfindingswithstrongeragreementandmul-tipleindependentlinesofevidence.Thedegreeofcertaintyineachkeyfindingoftheassessmentisbasedonthetype,amount,qualityandconsistencyofevidence(e.g.,data,mechanisticunderstanding,theory,models,expertjudgment)andthedegreeofagreement.Thesummarytermsforevidenceare:limited,mediumorrobust.Foragreement,theyarelow,mediumorhigh.Levelsofconfidenceincludefivequalifiers:verylow,low,medium,highandveryhigh,andaretypesetinitalics,e.g.,mediumconfidence.Thelikelihood,orprobability,ofsomewell-definedoutcomehavingoccurredoroccurringinthefuturecanbedescribedquantitativelythroughthefollo-wingterms:virtuallycertain,99–100%probability;extremelylikely,95–100%;verylikely,90–100%;likely,66–100%;morelikelythannot,>50–100%;aboutaslikelyasnot,33–66%;unlikely,0–33%;veryunlikely,0–10%;extremelyunlikely,0–5%;andexceptionallyunlikely,0–1%.Additionalterms(extremelylikely,95–100%;morelikelythannot,>50–100%;moreunlikelythanlikely,0–<50%;andextremelyunlikely,0–5%)mayalsobeusedwhenappropriate.Assessedlikelihoodistypesetinitalics,e.g.,verylikely.Unlessotherwiseindicated,findingsassignedalikelihoodtermareassociatedwithhighorveryhighconfidence.Whereappropriate,findingsarealsoformulatedasstatementsoffactwithoutusinguncertaintyqualifiers.{WGISPMB,WGIIBackgroundBoxSPM.3,WGIII2.1}aMastrandrea,M.D.,C.B.Field,T.F.Stocker,O.Edenhofer,K.L.Ebi,D.J.Frame,H.Held,E.Kriegler,K.J.Mach,P.R.Matschoss,G.-K.Plattner,G.W.YoheandF.W.Zwiers,2010:GuidanceNoteforLeadAuthorsoftheIPCCFifthAssessmentReportonConsistentTreatmentofUncertainties.IntergovernmentalPanelonClimateChange(IPCC),Geneva,Switzerland,4pp.37IntroductionIntroduction1ObservedChangesandtheirCauses39Topic1ObservedChangesandtheirCausesTopic1:ObservedChangesandtheirCausesHumaninfluenceontheclimatesystemisclear,andrecentanthropogenicemissionsofgreenhousegasesarethehighestinhistory.Recentclimatechangeshavehadwidespreadimpactsonhumanandnaturalsystems.Topic1focusesonobservationalevidenceofachangingclimate,theimpactscausedbythischangeandthehumancontributionstoit.Itdiscussesobservedchangesinclimate(1.1)andexternalinfluencesonclimate(forcings),differentiatingthoseforcingsthatareofanthropogenicorigin,andtheircontributionsbyeconomicsectorsandgreenhousegases(GHGs)(1.2).Section1.3attributesobservedclimatechangetoitscausesandattributesimpactsonhumanandnaturalsystemstoclimatechange,determiningthedegreetowhichthoseimpactscanbeattributedtoclimatechange.ThechangingprobabilityofextremeeventsandtheircausesarediscussedinSection1.4,followedbyanaccountofexposureandvulnerabilitywithinariskcontext(1.5)andasectiononadaptationandmitigationexperience(1.6).11.1ObservedchangesintheclimatesystemBasedonmultipleindependentanalysesofmeasurements,itisvirtu-allycertainthatgloballythetropospherehaswarmedandthelowerWarmingoftheclimatesystemisunequivocal,andstratospherehascooledsincethemid-20thcentury.Thereismediumsincethe1950s,manyoftheobservedchangesareconfidenceintherateofchangeanditsverticalstructureintheNorth-unprecedentedoverdecadestomillennia.Theatmo-ernHemisphereextratropicaltroposphere.{WGISPMB.1,2.4.4}sphereandoceanhavewarmed,theamountsofsnowConfidenceinprecipitationchangeaveragedovergloballandareasandicehavediminished,andsealevelhasrisen.since1901islowpriorto1951andmediumafterwards.Averagedoverthemid-latitudelandareasoftheNorthernHemisphere,precipitationhaslikelyincreasedsince1901(mediumconfidencebeforeandhigh1.1.1Atmosphereconfidenceafter1951).Forotherlatitudesarea-averagedlong-termpositiveornegativetrendshavelowconfidence(Figure1.1).{WGIEachofthelastthreedecadeshasbeensuccessivelywarmeratSPMB.1,FigureSPM.2,2.5.1}theEarth’ssurfacethananyprecedingdecadesince1850.Theperiodfrom1983to2012wasverylikelythewarmest30-yearperiodofthelast800yearsintheNorthernHemisphere,wheresuchassess-1.1.2Oceanmentispossible(highconfidence)andlikelythewarmest30-yearperiodofthelast1400years(mediumconfidence).{WGI2.4.3,5.3.5}Oceanwarmingdominatestheincreaseinenergystoredintheclimatesystem,accountingformorethan90%oftheenergyThegloballyaveragedcombinedlandandoceansurfacetemperatureaccumulatedbetween1971and2010(highconfidence)withdataascalculatedbyalineartrendshowawarmingof0.85[0.65onlyabout1%storedintheatmosphere(Figure1.2).Onato1.06]°C20overtheperiod1880to2012,forwhichmultipleinde-globalscale,theoceanwarmingislargestnearthesurface,andpendentlyproduceddatasetsexist.Thetotalincreasebetweenthetheupper75mwarmedby0.11[0.09to0.13]°Cperdecadeaverageofthe1850–1900periodandthe2003–2012periodis0.78overtheperiod1971to2010.Itisvirtuallycertainthatthe[0.72to0.85]°C,basedonthesinglelongestdatasetavailable.Fortheupperocean(0−700m)warmedfrom1971to2010,anditlikelylongestperiodwhencalculationofregionaltrendsissufficientlycom-warmedbetweenthe1870sand1971.Itislikelythattheoceanplete(1901to2012),almosttheentireglobehasexperiencedsurfacewarmedfrom700to2000mfrom1957to2009andfrom3000mwarming(Figure1.1).{WGISPMB.1,2.4.3}tothebottomfortheperiod1992to2005(Figure1.2).{WGISPMB.2,3.2,Box3.1}Inadditiontorobustmulti-decadalwarming,thegloballyaveragedsurfacetemperatureexhibitssubstantialdecadalandinterannualvari-Itisverylikelythatregionsofhighsurfacesalinity,whereevaporationability(Figure1.1).Duetothisnaturalvariability,trendsbasedonshortdominates,havebecomemoresaline,whileregionsoflowsalinity,whererecordsareverysensitivetothebeginningandenddatesanddonotprecipitationdominates,havebecomefreshersincethe1950s.Theseingeneralreflectlong-termclimatetrends.Asoneexample,therateregionaltrendsinoceansalinityprovideindirectevidenceforchangesofwarmingoverthepast15years(1998–2012;0.05[–0.05to0.15]inevaporationandprecipitationovertheoceansandthusforchanges°Cperdecade),whichbeginswithastrongElNiño,issmallerthanintheglobalwatercycle(mediumconfidence).Thereisnoobservationaltheratecalculatedsince1951(1951–2012;0.12[0.08to0.14]°Cperevidenceofalong-termtrendintheAtlanticMeridionalOverturningdecade;seeBox1.1).{WGISPMB.1,2.4.3}Circulation(AMOC).{WGISPMB.2,2.5,3.3,3.4.3,3.5,3.6.3}20Rangesinsquarebracketsindicatea90%uncertaintyintervalunlessotherwisestated.The90%uncertaintyintervalisexpectedtohavea90%likelihoodofcoveringthevaluethatisbeingestimated.Uncertaintyintervalsarenotnecessarilysymmetricaboutthecorrespondingbestestimate.Abestestimateofthatvalueisalsogivenwhereavailable.40ObservedChangesandtheirCausesTopic1(a)Observedgloballyaveragedcombinedlandand(c)Seaiceextent15oceansurfacetemperatureanomaly1850–2012Seaiceextent(millionkm2)Arctic(July-August-September)Introduction0.2Annualaverage100Temperature(°C)relativeto1986–2005−0.25Antarctic(February)−0.4−0.60−0.8190019201940196019802000−1Year0.2Decadalaverage(d)Globalmeansealevelchange1900–2010Globalaveragesealevel(m)0.1relativeto1986–20050−0.201−0.4−0.6−0.1−0.8−1−0.21850190019502000190019201940196019802000YearYear(b)Observedchangeinsurfacetemperature(e)Observedchangeinannualprecipitationoverland1951–20101901–2012−0.6−0.4−0.200.20.40.60.81.01.251.51.752.5−100−50−25−10−5−2.502.55102550100(mm/yrperdecade)(°C)Figure1.1Multipleobservedindicatorsofachangingglobalclimatesystem.(a)Observedgloballyaveragedcombinedlandandoceansurfacetemperatureanomalies(relativetothemeanof1986to2005period,asannualanddecadalaverages)withanestimateofdecadalmeanuncertaintyincludedforonedataset(greyshading).{WGIFigureSPM.1,Figure2.20;alistingofdatasetsandfurthertechnicaldetailsaregivenintheWGITechnicalSummarySupplementaryMaterialWGITS.SM.1.1}(b)Mapoftheobservedsurfacetemperaturechange,from1901to2012,derivedfromtemperaturetrendsdeterminedbylinearregressionfromonedataset(orangelineinPanela).Trendshavebeencalculatedwheredataavailabilitypermittedarobustestimate(i.e.,onlyforgridboxeswithgreaterthan70%completerecordsandmorethan20%dataavailabilityinthefirstandlast10%ofthetimeperiod),otherareasarewhite.Gridboxeswherethetrendissignificant,atthe10%level,areindicatedbya+sign.{WGIFigureSPM.1,Figure2.21,FigureTS.2;alist-ingofdatasetsandfurthertechnicaldetailsaregivenintheWGITechnicalSummarySupplementaryMaterialWGITS.SM.1.2}(c)Arctic(JulytoSeptemberaverage)andAntarctic(February)seaiceextent.{WGIFigureSPM.3,Figure4.3,Figure4.SM.2;alistingofdatasetsandfurthertechnicaldetailsaregivenintheWGITechnicalSummarySupplementaryMaterialWGITS.SM.3.2}.(d)Globalmeansealevelrelativetothe1986–2005meanofthelongestrunningdataset,andwithalldatasetsalignedtohavethesamevaluein1993,thefirstyearofsatellitealtimetrydata.Alltimeseries(colouredlinesindicatingdifferentdatasets)showannualvalues,andwhereassessed,uncertaintiesareindicatedbycolouredshading.{WGIFigureSPM.3,Figure3.13;alistingofdatasetsandfurthertechnicaldetailsaregivenintheWGITechnicalSummarySupplementaryMaterialWGITS.SM.3.4}.(e)Mapofobservedprecipitationchange,from1951to2010;trendsinannualaccumulationcalculatedusingthesamecriteriaasinPanelb.{WGIFigureSPM.2,TSTFE.1,Figure2,Figure2.29.AlistingofdatasetsandfurthertechnicaldetailsaregivenintheWGITechnicalSummarySupplementaryMaterialWGITS.SM.2.1}Sincethebeginningoftheindustrialera,oceanicuptakeofCO2hasthermoclineinmanyoceanregionssincethe1960s,withalikelyresultedinacidificationoftheocean;thepHofoceansurfacewaterexpansionoftropicaloxygenminimumzonesinrecentdecades.{WGIhasdecreasedby0.1(highconfidence),correspondingtoa26%SPMB.5,TS2.8.5,3.8.1,3.8.2,3.8.3,3.8.5,Figure3.20}increaseinacidity,measuredashydrogenionconcentration.Thereismediumconfidencethat,inparalleltowarming,oxygenconcen-trationshavedecreasedincoastalwatersandintheopenocean41Topic1ObservedChangesandtheirCausesEnergyaccumulationwithintheEarth’sclimatesystemTheannualmeanArcticseaiceextentdecreasedovertheperiod1979(whensatelliteobservationscommenced)to2012.Therateofdecrease300wasverylikelyintherange3.5to4.1%perdecade.ArcticseaiceextenthasdecreasedineveryseasonandineverysuccessivedecadesinceUpperocean1979,withthemostrapiddecreaseindecadalmeanextentinsummer(highconfidence).Forthesummerseaiceminimum,thedecreasewasDeepoceanverylikelyintherangeof9.4to13.6%perdecade(rangeof0.73to1.07millionkm2perdecade)(seeFigure1.1).Itisverylikelythatthe250IceannualmeanAntarcticseaiceextentincreasedintherangeof1.2to1.8%perdecade(rangeof0.13to0.20millionkm2perdecade)Landbetween1979and2012.However,thereishighconfidencethattherearestrongregionaldifferencesinAntarctica,withextentincreasinginAtmospheresomeregionsanddecreasinginothers.{WGISPMB.5,4.2.2,4.2.3}Uncertainty20015011021J100ThereisveryhighconfidencethattheextentofNorthernHemispheresnowcoverhasdecreasedsincethemid-20thcenturyby1.6[0.8to502.4]%perdecadeforMarchandApril,and11.7%perdecadeforJune,overthe1967to2012period.Thereishighconfidencethatpermafrost0temperatureshaveincreasedinmostregionsoftheNorthernHemi-spheresincetheearly1980s,withreductionsinthicknessandarealextentinsomeregions.Theincreaseinpermafrosttemperatureshasoccurredinresponsetoincreasedsurfacetemperatureandchangingsnowcover.{WGISPMB.3,4.5,4.7.2}−501.1.4Sealevel−100Overtheperiod1901–2010,globalmeansealevelroseby0.19[0.17to0.21]m(Figure1.1).Therateofsealevelrisesincethe1980199020002010mid-19thcenturyhasbeenlargerthanthemeanrateduringtheprevioustwomillennia(highconfidence).{WGISPMB.4,3.7.2,Year5.6.3,13.2}Figure1.2EnergyaccumulationwithintheEarth’sclimatesystem.Estimatesarein1021J,andaregivenrelativeto1971andfrom1971to2010,unlessotherwiseItisverylikelythatthemeanrateofglobalaveragedsealevelrisewasindicated.Componentsincludedareupperocean(above700m),deepocean(below1.7[1.5to1.9]mm/yrbetween1901and2010and3.2[2.8to3.6]700m;includingbelow2000mestimatesstartingfrom1992),icemelt(forglaciersmm/yrbetween1993and2010.Tidegaugeandsatellitealtimeterdataandicecaps,GreenlandandAntarcticicesheetestimatesstartingfrom1992,andArcticareconsistentregardingthehigherrateduringthelatterperiod.Itisseaiceestimatefrom1979to2008),continental(land)warming,andatmosphericlikelythatsimilarlyhighratesoccurredbetween1920and1950.{WGIwarming(estimatestartingfrom1979).UncertaintyisestimatedaserrorfromallfiveSPMB.4,3.7,13.2}componentsat90%confidenceintervals.{WGIBox3.1,Figure1}Sincetheearly1970s,glaciermasslossandoceanthermalexpansion1.1.3Cryospherefromwarmingtogetherexplainabout75%oftheobservedglobalmeansealevelrise(highconfidence).Overtheperiod1993–2010,Overthelasttwodecades,theGreenlandandAntarcticiceglobalmeansealevelriseis,withhighconfidence,consistentwithsheetshavebeenlosingmass(highconfidence).Glaciershavethesumoftheobservedcontributionsfromoceanthermalexpansion,continuedtoshrinkalmostworldwide(highconfidence).North-duetowarming,fromchangesinglaciers,theGreenlandicesheet,ernHemispherespringsnowcoverhascontinuedtodecreasetheAntarcticicesheetandlandwaterstorage.{WGISPMB.4,13.3.6}inextent(highconfidence).ThereishighconfidencethattherearestrongregionaldifferencesinthetrendinAntarcticseaiceRatesofsealevelriseoverbroadregionscanbeseveraltimeslargerextent,withaverylikelyincreaseintotalextent.{WGISPMB.3,orsmallerthantheglobalmeansealevelriseforperiodsofseveral4.2–4.7}decades,duetofluctuationsinoceancirculation.Since1993,theregionalratesfortheWesternPacificareuptothreetimeslargerthanGlaciershavelostmassandcontributedtosealevelrisethroughouttheglobalmean,whilethoseformuchoftheEasternPacificarenearthe20thcentury.TherateoficemasslossfromtheGreenlandicesheetzeroornegative.{WGI3.7.3,FAQ13.1}hasverylikelysubstantiallyincreasedovertheperiod1992to2011,resultinginalargermasslossover2002to2011thanover1992toThereisveryhighconfidencethatmaximumglobalmeansealevel2011.TherateoficemasslossfromtheAntarcticicesheet,mainlyduringthelastinterglacialperiod(129,000to116,000yearsago)fromthenorthernAntarcticPeninsulaandtheAmundsenSeasectorofwas,forseveralthousandyears,atleast5mhigherthanpresentandWestAntarctica,isalsolikelylargerover2002to2011.{WGISPMB.3,SPMB.4,4.3.3,4.4.2,4.4.3}42ObservedChangesandtheirCausesTopic1Box1.1RecentTemperatureTrendsandtheirImplicationsRelativefrequencyIntroductionTheobservedreductioninsurfacewarmingtrendovertheperiod1998to2012ascomparedtotheperiod1951to2012,isdueinroughlyequalmeasuretoareducedtrendinradiativeforcingandacoolingcontributionfromnaturalinternalvariability,whichincludesapossibleredistributionofheatwithintheocean(mediumconfidence).Therateofwarmingoftheobservedglobalmeansurfacetemperatureovertheperiodfrom1998to2012isestimatedtobearoundone-thirdtoone-halfofthetrendovertheperiodfrom1951to2012(Box1.1,Figures1aand1c).Evenwiththisreductioninsurfacewarmingtrend,theclimatesystemhasverylikelycontinuedtoaccumulateheatsince1998(Figure1.2)andsealevelhascontinuedtorise(Figure1.1).{WGISPMD.1,Box9.2}Theradiativeforcingoftheclimatesystemhascontinuedtoincreaseduringthe2000s,ashasitslargestcontributor,theatmosphericconcentrationofCO2.However,theradiativeforcinghasbeenincreasingatalowerrateovertheperiodfrom1998to2011,comparedto1984to1998or1951to2011,duetocoolingeffectsfromvolcaniceruptionsandthecoolingphaseofthesolarcycleovertheperiodfrom2000to2009.Thereis,however,lowconfidenceinquantifyingtheroleoftheforcingtrendincausingthereductionintherateofsurfacewarming.{WGI8.5.2,Box9.2}1Fortheperiodfrom1998to2012,111ofthe114availableclimate-modelsimulationsshowasurfacewarmingtrendlargerthantheobservations(Box1.1,Figure1a).Thereismediumconfidencethatthisdifferencebetweenmodelsandobservationsistoasubstantialdegreecausedbynaturalinternalclimatevariability,whichsometimesenhancesandsometimescounteractsthelong-termexternallyforcedwarmingtrend(compareBox1.1,Figures1aand1b;duringtheperiodfrom1984to1998,mostmodelsimulationsshowasmallerwarmingtrendthanobserved).Naturalinternalvariabilitythusdiminishestherelevanceofshorttrendsforlong-termclimatechange.Thedifferencebetweenmodelsandobservationsmayalsocontaincontributionsfrominadequaciesinthesolar,volcanicandaerosolforcingsusedbythemodelsand,insomemodels,fromanoverestimateoftheresponsetoincreasinggreenhousegasandotheranthropogenicforcing(thelatterdominatedbytheeffectsofaerosols).{WGI2.4.3,Box9.2,9.4.1,10.3.1.1}Forthelongerperiodfrom1951to2012,simulatedsurfacewarmingtrendsareconsistentwiththeobservedtrend(veryhighconfidence)(Box1.1,Figure1c).Furthermore,theindependentestimatesofradiativeforcing,ofsurfacewarmingandofobservedheatstorage(thelatteravailablesince1970)combinetogiveaheatbudgetfortheEarththatisconsistentwiththeassessedlikelyrangeofequilibriumclimatesensitivity20(1.5–4.5ºC)21.Therecordofobservedclimatechangehasthusallowedcharacterizationofthebasicpropertiesoftheclimatesystemthathaveimplicationsforfuturewarming,includingtheequilibriumclimatesensitivityandthetransientclimateresponse(seeTopic2).{WGIBox9.2,10.8.1,10.8.2,Box12.2,Box13.1}(a)1998–2012(b)1984–1998(c)1951–201286Observations4Models200.00.20.40.60.00.20.40.60.00.20.40.6(°Cperdecade)(°Cperdecade)(°Cperdecade)Box1.1,Figure1Trendsintheglobalmeansurfacetemperatureovertheperiodsfrom1998to2012(a),1984to1998(b),and1951to2012(c),fromobservations(red)andthe114availablesimulationswithcurrent-generationclimatemodels(greybars).Theheightofeachgreybarindicateshowoftenatrendofacertainmagnitude(in°Cperdecade)occursamongthe114simulations.Thewidthofthered-hatchedareaindicatesthestatisticaluncertaintythatarisesfromconstructingaglobalaveragefromindividualstationdata.ThisobservationaluncertaintydiffersfromtheonequotedinthetextofSection1.1.1;there,anestimateofnaturalinternalvariabilityisalsoincluded.Here,bycontrast,themagnitudeofnaturalinternalvariabilityischaracterisedbythespreadofthemodelensemble.{basedonWGIBox9.2,Figure1}21Theconnectionbetweentheheatbudgetandequilibriumclimatesensitivity,whichisthelong-termsurfacewarmingunderanassumeddoublingoftheatmosphericCO2concentration,arisesbecauseawarmersurfacecausesenhancedradiationtospacewhichcounteractstheincreaseintheEarth’sheatcontent.Howmuchtheradiationtospaceincreasesforagivenincreaseinsurfacetemperaturedependsonthesamefeedbackprocesses(e.g.,cloudfeedback,watervapourfeedback)thatdetermineequilibriumclimatesensitivity.43Topic1ObservedChangesandtheirCauseshighconfidencethatitdidnotexceed10mabovepresent.DuringtheGloballyaveragedgreenhousegasconcentrationslastinterglacialperiod,theGreenlandicesheetverylikelycontributedbetween1.4and4.3mtothehigherglobalmeansealevel,implying400withmediumconfidenceanadditionalcontributionfromtheAntarcticicesheet.ThischangeinsealeveloccurredinthecontextofdifferentCO2(ppm)370Icecoresorbitalforcingandwithhigh-latitudesurfacetemperature,averagedoverseveralthousandyears,atleast2°Cwarmerthanpresent(highAtmosphericmeasurementsconfidence).{WGISPMB.4,5.3.4,5.6.2,13.2.1}34031028019001600CH4(ppb)13001.2Pastandrecentdriversofclimatechange1000700320AnthropogenicgreenhousegasemissionshaveN2O(ppb)increasedsincethepre-industrialeradrivenlargely3001byeconomicandpopulationgrowth.From2000to2802010emissionswerethehighestinhistory.Historicalemissionshavedrivenatmosphericconcentrationsof260185017501800190019502000carbondioxide,methaneandnitrousoxidetolevelsYearthatareunprecedentedinatleastthelast800,000Figure1.3Observedchangesinatmosphericgreenhousegasconcentrations.years,leadingtoanuptakeofenergybytheclimateAtmosphericconcentrationsofcarbondioxide(CO2,green),methane(CH4,orange),andnitrousoxide(N2O,red).Datafromicecores(symbols)anddirectatmosphericmeasure-system.ments(lines)areoverlaid.{WGI2.2,6.2,6.3,Figure6.11}NaturalandanthropogenicsubstancesandprocessesthataltertheFourthAssessmentReport(AR4)fortheyear2005.ThisiscausedbyEarth’senergybudgetarephysicaldriversofclimatechange.RadiativeacombinationofcontinuedgrowthinmostGHGconcentrationsandforcingquantifiestheperturbationofenergyintotheEarthsystemanimprovedestimateofradiativeforcingfromaerosols.{WGISPMC,causedbythesedrivers.Radiativeforcingslargerthanzeroleadtoa8.5.1}near-surfacewarming,andradiativeforcingssmallerthanzeroleadtoacooling.Radiativeforcingisestimatedbasedonin-situandremoteTheradiativeforcingfromaerosols,whichincludescloudobservations,propertiesofGHGsandaerosols,andcalculationsusingadjustments,isbetterunderstoodandindicatesaweakernumericalmodels.Theradiativeforcingoverthe1750–2011periodiscoolingeffectthaninAR4.TheaerosolradiativeforcingovershowninFigure1.4inmajorgroupings.The‘OtherAnthropogenic’1750–2011isestimatedas–0.9[–1.9to−0.1]W/m2(mediumgroupisprincipallycomprisedofcoolingeffectsfromaerosolchanges,confidence).Radiativeforcingfromaerosolshastwocompetingwithsmallercontributionsfromozonechanges,landusereflectancecomponents:adominantcoolingeffectfrommostaerosolsandchangesandotherminorterms.{WGISPMC,8.1,8.5.1}theircloudadjustmentsandapartiallyoffsettingwarmingcon-tributionfromblackcarbonabsorptionofsolarradiation.There1.2.1Naturalandanthropogenicradiativeforcingsishighconfidencethattheglobalmeantotalaerosolradiativeforcinghascounteractedasubstantialportionofradiativeforcingfromwell-AtmosphericconcentrationsofGHGsareatlevelsthataremixedGHGs.Aerosolscontinuetocontributethelargestuncertaintytounprecedentedinatleast800,000years.Concentrationsofthetotalradiativeforcingestimate.{WGISPMC,7.5,8.3,8.5.1}carbondioxide(CO2),methane(CH4)andnitrousoxide(N2O)haveallshownlargeincreasessince1750(40%,150%and20%,Changesinsolarirradianceandvolcanicaerosolscausenatu-respectively)(Figure1.3).CO2concentrationsareincreasingattheralradiativeforcing(Figure1.4).Theradiativeforcingfromstrato-fastestobserveddecadalrateofchange(2.0±0.1ppm/yr)for2002–sphericvolcanicaerosolscanhavealargecoolingeffectontheclimate2011.AfteralmostonedecadeofstableCH4concentrationssincethesystemforsomeyearsaftermajorvolcaniceruptions.Changesintotallate1990s,atmosphericmeasurementshaveshownrenewedincreasessolarirradiancearecalculatedtohavecontributedonlyaround2%since2007.N2Oconcentrationshavesteadilyincreasedatarateofofthetotalradiativeforcingin2011,relativeto1750.{WGISPMC,0.73±0.03ppb/yroverthelastthreedecades.{WGISPMB5,2.2.1,FigureSPM.5,8.4}6.1.2,6.1.3,6.3}Thetotalanthropogenicradiativeforcingover1750–2011iscalculatedtobeawarmingeffectof2.3[1.1to3.3]W/m2(Figure1.4),andithasincreasedmorerapidlysince1970thanduringpriordecades.Carbondioxideisthelargestsinglecon-tributortoradiativeforcingover1750–2011anditstrendsince1970.Thetotalanthropogenicradiativeforcingestimatefor2011issubstantiallyhigher(43%)thantheestimatereportedintheIPCC44ObservedChangesandtheirCausesTopic1Radiativeforcingin2011relativeto17502040±310GtCO2wereaddedtotheatmospherebetween1750and2011.Since1970,cumulativeCO2emissionsfromfossilfuelWMGHGCO2CH4N2Ocombustion,cementproductionandflaringhavetripled,andcumula-IntroductionOtherAnthrop.HalocarbonstiveCO2emissionsfromforestryandotherlanduse21(FOLU)22haveincreasedbyabout40%(Figure1.5)23.In2011,annualCO2emis-TotalAnthrop.sionsfromfossilfuelcombustion,cementproductionandflaringwere34.8±2.9GtCO2/yr.For2002–2011,averageannualemissionsfromFOLUwere3.3±2.9GtCO2/yr.{WGI6.3.1,6.3.2,WGIIISPM.3}NaturalAbout40%oftheseanthropogenicCO2emissionshaveremainedintheatmosphere(880±35GtCO2)since1750.The−2−101234restwasremovedfromtheatmospherebysinks,andstoredin(W/m2)naturalcarboncyclereservoirs.Sinksfromoceanuptakeandvege-Figure1.4Radiativeforcingofclimatechangeduringtheindustrialeratationwithsoilsaccount,inroughlyequalmeasures,fortheremainder((W17M5G0H–2G0),1o1t)h.erBaarnsthsrhoopwogernaidciaftoivrceingfos,rctinogtalfraonmthrowpeollg-menixicedforgcrienegnshaonudsenagtausreaslooffththeecuemmuiltatetidveaCnOth2reompoisgseionnics.TChOe2o,cecaaunshinagsaobcseoarnbedacaibdoifuicta3ti0o%n.1forcings.Theerrorbarsindicatethe5to95%uncertainty.Otheranthropogenicforc-ingsincludeaerosol,landusesurfacereflectanceandozonechanges.Naturalforcings{WGI3.8.1,6.3.1}includesolarandvolcaniceffects.Thetotalanthropogenicradiativeforcingfor2011TotalannualanthropogenicGHGemissionshavecontinuedtorelativeto1750is2.3W/m2(uncertaintyrange1.1to3.3W/m2).ThiscorrespondstoaCO2-equivalentconcentration(seeGlossary)of430ppm(uncertaintyrange340toincreaseover1970to2010withlargerabsoluteincreasesbetween520ppm).{DatafromWGI7.5andTable8.6}2000and2010(highconfidence).Despiteagrowingnumberofclimatechangemitigationpolicies,annualGHGemissionsgrewonaverageby1.0GtCO2-eq(2.2%)peryear,from2000to2010,com-1.2.2Humanactivitiesaffectingemissiondriversparedto0.4GtCO2-eq(1.3%)peryear,from1970to2000(Figure1.6)24.TotalanthropogenicGHGemissionsfrom2000to2010weretheAbouthalfofthecumulativeanthropogenicCO2emissionshighestinhumanhistoryandreached49(±4.5)GtCO2-eq/yrin2010.between1750and2011haveoccurredinthelast40yearsTheglobaleconomiccrisisof2007/2008reducedemissionsonlytem-(highconfidence).CumulativeanthropogenicCO2emissionsofporarily.{WGIIISPM.3,1.3,5.2,13.3,15.2.2,BoxTS.5,Figure15.1}GlobalanthropogenicCO2emissionsCumulativeCO2emissionsQuantitativeinformationofCH4andN2Oemissiontimeseriesfrom1850to1970islimited402000150035Fossilfuels,cementandﬂaring30Forestryandotherlanduse(GtCO2/yr)25(GtCO2)20100015105005001900Year19502000175017501850––19702011Figure1.5Annualglobalanthropogeniccarbondioxide(CO2)emissions(gigatonneofCO2-equivalentperyear,GtCO2/yr)fromfossilfuelcombustion,cementproductionandflaring,andforestryandotherlanduse(FOLU),1750–2011.Cumulativeemissionsandtheiruncertaintiesareshownasbarsandwhiskers,respectively,ontheright-handside.Theglobaleffectsoftheaccumulationofmethane(CH4)andnitrousoxide(N2O)emissionsareshowninFigure1.3.Greenhousegasemissiondatafrom1970to2010areshowninFigure1.6.{modifiedfromWGIFigureTS.4andWGIIIFigureTS.2}22Forestryandotherlanduse(FOLU)—alsoreferredtoasLULUCF(landuse,landusechangeandforestry)—isthesubsetofagriculture,forestryandotherlanduse(AFOLU)emissionsandremovalsofGHGsrelatedtodirecthuman-inducedLULUCFactivities,excludingagriculturalemissionsandremovals(seeWGIIIAR5Glossary).23NumbersfromWGI6.3convertedintoGtCO2units.SmalldifferencesincumulativeemissionsfromWorkingGroupIII{WGIIISPM.3,TS.2.1}areduetodifferentapproachestorounding,differentendyearsandtheuseofdifferentdatasetsforemissionsfromFOLU.Estimatesremainextremelyclose,giventheiruncertainties.24CO2-equivalentemissionisacommonscaleforcomparingemissionsofdifferentGHGs.ThroughouttheSYR,whenhistoricalemissionsofGHGsareprovidedinGtCO2-eq,theyareweightedbyGlobalWarmingPotentialswitha100-yeartimehorizon(GWP100),takenfromtheIPCCSecondAssessmentReportunlessotherwisestated.AunitabbreviationofGtCO2-eqisused.{Box3.2,Glossary}45Topic1ObservedChangesandtheirCausesTotalannualanthropogenicGHGemissionsbygases1970–2010+2.2%/yr52Gt2000–20102.2%5.0%5049Gt+1.3%/yr1970–20002.0%6.2%GHGemissions(GtCO2-eq/yr)4038Gt16%20%0.81%11%10%7.4%18%3027Gt0.44%16%7.9%19%20117%Gas65%62%F-Gases1059%N2O55%CH4CO2FOLUCO2Fossilfuelandindustrialprocesses020102010197019751980198519901995200020052010(GWP100SAR)(GWP100AR5)YearFigure1.6Totalannualanthropogenicgreenhousegas(GHG)emissions(gigatonneofCO2-equivalentperyear,GtCO2-eq/yr)fortheperiod1970to2010,bygases:CO2fromfossilfuelcombustionandindustrialprocesses;CO2fromForestryandOtherLandUse(FOLU);methane(CH4);nitrousoxide(N2O);fluorinatedgasescoveredundertheKyotoProtocol(F-gases).Righthandsideshows2010emissions,usingalternativelyCO2-equivalentemissionweightingsbasedonIPCCSecondAssessmentReport(SAR)andAR5values.Unlessotherwisestated,CO2-equivalentemissionsinthisreportincludethebasketofKyotogases(CO2,CH4,N2OaswellasF-gases)calculatedbasedon100-yearGlobalWarmingPotential(GWP100)valuesfromtheSAR(seeGlossary).UsingthemostrecentGWP100valuesfromtheAR5(right-handbars)wouldresultinhighertotalannualGHGemissions(52GtCO2-eq/yr)fromanincreasedcontributionofmethane,butdoesnotchangethelong-termtrendsignificantly.Othermetricchoiceswouldchangethecontributionsofdifferentgases(seeBox3.2).The2010valuesareshownagainbrokendownintotheircomponentswiththeassociateduncertainties(90%confidenceinterval)indicatedbytheerrorbars.GlobalCO2emissionsfromfossilfuelcombustionareknownwithan8%uncertaintymargin(90%confidenceinterval).Thereareverylargeuncertainties(oftheorderof±50%)attachedtotheCO2emissionsfromFOLU.UncertaintyabouttheglobalemissionsofCH4,N2OandtheF-gaseshasbeenestimatedat20%,60%and20%,respectively.2010wasthemostrecentyearforwhichemissionstatisticsonallgasesaswellasassessmentsofuncertaintieswereessentiallycompleteatthetimeofdatacutoffforthisreport.Theuncertaintyestimatesonlyaccountforuncertaintyinemissions,notintheGWPs(asgiveninWGI8.7).{WGIIIFigureSPM.1}CO2emissionsfromfossilfuelcombustionandindustrialpro-industrysectors(highconfidence).Since2000,GHGemissionshavecessescontributedabout78%tothetotalGHGemissionbeengrowinginallsectors,exceptinagriculture,forestryandotherincreasebetween1970and2010,withacontributionofsim-landuse(AFOLU)22.In2010,35%ofGHGemissionswerereleasedbyilarpercentageoverthe2000–2010period(highconfidence).theenergysector,24%(netemissions)fromAFOLU,21%byindustry,Fossil-fuel-relatedCO2emissionsreached32(±2.7)GtCO2/yr,in2010,14%bytransportand6.4%bythebuildingsector.Whenemissionsandgrewfurtherbyabout3%between2010and2011,andbyaboutfromelectricityandheatproductionareattributedtothesectorsthat1to2%between2011and2012.CO2remainsthemajoranthropo-usethefinalenergy(i.e.,indirectemissions),thesharesoftheindustrygenicGHG,accountingfor76%oftotalanthropogenicGHGemissionsandbuildingsectorsinglobalGHGemissionsareincreasedto31%in2010.Ofthetotal,16%comesfromCH4,6.2%fromN2O,and2.0%and19%,respectively(Figure1.7).{WGIIISPM.3,7.3,8.1,9.2,10.3,fromfluorinatedgases(F-gases)(Figure1.6)25.Annually,since1970,11.2}SeealsoBox3.2forcontributionsfromvarioussectors,basedonabout25%ofanthropogenicGHGemissionshavebeenintheformofmetricsotherthan100-yearGlobalWarmingPotential(GWP100).non-CO2gases26.{WGIIISPM.3,1.2,5.2}Globally,economicandpopulationgrowthcontinuetobetheTotalannualanthropogenicGHGemissionshaveincreasedbymostimportantdriversofincreasesinCO2emissionsfromabout10GtCO2-eqbetween2000and2010.Thisincreasedirectlyfossilfuelcombustion.Thecontributionofpopulationgrowthcamefromtheenergy(47%),industry(30%),transport(11%)between2000and2010remainedroughlyidenticaltothatofandbuilding(3%)sectors(mediumconfidence).Accountingforthepreviousthreedecades,whilethecontributionofeconomicindirectemissionsraisesthecontributionsbythebuildingandgrowthhasrisensharply(highconfidence).Between2000and25Usingthemostrecent100-yearGlobalWarmingPotential(GWP100)valuesfromtheAR5{WGI8.7}insteadofGWP100valuesfromtheIPCCSecondAssessmentReport,globalGHGemissiontotalswouldbeslightlyhigher(52GtCO2-eq/yr)andnon-CO2emissionshareswouldbe20%forCH4,5%forN2Oand2.2%forF-gases.26Forthisreport,dataonnon-CO2GHGs,includingF-gases,weretakenfromtheElectronicDataGathering,Analysis,andRetrieval(EDGAR)database{WGIIIAnnexII.9},whichcoverssubstancesincludedintheKyotoProtocolinitsfirstcommitmentperiod.46ObservedChangesandtheirCausesTopic1Greenhousegasemissionsbyeconomicsectors2010,bothdriversoutpacedemissionreductionsfromimprovementsinenergyintensityofgrossdomesticproduct(GDP)(Figure1.8).Increaseduseofcoalrelativetootherenergysourceshasreversedthelong-standingtrendingradualdecarbonization(i.e.,reducingthecarbonintensityofenergy)oftheworld’senergysupply.{WGIIISPM.3,TS.2.2,1.3,5.3,7.2,7.3,14.3}1.3AttributionofclimatechangesandimpactsChangeinannualCO2emissionsbydecade(GtCO2/yr)ElectricityEnergyandheatproduction1.4%Introduction25%AFOLUIndustry24%11%Buildings6.4%TransportTotal:49GtCO2-eqTransport14%(2010)0.3%IndustryBuildingsTheevidenceforhumaninfluenceontheclimate21%12%systemhasgrownsinceAR4.HumaninfluencehasbeendetectedinwarmingoftheatmosphereandtheOtherocean,inchangesintheglobalwatercycle,inreduc-1energyAFOLUtionsinsnowandice,andinglobalmeansealevel9.6%0.87%rise;anditisextremelylikelytohavebeenthedomi-DirectGHGemissionsIndirectCO2emissionsnantcauseoftheobservedwarmingsincethemid-20thcentury.Inrecentdecades,changesinclimateFigure1.7Totalanthropogenicgreenhousegas(GHG)emissions(gigatonneofCO2-havecausedimpactsonnaturalandhumansystemsequivalentperyear,GtCO2-eq/yr)fromeconomicsectorsin2010.Thecircleshowstheonallcontinentsandacrosstheoceans.ImpactsaresharesofdirectGHGemissions(in%oftotalanthropogenicGHGemissions)fromfiveduetoobservedclimatechange,irrespectiveofitseconomicsectorsin2010.Thepull-outshowshowsharesofindirectCO2emissionscause,indicatingthesensitivityofnaturalandhuman(in%oftotalanthropogenicGHGemissions)fromelectricityandheatproductionaresystemstochangingclimate.attributedtosectorsoffinalenergyuse.‘Otherenergy’referstoallGHGemissionsourcesintheenergysectorasdefinedinWGIIIAnnexII,otherthanelectricityandheatproduction{WGIIIAnnexII.9.1}.Theemissiondataonagriculture,forestryandotherlanduse(AFOLU)includesland-basedCO2emissionsfromforestfires,peatfiresThecausesofobservedchangesintheclimatesystem,aswellasinanyandpeatdecaythatapproximatetonetCO2fluxfromthesub-sectorsofforestryandnaturalorhumansystemimpactedbyclimate,areestablishedfollow-otherlanduse(FOLU)asdescribedinChapter11oftheWGIIIreport.Emissionsareingaconsistentsetofmethods.DetectionaddressesthequestionofwhetherclimateoranaturalorhumansystemaffectedbyclimatehasconvertedintoCO2-equivalentsbasedon100-yearGlobalWarmingPotential(GWP100),takenfromtheIPCCSecondAssessmentReport(SAR).SectordefinitionsareprovidedinWGIIIAnnexII.9.{WGIIIFigureSPM.2}actuallychangedinastatisticalsense,whileattributionevaluatestherelativecontributionsofmultiplecausalfactorstoanobservedchangeDecompositionofthechangeintotalglobalCO2emissionsfromfossilfuelcombustionbydecade1210CarbonintensityofenergyPopulationEnergyintensityofGDPTotalchange8GDPpercapita66.844.022.92.50–2–4–61980–19901990–20002000–20101970–1980Figure1.8Decompositionofthechangeintotalannualcarbondioxide(CO2)emissionsfromfossilfuelcombustionbydecadeandfourdrivingfactors:population,income(grossdomesticproduct,GDP)percapita,energyintensityofGDPandcarbonintensityofenergy.Thebarsegmentsshowthechangesassociatedwitheachindividualfactor,holdingtherespectiveotherfactorsconstant.Totalemissionchangesareindicatedbyatriangle.ThechangeinemissionsovereachdecadeismeasuredingigatonnesofCO2peryear(GtCO2/yr);incomeisconvertedintocommonunits,usingpurchasingpowerparities.{WGIIISPM.3}47Topic1ObservedChangesandtheirCausesoreventwithanassignmentofstatisticalconfidence27.AttributionofTogethertheseassessedcontributionsareconsistentwiththeobservedclimatechangetocausesquantifiesthelinksbetweenobservedclimatewarmingofapproximately0.6°Cto0.7°Coverthisperiod.{WGISPMD.3,changeandhumanactivity,aswellasother,natural,climatedrivers.In10.3.1}contrast,attributionofobservedimpactstoclimatechangeconsidersthelinksbetweenobservedchangesinnaturalorhumansystemsandItisverylikelythatanthropogenicinfluence,particularlyGHGsandobservedclimatechange,regardlessofitscause.Resultsfromstudiesstratosphericozonedepletion,hasledtoadetectableobservedpat-attributingclimatechangetocausesprovideestimatesofthemagni-ternoftroposphericwarmingandacorrespondingcoolinginthelowertudeofwarminginresponsetochangesinradiativeforcingandhencestratospheresince1961.{WGISPMD.3,2.4.4,9.4.1,10.3.1}supportprojectionsoffutureclimatechange(Topic2).Resultsfromstudiesattributingimpactstoclimatechangeprovidestrongindica-OvereverycontinentalregionexceptAntarctica,anthropogenictionsforthesensitivityofnaturalorhumansystemstofutureclimateforcingshavelikelymadeasubstantialcontributiontosurfacechange.{WGI10.8,WGIISPMA-1,WGI/II/III/SYRGlossaries}temperatureincreasessincethemid-20thcentury(Figure1.10).ForAntarctica,largeobservationaluncertaintiesresultinlowconfi-dencethatanthropogenicforcingshavecontributedtotheobserved11.3.1Anatttruirbaultiinofnluoefnccleimsoatnetchheacnlgimesatteoshyusmteamnandwarmingaveragedoveravailablestations.Incontrast,itislikelythattherehasbeenananthropogeniccontributiontotheverysubstantialArcticwarmingsincethemid-20thcentury.HumaninfluencehaslikelyItisextremelylikelythatmorethanhalfoftheobservedcontributedtotemperatureincreasesinmanysub-continentalregions.increaseinglobalaveragesurfacetemperaturefrom1951to{WGISPMD.3,TS.4.8,10.3.1}2010wascausedbytheanthropogenicincreaseinGHGconcen-trationsandotheranthropogenicforcingstogether(Figure1.9).AnthropogenicinfluenceshaveverylikelycontributedtoArcticThebestestimateofthehumaninducedcontributiontowarmingisseaicelosssince1979(Figure1.10).Thereislowconfidenceinthesimilartotheobservedwarmingoverthisperiod.GHGscontributedascientificunderstandingofthesmallobservedincreaseinAntarcticseaglobalmeansurfacewarminglikelytobeintherangeof0.5°Cto1.3°Ciceextentduetotheincompleteandcompetingscientificexplanationsovertheperiod1951to2010,withfurthercontributionsfromotherforthecausesofchangeandlowconfidenceinestimatesofnaturalanthropogenicforcings,includingthecoolingeffectofaerosols,frominternalvariabilityinthatregion.{WGISPMD.3,10.5.1,Figure10.16}naturalforcings,andfromnaturalinternalvariability(seeFigure1.9).AnthropogenicinfluenceslikelycontributedtotheretreatofglaciersContributionstoobservedsurfacetemperaturechangeovertheperiod1951–2010sincethe1960sandtotheincreasedsurfacemeltingoftheGreen-landicesheetsince1993.Duetoalowlevelofscientificunderstand-ing,however,thereislowconfidenceinattributingthecausesoftheOBSERVEDWARMINGobservedlossofmassfromtheAntarcticicesheetoverthepasttwoGreenhousegasesdecades.Itislikelythattherehasbeenananthropogeniccontribu-tiontoobservedreductionsinNorthernHemispherespringsnowcoverOtheranthropogenicforcingssince1970.{WGI4.3.3,10.5.2,10.5.3}CombinedanthropogenicforcingsNaturalforcingsItislikelythatanthropogenicinfluenceshaveaffectedtheNaturalinternalvariabilityglobalwatercyclesince1960.Anthropogenicinfluenceshavecontributedtoobservedincreasesinatmosphericmoisturecontent–0.50.00.51.0(mediumconfidence),toglobal-scalechangesinprecipitationpatternsoverland(mediumconfidence),tointensificationofheavyprecipita-(°C)tionoverlandregionswheredataaresufficient(mediumconfidence)(see1.4)andtochangesinsurfaceandsubsurfaceoceansalinity(veryFigure1.9Assessedlikelyranges(whiskers)andtheirmid-points(bars)forwarminglikely).{WGISPMD.3,2.5.1,2.6.2,3.3.2,3.3.3,7.6.2,10.3.2,10.4.2,trendsoverthe1951–2010periodfromwell-mixedgreenhousegases,otheranthro-10.6}pogenicforcings(includingthecoolingeffectofaerosolsandtheeffectoflandusechange),combinedanthropogenicforcings,naturalforcings,andnaturalinternalcli-Itisverylikelythatanthropogenicforcingshavemadeasub-matevariability(whichistheelementofclimatevariabilitythatarisesspontaneouslystantialcontributiontoincreasesinglobalupperoceanheatwithintheclimatesystem,evenintheabsenceofforcings).Theobservedsurfacetem-content(0–700m)observedsincethe1970s(Figure1.10).Thereperaturechangeisshowninblack,withthe5to95%uncertaintyrangeduetoobser-isevidenceforhumaninfluenceinsomeindividualoceanbasins.Itisvationaluncertainty.Theattributedwarmingranges(colours)arebasedonobservationsverylikelythatthereisasubstantialanthropogeniccontributiontothecombinedwithclimatemodelsimulations,inordertoestimatethecontributionbyanglobalmeansealevelrisesincethe1970s.Thisisbasedonthehighindividualexternalforcingtotheobservedwarming.Thecontributionfromthecom-confidenceinananthropogenicinfluenceonthetwolargestcontribu-binedanthropogenicforcingscanbeestimatedwithlessuncertaintythantheseparatetionstosealevelrise:thermalexpansionandglaciermassloss.Oceaniccontributionsfromgreenhousegasesandotheranthropogenicforcingsseparately.Thisisbecausethesetwocontributionspartiallycompensate,resultinginasignalthatisbetterconstrainedbyobservations.{BasedonFigureWGITS.10}27DefinitionsweretakenfromtheGoodPracticeGuidancePaperonDetectionandAttribution,theagreedproductoftheIPCCExpertMeetingonDetectionandAttributionRelatedtoAnthropogenicClimateChange;seeGlossary.48ObservedChangesandtheirCausesTopic1SeaIce(106km2)ArcticIntroduction20–22NorthAmerica–419602010Europe119100T(°C)2AsiaT(°C)12NorthPaciﬁc–1191019602010NorthAtlantic0T(°C)1–10OHC(1022J)4–119102OHC(1022J)4219602010191019602010Africa02–20191019602010–2T(°C)119101960201002SouthAmerica–1191019601SouthAtlantic04–1191019602010201SouthPaciﬁc420–2OHC(1022J)T(°C)OHC(1022J)OHC(1022J)2010T(°C)AustraliaIndianOcean214020191019602010Antarctic–219602010–2–119101960201021910Antarctica191019602010SeaIce(106km2)SouthernOcean24OHC(1022J)012–2T(°C)00–4–1–2191019602010191019602010191019602010LandsurfaceGlobalaveragesOceanheatcontent2Landandoceansurface220T(°C)1110T(°C)OHC(1022J)000–10–1191019602010–1191019602010191019602010ObservationsModelsusingonlynaturalforcingsModelsusingbothnaturalandanthropogenicforcingsFigure1.10Comparisonofobservedandsimulatedchangeincontinentalsurfacetemperaturesonland(yellowpanels),ArcticandAntarcticSeptemberseaiceextent(whitepanels),andupperoceanheatcontentinthemajoroceanbasins(bluepanels).Globalaveragechangesarealsogiven.Anomaliesaregivenrelativeto1880–1919forsurfacetemperatures,to1960–1980foroceanheatcontent,andto1979–1999forseaice.Alltimeseriesaredecadalaverages,plottedatthecentreofthedecade.Fortemperaturepanels,observationsaredashedlinesifthespatialcoverageofareasbeingexaminedisbelow50%.Foroceanheatcontentandseaicepanels,thesolidlinesarewherethecoverageofdataisgoodandhigherinquality,andthedashedlinesarewherethedatacoverageisonlyadequate,and,thus,uncertaintyislarger(notethatdifferentlinesindicatedifferentdatasets;fordetails,seeWGIFigureSPM.6).ModelresultsshownareCoupledModelIntercomparisonProjectPhase5(CMIP5)multi-modelensembleranges,withshadedbandsindicatingthe5to95%confidenceintervals.{WGIFigureSPM6;fordetail,seeWGIFigureTS.12}uptakeofanthropogenicCO2hasresultedingradualacidificationofofitscause,indicatingthesensitivityofnaturalandhumanoceansurfacewaters(highconfidence).{WGISPMD.3,3.2.3,3.8.2,systemstochangingclimate.Evidenceofobservedclimatechange10.4.1,10.4.3,10.4.4,10.5.2,13.3,Box3.2,TS.4.4,WGII6.1.1.2,impactsisstrongestandmostcomprehensivefornaturalsystems.BoxCC-OA}Someimpactsonhumansystemshavealsobeenattributedtoclimatechange,withamajororminorcontributionofclimatechangedistin-1.3.2Observedimpactsattributedtoclimatechangeguishablefromotherinfluences(Figure1.11).Impactsonhumansys-temsareoftengeographicallyheterogeneousbecausetheydependnotInrecentdecades,changesinclimatehavecausedimpactsononlyonchangesinclimatevariablesbutalsoonsocialandeconomicnaturalandhumansystemsonallcontinentsandacrossthefactors.Hence,thechangesaremoreeasilyobservedatlocallevels,oceans.Impactsareduetoobservedclimatechange,irrespectivewhileattributioncanremaindifficult.{WGIISPMA-1,SPMA-3,18.1,18.3–18.6}49Topic1ObservedChangesandtheirCauses(a)WidespreadimpactsattributedtoclimatechangebasedontheavailablescientiﬁcliteraturesincetheAR4POLARREGIONS(ArcticandAntarctic)NORTHAMERICAEUROPEASIASMALLISLANDS1054419329AFRICACENTRALANDSOUTHAMERICA8101AUSTRALASIA198729823255ConﬁdenceinattributionObservedimpactsattributedtoclimatechangefortoclimatechangePhysicalsystemsBiologicalsystemsHumanandmanagedsystemsImpactsidentiﬁedvloewrylowmedhighhveigrhyGlaciers,snow,iceTerrestrialFoodproductionbasedonavailabilityindicatesand/orpermafrostecosystemsofstudiesacrossconﬁdencerangeLivelihoods,healtharegionRivers,lakes,ﬂoodsWildﬁreand/oreconomics(b)and/ordrought400CoastalerosionMarineecosystemsand/orsealeveleffectsOutlinedsymbols=MinorcontributionofclimatechangeFilledsymbols=Majorcontributionofclimatechange(c)(3)Cooler2StandarderrorMean(19)(27)(18)(10)(13)(12)StandarderrorDistributionchange(kmperdecade)Yieldimpact(%changeperdecade)0(13)−2100(20)(29)(9)(111)(359)−4(46)(29)90thpercentile(90)(9)2075thpercentile0Warmer−6Median–2025thpercentileicalgaedariansolluscsustacea(other)lanktonlanktonyﬁshesyﬁshesyﬁshestaxa10thpercentilenthhiccnithicmthiccrinvert.hytopZoopalbonn-bonBonAllBeBentBenBennthicPLarvNoTropicalTemperateWheatSoyRiceMaizeRegionBeCroptype50ObservedChangesandtheirCausesTopic1Figure1.11Widespreadimpactsinachangingworld:(a)BasedontheavailablescientificliteraturesincetheIPCCFourthAssessmentReport(AR4),therearesubstantiallyIntroductionmoreimpactsinrecentdecadesnowattributedtoclimatechange.Attributionrequiresdefinedscientificevidenceontheroleofclimatechange.Absencefromthemapofadditionalimpactsattributedtoclimatechangedoesnotimplythatsuchimpactshavenotoccurred.Thepublicationssupportingattributedimpactsreflectagrowingknowledgebase,butpublicationsarestilllimitedformanyregions,systemsandprocesses,highlightinggapsindataandstudies.Symbolsindicatecategoriesofattributedimpacts,therelativecontri-butionofclimatechange(majororminor)totheobservedimpactandconfidenceinattribution.EachsymbolreferstooneormoreentriesinWGIITableSPM.A1,groupingrelatedregional-scaleimpacts.Numbersinovalsindicateregionaltotalsofclimatechangepublicationsfrom2001to2010,basedontheScopusbibliographicdatabaseforpublicationsinEnglishwithindividualcountriesmentionedintitle,abstractorkeywords(asofJuly2011).Thesenumbersprovideanoverallmeasureoftheavailablescientificliteratureonclimatechangeacrossregions;theydonotindicatethenumberofpublicationssupportingattributionofclimatechangeimpactsineachregion.Studiesforpolarregionsandsmallislandsaregroupedwithneighbouringcontinentalregions.TheinclusionofpublicationsforassessmentofattributionfollowedIPCCscientificevidencecriteriadefinedinWGIIChapter18.PublicationsconsideredintheattributionanalysescomefromabroaderrangeofliteratureassessedintheWGIIAR5.SeeWGIITableSPM.A1fordescriptionsoftheattributedimpacts.(b)Averageratesofchangeindistribution(kmperdecade)formarinetaxonomicgroupsbasedonobservationsover1900–2010.Positivedistributionchangesareconsistentwithwarming(movingintopreviouslycoolerwaters,generallypoleward).Thenumberofresponsesanalysedisgivenforeachcategory.(c)Summaryofestimatedimpactsofobservedclimatechangesonyieldsover1960–2013forfourmajorcropsintemperateandtropicalregions,withthenumberofdatapointsanalysedgivenwithinparenthesesforeachcategory.{WGIIFigureSPM.2,BoxTS.1Figure1}1Inmanyregions,changingprecipitationormeltingsnowandAssessmentofmanystudiescoveringawiderangeofregionsicearealteringhydrologicalsystems,affectingwaterresourcesandcropsshowsthatnegativeimpactsofclimatechangeonintermsofquantityandquality(mediumconfidence).Glacierscropyieldshavebeenmorecommonthanpositiveimpactscontinuetoshrinkalmostworldwideduetoclimatechange(highcon-(highconfidence).Thesmallernumberofstudiesshowingpositivefidence),affectingrunoffandwaterresourcesdownstream(mediumimpactsrelatemainlytohigh-latituderegions,thoughitisnotyetconfidence).Climatechangeiscausingpermafrostwarmingandthaw-clearwhetherthebalanceofimpactshasbeennegativeorpositiveinginhigh-latituderegionsandinhigh-elevationregions(highconfi-intheseregions(highconfidence).Climatechangehasnegativelydence).{WGIISPMA-1}affectedwheatandmaizeyieldsformanyregionsandintheglobalaggregate(mediumconfidence).EffectsonriceandsoybeanyieldManyterrestrial,freshwaterandmarinespecieshaveshiftedhavebeensmallerinmajorproductionregionsandglobally,withtheirgeographicranges,seasonalactivities,migrationpatterns,amedianchangeofzeroacrossallavailabledatawhicharefewerabundancesandspeciesinteractionsinresponsetoongoingcli-forsoycomparedtotheothercrops(seeFigure1.11c).Observedmatechange(highconfidence).Whileonlyafewrecentspeciesimpactsrelatemainlytoproductionaspectsoffoodsecurityratherextinctionshavebeenattributedasyettoclimatechange(highcon-thanaccessorothercomponentsoffoodsecurity.SinceAR4,severalfidence),naturalglobalclimatechangeatratesslowerthancurrentperiodsofrapidfoodandcerealpriceincreasesfollowingclimateanthropogenicclimatechangecausedsignificantecosystemshiftsandextremesinkeyproducingregionsindicateasensitivityofcurrentspeciesextinctionsduringthepastmillionsofyears(highconfidence).marketstoclimateextremesamongotherfactors(mediumcon-Increasedtreemortality,observedinmanyplacesworldwide,hasbeenfidence).{WGIISPMA-1}attributedtoclimatechangeinsomeregions.Increasesinthefre-quencyorintensityofecosystemdisturbancessuchasdroughts,wind-Atpresenttheworldwideburdenofhumanill-healthfromcli-storms,firesandpestoutbreakshavebeendetectedinmanypartsofmatechangeisrelativelysmallcomparedwitheffectsofothertheworldandinsomecasesareattributedtoclimatechange(mediumstressorsandisnotwellquantified.However,therehasbeenconfidence).Numerousobservationsoverthelastdecadesinalloceanincreasedheat-relatedmortalityanddecreasedcold-relatedmortalitybasinsshowchangesinabundance,distributionshiftspolewardand/insomeregionsasaresultofwarming(mediumconfidence).Localortodeeper,coolerwatersformarinefishes,invertebratesandphyto-changesintemperatureandrainfallhavealteredthedistributionofplankton(veryhighconfidence),andalteredecosystemcompositionsomewater-borneillnessesanddiseasevectors(mediumconfidence).(highconfidence),trackingclimatetrends.Somewarm-watercorals{WGIISPMA-1}andtheirreefshaverespondedtowarmingwithspeciesreplacement,bleaching,anddecreasedcoralcovercausinghabitatloss(highconfi-‘Cascading’impactsofclimatechangecannowbeattributeddence).Someimpactsofoceanacidificationonmarineorganismshavealongchainsofevidencefromphysicalclimatethroughtointer-beenattributedtohumaninfluence,fromthethinningofpteropodandmediatesystemsandthentopeople(Figure1.12).Thechangesforaminiferanshells(mediumconfidence)tothedeclininggrowthratesinclimatefeedingintothecascade,insomecases,arelinkedtohumanofcorals(lowconfidence).Oxygenminimumzonesareprogressivelydrivers(e.g.,adecreasingamountofwaterinspringsnowpackinwest-expandinginthetropicalPacific,AtlanticandIndianOceans,duetoernNorthAmerica),while,inothercases,assessmentsofthecausesofreducedventilationandO2solubilityinwarmer,morestratifiedoceans,observedclimatechangeleadingintothecascadearenotavailable.Inandareconstrainingfishhabitat(mediumconfidence).{WGIISPMA-1,allcases,confidenceindetectionandattributiontoobservedclimateTableSPM.A1,TSA-1,6.3.2.5,6.3.3,18.3–18.4,30.5.1.1,BoxCC-OA,changedecreasesforeffectsfurtherdowneachimpactchain.{WGIIBoxCC-CR}18.6.3}51Topic1ObservedChangesandtheirCausesCryosphereWesternNorthAmericaWesternAndesAsiaArcticDecreasingspringEarlyspringpeakChangesinriverdischargesnowpack(high/high)ﬂow(high/high)patterns(medium/medium)LandsurfaceGlacialshrinkageIncreasedrunoffinwarming(veryhigh/high)glacial-fedrivers(high/high)PermafrostdegradationChangesinlocationsofImpactsonlivelihoodsofindigenous(high/high)thermokarstlakes(high/high)peoples(medium/medium)OceansurfaceandIncreasedcoastalerosionatmosphericwarming(medium/medium)Seaicerecession,earlierEffectsonnon-migratorymarineanimals(high/high)1Windandoceanbreakup(veryhigh/high)circulationchangesOceanPhysicalimpactsBiologicalimpactsImpactsonmanagedsystemsIncreasedthermalRangeshiftsofﬁshandImpactsonlargenon-ﬁshChangesinstratiﬁcation(verymacroalgae(high/high)species(high/high)ﬁsheryyieldshigh/veryhigh)Increasedcoralmortalityand(low/low)bleaching(veryhigh/high)OceanExpansionofhypoxicRegionalchangesinsurfacezones(medium/low)Increasedprimaryproductionatspeciesabundancewarminghighlatitudes(medium/medium)Arcticseaiceretreat(high/medium)(veryhigh/high)ChangesinspeciesOceanandrichness(high/medium)atmospherecirculationchangesForestsHighelevationislandsWesternNorthAmericaWesternSahelAtmosphericwarmingUpwardshiftintreelinesUpwardshiftinfaunaPrecipitationchanges(low/low)(low/low)IncreaseininsectpestsIncreasedtreemortality(medium/low)(medium/low)IncreasedsoilmoisturedroughtDecreasedtreedensity(medium/medium)(medium/medium)DescriptionofimpactAttributionofclimatechangerole(conﬁdenceindetection/conﬁdenceinattribution)MajorroleMinorroleFigure1.12Majorsystemswherenewevidenceindicatesinterconnected,‘cascading’impactsfromrecentclimatechangethroughseveralnaturalandhumansubsystems.Bracketedtextindicatesconfidenceinthedetectionofaclimatechangeeffectandtheattributionofobservedimpactstoclimatechange.Theroleofclimatechangecanbemajor(solidarrow)orminor(dashedarrow).Initialevidenceindicatesthatoceanacidificationisfollowingsimilartrendswithrespecttoimpactonhumansystemsasoceanwarming.{WGIIFigure18-4}52ObservedChangesandtheirCausesTopic11.4ExtremeeventsThereislowconfidenceinobservedglobal-scaletrendsinIntroductiondroughts,duetolackofdirectobservations,dependenciesofChangesinmanyextremeweatherandclimateeventsinferredtrendsonthechoiceofthedefinitionfordrought,andhavebeenobservedsinceabout1950.Someoftheseduetogeographicalinconsistenciesindroughttrends.Therechangeshavebeenlinkedtohumaninfluences,includ-isalsolowconfidenceintheattributionofchangesindroughtoveringadecreaseincoldtemperatureextremes,angloballandareassincethemid-20thcentury,duetothesameobserva-increaseinwarmtemperatureextremes,anincreaseintionaluncertaintiesanddifficultiesindistinguishingdecadalscalevar-extremehighsealevelsandanincreaseinthenumberiabilityindroughtfromlong-termtrends.{WGITableSPM.1,2.6.2.3,ofheavyprecipitationeventsinanumberofregions.10.6,Figure2.33,WGII3.ES,3.2.7}Thereislowconfidencethatlong-termchangesintropicalcycloneactivityarerobust,andthereislowconfidenceintheItisverylikelythatthenumberofcolddaysandnightshasattributionofglobalchangestoanyparticularcause.However,itdecreasedandthenumberofwarmdaysandnightshasisvirtuallycertainthatintensetropicalcycloneactivityhasincreasediniwnacvreesasheadsionncrtehaesegdloinbalalrgsceaplea.rtIstoisflEikuerloypteh,aAtstihaeafnredqAuuesntcryaloiaf.hIetaisttheNorthAtlanticsince1970.{WGITableSPM.1,2.6.3,10.6}1verylikelythathumaninfluencehascontributedtotheobservedglobalItislikelythatextremesealevels(forexample,asexperiencedscalechangesinthefrequencyandintensityofdailytemperatureinstormsurges)haveincreasedsince1970,beingmainlytheextremessincethemid-20thcentury.Itislikelythathumaninfluenceresultofmeansealevelrise.Duetoashortageofstudiesandthehasmorethandoubledtheprobabilityofoccurrenceofheatwavesindifficultyofdistinguishinganysuchimpactsfromothermodificationssomelocations.{WGISPMB.1,SPMD.3,TableSPM.1,FAQ2.2,2.6.1,tocoastalsystems,limitedevidenceisavailableontheimpactsofsea10.6}levelrise.{WGI3.7.4–3.7.6,Figure3.15,WGII5.3.3.2,18.3}ThereismediumconfidencethattheobservedwarminghasImpactsfromrecentclimate-relatedextremes,suchasheatincreasedheat-relatedhumanmortalityanddecreasedcold-waves,droughts,floods,cyclonesandwildfires,revealsignifi-relatedhumanmortalityinsomeregions.Extremeheateventscur-cantvulnerabilityandexposureofsomeecosystemsandmanyrentlyresultinincreasesinmortalityandmorbidityinNorthAmericahumansystemstocurrentclimatevariability(veryhighconfi-(veryhighconfidence),andinEuropewithimpactsthatvaryaccordingdence).Impactsofsuchclimate-relatedextremesincludealterationoftopeople’sage,locationandsocio-economicfactors(highconfidence).ecosystems,disruptionoffoodproductionandwatersupply,damage{WGIISPMA-1,11.4.1,Table23-1,26.6.1.2}toinfrastructureandsettlements,humanmorbidityandmortalityandconsequencesformentalhealthandhumanwell-being.ForcountriesTherearelikelymorelandregionswherethenumberofheavyatalllevelsofdevelopment,theseimpactsareconsistentwithasig-precipitationeventshasincreasedthanwhereithasdecreased.nificantlackofpreparednessforcurrentclimatevariabilityinsomeThefrequencyandintensityofheavyprecipitationeventshaslikelysectors.{WGIISPMA-1,3.2,4.2-3,8.1,9.3,10.7,11.3,11.7,13.2,14.1,increasedinNorthAmericaandEurope.Inothercontinents,confidence18.6,22.2.3,22.3,23.3.1.2,24.4.1,25.6-8,26.6-7,30.5,Table18-3,intrendsisatmostmedium.Itisverylikelythatglobalnear-surfaceTable23-1,Figure26-2,Box4-3,Box4-4,Box25-5,Box25-6,andtroposphericairspecifichumidityhasincreasedsincethe1970s.Box25-8,BoxCC-CR}Inlandregionswhereobservationalcoverageissufficientforassess-ment,thereismediumconfidencethatanthropogenicforcinghascon-Directandinsuredlossesfromweather-relateddisastershavetributedtoaglobal-scaleintensificationofheavyprecipitationoverincreasedsubstantiallyinrecentdecades,bothgloballyandthesecondhalfofthe20thcentury.{WGISPMB-1,2.5.1,2.5.4–2.5.5,regionally.Increasingexposureofpeopleandeconomicassetshas2.6.2,10.6,TableSPM.1,FAQ2.2,SREXTable3-1,3.2}beenthemajorcauseoflong-termincreasesineconomiclossesfromweather-andclimate-relateddisasters(highconfidence).{WGII10.7.3,ThereislowconfidencethatanthropogenicclimatechangehasSREXSPMB,4.5.3.3}affectedthefrequencyandmagnitudeoffluvialfloodsonaglobalscale.Thestrengthoftheevidenceislimitedmainlybyalackoflong-termrecordsfromunmanagedcatchments.Moreover,floodsarestronglyinfluencedbymanyhumanactivitiesimpactingcatchments,makingtheattributionofdetectedchangestoclimatechangedifficult.However,recentdetectionofincreasingtrendsinextremeprecipitationanddischargesinsomecatchmentsimpliesgreaterrisksoffloodingonaregionalscale(mediumconfidence).Costsrelatedtoflooddamage,worldwide,havebeenincreasingsincethe1970s,althoughthisispartlyduetotheincreasingexposureofpeopleandassets.{WGI2.6.2,WGII3.2.7,SREXSPMB}53Topic1ObservedChangesandtheirCauses1.5Exposureandvulnerability1.6Humanresponsestoclimatechange:adaptationandmitigationThecharacterandseverityofimpactsfromclimatechangeandextremeeventsemergefromriskthatAdaptationandmitigationexperienceisaccumulatingdependsnotonlyonclimate-relatedhazardsbutalsoacrossregionsandscales,evenwhileglobalonexposure(peopleandassetsatrisk)andvulner-anthropogenicgreenhousegasemissionshaveability(susceptibilitytoharm)ofhumanandnaturalcontinuedtoincrease.systems.Throughouthistory,peopleandsocietieshaveadjustedtoandcopedExposureandvulnerabilityareinfluencedbyawiderangeofwithclimate,climatevariabilityandextremes,withvaryingdegreessocial,economicandculturalfactorsandprocessesthathaveofsuccess.Intoday’schangingclimate,accumulatingexperiencewithbeenincompletelyconsideredtodateandthatmakequanti-adaptationandmitigationeffortscanprovideopportunitiesforlearn-1tdaetnivcee).aTshseessesmfaecntotsrsoinfctluhdeeirwfueatultrheatnrdenitdssdidsitfrfibicuutilotn(haicgrohsscosnocfii--ingandrefinement(3,4).{WGIISPMA-2}ety,demographics,migration,accesstotechnologyandinformation,Adaptationisbecomingembeddedinsomeplanningpro-employmentpatterns,thequalityofadaptiveresponses,societalcesses,withmorelimitedimplementationofresponses(highvalues,governancestructuresandinstitutionstoresolveconflict.{WGIIconfidence).EngineeredandtechnologicaloptionsarecommonlySPMA-3,SREXSPMB}implementedadaptiveresponses,oftenintegratedwithinexistingpro-grammes,suchasdisasterriskmanagementandwatermanagement.Differencesinvulnerabilityandexposurearisefromnon-climaticThereisincreasingrecognitionofthevalueofsocial,institutionalandfactorsandfrommultidimensionalinequalitiesoftenproducedecosystem-basedmeasuresandoftheextentofconstraintstoadap-byunevendevelopmentprocesses(veryhighconfidence).Thesetation.{WGIISPMA-2,4.4,5.5,6.4,8.3,9.4,11.7,14.1,14.3–14.4,differencesshapedifferentialrisksfromclimatechange.People15.2–15.5,17.2–17.3,21.3,21.5,22.4,23.7,25.4,26.8–26.9,30.6,whoaresocially,economically,culturally,politically,institutionallyorBox25-1,Box25-2,Box25-9,BoxCC-EA}otherwisemarginalizedareespeciallyvulnerabletoclimatechangeandalsotosomeadaptationandmitigationresponses(mediumGovernmentsatvariouslevelshavebeguntodevelopadapta-evidence,highagreement).Thisheightenedvulnerabilityisrarelytionplansandpoliciesandintegrateclimatechangeconsider-duetoasinglecause.Rather,itistheproductofintersectingsocialationsintobroaderdevelopmentplans.Examplesofadaptationprocessesthatresultininequalitiesinsocio-economicstatusandarenowavailablefromallregionsoftheworld(seeTopic4fordetailsincome,aswellasinexposure.Suchsocialprocessesinclude,foronadaptationoptionsandpoliciestosupporttheirimplementation).example,discriminationonthebasisofgender,class,ethnicity,age{WGIISPMA-2,22.4,23.7,24.4–24.6,24.9,25.4,25.10,26.7–26.9,and(dis)ability.{WGIISPMA-1,FigureSPM.1,8.1–8.2,9.3–9.4,10.9,27.3,28.2,28.4,29.3,29.6,30.6,Table25-2,Table29-3,Figure29-1,11.1,11.3–11.5,12.2–12.5,13.1–13.3,14.1–14.3,18.4,19.6,23.5,Box5-1,Box23-3,Box25-1,Box25-2,Box25-9,BoxCC-TC}25.8,26.6,26.8,28.4,BoxCC-GC}GlobalincreasesinanthropogenicemissionsandclimateClimate-relatedhazardsexacerbateotherstressors,oftenwithimpactshaveoccurred,evenwhilemitigationactivitieshavenegativeoutcomesforlivelihoods,especiallyforpeoplelivingtakenplaceinmanypartsoftheworld.Thoughvariousmitiga-inpoverty(highconfidence).Climate-relatedhazardsaffectpoortioninitiativesbetweenthesub-nationalandglobalscaleshavebeenpeople’slivesdirectlythroughimpactsonlivelihoods,reductionsindevelopedorimplemented,afullassessmentoftheirimpactmaybecropyieldsorthedestructionofhomes,andindirectlythrough,forpremature.{WGIIISPM.3,SPM.5}example,increasedfoodpricesandfoodinsecurity.Observedpositiveeffectsforpoorandmarginalizedpeople,whicharelimitedandoftenindirect,includeexamplessuchasdiversificationofsocialnetworksandofagriculturalpractices.{WGIISPMA-1,8.2–8.3,9.3,11.3,13.1–13.3,22.3,24.4,26.8}Violentconflictincreasesvulnerabilitytoclimatechange(mediumevidence,highagreement).Large-scaleviolentconflictharmsassetsthatfacilitateadaptation,includinginfrastructure,insti-tutions,naturalresources,socialcapitalandlivelihoodopportunities.{WGIISPMA-1,12.5,19.2,19.6}54Introduction2FutureClimateChanges,RisksandImpacts55Topic2FutureClimateChanges,RiskandImpactsTopic2:FutureClimateChanges,RiskandImpactsContinuedemissionofgreenhousegaseswillcausefurtherwarmingandlong-lastingchangesinallcomponentsoftheclimatesystem,increasingthelikelihoodofsevere,pervasiveandirreversibleimpactsforpeopleandecosystems.Limit-ingclimatechangewouldrequiresubstantialandsustainedreductionsingreenhousegasemissionswhich,togetherwithadaptation,canlimitclimatechangerisks.Topic2assessesprojectionsoffutureclimatechangeandtheresultingrisksandimpacts.Factorsthatdeterminefutureclimatechange,includingscenariosforfuturegreenhousegas(GHG)emissions,areoutlinedinSection2.1.Descriptionsofthemethodsandtoolsusedtomakeprojectionsofclimate,impactsandrisks,andtheirdevelopmentsincetheIPCCFourthAssessmentReport(AR4),areprovidedinBoxes2.1to2.3.Detailsofprojectedchangesintheclimatesystem,includingtheassociateduncertaintyandthedegreeofexpertconfidenceintheprojectionsareprovidedinSection2.2.ThefutureimpactsofclimatechangeonnaturalandhumansystemsandassociatedrisksareassessedinSection2.3.Topic2concludeswithanassessmentofirreversiblechanges,abruptchangesandchangesbeyond2100inSection2.4.2.1Keydriversoffutureclimateandtheaspects,includingthetemperatureoftheatmosphereandtheoceans,basisonwhichprojectionsaremadeprecipitation,winds,clouds,oceancurrentsandsea-iceextent.Themodelsareextensivelytestedagainsthistoricalobservations(Box2.1).CumulativeemissionsofCO2largelydetermineglobal{WGI1.5.2,9.1.2,9.2,9.8.1}meansurfacewarmingbythelate21stcenturyandInordertoobtainclimatechangeprojections,theclimatemodelsuse2beyond.ProjectionsofgreenhousegasemissionsvaryinformationdescribedinscenariosofGHGandairpollutantemis-overawiderange,dependingonbothsocio-economicsionsandlandusepatterns.Scenariosaregeneratedbyarangeofdevelopmentandclimatepolicy.approaches,fromsimpleidealisedexperimentstoIntegratedAssess-mentModels(IAMs,seeGlossary).KeyfactorsdrivingchangesinanthropogenicGHGemissionsareeconomicandpopulationgrowth,Climatemodelsaremathematicalrepresentationsofprocessesimpor-lifestyleandbehaviouralchanges,associatedchangesinenergyusetantintheEarth’sclimatesystem.Resultsfromahierarchyofclimateandlanduse,technologyandclimatepolicy,whicharefundamentallymodelsareconsideredinthisreport;rangingfromsimpleidealizeduncertain.{WGI11.3,12.4,WGIII5,6,6.1}models,tomodelsofintermediatecomplexity,tocomprehensiveGen-eralCirculationModels(GCMs),includingEarthSystemModels(ESMs)ThestandardsetofscenariosusedintheAR5iscalledRepresentativethatalsosimulatethecarboncycle.TheGCMssimulatemanyclimateConcentrationPathways(RCPs,Box2.2).{WGIBoxSPM.1}Box2.1Advances,ConfidenceandUncertaintyinModellingtheEarth’sClimateSystemImprovementsinclimatemodelssincetheIPCCFourthAssessmentReport(AR4)areevidentinsimulationsofcontinental-scalesurfacetemperature,large-scaleprecipitation,themonsoon,Arcticseaice,oceanheatcontent,someextremeevents,thecarboncycle,atmosphericchemistryandaerosols,theeffectsofstratosphericozoneandtheElNiño-SouthernOscillation.Climatemodelsreproducetheobservedcontinental-scalesurfacetemperaturepatternsandmulti-decadaltrends,includ-ingthemorerapidwarmingsincethemid-20thcenturyandthecoolingimmediatelyfollowinglargevolcaniceruptions(veryhighconfidence).Thesimulationoflarge-scalepatternsofprecipitationhasimprovedsomewhatsincetheAR4,althoughmodelscontinuetoperformlesswellforprecipitationthanforsurfacetemperature.Confidenceintherepresentationofprocessesinvolvingcloudsandaerosolsremainslow.{WGISPMD.1,7.2.3,7.3.3,7.6.2,9.4,9.5,9.8,10.3.1}Theabilitytosimulateoceanthermalexpansion,glaciersandicesheets,andthussealevel,hasimprovedsincetheAR4,butsignificantchallengesremaininrepresentingthedynamicsoftheGreenlandandAntarcticicesheets.This,togetherwithadvancesinscientificunderstandingandcapability,hasresultedinimprovedsealevelprojectionsinthisreport,comparedwiththeAR4.{WGISPME.6,9.1.3,9.2,9.4.2,9.6,9.8,13.1,13.4,13.5}ThereisoverallconsistencybetweentheprojectionsfromclimatemodelsinAR4andAR5forlarge-scalepatternsofchangeandthemagnitudeoftheuncertaintyhasnotchangedsignificantly,butnewexperimentsandstudieshaveledtoamorecompleteandrigorouscharacterizationoftheuncertaintyinlong-termprojections.{WGI12.4}56FutureClimateChanges,RiskandImpactsTopic2Box2.2TheRepresentativeConcentrationPathwaysIntroductionTheRepresentativeConcentrationPathways(RCPs)describefourdifferent21stcenturypathwaysofgreenhousegas(GHG)emissionsandatmosphericconcentrations,airpollutantemissionsandlanduse.TheRCPshavebeendevelopedusingIntegratedAssessmentModels(IAMs)asinputtoawiderangeofclimatemodelsimulationstoprojecttheirconsequencesforthecli-matesystem.Theseclimateprojections,inturn,areusedforimpactsandadaptationassessment.TheRCPsareconsistentwiththewiderangeofscenariosinthemitigationliteratureassessedbyWGIII2820.Thescenariosareusedtoassessthecostsassociatedwithemissionreductionsconsistentwithparticularconcentrationpathways.TheRCPsrepresenttherangeofGHGemissionsinthewiderliteraturewell(Box2.2,Figure1);theyincludeastringentmitigationscenario(RCP2.6),twointermediatescenarios(RCP4.5andRCP6.0),andonescenariowithveryhighGHGemissions(RCP8.5).Scenarioswithoutadditionaleffortstoconstrainemissions(‘baselinescenarios’)leadtopathwaysrangingbetweenRCP6.0andRCP8.5.RCP2.6isrepresentativeofascenariothataimstokeepglobalwarminglikelybelow2°Cabovepre-industrialtemperatures.ThemajorityofmodelsindicatethatscenariosmeetingforcinglevelssimilartoRCP2.6arecharacterizedbysubstantialnetnegativeemissions2921by2100,onaveragearound2GtCO2/yr.ThelandusescenariosofRCPs,together,showawiderangeofpossiblefutures,rangingfromanetreforestationtofurtherdeforestation,consistentwithprojectionsinthefullscenarioliterature.Forairpollutantssuchassulfurdioxide(SO2),theRCPscenariosassumeaconsistentdecreaseinemissionsasaconsequenceofassumedairpollutioncontrolandGHGmitigationpolicy(Box2.2,Figure1).Importantly,thesefuturescenariosdonotaccountforpossiblechangesinnaturalforcings(e.g.,volcaniceruptions)(seeBox1.1).{WGIBoxSPM.1,6.4,8.5.3,12.3,AnnexII,WGII19,21,WGIII6.3.2,6.3.6}TheRCPscoverawiderrangethanthescenariosfromtheSpecialReportonEmissionsScenarios(SRES)usedinpreviousassessments,astheyalsorepresentscenarioswithclimatepolicy.Intermsofoverallforcing,RCP8.5isbroadlycomparabletotheSRESA2/A1FIscenario,RCP6.0toB2andRCP4.5toB1.ForRCP2.6,thereisnoequivalentscenarioinSRES.Asaresult,thediffer-2encesinthemagnitudeofAR4andAR5climateprojectionsarelargelyduetotheinclusionofthewiderrangeofemissionsassessed.{WGITSBoxTS.6,12.4.9}(a)CO2emissions(b)CH4emissions2001000HistoricalWGIIIscenarioscategorizedby2100emissionsCO2-eqconcentration(ppm),5to95%100800RCPscenarios>1000(GtCO2/yr)0(TgCH4/yr)600RCP8.5720−1000RCP6.0580−720−100400RCP4.5530−5801950RCP2.6480−530430−480(c)200FullrangeoftheWGIIIAR530scenariodatabasein210020102000205021000019502000205021001950YearYear(e)CO2-eqconcentration(ppm)N2Oemissions(d)SO2emissions25050075010001500(TgN2O/yr)(TgSO2/yr)100RCP8.5OtherAnthropogenicRCP6.0RCP4.5CO2CH4N2ORCP2.6HalocarbonsTotal50WGIIIscenarios5to95%20002050210002100R−ad2iative0forcing2in21004relativ6eto17850(W/1m02)195020002050YearYearBox2.2,Figure1EmissionscenariosandtheresultingradiativeforcinglevelsfortheRepresentativeConcentrationPathways(RCPs,lines)andtheassociatedscenarioscategoriesusedinWGIII(colouredareas,seeTable3.1).Panelsatodshowtheemissionsofcarbondioxide(CO2),methane(CH4),nitrousoxide(N2O)andsulfurdioxide(SO2).PaneleshowsfutureradiativeforcinglevelsfortheRCPscalculatedusingthesimplecarboncycleclimatemodel,ModelfortheAssessmentofGreenhouseGasInducedClimateChange(MAGICC),fortheRCPs(perforcingagent)andfortheWGIIIscenariocategories(total){WGI8.2.2,8.5.3,Figure8.2,AnnexII,WGIIITableSPM.1,Table6.3}.TheWGIIIscenariocategoriessummarizethewiderangeofemissionscenariospublishedinthescientificliteratureandaredefinedbasedontotalCO2-equivalentconcentrations(inppm)in2100(Table3.1).Theverticallinestotherightofthepanels(panela–d)indicatethefullrangeoftheWGIIIAR5scenariodatabase.28Roughly300baselinescenariosand900mitigationscenariosarecategorizedbyCO2-equivalentconcentration(CO2-eq)by2100.TheCO2-eqincludestheforcingduetoallGHGs(includinghalogenatedgasesandtroposphericozone),aerosolsandalbedochange(seeGlossary).29NetnegativeemissionscanbeachievedwhenmoreGHGsaresequesteredthanarereleasedintotheatmosphere(e.g.,byusingbio-energyincombinationwithcarbondioxidecaptureandstorage).57Topic2FutureClimateChanges,RiskandImpactsThemethodsusedtoestimatefutureimpactsandrisksresultingfromandconsequence,itisimportanttoconsiderthefullrangeofpossibleclimatechangearedescribedinBox2.3.Modelledfutureimpactsoutcomes,includinglow-probability,high-consequenceimpactsthatassessedinthisreportaregenerallybasedonclimate-modelprojec-aredifficulttosimulate.{WGII2.1–2.4,3.6,4.3,11.3,12.6,19.2,19.6,tionsusingtheRCPs,andinsomecases,theolderSpecialReporton21.3–21.5,22.4,25.3–25.4,25.11,26.2}EmissionsScenarios(SRES).{WGIBoxSPM.1,WGII1.1,1.3,2.2–2.3,19.6,20.2,21.3,21.5,26.2,BoxCC-RC}2.2ProjectedchangesintheclimatesystemRiskofclimate-relatedimpactsresultsfromtheinteractionbetweenclimate-relatedhazards(includinghazardouseventsSurfacetemperatureisprojectedtoriseovertheandtrends)andthevulnerabilityandexposureofhumanand21stcenturyunderallassessedemissionscenarios.Itnaturalsystems.Alternativedevelopmentpathsinfluenceriskbyisverylikelythatheatwaveswilloccurmoreoftenchangingthelikelihoodofclimaticeventsandtrends,throughtheirandlastlonger,andthatextremeprecipitationeventseffectsonGHGs,pollutantsandlanduse,andbyalteringvulnerabilitywillbecomemoreintenseandfrequentinmanyandexposure.{WGIISPM,19.2.4,Figure19-1,Box19-2}regions.Theoceanwillcontinuetowarmandacidify,Experiments,observationsandmodelsusedtoestimatefutureandglobalmeansealeveltorise.impactsandriskshaveimprovedsincetheAR4,withincreas-ingunderstandingacrosssectorsandregions.Forexample,animprovedknowledgebasehasenabledexpandedassessmentofTheprojectedchangesinSection2.2arefor2081–2100relativetorisksforhumansecurityandlivelihoodsandfortheoceans.Forsome1986–2005,unlessotherwiseindicated.aspectsofclimatechangeandclimatechangeimpacts,uncertaintyaboutfutureoutcomeshasnarrowed.Forothers,uncertaintywillper-2.2.1Airtemperature2021sist.Someofthepersistentuncertaintiesaregroundedinthemecha-2nismsthatcontrolthemagnitudeandpaceofclimatechange.OthersTheglobalmeansurfacetemperaturechangefortheperiod2016–emergefrompotentiallycomplexinteractionsbetweenthechanging2035relativeto1986–2005issimilarforthefourRCPs,andwillclimateandtheunderlyingvulnerabilityandexposureofpeople,soci-likelybeintherange0.3°Cto0.7°C(mediumconfidence)302.Thisetiesandecosystems.Thecombinationofpersistentuncertaintyinrangeassumesnomajorvolcaniceruptionsorchangesinsomenaturalkeymechanismsplustheprospectofcomplexinteractionsmotivatessources(e.g.,methane(CH4)andnitrousoxide(N2O)),orunexpectedafocusonriskinthisreport.Becauseriskinvolvesbothprobabilitychangesintotalsolarirradiance.FutureclimatewilldependonBox2.3ModelsandMethodsforEstimatingClimateChangeRisks,VulnerabilityandImpactsFutureclimate-relatedrisks,vulnerabilitiesandimpactsareestimatedintheAR5throughexperiments,analogiesandmodels,asinpreviousassessments.‘Experiments’involvedeliberatelychangingoneormoreclimate-systemfactorsaffectingasubjectofinteresttoreflectanticipatedfutureconditions,whileholdingtheotherfactorsaffectingthesubjectconstant.‘Analogies’makeuseofexistingvariationsandareusedwhencontrolledexperimentsareimpracticalduetoethicalconstraints,thelargeareaorlongtimerequiredorhighsystemcomplexity.Twotypesofanalogiesareusedinprojectionsofclimateandimpacts.Spatialanalo-giesidentifyanotherpartoftheworldcurrentlyexperiencingsimilarconditionstothoseanticipatedtobeexperiencedinthefuture.Temporalanalogiesusechangesinthepast,sometimesinferredfrompaleo-ecologicaldata,tomakeinferencesaboutchangesinthefuture.‘Models’aretypicallynumericalsimulationsofreal-worldsystems,calibratedandvalidatedusingobservationsfromexperi-mentsoranalogies,andthenrunusinginputdatarepresentingfutureclimate.Modelscanalsoincludelargelydescriptivenarrativesofpossiblefutures,suchasthoseusedinscenarioconstruction.Quantitativeanddescriptivemodelsareoftenusedtogether.Impactsaremodelled,amongotherthings,forwaterresources,biodiversityandecosystemservicesonland,inlandwaters,theoceansandicebodies,aswellasforurbaninfrastructure,agriculturalproductivity,health,economicgrowthandpoverty.{WGII2.2.1,2.4.2,3.4.1,4.2.2,5.4.1,6.5,7.3.1,11.3.6,13.2.2}RisksareevaluatedbasedontheinteractionofprojectedchangesintheEarthsystemwiththemanydimensionsofvul-nerabilityinsocietiesandecosystems.Thedataareseldomsufficienttoallowdirectestimationofprobabilitiesofagivenoutcome;therefore,expertjudgmentusingspecificcriteria(largemagnitude,highprobabilityorirreversibilityofimpacts;timingofimpacts;persistentvulnerabilityorexposurecontributingtorisks;orlimitedpotentialtoreducerisksthroughadaptationormitigation)isusedtointegratethediverseinformationsourcesrelatingtotheseverityofconsequencesandthelikelihoodofoccurrenceintoariskevalu-ation,consideringexposureandvulnerabilityinthecontextofspecifichazards.{WGII11.3,19.2,21.1,21.3–21.5,25.3–25.4,25.11,26.2}30The1986–2005periodwasapproximately0.61[0.55to0.67]°Cwarmerthantheperiod1850–1900.{WGISPME,2.4.3}58FutureClimateChanges,RiskandImpactsTopic2(a)GlobalaveragesurfacetemperaturechangeIntroduction(relativeto1986–2005)12129(°C)63394203212190019502000205021002150220022502300Year(b)GlobalaveragesurfacetemperaturechangeMeanover(c)NorthernHemisphereMeanover(relativeto1986–2005)2081–2100Septemberseaiceextent2081–21006102(°C)4RCP2.6839RCP4.52100RCP6.063Meanover2RCP8.542081–2100032(106km2)521002–20RCP2.62000RCP4.52050210020002050RCP6.0(d)YearYearRCP8.51GlobalmeansealevelriseMeanover(e)GlobalsurfaceoceanpH0.8(relativeto1986–2005)2081–21000.68.290.4210.2(m)RCP2.6810RCP2.621RCP4.5RCP4.502050RCP6.07.82050RCP6.02000RCP8.5YearRCP8.5Year(pH)7.621002000Figure2.1(a)Timeseriesofglobalannualchangeinmeansurfacetemperatureforthe1900–2300period(relativeto1986–2005)fromCoupledModelIntercomparisonProjectPhase5(CMIP5)concentration-drivenexperiments.Projectionsareshownforthemulti-modelmean(solidlines)andthe5to95%rangeacrossthedistributionofindividualmodels(shading).GreylinesandshadingrepresenttheCMIP5historicalsimulations.Discontinuitiesat2100areduetodifferentnumbersofmodelsperformingtheextensionrunsbeyondthe21stcenturyandhavenophysicalmeaning.(b)Sameas(a)butforthe2006–2100period(relativeto1986–2005).(c)ChangeinNorthernHemisphereSeptembersea-iceextent(5yearrunningmean).Thedashedlinerepresentsnearlyice-freeconditions(i.e.,whenSeptembersea-iceextentislessthan106km2foratleastfiveconsecutiveyears).(d)Changeinglobalmeansealevel.(e)ChangeinoceansurfacepH.Forallpanels,timeseriesofprojectionsandameasureofuncertainty(shading)areshownforscenariosRCP2.6(blue)andRCP8.5(red).ThenumberofCMIP5modelsusedtocalculatethemulti-modelmeanisindicated.Themeanandassociateduncertaintiesaveragedoverthe2081–2100periodaregivenforallRCPscenariosascolouredverticalbarsontherighthandsideofpanels(b)to(e).Forsea-iceextent(c),theprojectedmeananduncertainty(minimum–maximumrange)isonlygivenforthesubsetofmodelsthatmostcloselyreproducetheclimatologicalmeanstateandthe1979–2012trendintheArcticseaice.Forsealevel(d),basedoncurrentunderstanding(fromobservations,physicalunderstandingandmodelling),onlythecollapseofmarine-basedsectorsoftheAntarcticicesheet,ifinitiated,couldcauseglobalmeansealeveltorisesubstantiallyabovethelikelyrangeduringthe21stcentury.However,thereismediumconfidencethatthisadditionalcontributionwouldnotexceedseveraltenthsofameterofsealevelriseduringthe21stcentury.{WGIFigureSPM.7,FigureSPM.9,Figure12.5,6.4.4,12.4.1,13.4.4,13.5.1}committedwarmingcausedbypastanthropogenicemissions,aswellparticularRCPs(Table2.1),andthosegivenbelowinSection2.2,asfutureanthropogenicemissionsandnaturalclimatevariability.primarilyarisefromdifferencesinthesensitivityofclimatemodelstoBythemid-21stcentury,themagnitudeoftheprojectedclimatetheimposedforcing.{WGISPME.1,11.3.2,12.4.1}changeissubstantiallyaffectedbythechoiceofemissionsscenarios.Climatechangecontinuestodivergeamongthescenariosthrough59to2100andbeyond(Table2.1,Figure2.1).TherangesprovidedforTopic2FutureClimateChanges,RiskandImpactsTable2.1Projectedchangeinglobalmeansurfacetemperatureandglobalmeansealevelriseforthemid-andlate21stcentury,relativetothe1986–2005period.{WGITableSPM.2,12.4.1,13.5.1,Table12.2,Table13.5}GlobalMeanSurfaceScenarioMean2046–2065Mean2081–2100TemperatureChange(°C)aRCP2.61.0Likelyrangec1.0LikelyrangecRCP4.51.40.4to1.61.80.3to1.7GlobalMeanSeaLevelRise(m)bRCP6.01.30.9to2.02.21.1to2.6RCP8.52.00.8to1.83.71.4to3.11.4to2.62.6to4.8ScenarioMeanLikelyrangedMeanLikelyrangedRCP2.60.240.17to0.320.400.26to0.55RCP4.50.260.19to0.330.470.32to0.63RCP6.00.250.18to0.320.480.33to0.63RCP8.50.300.22to0.380.630.45to0.82Notes:aBasedontheCoupledModelIntercomparisonProjectPhase5(CMIP5)ensemble;changescalculatedwithrespecttothe1986–2005period.UsingHadleyCentreClimaticResearchUnitGriddedSurfaceTemperatureDataSet4(HadCRUT4)anditsuncertaintyestimate(5to95%confidenceinterval),theobservedwarmingfrom1850–1900tothereferenceperiod1986–2005is0.61[0.55to0.67]°C.Likelyrangeshavenotbeenassessedherewithrespecttoearlierreferenceperiodsbecausemethodsarenotgen-erallyavailableintheliteratureforcombiningtheuncertaintiesinmodelsandobservations.Addingprojectedandobservedchangesdoesnotaccountforpotentialeffectsofmodelbiasescomparedtoobservations,andfornaturalinternalvariabilityduringtheobservationalreferenceperiod.{WGI2.4.3,11.2.2,12.4.1,Table12.2,Table12.3}bBasedon21CMIP5models;changescalculatedwithrespecttothe1986–2005period.Basedoncurrentunderstanding(fromobservations,physicalunderstandingandmodelling),onlythecollapseofmarine-basedsectorsoftheAntarcticicesheet,ifinitiated,couldcauseglobalmeansealeveltorisesubstantiallyabovethelikelyrange2duringthe21stcentury.Thereismediumconfidencethatthisadditionalcontributionwouldnotexceedseveraltenthsofameterofsealevelriseduringthe21stcentury.cCalculatedfromprojectionsas5to95%modelranges.Theserangesarethenassessedtobelikelyrangesafteraccountingforadditionaluncertaintiesordifferentlevelsofconfidenceinmodels.Forprojectionsofglobalmeansurfacetemperaturechangein2046–2065,confidenceismedium,becausetherelativeimportanceofnaturalinternalvariability,anduncertaintyinnon-greenhousegasforcingandresponse,arelargerthanforthe2081–2100period.Thelikelyrangesfor2046–2065donottakeintoaccountthepossibleinfluenceoffactorsthatleadtotheassessedrangefornearterm(2016–2035)changeinglobalmeansurfacetemperaturethatislowerthanthe5to95%modelrange,becausetheinfluenceofthesefactorsonlongertermprojectionshasnotbeenquantifiedduetoinsufficientscientificunderstanding.{WGI11.3.1}dCalculatedfromprojectionsas5to95%modelranges.Theserangesarethenassessedtobelikelyrangesafteraccountingforadditionaluncertaintiesordifferentlevelsofconfidenceinmodels.Forprojectionsofglobalmeansealevelriseconfidenceismediumforbothtimehorizons.Relativeto1850–1900,globalsurfacetemperaturechangefortheRCP8.5scenario.Inmanymid-latitudeandsubtropicaldryregions,theendofthe21stcentury(2081–2100)isprojectedtolikelymeanprecipitationwilllikelydecrease,whileinmanymid-latitudewetexceed1.5°CforRCP4.5,RCP6.0andRCP8.5(highconfidence).regions,meanprecipitationwilllikelyincreaseundertheRCP8.5sce-Warmingislikelytoexceed2°CforRCP6.0andRCP8.5(highnario(Figure2.2).{WGISPME.2,7.6.2,12.4.5,14.3.1,14.3.5}confidence),morelikelythannottoexceed2°CforRCP4.5(mediumconfidence),butunlikelytoexceed2°CforRCP2.6Extremeprecipitationeventsovermostmid-latitudelandmassesand(mediumconfidence).{WGISPME.1,12.4.1,Table12.3}overwettropicalregionswillverylikelybecomemoreintenseandmorefrequentasglobalmeansurfacetemperatureincreases.{WGITheArcticregionwillcontinuetowarmmorerapidlythantheglobalSPME.2,7.6.2,12.4.5}mean(Figure2.2)(veryhighconfidence).Themeanwarmingoverlandwillbelargerthanovertheocean(veryhighconfidence)andGlobally,inallRCPs,itislikelythattheareaencompassedbymonsoonlargerthanglobalaveragewarming(Figure2.2).{WGISPME.1,11.3.2,systemswillincreaseandmonsoonprecipitationislikelytointensify12.4.3,14.8.2}andElNiño-SouthernOscillation(ENSO)relatedprecipitationvaria-bilityonregionalscaleswilllikelyintensify.{WGISPME.2,14.2,14.4}Itisvirtuallycertainthattherewillbemorefrequenthotandfewercoldtemperatureextremesovermostlandareasondaily2.2.3Ocean,cryosphereandsealevelandseasonaltimescales,asglobalmeansurfacetemperatureincreases.ItisverylikelythatheatwaveswilloccurwithahigherTheglobaloceanwillcontinuetowarmduringthe21stcentury.frequencyandlongerduration.OccasionalcoldwinterextremeswillThestrongestoceanwarmingisprojectedforthesurfaceintropicalcontinuetooccur.{WGISPME.1,12.4.3}andNorthernHemispheresubtropicalregions.AtgreaterdepththewarmingwillbemostpronouncedintheSouthernOcean(highconfi-2.2.2Watercycledence).{WGISPME.4,6.4.5,12.4.7}Changesinprecipitationinawarmingworldwillnotbeuniform.ItisverylikelythattheAtlanticMeridionalOverturningCir-ThehighlatitudesandtheequatorialPacificarelikelytoexperienceanculation(AMOC)willweakenoverthe21stcentury,withbestincreaseinannualmeanprecipitationbytheendofthiscenturyunderestimatesandmodelrangesforthereductionof11%(1to24%)for60FutureClimateChanges,RiskandImpactsTopic239RCP2.6RCP8.5(a)Changeinaveragesurfacetemperature(1986−2005to2081−2100)Introduction32(°C)−2−1.5−1−0.500.511.523457911(b)Changeinaverageprecipitation(1986−2005to2081−2100)32392(%)−50−40−30−20−1001020304050(c)Changeinaveragesealevel(1986−2005to2081−2100)2121(m)−0.4−0.3−0.2−0.100.10.20.30.40.50.60.70.8Figure2.2CoupledModelIntercomparisonProjectPhase5(CMIP5)multi-modelmeanprojections(i.e.,theaverageofthemodelprojectionsavailable)forthe2081–2100periodundertheRCP2.6(left)andRCP8.5(right)scenariosfor(a)changeinannualmeansurfacetemperatureand(b)changeinannualmeanprecipitation,inpercentages,and(c)changeinaveragesealevel.Changesareshownrelativetothe1986–2005period.ThenumberofCMIP5modelsusedtocalculatethemulti-modelmeanisindicatedintheupperrightcornerofeachpanel.Stippling(dots)on(a)and(b)indicatesregionswheretheprojectedchangeislargecomparedtonaturalinternalvariability(i.e.,greaterthantwostandarddeviationsofinternalvariabilityin20-yearmeans)andwhere90%ofthemodelsagreeonthesignofchange.Hatching(diagonallines)on(a)and(b)showsregionswheretheprojectedchangeislessthanonestandarddeviationofnaturalinternalvariabilityin20-yearmeans.{WGIFigureSPM.8,Figure13.20,Box12.1}61Topic2FutureClimateChanges,RiskandImpactstheRCP2.6scenario,34%(12to54%)fortheRCP8.5.Nevertheless,continuedlandcarbonuptakeunderallRCPs,butsomemodelssimulateitisveryunlikelythattheAMOCwillundergoanabrupttransitionoralandcarbonlossduetothecombinedeffectofclimatechangeandcollapseinthe21stcentury.{WGISPME.4,12.4.7.2}landusechange.{WGISPME.7,6.4.2,6.4.3}Year-roundreductionsinArcticseaiceareprojectedforallRCPBasedonEarthSystemModels,thereishighconfidencethatscenarios.Thesubsetofmodelsthatmostcloselyreproducetheobser-thefeedbackbetweenclimatechangeandthecarboncyclewillvations3123projectthatanearlyice-freeArcticOcean3224inSeptemberisamplifyglobalwarming.ClimatechangewillpartiallyoffsetincreaseslikelyforRCP8.5beforemid-century(mediumconfidence)(Figure2.1).inlandandoceancarbonsinkscausedbyrisingatmosphericCO2.AsaIntheAntarctic,adecreaseinseaiceextentandvolumeisprojectedresultmoreoftheemittedanthropogenicCO2willremainintheatmos-withlowconfidence.{WGISPME.5,12.4.6.1}phere,reinforcingthewarming.{WGISPME.7,6.4.2,6.4.3}TheareaofNorthernHemispherespringsnowcoverislikelytoEarthSystemModelsprojectaglobalincreaseinoceanacidifi-decreaseby7%forRCP2.6andby25%inRCP8.5bytheendofthecationforallRCPscenariosbytheendofthe21stcentury,with21stcenturyforthemulti-modelaverage(mediumconfidence).{WGIaslowrecoveryaftermid-centuryunderRCP2.6.ThedecreaseinSPME.5,12.4.6}surfaceoceanpHisintherangeof0.06to0.07(15to17%increaseinacidity)forRCP2.6,0.14to0.15(38to41%)forRCP4.5,0.20to0.21Itisvirtuallycertainthatnear-surfacepermafrostextentathigh(58to62%)forRCP6.0,and0.30to0.32(100to109%)forRCP8.5northernlatitudeswillbereducedasglobalmeansurfacetem-(Figure2.1).{WGISPME.7,6.4.4}peratureincreases.Theareaofpermafrostnearthesurface(upper3.5m)islikelytodecreaseby37%(RCP2.6)to81%(RCP8.5)fortheItisverylikelythatthedissolvedoxygencontentoftheoceanmulti-modelaverage(mediumconfidence).{WGISPME.5,12.4.6}willdecreasebyafewpercentduringthe21stcenturyinresponsetosurfacewarming,predominantlyinthesubsurfaceTheglobalglaciervolume,excludingglaciersontheperipheryofAnt-mid-latitudeoceans.Thereisnoconsensusonthefuturevolumeof2arctica(andexcludingtheGreenlandandAntarcticicesheets),ispro-lowoxygenwatersintheopenoceanbecauseoflargeuncertaintiesinjectedtodecreaseby15to55%forRCP2.6andby35to85%forpotentialbiogeochemicaleffectsandintheevolutionoftropicaloceanRCP8.5(mediumconfidence).{WGISPME.5,13.4.2,13.5.1}dynamics.{WGITS5.6,6.4.5,WGIITSB-2,6.1}Globalmeansealevelwillcontinuetoriseduringthe21stcen-2.2.5Climatesystemresponsestury(Table2.1,Figure2.1).TherehasbeensignificantimprovementinunderstandingandprojectionofsealevelchangesincetheAR4.ClimatesystempropertiesthatdeterminetheresponsetoexternalUnderallRCPscenarios,therateofsealevelrisewillverylikelyexceedforcinghavebeenestimatedbothfromclimatemodelsandfromanal-theobservedrateof2.0[1.7–2.3]mm/yrduring1971–2010,withtheysisofpastandrecentclimatechange.Theequilibriumclimatesensi-rateofriseforRCP8.5during2081–2100of8to16mm/yr(mediumtivity(ECS)3325islikelyintherange1.5°Cto4.5°C,extremelyunlikelyconfidence).{WGISPMB4,SPME.6,13.5.1}lessthan1°C,andveryunlikelygreaterthan6°C.{WGISPMD.2,TSTFE.6,10.8.1,10.8.2,12.5.4,Box12.2}Sealevelrisewillnotbeuniformacrossregions.Bytheendofthe21stcentury,itisverylikelythatsealevelwillriseinmorethanCumulativeemissionsofCO2largelydetermineglobalmeansur-about95%oftheoceanarea.Sealevelrisedependsonthepathwayfacewarmingbythelate21stcenturyandbeyond.MultiplelinesofofCO2emissions,notonlyonthecumulativetotal;reducingemissionsevidenceindicateastrongandconsistentnear-linearrelationshipacrossearlierratherthanlater,forthesamecumulativetotal,leadstoalargerallscenariosconsideredbetweennetcumulativeCO2emissions(includ-mitigationofsealevelrise.About70%ofthecoastlinesworldwideingtheimpactofCO2removal)andprojectedglobaltemperaturechangeareprojectedtoexperiencesealevelchangewithin±20%ofthetotheyear2100(Figure2.3).Pastemissionsandobservedwarmingsup-globalmean(Figure2.2).Itisverylikelythattherewillbeasignificantportthisrelationshipwithinuncertainties.AnygivenlevelofwarmingincreaseintheoccurrenceoffuturesealevelextremesinsomeregionsisassociatedwitharangeofcumulativeCO2emissions(dependingonby2100.{WGISPME.6,TS5.7.1,12.4.1,13.4.1,13.5.1,13.6.5,13.7.2,non-CO2drivers),andtherefore,forexample,higheremissionsinearlierTable13.5}decadesimplyloweremissionslater.{WGISPME.8,TSTFE.8,12.5.4}2.2.4CarboncycleandbiogeochemistryTheglobalmeanpeaksurfacetemperaturechangepertrilliontonnesofcarbon(1000GtC)emittedasCO2islikelyintherangeOceanuptakeofanthropogenicCO2willcontinueunderallfourof0.8°Cto2.5°C.Thisquantity,calledthetransientclimateresponseRCPsthroughto2100,withhigheruptakeforhigherconcen-tocumulativecarbonemissions(TCRE),issupportedbybothmodellingtrationpathways(veryhighconfidence).Thefutureevolutionofandobservationalevidenceandappliestocumulativeemissionsuptothelandcarbonuptakeislesscertain.Amajorityofmodelsprojectsaabout2000GtC.{WGISPMD.2,TSTFE.6,12.5.4,Box12.2}31Climatologicalmeanstateandthe1979–2012trendinArcticsea-iceextent.32Whensea-iceextentislessthanonemillionkm2foratleastfiveconsecutiveyears.33DefinedastheequilibriumglobalaveragesurfacewarmingfollowingadoublingofCO2concentration(relativetopre-industrial).62FutureClimateChanges,RiskandImpactsTopic2CumulativetotalanthropogenicCO2emissionsfrom1870(GtCO2)Temperaturechangerelativeto1861–1880(°C)510002000300040005000600070008000Introduction2090sRCP8.5Totalhuman-inducedwarming4baselines720–1000RCP6.02090s3RCP4.52090s580–7202530–580RCP2.6480–530CO2-inducedwarming2090s430–48012000sobserved2000s21990s1940s25001970s05001000150020001880s0CumulativetotalanthropogenicCO2emissionsfrom1870(GtC)Figure2.3Globalmeansurfacetemperatureincreaseasafunctionofcumulativetotalglobalcarbondioxide(CO2)emissionsfromvariouslinesofevidence.Multi-modelresultsfromahierarchyofclimatecarbon-cyclemodelsforeachRepresentativeConcentrationPathway(RCP)until2100areshown(colouredlines).Modelresultsoverthehistoricalperiod(1860to2010)areindicatedinblack.Thecolouredplumeillustratesthemulti-modelspreadoverthefourRCPscenariosandfadeswiththedecreasingnumberofavailablemodelsinRCP8.5.Dotsindicatedecadalaverages,withselecteddecadeslabelled.Ellipsesshowtotalanthropogenicwarmingin2100versuscumulativeCO2emissionsfrom1870to2100fromasimpleclimatemodel(medianclimateresponse)underthescenariocategoriesusedinWGIII.Temperaturevaluesarealwaysgivenrelativetothe1861–1880period,andemissionsarecumulativesince1870.Blackfilledellipseshowsobservedemissionsto2005andobservedtemperaturesinthedecade2000–2009withassociateduncertainties.{WGISPME.8,TSTFE.8,Figure1,TS.SM.10,12.5.4,Figure12.45,WGIIITableSPM.1,Table6.3}WarmingcausedbyCO2emissionsiseffectivelyirreversible2150]GtCO2wereemittedby2011,leavingabout1000GtCO2tobeovermulti-centurytimescalesunlessmeasuresaretakentoconsistentwiththistemperaturegoal.Estimatedtotalfossilcarbonreservesexceedthisremainingamountbyafactorof4to7,withremoveCO2fromtheatmosphere.EnsuringCO2-inducedwarmingresourcesmuchlargerstill.{WGISPME.8,TSTFE.8,Figure1,TS.SM.10,remainslikelylessthan2°CrequirescumulativeCO2emissionsfromall12.5.4,Figure12.45,WGIIITableSPM.1,Table6.3,Table7.2}anthropogenicsourcestoremainbelowabout3650GtCO2(1000GtC),overhalfofwhichwerealreadyemittedby2011.{WGISPME.8,TSTFE.8,12.5.2,12.5.3,12.5.4}Multi-modelresultsshowthatlimitingtotalhuman-inducedwarming(accountingforbothCO2andotherhumaninfluencesonclimate)tolessthan2°Crelativetotheperiod1861–1880withaprobabilityof>66%wouldrequiretotalCO2emissionsfromallanthropogenicsourcessince1870tobelimitedtoabout2900GtCO2whenaccountingfornon-CO2forcingasintheRCP2.6scenario,witharangeof2550to3150GtCO2arisingfromvariationsinnon-CO2climatedriversacrossthescenariosconsideredbyWGIII(Table2.2).About1900[1650to63Topic2FutureClimateChanges,RiskandImpactsTable2.2Cumulativecarbondioxide(CO2)emissionconsistentwithlimitingwarmingtolessthanstatedtemperaturelimitsatdifferentlevelsofprobability,basedondifferentlinesofevidence.{WGI12.5.4,WGIII6}CumulativeCO2emissionsfrom1870inGtCO2Netanthropogenicwarminga<1.5°C<2°C<3°CFractionofsimulations66%50%33%66%50%33%66%50%33%meetinggoalbComplexmodels,RCP225022502550290030003300420045004850scenariosonlycSimplemodel,WGIIINodata2300to2400to2550to31502900to2950ton.a.e4150to5250to6000scenariosd23502950320038005750CumulativeCO2emissionsfrom2011inGtCO2Complexmodels,RCP400550850100013001500240028003250scenariosonlycSimplemodel,WGIIINodata550to600600to1150750to14001150to1150ton.a.e2350to3500to4250scenariosd140020504000Totalfossilcarbonavailablein2011f:3670to7100GtCO2(reserves)and31300to50050GtCO2(resources)Notes:aWarmingduetoCO2andnon-CO2drivers.Temperaturevaluesaregivenrelativetothe1861–1880baseperiod.bNotethatthe66%rangeinthistableshouldnotbeequatedtothelikelihoodstatementsinTableSPM.1andTable3.1andWGIIITableSPM.1.TheassessmentintheselattertablesisnotonlybasedontheprobabilitiescalculatedforthefullensembleofscenariosinWGIIIusingasingleclimatemodel,butalsotheassessmentinWGIoftheuncertaintyofthetemperatureprojectionsnotcoveredbyclimatemodels.2cCumulativeCO2emissionsatthetimethetemperaturethresholdisexceededthatarerequiredfor66%,50%or33%oftheCoupledModelIntercomparisonProjectPhase5(CMIP5)complexmodelsEarthSystemModel(ESM)andEarthSystemModelsofIntermediateComplexity(EMIC)simulations,assumingnon-CO2forcingfollowstheRCP8.5scenario.SimilarcumulativeemissionsareimpliedbyotherRCPscenarios.Formostscenario–thresholdcombinations,emissionsandwarmingcontinueafterthethresholdisexceeded.Nevertheless,becauseofthecumulativenatureofCO2emissions,thesefiguresprovideanindicationofthecumulativeCO2emissionsimpliedbytheCMIP5modelsimulationsunderRCP-likescenarios.Valuesareroundedtothenearest50.dCumulativeCO2emissionsatthetimeofpeakwarmingfromWGIIIscenariosforwhichafractionofgreaterthan66%(66to100%),greaterthan50%(50to66%)orgreaterthan33%(33to50%)ofclimatesimulationskeepglobalmeantemperatureincreasetobelowthestatedthreshold.RangesindicatethevariationincumulativeCO2emissionsarisingfromdifferencesinnon-CO2driversacrosstheWGIIIscenarios.Thefractionofclimatesimulationsforeachscenarioisderivedfroma600-memberparameterensembleofasimplecarbon-cycleclimatemodel,ModelfortheAssessmentofGreenhouseGasInducedClimateChange(MAGICC),inaprobabilisticmode.Parameterandscenariouncertaintyareexploredinthisensemble.Structuraluncertaintiescannotbeexploredwithasinglemodelset-up.Rangesshowtheimpactofscenariouncertainty,with80%ofscenariosgivingcumulativeCO2emissionswithinthestatedrangeforthegivenfractionofsimulations.Simplemodelestimatesareconstrainedbyobservedchangesoverthepastcentury,donotaccountforuncertaintyinmodelstructureandmayomitsomefeedbackprocesses:theyarehenceslightlyhigherthantheCMIP5complexmodelsestimates.Valuesareroundedtothenearest50.eThenumericalresultsforthecumulativeCO2emissionsforstayingbelow3°Cwithgreaterthan66%(66to100%)isgreatlyinfluencedbyalargenumberofscenariosthatwouldalsomeetthe2°Cobjectiveandthereforenotcomparablewithnumbersprovidedfortheothertemperaturethreshold.fReservesarequantitiesabletoberecoveredunderexistingeconomicandoperatingconditions;resourcesarethosewhereeconomicextractionispotentiallyfeasible.{WGIIITable7.2}2.3Futurerisksandimpactscausedtheirabilitytoadapt.Risingratesandmagnitudesofwarmingandbyachangingclimateotherchangesintheclimatesystem,accompaniedbyoceanacidifica-tion,increasetheriskofsevere,pervasive,andinsomecases,irrevers-Climatechangewillamplifyexistingrisksandcreateibledetrimentalimpacts.Futureclimatechangewillamplifyexistingnewrisksfornaturalandhumansystems.Risksareclimate-relatedrisksandcreatenewrisks.{WGIISPMB,FigureSPM.1}unevenlydistributedandaregenerallygreaterfordisadvantagedpeopleandcommunitiesincountriesKeyrisksarepotentiallysevereimpactsrelevanttounderstandingdan-atalllevelsofdevelopment.Increasingmagnitudesofgerousanthropogenicinterferencewiththeclimatesystem.Risksarewarmingincreasethelikelihoodofsevere,pervasiveconsideredkeyduetohighhazardorhighvulnerabilityofsocietiesandandirreversibleimpactsforpeople,speciesandsystemsexposed,orboth.Theiridentificationisbasedonlargemagni-ecosystems.Continuedhighemissionswouldleadtotudeorhighprobabilityofimpacts;irreversibilityortimingofimpacts;mostlynegativeimpactsforbiodiversity,ecosystempersistentvulnerabilityorexposure;orlimitedpotentialtoreducerisks.servicesandeconomicdevelopmentandamplifyrisksSomerisksareparticularlyrelevantforindividualregions(Figure2.4),forlivelihoodsandforfoodandhumansecurity.whileothersareglobal(Table2.3).Forriskassessmentitisimportanttoevaluatethewidestpossiblerangeofimpacts,includinglow-probabilityRiskofclimate-relatedimpactsresultsfromtheinteractionofcli-outcomeswithlargeconsequences.Risklevelsoftenincreasewithmate-relatedhazards(includinghazardouseventsandtrends)withthetemperature(Box2.4)andaresometimesmoredirectlylinkedtoothervulnerabilityandexposureofhumanandnaturalsystems,includingdimensionsofclimatechange,suchastherateofwarming,aswell64asthemagnitudesandratesofoceanacidificationandsealevelrise(Figure2.5).{WGIISPMA-3,SPMB-1}FutureClimateChanges,RiskandImpactsTopic2RepresentativekeyrisksforeachregionforRegionalkeyrisksandPhysicalsystemsBiologicalsystemsHumanandmanagedsystemsIntroductionpotentialforriskreductionGlaciers,Rivers,lakes,CoastalerosionTerrestrialWildﬁreMarineFoodLivelihoods,healthsnow,iceﬂoodsand/orand/orsealevelecosystemsecosystemsproductionand/oreconomicsand/ordroughteffectspermafrostVeryRisklevelVeryPolarRegions(ArcticandAntarctic)RisksforhealthUnprecedentedchallenges,lowMediumhighRisksforecosystemsandwell-beingespeciallyfromrateofchangePresentNearterm(2030–2040)Longterm2°C(2080–2100)4°CNorthAmericaIncreaseddamagesfromEuropeRisklevelwithPotentialforriverandcoastalﬂoodshighadaptationadditionalRisklevelwithHeat-relatedadaptationtocurrentadaptationhumanmortalityreduceriskIncreaseddamagesIncreaseddamagesAsiafromwildﬁresfromriverandcoastalurbanﬂoodsIncreasedwaterrestrictionsIncreaseddamagesIncreasedﬂooddamagetoIncreaseddrought-fromextremeheatrelatedwaterandeventsandwildﬁresfoodshortageinfrastructure,livelihoodsHeat-relatedandsettlementshumanmortalityTheOceanCentralandSouthAmericaAfricaDistributionalReducedwateravailabilityandshiftandreducedincreasedﬂoodingandlandslidesCompoundedstressﬁsheriescatchonwaterresourcespotentialatlowlatitudesReducedfoodproductionandqualitySmallislandsAustralasiaIncreasedmasscoralSpreadofvector-bornediseasesbleachingandmortalitynotassessedLossoflivelihoods,Signiﬁcantchangeincompositionnotassessedsettlements,infrastructure,andstructureofcoralreefsystemsCoastalinundationecosystemservicesandandhabitatlosseconomicstability2ReducedcropproductivityandlivelihoodandfoodsecurityVector-andwater-Risksforlow-lyingIncreasedﬂooddamageIncreasedriskstobornediseasescoastalareastoinfrastructureandcoastalinfrastructuresettlementsandlow-lyingecosystemsFigure2.4Representativekeyrisksforeachregion,includingthepotentialforriskreductionthroughadaptationandmitigation,aswellaslimitstoadaptation.Identificationofkeyriskswasbasedonexpertjudgmentusingthefollowingspecificcriteria:largemagnitude,highprobabilityorirreversibilityofimpacts;timingofimpacts;persistentvulnerabilityorexposurecontributingtorisks;orlimitedpotentialtoreducerisksthroughadaptationormitigation.Risklevelsareassessedasverylow,low,medium,highorveryhighforthreetimeframes:thepresent,nearterm(here,for2030–2040)andlongterm(here,for2080–2100).Inthenearterm,projectedlevelsofglobalmeantemperatureincreasedonotdivergesubstantiallyacrossdifferentemissionscenarios.Forthelongterm,risklevelsarepresentedfortwopossiblefutures(2°Cand4°Cglobalmeantemperatureincreaseabovepre-industriallevels).Foreachtimeframe,risklevelsareindicatedforacontinuationofcurrentadaptationandassuminghighlevelsofcurrentorfutureadaptation.Risklevelsarenotnecessarilycomparable,especiallyacrossregions.{WGIISPMAssessmentBoxSPM.2Table1}KeyrisksthatspansectorsandregionsincludethefollowingTheoverallrisksoffutureclimatechangeimpactscanbe(highconfidence){WGIISPMB-1}:reducedbylimitingtherateandmagnitudeofclimatechange,includingoceanacidification.Somerisksareconsiderableevenat1.Riskofsevereill-healthanddisruptedlivelihoodsresultingfrom1°Cglobalmeantemperatureincreaseabovepre-industriallevels.stormsurges,sealevelriseandcoastalflooding;inlandfloodinginManyglobalrisksarehightoveryhighforglobaltemperatureincreasessomeurbanregions;andperiodsofextremeheat.of4°Cormore(seeBox2.4).Theserisksincludesevereandwide-spreadimpactsonuniqueandthreatenedsystems,theextinctionof2.Systemicrisksduetoextremeweathereventsleadingtobreak-manyspecies,largeriskstofoodsecurityandcompromisednormaldownofinfrastructurenetworksandcriticalservices.humanactivities,includinggrowingfoodorworkingoutdoorsinsomeareasforpartsoftheyear,duetothecombinationofhightemperature3.Riskoffoodandwaterinsecurityandlossofrurallivelihoodsandandhumidity(highconfidence).Thepreciselevelsofclimatechangeincome,particularlyforpoorerpopulations.sufficienttotriggerabruptandirreversiblechangeremainuncertain,buttheriskassociatedwithcrossingsuchthresholdsintheearth4.Riskoflossofecosystems,biodiversityandecosystemgoods,func-systemorininterlinkedhumanandnaturalsystemsincreaseswithtionsandservices.risingtemperature(mediumconfidence).{WGIISPMB-1}6566Topic22(a)RiskforterrestrialandfreshwaterspeciesIncreasingriskfromRCP2.6toRCP8.5(c)Riskforcoastalhumanandnaturalsystemsimpactedimpactedbytherateofwarming(b)Riskformarinespeciesimpactedbyoceanacidificationbysealevelrise?only,oradditionallybywarmingextremes0.08Mostcarnivorous3andsplit-hoofedmammalscan’tkeepup0.06Rateofclimatechange(°C/yr)900GlobalaverageFlatlandscapesRCP8.5pH7.80,+3.7ºCRCP8.52.5HighCO2(2050–2090)AtmosphericCO2(ppm)Oceanacidificationonly2ScenariogroupsOceanacidificationandwarming700VulnerabletaxaSealevelrise(m,relativeto1986–2005)?increasinglypH7.91,+2.2ºCRCP6.0Sealevelriseaffected,warm-MediumCO20.04waterreefs1.5CoastalprotectionandRCP6.0ecosystemadaptation?(2050–2090)marginalizedreachlimitsatmanyRCP4.5LowCO2Mostrodents(2050–2090)pH7.97,+1.8ºCRCP4.51locationsRCPsRCP2.68.5andprimates(2050–2090)50020to50%ofcorals,Adaptationtoreduce6.04.52.60.02can’tkeepupechinodermsandriskneededatmanymolluscsaffectedpH8.05,+1.0ºCRCP2.60.5locationsSomepH8.11,0ºCRecent(1986–2005)CoastalrisksincreasedforaminiferaMosttreesandandpteropodsnearlyglobally2081–21002300herbscan’tkeepup0300affectedPre-industrialThefewavailableprojections0.00for2300likelyunderestimatepH8.17,–0.6ºC(1850–1900)AntarcticicesheetcontributionProjectedpH,temperatureforLevelofadditionalriskduetoclimatechange2081–2100ObservedpH,temperatureUndetectableModerateHighVeryhigh(temperatureinºCrelativeto1986–2005)Figure2.5Therisksof:(a)disruptionofthecommunitycompositionofterrestrialandfreshwaterecosystemsduetotherateofwarming;(b)marineorganismsimpactedbyoceanacidification(OA)orwarmingextremescombinedwithFutureClimateChanges,RiskandImpactsOA;and(c)coastalhumanandnaturalsystemsimpactedbysealevelrise.TherisklevelcriteriaareconsistentwiththoseusedinBox2.4andtheircalibrationisillustratedbytheannotationstoeachpanel.(a)Athighratesofwarming,majorgroupsofterrestrialandfreshwaterspeciesareunabletomovefastenoughtostaywithinthespatiallyshiftingclimateenvelopestowhichtheyareadapted.Themedianobservedormodelledspeedsatwhichspeciespopulationsmove(km/decade)arecomparedagainstthespeedatwhichclimateenvelopesmoveacrossthelandscape,giventheprojectedclimatechangeratesforeachRepresentativeConcentrationPathway(RCP)overthe2050–2090period.Theresultsarepresentedfortheaverageofalllandscapes,globally,aswellasforflatlandscapes,wheretheclimateenvelopemovesespeciallyfast.(b)Sensitivitytooceanacidificationishighinmarineorganismsbuildingacalciumcarbonateshell.TherisksfromOAincreasewithwarmingbecauseOAlowersthetoleratedlevelsofheatexposure,asseenincoralsandcrustaceans.(c)Theheightofa50-yearfloodeventhasalreadyincreasedinmanycoastallocations.A10-tomorethan100-foldincreaseinthefrequencyoffloodsinmanyplaceswouldresultfroma0.5mriseinsealevelintheabsenceofadaptation.Localadaptationcapacity(and,inparticular,protection)reachesitslimitsforecosystemsandhumansystemsinmanyplacesundera1msealevelrise.(2.2.4,Table2.1,Figure2.8){WGI3.7.5,3.8,6.4.4,Figure13.25,WGIIFigureSPM.5,Figure4-5,Figure6-10,BoxCC-OA,4.4.2.5,5.2,5.3–5.5,5.4.4,5.5.6,6.3}FutureClimateChanges,RiskandImpactsTopic2Adaptationcansubstantiallyreducetherisksofclimatechangeaddstothethreatsofover-fishingandothernon-climaticstressorsimpacts,butgreaterratesandmagnitudeofclimatechange(highconfidence).{WGIISPMB-2,6.3–6.5,7.4,25.6,28.3,29.3,Introductionincreasethelikelihoodofexceedingadaptationlimits(high30.6–30.7,BoxCC-MB,BoxCC-PP}confidence).Thepotentialforadaptation,aswellasconstraintsandlimitstoadaptation,variesamongsectors,regions,communitiesandMarineecosystems,especiallycoralreefsandpolarecosystems,ecosystems.Thescopeforadaptationchangesovertimeandiscloselyareatriskfromoceanacidification(mediumtohighconfidence).linkedtosocio-economicdevelopmentpathwaysandcircumstances.Oceanacidificationhasimpactsonthephysiology,behaviourandpop-SeeFigure2.4andTable2.3,alongwithTopics3and4.{WGIISPMB,ulationdynamicsoforganisms.TheimpactsonindividualspeciesandSPMC,TSB,TSC}thenumberofspeciesaffectedinspeciesgroupsincreasefromRCP4.5toRCP8.5.Highlycalcifiedmolluscs,echinodermsandreef-buildingcoralsaremoresensitivethancrustaceans(highconfidence)and2.3.1Ecosystemsandtheirservicesintheoceans,fishes(lowconfidence)(Figure2.6b).Oceanacidificationactstogetheralongcoasts,onlandandinfreshwaterwithotherglobalchanges(e.g.,warming,progressivelyloweroxygenlevels)andwithlocalchanges(e.g.,pollution,eutrophication)(highRisksofharmfulimpactsonecosystemsandhumansystemsconfidence),leadingtointeractive,complexandamplifiedimpactsforincreasewiththeratesandmagnitudesofwarming,oceanspeciesandecosystems(Figure2.5b).{WGIISPMB-2,FigureSPM.6B,acidification,sealevelriseandotherdimensionsofclimate5.4,6.3.2,6.3.5,22.3,25.6,28.3,30.5,Figure6-10,BoxCC-CR,change(highconfidence).FutureriskisindicatedtobehighbytheBoxCC-OA,BoxTS.7}observationthatnaturalglobalclimatechangeatrateslowerthancurrentanthropogenicclimatechangecausedsignificantecosystemCarbonstoredintheterrestrialbiosphereissusceptibletolossshiftsandspeciesextinctionsduringthepastmillionsofyearsonlandtotheatmosphereasaresultofclimatechange,deforestationandintheoceans(highconfidence).Manyplantandanimalspeciesandecosystemdegradation(highconfidence).Theaspectsofcli-willbeunabletoadaptlocallyormovefastenoughduringthematechangewithdirecteffectsonstoredterrestrialcarboninclude21stcenturytotracksuitableclimatesundermid-andhighrangerateshightemperatures,droughtandwindstorms;indirecteffectsinclude2ofclimatechange(RCP4.5,RCP6.0andRCP8.5)(mediumconfidence)increasedriskoffires,pestanddiseaseoutbreaks.Increasedtree(Figure2.5a).Coralreefsandpolarecosystemsarehighlyvulnerable.mortalityandassociatedforestdiebackisprojectedtooccurinmany{WGIISPMA-1,SPMB-2,4.3–4,5.4,6.1,6.3,6.5,25.6,26.4,29.4,regionsoverthe21stcentury(mediumconfidence),posingrisksforBoxCC-CR,BoxCC-MB,BoxCC-RF}carbonstorage,biodiversity,woodproduction,waterquality,amen-ityandeconomicactivity.ThereisahighriskofsubstantialcarbonAlargefractionofterrestrial,freshwaterandmarinespeciesandmethaneemissionsasaresultofpermafrostthawing.{WGIISPM,facesincreasedextinctionriskduetoclimatechangeduringand4.2–4.3,Figure4-8,Box4-2,Box4-3,Box4-4}beyondthe21stcentury,especiallyasclimatechangeinteractswithotherstressors(highconfidence).ExtinctionriskisincreasedCoastalsystemsandlow-lyingareaswillincreasinglyexperiencerelativetopre-industrialandpresentperiods,underallRCPscenarios,submergence,floodinganderosionthroughoutthe21stcenturyasaresultofboththemagnitudeandrateofclimatechange(highandbeyond,duetosealevelrise(veryhighconfidence).Theconfidence).Extinctionswillbedrivenbyseveralclimate-associatedpopulationandassetsprojectedtobeexposedtocoastalrisksaswelldrivers(warming,sea-iceloss,variationsinprecipitation,reducedriverashumanpressuresoncoastalecosystemswillincreasesignificantlyinflows,oceanacidificationandloweredoceanoxygenlevels)andthethecomingdecadesduetopopulationgrowth,economicdevelopmentinteractionsamongthesedriversandtheirinteractionwithsimul-andurbanization(highconfidence).Climaticandnon-climaticdriverstaneoushabitatmodification,over-exploitationofstocks,pollution,affectingcoralreefswillerodehabitats,increasecoastlineexposureeutrophicationandinvasivespecies(highconfidence).{WGIISPMB-2,towavesandstormsanddegradeenvironmentalfeaturesimportant4.3–4.4,6.1,6.3,6.5,25.6,26.4,BoxCC-RF,BoxCC-MB}tofisheriesandtourism(highconfidence).Somelow-lyingdevelop-ingcountriesandsmallislandstatesareexpectedtofaceveryhighGlobalmarinespeciesredistributionandmarinebiodiversityimpactsthatcouldhaveassociateddamageandadaptationcostsreductioninsensitiveregions,underclimatechange,willchal-ofseveralpercentagepointsofgrossdomesticproduct(GDP)lengethesustainedprovisionoffisheriesproductivityand(Figure2.5c).{WGII5.3–5.5,22.3,24.4,25.6,26.3,26.8,29.4,otherecosystemservices,especiallyatlowlatitudes(highcon-Table26-1,Box25-1,BoxCC-CR}fidence).Bythemid-21stcentury,under2°Cglobalwarmingrela-tivetopre-industrialtemperatures,shiftsinthegeographicalrangeofmarinespecieswillcausespeciesrichnessandfisheriescatch2.3.2Water,foodandurbansystems,humanpotentialtoincrease,onaverage,atmidandhighlatitudes(highcon-health,securityandlivelihoodsfidence)andtodecreaseattropicallatitudesandinsemi-enclosedseas(Figure2.6a)(mediumconfidence).TheprogressiveexpansionofThefractionsoftheglobalpopulationthatwillexperienceOxygenMinimumZonesandanoxic‘deadzones’intheoceanswillwaterscarcityandbeaffectedbymajorriverfloodsarepro-furtherconstrainfishhabitats(mediumconfidence).Open-oceannetjectedtoincreasewiththelevelofwarminginthe21stcenturyprimaryproductionisprojectedtoredistributeandtodecreaseglobally,(robustevidence,highagreement).{WGII3.4–3.5,26.3,29.4,by2100,underallRCPscenarios(mediumconfidence).ClimatechangeTable3-2,Box25-8}67Topic2FutureClimateChanges,RiskandImpacts(a)Changeinmaximumcatchpotential(2051–2060comparedto2001–2010,SRESA1B)<–50%–21to–50%–6to–20%–1to–5%nodata0to4%5to19%20to49%50to100%>100%(b)ChangeinpH(2081–2100comparedto1986–2005,RCP8.5)2–0.60–0.55–0.50–0.45–0.40–0.35–0.30–0.25–0.20–0.15–0.10–0.05MolluscandcrustaceanﬁsheriesCold-waterWarm-watercoralscorals(present-dayannualcatchrate≥0.005tonnes/km2)MolluscsCrustaceansCold-watercoralsWarm-watercorals100401615312910037491823100747531002691523208080Species(%)60808060Positiveeffect4040Noeffect20606020Negativeeffect00ntrol–650–850137029004040ntrol–650–85013702900Co500651851–1371–Co500651851–371–2020100trol650850370900ntrol–650–85013702900on500–651–51–171–2CCo5006518511–371–813pCO2(μatm)Figure2.6Climatechangerisksforfisheries.(a)Projectedglobalredistributionofmaximumcatchpotentialof~1000speciesofexploitedfishesandinvertebrates,comparingthe10-yearaveragesover2001–2010and2051–2060,usingoceanconditionsbasedonasingleclimatemodelunderamoderatetohighwarmingscenario(2°Cwarmingrelativetopre-industrialtemperatures),withoutanalysisofpotentialimpactsofoverfishingoroceanacidification.(b)Marinemolluscandcrustaceanfisheries(present-dayestimatedannualcatchrates≥0.005tonnes/km2)andknownlocationsofcold-andwarm-watercorals,depictedonaglobalmapshowingtheprojecteddistributionofsurfaceoceanacidificationby2100underRCP8.5.Thebottompanelcomparesthepercentageofspeciessensitivetooceanacidificationforcorals,molluscsandcrustaceans,vulnerableanimalphylawithsocio-economicrelevance(e.g.,forcoastalprotectionandfisheries).ThenumberofspeciesanalysedacrossstudiesisgivenontopofthebarsforeachcategoryofelevatedCO2.For2100,RCPscenariosfallingwithineachpCO2categoryareasfollows:RCP4.5for500to650μatm,RCP6.0for651to850μatmandRCP8.5for851to1370μatm.By2150,RCP8.5fallswithinthe1371to2900μatmcategory.Thecontrolcategorycorrespondsto380μatm(Theunitμatmisapproximatelyequivalenttoppmintheatmosphere).{WGIFigureSPM.8,BoxSPM.1,WGIISPMB-2,FigureSPM.6,6.1,6.3,30.5,Figure6-10,Figure6-14}68FutureClimateChanges,RiskandImpactsTopic2Climatechangeoverthe21stcenturyisprojectedtoreduceclimatechangeisexpectedtoleadtoincreasesinill-healthinrenewablesurfacewaterandgroundwaterresourcesinmostmanyregionsandespeciallyindevelopingcountrieswithlowPercentageofyieldprojectionsdrysubtropicalregions(robustevidence,highagreement),income,ascomparedtoabaselinewithoutclimatechangeIntroductionintensifyingcompetitionforwateramongsectors(limitedevi-(highconfidence).Healthimpactsincludegreaterlikelihoodofinjurydence,mediumagreement).Inpresentlydryregions,thefrequencyanddeathduetomoreintenseheatwavesandfires,increasedrisksofdroughtswilllikelyincreasebytheendofthe21stcenturyunderfromfoodborneandwaterbornediseasesandlossofworkcapacityRCP8.5(mediumconfidence).Incontrast,waterresourcesarepro-andreducedlabourproductivityinvulnerablepopulations(highconfi-jectedtoincreaseathighlatitudes(robustevidence,highagreement).dence).Risksofundernutritioninpoorregionswillincrease(highcon-Theinteractionofincreasedtemperature;increasedsediment,nutrientfidence).Risksfromvector-bornediseasesareprojectedtogenerallyandpollutantloadingsfromheavyrainfall;increasedconcentrationsincreasewithwarming,duetotheextensionoftheinfectionareaandofpollutantsduringdroughts;anddisruptionoftreatmentfacilitiesseason,despitereductionsinsomeareasthatbecometoohotfordis-duringfloodswillreducerawwaterqualityandposeriskstodrinkingeasevectors(mediumconfidence).Globally,themagnitudeandsever-waterquality(mediumevidence,highagreement).{WGI12.4,WGII3.2,ityofnegativeimpactswillincreasinglyoutweighpositiveimpacts3.4–3.6,22.3,23.9,25.5,26.3,Table3-2,Table23-3,Box25-2,BoxCC-RF,(highconfidence).By2100forRCP8.5,thecombinationofhightem-BoxCC-WE}peratureandhumidityinsomeareasforpartsoftheyearisexpectedtocompromisecommonhumanactivities,includinggrowingfoodandAllaspectsoffoodsecurityarepotentiallyaffectedbyclimateworkingoutdoors(highconfidence).{WGIISPMB-2,8.2,11.3–11.8,change,includingfoodproduction,access,useandpricesta-19.3,22.3,25.8,26.6,Figure25-5,BoxCC-HS}bility(highconfidence).Forwheat,riceandmaizeintropicalandtemperateregions,climatechangewithoutadaptationisprojectedtoInurbanareas,climatechangeisprojectedtoincreaserisksfornegativelyimpactproductionatlocaltemperatureincreasesof2°Corpeople,assets,economiesandecosystems,includingrisksfrommoreabovelate20thcenturylevels,althoughindividuallocationsmayheatstress,stormsandextremeprecipitation,inlandandcoastalbenefit(mediumconfidence).Projectedimpactsvaryacrosscropsandflooding,landslides,airpollution,drought,waterscarcity,searegionsandadaptationscenarios,withabout10%ofprojectionsforlevelriseandstormsurges(veryhighconfidence).Theserisks2the2030–2049periodshowingyieldgainsofmorethan10%,andwillbeamplifiedforthoselackingessentialinfrastructureandservicesabout10%ofprojectionsshowingyieldlossesofmorethan25%,com-orlivinginexposedareas.{WGII3.5,8.2–8.4,22.3,24.4–24.5,26.8,paredwiththelate20thcentury.Globaltemperatureincreasesof~4°CTable8-2,Box25-9,BoxCC-HS}ormoreabovelate20thcenturylevels,combinedwithincreasingfooddemand,wouldposelargeriskstofoodsecurity,bothgloballyandRuralareasareexpectedtoexperiencemajorimpactsonregionally(highconfidence)(Figure2.4,2.7).Therelationshipbetweenwateravailabilityandsupply,foodsecurity,infrastructureglobalandregionalwarmingisexplainedin2.2.1.{WGII6.3–6.5,andagriculturalincomes,includingshiftsintheproduction7.4–7.5,9.3,22.3,24.4,25.7,26.5,Table7-2,Table7-3,Figure7-1,areasoffoodandnon-foodcropsaroundtheworld(highFigure7-4,Figure7-5,Figure7-6,Figure7-7,Figure7-8,Box7-1}confidence).Theseimpactswilldisproportionatelyaffectthewel-fareofthepoorinruralareas,suchasfemale-headedhouseholdsUntilmid-century,projectedclimatechangewillimpacthumanandthosewithlimitedaccesstoland,modernagriculturalinputs,healthmainlybyexacerbatinghealthproblemsthatalreadyinfrastructureandeducation.{WGII5.4,9.3,25.9,26.8,28.2,28.4,exist(veryhighconfidence).Throughoutthe21stcentury,Box25-5}100Rangeofyieldchange80increase50to100%inyield25to50%6010to25%405to10%200to5%0decrease0to–5%2010–20292030–20492050–20692070–20892090–2109inyield–5to–10%–10to–25%–25to–50%–50to–100%Figure2.7Summaryofprojectedchangesincropyields(mostlywheat,maize,riceandsoy)duetoclimatechangeoverthe21stcentury.Thefigurecombines1090datapointsfromcropmodelprojections,coveringdifferentemissionscenarios,tropicalandtemperateregionsandadaptationandno-adaptationcases.Theprojectionsaresortedintothe20-yearperiods(horizontalaxis)duringwhichtheirmidpointoccurs.Changesincropyieldsarerelativetolate20thcenturylevelsanddataforeachtimeperiodsumto100%.Relativelyfewstudieshaveconsideredimpactsoncroppingsystemsforscenarioswhereglobalmeantemperaturesincreaseby4°Cormore.{WGIIFigureSPM.7}69Topic2FutureClimateChanges,RiskandImpactsTable2.3Examplesofglobalkeyrisksfordifferentsectors,includingthepotentialforriskreductionthroughadaptationandmitigation,aswellaslimitstoadaptation.Eachkeyriskisassessedasverylow,low,medium,highorveryhigh.Risklevelsarepresentedforthreetimeframes:present,nearterm(here,for2030–2040)andlongterm(here,for2080–2100).Inthenearterm,projectedlevelsofglobalmeantemperatureincreasedonotdivergesubstantiallyacrossdifferentemissionscenarios.Forthelongterm,risklevelsarepresentedfortwopossiblefutures(2°Cand4°Cglobalmeantemperatureincreaseabovepre-industriallevels).Foreachtimeframe,risklevelsareindicatedforacontinuationofcurrentadaptationandassuminghighlevelsofcurrentorfutureadaptation.Risklevelsarenotnecessarilycomparable,especiallyacrossregions.Relevantclimatevariablesareindicatedbyicons.{WGIITableTS.4}Climate-relateddriversofimpactsLevelofrisk&potentialforadaptationPotentialforadditionaladaptationtoreduceriskWarmingExtremeDryingExtremeDamagingFloodingStormOCOOCORisklevelwithRisklevelwithtrendtemperaturetrendprecipitationcyclonesurgehighadaptationcurrentadaptationOceanCarbondioxideacidiﬁcationfertilisationGlobalRisksKeyriskAdaptationissues&prospectsClimaticTimeframeRisk&potentialfordriversPresentadaptationNeartermReductioninterrestrialcarbonsink:Carbonstoredinterrestrial•Adaptationoptionsincludemanaginglanduse(2030–2040)VeryMediumVerylowhighecosystemsisvulnerabletolossbackintotheatmosphere,resultingfrom(includingdeforestation),ﬁreandotherdisturbances,increasedﬁrefrequencyduetoclimatechangeandthesensitivityofandnon-climaticstressors.ecosystemrespirationtorisingtemperatures(mediumconﬁdence){WGII4.2,4.3}Longterm2°C(2080–2100)4°CBorealtippingpoint:Arcticecosystemsarevulnerabletoabrupt•TherearefewadaptationoptionsintheArctic.VeryMediumVerychangerelatedtothethawingofpermafrost,spreadofshrubsinlowhightundraandincreaseinpestsandﬁresinborealforests(mediumconﬁdence)PresentNearterm2(2030–2040){WGII4.3,Box4-4}Longterm2°C(2080–2100)4°CAmazontippingpoint:MoistAmazonforestscouldchangeabruptly•PolicyandmarketmeasurescanreducedeforestationVeryMediumVerytoless-carbon-dense,drought-andﬁre-adaptedecosystemsandﬁre.lowhigh(lowconﬁdence)Present{WGII4.3,Box4-3}Nearterm(2030–2040)Longterm2°C(2080–2100)4°CIncreasedriskofspeciesextinction:Alargefractionofthespecies•AdaptationoptionsincludereductionofhabitatVeryMediumVeryassessedisvulnerabletoextinctionduetoclimatechange,ofteninmodiﬁcationandfragmentation,pollution,lowhighinteractionwithotherthreats.Specieswithanintrinsicallylowover-exploitationandinvasivespecies;protectedareadispersalrate,especiallywhenoccupyingﬂatlandscapeswheretheexpansion;assisteddispersal;andexsituconservation.Presentprojectedclimatevelocityishigh,andspeciesinisolatedhabitatssuchNeartermasmountaintops,islandsorsmallprotectedareasareespeciallyatrisk.(2030–2040)Cascadingeffectsthroughorganisminteractions,especiallythosevulnerabletophenologicalchanges,amplifyrisk(highconﬁdence)Longterm2°C(2080–2100){WGII4.3,4.4}4°CGlobalredistributionanddecreaseoflow-latitudeﬁsheriesyields,•IncreasingcoastalpovertyatlowlatitudesasﬁsheriesVeryMediumVeryparalleledbyaglobaltrendtocatcheshavingsmallerﬁshesbecomesmaller–partiallycompensatedbythegrowthlowhigh(mediumconﬁdence)ofaquacultureandmarinespatialplanning,aswellas{WGII6.3to6.5,30.5,30.6}enhancedindustrializedﬁshingeffortsPresentNearterm(2030–2040)Longterm2°C(2080–2100)4°CReducedgrowthandsurvivalofcommerciallyvaluableshellﬁshand•EvidencefordifferentialresistanceandevolutionaryVeryMediumVeryothercalciﬁers(e.g.,reefbuildingcorals,calcareousredalgae)duetoadaptationofsomespeciesexists,buttheyarelikelytobelowhighoceanacidiﬁcation(highconﬁdence)limitedathigherCO2concentrationsandtemperatures.•AdaptationoptionsincludeexploitingmoreresilientPresent{WGII5.3,6.1,6.3,6.4,30.3,BoxCC-OA}speciesorprotectinghabitatswithlownaturalCO2levels,aswellasreducingotherstresses,mainlypollution,andNeartermlimitingpressuresfromtourismandﬁshing.(2030–2040)OCOLongterm2°C(2080–2100)4°CMarinebiodiversitylosswithhighrateofclimatechange•Adaptationoptionsarelimitedtoreducingotherstresses,VeryMediumVery(mediumconﬁdence)mainlypollution,andlimitingpressuresfromcoastalhumanlowhighactivitiessuchastourismandﬁshing.{WGII6.3,6.4,Table30-4,BoxCC-MB}PresentOCONearterm(2030–2040)Longterm2°C(2080–2100)4°C70FutureClimateChanges,RiskandImpactsTopic2Table2.3(continued)GlobalRisksClimaticTimeframeRisk&potentialforIntroductiondriversadaptationKeyriskAdaptationissues&prospectsPresentNegativeimpactsonaveragecropyieldsandOCONeartermVeryMediumVeryincreasesinyieldvariabilityduetoclimate•Projectedimpactsvaryacrosscropsandregionsandadaptationscenarios,(2030–2040)lowhighchange(highconﬁdence)withabout10%ofprojectionsfortheperiod2030–2049showingyieldgains{WGII7.2to7.5,Figure7-5,Box7-1}ofmorethan10%,andabout10%ofprojectionsshowingyieldlossesofmorethan25%,comparedtothelate20thcentury.After2050theriskofmoresevereyieldimpactsincreasesanddependsonthelevelofwarming.Longterm2°C(2080–2100)4°CUrbanrisksassociatedwithwatersupply•AdaptationoptionsincludechangestonetworkinfrastructureaswellasVeryMediumVerysystems(highconﬁdence)demand-sidemanagementtoensuresufﬁcientwatersuppliesandquality,lowhighincreasedcapacitiestomanagereducedfreshwateravailability,andﬂoodrisk{WGII8.2,8.3}reduction.PresentNearterm(2030–2040)Longterm2°C(2080–2100)4°CUrbanrisksassociatedwithenergysystems•Mosturbancentersareenergyintensive,withenergy-relatedclimatepoliciesVeryMediumVery(highconﬁdence)focusedonlyonmitigationmeasures.Afewcitieshaveadaptationinitiativeslowhighunderwayforcriticalenergysystems.Thereispotentialfornon-adapted,{WGII8.2,8.4}centralisedenergysystemstomagnifyimpacts,leadingtonationalandPresenttransboundaryconsequencesfromlocalisedextremeevents.Nearterm(2030–2040)Longterm2°C(2080–2100)4°CUrbanrisksassociatedwith•Poorquality,inappropriatelylocatedhousingisoftenmostvulnerabletoVeryMedium2Veryhousing(highconﬁdence)extremeevents.Adaptationoptionsincludeenforcementofbuildingregulationslowandupgrading.SomecitystudiesshowthepotentialtoadapthousingandPresenthigh{WGII8.3}promotemitigation,adaptationanddevelopmentgoalssimultaneously.RapidlyNeartermgrowingcities,orthoserebuildingafteradisaster,especiallyhaveopportunities(2030–2040)toincreaseresilience,butthisisrarelyrealised.Withoutadaptation,risksofeconomiclossesfromextremeeventsaresubstantialincitieswithhigh-valueLongterm2°Cinfrastructureandhousingassets,withbroadereconomiceffectspossible.(2080–2100)4°CDisplacementassociatedwithextremeevents•Adaptationtoextremeeventsiswellunderstood,butpoorlyimplementedVeryMediumVery(highconﬁdence)evenunderpresentclimateconditions.Displacementandinvoluntarymigrationlowhighareoftentemporary.Withincreasingclimaterisks,displacementismorelikely{WGII12.4}toinvolvepermanentmigration.PresentNearterm(2030–2040)Longterm2°C(2080–2100)4°CViolentconﬂictarisingfromdeteriorationinAdaptationoptions:VeryMediumVeryresource-dependentlivelihoodssuchas•Bufferingruralincomesagainstclimateshocks,forexamplethroughlowhighagricultureandpastoralism(highconﬁdence)livelihooddiversiﬁcation,incometransfersandsocialsafetynetprovision•EarlywarningmechanismstopromoteeffectiveriskreductionPresent{WGII12.5}•Well-establishedstrategiesformanagingviolentconﬂictthatareeffectiveNeartermbutrequiresigniﬁcantresources,investmentandpoliticalwill(2030–2040)Longterm2°C(2080–2100)4°CDecliningworkproductivity,increasing•AdaptationoptionsarelimitedforpeoplewhoaredependentonagricultureVeryMediumVerymorbidity(e.g.,dehydration,heatstrokeandandcannotaffordagriculturalmachinery.lowhighheatexhaustion),andmortalityfrom•Adaptationoptionsarelimitedintheconstructionsectorwheremanypoorexposuretoheatwaves.Particularlyatriskpeopleworkunderinsecurearrangements.Presentareagriculturalandconstructionworkersas•Adaptationlimitsmaybeexceededincertainareasina+4oCworld.Neartermwellaschildren,homelesspeople,the(2030–2040)elderly,andwomenwhohavetowalklong•Adaptationthroughreducingwateruseisnotanoptionforthemanypeoplehourstocollectwater(highconﬁdence)alreadylackingadequateaccesstosafewater.AccesstowaterissubjecttoLongterm2°C{WGII13.2,Box13-1}variousformsofdiscrimination,forinstanceduetogenderandlocation.Poor(2080–2100)andmarginalisedwaterusersareunabletocompetewithwaterextractionbyReducedaccesstowaterforruralandurbanindustries,large-scaleagricultureandotherpowerfulusers.4°CpoorpeopleduetowaterscarcityandincreasingcompetitionforwaterVeryMediumVery(highconﬁdence)lowhigh{WGII13.2,Box13-1}PresentNearterm(2030–2040)Longterm2°C(2080–2100)4°C71Topic2FutureClimateChanges,RiskandImpactsBox2.4ReasonsForConcernRegardingClimateChangeFiveReasonsForConcern(RFCs)haveprovidedaframeworkforsummarizingkeyriskssincetheIPCCThirdAssessmentReport.Theyillustratetheimplicationsofwarmingandofadaptationlimitsforpeople,economiesandecosystemsacrosssectorsandregions.Theyprovideonestartingpointforevaluatingdangerousanthropogenicinterferencewiththeclimatesystem.AllwarminglevelsinthetextofBox2.4arerelativetothe1986–2005period.Adding~0.6°Ctothesewarminglevelsroughlygiveswarmingrelativetothe1850–1900period,usedhereasaproxyforpre-industrialtimes(right-handscaleinBox2.4,Figure1).{WGIIAssessmentBoxSPM.1}ThefiveRFCsareassociatedwith:1.Uniqueandthreatenedsystems:Someecosystemsandculturesarealreadyatriskfromclimatechange(highconfidence).Withadditionalwarmingofaround1°C,thenumberofuniqueandthreatenedsystemsatriskofsevereconsequencesincreases.Manysystemswithlimitedadaptivecapacity,particularlythoseassociatedwithArcticseaiceandcoralreefs,aresubjecttoveryhighriskswithadditionalwarmingof2°C.Inadditiontorisksresultingfromthemagnitudeofwarming,terrestrialspeciesarealsosensitivetotherateofwarming,marinespeciestotherateanddegreeofoceanacidificationandcoastalsystemstosealevelrise(Figure2.5).2.Extremeweatherevents:Climatechangerelatedrisksfromextremeevents,suchasheatwaves,heavyprecipitationandcoastalflooding,arealreadymoderate(highconfidence).With1°Cadditionalwarming,risksarehigh(mediumconfidence).Risksassociatedwithsometypesofextremeevents(e.g.,extremeheat)increaseprogressivelywithfurtherwarming(highconfidence).23.Distributionofimpacts:Risksareunevenlydistributedbetweengroupsofpeopleandbetweenregions;risksaregenerallygreaterfordisadvantagedpeopleandcommunitieseverywhere.Risksarealreadymoderatebecauseofregionaldifferencesinobservedclimatechangeimpacts,particularlyforcropproduction(mediumtohighconfidence).Basedonprojecteddecreasesinregionalcropyieldsandwateravailability,risksofunevenlydistributedimpactsarehighunderadditionalwarmingofabove2°C(mediumconfidence).4.Globalaggregateimpacts:Risksofglobalaggregateimpactsaremoderateunderadditionalwarmingofbetween1°Cand2°C,reflectingimpactsonboththeEarth’sbiodiversityandtheoverallglobaleconomy(mediumconfidence).Extensivebiodiversityloss,withassociatedlossofecosystemgoodsandservices,leadstohighrisksataround3°Cadditionalwarming(highconfidence).Aggregateeconomicdamagesacceleratewithincreasingtemperature(limitedevidence,highagreement),butfewquantitativeestimatesareavailableforadditionalwarmingofabove3°C.5.Large-scalesingularevents:Withincreasingwarming,somephysicalandecologicalsystemsareatriskofabruptand/orirre-versiblechanges(seeSection2.4).Risksassociatedwithsuchtippingpointsaremoderatebetween0and1°Cadditionalwarming,sincetherearesignsthatbothwarm-watercoralreefsandArcticecosystemsarealreadyexperiencingirreversibleregimeshifts(mediumconfidence).Risksincreaseatasteepeningrateunderanadditionalwarmingof1to2°Candbecomehighabove3°C,duetothepotentialforlargeandirreversiblesealevelrisefromicesheetloss.Forsustainedwarmingabovesomethresholdgreaterthan~0.5°Cadditionalwarming(lowconfidence)butlessthan~3.5°C(mediumconfidence),near-completelossoftheGreenlandicesheetwouldoccuroveramillenniumormore,eventuallycontributingupto7mtoglobalmeansealevelrise.(continuedonnextpage)72FutureClimateChanges,RiskandImpactsTopic2Box2.4(continued)Globalmeantemperaturechange(°Crelativeto1986–2005)5(°Crelativeto1850–1900,asanapproximationofpre-industriallevels)Introduction5443322112003–20120-0.610Unique&ExtremeDistributionGlobalLarge-scale°Cthreatenedweatherofimpactsaggregatesingular°CsystemseventsimpactseventsLevelofadditionalriskduetoclimatechangeUndetectableModerateHighVeryhighBox2.4,Figure1RisksassociatedwithReasonsForConcernataglobalscaleareshownforincreasinglevelsofclimatechange.Thecolourshadingindicatestheadditionalriskduetoclimatechangewhenatemperaturelevelisreachedandthensustainedorexceeded.Whiteindicatesnoassociatedimpactsaredetectableandattributabletoclimatechange.Yellowindicatesthatassociatedimpactsarebothdetectableandattributabletoclimatechangewithatleastmediumconfidence.Red2indicatessevereandwidespreadimpacts.Purple,introducedinthisassessment,showsthatveryhighriskisindicatedbyallkeyriskcriteria.{WGIIAssessmentBoxSPM.1,Figure19-4}Aggregateeconomiclossesacceleratewithincreasingtempera-droughts.Expandingopportunitiesformobilitycanreducevulnerabilityture(limitedevidence,highagreement),butglobaleconomicforsuchpopulations.Changesinmigrationpatternscanberesponsesimpactsfromclimatechangearecurrentlydifficulttoestimate.tobothextremeweathereventsandlongertermclimatevariabilityandWithrecognizedlimitations,theexistingincompleteestimatesofglobalchange,andmigrationcanalsobeaneffectiveadaptationstrategy.annualeconomiclossesforwarmingof~2.5°Cabovepre-industrial{WGII9.3,12.4,19.4,22.3,25.9}levelsare0.2to2.0%ofincome(mediumevidence,mediumagree-ment).Changesinpopulation,agestructure,income,technology,rela-Climatechangecanindirectlyincreaserisksofviolentconflicttiveprices,lifestyle,regulationandgovernanceareprojectedtohavebyamplifyingwell-documenteddriversoftheseconflicts,suchrelativelylargerimpactsthanclimatechange,formosteconomicsec-aspovertyandeconomicshocks(mediumconfidence).Multipletors(mediumevidence,highagreement).Moresevereand/orfrequentlinesofevidencerelateclimatevariabilitytosomeformsofconflict.weatherhazardsareprojectedtoincreasedisaster-relatedlossesand{WGIISPM,12.5,13.2,19.4}lossvariability,posingchallengesforaffordableinsurance,particularlyindevelopingcountries.Internationaldimensionssuchastradeand2.4Climatechangebeyond2100,relationsamongstatesarealsoimportantforunderstandingtherisksirreversibilityandabruptchangesofclimatechangeatregionalscales.(Box3.1){WGII3.5,10.2,10.7,10.9–10.10,17.4–17.5,25.7,26.7–26.9,Box25-7}Manyaspectsofclimatechangeanditsassociatedimpactswillcontinueforcenturies,evenifanthropo-Fromapovertyperspective,climatechangeimpactsarepro-genicemissionsofgreenhousegasesarestopped.Thejectedtoslowdowneconomicgrowth,makepovertyreductionrisksofabruptorirreversiblechangesincreaseasthemoredifficult,furthererodefoodsecurityandprolongexist-magnitudeofthewarmingincreases.ingpovertytrapsandcreatenewones,thelatterparticularlyinurbanareasandemerginghotspotsofhunger(mediumconfi-Warmingwillcontinuebeyond2100underallRCPscenariosdence).ClimatechangeimpactsareexpectedtoexacerbatepovertyinexceptRCP2.6.Surfacetemperatureswillremainapproximatelycon-mostdevelopingcountriesandcreatenewpovertypocketsincountriesstantatelevatedlevelsformanycenturiesafteracompletecessationwithincreasinginequality,inbothdevelopedanddevelopingcountriesofnetanthropogenicCO2emissions(seeSection2.2.5fortherelation-(Figure2.4).{WGII8.1,8.3–8.4,9.3,10.9,13.2–13.4,22.3,26.8}shipbetweenCO2emissionsandglobaltemperaturechange.).AlargefractionofanthropogenicclimatechangeresultingfromCO2emissionsClimatechangeisprojectedtoincreasedisplacementofpeopleisirreversibleonamulti-centurytomillennialtimescale,exceptinthe(mediumevidence,highagreement).Displacementriskincreaseswhenpopulationsthatlacktheresourcesforplannedmigrationexpe-73riencehigherexposuretoextremeweatherevents,suchasfloodsandTopic2FutureClimateChanges,RiskandImpacts(a)AtmosphericCO2confidence),andtheimpactwillbeexacerbatedbyrisingtemperatureextremes(Figure2.5b).{WGI3.8.2,6.4.4,WGII(ppm)2000RCP8.5SPMB-2,6.3.2,6.3.5,30.5,BoxCC-OA}RCP6.01500RCP4.5GlobalmeansealevelrisewillcontinueformanycenturiesRCP2.6beyond2100(virtuallycertain).Thefewavailableanalysesthatgo1000beyond2100indicatesealevelrisetobelessthan1mabovethe21002200230024002500pre-industriallevelby2300forGHGconcentrationsthatpeakand500declineandremainbelow500ppmCO2-eq,asinscenarioRCP2.6.ForYeararadiativeforcingthatcorrespondstoaCO2-eqconcentrationin21002000thatisabove700ppmbutbelow1500ppm,asinscenarioRCP8.5,theSurfacetemperaturechangeprojectedriseis1mtomorethan3mby2300(mediumconfidence)(b)(relativeto1986–2005)(Figure2.8c).Thereislowconfidenceintheavailablemodels’abilitytoprojectsolidicedischargefromtheAntarcticicesheet.Hence,10(°C)thesemodelslikelyunderestimatetheAntarcticaicesheetcontribu-8tion,resultinginanunderestimationofprojectedsealevelrisebeyond62100.{WGISPME.8,13.4.4,13.5.4}420Thereislittleevidenceinglobalclimatemodelsofatippingpointor2500criticalthresholdinthetransitionfromaperenniallyice-coveredtoa20002100220023002400seasonallyice-freeArcticOcean,beyondwhichfurthersea-icelossisYearunstoppableandirreversible.{WGI12.5.5}(c)GlobalmeansealevelriseThereislowconfidenceinassessingtheevolutionoftheAtlanticMeridionalOverturningCirculationbeyondthe21stcenturybecause(relativeto1986–2005)ofthelimitednumberofanalysesandequivocalresults.However,acollapsebeyondthe21stcenturyforlargesustainedwarmingcannot27beexcluded.{WGISPME.4,12.4.7,12.5.5}65HighCO22MediumCO(m)4LowCO2321Sustainedmasslossbyicesheetswouldcauselargersealevelrise,andpartofthemasslossmightbeirreversible.Thereis0highconfidencethatsustainedglobalmeanwarminggreaterthanathresholdwouldleadtothenear-completelossoftheGreenlandice200021002200230024002500sheetoveramillenniumormore,causingasealevelriseofupto7m.CurrentestimatesindicatethatthethresholdisgreaterthanaboutYear1°C(lowconfidence)butlessthanabout4°C(mediumconfidence)ofglobalwarmingwithrespecttopre-industrialtemperatures.AbruptFigure2.8(a)Atmosphericcarbondioxide(CO2)and(b)projectedglobalmeanandirreversibleicelossfromapotentialinstabilityofmarine-basedsurfacetemperaturechangeassimulatedbyEarthSystemModelsofIntermediateCom-sectorsoftheAntarcticicesheetinresponsetoclimateforcingispos-plexity(EMICs)forthefourRepresentativeConcentrationPathways(RCPs)upto2300sible,butcurrentevidenceandunderstandingisinsufficienttomake(relativeto1986–2005)followedbyaconstant(year2300level)radiativeforcing.Aaquantitativeassessment.{WGISPME.8,5.6.2,5.8.1,13.4.3,13.5.4}10-yearsmoothingwasapplied.Thedashedlineon(a)indicatesthepre-industrialCO2concentration.(c)SealevelchangeprojectionsgroupedintothreecategoriesaccordingWithinthe21stcentury,magnitudesandratesofclimatechangetotheconcentrationofgreenhousegas(inCO2-eq)in2100(low:concentrationsthatassociatedwithmediumtohighemissionscenarios(RCP4.5,peakanddeclineandremainbelow500ppm,asinscenarioRCP2.6;medium:500toRCP6.0andRCP8.5)poseahighriskofabruptandirreversible700ppm,includingRCP4.5;high:concentrationsthatareabove700ppmbutbelowregional-scalechangeinthecomposition,structureandfunction1500ppm,asinscenarioRCP6.0andRCP8.5).Thebarsin(c)showthemaximumpos-ofmarine,terrestrialandfreshwaterecosystems,includingwet-siblespreadthatcanbeobtainedwiththefewavailablemodelresults(andshouldnotlands(mediumconfidence),aswellaswarmwatercoralreefsbeinterpretedasuncertaintyranges).ThesemodelslikelyunderestimatetheAntarctica(highconfidence).Examplesthatcouldsubstantiallyamplifyclimateicesheetcontribution,resultinginanunderestimationofprojectedsealevelrisebeyondchangearetheboreal-tundraArcticsystem(mediumconfidence)and2100.{WGIFigure12.43,Figure13.13,Table13.8,WGIISPMB-2}theAmazonforest(lowconfidence).{WGII4.3.3.1,Box4.3,Box4.4,5.4.2.4,6.3.1–6.3.4,6.4.2,30.5.3–30.5.6,BoxCC-CR,BoxCC-MB}caseofalargenetremovalofCO2fromtheatmosphereoverasus-tainedperiod(Figure2.8a,b).{WGISPME.1,SPME.8,12.5.2}Areductioninpermafrostextentisvirtuallycertainwithcontin-uedriseinglobaltemperatures.Currentpermafrostareasarepro-Stabilizationofglobalaveragesurfacetemperaturedoesnotjectedtobecomeanetemitterofcarbon(CO2andCH4)withalossofimplystabilizationforallaspectsoftheclimatesystem.Shifting180to920GtCO2(50to250GtC)underRCP8.5overthe21stcenturybiomes,re-equilibratingsoilcarbon,icesheets,oceantemperatures(lowconfidence).{WGITFE.5,6.4.3.4,12.5.5,WGII4.3.3.4}andassociatedsealevelriseallhavetheirownintrinsiclongtimes-calesthatwillresultinongoingchangesforhundredstothousandsofyearsafterglobalsurfacetemperaturehasbeenstabilized.{WGISPME.8,12.5.2–12.5.4,WGII4.2}OceanacidificationwillcontinueforcenturiesifCO2emissionscontinue,itwillstronglyaffectmarineecosystems(high74IntroductionFuturePathwaysfor3Adaptation,MitigationandSustainableDevelopment75Topic3FuturePathwaysforAdaptation,MitigationandSustainableDevelopmentTopic3:FuturePathwaysforAdaption,MitigationandSustainableDevelopmentAdaptationandmitigationarecomplementarystrategiesforreducingandmanagingtherisksofclimatechange.Sub-stantialemissionsreductionsoverthenextfewdecadescanreduceclimaterisksinthe21stcenturyandbeyond,increaseprospectsforeffectiveadaptation,reducethecostsandchallengesofmitigationinthelongertermandcontributetoclimate-resilientpathwaysforsustainabledevelopment.Adaptationandmitigationaretwocomplementarystrategiesforrespondingtoclimatechange.Adaptationistheprocessofadjustmenttoactualorexpectedclimateanditseffectsinordertoeitherlessenoravoidharmorexploitbeneficialopportunities.Mitigationistheprocessofreducingemissionsorenhancingsinksofgreenhousegases(GHGs),soastolimitfutureclimatechange.Bothadaptationandmitigationcanreduceandmanagetherisksofclimatechangeimpacts.Yetadaptationandmitigationcanalsocreateotherrisks,aswellasbenefits.Strategicresponsestoclimatechangeinvolveconsiderationofclimate-relatedrisksalongwiththerisksandco-benefitsofadaptationandmitigationactions.{WGIISPMA-3,SPMC,Glossary,WGIIISPM.2,4.1,5.1,Glossary}Mitigation,adaptationandclimateimpactscanallresultintransformationstoandchangesinsystems.Dependingontherateandmagnitudeofchangeandthevulnerabilityandexposureofhumanandnaturalsystems,climatechangewillalterecosystems,foodsystems,infrastructure,coastal,urbanandruralareas,humanhealthandlivelihoods.Adaptiveresponsestoachangingclimaterequireactionsthatrangefromincre-mentalchangestomorefundamental,transformationalchanges34.20Mitigationcaninvolvefundamentalchangesinthewaythathumansocietiesproduceanduseenergyservicesandland.{WGIIB,C,TSC,BoxTS.8,Glossary,WGIIISPM.4}Topic3ofthisreportexaminesthefactorsthatinfluencetheassessmentofmitigationandadaptationstrategies.Itconsidersthebenefits,risks,incrementalchangesandpotentialtransformationsfromdifferentcombinationsofmitigation,adaptationandresidualclimate-relatedimpacts.Itconsidershowresponsesinthecomingdecadeswillinfluenceoptionsforlimitinglong-termclimatechangeandopportunitiesforadaptingtoit.Finally,itconsidersfactors—includinguncertainty,ethicalconsiderationsandlinkstoothersocietalgoals—thatmayinfluencechoicesaboutmitigationandadaptation.Topic4thenassessestheprospectsformitigationandadaptationonthebasisofcurrentknowledgeoftools,optionsandpolicies.3.1Foundationsofdecision-makingeffectslocally,nationallyandinternationally,dependingonwhoaboutclimatechangepaysandwhobenefits.Theprocessofdecision-makingaboutclimatechange,andthedegreetowhichitrespectstherightsandviewsof3Effectivedecision-makingtolimitclimatechangeanda1l3l.4th,o1s7e.3a,ff2e0c.t2e,d,2i0s.5a,lsWoGaIIIcoSnPcMer.n2,o3f.3ju,s3ti.c1e0.,{W4.G1.I2I,24.2.2,,24.3.3,,134..35,,itseffectscanbeinformedbyawiderangeofana-4.6,4.8}lyticalapproachesforevaluatingexpectedrisksandbenefits,recognizingtheimportanceofgovernance,Effectivemitigationwillnotbeachievedifindividualagentsethicaldimensions,equity,valuejudgments,economicadvancetheirowninterestsindependently.Climatechangehasassessmentsanddiverseperceptionsandresponsestothecharacteristicsofacollectiveactionproblemattheglobalscale,riskanduncertainty.becausemostGHGsaccumulateovertimeandmixglobally,andemis-sionsbyanyagent(e.g.,individual,community,company,country)Sustainabledevelopmentandequityprovideabasisforassess-affectotheragents.Cooperativeresponses,includinginternationalingclimatepolicies.Limitingtheeffectsofclimatechangeiscooperation,arethereforerequiredtoeffectivelymitigateGHGemis-necessarytoachievesustainabledevelopmentandequity,sionsandaddressotherclimatechangeissues.Theeffectivenessofincludingpovertyeradication.Countries’pastandfuturecontribu-adaptationcanbeenhancedthroughcomplementaryactionsacrosstionstotheaccumulationofGHGsintheatmospherearedifferent,andlevels,includinginternationalcooperation.Theevidencesuggestscountriesalsofacevaryingchallengesandcircumstancesandhavedif-thatoutcomesseenasequitablecanleadtomoreeffectivecooper-ferentcapacitiestoaddressmitigationandadaptation.Mitigationandation.{WGII20.3.1,WGIIISPM.2,TS.1,1.2,2.6,3.2,4.2,13.2,13.3}adaptationraiseissuesofequity,justiceandfairnessandarenecessarytoachievesustainabledevelopmentandpovertyeradication.ManyDecision-makingaboutclimatechangeinvolvesvaluationandofthosemostvulnerabletoclimatechangehavecontributedandmediationamongdiversevaluesandmaybeaidedbytheana-contributelittletoGHGemissions.Delayingmitigationshiftsburdenslyticmethodsofseveralnormativedisciplines.Ethicsanalysesfromthepresenttothefuture,andinsufficientadaptationresponsestothedifferentvaluesinvolvedandtherelationsbetweenthem.Recentemergingimpactsarealreadyerodingthebasisforsustainablepoliticalphilosophyhasinvestigatedthequestionofresponsibilityfordevelopment.Bothadaptationandmitigationcanhavedistributionaltheeffectsofemissions.Economicsanddecisionanalysisprovide34Transformationisusedinthisreporttorefertoachangeinthefundamentalattributesofasystem(seeGlossary).Transformationscanoccuratmultiplelevels;atthenationallevel,transformationisconsideredmosteffectivewhenitreflectsacountry’sownvisionsandapproachestoachievingsustainabledevelopmentinaccordancewithitsnationalcircumstancesandpriorities.{WGIISPMC-2,2–13,20.5,WGIIISPM,6–12}76FuturePathwaysforAdaptation,MitigationandSustainableDevelopmentTopic3quantitativemethodsofvaluationwhichcanbeusedforestima-Therisksofclimatechange,adaptationandmitigationdifferintingthesocialcostofcarbon(seeBox3.1),incost–benefitandcost-nature,timescale,magnitudeandpersistence(highconfidence).Introductioneffectivenessanalyses,foroptimizationinintegratedmodelsandRisksfromadaptationincludemaladaptationandnegativeancillaryelsewhere.Economicmethodscanreflectethicalprinciples,andtakeimpacts.Risksfrommitigationincludepossibleadversesideeffectsaccountofnon-marketedgoods,equity,behaviouralbiases,ancil-oflarge-scaledeploymentoflow-carbontechnologyoptionsandeco-larybenefitsandcostsandthedifferingvaluesofmoneytodifferentnomiccosts.Climatechangerisksmaypersistformillenniaandcanpeople.Theyare,however,subjecttowell-documentedlimitations.involveveryhighriskofsevereimpactsandthepresenceofsignificant{WGII2.2,2.3,WGIIISPM.2,BoxTS.2,2.4,2.5,2.6,3.2–3.6,3.9.4}irreversibilitiescombinedwithlimitedadaptivecapacity.Incontrast,thestringencyofclimatepoliciescanbeadjustedmuchmorequicklyAnalyticalmethodsofvaluationcannotidentifyasinglebestinresponsetoobservedconsequencesandcostsandcreatelowerrisksbalancebetweenmitigation,adaptationandresidualclimateofirreversibleconsequences(3.3,3.4,4.3).{WGISPME.8,12.4,12.5.2,impacts.Importantreasonsforthisarethatclimatechangeinvolves13.5,WGII4.2,17.2,19.6,WGIIITS.3.1.4,TableTS.4,TableTS.5,extremelycomplexnaturalandsocialprocesses,thereisextensivedis-TableTS.6,TableTS.7,TableTS.8,2.5,6.6}agreementaboutthevaluesconcerned,andclimatechangeimpactsandmitigationapproacheshaveimportantdistributionaleffects.Nev-Mitigationandadaptationarecomplementaryapproachesforertheless,informationontheconsequencesofemissionspathwaysreducingrisksofclimatechangeimpacts.Theyinteractwithonetoalternativeclimategoalsandrisklevelscanbeausefulinputintoanotherandreducerisksoverdifferenttimescales(highconfi-decision-makingprocesses.Evaluatingresponsestoclimatechangedence).Benefitsfromadaptationcanalreadyberealizedinaddressinginvolvesassessmentofthewidestpossiblerangeofimpacts,includingcurrentrisksandcanberealizedinthefutureforaddressingemerginglow-probabilityoutcomeswithlargeconsequences.{WGII1.1.4,2.3,risks.Adaptationhasthepotentialtoreduceclimatechangeimpacts2.4,17.3,19.6,19.7,WGIII2.5,2.6,3.4,3.7,Box3-9}overthenextfewdecades,whilemitigationhasrelativelylittleinflu-enceonclimateoutcomesoverthistimescale.Near-termandlonger-Effectivedecision-makingandriskmanagementinthecomplextermmitigationandadaptation,aswellasdevelopmentpathways,willenvironmentofclimatechangemaybeiterative:strategiescandeterminetherisksofclimatechangebeyondmid-century.Thepoten-oftenbeadjustedasnewinformationandunderstandingdevel-tialforadaptationdiffersacrosssectorsandwillbelimitedbyinstitu-opsduringimplementation.However,adaptationandmitigationtionalandcapacityconstraints,increasingthelong-termbenefitsofchoicesintheneartermwillaffecttherisksofclimatechangethrough-mitigation(highconfidence).Thelevelofmitigationwillinfluencetheoutthe21stcenturyandbeyond,andprospectsforclimate-resilientrateandmagnitudeofclimatechange,andgreaterratesandmagni-pathwaysforsustainabledevelopmentdependonwhatisachievedtudeofclimatechangeincreasethelikelihoodofexceedingadaptationthroughmitigation.Opportunitiestotakeadvantageofpositivesyn-limits(highconfidence)(3.3).{WGI11.3,12.4,WGIISPMA-3,SPMB-2,ergiesbetweenadaptationandmitigationmaydecreasewithtime,SPMC-2,1.1.4.4,2.5,16.3–16.6,17.3,19.2,20.2.3,20.3,20.6}particularlyifmitigationisdelayedtoolong.Decision-makingabout3climatechangeisinfluencedbyhowindividualsandorganizationsper-Withoutadditionalmitigationeffortsbeyondthoseinplaceceiverisksanduncertaintiesandtakethemintoaccount.Theysome-today,andevenwithadaptation,warmingbytheendofthetimesusesimplifieddecisionrules,overestimateorunderestimaterisks21stcenturywillleadtohightoveryhighriskofsevere,wide-andarebiasedtowardsthestatusquo.Theydifferintheirdegreeofspreadandirreversibleimpactsglobally(highconfidence)riskaversionandtherelativeimportanceplacedonnear-termversus(Topic2andFigure3.1a).Estimatesofwarmingin2100withoutlong-termramificationsofspecificactions.Formalizedanalyticalmeth-additionalclimatemitigationeffortsarefrom3.7°Cto4.8°Ccomparedodsfordecision-makingunderuncertaintycanaccountaccuratelyforwithpre-industriallevels(medianclimateresponse);therangeis2.5°Crisk,andfocusattentiononbothshort-andlong-termconsequences.to7.8°Cwhenusingthe5thto95thpercentilerangeofthemedian{WGIISPMA-3,SPMC-2,2.1–2.4,3.6,14.1–14.3,15.2–15.4,17.1–climateresponse(Figure3.1).Therisksassociatedwithtemperatures17.3,17.5,20.2,20.3,20.6,WGIIISPM.2,2.4,2.5,5.5,16.4}atorabove4°Cincludesevereandwidespreadimpactsonuniqueandthreatenedsystems,substantialspeciesextinction,largeriskstoglobalandregionalfoodsecurity,consequentialconstraintsoncommon3.2Climatechangerisksreducedbyhumanactivities,increasedlikelihoodoftriggeringtippingpoints(criti-adaptationandmitigationcalthresholds)andlimitedpotentialforadaptationinsomecases(highconfidence).Somerisksofclimatechange,suchasriskstouniqueandWithoutadditionalmitigationeffortsbeyondthoseinthreatenedsystemsandrisksassociatedwithextremeweatherevents,placetoday,andevenwithadaptation,warmingbythearemoderatetohighattemperatures1°Cto2°Cabovepre-industrialendofthe21stcenturywillleadtohightoveryhighlevels.{WGIISPMB-1,SPMC-2,WGIIISPM.3}riskofsevere,widespreadandirreversibleimpactsSubstantialcutsinGHGemissionsoverthenextfewdecadesglobally(highconfidence).Mitigationinvolvessomecansubstantiallyreducerisksofclimatechangebylimitinglevelofco-benefitsandofrisksduetoadversesidewarminginthesecondhalfofthe21stcenturyandbeyondeffects,buttheserisksdonotinvolvethesamepos-(highconfidence).Globalmeansurfacewarmingislargelydeter-sibilityofsevere,widespreadandirreversibleimpactsminedbycumulativeemissions,whichare,inturn,linkedtoemissionsasrisksfromclimatechange,increasingthebenefitsoverdifferenttimescales(Figure3.1).LimitingrisksacrossReasonsfromnear-termmitigationefforts.ForConcernwouldimplyalimitforcumulativeemissionsofCO2.77Topic3FuturePathwaysforAdaptation,MitigationandSustainableDevelopment(a)Risksfromclimatechange...(b)...dependoncumulativeCO2emissions...5Globalmeantemperaturechange(°Crelativetopre-industriallevels)4baselines3720–1000580–7202530–580480–530430–4801observed2000ssystemsreventsimpactspactsevents010002000300040005000600070008000m100CumulativeanthropogenicCO2emissionsfrom1870(GtCO2)atenedweathetionofegateiingular50thretremeistribulaggrcales&DGlobaarge-sChangeinannualGHGemissions0baselinesiqueExin2050(%relativeto2010levels)UnLemissionemission720–1000reductionsincreaseLevelofadditional580–720riskduetoclimatechange(seeBox2.4)nochangerelativeto2010530–5803Veryhigh480–530−50430–480HighModerate−100Undetectable(c)…whichinturndependonannualGHGemissionsoverthenextdecadesFigure3.1Therelationshipbetweenrisksfromclimatechange,temperaturechange,cumulativecarbondioxide(CO2)emissionsandchangesinannualgreenhousegas(GHG)emissionsby2050.LimitingrisksacrossReasonsForConcern(a)wouldimplyalimitforcumulativeemissionsofCO2(b),whichwouldconstrainannualemissionsoverthenextfewdecades(c).PanelareproducesthefiveReasonsForConcern(Box2.4).PanelblinkstemperaturechangestocumulativeCO2emissions(inGtCO2),from1870.TheyarebasedonCoupledModelIntercomparisonProjectPhase5(CMIP5)simulations(pinkplume)andonasimpleclimatemodel(medianclimateresponsein2100)forthebaselinesandfivemitigationscenariocategories(sixellipses).DetailsareprovidedinFigure2.3.PanelcshowstherelationshipbetweenthecumulativeCO2emissions(inGtCO2)ofthescenariocategoriesandtheirassociatedchangeinannualGHGemissionsby2050,expressedinpercentagechange(inpercentGtCO2-eqperyear)relativeto2010.TheellipsescorrespondtothesamescenariocategoriesasinPanelb,andarebuiltwithasimilarmethod(seedetailsinFigure2.3).SuchalimitwouldrequirethatglobalnetemissionsofCO2even-Mitigationinvolvessomelevelofco-benefitsandrisks,butthesetuallydecreasetozero(Figure3.1a,b)(highconfidence).Reducingrisksdonotinvolvethesamepossibilityofsevere,widespreadrisksofclimatechangethroughmitigationwouldinvolvesubstan-andirreversibleimpactsasrisksfromclimatechange(highcon-tialcutsinGHGemissionsoverthenextfewdecades(Figure3.1c).fidence).Scenariosthatarelikelytolimitwarmingtobelow2°CorButsomerisksfromresidualdamagesareunavoidable,evenwitheven3°Ccomparedwithpre-industrialtemperaturesinvolvelarge-scalemitigationandadaptation(veryhighconfidence).Asubsetofrelevantchangesinenergysystemsandpotentiallylanduseoverthecomingclimatechangeriskshasbeenestimatedusingaggregateeconomicdecades(3.4).Associatedrisksincludethoselinkedtolarge-scaleindicators.Sucheconomicestimateshaveimportantlimitationsanddeploymentoftechnologyoptionsforproducinglow-carbonenergy,thearethereforeausefulbutinsufficientbasisfordecision-makingonpotentialforhighaggregateeconomiccostsofmitigationandimpactslong-termmitigationtargets(seeBox3.1).{WGII19.7.1,WGIIISPM.3,onvulnerablecountriesandindustries.Otherrisksandco-benefitsareFigure3.1}associatedwithhumanhealth,foodsecurity,energysecurity,poverty78FuturePathwaysforAdaptation,MitigationandSustainableDevelopmentTopic3reduction,biodiversityconservation,wateravailability,incomedistri-3.3Characteristicsofadaptationpathwaysbution,efficiencyoftaxationsystems,laboursupplyandemployment,Introductionurbansprawl,fossilfuelexportrevenuesandtheeconomicgrowthofdevelopingcountries(Table4.5).{WGIIISPM.4.1,SPM.4.2,TS.3.1.4,AdaptationcanreducetherisksofclimatechangeTableTS.4,TableTS.5,TableTS.6,TableTS.7,TableTS.8,6.6}impacts,buttherearelimitstoitseffectiveness,espe-Inertiaintheeconomicandclimatesystemsandthepossibil-ciallywithgreatermagnitudesandratesofclimateityofirreversibleimpactsfromclimatechangeincreasethechange.Takingalonger-termperspective,inthecon-benefitsofnear-termmitigationefforts(highconfidence).Thetextofsustainabledevelopment,increasesthelikeli-actionstakentodayaffecttheoptionsavailableinthefuturetoreducehoodthatmoreimmediateadaptationactionswillemissions,limittemperaturechangeandadapttoclimatechange.alsoenhancefutureoptionsandpreparedness.Near-termchoicescancreate,amplifyorlimitsignificantelementsoflock-inthatareimportantfordecision-making.Lock-insandirrevers-Adaptationcancontributetothewell-beingofcurrentandibilitiesoccurintheclimatesystemduetolargeinertiainsomeofitsfuturepopulations,thesecurityofassetsandthemaintenancecomponentssuchasheattransferfromtheoceansurfacetodepthofecosystemgoods,functionsandservicesnowandintheleadingtocontinuedoceanwarmingforcenturiesregardlessofemis-future.Adaptationisplace-andcontext-specific,withnosinglesionscenarioandtheirreversibilityofalargefractionofanthropogenicapproachforreducingrisksappropriateacrossallsettings(highclimatechangeresultingfromCO2emissionsonamulti-centurytomil-confidence).Effectiveriskreductionandadaptationstrategiescon-lennialtimescaleunlessCO2weretoberemovedfromtheatmospheresidervulnerabilityandexposureandtheirlinkageswithsocio-economicthroughlarge-scalehumaninterventionsoverasustainedperiod(seeprocesses,sustainabledevelopment,andclimatechange.AdaptationalsoBox3.3).Irreversibilitiesinsocio-economicandbiologicalsystemsresearchsincetheIPCCFourthAssessmentReport(AR4)hasevolvedalsoresultfrominfrastructuredevelopmentandlong-livedproductsfromadominantconsiderationofengineeringandtechnologicaladap-andfromclimatechangeimpacts,suchasspeciesextinction.Thetationpathwaystoincludemoreecosystem-based,institutionalandlargerpotentialforirreversibilityandpervasiveimpactsfromclimatesocialmeasures.Apreviousfocusoncost–benefitanalysis,optimiza-changerisksthanfrommitigationrisksincreasesthebenefitofshort-tionandefficiencyapproacheshasbroadenedwiththedevelopmentoftermmitigationefforts.Delaysinadditionalmitigationorconstraintsmulti-metricevaluationsthatincluderiskanduncertaintydimensionsontechnologicaloptionslimitthemitigationoptionsandincreasetheintegratedwithinwiderpolicyandethicalframeworkstoassesstrade-long-termmitigationcostsaswellasotherrisksthatwouldbeincurredoffsandconstraints.Therangeofspecificadaptationmeasureshasinthemediumtolongtermtoholdclimatechangeimpactsatagivenalsoexpanded(4.2,4.4.2.1),ashavethelinkstosustainabledevel-level(TableWGIIISPM.2,bluesegment).{WGISPME-8,WGIISPMB-2,opment(3.5).Therearemanystudiesonlocalandsectoraladaptation2.1,19.7,20.3,Box20-4,WGIIISPM.4.1,SPM.4.2.1,3.6,6.4,6.6,6.9}costsandbenefits,butfewglobalanalysesandverylowconfidence3Box3.1TheLimitsoftheEconomicAssessmentofClimateChangeRisksAsubsetofclimatechangerisksandimpactsareoftenmeasuredusingaggregateeconomicindicators,suchasgrossdomesticproduct(GDP)oraggregateincome.Estimates,however,arepartialandaffectedbyimportantconceptualandempiricallimitations.Theseincompleteestimatesofglobalannualeconomiclossesfortemperatureincreasesof~2.5°Cabovepre-industriallevelsarebetween0.2and2.0%ofincome(mediumevidence,mediumagreement).Lossesaremorelikelythannottobegreater,ratherthansmaller,thanthisrange(limitedevidence,highagreement).Estimatesoftheincrementalaggregateeconomicimpactofemittingonemoretonneofcarbondioxide(thesocialcostofcarbon)arederivedfromthesestudiesandliebetweenafewdollarsandseveralhundredsofdollarspertonneofcarbonin2000to2015(robustevidence,mediumagreement).Theseimpactesti-matesareincompleteanddependonalargenumberofassumptions,manyofwhicharedisputable.Manyestimatesdonotaccountforthepossibilityoflarge-scalesingulareventsandirreversibility,tippingpointsandotherimportantfactors,especiallythosethataredifficulttomonetize,suchaslossofbiodiversity.Estimatesofaggregatecostsmasksignificantdifferencesinimpactsacrosssectors,regions,countriesandcommunities,andtheythereforedependonethicalconsiderations,especiallyontheaggregationoflossesacrossandwithincountries(highconfidence).Estimatesofglobalaggregateeconomiclossesexistonlyforlimitedwarminglevels.Theselevelsareexceededinscenariosforthe21stcenturyunlessadditionalmitigationactionisimplemented,leadingtoadditionaleconomiccosts.Thetotaleconomiceffectsatdifferenttemperaturelevelswouldincludemitigationcosts,co-benefitsofmitigation,adversesideeffectsofmitigation,adaptationcostsandclimatedamages.Asaresult,mitigationcostandclimatedamageestimatesatanygiventemperaturelevelcannotbecomparedtoevaluatethecostsandbenefitsofmitigation.Verylittleisknownabouttheeconomiccostofwarmingabove3°Crelativetothecurrenttemperaturelevel.Accuratelyestimatingclimatechangerisks(andthusthebenefitsofmitigation)takesintoaccountthefullrangeofpossibleimpactsofclimatechange,includingthosewithhighconsequencesbutalowprobabilityofoccurrence.Thebenefitsofmitigationmayotherwisebeunderestimated(highconfidence).Somelimitationsofcurrentestimatesmaybeunavoidable,evenwithmoreknowledge,suchasissueswithaggregatingimpactsovertimeandacrossindividualswhenvaluesareheterogeneous.Inviewoftheselimitations,itisoutsidethescopeofsciencetoidentifyasinglebestclimatechangetargetandclimatepolicy(3.1,3.4).{WGIISPMB-2,10.9.2,10.9.4,13.2,17.2–17.3,18.4,19.6,WGIII3.6}79Topic3FuturePathwaysforAdaptation,MitigationandSustainableDevelopmentintheirresults.{WGIISPMC-1,TableSPM.1,14.1,14.ES,15.2,15.5,Greaterratesandmagnitudeofclimatechangeincreasethe17.2,17.ES}likelihoodofexceedingadaptationlimits(highconfidence).Limitstoadaptationoccurwhenadaptiveactionstoavoidintolera-Adaptationplanningandimplementationatalllevelsofgov-blerisksforanactor’sobjectivesorfortheneedsofasystemarenoternancearecontingentonsocietalvalues,objectivesandriskpossibleorarenotcurrentlyavailable.Value-basedjudgmentsofwhatperceptions(highconfidence).Recognitionofdiverseinterests,constitutesanintolerableriskmaydiffer.Limitstoadaptationemergecircumstances,social-culturalcontextsandexpectationscanbenefitfromtheinteractionamongclimatechangeandbiophysicaland/ordecision-makingprocesses.Indigenous,localandtraditionalknowl-socio-economicconstraints.Opportunitiestotakeadvantageofpositiveedgesystemsandpractices,includingindigenouspeoples’holisticsynergiesbetweenadaptationandmitigationmaydecreasewithtime,viewofcommunityandenvironment,areamajorresourceforadapt-particularlyiflimitstoadaptationareexceeded.Insomepartsoftheingtoclimatechange,butthesehavenotbeenusedconsistentlyworld,insufficientresponsestoemergingimpactsarealreadyerodinginexistingadaptationefforts.Integratingsuchformsofknowledgethebasisforsustainabledevelopment.Formostregionsandsectors,intopracticesincreasestheeffectivenessofadaptationasdoeffec-empiricalevidenceisnotsufficienttoquantifymagnitudesofclimatetivedecisionsupport,engagementandpolicyprocesses(4.4.2).{WGIIchangethatwouldconstituteafutureadaptationlimit.Furthermore,SPMC-1}economicdevelopment,technologyandculturalnormsandvaluescanchangeovertimetoenhanceorreducethecapacityofsystemstoavoidAdaptationplanningandimplementationcanbeenhancedlimits.Asaconsequence,somelimitsare‘soft’inthattheymaybealle-throughcomplementaryactionsacrosslevels,fromindividu-viatedovertime.Otherlimitsare‘hard’inthattherearenoreasonablealstogovernments(highconfidence).Nationalgovernmentscanprospectsforavoidingintolerablerisks.{WGIISPMC-2,TS}coordinateadaptationeffortsoflocalandsub-nationalgovernments,forexamplebyprotectingvulnerablegroups,bysupportingeconomicTransformationsineconomic,social,technologicalandpoliticaldiversificationandbyprovidinginformation,policyandlegalframe-decisionsandactionscanenhanceadaptationandpromotesus-worksandfinancialsupport(robustevidence,highagreement).Localtainabledevelopment(highconfidence).Restrictingadaptationgovernmentandtheprivatesectorareincreasinglyrecognizedascrit-responsestoincrementalchangestoexistingsystemsandstructuresicaltoprogressinadaptation,giventheirrolesinscalingupadapta-withoutconsideringtransformationalchangemayincreasecostsandtionofcommunities,householdsandcivilsocietyandinmanagingrisklossesandmissopportunities.Forexample,enhancinginfrastructuretoinformationandfinancing(mediumevidence,highagreement).{WGIIprotectotherbuiltassetscanbeexpensiveandultimatelynotdefraySPMC-1}increasingcostsandrisks,whereasoptionssuchasrelocationorusingecosystemservicestoadaptmayprovidearangeofbenefitsnowandAfirststeptowardsadaptationtofutureclimatechangeisinthefuture.Transformationaladaptationcanincludeintroductionofreducingvulnerabilityandexposuretopresentclimatevariabil-newtechnologiesorpractices,formationofnewfinancialstructures3ity(highconfidence),butsomenear-termresponsestoclimateorsystemsofgovernance,adaptationatgreaterscalesormagnitudeschangemayalsolimitfuturechoices.Integrationofadaptationandshiftsinthelocationofactivities.Planningandimplementationintoplanning,includingpolicydesign,anddecision-makingcanpro-oftransformationaladaptationcouldreflectstrengthened,alteredormotesynergieswithdevelopmentanddisasterriskreduction.How-alignedparadigmsandconsequentlymayplacenewandincreasedever,poorplanningorimplementation,overemphasizingshort-termdemandsongovernancestructurestoreconciledifferentgoalsandoutcomesorfailingtosufficientlyanticipateconsequencescanresultvisionsforthefutureandtoaddresspossibleequityandethicalimpli-inmaladaptation,increasingthevulnerabilityorexposureofthetargetcations:transformationaladaptationpathwaysareenhancedbyiter-groupinthefutureorthevulnerabilityofotherpeople,placesorsec-ativelearning,deliberativeprocesses,andinnovation.Atthenationaltors(mediumevidence,highagreement).Forexample,enhancedpro-level,transformationisconsideredmosteffectivewhenitreflectsatectionofexposedassetscanlockindependenceonfurtherprotectioncountry’sownvisionsandapproachestoachievingsustainabledevel-measures.Appropriateadaptationoptionscanbebetterassessedbyopmentinaccordancewithitsnationalcircumstancesandpriorities.includingco-benefitsandmitigationimplications(3.5and4.2).{WGII{WGIISPMC-2,1.1,2.5,5.5,8.4,14.1,14.3,16.2-7,20.3.3,20.5,SPMC-1}25.10,Table14-4,Table16-3,Box16.1,Box16.4,Box25.1}Numerousinteractingconstraintscanimpedeadaptationplan-Buildingadaptivecapacityiscrucialforeffectiveselectionningandimplementation(highconfidence).Commonconstraintsandimplementationofadaptationoptions(robustevidence,onimplementationarisefromthefollowing:limitedfinancialandhighagreement).Successfuladaptationrequiresnotonlyidenti-humanresources;limitedintegrationorcoordinationofgovernance;fyingadaptationoptionsandassessingtheircostsandbenefits,butuncertaintiesaboutprojectedimpacts;differentperceptionsofrisks;alsoincreasingtheadaptivecapacityofhumanandnaturalsystemscompetingvalues;absenceofkeyadaptationleadersandadvocates;(mediumevidence,highagreement).Thiscaninvolvecomplexgovern-andlimitedtoolstomonitoradaptationeffectiveness.Othercon-ancechallengesandnewinstitutionsandinstitutionalarrangements.straintsincludeinsufficientresearch,monitoringandobservationand(4.2){WGII8.1,12.3,14.1-3,16.2,16.3,16.5,16.8}thefinancialandotherresourcestomaintainthem.Underestimatingthecomplexityofadaptationasasocialprocesscancreateunrealis-Significantco-benefits,synergiesandtrade-offsexistbetweenticexpectationsaboutachievingintendedadaptationoutcomes(seemitigationandadaptationandamongdifferentadaptationSections4.1and4.2fordetailsinrelationtoimplementation).{WGIIresponses;interactionsoccurbothwithinandacrossregions(verySPMC-1}highconfidence).Increasingeffortstomitigateandadapttoclimate80FuturePathwaysforAdaptation,MitigationandSustainableDevelopmentTopic3changeimplyanincreasingcomplexityofinteractions,particularlyattheManydifferentcombinationsoftechnological,behaviouralandintersectionsamongwater,energy,landuseandbiodiversity,buttoolstopolicyoptionscanbeusedtoreduceemissionsandlimittem-Introductionunderstandandmanagetheseinteractionsremainlimited.Examplesofperaturechange(highconfidence).Toevaluatepossiblepathwaysactionswithco-benefitsinclude(i)improvedenergyefficiencyandcleanertolong-termclimategoals,about900mitigationscenarioswerecol-energysources,leadingtoreducedemissionsofhealth-damaging,lectedforthisassessment,eachofwhichdescribesdifferenttechno-climate-alteringairpollutants;(ii)reducedenergyandwaterconsump-logical,socio-economicandinstitutionalchanges.Emissionreductionstioninurbanareasthroughgreeningcitiesandrecyclingwater;(iii)underthesescenariosleadtoconcentrationsin2100from430ppmsustainableagricultureandforestry;and(iv)protectionofecosystemsCO2-eqtoabove720ppmCO2-eqwhichiscomparabletothe2100forcarbonstorageandotherecosystemservices.{WGIISPMC-1}forcinglevelsbetweenRCP2.6andRCP6.0.Scenarioswithconcen-trationlevelsofbelow430ppmCO2-eqby2100werealsoassessed.{WGIIISPM.4.1,TS3.1,6.1,6.2,6.3,AnnexII}3.4CharacteristicsofmitigationpathwaysScenariosleadingtoCO2-eqconcentrationsin2100ofaboutTherearemultiplemitigationpathwaysthatarelikely450ppmorlowerarelikelytomaintainwarmingbelow2°Coverthetolimitwarmingtobelow2°Crelativetopre-industrial21stcenturyrelativetopre-industriallevels(highconfidence).Miti-levels.Thesepathwayswouldrequiresubstantialemis-gationscenariosreachingconcentrationlevelsofabout500ppmCO2-eqsionsreductionsoverthenextfewdecadesandnearby2100aremorelikelythannottolimitwarmingtolessthan2°CzeroemissionsofCO2andotherlong-livedgreenhouserelativetopre-industriallevels,unlessconcentrationlevelstemporarilygasesbytheendofthecentury.Implementingsuchexceedroughly530ppmCO2-eqbefore2100.Inthiscase,warmingreductionsposessubstantialtechnological,economic,isaboutaslikelyasnottoremainbelow2°Crelativetopre-industrialsocialandinstitutionalchallenges,whichincreaselevels.Scenariosthatexceedabout650ppmCO2-eqby2100arewithdelaysinadditionalmitigationandifkeytech-unlikelytolimitwarmingtobelow2°Crelativetopre-industriallevels.nologiesarenotavailable.LimitingwarmingtolowerMitigationscenariosinwhichwarmingismorelikelythannottobelessorhigherlevelsinvolvessimilarchallengesbutonthan1.5°Crelativetopre-industriallevelsby2100arecharacterizeddifferenttimescales.byconcentrationlevelsby2100ofbelow430ppmCO2-eq.Inthesescenarios,temperaturepeaksduringthecenturyandsubsequentlydeclines(Table3.1).{WGIIISPM.4.1,TableSPM.1,TS.3.1,BoxTS.6,6.3}WithoutadditionaleffortstoreduceGHGemissionsbeyondthoseinplacetoday,globalemissiongrowthisexpectedtoMitigationscenariosreachingabout450ppmCO2-eqin2100persistdrivenbygrowthinglobalpopulationandeconomic(consistentwithalikelychancetokeepwarmingbelow2°Crel-activities(highconfidence)(Figure3.2).GlobalGHGemissionsativetopre-industriallevel)typicallyinvolvetemporaryover-undermostscenarioswithoutadditionalmitigation(baselinescenar-shoot3823ofatmosphericconcentrations,asdomanyscenarios3ios)arebetweenabout75GtCO2-eq/yrandalmost140GtCO2-eq/yrreachingabout500ppmCO2-eqtoabout550ppmCO2-eqbyin21003520whichisapproximatelybetweenthe2100emissionlevels2100(Table3.1).Dependingonthelevelofovershoot,over-intheRCP6.0andRCP8.5pathways(Figure3.2)3621.Baselinescenariosshootscenariostypicallyrelyontheavailabilityandwide-exceed450ppmCO2-eqby2030andreachCO2-eqconcentrationlevelsspreaddeploymentofbioenergywithcarbondioxidecapturebetweenabout750ppmCO2-eqandmorethan1300ppmCO2-eqbyandstorage(BECCS)andafforestationinthesecondhalfofthe2100.Globalmeansurfacetemperatureincreasesin2100rangefromcentury(highconfidence).Theavailabilityandscaleoftheseandabout3.7°Cto4.8°Cabovetheaveragefor1850–1900foramedianotherCarbonDioxideRemoval(CDR)technologiesandmethodsareclimateresponse.Theyrangefrom2.5°Cto7.8°Cwhenincludingcli-uncertain,andCDRtechnologiesandmethodsare,tovaryingdegrees,mateuncertainty(5thto95thpercentilerange)372.Thefuturescenariosassociatedwithchallengesandrisks(seeBox3.3)3924.CDRisalsoprev-donotaccountforpossiblechangesinnaturalforcingsinthecli-alentinmanyscenarioswithoutovershoottocompensateforresidualmatesystem(seeBox1.1).{WGIIISPM.3,SPM.4.1,TS.2.2,TS.3.1,6.3,emissionsfromsectorswheremitigationismoreexpensive.{WGIIIBoxTS.6}SPM.4.1,TableSPM.1,TS.3.1,6.3,6.9.1,Figure6.7,7.11,11.13}35Unlessotherwisenoted,scenariorangescitedinTopic3andTopic4refertothe10thto90thpercentileranges(seeTable3.1).36ForadiscussiononCO2-equivalent(CO2-eq)emissionsandconcentrations,seeBox3.2onGHGmetricsandmitigationpathwaysandtheGlossary.37Therangequotedhereisbasedonthewarmingresultsofasimpleclimatemodelfortheemissionsofaround300baselinescenarios,expressedcomparedtothe1850–1900period.ThewarmingresultsquotedinSection2.2areobtainedbyprescribingfutureconcentrationsofGHGinCMIP5EarthSystemModels.Thisresultsinameanwarmingof1.0°C(5thto95thpercentilerange:0.3°Cto1.7°C)forRCP2.6,andameanwarmingof3.7°C(2.6°Cto4.8°C)forRCP8.5relativetotheperiod1986–2005.Forthesameconcentration-drivenexperiments,thesimpleclimatemodelapproachgivesconsistentresults.Themedianwarmingis0.9°C(0.5°Cto1.6°C)forRCP2.6and3.7°C(2.5°Cto5.9°C)forRCP8.5relativetotheperiod1986–2005.However,thehigh-endoftheCMIP5ESMsrangeismoreconstrained.Inaddition,thebaselinetemperatureincreasequotedhereiswiderthanthatoftheconcentration-drivenRCP8.5experimentsmentionedaboveasitisbasedonawidersetofscenarios,includescarboncycleresponseuncertainty,andusesadifferentbaseyear(2.2,3.4).38Inconcentration‘overshoot’scenarios,concentrationspeakduringthecenturyandthendecline.39CDRmethodshavebiogeochemicalandtechnologicallimitationstotheirpotentialontheglobalscale.ThereisinsufficientknowledgetoquantifyhowmuchCO2emissionscouldbepartiallyoffsetbyCDRonacenturytimescale.CDRmethodsmaycarrysideeffectsandlong-termconsequencesonaglobalscale.81Topic3FuturePathwaysforAdaptation,MitigationandSustainableDevelopment(a)GHGemissionpathways2000–2100:AllAR5scenarios140>1000ppmCO2-eq90thPercentileRCP8.5120720–1000ppmCO2-eqMedianAnnualGHGemissions(GtCO2-eq/yr)580–720ppmCO2-eq10thPercentileBaseline100530–580ppmCO2-eq480–530ppmCO2-eq80430–480ppmCO2-eqFullAR5databaserange60RCP6.04020RCP4.5RCP2.60–202000202020402060208021002100Year(b)Associatedupscalingoflow-carbonenergysupply100Low-carbonenergyshareofprimaryenergy(%)580–720ppmCO2-eq530–580ppmCO2-eq480–530ppmCO2-eq430–480ppmCO2-eq80+95%Percentile+180%60Max75thMedian25thMin40+135%+135%+185%+275%3+145%+310%2020502100203020502100203020502100203020100205021002030Figure3.2Globalgreenhousegas(GHG)emissions(gigatonneofCO2-equivalentperyear,GtCO2-eq/yr)inbaselineandmitigationscenariosfordifferentlong-termconcentrationlevels(a)andassociatedscale-uprequirementsoflow-carbonenergy(%ofprimaryenergy)for2030,2050and2100,comparedto2010levels,inmitigationscenarios(b).{WGIIISPM.4,Figure6.7,Figure7.16}[Note:CO2-eqemissionsincludethebasketofKyotogases(carbondioxide(CO2),methane(CH4),nitrousoxide(N2O)aswellasfluorinatedgases)calculatedbasedon100-yearGlobalWarmingPotential(GWP100)valuesfromtheIPCCSecondAssessmentReport.]Limitingwarmingwithalikelychancetolessthan2°Crela-andemissionslevelsnearzeroorbelowin2100(Figure3.2,Table3.1).tivetopre-industriallevelswouldrequiresubstantialcutsinScenarioswithhigheremissionsin2050arecharacterizedbyagreateranthropogenicGHGemissions4025bymid-centurythroughlarge-relianceonCDRtechnologiesbeyondmid-century,andviceversa.scalechangesinenergysystemsandpossiblylanduse.Limit-Scenariosthatarelikelytomaintainwarmingatbelow2°Cincludeingwarmingtohigherlevelswouldrequiresimilarchangesbutmorerapidimprovementsinenergyefficiencyandatriplingtonearlylessquickly.Limitingwarmingtolowerlevelswouldrequireaquadruplingoftheshareofzero-andlow-carbonenergysupplythesechangesmorequickly(highconfidence).Scenariosthatfromrenewableenergy,nuclearenergyandfossilenergywithcarbonarelikelytomaintainwarmingatbelow2°Carecharacterizedbyadioxidecaptureandstorage(CCS)orBECCSbytheyear2050(Figure3.2b).40to70%reductioninGHGemissionsby2050,relativeto2010levels,Thescenariosdescribeawiderangeofchangesinlanduse,reflecting40ThisrangediffersfromtherangeprovidedforasimilarconcentrationcategoryinAR4(50to85%lowerthanin2000forCO2only).ReasonsforthisdifferenceincludethatthisreporthasassessedasubstantiallylargernumberofscenariosthaninAR4andlooksatallGHGs.Inaddition,alargeproportionofthenewscenariosincludeCDRtechnologies.Otherfactorsincludetheuseof2100concentrationlevelsinsteadofstabilizationlevelsandtheshiftinreferenceyearfrom2000to2010.Scenarioswithhigheremissionlevelsby2050arecharacterizedbyagreaterrelianceonCDRtechnologiesbeyondmid-century.82FuturePathwaysforAdaptation,MitigationandSustainableDevelopmentTopic3Table3.1KeycharacteristicsofthescenarioscollectedandassessedforWGIIIAR5.Forallparametersthe10thto90thpercentileofthescenariosisshowna.CO2-eqCon-ChangeinCO2-eqemissionsLikelihoodofstayingbelowaspecifictemperaturelevelIntroductioncentrationsincomparedto2010(in%)coverthe21stcentury(relativeto1850–1900)d,e2100SubcategoriesRelative205021001.5ºC2ºC3ºC4ºC(ppmCO2-eq)fpositionofTotalrangea,gtheRCPsdCategorylabelNoovershootof(conc.range)530ppmCO2-eqOnlyalimitednumberofindividualmodelstudieshaveexploredlevelsbelow430ppmCO2-eqjOvershootof530<430RCP2.6–72to–41–118to–78MoreunlikelyLikely450ppmCO2-eqthanlikely(430to480)Noovershootof580ppmCO2-eq–57to–42–107to–73Morelikely500Overshootof580thannot(480to530)ppmCO2-eq–55to–25–114to–90Aboutas550likelyasnot(530to580)Likely–47to–19–81to–59UnlikelyMoreunlikelyLikely–16to7–183to–86thanlikelyi(580to650)TotalrangeRCP4.5–38to24–134to–50UnlikelyhUnlikelyMorelikelyMoreunlikely(650to720)TotalrangeRCP6.0–11to17–54to–21Unlikelyhthannotthanlikely(720to1000)bTotalrangeRCP8.518to54–7to72MoreunlikelyTotalrange52to9574to178thanlikely>1000bUnlikelyNotes:aThe‘totalrange’forthe430to480ppmCO2-eqconcentrationsscenarioscorrespondstotherangeofthe10thto90thpercentileofthesubcategoryofthesescenariosshowninTable6.3oftheWorkingGroupIIIreport.bBaselinescenariosfallintothe>1000and720to1000ppmCO2-eqcategories.Thelattercategoryalsoincludesmitigationscenarios.Thebaselinescenariosinthelattercategoryreachatemperaturechangeof2.5°Cto5.8°Cabovetheaveragefor1850–1900in2100.Togetherwiththebaselinescenariosinthe>1000ppmCO2-eqcategory,thisleadstoanoverall2100temperaturerangeof2.5°Cto7.8°C(rangebasedonmedianclimateresponse:3.7°Cto4.8°C)forbaselinescenariosacrossbothconcentrationcategories.3cTheglobal2010emissionsare31%abovethe1990emissions(consistentwiththehistoricgreenhousegasemissionestimatespresentedinthisreport).CO2-eqemissionsincludethebasketofKyotogases(carbondioxide(CO2),methane(CH4),nitrousoxide(N2O)aswellasfluorinatedgases).dTheassessmenthereinvolvesalargenumberofscenariospublishedinthescientificliteratureandisthusnotlimitedtotheRepresentativeConcentrationPathways(RCPs).ToevaluatetheCO2-eqconcentrationandclimateimplicationsofthesescenarios,theModelfortheAssessmentofGreenhouseGasInducedClimateChange(MAGICC)wasusedinaprobabilisticmode.ForacomparisonbetweenMAGICCmodelresultsandtheoutcomesofthemodelsusedinWGI,seeWGI12.4.1.2,12.4.8andWGIII6.3.2.6.eTheassessmentinthistableisbasedontheprobabilitiescalculatedforthefullensembleofscenariosinWGIIIusingMAGICCandtheassessmentinWGIoftheuncertaintyofthetemperatureprojectionsnotcoveredbyclimatemodels.ThestatementsarethereforeconsistentwiththestatementsinWGI,whicharebasedontheCoupledModelIntercomparisonProjectPhase5(CMIP5)runsoftheRCPsandtheassesseduncertainties.Hence,thelikelihoodstatementsreflectdifferentlinesofevidencefrombothWGs.ThisWGImethodwasalsoappliedforscenarioswithintermediateconcentrationlevelswherenoCMIP5runsareavailable.Thelikelihoodstatementsareindicativeonly{WGIII6.3}andfollowbroadlythetermsusedbytheWGISPMfortemperatureprojections:likely66–100%,morelikelythannot>50–100%,aboutaslikelyasnot33–66%,andunlikely0–33%.Inadditionthetermmoreunlikelythanlikely0–<50%isused.fTheCO2-equivalentconcentration(seeGlossary)iscalculatedonthebasisofthetotalforcingfromasimplecarboncycle/climatemodel,MAGICC.TheCO2-equivalentconcentra-tionin2011isestimatedtobe430ppm(uncertaintyrange340to520ppm).Thisisbasedontheassessmentoftotalanthropogenicradiativeforcingfor2011relativeto1750inWGI,i.e.,2.3W/m2,uncertaintyrange1.1to3.3W/m2.gThevastmajorityofscenariosinthiscategoryovershootthecategoryboundaryof480ppmCO2-eqconcentration.hForscenariosinthiscategory,noCMIP5runorMAGICCrealizationstaysbelowtherespectivetemperaturelevel.Still,anunlikelyassignmentisgiventoreflectuncertaintiesthatmaynotbereflectedbythecurrentclimatemodels.iScenariosinthe580to650ppmCO2-eqcategoryincludebothovershootscenariosandscenariosthatdonotexceedtheconcentrationlevelatthehighendofthecategory(e.g.,RCP4.5).Thelattertypeofscenarios,ingeneral,haveanassessedprobabilityofmoreunlikelythanlikelytostaybelowthe2°Ctemperaturelevel,whiletheformeraremostlyassessedtohaveanunlikelyprobabilityofstayingbelowthislevel.jInthesescenarios,globalCO2-eqemissionsin2050arebetween70to95%below2010emissions,andtheyarebetween110to120%below2010emissionsin2100.differentassumptionsaboutthescaleofbioenergyproduction,affores-tolimitwarmingto1.5°Cby2100;thesescenariosarecharacterizedtationandreduceddeforestation.Scenariosleadingtoconcentra-byconcentrationsbelow430ppmCO2-eqby2100and2050emis-tionsof500ppmCO2-eqby2100arecharacterizedbya25to55%sionreductionbetween70and95%below2010.Foracomprehen-reductioninGHGemissionsby2050,relativeto2010levels.Scenariossiveoverviewofthecharacteristicsofemissionsscenarios,theirthatarelikelytolimitwarmingto3°Crelativetopre-industriallevelsCO2-equivalentconcentrationsandtheirlikelihoodtokeepwarmingreduceemissionslessrapidlythanthoselimitingwarmingto2°C.Onlyatobelowarangeoftemperaturelevels,seeTable3.1.{WGIIISPM.4.1,limitednumberofstudiesprovidescenariosthataremorelikelythannotTS.3.1,6.3,7.11}83Topic3FuturePathwaysforAdaptation,MitigationandSustainableDevelopmentBefore2030After2030Shareofzeroandlow-carbonenergyAnnualGHGemissionsRateofCO2emissionschange100Cancún680PledgesPast1900–2010603552000–2010500Future2030–20506045–3404035–6(GtCO2-eq/yr)(%/yr)(%)+90%+240%3020–9201025AnnualGHGAR5scenariorange0203020502100203020502100emissionsin2030Interquartilerangeandmedianofmodelcomparisonswith<50GtCO2-eq–122030targets20>55GtCO2-eq200520102015202020252030YearFigure3.3Theimplicationsofdifferent2030greenhousegas(GHG)emissionslevelsfortherateofcarbondioxide(CO2)emissionreductionsandlow-carbonenergyupscalinginmitigationscenariosthatareatleastaboutaslikelyasnottokeepwarmingthroughoutthe21stcenturybelow2°Crelativetopre-industriallevels(2100CO2-eqconcentrations430to530ppm).Thescenariosaregroupedaccordingtodifferentemissionslevelsby2030(colouredindifferentshadesofgreen).TheleftpanelshowsthepathwaysofGHG3emissions(GtCO2-eq/yr)leadingtothese2030levels.BlackdotwithwhiskersgiveshistoricGHGemissionlevelsandassociateduncertaintiesin2010asreportedinFigure1.6.TheblackbarshowstheestimateduncertaintyrangeofGHGemissionsimpliedbytheCancúnPledges.ThemiddlepaneldenotestheaverageannualCO2emissionreductionratesforthe2030–2050period.Itcomparesthemedianandinterquartilerangeacrossscenariosfromrecentintermodelcomparisonswithexplicit2030interimgoalstotherangeofscenariosintheScenarioDatabaseforWGIIIAR5.Annualratesofhistoricalemissionchanges(sustainedoveraperiodof20years)areshownaswell.Thearrowsintherightpanelshowthemagnitudeofzeroandlow-carbonenergysupplyupscalingfrombetween2030and2050,subjecttodifferent2030GHGemissionlevels.Zero-andlow-carbonenergysupplyincludesrenewableenergy,nuclearenergyandfossilenergywithcarbondioxidecaptureandstorage(CCS)orbioenergywithCCS(BECCS).Onlyscenariosthatapplythefull,unconstrainedmitigationtechnologyportfoliooftheunderlyingmodels(defaulttechnologyassumption)areshown.Scenarioswithlargenetnegativeglobalemissions(>20GtCO2-eq/yr),scenarioswithexogenouscarbonpriceassumptions,andscenarioswith2010emissionlevelsthataresignificantlyoutsidethehistoricalrangeareexcluded.{WGIIIFigureSPM.5,Figure6.32,Figure7.16,13.13.1.3}Reducingemissionsofnon-CO2climateforcingagentscanbedrivenmainlybyCO2emissions.Therearelargeuncertaintiesrelatedanimportantelementofmitigationstrategies.Emissionsofnon-totheclimateimpactsofsomeoftheshort-livedclimateforcingCO2gases(methane(CH4),nitrousoxide(N2O),andfluorinatedgases)agents.AlthoughtheeffectsofCH4emissionsarewellunderstood,contributedabout27%tothetotalemissionsofKyotogasesin2010.therearelargeuncertaintiesrelatedtotheeffectsofblackcarbon.Formostnon-CO2gases,near-term,low-costoptionsareavailabletoCo-emittedcomponentswithcoolingeffectsmayfurthercomplicatereducetheiremissions.However,somesourcesofthesenon-CO2gasesandreducetheclimateimpactsofemissionreductions.Reducingemis-aredifficulttomitigate,suchasN2Oemissionsfromfertilizeruseandsionsofsulfurdioxide(SO2)wouldcausewarming.Near-termreduc-CH4emissionsfromlivestock.Asaresult,emissionsofmostnon-CO2tionsinshort-livedclimateforcingagentscanhavearelativelyfastgaseswillnotbereducedtozero,evenunderstringentmitigationimpactonclimatechangeandpossibleco-benefitsforairpollution.scenarios(seeFigure4.1).Thedifferencesinradiativepropertiesand{WGI8.2.3,8.3.2,8.3.4,8.5.1,8.7.2,FAQ8.2,12.5,WGIII6.6.2.1}lifetimesofCO2andnon-CO2climateforcingagentshaveimportantimplicationsformitigationstrategies(seealsoBox3.2).{WGIII6.3.2}Delayingadditionalmitigationto2030willsubstantiallyincreasethechallengesassociatedwithlimitingwarmingAllcurrentGHGemissionsandotherclimateforcingagentsoverthe21stcenturytobelow2°Crelativetopre-industrialaffecttherateandmagnitudeofclimatechangeoverthenextlevels(highconfidence).GHGemissionsin2030liebetweenaboutfewdecades.Reducingtheemissionsofcertainshort-livedclimate30GtCO2-eq/yrand50GtCO2-eq/yrincost-effectivescenariosthatareforcingagentscanreducetherateofwarmingintheshorttermlikelytoaboutaslikelyasnottolimitwarmingtolessthan2°Cthiscen-butwillhaveonlyalimitedeffectonlong-termwarming,whichisturyrelativetopre-industriallevels(2100atmosphericconcentration84FuturePathwaysforAdaptation,MitigationandSustainableDevelopmentTopic3Globalmitigationcostsandconsumptiongrowthinbaselinescenarios10002100Percentagepointreductioninannualizedconsumptiongrowthrateover21stcentury(%-point)Introduction800Consumptionincorrespondingbaseline0.030.040.060.06scenarios(%increasefrom2010)(0.01to0.05)(0.01to0.09)(0.03to0.13)(0.04to0.14)1284thPercentile10600Reductioninconsumptionrelativetobaseline(%)8400203020506210042030Median200205016thPercentile200550(530–580)500(480–530)450(430–480)Corresponding580–650baselinescenariosCO2-eqconcentrationsin2100(ppm)Figure3.4Globalmitigationcostsincost-effectivescenariosatdifferentatmosphericconcentrationslevelsin2100(rightpanel)andgrowthineconomicconsumptioninthecorrespondingbaselinescenarios(thosewithoutadditionalmitigation)(leftpanel).Thetableatthetopshowspercentagepointsofannualizedconsumptiongrowthreductionsrelativetoconsumptiongrowthinthebaselineof1.6to3%peryear(e.g.,ifthereductionis0.06percentagepointsperyearduetomitigation,andbaselinegrowthis2.0%peryear,thenthegrowthratewithmitigationwouldbe1.94%peryear).Cost-effectivescenariosassumeimmediatemitigationinallcountriesandasingleglobalcarbonprice,andtheyimposenoadditionallimitationsontechnologyrelativetothemodels’defaulttechnologyassumptions.Consumptionlossesareshownrelativetoabaselinedevelopmentwithoutclimatepolicy.Costestimatesshowninthistabledonotconsiderthebenefitsofreducedclimatechangenorco-benefitsandadversesideeffectsofmitigation.Estimatesatthehighendofthesecostrangesarefrommodelsthatarerelativelyinflexibletoachievethedeepemissionsreductionsthatwouldberequiredinthelongruntomeetthesegoalsand/orincludeassumptionsaboutmarketimperfectionsthatwouldraisecosts.{WGIIITableSPM.2,FigureTS.12,6.3.6,Figure6.21}levelsofabout450ppmCO2-eqtoabout500ppmCO2-eq)(Figure3.3,whichthereisasingleglobalcarbonprice,andinwhichallkeytech-3leftpanel).ScenarioswithGHGemissionlevelsofabove55GtCO2-eq/yrnologiesareavailablehavebeenusedasacost-effectivebenchmarkrequiresubstantiallyhigherratesofemissionsreductionsbetweenforestimatingmacroeconomicmitigationcosts(Figure3.4).Under2030and2050(medianestimateof6%/yrascomparedto3%/yrintheseassumptions,mitigationscenariosthatarelikelytolimitwarm-cost-effectivescenarios;Figure3.3,middlepanel);muchmorerapidingtobelow2°Cthroughthe21stcenturyrelativetopre-industrialscale-upofzeroandlow-carbonenergyoverthisperiod(morethanalevelsentaillossesinglobalconsumption—notincludingbenefitsoftriplingcomparedtoadoublingofthelow-carbonenergysharerela-reducedclimatechange(3.2)aswellasco-benefitsandadversesidetiveto2010;Figure3.3,rightpanel);alargerrelianceonCDRtech-effectsofmitigation(3.5,4.3)—of1to4%(median:1.7%)in2030,nologiesinthelongterm;andhighertransitionalandlong-term2to6%(median:3.4%)in2050,and3%to11%(median:4.8%)ineconomicimpacts(Table3.2).(3.5,4.3){WGIIISPM.4.1,TS.3.1,6.4,7.11}2100,relativetoconsumptioninbaselinescenariosthatgrowsany-wherefrom300%tomorethan900%overthecentury41.62Thesenum-Estimatedglobalemissionlevelsby2020basedontheCancúnberscorrespondtoanannualizedreductionofconsumptiongrowthbyPledgesarenotconsistentwithcost-effectivelong-termmitiga-0.04to0.14(median:0.06)percentagepointsoverthecenturyrelativetiontrajectoriesthatareatleastaboutaslikelyasnottolimittoannualizedconsumptiongrowthinthebaselinethatisbetweenwarmingtobelow2°Crelativetopre-industriallevels(21001.6%and3%peryear(Figure3.4).Intheabsenceorunderlimitedconcentrationlevelsofabout500ppmCO2-eqorbelow),butavailabilityofmitigationtechnologies(suchasbioenergy,CCS,andtheydonotprecludetheoptiontomeetthisgoal(highconfi-theircombinationBECCS,nuclear,windandsolar),mitigationcostsdence).TheCancúnPledgesarebroadlyconsistentwithcost-effectivecanincreasesubstantiallydependingonthetechnologyconsideredscenariosthatarelikelytolimittemperaturechangetobelow3°Crel-(Table3.2).Delayingadditionalmitigationreducesnear-termcostsativetopre-industriallevels.{WGIIISPM.4.1,6.4,13.13,FigureTS.11}butincreasesmitigationcostsinthemedium-tolong-term(Table3.2).Manymodelscouldnotlimitlikelywarmingtobelow2°CovertheEstimatesoftheaggregateeconomiccostsofmitigationvary21stcenturyrelativetopre-industriallevels,ifadditionalmitigationiswidelydependingonmethodologiesandassumptionsbutincreaseconsiderablydelayed,orifavailabilityofkeytechnologies,suchasbio-withthestringencyofmitigation(highconfidence).Scenariosinenergy,CCSandtheircombination(BECCS)arelimited(highconfidence)whichallcountriesoftheworldbeginmitigationimmediately,in(Table3.2).{WGIIISPM.4.1,TableSPM.2,TableTS.2,TS.3.1,6.3,6.6}41Mitigationcostrangescitedhererefertothe16thto84thpercentileoftheunderlyingsample(seeFigure3.4).85Topic3FuturePathwaysforAdaptation,MitigationandSustainableDevelopmentMitigationeffortsandassociatedcostareexpectedtovaryundertheassumptionofaglobalcarbonmarket,haveestimatedsub-acrosscountries.Thedistributionofcostscandifferfromthestantialglobalfinancialflowsassociatedwithmitigationinscenariosdistributionoftheactionsthemselves(highconfidence).Inglob-thatarelikelytomoreunlikelythanlikelytolimitwarmingduringtheallycost-effectivescenarios,themajorityofmitigationeffortstakes21stcenturytolessthan2°Crelativetopre-industriallevels.{WGIIIplaceincountrieswiththehighestfutureGHGemissionsinbaselineSPM.4.1,TS.3.1,Box3.5,4.6,6.3.6,Table6.4,Figure6.9,Figure6.27,scenarios.Somestudiesexploringparticulareffort-sharingframeworks,Figure6.28,Figure6.29,13.4.2.4}Table3.2Increaseinglobalmitigationcostsduetoeitherlimitedavailabilityofspecifictechnologiesordelaysinadditionalmitigationarelativetocost-effectivescenariosb.Theincreaseincostsisgivenforthemedianestimateandthe16thto84thpercentilerangeofthescenarios(inparentheses).Thesamplesizeofeachscenariosetisprovidedinthecolouredsymbolsc.Thecoloursofthesymbolsindicatethefractionofmodelsfromsystematicmodelcomparisonexercisesthatcouldsuccessfullyreachthetargetedconcentrationlevel.{WGIIITableSPM.2,TableTS.2,FigureTS.13,Figure6.24,Figure6.25}MitigationcostincreasesinscenarioswithMitigationcostincreasesduetodelay-limitedavailabilityoftechnologiesdedadditionalmitigationuntil2030[%increaseintotaldiscountedemitigationcosts[%increaseinmitigationcosts(2015–2100)relativetodefaulttechnologyassumptions]relativetoimmediatemitigation]2100noCCSnuclearphaseoutlimitedsolar/windlimitedbioenergymediumtermcostslongtermcostsconcentrations(2030–2050)(2050–2100)(ppmCO2-eq)138%7%6%64%44%37%450(29to297%)(4to18%)(2to29%)(2to78%)(16to82%)(430to480)}(44to78%)notavailablen.a.n.a.n.a.500(n.a.)(480to530)55039%13%8%18%}15%16%(530to580)(18to78%)(2to23%)(5to15%)(4to66%)(3to32%)(5to24%)580to650n.a.n.a.n.a.n.a.Symbollegend—fractionofmodelssuccessfulinproducingscenarios(numbersindicatethenumberofsuccessfulmodels)3:allmodelssuccessful:between50and80%ofmodelssuccessful:lessthan50%ofmodelssuccessful:between80and100%ofmodelssuccessfulNotes:aDelayedmitigationscenariosareassociatedwithgreenhousegasemissionofmorethan55GtCO2-eqin2030,andtheincreaseinmitigationcostsismeasuredrelativetocost-effectivemitigationscenariosforthesamelong-termconcentrationlevel.bCost-effectivescenariosassumeimmediatemitigationinallcountriesandasingleglobalcarbonprice,andimposenoadditionallimitationsontechnologyrelativetothemodels’defaulttechnologyassumptions.cTherangeisdeterminedbythecentralscenariosencompassingthe16thto84thpercentilerangeofthescenarioset.Onlyscenarioswithatimehorizonuntil2100areincluded.Somemodelsthatareincludedinthecostrangesforconcentrationlevelsabove530ppmCO2-eqin2100couldnotproduceassociatedscenariosforconcentrationlevelsbelow530ppmCO2-eqin2100withassumptionsaboutlimitedavailabilityoftechnologiesand/ordelayedadditionalmitigation.dNoCCS:carbondioxidecaptureandstorageisnotincludedinthesescenarios.Nuclearphaseout:noadditionofnuclearpowerplantsbeyondthoseunderconstruction,andoperationofexistingplantsuntiltheendoftheirlifetime.LimitedSolar/Wind:amaximumof20%globalelectricitygenerationfromsolarandwindpowerinanyyearofthesescenarios.LimitedBioenergy:amaximumof100EJ/yrmodernbioenergysupplyglobally(modernbioenergyusedforheat,power,combinationsandindustrywasaround18EJ/yrin2008).EJ=Exajoule=1018Joule.ePercentageincreaseofnetpresentvalueofconsumptionlossesinpercentofbaselineconsumption(forscenariosfromgeneralequilibriummodels)andabatementcostsinpercentofbaselinegrossdomesticproduct(GDP,forscenariosfrompartialequilibriummodels)fortheperiod2015–2100,discountedat5%peryear.86FuturePathwaysforAdaptation,MitigationandSustainableDevelopmentTopic3Box3.2GreenhouseGasMetricsandMitigationPathwaysIntroductionThisboxfocusesonemission-basedmetricsthatareusedforcalculatingCO2-equivalentemissionsfortheformulationandevaluationofmitigationstrategies.Theseemissionmetricsaredistinctfromtheconcentration-basedmetricusedinSYR(CO2-equivalentconcen-tration).ForanexplanationofCO2-equivalentemissionsandCO2-equivalentconcentrations,seeGlossary.Emissionmetricsfacilitatemulti-componentclimatepoliciesbyallowingemissionsofdifferentgreenhousegases(GHGs)andotherclimateforcingagentstobeexpressedinacommonunit(so-called‘CO2-equivalentemissions’).TheGlobalWarmingPotential(GWP)wasintroducedintheIPCCFirstAssessmentReport,whereitwasalsousedtoillustratethedifficultiesincomparingcomponentswithdifferingphysicalpropertiesusingasinglemetric.The100-yearGWP(GWP100)wasadoptedbytheUnitedNationsFrameworkConventiononClimateChange(UNFCCC)anditsKyotoProtocolandisnowusedwidelyasthedefaultmetric.Itisonlyoneofseveralpossibleemissionmetricsandtimehorizons.{WGI8.7,WGIII3.9}Thechoiceofemissionmetricandtimehorizondependsontypeofapplicationandpolicycontext;hence,nosinglemetricisoptimalforallpolicygoals.Allmetricshaveshortcomings,andchoicescontainvaluejudgments,suchastheclimateeffectcon-sideredandtheweightingofeffectsovertime(whichexplicitlyorimplicitlydiscountsimpactsovertime),theclimatepolicygoalandthedegreetowhichmetricsincorporateeconomicoronlyphysicalconsiderations.Therearesignificantuncertaintiesrelatedtometrics,andthemagnitudesoftheuncertaintiesdifferacrossmetrictypeandtimehorizon.Ingeneral,theuncertaintyincreasesformetricsalongthecause–effectchainfromemissiontoeffects.{WGI8.7,WGIII3.9}Theweightassignedtonon-CO2climateforcingagentsrelativetoCO2dependsstronglyonthechoiceofmetricandtimehorizon(robustevidence,highagreement).GWPcomparescomponentsbasedonradiativeforcing,integrateduptoachosentimehorizon.GlobalTemperaturechangePotential(GTP;seeGlossary)isbasedonthetemperatureresponseataspecificpointintimewithnoweightontemperatureresponsebeforeorafterthechosenpointintime.Adoptionofafixedhorizonof,forexample,20,100or500yearsforthesemetricswillinevitablyputnoweightonclimateoutcomesbeyondthetimehorizon,whichissignificantforCO2aswellasotherlong-livedgases.Thechoiceoftimehorizonmarkedlyaffectstheweightingespeciallyofshort-livedclimateforcingagents,suchasmethane(CH4)(seeBox3.2,Table1;Box3.2,Figure1a).Forsomemetrics(e.g.,thedynamicGTP;seeGlossary),theweightingchangesovertimeasachosentargetyearisapproached.{WGI8.7,WGIII3.9}Box3.2,Table1ExamplesofemissionmetricvaluesfromWGIa.3GWPGTPLifetime(yr)CumulativeforcingCumulativeforcingTemperatureTemperatureover20yearsover100yearschangeafter20changeafter100yearsyearsCO2b1111CH412.48428674N2O121.0264265277234CF450,000.04880663052708040HFC-152a1.550613817419Notes:aGlobalWarmingPotential(GWP)valueshavebeenupdatedinsuccessiveIPCCreports;theAR5GWP100valuesaredifferentfromthoseadoptedfortheKyotoProtocol’sFirstCommitmentPeriodwhicharefromtheIPCCSecondAssessmentReport(SAR).Notethatforconsistency,equivalentCO2emissionsgivenelsewhereinthisSynthesisReportarealsobasedonSAR,notAR5values.ForacomparisonofemissionsusingSARandAR5GWP100valuesfor2010emissions,seeFigure1.6.bNosinglelifetimecanbegivenforCO2.{WGIBox6.1,6.1.1,8.7}Thechoiceofemissionmetricaffectsthetimingandemphasisplacedonabatingshort-andlong-livedclimateforcingagents.Formostmetrics,globalcostdifferencesaresmallunderscenariosofglobalparticipationandcost-minimizingmitigationpathways,butimplicationsforsomeindividualcountriesandsectorscouldbemoresignificant(mediumevi-dence,highagreement).Differentmetricsandtimehorizonssignificantlyaffectthecontributionsfromvarioussources/sectorsandcomponents,particularlyshort-livedclimateforcingagents(Box3.2,Figure1b).Afixedtimeindependentmetricthatgiveslessweighttoshort-livedagentssuchasCH4(e.g.,usingGTP100insteadofGWP100)wouldrequireearlierandmorestringentCO2abatementtoachievethesameclimateoutcomefor2100.Usingatime-dependentmetric,suchasadynamicGTP,leadstolessCH4mitigation87Topic3FuturePathwaysforAdaptation,MitigationandSustainableDevelopmentBox3.2(continued)intheneartermbuttomoreinthelongtermasthetargetdateisbeingapproached.Thisimpliesthatforsome(short-lived)agents,themetricchoiceinfluencesthechoiceofpoliciesandthetimingofmitigation(especiallyforsectorsandcountrieswithhighnon-CO2emissionlevels).{WGI8.7,WGIII6.3}(a)Weightingofcurrentemissionsovertime1.8Integratedradiativeforcing1.41.6(normalized)1.41.21.2Temperatureresponse(normalized)110.8CO20.8CO20.6CH40.4CH40.6N2O0.2N2O200000.40.2050100150200050100150YearsafteremissionsYearsafteremissions(b)ContributionsbysectorstototalGHGemissionsusingdifferentmetricsGWP100GWP20GTP1006.7%7.2%13%Forestryand16%Agricultureotherlanduse8.2%14%11%22%30%Buildings21%6.2%6.3%Electricityand17%heatproduction3Transport24%5.7%14%9.8%17%Industry21%11%Otherenergy20%Box3.2,Figure1Implicationsofmetricchoicesontheweightingofgreenhousegas(GHG)emissionsandcontributionsbysectorsforillustrativetimehorizons.Panel(a):integratedradiativeforcing(leftpanel)andwarmingresultingatagivenfuturepointintime(rightpanel)fromglobalnetemissionsofcarbondioxide(CO2),methane(CH4)andnitrousoxide(N2O)intheyear2010(andnoemissionsthereafter),fortimehorizonsofupto200years.IntegratedradiativeforcingisusedinthecalculationofGlobalWarmingPotentials(GWP),whilethewarmingatafuturepointintimeisusedinthecalculationofGlobalTemperaturechangePotentials(GTP).Radiativeforcingandwarmingwerecalculatedbasedonglobal2010emissiondatafromWGIII5.2andabsoluteGWPsandabsoluteGTPsfromWGI8.7,normalizedtotheintegratedradiativeforcingandwarming,respectively,after100years,dueto2010netCO2emissions.Panel(b):Illustrativeexamplesshowingcontributionsfromdifferentsectorstototalmetric-weightedglobalGHGemissionsintheyear2010,calculatedusing100-yearGWP(GWP100,left),20-yearGWP(GWP20,middle)or100-yearGTP(GTP100,right)andtheWGIII2010emissionsdatabase.{WGIII5.2}NotethatpercentagesdifferslightlyfortheGWP100caseifvaluesfromtheIPCCSecondAssessmentReportareused;seeTopic1,Figure1.7.SeeWGIIIfordetailsofactivitiesresultinginemissionsineachsector.88FuturePathwaysforAdaptation,MitigationandSustainableDevelopmentTopic3Box3.3CarbonDioxideRemovalandSolarRadiationManagementGeoengineeringTechnologies—IntroductionPossibleRoles,Options,RisksandStatusGeoengineeringreferstoabroadsetofmethodsandtechnologiesoperatingonalargescalethataimtodeliberatelyaltertheclimatesysteminordertoalleviatetheimpactsofclimatechange.Mostmethodsseektoeitherreducetheamountofabsorbedsolarenergyintheclimatesystem(SolarRadiationManagement,SRM)orincreasetheremovalofcarbondioxide(CO2)fromtheatmospherebysinkstoalterclimate(CarbonDioxideRemoval,CDR,seeGlossary).Limitedevidenceprecludesacomprehensiveassessmentoffeasi-bility,cost,sideeffectsandenvironmentalimpactsofeitherCDRorSRM.{WGISPME.8,6.5,7.7,WGII6.4,Table6-5,Box20-4,WGIIITS.3.1.3,6.9}CDRplaysamajorroleinmanymitigationscenarios.Bioenergywithcarbondioxidecaptureandstorage(BECCS)andafforesta-tionaretheonlyCDRmethodsincludedinthesescenarios.CDRtechnologiesareparticularlyimportantinscenariosthattemporarilyovershootatmosphericconcentrations,buttheyarealsoprevalentinmanyscenarioswithoutovershoottocompensateforresidualemissionsfromsectorswheremitigationismoreexpensive.Similartomitigation,CDRwouldneedtobedeployedonalargescaleandoveralongtimeperiodtobeabletosignificantlyreduceCO2concentrations(seeSection3.1).{WGII6.4,WGIIISPM4.1,TS.3.1.2,TS3.1.3,6.3,6.9}SeveralCDRtechniquescouldpotentiallyreduceatmosphericgreenhousegas(GHG)levels.However,therearebiogeo-chemical,technicalandsocietallimitationsthat,tovaryingdegrees,makeitdifficulttoprovidequantitativeestimatesofthepotentialforCDR.TheemissionmitigationfromCDRislessthantheremovedCO2,assomeCO2isreleasedfromthatprevi-ouslystoredinoceansandterrestrialcarbonreservoirs.Sub-seageologicstoragehasbeenimplementedonaregionalscale,withnoevidencetodateofoceanimpactfromleakage.TheclimaticandenvironmentalsideeffectsofCDRdependontechnologyandscale.Examplesareassociatedwithalteredsurfacereflectancefromafforestationandoceande-oxygenationfromoceanfertilization.MostterrestrialCDRtechniqueswouldinvolvecompetingdemandsforlandandcouldinvolvelocalandregionalrisks,whilemaritimeCDRtechniquesmayinvolvesignificantrisksforoceanecosystems,sothattheirdeploymentcouldposeadditionalchallengesforcoopera-tionbetweencountries.{WGI6.5,FAQ7.3,WGII6.4,Table6.5,WGIII6.9}SRMisuntested,andisnotincludedinanyofthemitigationscenarios,but,ifrealisable,couldtosomedegreeoffsetglobaltemperatureriseandsomeofitseffects.ItcouldpossiblyproviderapidcoolingincomparisontoCO2mitigation.ThereismediumconfidencethatSRMthroughstratosphericaerosolinjectionisscalabletocounterradiativeforcingfromatwofoldincreaseinCO2concentrationsandsomeoftheclimateresponsesassociatedwithwarming.Duetoinsufficientunderstandingthereis3noconsensusonwhetherasimilarlylargenegativecounterradiativeforcingcouldbeachievedfromcloudbrightening.Landalbedochangedoesnotappeartobeabletoproducealargecounterradiativeforcing.EvenifSRMcouldcountertheglobalmeanwarming,differencesinspatialpatternswouldremain.ThescarcityofliteratureonotherSRMtechniquesprecludestheirassessment.{WGI7.7,WGIIITS.3.1.3,6.9}Ifitweredeployed,SRMwouldentailnumerousuncertainties,sideeffects,risksandshortcomings.SeverallinesofevidenceindicatethatSRMwoulditselfproduceasmallbutsignificantdecreaseinglobalprecipitation(withlargerdifferencesonregionalscales).StratosphericaerosolSRMislikelytomodestlyincreaseozonelossesinthepolarstratosphere.SRMwouldnotpreventtheCO2effectsonecosystemsandoceanacidificationthatareunrelatedtowarming.Therecouldalsobeotherunanticipatedconsequences.ForallfuturescenariosconsideredinAR5,SRMwouldneedtoincreasecommensurately,tocountertheglobalmeanwarming,whichwouldexacerbatesideeffects.Additionally,ifSRMwereincreasedtosubstantiallevelsandthenterminated,thereishighconfidencethatsurfacetemperatureswouldriseveryrapidly(withinadecadeortwo).Thiswouldstresssystemsthataresensitivetotherateofwarming.{WGI7.6–7.7,FAQ7.3,WGII19.5,WGIII6.9}SRMtechnologiesraisequestionsaboutcosts,risks,governanceandethicalimplicationsofdevelopmentanddeploy-ment.Therearespecialchallengesemergingforinternationalinstitutionsandmechanismsthatcouldcoordinateresearchandpossiblyrestraintestinganddeployment.EvenifSRMwouldreducehuman-madeglobaltemperatureincrease,itwouldimplyspatialandtemporalredistributionsofrisks.SRMthusintroducesimportantquestionsofintragenerationalandintergenerationaljustice.ResearchonSRM,aswellasitseventualdeployment,hasbeensubjecttoethicalobjections.InspiteoftheestimatedlowpotentialcostsofsomeSRMdeploymenttechnologies,theywillnotnecessarilypassabenefit–costtestthattakesaccountoftherangeofrisksandsideeffects.ThegovernanceimplicationsofSRMareparticularlychallenging,especiallyasunilateralactionmightleadtosignificanteffectsandcostsforothers.{WGIIITS.3.1.3,1.4,3.3,6.9,13.4}89Topic3FuturePathwaysforAdaptation,MitigationandSustainableDevelopment3.5Interactionamongmitigation,adaptationBothadaptationandmitigationcanbringsubstantialco-benefitsandsustainabledevelopment(mediumconfidence).Examplesofactionswithco-benefitsinclude(i)improvedairquality(seeFigure3.5);(ii)enhancedenergysecurity,Climatechangeisathreattoequitableandsustain-(iii)reducedenergyandwaterconsumptioninurbanareasthroughabledevelopment.Adaptation,mitigationandsus-greeningcitiesandrecyclingwater;(iv)sustainableagricultureandtainabledevelopmentarecloselyrelated,withpoten-forestry;and(v)protectionofecosystemsforcarbonstorageandothertialforsynergiesandtrade-offs.ecosystemservices.{WGIISPMC-1,WGIIISPM.4.1}ClimatechangeposesanincreasingthreattoequitableandStrategiesandactionscanbepursuednowthatwillmovesustainabledevelopment(highconfidence).Someclimate-relatedtowardsclimate-resilientpathwaysforsustainabledevelop-impactsondevelopmentarealreadybeingobserved.Climatechangement,whileatthesametimehelpingtoimprovelivelihoods,isathreatmultiplier.Itexacerbatesotherthreatstosocialandnaturalsocialandeconomicwell-beingandeffectiveenvironmentalsystems,placingadditionalburdensparticularlyonthepoorandcon-management(highconfidence).Prospectsforclimate-resilientstrainingpossibledevelopmentpathsforall.Developmentalongcur-pathwaysarerelatedfundamentallytowhattheworldaccomplishesrentglobalpathwayscancontributetoclimateriskandvulnerability,withclimatechangemitigation(highconfidence).Sincemitigationfurthererodingthebasisforsustainabledevelopment.{WGIISPMB-2,reducestherateaswellasthemagnitudeofwarming,italsoincreases2.5,10.9,13.1–13.3,20.1,20.2,20.6,WGIIISPM.2,4.2}thetimeavailableforadaptationtoaparticularlevelofclimatechange,potentiallybyseveraldecades.DelayingmitigationactionsAligningclimatepolicywithsustainabledevelopmentrequiresmayreduceoptionsforclimate-resilientpathwaysinthefuture.{WGIIattentiontobothadaptationandmitigation(highconfidence).SPMC-2,20.2,20.6.2}Interactionamongadaptation,mitigationandsustainabledevelop-mentoccursbothwithinandacrossregionsandscales,ofteninthecontextofmultiplestressors.Someoptionsforrespondingtoclimatechangecouldimposerisksofotherenvironmentalandsocialcosts,haveadversedistributionaleffectsanddrawresourcesawayfromotherdevelopmentpriorities,includingpovertyeradication.{WGII2.5,8.4,9.3,13.3–13.4,20.2–20.4,21.4,25.9,26.8,WGIIISPM.2,4.8,6.6}3Co-beneﬁtsofclimatechangemitigationforairqualityImpactofstringentclimatepolicyonairpollutantemissions(Global,2005–2050)500BlackCarbonSulfurDioxidePercentileChangefrom2005(%)IncreasedMaxpollution75thDecreasedMedianpollution25thMinIndividualScenarios–50–100BaselineStringentclimatepolicyBaselineStringentclimatepolicyFigure3.5Airpollutantemissionlevelsofblackcarbon(BC)andsulfurdioxide(SO2)by2050,relativeto2005(0=2005levels).Baselinescenarioswithoutadditionaleffortstoreducegreenhousegas(GHG)emissionsbeyondthoseinplacetodayarecomparedtoscenarioswithstringentmitigationpolicies,whichareconsistentwithreachingabout450toabout500(430to530)ppmCO2-eqconcentrationlevelsby2100.{WGIIISPM.6,TS.14,Figure6.33}90FuturePathwaysforAdaptation,MitigationandSustainableDevelopmentTopic3Box3.4Co-benefitsandAdverseSideeffectsIntroductionAgovernmentpolicyorameasureintendedtoachieveoneobjectiveoftenaffectsotherobjectives,eitherpositivelyornegatively.Forexample,mitigationpoliciescaninfluencelocalairquality(seeFigure3.5).Whentheeffectsarepositivetheyarecalled‘co-benefits’,alsoreferredtoas‘ancillarybenefits’.Negativeeffectsarereferredtoas‘adversesideeffects’.Somemeasuresarelabelled‘noorlowregret’whentheirco-benefitsaresufficienttojustifytheirimplementation,evenintheabsenceofimmediatedirectbenefits.Co-benefitsandadversesideeffectscanbemeasuredinmonetaryornon-monetaryunits.Theeffectofco-benefitsandadversesideeffectsfromclimatepoliciesonoverallsocialwelfarehasnotyetbeenquantitativelyexamined,withtheexceptionofafewrecentmulti-objectivestudies.Manyofthesehavenotbeenwellquantified,andeffectscanbecaseandsite-specificastheywilldependonlocalcircumstances.{WGII11.9,16.3.1,17.2,20.4.1,WGIIIBoxTS.11,3.6,5.7}Co-benefitsofmitigationcouldaffectachievementofotherobjectives,suchasthoserelatedtoenergysecurity,airqual-ity,effortstoaddressecosystemimpacts,incomedistribution,laboursupplyandemploymentandurbansprawl(seeTable4.2andTable4.5).Intheabsenceofcomplementarypolicies,however,somemitigationmeasuresmayhaveadversesideeffects(atleastintheshortterm),forexampleonbiodiversity,foodsecurity,energyaccess,economicgrowthandincomedistribu-tion.Theco-benefitsofadaptationpoliciesmayincludeimprovedaccesstoinfrastructureandservices,extendededucationandhealthsystems,reduceddisasterlosses,bettergovernanceandothers.{WGII4.4.4,11.9,15.2,17.2,20.3.3,20.4.1,WGIIIBoxTS.11,6.6}Comprehensivestrategiesinresponsetoclimatechangethatareconsistentwithsustainabledevelopmenttakeintoaccounttheco-benefits,adversesideeffectsandrisksthatmayarisefrombothadaptationandmitigationoptions.Theassessmentofoverallsocialwelfareimpactsiscomplicatedbythisinteractionbetweenclimatechangeresponseoptionsandpre-existingnon-climatepolicies.Forexample,intermsofairquality,thevalueoftheextratonneofsulfurdioxide(SO2)reductionthatoccurswithclimatechangemitigationthroughreducedfossilfuelcombustiondependsgreatlyonthestringencyofSO2controlpolicies.IfSO2policyisweak,thevalueofSO2reductionsmaybelarge,butifSO2policyisstringent,itmaybenearzero.Similarly,intermsofadaptationanddisasterriskmanagement,weakpoliciescanleadtoanadaptationdeficitthatincreaseshumanandeconomiclossesfromnaturalclimatevariability.‘Adaptationdeficit’referstothelackofcapacitytomanageadverseimpactsofcurrentclimatevari-ability.Anexistingadaptationdeficitincreasesthebenefitsofadaptationpoliciesthatimprovethemanagementofclimatevariabilityandchange.{WGII20.4.1,WGIIIBoxTS.11,6.3}3913Introduction4AdaptationandMitigation93Topic4AdaptationandMitigationTopic4:AdaptationandMitigationManyadaptationandmitigationoptionscanhelpaddressclimatechange,butnosingleoptionissufficientbyitself.Effectiveimplementationdependsonpoliciesandcooperationatallscalesandcanbeenhancedthroughintegratedresponsesthatlinkmitigationandadaptationwithothersocietalobjectives.Topic3demonstratestheneedandstrategicconsiderationsforbothadaptationandglobal-scalemitigationtomanagerisksfromclimatechange.Buildingontheseinsights,Topic4presentsnear-termresponseoptionsthatcouldhelpachievesuchstrategicgoals.Near-termadaptationandmitigationactionswilldifferacrosssectorsandregions,reflectingdevelopmentstatus,responsecapacitiesandnear-andlong-termaspirationswithregardtobothclimateandnon-climateoutcomes.Becauseadaptationandmitigationinevitablytakeplaceinthecontextofmultipleobjectives,particularattentionisgiventotheabilitytodevelopandimplementintegratedapproachesthatcanbuildonco-benefitsandmanagetrade-offs.4.1Commonenablingfactorsandconstraintslifestylescancontributetohigherenergyandresourceconsumption,foradaptationandmitigationresponsesdrivinggreaterenergyproductionandGHGemissionsandincreasingmitigationcosts.Incontrast,emissionscanbesubstantiallyloweredAdaptationandmitigationresponsesareunderpinnedthroughchangesinconsumptionpatterns(see4.3fordetails).Thebycommonenablingfactors.Theseincludeeffectivesocialacceptabilityand/oreffectivenessofclimatepoliciesareinflu-institutionsandgovernance,innovationandinvest-encedbytheextenttowhichtheyincentivizeordependonregionallymentsinenvironmentallysoundtechnologiesandappropriatechangesinlifestylesorbehaviours.Similarly,livelihoodsinfrastructure,sustainablelivelihoodsandbehaviouralthatdependonclimate-sensitivesectorsorresourcesmaybepar-andlifestylechoices.ticularlyvulnerabletoclimatechangeandclimatechangepolicies.EconomicdevelopmentandurbanizationoflandscapesexposedtoclimatehazardsmayincreasetheexposureofhumansettlementsandInnovationandinvestmentsinenvironmentallysoundinfra-reducetheresilienceofnaturalsystems.{WGIISPMA-2,SPMB-2,structureandtechnologiescanreducegreenhousegas(GHG)TableSPM.1,TSA-1,TSA-2,TSC-1,TSC-2,16.3.2.7,WGIIISPM.4.2,emissionsandenhanceresiliencetoclimatechange(veryhighTS.2.2,4.2}confidence).Innovationandchangecanexpandtheavailabilityand/oreffectivenessofadaptationandmitigationoptions.Forexample,Formanyregionsandsectors,enhancedcapacitiestomitigateinvestmentsinlow-carbonandcarbon-neutralenergytechnologiesandadaptarepartofthefoundationessentialformanag-canreducetheenergyintensityofeconomicdevelopment,thecarboningclimatechangerisks(highconfidence).Suchcapacitiesareintensityofenergy,GHGemissions,andthelong-termcostsofmit-place-andcontext-specificandthereforethereisnosingleapproachigation.Similarly,newtechnologiesandinfrastructurecanincreaseforreducingriskthatisappropriateacrossallsettings.Forexample,theresilienceofhumansystemswhilereducingadverseimpactsondevelopingnationswithlowincomelevelshavethelowestfinan-naturalsystems.Investmentsintechnologyandinfrastructurerelyoncial,technologicalandinstitutionalcapacitiestopursuelow-carbon,anenablingpolicyenvironment,accesstofinanceandtechnologyclimate-resilientdevelopmentpathways.Althoughdeveloped4andbroadereconomicdevelopmentthatbuildscapacity(Table4.1,nationsgenerallyhavegreaterrelativecapacitytomanagetheSection4.4).{WGIISPMC-2,TableSPM.1,TableTS.8,WGIIISPM.4.1,risksofclimatechange,suchcapacitydoesnotnecessarilytrans-TableSPM.2,TS.3.1.1,TS3.1.2,TS.3.2.1}lateintotheimplementationofadaptationandmitigationoptions.{WGIISPMB-1,SPMB-2,TSB-1,TSB-2,16.3.1.1,16.3.2,16.5,WGIIIAdaptationandmitigationareconstrainedbytheinertiaofSPM.5.1,TS.4.3,TS.4.5,4.6}globalandregionaltrendsineconomicdevelopment,GHGemis-sions,resourceconsumption,infrastructureandsettlementpat-Improvinginstitutionsaswellasenhancingcoordinationterns,institutionalbehaviourandtechnology(mediumevidence,andcooperationingovernancecanhelpovercomeregionalhighagreement).SuchinertiamaylimitthecapacitytoreduceGHGconstraintsassociatedwithmitigation,adaptationanddisas-emissions,remainbelowparticularclimatethresholdsoravoidadverseterriskreduction(veryhighconfidence).Despitethepresenceimpacts(Table4.1).Someconstraintsmaybeovercomethroughnewofawidearrayofmultilateral,nationalandsub-nationalinstitu-technologies,financialresources,increasedinstitutionaleffectivenesstionsfocusedonadaptationandmitigation,globalGHGemissionsandgovernanceorchangesinsocialandculturalattitudesandbehav-continuetoincreaseandidentifiedadaptationneedshavenotiours.{WGIISPMC-1,WGIIISPM.3,SPM.4.2,TableSPM.2}beenadequatelyaddressed.Theimplementationofeffectiveadap-tationandmitigationoptionsmaynecessitatenewinstitutionsVulnerabilitytoclimatechange,GHGemissions,andthecapac-andinstitutionalarrangementsthatspanmultiplescales(mediumityforadaptationandmitigationarestronglyinfluencedbyconfidence)(Table4.1).{WGIISPMB-2,TSC-1,16.3.2.4,16.8,livelihoods,lifestyles,behaviourandculture(mediumevidence,WGIIISPM.4.2.5,SPM.5.1,SPM.5.2,TS.1,TS.3.1.3,TS.4.1,TS.4.2,mediumagreement)(Table4.1).Shiftstowardmoreenergy-intensiveTS.4.4}94AdaptationandMitigationTopic4Table4.1CommonfactorsthatconstraintheimplementationofadaptationandmitigationoptionsConstrainingFactorPotentialImplicationsforAdaptationPotentialImplicationsforMitigationIntroductionAdverseexternalitiesofpopula-Increaseexposureofhumanpopulationstoclimatevariabilitytiongrowthandurbanizationandchangeaswellasdemandsfor,andpressureson,naturalDriveeconomicgrowth,energydemandandenergyconsumption,Deficitsofknowledge,edu-resourcesandecosystemservices{WGII16.3.2.3,Box16-3}resultinginincreasesingreenhousegasemissions{WGIIISPM.3}cationandhumancapitalReducenational,institutionalandindividualperceptionsoftherisksposedbyclimatechangeaswellasthecostsandReducenational,institutionalandindividualriskperception,Divergencesinsocialandculturalbenefitsofdifferentadaptationoptions{WGII16.3.2.1}willingnesstochangebehaviouralpatternsandpracticesandtoattitudes,valuesandbehavioursadoptsocialandtechnologicalinnovationstoreduceemissionsReducesocietalconsensusregardingclimateriskandtherefore{WGIIISPM.3,SPM.5.1,2.4.1,3.10.1.5,4.3.5,9.8,11.8.1}Challengesingovernanceanddemandforspecificadaptationpoliciesandmeasures{WGIIinstitutionalarrangements16.3.2.7}Influenceemissionpatterns,societalperceptionsoftheutilityofmitigationpoliciesandtechnologies,andwilling-LackofaccesstonationalandReducetheabilitytocoordinateadaptationpoliciesandnesstopursuesustainablebehavioursandtechnologiesinternationalclimatefinancemeasuresandtodelivercapacitytoactorstoplanandimplement{WGIIISPM.2,2.4.5,2.6.6.1,3.7.2.2,3.9.2,4.3.4,5.5.1}Inadequatetechnologyadaptation{WGII16.3.2.8}Underminepolicies,incentivesandcooperationregardingtheInsufficientqualityand/orquan-Reducesthescaleofinvestmentinadaptationpoliciesanddevelopmentofmitigationpoliciesandtheimplementationoftityofnaturalresourcesmeasuresandthereforetheireffectiveness{WGII16.3.2.5}efficient,carbon-neutralandrenewableenergytechnologiesAdaptationanddevelopmentdeficits{WGIIISPM.3,SPM.5.2,4.3.2,6.4.3,14.1.3.1,14.3.2.2,15.12.2,Reducestherangeofavailableadaptationoptionsaswellas16.5.3}Inequalitytheireffectivenessinreducingoravoidingriskfromincreasingratesormagnitudesofclimatechange{WGII16.3.2.1}Reducesthecapacityofdevelopedand,particularly,developingReducethecopingrangeofactors,vulnerabilitytonon-climaticnationstopursuepoliciesandtechnologiesthatreduceemissi-factorsandpotentialcompetitionforresourcesthatenhancesons.{WGIIITS.4.3,12.6.2,16.2.2.2}vulnerability{WGII16.3.2.3}IncreasevulnerabilitytocurrentclimatevariabilityaswellasSlowstherateatwhichsocietycanreducethecarbonintensityoffutureclimatechange{WGIITSA-1,TableTS5,16.3.2.4}energyservicesandtransitiontowardlow-carbonandcarbon-neutraltechnologies{WGIIITS.3.1.3,4.3.6,6.3.2.2,11.8.4}Placestheimpactsofclimatechangeandtheburdenofadapta-tiondisproportionatelyonthemostvulnerableand/ortransfersReducethelong-termsustainabilityofdifferentenergythemtofuturegenerations{WGIITSB-2,BoxTS4,Box13-1,technologies{WGIII4.3.7,4.4.1,11.8.3}16.7}Reducemitigativecapacityandundermineinternationalcooperativeeffortsonclimateowingtoacontentiouslegacyofcooperationondevelopment{WGIII4.3.1,4.6.1}Constrainstheabilityfordevelopingnationswithlowincomelevels,ordifferentcommunitiesorsectorswithinnations,tocontributetogreenhousegasmitigation{WGIII4.6.2.1}4.2Responseoptionsforadaptation•Social,ecologicalassetandinfrastructuredevelopment•Technologicalprocessoptimization•IntegratednaturalresourcesmanagementAdaptationoptionsexistinallsectors,buttheir•Institutional,educationalandbehaviouralchangeorreinforcementcontextforimplementationandpotentialtoreduceclimate-relatedrisksdiffersacrosssectorsandregions.•Financialservices,includingrisktransfer4Someadaptationresponsesinvolvesignificant•Informationsystemstosupportearlywarningandproactiveplanningco-benefits,synergiesandtrade-offs.IncreasingThereisincreasingrecognitionofthevalueofsocial(includinglocalandclimatechangewillincreasechallengesformanyindigenous),institutional,andecosystem-basedmeasuresandoftheextentadaptationoptions.ofconstraintstoadaptation.Effectivestrategiesandactionsconsiderthepotentialforco-benefitsandopportunitieswithinwiderstrategicgoalsanddevelopmentplans.{WGIISPMA-2,SPMC-1,TSA-2,6.4,8.3,9.4,15.3}People,governmentsandtheprivatesectorarestartingtoadapttoachangingclimate.SincetheIPCCFourthAssessmentReportOpportunitiestoenableadaptationplanningandimplementation(AR4),understandingofresponseoptionshasincreased,withexistinallsectorsandregions,withdiversepotentialandapproachesimprovedknowledgeoftheirbenefits,costsandlinkstosus-dependingoncontext.Theneedforadaptationalongwithasso-tainabledevelopment.Adaptationcantakeavarietyofapproachesciatedchallengesisexpectedtoincreasewithclimatechangedependingonitscontextinvulnerabilityreduction,disasterriskman-(veryhighconfidence).Examplesofkeyadaptationapproachesagementorproactiveadaptationplanning.Theseinclude(seeTable4.2forparticularsectors,includingconstraintsandlimits,aresummarizedforexamplesanddetails):below.{WGIISPMB,SPMC,16.4,16.6,17.2,19.6,19.7,Table16.3}95Topic4AdaptationandMitigationTable4.2Approachesformanagingtherisksofclimatechangethroughadaptation.Theseapproachesshouldbeconsideredoverlappingratherthandiscrete,andtheyareoftenpursuedsimultaneously.Examplesarepresentedinnospeciﬁcorderandcanberelevanttomorethanonecategory.{WGIITableSPM.1}OverlappingCategoryExamplesWGIIReferencesApproachesVulnerability&ExposureReductionHumanImprovedaccesstoeducation,nutrition,healthfacilities,energy,safehousing&settlementstructures,8.3,9.3,13.1-3,14.2-3,22.4development&socialsupportstructures;Reducedgenderinequality&marginalizationinotherforms.throughdevelopment,planning&practicesincludingmanylow-regretsmeasuresPovertyalleviationImprovedaccessto&controloflocalresources;Landtenure;Disasterriskreduction;Socialsafetynets8.3-4,9.3,13.1-3Adaptation&socialprotection;Insuranceschemes.includingincremental&transformationaladjustmentsLivelihoodsecurityIncome,asset&livelihooddiversification;Improvedinfrastructure;Accesstotechnology&decision-7.5,9.4,13.1-3,22.3-4,23.4,26.5,makingfora;Increaseddecision-makingpower;Changedcropping,livestock&aquaculturepractices;27.3,29.6,TableSM24-7Relianceonsocialnetworks.DisasterriskEarlywarningsystems;Hazard&vulnerabilitymapping;Diversifyingwaterresources;Improved8.2-4,11.7,14.3,15.4,22.4,24.4,managementdrainage;Flood&cycloneshelters;Buildingcodes&practices;Storm&wastewatermanagement;26.6,28.4,Box25-1,Table3-3Transport&roadinfrastructureimprovements.EcosystemMaintainingwetlands&urbangreenspaces;Coastalafforestation;Watershed&reservoir4.3-4,8.3,22.4,Table3-3,Boxes4-3,managementmanagement;Reductionofotherstressorsonecosystems&ofhabitatfragmentation;Maintenance8-2,15-1,25-8,25-9&CC-EAofgeneticdiversity;Manipulationofdisturbanceregimes;Community-basednaturalresourcemanagement.Spatialorland-useProvisioningofadequatehousing,infrastructure&services;Managingdevelopmentinfloodprone&4.4,8.1-4,22.4,23.7-8,27.3,Box25-8planningotherhighriskareas;Urbanplanning&upgradingprograms;Landzoninglaws;Easements;Protectedareas.Engineered&built-environmentoptions:Seawalls&coastalprotectionstructures;Floodlevees;3.5-6,5.5,8.2-3,10.2,11.7,23.3,Waterstorage;Improveddrainage;Flood&cycloneshelters;Buildingcodes&practices;Storm&24.4,25.7,26.3,26.8,Boxes15-1,wastewatermanagement;Transport&roadinfrastructureimprovements;Floatinghouses;Powerplant25-1,25-2&25-8&electricitygridadjustments.Technologicaloptions:Newcrop&animalvarieties;Indigenous,traditional&localknowledge,7.5,8.3,9.4,10.3,15.4,22.4,24.4,technologies&methods;Efficientirrigation;Water-savingtechnologies;Desalinisation;Conservation26.3,26.5,27.3,28.2,28.4,29.6-7,agriculture;Foodstorage&preservationfacilities;Hazard&vulnerabilitymapping&monitoring;EarlyBoxes20-5&25-2,Tables3-3&15-1warningsystems;Buildinginsulation;Mechanical&passivecooling;Technologydevelopment,transferStructural/physical&diffusion.Ecosystem-basedoptions:Ecologicalrestoration;Soilconservation;Afforestation&reforestation;4.4,5.5,6.4,8.3,9.4,11.7,15.4,22.4,Mangroveconservation&replanting;Greeninfrastructure(e.g.,shadetrees,greenroofs);Controlling23.6-7,24.4,25.6,27.3,28.2,29.7,overfishing;Fisheriesco-management;Assistedspeciesmigration&dispersal;Ecologicalcorridors;30.6,Boxes15-1,22-2,25-9,26-2Seedbanks,genebanks&otherexsituconservation;Community-basednaturalresourcemanagement.&CC-EAServices:Socialsafetynets&socialprotection;Foodbanks&distributionoffoodsurplus;Municipal3.5-6,8.3,9.3,11.7,11.9,22.4,29.6,servicesincludingwater&sanitation;Vaccinationprograms;Essentialpublichealthservices;EnhancedBox13-2emergencymedicalservices.Economicoptions:Financialincentives;Insurance;Catastrophebonds;Paymentsforecosystem8.3-4,9.4,10.7,11.7,13.3,15.4,17.5,services;Pricingwatertoencourageuniversalprovisionandcarefuluse;Microfinance;Disaster22.4,26.7,27.6,29.6,Box25-7contingencyfunds;Cashtransfers;Public-privatepartnerships.InstitutionalLaws&regulations:Landzoninglaws;Buildingstandards&practices;Easements;Waterregulations4.4,8.3,9.3,10.5,10.7,15.2,15.4,&agreements;Lawstosupportdisasterriskreduction;Lawstoencourageinsurancepurchasing;17.5,22.4,23.4,23.7,24.4,25.4,26.3,Definedpropertyrights&landtenuresecurity;Protectedareas;Fishingquotas;Patentpools&27.3,30.6,Table25-2,BoxCC-CRtechnologytransfer.National&governmentpolicies&programs:National&regionaladaptationplansincluding2.4,3.6,4.4,5.5,6.4,7.5,8.3,11.7,mainstreaming;Sub-national&localadaptationplans;Economicdiversification;Urbanupgrading15.2-5,22.4,23.7,25.4,25.8,26.8-9,programs;Municipalwatermanagementprograms;Disasterplanning&preparedness;Integrated27.3-4,29.6,Boxes25-1,25-2&25-9,waterresourcemanagement;Integratedcoastalzonemanagement;Ecosystem-basedmanagement;Tables9-2&17-14Community-basedadaptation.Educationaloptions:Awarenessraising&integratingintoeducation;Genderequityineducation;8.3-4,9.4,11.7,12.3,15.2-4,22.4,Extensionservices;Sharingindigenous,traditional&localknowledge;Participatoryactionresearch&25.4,28.4,29.6,Tables15-1&25-2sociallearning;Knowledge-sharing&learningplatforms.SocialInformationaloptions:Hazard&vulnerabilitymapping;Earlywarning&responsesystems;2.4,5.5,8.3-4,9.4,11.7,15.2-4,22.4,Systematicmonitoring&remotesensing;Climateservices;Useofindigenousclimateobservations;23.5,24.4,25.8,26.6,26.8,27.3,28.2,Participatoryscenariodevelopment;Integratedassessments.28.5,30.6,Table25-2,Box26-3TransformationBehaviouraloptions:Householdpreparation&evacuationplanning;Migration;Soil&water5.5,7.5,9.4,12.4,22.3-4,23.4,23.7,conservation;Stormdrainclearance;Livelihooddiversification;Changedcropping,livestock&25.7,26.5,27.3,29.6,TableSM24-7,aquaculturepractices;Relianceonsocialnetworks.Box25-5Practical:Social&technicalinnovations,behaviouralshifts,orinstitutional&managerialchangesthat8.3,17.3,20.5,Box25-5producesubstantialshiftsinoutcomes.SpheresofchangePolitical:Political,social,cultural&ecologicaldecisions&actionsconsistentwithreducing14.2-3,20.5,25.4,30.7,Table14-1vulnerability&risk&supportingadaptation,mitigation&sustainabledevelopment.Personal:Individual&collectiveassumptions,beliefs,values&worldviewsinfluencingclimate-change14.2-3,20.5,25.4,Table14-1responses.96AdaptationandMitigationTopic4Freshwaterresourcesreducedasthermalstressandoceanacidificationincrease.{WGIIAdaptivewatermanagementtechniques,includingscenarioSPMB-2,SPMAssessmentBoxSPM.2Table1,TSB-2,5.5,6.4,7.5,Introductionplanning,learning-basedapproachesandflexibleandlow-regret25.6.2,29.4,30.6-7,BoxCC-MB,BoxCC-CR}solutions,canhelpadjusttouncertainhydrologicalchangesduetoclimatechangeandtheirimpacts(limitedevidence,Foodproductionsystem/Ruralareashighagreement).Strategiesincludeadoptingintegratedwaterman-Adaptationoptionsforagricultureincludetechnologicalagement,augmentingsupply,reducingthemismatchbetweenwaterresponses,enhancingsmallholderaccesstocreditandothersupplyanddemand,reducingnon-climatestressors,strengtheningcriticalproductionresources,strengtheninginstitutionsatlocalinstitutionalcapacitiesandadoptingmorewater-efficienttechnologiestoregionallevelsandimprovingmarketaccessthroughtradeandwater-savingstrategies.{WGIISPMB-2,AssessmentBoxSPM.2reform(mediumconfidence).Responsestodecreasedfoodpro-Table1,SPMB-3,3.6,22.3–22.4,23.4,23.7,24.4,27.2–27.3,Box25-2}ductionandqualityinclude:developingnewcropvarietiesadaptedtochangesinCO2,temperature,anddrought;enhancingthecapacityforTerrestrialandfreshwaterecosystemsclimateriskmanagement;andoffsettingeconomicimpactsoflanduseManagementactionscanreducebutnoteliminaterisksofchange.Improvingfinancialsupportandinvestingintheproductionofimpactstoterrestrialandfreshwaterecosystemsduetoclimatesmall-scalefarmscanalsoprovidebenefits.Expandingagriculturalmar-change(highconfidence).Actionsincludemaintenanceofgeneticketsandimprovingthepredictabilityandreliabilityoftheworldtrad-diversity,assistedspeciesmigrationanddispersal,manipulationingsystemcouldresultinreducedmarketvolatilityandhelpmanageofdisturbanceregimes(e.g.,fires,floods)andreductionofotherfoodsupplyshortagescausedbyclimatechange.{WGIISPMB-2,stressors.Managementoptionsthatreducenon-climaticstressors,SPMB-3,7.5,9.3,22.4,22.6,25.9,27.3}suchashabitatmodification,overexploitation,pollutionandinvasivespecies,increasetheinherentcapacityofecosystemsandtheirspeciesUrbanareas/Keyeconomicsectorsandservicestoadapttoachangingclimate.OtheroptionsincludeimprovingearlyUrbanadaptationbenefitsfromeffectivemulti-levelgovern-warningsystemsandassociatedresponsesystems.Enhancedconnec-ance,alignmentofpoliciesandincentives,strengthenedlocaltivityofvulnerableecosystemsmayalsoassistautonomousadapta-governmentandcommunityadaptationcapacity,synergiestion.Translocationofspeciesiscontroversialandisexpectedtobecomewiththeprivatesectorandappropriatefinancingandinstitu-lessfeasiblewherewholeecosystemsareatrisk.{WGIISPMB-2,tionaldevelopment(mediumconfidence).EnhancingthecapacitySPMB-3,FigureSPM.5,TableTS.8,4.4,25.6,26.4,BoxCC-RF}oflow-incomegroupsandvulnerablecommunitiesandtheirpartner-shipswithlocalgovernmentscanalsobeaneffectiveurbanclimateCoastalsystemsandlow-lyingareasadaptationstrategy.ExamplesofadaptationmechanismsincludeIncreasingly,coastaladaptationoptionsincludethosebasedonlarge-scalepublic-privateriskreductioninitiativesandeconomicdiver-integratedcoastalzonemanagement,localcommunitypartici-sificationandgovernmentinsuranceforthenon-diversifiableportionpation,ecosystems-basedapproachesanddisasterriskreduc-ofrisk.Insomelocations,especiallyattheupperendofprojectedcli-tion,mainstreamedintorelevantstrategiesandmanagementmatechanges,responsescouldalsorequiretransformationalchangesplans(highconfidence).Theanalysisandimplementationofcoastalsuchasmanagedretreat.{WGIISPMB-2,8.3–8.4,24.4,24.5,26.8,adaptationhasprogressedmoresignificantlyindevelopedcountriesBox25-9}thanindevelopingcountries(highconfidence).TherelativecostsofcoastaladaptationareexpectedtovarystronglyamongandwithinHumanhealth,securityandlivelihoodsregionsandcountries.{WGIISPMB-2,SPMB-3,5.5,8.3,22.3,24.4,Adaptationoptionsthatfocusonstrengtheningexistingdeliv-26.8,Box25-1}erysystemsandinstitutions,aswellasinsuranceandsocialpro-Marinesystemsandoceanstectionstrategies,canimprovehealth,securityandlivelihoods4inthenearterm(highconfidence).ThemosteffectivevulnerabilityMarineforecastingandearlywarningsystemsaswellasreduc-reductionmeasuresforhealthintheneartermareprogrammesthatingnon-climaticstressorshavethepotentialtoreducerisksforimplementandimprovebasicpublichealthmeasuressuchasprovisionsomefisheriesandaquacultureindustries,butoptionsforuniqueofcleanwaterandsanitation,secureessentialhealthcareincludingecosystemssuchascoralreefsarelimited(highconfidence).vaccinationandchildhealthservices,increasecapacityfordisasterpre-Fisheriesandsomeaquacultureindustrieswithhigh-technologyparednessandresponseandalleviatepoverty(veryhighconfidence).and/orlargeinvestmentshavehighcapacitiesforadaptationduetoOptionstoaddressheatrelatedmortalityincludehealthwarningsys-greaterdevelopmentofenvironmentalmonitoring,modellingandtemslinkedtoresponsestrategies,urbanplanningandimprovementsresourceassessments.Adaptationoptionsincludelarge-scaletranslo-tothebuiltenvironmenttoreduceheatstress.Robustinstitutionscationofindustrialfishingactivitiesandflexiblemanagementthatcancanmanagemanytransboundaryimpactsofclimatechangetoreducereacttovariabilityandchange.Forsmaller-scalefisheriesandnationsriskofconflictsoversharednaturalresources.Insuranceprogrammes,withlimitedadaptivecapacities,buildingsocialresilience,alternativesocialprotectionmeasuresanddisasterriskmanagementmayenhancelivelihoodsandoccupationalflexibilityareimportantstrategies.Adap-long-termlivelihoodresilienceamongthepoorandmarginalizedtationoptionsforcoralreefsystemsaregenerallylimitedtoreduc-people,ifpoliciesaddressmulti-dimensionalpoverty.{WGIISPMingotherstressors,mainlybyenhancingwaterqualityandlimitingB-2,SPMB-3,8.2,10.8,11.7–11.8,12.5–12.6,22.3,23.9,25.8,26.6,pressuresfromtourismandfishing,buttheirefficacywillbeseverelyBoxCC-HS}97Topic4AdaptationandMitigationTable4.3Examplesofpotentialtrade-offsassociatedwithanillustrativesetofadaptationoptionsthatcouldbeimplementedbyactorstoachievespecificmanagementobjec-tives.{WGIITable16-2}SectorActor’sadaptationobjectiveAdaptationoptionRealorperceivedtrade-offAgricultureEnhancedroughtandpestresistance;enhanceyieldsPerceivedrisktopublichealthandsafety;BiotechnologyandecologicalrisksassociatedwithintroductionofBiodiversitygeneticallymodifiedcropsnewgeneticvariantstonaturalenvironmentsCoastsProvidefinancialsafetynetforfarmerstoSubsidizeddroughtCreatesmoralhazardanddistributionalWaterresourcesensurecontinuationoffarmingenterprisesassistance;cropinsuranceinequalitiesifnotappropriatelyadministeredmanagementMaintainorenhancecropyields;suppressIncreaseduseofchemicalIncreaseddischargeofnutrientsandchemicalpollutionopportunisticagriculturalpestsandinvasivespeciesfertilizerandpesticidestotheenvironment;adverseimpactsofpesticideuseonnon-targetspecies;increasedemissionsofgreenhouseEnhancecapacityfornaturaladaptationandMigrationcorridors;gases;increasedhumanexposuretopollutantsmigrationtochangingclimaticconditionsexpansionofconservationareasUnknownefficacy;concernsoverpropertyrightsEnhanceregulatoryprotectionsforspeciespotentiallyregardinglandacquisition;governancechallengesatriskduetoclimateandnon-climaticchangesProtectionofcriticalhabitatforvulnerablespeciesAddressessecondaryratherthanprimarypressuresonspecies;concernsoverpropertyrights;regulatoryFacilitateconservationofvaluedspeciesAssistedmigrationbarrierstoregionaleconomicdevelopmentbyshiftingpopulationstoalternativeareasastheclimatechangesSeawallsDifficulttopredictultimatesuccessofassistedmigration;ManagedretreatpossibleadverseimpactsonindigenousfloraandfaunaProvidenear-termprotectiontofinancialMigrationoutoffromintroductionofspeciesintonewecologicalregionsassetsfrominundationand/orerosionlow-lyingareasDesalinationHighdirectandopportunitycosts;equityconcerns;Allownaturalcoastalandecologicalprocessestoecologicalimpactstocoastalwetlandsproceed;reducelong-termrisktopropertyandassetsUnderminesprivatepropertyrights;significantgovernancePreservepublichealthandsafety;minimizechallengesassociatedwithimplementationpropertydamageandriskofstrandedassetsLossofsenseofplaceandculturalidentity;erosionofIncreasewaterresourcereliabilitykinshipandfamilialties;impactstoreceivingcommunitiesanddroughtresilienceEcologicalriskofsalinedischarge;highenergyMaximizeefficiencyofwatermanagementWatertradingdemandandassociatedcarbonemissions;anduse;increaseflexibilityWaterrecycling/reusecreatesdisincentivesforconservationEnhanceefficiencyofavailablewaterresourcesUnderminespublicgood/socialaspectsofwaterPerceivedrisktopublichealthandsafetySignificantco-benefits,synergiesandtrade-offsexistbetween4.3Responseoptionsformitigationadaptationandmitigationandamongdifferentadaptationresponses;interactionsoccurbothwithinandacrossregionsMitigationoptionsareavailableineverymajorsector.Mitigationcanbemorecost-effectiveifusingan4andsectors(veryhighconfidence).Forexample,investmentsinintegratedapproachthatcombinesmeasurestoreduceenergyuseandthegreenhousegasintensityofend-usecropvarietiesadaptedtoclimatechangecanincreasethecapacitysectors,decarbonizeenergysupply,reducenetemis-tocopewithdrought,andpublichealthmeasurestoaddresssionsandenhancecarbonsinksinland-basedsectors.vector-bornediseasescanenhancethecapacityofhealthsys-temstoaddressotherchallenges.Similarly,locatinginfrastructureawayfromlow-lyingcoastalareashelpssettlementsandeco-systemsadapttosealevelrisewhilealsoprotectingagainsttsunamis.However,someadaptationoptionsmayhaveadverseAbroadrangeofsectoralmitigationoptionsisavailablethatsideeffectsthatimplyrealorperceivedtrade-offswithothercanreduceGHGemissionintensity,improveenergyintensityadaptationobjectives(seeTable4.3forexamples),mitigationthroughenhancementsoftechnology,behaviour,productionandobjectivesorbroaderdevelopmentgoals.Forexample,whilepro-resourceefficiencyandenablestructuralchangesorchangestectionofecosystemscanassistadaptationtoclimatechangeinactivity.Inaddition,directoptionsinagriculture,forestryandandenhancecarbonstorage,increaseduseofairconditioningtootherlanduse(AFOLU)involvereducingCO2emissionsbyreducingmaintainthermalcomfortinbuildingsortheuseofdesalinationdeforestation,forestdegradationandforestfires;storingcarbonintoenhancewaterresourcesecuritycanincreaseenergydemand,terrestrialsystems(forexample,throughafforestation);andprovid-andtherefore,GHGemissions.{WGIISPMB-2,SPMC-1,5.4.2,ingbioenergyfeedstocks.Optionstoreducenon-CO2emissionsexist16.3.2.9,17.2.3.1,Table16-2}acrossallsectorsbutmostnotablyinagriculture,energysupplyand98AdaptationandMitigationTopic4SectoralCO2andnon-CO2GHGemissionsinbaselineandmitigationscenarioswithandwithoutCCSBaselines450ppmCO2-eqwithCCS450ppmCO2-eqwithoutCCSIntroduction505050Percentile80GtCO2/yrDirectemissionsonlyCO2Transportmax40Annualemissions(GtCO2-eq/yr)40Directandindirectemissions3040CO2Buildings75th3020median20CO2Industry25thCO2Electricity210030CO2NetAFOLUNon-CO2(Allsectors)min2050Actual2010levelIndividual20scenarios2030203020502100203020501010102100000–10–10–10–20–20–20TransportBuildingsIndustryElectricityNetNon-CO2TransportBuildingsIndustryElectricityNetNon-CO2TransportBuildingsIndustryElectricityNetNon-CO2AFOLUAFOLUAFOLUn=939378777768808065686859808065686859147147127131131118121121107292929222222222236363232363636555333566662232355636363Figure4.1Carbondioxide(CO2)emissionsbysectorandtotalnon-CO2greenhousegas(GHG)emissions(Kyotogases)acrosssectorsinbaseline(leftpanel)andmitigationscenariosthatreachabout450(430to480)ppmCO2-eq(likelytolimitwarmingto2°Cabovepre-industriallevels)withcarbondioxidecaptureandstorage(CCS,middlepanel)andwithoutCCS(rightpanel).LightyellowbackgrounddenotesdirectCO2andnon-CO2GHGemissionsforboththebaselineandmitigationscenarios.Inaddition,forthebaselinescenarios,thesumofdirectandindirectemissionsfromtheenergyend-usesectors(transport,buildingsandindustry)isalsoshown(darkyellowbackground).Mitigationscenariosshowdirectemissionsonly.However,mitigationintheend-usesectorsleadsalsotoindirectemissionsreductionsintheupstreamenergysupplysector.Directemissionsoftheend-usesectorsthusdonotincludetheemissionreductionpotentialatthesupply-sidedueto,forexample,reducedelectricitydemand.Notethatforcalculatingtheindirectemissionsonlyelectricityemissionsareallocatedfromenergysupplytoend-usesectors.Thenumbersatthebottomofthegraphsrefertothenumberofscenariosincludedintherange,whichdiffersacrosssectorsandtimeduetodifferentsectoralresolutionandtimehorizonofmodels.Notethatmanymodelscannotreachconcentrationsofabout450ppmCO2-eqby2100intheabsenceofCCS,resultinginalownumberofscenariosfortherightpanel.Negativeemissionsintheelectricitysectorareduetotheapplicationofbioenergywithcarbondioxidecaptureandstorage(BECCS).‘Net’agriculture,forestryandotherlanduse(AFOLU)emissionsconsiderafforestation,reforestationaswellasdeforestationactivities.{WGIIIFigureSPM.7,FigureTS.15}industry.Anoverviewofsectoralmitigationoptionsandpotentialsisoftheworld’surbanareaswillbedevelopedduringthisperiod.{WGIIIprovidedinTable4.4.{WGIIITS3.2.1}SPM.4.2,TS.3.2}Well-designedsystemicandcross-sectoralmitigationstrate-Decarbonizing(i.e.,reducingthecarbonintensityof)electricitygiesaremorecost-effectiveincuttingemissionsthanafocusgenerationisakeycomponentofcost-effectivemitigationonindividualtechnologiesandsectorswitheffortsinonestrategiesinachievinglowstabilizationlevels(ofabout450sectoraffectingtheneedformitigationinothers(mediumtoabout500ppmCO2-eq,atleastaboutaslikelyasnottoconfidence).Inbaselinescenarioswithoutnewmitigationpolicies,limitwarmingto2°Cabovepre-industriallevels)(mediumevi-GHGemissionsareprojectedtogrowinallsectors,exceptfornetCO2dence,highagreement).Inmostintegratedmodellingscenarios,4emissionsintheAFOLUsector(Figure4.1,leftpanel).Mitigationsce-decarbonizationhappensmorerapidlyinelectricitygenerationthaninnariosreachingaround450ppmCO2-eq4227concentrationby210043theindustry,buildingsandtransportsectors.Inscenariosreaching28(likelytolimitwarmingto2°Cabovepre-industriallevels)showlarge-450ppmCO2-eqconcentrationsby2100,globalCO2emissionsfromscaleglobalchangesintheenergysupplysector(Figure4.1,middletheenergysupplysectorareprojectedtodeclineoverthenextdecadeandrightpanel).Whilerapiddecarbonizationofenergysupplygen-andarecharacterizedbyreductionsof90%ormorebelow2010levelserallyentailsmoreflexibilityforend-useandAFOLUsectors,strongerbetween2040and2070.{WGIIISPM.4.2,6.8,7.11}demandreductionslessenthemitigationchallengeforthesupplysideoftheenergysystem(Figures4.1and4.2).Therearethusstronginter-Efficiencyenhancementsandbehaviouralchanges,inordertodependenciesacrosssectorsandtheresultingdistributionofthemiti-reduceenergydemandcomparedtobaselinescenarioswithoutgationeffortisstronglyinfluencedbytheavailabilityandperformancecompromisingdevelopment,areakeymitigationstrategyinoffuturetechnologies,particularlyBECCSandlargescaleafforestationscenariosreachingatmosphericCO2-eqconcentrationsofabout(Figure4.1,middleandrightpanel).Thenexttwodecadespresenta450toabout500ppmby2100(robustevidence,highagree-windowofopportunityformitigationinurbanareas,asalargeportionment).Near-termreductionsinenergydemandareanimportant42SeeGlossaryfordefinitionofCO2-eqconcentrationsandemissions;alsoBox3.2formetricstocalculatetheCO2-equivalenceofnon-CO2emissionsandtheirinfluenceonsectoralabatementstrategies.43Forcomparison,theCO2-eqconcentrationin2011isestimatedtobe430[340to520]ppm.99Topic4AdaptationandMitigationLiquidsandhydrogenElectricitygenerationOil60OtherliquidsandH260Coalandnaturalgas60Non-fossil160PercentileHighenergydemand140LowenergydemandSecondaryenergysupply(EJ/yr)12050MaxSecondaryenergysupply(EJ/yr)5050In430-530ppmCO2-eqSecondaryenergysupply(EJ/yr)100Secondaryenergysupply(EJ/yr)mitigationscenarios8075th6040Median204025th40400Min303030202020101010000OilproductsCoalw/oCCSLiquidscoalGasw/oCCSLiquidsgasCoalw/CCSLiquidsbiomassGasw/CCSHydrogenNuclearBiomassw/oCCSBiomassw/CCSSolarWindGeothermalHydro1234HighenergyInhighenergydemandscenarios,alternativeHighenergydemandscenariosshowInhighenergydemandscenariosnon-fossildemandscenariosliquidandhydrogentechnologiesarescaledamorerapidup-scalingofCCSelectricitygenerationtechnologiesarescaledupshowhigherlevelsupmorerapidly.technologiesbutamorerapidphase-morerapidly.ofoilsupply.outofunabatedfossilfuelconversiontechnologies.Figure4.2Influenceofenergydemandonthedeploymentofenergysupplytechnologiesin2050inmitigationscenariosreachingabout450toabout500ppmCO2-eqcon-centrationsby2100(atleastaboutaslikelyasnottolimitwarmingto2°Cabovepre-industriallevels).Bluebarsfor‘lowenergydemand’showthedeploymentrangeofscenarioswithlimitedgrowthinfinalenergydemandof<20%in2050comparedto2010.Redbarsshowthedeploymentrangeoftechnologiesinacaseof‘highenergydemand’(>20%growthin2050comparedto2010).Foreachtechnology,themedian,interquartileandfulldeploymentrangeisdisplayed.Notes:Scenariosassumingtechnologyrestrictionsareexcluded.Rangesincluderesultsfrommanydifferentintegratedmodels.Multiplescenarioresultsfromthesamemodelwereaveragedtoavoidsamplingbiases.{WGIIIFigureTS.16}elementofcost-effectivemitigationstrategies,providemoreflexibilityhaveachievedalevelofmaturitytoenabledeploymentatsignificantforreducingcarbonintensityintheenergysupplysector,hedgeagainstscalesinceAR4(robustevidence,highagreement)andnuclearenergyrelatedsupply-siderisks,avoidlock-intocarbon-intensiveinfra-isamaturelow-GHGemissionsourceofbaseloadpower,butitsshare4structuresandareassociatedwithimportantco-benefits(Figure4.2,ofglobalelectricitygenerationhasbeendeclining(since1993).GHGTable4.4).Emissionscanbesubstantiallyloweredthroughchangesinemissionsfromenergysupplycanbereducedsignificantlybyreplacingconsumptionpatterns(e.g.,mobilitydemandandmode,energyuseincurrentworldaveragecoal‐firedpowerplantswithmodern,highlyeffi-households,choiceoflonger-lastingproducts)anddietarychangeandcientnaturalgascombined‐cyclepowerplantsorcombinedheatandreductioninfoodwastes.Anumberofoptionsincludingmonetaryandpowerplants,providedthatnaturalgasisavailableandthefugitivenon-monetaryincentivesaswellasinformationmeasuresmayfacili-emissionsassociatedwithextractionandsupplyarelowormitigated.tatebehaviouralchanges.{WGIIISPM.4.2}{WGIIISPM.4.2}Decarbonizationoftheenergysupplysector(i.e.,reducingtheBehaviour,lifestyleandculturehaveaconsiderableinfluencecarbonintensity)requiresupscalingoflow-andzero-carbononenergyuseandassociatedemissions,withhighmitigationelectricitygenerationtechnologies(highconfidence).Inthepotentialinsomesectors,inparticularwhencomplementingmajorityoflow‐concentrationstabilizationscenarios(about450totechnologicalandstructuralchange(mediumevidence,mediumabout500ppmCO2-eq,atleastaboutaslikelyasnottolimitwarmingagreement).Inthetransportsector,technicalandbehaviouralmitiga-to2°Cabovepre-industriallevels),theshareoflow‐carbonelectricitytionmeasuresforallmodes,plusnewinfrastructureandurbanrede-supply(comprisingrenewableenergy(RE),nuclearandCCS,includ-velopmentinvestments,couldreducefinalenergydemandsignificantlyingBECCS)increasesfromthecurrentshareofapproximately30%belowbaselinelevels(robustevidence,mediumagreement)(Table4.4).tomorethan80%by2050and90%by2100,andfossilfuelpowerWhileopportunitiesforswitchingtolow-carbonfuelsexist,therategenerationwithoutCCSisphasedoutalmostentirelyby2100.Amongofdecarbonizationinthetransportsectormightbeconstrainedbytheselow-carbontechnologies,agrowingnumberofREtechnologieschallengesassociatedwithenergystorageandtherelativelylow100AdaptationandMitigationTopic4Table4.4Sectoralcarbondioxide(CO2)emissions,associatedenergysystemchangesandexamplesofmitigationmeasures(includingfornon-CO2gases;seeBox3.2formetricsIntroductionregardingtheweightingandabatementofnon-CO2emissions).{WGIIISPM.7,FigureSPM.8,TableTS.2,7.11.3,7.13,7.14}SectoralCO2emissionsandrelatedenergysystemchangesExamplesforsectoralmitigationmeasuresSectorCO2emissionLow-carbonfuelFinalenergydemandKeylow-carbonKeyenergysavingoptionsOtheroptions(GtCO2,2050)share(%,2050)(EJ,2050)energyoptionsEnergysupplya201020102010Renewables(wind,solarEnergyefﬁciencyimprove-FugitiveCH4emissionscontrolbioenergy,geothermal,hydro,mentsofenergysupplyBaselinesetc.),nuclear,CCS,BECCS,technologies,improvedfossilfuelswitchingtransmissionanddistribution,CHPandcogeneration530–650ppmCO2-eq430–530ppmCO2-eq–2002040600204060801000100200300400500Transport201020102010Fuelswitchingtolow-carbonEfﬁciencyimprovementsTransport(infrastructure)Baselinesfuels(e.g.,hydrogen/electricity(engines,vehicledesign,planning,urbanplanningfromlow-carbonsources),appliances,lightermaterials),biofuelsmodalshift(e.g.,fromLDVs530–650topublictransportorfromppmCO2-eqaviationtoHDVstorail),430–530ppmCO2-eqeco-driving,improvedfreightlogistics,journeyavoidance,higheroccupancyrates05101520250204060801000100200300400500Building201020102010BaselinesBuildingintegratedRES,fuelDeviceefﬁciencyUrbanplanning,buildingswitchingtolow-carbon(heating/coolingsystems,lifetime,durabilityofbuildingfuels(e.g.,electricityfromwaterheating,cooking,componentsandappliances,low-carbonsources,biofuels)lighting,appliances),systemiclowenergy/GHGintensiveefﬁciency(integrateddesign,constructionandmaterials530–650low/zeroenergybuildings,ppmCO2-eqdistrictheating/cooling,CHP,smartmeters/grids),430–530behaviouralandlifestyleppmCO2-eqchanges(e.g.,applianceuse,thermostatsetting,dwelling02468100204060801000100200300400500size)Industry201020102010Processemissionsreductions,EnergyefﬁciencyandBATHFCreplacementandleakBaselinesuseofwasteandCCSin(e.g.,furnace/boilers,steamrepair,materialefﬁciency(e.g.,industry,fuelswitchingamongsystems,electricmotorsandprocessinnovation,re-using530–650fossilfuelsandswitchtocontrolsystems,(waste)oldmaterials,productdesign,4ppmCO2-eqlow-carbonenergy(e.g.,heatexchanges,recycling),etc.)430–530electricity)orbiomassreductionofdemandforppmCO2-eqgoods,moreintensiveuseofgoods(e.g.,improvedurabilityorcarsharing)05101520250204060801000100200300400500AFOLU2010Emissionsreductionmeasures:Sequestrationoptions:Substitutionoptions:Demand-sidemeasures:BaselinesPercentileMethane(e.g.,livestockmanagement),IncreasingexistingcarbonUseofbiologicalproductsReductionoflossandnitrousoxide(e.g.,fertilizeruse),pools(e.g.,afforestation,insteadoffossil/GHGwasteoffood,changes530–650min25th75thmaxconservationofexistingcarbonpoolsreforestation,integratedintensiveproducts(e.g.,inhumandiets,useofppmCO2-eq(sustainableforestmanagement,reducedsystems,carbonbioenergy,insulationlong-livedwoodproductsdeforestationandforestdegradation,ﬁresequestrationinsoils)products)430–530medianprevention,agroforestry),reductioninppmCO2-eqemissionsintensity–10–50510aCO2emissions,lowcarbonfuelshares,andfinalenergydemandareshownforelectricitygenerationonly101Topic4AdaptationandMitigationenergydensityoflow-carbontransportfuels(mediumconfidence).InmitigationmeasuresaresummarizedinTable4.5.Overall,thepotentialthebuildingsector,recentadvancesintechnologies,know-howandforco-benefitsforenergyend-usemeasuresoutweighthepotentialpoliciesprovideopportunitiestostabilizeorreduceglobalenergyuseforadversesideeffects,whereastheevidencesuggeststhismaynottoaboutcurrentlevelsbymid-century.Inaddition,recentimprove-bethecaseforallenergysupplyandAFOLUmeasures.{WGIIISPM.2}mentsinperformanceandcostsmakeverylowenergyconstructionandretrofitsofbuildingseconomicallyattractive,sometimesevenat4.4Policyapproachesforadaptationandnetnegativecosts(robustevidence,highagreement).Intheindustrymitigation,technologyandfinancesector,improvementsinGHGemissionefficiencyandintheefficiencyofmaterialuse,recyclingandreuseofmaterialsandproducts,andEffectiveadaptationandmitigationresponseswilloverallreductionsinproductdemand(e.g.,throughamoreintensivedependonpoliciesandmeasuresacrossmultiplescales:useofproducts)andservicedemandcould,inadditiontoenergyeffi-international,regional,nationalandsub-national.ciency,helpreduceGHGemissionsbelowthebaselinelevel.PrevalentPoliciesacrossallscalessupportingtechnologydevel-approachesforpromotingenergyefficiencyinindustryincludeinfor-opment,diffusionandtransfer,aswellasfinanceformationprogrammesfollowedbyeconomicinstruments,regulatoryresponsestoclimatechange,cancomplementandapproachesandvoluntaryactions.Importantoptionsformitigationenhancetheeffectivenessofpoliciesthatdirectlypro-inwastemanagementarewastereduction,followedbyre-use,recy-moteadaptationandmitigation.clingandenergyrecovery(robustevidence,highagreement).{WGIIISPM.4.2,BoxTS.12,TS.3.2}Themostcost-effectivemitigationoptionsinforestryareafforestation,sustainableforestmanagementandreducing4.4.1Internationalandregionalcooperationdeforestation,withlargedifferencesintheirrelativeimpor-onadaptationandmitigationtanceacrossregions.Inagriculture,themostcost-effectivemit-igationoptionsarecroplandmanagement,grazinglandman-Becauseclimatechangehasthecharacteristicsofacollectiveactionagementandrestorationoforganicsoils(mediumevidence,problemattheglobalscale(see3.1),effectivemitigationwillnotbehighagreement).Aboutathirdofmitigationpotentialinforestryachievedifindividualagentsadvancetheirowninterestsindependently,canbeachievedatacost<20USD/tCO2-eqemission.Demand‐sideeventhoughmitigationcanalsohavelocalco-benefits.Cooperativemeasures,suchaschangesindietandreductionsoflossesinthefoodresponses,includinginternationalcooperation,arethereforerequiredsupplychain,haveasignificant,butuncertain,potentialtoreducetoeffectivelymitigateGHGemissionsandaddressotherclimateGHGemissionsfromfoodproduction(mediumevidence,mediumchangeissues.Whileadaptationfocusesprimarilyonlocaltonationalagreement).{WGIIISPM4.2.4}scaleoutcomes,itseffectivenesscanbeenhancedthroughcoordina-tionacrossgovernancescales,includinginternationalcooperation.InBioenergycanplayacriticalroleformitigation,buttherearefact,internationalcooperationhashelpedtofacilitatethecreationissuestoconsider,suchasthesustainabilityofpracticesandofadaptationstrategies,plans,andactionsatnational,sub-national,theefficiencyofbioenergysystems(robustevidence,mediumandlocallevels.Avarietyofclimatepolicyinstrumentshavebeenagreement).Evidencesuggeststhatbioenergyoptionswithlowlife-employed,andevenmorecouldbeemployed,atinternationalandcycleemissions,somealreadyavailable,canreduceGHGemissions;regionallevelstoaddressmitigationandtosupportandpromoteoutcomesaresite‐specificandrelyonefficientintegrated‘biomass‐adaptationatnationalandsub-nationalscales.Evidencesuggeststhatto‐bioenergysystems’,andsustainablelandusemanagementandoutcomesseenasequitablecanleadtomoreeffectivecooperation.4governance.Barrierstolarge‐scaledeploymentofbioenergyinclude{WGIISPMC-1,2.2,15.2,WGIII13.ES,14.3,15.8,SREXSPM,7.ES}concernsaboutGHGemissionsfromland,foodsecurity,waterresources,biodiversityconservationandlivelihoods.{WGIIISPM.4.2}TheUnitedNationsFrameworkConventiononClimateChange(UNFCCC)isthemainmultilateralforumfocusedonaddress-Mitigationmeasuresintersectwithothersocietalgoals,cre-ingclimatechange,withnearlyuniversalparticipation.UNFCCCatingthepossibilityofco‐benefitsoradverseside‐effects.activitiessince2007,whichincludethe2010CancúnAgreementsTheseintersections,ifwell‐managed,canstrengthenthebasisandthe2011DurbanPlatformforEnhancedAction,havesoughttoforundertakingclimatemitigationactions(robustevidence,enhanceactionsundertheConvention,andhaveledtoanincreas-mediumagreement).Mitigationcanpositivelyornegativelyinflu-ingnumberofinstitutionsandotherarrangementsforinternationalencetheachievementofothersocietalgoals,suchasthoserelatedtoclimatechangecooperation.Otherinstitutionsorganizedatdifferenthumanhealth,foodsecurity,biodiversity,localenvironmentalquality,levelsofgovernancehaveresultedindiversifyinginternationalclimateenergyaccess,livelihoodsandequitablesustainabledevelopment(seechangecooperation.{WGIIISPM.5.2,13.5}alsoSection4.5).Ontheotherhand,policiestowardsothersocietalgoalscaninfluencetheachievementofmitigationandadaptationExistingandproposedinternationalclimatechangecoopera-objectives.Theseinfluencescanbesubstantial,althoughsometimestionarrangementsvaryintheirfocusanddegreeofcentrali-difficulttoquantify,especiallyinwelfareterms.Thismulti‐objectivezationandcoordination.Theyspan:multilateralagreements,har-perspectiveisimportantinpartbecauseithelpstoidentifyareasmonizednationalpoliciesanddecentralizedbutcoordinatednationalwheresupportforpoliciesthatadvancemultiplegoalswillberobust.policies,aswellasregionalandregionally-coordinatedpolicies(seePotentialco-benefitsandadversesideeffectsofthemainsectoralFigure4.3).{WGIIISPM.5.2}102Table4.5Potentialco-benefits(bluetext)andadversesideeffects(redtext)ofthemainsectoralmitigationmeasures.Co-benefitsandadversesideeffects,andtheiroverallpositiveornegativeeffect,alldependonlocalcircumstancesasAdaptationandMitigationwellasontheimplementationpractice,paceandscale.Foranassessmentofmacroeconomic,cross-sectoraleffectsassociatedwithmitigationpolicies,seeSection3.4.Theuncertaintyqualifiersbetweenbracketsdenotethelevelofevidenceandagreementontherespectiveeffect.Abbreviationsforevidence:l=limited,m=medium,r=robust;foragreement:l=low,m=medium,h=high.{WGIIITableTS.3,TableTS.4,TableTS.5,TableTS.6,TableTS.7,Table6.7}SectoralmitigationmeasuresEffectonadditionalobjectives/concernsEnergySupplyEconomicSocialEnvironmentalNuclearreplacingcoalpowerForpossibleupstreameffectsofbiomasssupplyforbioenergy,seeAFOLU.Mixedecosystemimpactviareducedairpollution(m/h)andcoalRenewableenergy(wind,PV,CSP,mining(l/h),nuclearaccidents(m/m)hydro,geothermal,bioenergy)repla-Energysecurity(reducedexposuretofuelpricevolatility)MixedhealthimpactviareducedairpollutionandcoalminingcingcoalMixedecosystemimpactviareducedairpollution(exceptbioe-(m/m);localemploymentimpact(butuncertainneteffect)accidents(m/h),nuclearaccidentsandwastetreatment,uraniumnergy)(m/h)andcoalmining(l/h),habitatimpact(forsomehydroFossilenergywithCCSreplacingcoalenergy)(m/m),landscapeandwildlifeimpact(m/m);lower/higher(l/m);legacy/costofwasteandabandonedreactors(m/h)miningandmilling(m/l);safetyandwasteconcerns(r/h);prolifera-wateruse(forwind,PV(m/m);bioenergy,CSP,geothermalandCH4leakageprevention,captureorreservoirhydro(m/h))treatmenttionrisk(m/m)Ecosystemimpactviaadditionalupstreamsupply-chainactivitiesTransport(m/m)andhigherwateruse(m/h)Energysecurity(r/m);localemployment(butuncertainnetReducedhealthimpactviareducedairpollution(exceptbioenergy)ReductionofcarbonintensityoffuelReducedecosystemimpactviareducedairpollution(l/m)effect)(m/m);watermanagement(forsomehydroenergy)(r/h)andcoalminingaccidents(m/h);contributionto(off-grid)ReductionofenergyintensityMixedecosystemimpactofelectricityandhydrogenviareduced(m/h);extrameasurestomatchdemand(forPV,wind,someenergyaccess(m/l);threatofdisplacement(forlargehydrourbanairpollution(m/m)andmaterialuse(unsustainablemining)Compacturbanformandimproved(l/l)transportinfrastructureCSP)(r/h);higheruseofcriticalmetalsforPVanddirectdriveinstallations)(m/h)ModalshiftReducedecosystemandbiodiversityimpactviareducedurbanairwindturbines(r/m)pollution(m/h)JourneydistancereductionandavoidancePreservationvs.lock-inofhumanandphysicalcapitalintheHealthimpactviariskofCO2leakage(m/m)andadditionalReducedecosystemimpactviareducedurbanairpollution(r/h)Buildingsfossilindustry(m/m);long-termmonitoringofCO2storageupstreamsupply-chainactivities(m/h);safetyconcerns(CO2andlandusecompetition(m/m)ReductionofGHGemissionsintensity(m/h)storageandtransport)(m/h)(e.g.,fuelswitching,RESincorporation,Mixedecosystemimpactviareducedurbanairpollution(r/h),new/greenroofs)Energysecurity(potentialtousegasinsomecases)(l/h)Reducedhealthimpactviareducedairpollution(m/m);occupatio-shortershippingroutes(r/h);reducedlandusecompetitionfromtransportinfrastructure(r/h)Retrofitsofexistingbuildingsnalsafetyatcoalmines(m/m)ExemplarynewbuildingsReducedhealthimpactinresidentialbuildingsandecosystemEfficientequipmentForpossibleupstreameffectsoflow-carbonelectricity,seeEnergySupply.Forbiomasssupply,seeAFOLU.impact(viareducedfuelpoverty(r/h),indoor/outdoorairpollution(r/h)andUHIeffect)(l/m);urbanbiodiversity(forgreenroofs)Energysecurity(diversification,reducedoildependenceMixedhealthimpactviaincreased/reducedurbanairpollutionby(m/m)Reducedhealthandecosystemimpact(e.g.,viareducedfuelandexposuretooilpricevolatility)(m/m);technologicalelectricityandhydrogen(r/h),diesel(l/m);roadsafetyconcernspoverty(r/h),indoor/outdoorairpollution(r/h),UHIeffect(l/m),improvedindoorenvironmentalconditions(m/h));healthriskviaspillovers(l/l)(l/l)butreducedhealthimpactviareducednoise(l/m)ofelectricinsufficientventilation(m/m);reducedwaterconsumptionandsewageproduction(l/l)LDVsEnergysecurity(reducedoildependenceandexposuretooilReducedhealthimpactviareducedurbanairpollution(r/h);pricevolatility)(m/m)roadsafety(crash-worthinessdependingonthedesignofthestandards)(m/m)Energysecurity(reducedoildependenceandexposuretooilMixedhealthimpactfornon-motorizedmodesviaincreasedphysi-pricevolatility)(m/m);productivity(reducedurbanconge-calactivity(r/h),potentiallyhigherexposuretoairpollution(r/h),stionandtraveltimes,affordableandaccessibletransport)reducednoise(viamodalshiftandtravelreduction)(r/h);equitable(m/h)mobilityaccesstoemploymentopportunities(r/h);roadsafety(viamodalshift)(r/h)Energysecurity(reducedoildependenceandexposuretooilReducedhealthimpact(fornon-motorizedtransportmodes)(r/h)pricevolatility)(r/h);productivity(reducedurbancongestion/traveltimes,walking)(r/h)ForpossibleupstreameffectsoffuelswitchingandRES,seeEnergySupply.Energysecurity(m/h);employmentimpact(m/m);lowerFuelpovertyalleviationviareducedenergydemand(m/h);energyneedforenergysubsidies(l/l);assetvaluesofbuildings(l/m)access(forhigherenergycost)(l/m);productivetimeforwomen/children(forreplacedtraditionalcookstoves)(m/h)Energysecurity(m/h);employmentimpact(m/m);pro-Fuelpovertyalleviationviareducedenergydemand(forretrofitsductivity(forcommercialbuildings)(m/h);lessneedforandefficientequipment)(m/h);energyaccess(higherhousingenergysubsidies(l/l);assetvalueofbuildings(l/m);disastercost)(l/m);thermalcomfort(m/h);productivetimeforwomenandresilience(l/m)children(forreplacedtraditionalcookstoves)(m/h)4continueonnextpageTopic4103Introduction4Topic4104Table4.5(continued)Effectonadditionalobjectives/concernsSocialEnvironmentalSectoralmitigationmeasuresEconomicReducedhealthandecosystemimpact(e.g.,viaimprovedindoorBehaviouralchangesreducingenergyEnergysecurity(m/h);lessneedforenergysubsidies(l/l)environmentalconditions(m/h)andlessoutdoorairpollution(r/h))demandIndustryForpossibleupstreameffectsoflow-carbonenergysupply(incl.CCS),seeEnergySupplyandofbiomasssupply,seeAFOLU.Reducedecosystemimpact(viareducedlocalairandwaterpolluti-ReductionofCO2/non-CO2GHGon)(m/m);waterconservation(l/m)emissionintensityCompetitivenessandproductivity(m/h)ReducedhealthimpactviareducedlocalairpollutionandbetterReducedecosystemimpactviareducedfossilfuelextraction(l/l)andreducedlocalpollutionandwaste(m/m)Technicalenergyefficiencyimprove-workingconditions(PFCfromaluminium)(m/m)mentsvianewprocesses/technologiesReducedecosystemimpactviareducedlocalairandwaterpollu-Energysecurity(vialowerenergyintensity)(m/m);employ-Reducedhealthimpactviareducedlocalpollution(l/m);newbusi-tionandwastematerialdisposal(m/m);reduceduseofraw/virginMaterialefficiencyofgoods,recyclingmaterialsandnaturalresourcesimplyingreducedunsustainablementimpact(l/l);competitivenessandproductivity(m/h);nessopportunities(m/m);increasedwateravailabilityandqualityresourcemining(l/l)ProductdemandreductionsReducedpost-consumptionwaste(l/l)AFOLUtechnologicalspilloversinDCs(l/l)(l/l);improvedsafety,workingconditionsandjobsatisfactionSupplyside:forestry,land-basedagri-Mixedimpactonecosystemservicesvialarge-scalemonoculturesculture,livestock,integratedsystems(m/m)(r/h),ecosystemconservation,sustainablemanagementaswellandbioenergyassustainableagriculture(r/h);increasedlandusecompetitionDecreasednationalsalestaxrevenueinthemediumtermReducedhealthimpactsandsafetyconcerns(l/m);newbusiness(r/m);increasedsoilquality(r/h);decreasederosion(r/h);increasedDemandside:reducedlossesintheecosystemresilience(m/h);albedoandevaporation(r/h)foodsupplychain,changesinhuman(l/l);employmentimpact(wasterecycling)(l/l);competitive-opportunities(m/m)andreducedlocalconflicts(reducedresourceInstitutionalaspects:mixedimpactontenureanduserightsatdietsandindemandforwoodandthelocallevel(forindigenouspeopleandlocalcommunities)(r/h)forestryproductsnessinmanufacturing(l/l);newinfrastructureforindustrialextraction)(l/m)andonaccesstoparticipativemechanismsforlandmanagementdecisions(r/h);enforcementofexistingpoliciesforsustainableHumanSettlementsandInfra-clusters(l/l)resourcemanagement(r/h)structureCompactdevelopmentandinfra-DecreasednationalsalestaxrevenueinthemediumtermIncreasedwellbeingviadiverselifestylechoices(l/l)Preservationofopenspace(m/m)structureIncreasedaccessibility(l/l)Improvedairqualityandreducedecosystemandhealthimpacts(m/h)MixedlanduseNote:co-benefitsandadversesideeffectsdependonthedevelopmentcontextandthescaleoftheintervention(size).Improvedairqualityandreducedecosystemandhealthimpacts(m/h)Mixedemploymentimpactviaentrepreneurshipdevelop-Increasedfood-cropsproductionthroughintegratedsystemsment(m/h),useoflesslabour-intensivetechnologiesinagri-andsustainableagricultureintensification(r/m);decreasedfoodculture(m/m);diversificationofincomesourcesandaccessproduction(locally)duetolarge-scalemonoculturesofnon-foodtomarkets(r/h);additionalincometosustainablelandscapecrops(r/l);increasedculturalhabitatsandrecreationalareasmanagement(m/h);incomeconcentration(m/m);energyvia(sustainable)forestmanagementandconservation(m/m);security(resourcesufficiency)(m/h);Innovativefinancingimprovedhumanhealthandanimalwelfare(e.g.,throughlessmechanismsforsustainableresourcemanagement(m/h);useofpesticides,reducedburningpracticesandagroforestrytechnologyinnovationandtransfer(m/m)andsilvo-pastoralsystems)(m/h);humanhealthimpactrelatedtoburningpractices(inagricultureorbioenergy)(m/m);mixedimpactsongender,intra-andinter-generationalequityviaparti-cipationandfairbenefitsharing(r/h)andhigherconcentrationofbenefits(m/m)Forcompacturbanformandimprovedtransportinfrastructure,seealsoTransport.Increasedinnovationandefficientresourceuse(r/h);higherImprovedhealthfromincreasedphysicalactivity:seeTransportAdaptationandMitigationrentsandpropertyvalues(m/m)Commutesavings(r/h)Improvedhealthfromincreasedphysicalactivity:seeTransport;increasedsocialinteractionandmentalhealth(m/m)Commutesavings(r/h);higherrentsandpropertyvaluesImprovedhealthfromincreasedphysicalactivity(r/h);social(m/m)interactionandmentalhealth(l/m)AdaptationandMitigationTopic4CooperationUNFCCCObjectiveIntroductionoverendsCopenhagen/KyotoCancúnPledgesTargetsPledgeandReviewOtherIOGHGRegulationInternationalCooperationLinkedCap-and-TradeSystemsforSupportingAdaptationPlanningandHarmonizedCarbonTaxesMultilateralClubsGreenClimateFundBilateralFinancial/UNFCCC/Kyoto/CopenhagenMRVRulesTechnologyTransfersR&DTechnologyCooperationKyotoFlexibilityMechanismsLooseCoordinationofPoliciesOffsetCertiﬁcationSystemsCooperationRegionalETSovermeansDecentralizedauthorityCentralizedauthorityLoosecoordinationofpolicies:examplesincludetransnationalcitynetworksandNationallyAppropriateMitigationActions(NAMAs);R&Dtechnologycooperation:examplesincludetheMajorEconomiesForumonEnergyandClimate(MEF),GlobalMethaneInitiative(GMI),orRenewableEnergyandEnergyEfﬁciencyPartnership(REEEP);Otherinternationalorganization(IO)GHGregulation:examplesincludetheMontrealProtocol,InternationalCivilAviationOrganization(ICAO),InternationalMaritimeOrganization(IMO);SeeWGIIIFigure13.1forthedetailsoftheseexamples.Figure4.3Alternativeformsofinternationalcooperation.Thefigurerepresentsacompilationofexistingandpossibleformsofinternationalcooperation,baseduponasurveyofpublishedresearch,butisnotintendedtobeexhaustiveofexistingorpotentialpolicyarchitectures,norisitintendedtobeprescriptive.Examplesinorangeareexistingagree-ments.Examplesinbluearestructuresforagreementsproposedintheliterature.Thewidthofindividualboxesindicatestherangeofpossibledegreesofcentralizationforaparticularagreement.Thedegreeofcentralizationindicatestheauthorityanagreementconfersonaninternationalinstitution,nottheprocessofnegotiatingtheagreement.{WGIII4Figure13.2}Whileanumberofnewinstitutionsarefocusedonadaptationinventoriesthrough2012submittedtotheUNFCCCbyOctober2013,fundingandcoordination,adaptationhashistoricallyreceivedAnnexBPartieswithquantifiedemissionlimitations(andreductionlessattentionthanmitigationininternationalclimatepolicyobligations)inaggregatemayhavebetteredtheircollectiveemission(robustevidence,mediumagreement).Inclusionofadaptationisreductiontargetinthefirstcommitmentperiod,4429butsomeemissionsincreasinglyimportanttoreducetheriskfromclimatechangeimpactsreductionsthatwouldhaveoccurredeveninitsabsencewerealsoandmayengageagreaternumberofcountries.{WGIII13.2,13.3.3,counted.TheProtocol’sCleanDevelopmentMechanism(CDM)created13.5.1.1,13.14}amarketforemissionsoffsetsfromdevelopingcountries,thepurposebeingtwo-fold:tohelpAnnexIcountriesfulfilltheircommitmentsandTheKyotoProtocolofferslessonstowardsachievingtheulti-toassistnon-AnnexIcountriesachievesustainabledevelopment.ThemateobjectiveoftheUNFCCC,particularlywithrespecttopar-CDMgeneratedCertifiedEmissionReductions(offsets)equivalenttoticipation,implementation,flexibilitymechanisms,andenviron-emissionsofover1.4GtCO2-eq4242byOctober2013,ledtosignificantmentaleffectiveness(mediumevidence,lowagreement).Theprojectinvestments,andgeneratedinvestmentflowsforavarietyofProtocolwasthefirstbindingsteptowardimplementingtheprinci-functions,includingtheUNFCCCAdaptationFund.However,itsenvi-plesandgoalsprovidedbytheUNFCCC.AccordingtonationalGHGronmentaleffectivenesshasbeenquestionedbysome,particularly44ThefinalconclusionregardingcomplianceofAnnexBPartiesremainssubjecttothereviewprocessundertheKyotoProtocolasofOctober2014.105Topic4AdaptationandMitigationinregardtoitsearlyyears,duetoconcernsabouttheadditionalitymitigationobjectivesintradeagreementsorjointlyconstructinginfra-ofprojects(thatis,whetherprojectsbringaboutemissionsthatarestructuresthatfacilitatereductionincarbonemissions.{WGIIIdifferentfrombusinessasusual(BAU)circumstances),thevalidityofTableTS.9,13.13,14.4,14.5}baselines,andthepossibilityofemissionsleakage(mediumevidence,mediumagreement).SuchconcernsaboutadditionalityarecommonInternationalcooperationforsupportingadaptationplanningtoanyemission-reduction-credit(offset)program,andarenotspecificandimplementationhasassistedinthecreationofadaptationtotheCDM.Duetomarketforces,themajorityofsingleCDMprojectsstrategies,plansandactionsatnational,sub-nationalandlocalhavebeenconcentratedinalimitednumberofcountries,whilePro-levels(highconfidence).Forexample,arangeofmultilateralandgrammesofActivities,thoughlessfrequent,havebeenmoreevenlyregionallytargetedfundingmechanismshavebeenestablishedfordistributed.Inaddition,theKyotoProtocolcreatedtwoother‘flexibilityadaptation;UNagencies,internationaldevelopmentorganizationsandmechanisms’:JointImplementationandInternationalEmissionsTrad-non-governmentalorganisations(NGOs)haveprovidedinformation,ing.{WGIIISPM.5.2,TableTS.9,13.7,13.13.1.1,14.3}methodologiesandguidelines;andglobalandregionalinitiativessup-portedandpromotedthecreationofnationaladaptationstrategiesinSeveralconceptualmodelsforeffort-sharinghavebeeniden-bothdevelopinganddevelopedcountries.Closerintegrationofdisas-tifiedinresearch.However,realizeddistributionalimpactsfromterriskreductionandclimatechangeadaptationattheinternationalactualinternationalcooperativeagreementsdependnotonlyonthelevel,andthemainstreamingofbothintointernationaldevelopmentapproachtakenbutalsooncriteriaappliedtooperationalizeequityassistance,mayfostergreaterefficiencyintheuseofresourcesandandthemannerinwhichdevelopingcountries’emissionsreductioncapacity.However,strongereffortsattheinternationalleveldonotplansarefinanced.{WGIII4.6,13.4}necessarilyleadtosubstantiveandrapidresultsatthelocallevel.{WGII15.2,15.3,SREXSPM,7.4,8.2,8.5}Policylinkagesamongregional,nationalandsub-nationalcli-matepoliciesofferpotentialclimatechangemitigationben-4.4.2Nationalandsub-nationalpoliciesefits(mediumevidence,mediumagreement).Linkageshavebeenestablishedbetweencarbonmarketsandinprinciplecouldalso4.4.2.1Adaptationbeestablishedbetweenandamongaheterogeneoussetofpolicyinstrumentsincludingnon-market-basedpolicies,suchasperfor-Adaptationexperienceisaccumulatingacrossregionsinthemancestandards.Potentialadvantagesincludelowermitigationcosts,publicandprivatesectorandwithincommunities(highconfi-decreasedemissionleakageandincreasedmarketliquidity.{WGIIIdence).Adaptationoptionsadoptedtodate(seeTable4.6)emphasizeSPM.5.2,13.3,13.5,13.6,13.7,14.5}incrementaladjustmentsandco-benefitsandarestartingtoemphasizeflexibilityandlearning(mediumevidence,mediumagreement).MostRegionalinitiativesbetweennationalandglobalscalesareassessmentsofadaptationhavebeenrestrictedtoimpacts,vulnerabil-beingdevelopedandimplemented,buttheirimpactonglobalityandadaptationplanning,withveryfewassessingtheprocessesofmitigationhasbeenlimitedtodate(mediumconfidence).Someimplementationortheeffectsofadaptationactions(mediumevidence,climatepoliciescouldbemoreenvironmentallyandeconomicallyhighagreement).{WGIISPMA-2,TSA-2}effectiveifimplementedacrossbroadregions,suchasbyembodyingTable4.6Recentadaptationactionsinthepublicandprivatesectoracrossregions.{WGIISPMA-2}RegionExampleofactions4AfricaMostnationalgovernmentsareinitiatinggovernancesystemsforadaptation.Disasterriskmanagement,adjustmentsintechnologiesandinfrastructure,ecosystem-basedapproaches,basicpublichealthmeasuresandlivelihooddiversificationarereducingvulnerability,althougheffortstodatetendtobeEuropeisolated.AsiaAustralasiaAdaptationpolicyhasbeendevelopedacrossalllevelsofgovernment,withsomeadaptationplanningintegratedintocoastalandwatermanagement,NorthAmericaintoenvironmentalprotectionandlandplanningandintodisasterriskmanagement.CentralandSouthAmericaAdaptationisbeingfacilitatedinsomeareasthroughmainstreamingclimateadaptationactionintosub-nationaldevelopmentplanning,earlywarningTheArcticsystems,integratedwaterresourcesmanagement,agroforestryandcoastalreforestationofmangroves.SmallIslandsTheOceanPlanningforsealevelrise,andinsouthernAustraliaforreducedwateravailability,isbecomingadoptedwidely.Planningforsealevelrisehasevolvedconsiderablyoverthepasttwodecadesandshowsadiversityofapproaches,althoughitsimplementationremainspiecemeal.106Governmentsareengaginginincrementaladaptationassessmentandplanning,particularlyatthemunicipallevel.Someproactiveadaptationisoccurringtoprotectlonger-terminvestmentsinenergyandpublicinfrastructure.Ecosystem-basedadaptationincludingprotectedareas,conservationagreementsandcommunitymanagementofnaturalareasisoccurring.Resilientcropvarieties,climateforecastsandintegratedwaterresourcesmanagementarebeingadoptedwithintheagriculturalsectorinsomeareas.Somecommunitieshavebeguntodeployadaptiveco-managementstrategiesandcommunicationsinfrastructure,combiningtraditionalandscientificknowledge.Smallislandshavediversephysicalandhumanattributes;community-basedadaptationhasbeenshowntogeneratelargerbenefitswhendeliveredinconjunctionwithotherdevelopmentactivities.Internationalcooperationandmarinespatialplanningarestartingtofacilitateadaptationtoclimatechange,withconstraintsfromchallengesofspatialscaleandgovernanceissues.AdaptationandMitigationTopic4Nationalgovernmentsplaykeyrolesinadaptationplanning4.4.2.2Mitigationandimplementation(robustevidence,highagreement).ThereIntroductionhasbeensubstantialprogresssincetheAR4inthedevelopmentofTherehasbeenaconsiderableincreaseinnationalandsub‐nationaladaptationstrategiesandplans.ThisincludesNationalAdap-nationalmitigationplansandstrategiessinceAR4.In2012,67%tationProgrammesofAction(NAPAs)byleastdevelopedcountries,theofglobalGHGemissions42weresubjecttonationallegislationorstrat-NationalAdaptationPlan(NAP)process,andstrategicframeworksforegiesversus45%in2007.However,therehasnotyetbeenasubstan-nationaladaptationinOrganisationforEconomicCo-operationandtialdeviationinglobalemissionsfromthepasttrend.TheseplansandDevelopment(OECD)countries.Nationalgovernmentscancoordinatestrategiesareintheirearlystagesofdevelopmentandimplementationadaptationeffortsoflocalandsub-nationalgovernments,forexampleinmanycountries,makingitdifficulttoassesstheiraggregateimpactbyprotectingvulnerablegroups,bysupportingeconomicdiversifica-onfutureglobalemissions(mediumevidence,highagreement).{WGIIItion,andbyprovidinginformation,policyandlegalframeworksandSPM.5.1}financialsupport.{WGIISPMC-1,15.2}SinceAR4,therehasbeenanincreasedfocusonpoliciesWhilelocalgovernmentandtheprivatesectorhavedifferentdesignedtointegratemultipleobjectives,increaseco-benefitsfunctions,whichvaryregionally,theyareincreasinglyrecog-andreduceadversesideeffects(highconfidence).Governmentsnizedascriticaltoprogressinadaptation,giventheirrolesinoftenexplicitlyreferenceco-benefitsinclimateandsectoralplansandscalingupadaptationofcommunities,householdsandcivilsoci-strategies.{WGIIISPM.5.1}etyandinmanagingriskinformationandfinancing(mediumevidence,highagreement).ThereisasignificantincreaseintheSector-specificpolicieshavebeenmorewidelyusedthanecon-numberofplannedadaptationresponsesatthelocallevelinruralandomy-widepolicies(Table4.7)(mediumevidence,highagree-urbancommunitiesofdevelopedanddevelopingcountriessincethement).Althoughmosteconomictheorysuggeststhateconomy-wideAR4.However,localcouncilsandplannersareoftenconfrontedbythepoliciesformitigationwouldbemorecost-effectivethansector-specificcomplexityofadaptationwithoutadequateaccesstoguidinginfor-policies,administrativeandpoliticalbarriersmaymakeeconomy-widemationordataonlocalvulnerabilitiesandpotentialimpacts.Stepsforpolicieshardertodesignandimplementthansector-specificpolicies.mainstreamingadaptationintolocaldecision-makinghavebeeniden-Thelattermaybebettersuitedtoaddressbarriersormarketfailurestifiedbutchallengesremainintheirimplementation.Hence,scholarsspecifictocertainsectorsandmaybebundledinpackagesofcomple-stresstheimportantroleoflinkageswithnationalandsub-nationalmentarypolicies{WGIIISPM.5.1}levelsofgovernmentaswellaspartnershipsamongpublic,civicandprivatesectorsinimplementinglocaladaptationresponses.{WGIIInprinciple,mechanismsthatsetacarbonprice,includingcapSPMA-2,SPMC-1,14.2,15.2}andtradesystemsandcarbontaxes,canachievemitigationinacost-effectiveway,buthavebeenimplementedwithdiverseInstitutionaldimensionsofadaptationgovernance,includingtheeffectsdueinparttonationalcircumstancesaswellaspolicyintegrationofadaptationintoplanninganddecision-making,design.Theshort-runenvironmentaleffectsofcapandtradesys-playakeyroleinpromotingthetransitionfromplanningtotemshavebeenlimitedasaresultofloosecapsorcapsthathavenotimplementationofadaptation(robustevidence,highagree-provedtobeconstraining(limitedevidence,mediumagreement).Inment).Themostcommonlyemphasizedinstitutionalbarriersorena-somecountries,tax-basedpoliciesspecificallyaimedatreducingGHGblersforadaptationplanningandimplementationare:1)multilevelemissions—alongsidetechnologyandotherpolicies—havehelpedtoinstitutionalco-ordinationbetweendifferentpoliticalandadministra-weakenthelinkbetweenGHGemissionsandgrossdomesticproducttivelevelsinsociety;2)keyactors,advocatesandchampionsinitiating,(GDP)(highconfidence).Inaddition,inalargegroupofcountries,fuelmainstreamingandsustainingmomentumforclimateadaptation;3)taxes(althoughnotnecessarilydesignedforthepurposeofmitigation)4horizontalinterplaybetweensectors,actorsandpoliciesoperatingathavehadeffectsthatareakintosectoralcarbontaxes(robustevi-similaradministrativelevels;4)politicaldimensionsinplanninganddence,mediumagreement).Revenuesfromcarbontaxesorauctionedimplementation;and5)coordinationbetweenformalgovernmen-emissionallowancesareusedinsomecountriestoreduceothertaxestal,administrativeagenciesandprivatesectorsandstakeholderstoand/ortoprovidetransferstolow‐incomegroups.Thisillustratestheincreaseefficiency,representationandsupportforclimateadaptationgeneralprinciplethatmitigationpoliciesthatraisegovernmentreve-measures.{WGII15.2,15.5,16.3,Box15-1}nuegenerallyhavelowersocialcoststhanapproacheswhichdonot.{WGIIISPM.5.1}Existingandemergingeconomicinstrumentscanfosteradap-tationbyprovidingincentivesforanticipatingandreducingEconomicinstrumentsintheformofsubsidiesmaybeappliedimpacts(mediumconfidence).Instrumentsincludepublic-privateacrosssectors,andincludeavarietyofpolicydesigns,suchastaxfinancepartnerships,loans,paymentsforenvironmentalservices,rebatesorexemptions,grants,loansandcreditlines.Anincreas-improvedresourcepricing,chargesandsubsidies,normsandregula-ingnumberandvarietyofREpoliciesincludingsubsidies—motivatedtionsandrisksharingandtransfermechanisms.Riskfinancingmecha-bymanyfactors—havedrivenescalatedgrowthofREtechnologiesinnismsinthepublicandprivatesector,suchasinsuranceandriskpools,recentyears.Governmentpoliciesplayacrucialroleinacceleratingthecancontributetoincreasingresilience,butwithoutattentiontomajordeploymentofREtechnologies.Energyaccessandsocialandeconomicdesignchallenges,theycanalsoprovidedisincentives,causemarketdevelopmenthavebeentheprimarydriversinmostdevelopingcoun-failureanddecreaseequity.Governmentsoftenplaykeyrolesasregu-trieswhereassecureenergysupplyandenvironmentalconcernshavelators,providersorinsurersoflastresort.{WGIISPMC-1}beenmostimportantindevelopedcountries.Thefocusofpoliciesis107Topic4AdaptationandMitigationTable4.7SectoralPolicyInstruments.{WGIIITable15.2}PolicyEnergyTransportBuildingsIndustryAFOLUHumanSettlementsInstrumentsandInfrastructureEconomic-Carbontax(e.g.,-Fueltaxes-Carbonand/or-Carbontaxorenergy-Fertilizerornitrogen-Sprawltaxes,ImpactInstrumentsappliedtoelectricity-Congestioncharges,energytaxes(eithertaxtaxestoreducefees,exactions,–Taxesorfuels)sectoralornitrousoxide(N2O)split-rateproperty(carbontaxesvehicleregistrationeconomy-wide)-Wastedisposaltaxestaxes,taxincrementmaybefees,roadtollsorchargesfinance,bettermenteconomy-wide)-Vehicletaxestaxes,congestionchargesEconomic-Emissiontrading-Fuelandvehicle-Tradablecertificates-Emissiontrading-Emissioncredits-Urban-scalecapandInstruments-EmissioncreditsstandardsunderCDMtrade–Tradableforenergyefficiency-EmissioncreditsAllowancesundertheClean-Complianceschemes(maybeDevelopmentimprovements(whiteunderCDMoutsideKyotoeconomy-wide)Mechanism(CDM)protocol(national-TradableGreencertificates)-TradableGreenschemes)CertificatesCertificates-VoluntarycarbonmarketsEconomic-Fossilfuelsubsidy-Biofuelsubsidies-Subsidiesortax-Subsidies(e.g.,for-Creditlinesfor-SpecialImprovementInstrumentsremoval-Vehiclepurchaseexemptionsforenergyaudits)low-carbonorRedevelopment–Subsidiesinvestmentinagriculture,Districts-Feedintariffs(FITs)subsidiesefficientbuildings,-Fiscalincentives(e.g.,sustainableforestryforrenewableenergy-Feebatesretrofitsandforfuelswitching)products-SubsidizedloansRegulatory-Efficiencyor-Fueleconomy-Buildingcodesand-Energyefficiency-Nationalpoliciesto-MixedusezoningApproachesenvironmentalperformancestandardsstandardsforsupportREDD+-Developmentperformancestandardsequipmentincludingmonitoring,standards-Equipmentandreportingandrestrictions-Fuelqualityappliancestandards-Energymanagementverification-Affordablehousing-RenewablePortfoliostandardssystems(alsoStandards(RPS)for-Mandatesforenergyvoluntary)-Forestlawstoreducemandatesrenewableenergy-Greenhousegasretailerstoassistdeforestation-Siteaccesscontrols(RE)(GHG)emissioncustomersinvestin-Voluntary-Transferdevelopmentperformanceenergyefficiencyagreements(where-Airandwater-Equitableaccesstostandardsboundbyregulation)pollutioncontrolGHGrightselectricitygridprecursors-Designcodes-Regulatory-Labellingandpublic-Buildingcodes-Legalstatusofrestrictionstoprocurement-Landuseplanning-Streetcodeslong-termCO2encouragemodalregulationsandgovernance-Designstandardsstorageshifts(roadtorail)-Restrictiononuseofvehiclesincertainareas-Environmentalcapacityconstraintsonairports-UrbanplanningandzoningrestrictionsInformation-Fuellabelling-Energyaudits-Energyaudits-CertificationschemesProgrammes-Vehicleefficiency-Labelling-Benchmarkingforsustainableforest-Brokerageforpractices4labellingprogrammes-Energyadviceindustrial-InformationpoliciescooperationtosupportREDD+programmesincludingmonitoring,reportingandverificationGovernment-Researchand-Investmentintransit-Publicprocurement-Trainingand-Protectionof-ProvisionofutilityProvisionofdevelopmentandhumanpoweredofefficientbuildingseducationnational,state,andinfrastructure,suchPublicGoodsortransportandapplianceslocalforests.aselectricityServices-Infrastructure-Brokeragefordistribution,districtexpansion(district-Investmentinindustrial-Investmentinheating/coolingandheating/coolingoralternativefuelcooperationimprovementandwastewatercommoncarrier)infrastructurediffusionofconnections,etc.innovative-Low-emissionvehicletechnologiesin-Parkimprovementsprocurementagricultureand-Trailimprovementsforestry-UrbanrailVoluntary-Labelling-Voluntaryagreements-PromotionofActionsprogrammesforonenergytargets,sustainabilitybyefficientbuildingsadoptionofenergydevelopingstandards-Producteco-labellingmanagementsystems,andeducationalorresourceefficiencycampaigns108AdaptationandMitigationTopic4broadeningfromaconcentrationprimarilyonREelectricitytoincludeenergyaccess,livelihoodsandequitablesustainabledevelop-REheatingandcoolingandtransportation.{SRRENSPM.7}ment:{WGIIISPM.2}IntroductionThereductionofsubsidiesforGHG-relatedactivitiesinvari-•Mitigationscenariosreachingabout450or500ppmCO2-equivalentoussectorscanachieveemissionreductions,dependingontheby2100showreducedcostsforachievingairqualityandenergysocialandeconomiccontext(highconfidence).Whilesubsidiessecurityobjectives,withsignificantco-benefitsforhumanhealth,canaffectemissionsinmanysectors,mostoftherecentliteraturehasecosystemimpactsandsufficiencyofresourcesandresilienceoffocusedonsubsidiesforfossilfuels.SinceAR4asmallbutgrowingtheenergysystem.{WGIIISPM.4.1}literaturebasedoneconomy-widemodelshasprojectedthatcom-pleteremovalofsubsidiestofossilfuelsinallcountriescouldresult•Somemitigationpoliciesraisethepricesforsomeenergyser-inreductionsinglobalaggregateemissionsbymid-century(mediumvicesandcouldhampertheabilityofsocietiestoexpandaccessevidence,mediumagreement).Studiesvaryinmethodology,thetypetomodernenergyservicestounderservedpopulations(lowcon-anddefinitionofsubsidiesandthetimeframeforphaseoutconsid-fidence).Thesepotentialadversesideeffectscanbeavoidedwithered.Inparticular,thestudiesassesstheimpactsofcompleteremovaltheadoptionofcomplementarypoliciessuchasincometaxrebatesofallfossilfuelsubsideswithoutseekingtoassesswhichsubsidiesorotherbenefittransfermechanisms(mediumconfidence).Thearewastefulandinefficient,keepinginmindnationalcircumstances.costsofachievingnearlyuniversalaccesstoelectricityandclean{WGIIISPM.5.1}fuelsforcookingandheatingareprojectedtobebetweenUSD72to95billionperyearuntil2030withminimaleffectsonGHGemis-Regulatoryapproachesandinformationmeasuresarewidelysions(limitedevidence,mediumagreement)andmultiplebenefitsusedandareoftenenvironmentallyeffective(mediumevi-inhealthandairpollutantreduction(highconfidence).{WGIIIdence,mediumagreement).ExamplesofregulatoryapproachesSPM.5.1}includeenergyefficiencystandards;examplesofinformationpro-grammesincludelabellingprogrammesthatcanhelpconsumersmakeWhetherornotsideeffectsmaterialize,andtowhatextentsideeffectsbetter-informeddecisions.{WGIIISPM.5.1}materialize,willbecase-andsite-specific,anddependonlocalcir-cumstancesandthescale,scopeandpaceofimplementation.ManyMitigationpolicycoulddevaluefossilfuelassetsandreducerev-co-benefitsandadversesideeffectshavenotbeenwell-quantified.enuesforfossilfuelexporters,butdifferencesbetweenregions{WGIIISPM.4.1}andfuelsexist(highconfidence).Mostmitigationscenariosareassociatedwithreducedrevenuesfromcoalandoiltradeformajorexporters.Theeffectonnaturalgasexportrevenuesismoreuncertain.4.4.3TechnologydevelopmentandtransferTheavailabilityofCCSwouldreducetheadverseeffectofmitigationonthevalueoffossilfuelassets(mediumconfidence).{WGIIISPM.5.1}Technologypolicy(development,diffusionandtransfer)com-plementsothermitigationpoliciesacrossallscalesfrominter-Interactionsbetweenoramongmitigationpoliciesmaybesyn-nationaltosub-national,butworldwideinvestmentinresearchergisticormayhavenoadditiveeffectonreducingemissionsinsupportofGHGmitigationissmallrelativetooverallpublic(mediumevidence,highagreement).Forinstance,acarbontaxcanresearchspending(highconfidence).Technologypolicyincludeshaveanadditiveenvironmentaleffecttopoliciessuchassubsidiesfortechnology-push(e.g.,publicly-fundedR&D)anddemand-pull(e.g.,thesupplyofRE.Bycontrast,ifacapandtradesystemhasasufficientlygovernmentalprocurementprogrammes).Suchpoliciesaddressstringentcaptoaffectemission‐relateddecisions,thenotherpoliciesapervasivemarketfailurebecause,intheabsenceofgovernmenthavenofurtherimpactonreducingemissions(althoughtheymaypolicysuchaspatentprotection,theinventionofnewtechnologies4affectcostsandpossiblytheviabilityofmorestringentfuturetargets)andpracticesfromR&Deffortshasaspectsofapublicgoodand(mediumevidence,highagreement).Ineithercase,additionalpoliciesthustendstobeunder-providedbymarketforcesalone.Technologymaybeneededtoaddressmarketfailuresrelatingtoinnovationandsupportpolicieshavepromotedsubstantialinnovationanddiffusiontechnologydiffusion.{WGIIISPM.5.1}ofnewtechnologies,butthecost-effectivenessofsuchpoliciesisoftendifficulttoassess.TechnologypolicycanincreaseincentivesforSub-nationalclimatepoliciesareincreasinglyprevalent,bothparticipationandcompliancewithinternationalcooperativeefforts,incountrieswithnationalpoliciesandinthosewithout.Theseparticularlyinthelongrun.{WGIIISPM.5.1,2.6.5,3.11,13.9,13.12,policiesincludestateandprovincialclimateplanscombiningmarket,15.6.5}regulatoryandinformationinstruments,andsub-nationalcap-and-tradesystems.Inaddition,transnationalcooperationhasarisenamongManyadaptationeffortsalsocriticallyrelyondiffusionandsub-nationalactors,notablyamonginstitutionalinvestors,NGOstransferoftechnologiesandmanagementpractices,buttheirseekingtogoverncarbonoffsetmarkets,andnetworksofcitiesseek-effectiveusedependsonasuitableinstitutional,regulatory,ingtocollaborateingeneratinglow-carbonurbandevelopment.socialandculturalcontext(highconfidence).Adaptationtech-{WGIII13.5.2,15.2.4,15.8}nologiesareoftenfamiliarandalreadyappliedelsewhere.However,thesuccessoftechnologytransfermayinvolvenotonlytheprovisionCo-benefitsandadversesideeffectsofmitigationcouldaffectoffinanceandinformation,butalsostrengtheningofpolicyandreg-achievementofotherobjectivessuchasthoserelatedtohumanulatoryenvironmentsandcapacitiestoabsorb,employandimprovehealth,foodsecurity,biodiversity,localenvironmentalquality,technologiesappropriatetolocalcircumstances.{WGII15.4}109Topic4AdaptationandMitigation800700Changesinannualinvestmentﬂows2010–2029(billionUSD2010/yr)6005004003002001000–100OECDnon-OECDWorld–200–300MaxMedianMinMean–400RenewablesNuclearPowerplantsFossilfuelExtractionofEnergyefﬁciencywithCCSpowerplantsfossilfuelsacrosssectorsTotalelectricitywithoutCCSgeneration445n=445445445445445334Figure4.4Changeinannualinvestmentflowsfromtheaveragebaselineleveloverthenexttwodecades(2010to2029)formitigationscenariosthatstabilizeconcentrations(withoutovershoot)withintherangeofapproximately430to530ppmCO2-eqby2100.Totalelectricitygeneration(leftmostcolumn)isthesumofrenewableandnuclearenergy,powerplantswithCCS,andfossil-fuelpowerplantswithoutCCS.Theverticalbarsindicatetherangebetweentheminimumandmaximumestimate;thehorizontalbarindicatesthemedian.Thenumbersinthebottomrowshowthetotalnumberofstudiesintheliteratureusedintheassessment.Individualtechnologiesshownarefoundtobeusedindif-ferentmodelscenariosineitheracomplementaryorasynergisticway,dependinglargelyontechnology-specificassumptionsandthetimingandambitionlevelofthephase-inofglobalclimatepolicies.{WGIIIFigureSPM.9}44.4.4Investmentandfinanceannualincrementalenergyefficiencyinvestmentsintransport,industryandbuildingsisprojectedtoriseinthescenariosbyaboutUSD336Substantialreductionsinemissionswouldrequirelargechanges(1to641)billion.Globaltotalannualinvestmentintheenergysystemininvestmentpatterns(highconfidence).MitigationscenariosispresentlyaboutUSD1,200billion.Thisnumberincludesonlyenergyinwhichpoliciesstabilizeatmosphericconcentrations(withoutover-supplyofelectricityandheatandrespectiveupstreamanddownstreamshoot)intherangefrom430to530ppmCO2-eqby21004530leadtosub-activities.Energyefficiencyinvestmentorunderlyingsectorinvestmentstantialshiftsinannualinvestmentflowsduringtheperiod2010–2029isnotincluded(Figure4.4).{WGIIISPM.5.1,16.2}comparedtobaselinescenarios.Overthenexttwodecades(2010–2029),annualinvestmentsinconventionalfossilfueltechnologiesThereisnowidelyagreeddefinitionofwhatconstitutesclimateassociatedwiththeelectricitysupplysectorareprojectedtodeclineinfinance,butestimatesofthefinancialflowsassociatedwiththescenariosbyaboutUSD30(2to166)billion(median:–20%com-climatechangemitigationandadaptationareavailable.Seeparedto2010)whileannualinvestmentinlowcarbonelectricitysupplyFigure4.5foranoverviewofclimatefinanceflows.Publishedassess-(i.e.,renewables,nuclearandelectricitywithCCS)isprojectedtorisementsofallcurrentannualfinancialflowswhoseexpectedeffectisinthescenariosbyaboutUSD147(31to360)billion(median:+100%toreducenetGHGemissionsand/ortoenhanceresiliencetoclimatecomparedto2010)(limitedevidence,mediumagreement).Inaddition,changeandclimatevariabilityshowUSD343to385billionperyear45Thisrangecomprisesscenariosthatreach430to480ppmCO2-eqby2100(likelytolimitwarmingto2°Cabovepre-industriallevels)andscenariosthatreach480to530ppmCO2-eqby2100(withoutovershoot:morelikelythannottolimitwarmingto2°Cabovepre-industriallevels).110AdaptationandMitigationTopic4SourceofcapitalManagerofcapitalFinancialinstrumentProjectowner/sponsorProjectIntroductionCarbontaxesGovernmentsGrantsGovernments,AdaptationandauctionofcorporationsMitigationallowancesNational,Projectdebtandhouseholdsbilateraland(marketbased/(developedandGeneraltaxmultilateralconcessional)developingrevenueﬁnancialcountries)institutionsProjectlevelCDMlevyequityCommercialFundsfromﬁnancialBalancesheetcapitalmarketsinstitutionsﬁnancingCorporateCorporateCreditcashﬂowactorsandenhancement/institutionalRiskHouseholdinvestorsmanagementincome(privateandpublic)HouseholdsFigure4.5Overviewofclimatefinanceflows.Note:Capitalshouldbeunderstoodtoincludeallrelevantfinancialflows.Thesizeoftheboxesisnotrelatedtothemagnitudeofthefinancialflow.{WGIIIFigureTS.40}globally(mediumconfidence).Outofthis,totalpublicclimatefinanceinvestmentbyimprovingthereturnadjustedfortheriskforprivatethatflowedtodevelopingcountriesisestimatedtobebetweenUSD35actors.Public-privateriskreductioninitiatives(suchasinthecontextand49billionperyearin2011and2012(mediumconfidence).Esti-ofinsurancesystems)andeconomicdiversificationareexamplesofmatesofinternationalprivateclimatefinanceflowingtodevelopingadaptationactionenablingandrelyingonprivatesectorparticipation.countriesrangefromUSD10to72billionperyearincludingforeign{WGIISPMB-2,SPMC-1,WGIIISPM.5.1}directinvestmentasequityandloansintherangeofUSD10to37billionperyearovertheperiodof2008–2011(mediumconfidence).{WGIIIFinancialresourcesforadaptationhavebecomeavailableSPM.5.1}moreslowlythanformitigationinbothdevelopedanddevel-opingcountries.LimitedevidenceindicatesthatthereisagapInmanycountries,theprivatesectorplayscentralrolesinthebetweenglobaladaptationneedsandthefundsavailablefor4processesthatleadtoemissionsaswellastomitigationandadaptation(mediumconfidence).Potentialsynergiesbetweenadaptation.Withinappropriateenablingenvironments,thepri-internationalfinancefordisasterriskmanagementandadaptationvatesector,alongwiththepublicsector,canplayanimpor-toclimatechangehavenotyetbeenfullyrealized(highconfidence).tantroleinfinancingmitigationandadaptation(mediumevi-Thereisaneedforbetterassessmentofglobaladaptationcosts,fund-dence,highagreement).Theshareoftotalmitigationfinancefromingandinvestment.Studiesestimatingtheglobalcostofadaptationtheprivatesector,acknowledgingdatalimitations,isestimatedtobearecharacterizedbyshortcomingsindata,methodsandcoverageonaveragebetweentwo-thirdsandthree-fourthsonthegloballevel(highconfidence).{WGIISPMC-1,14.2,SREXSPM}(2010–2012)(limitedevidence,mediumagreement).Inmanycoun-tries,publicfinanceinterventionsbygovernmentsandinternationaldevelopmentbanksencourageclimateinvestmentsbytheprivatesectorandprovidefinancewhereprivatesectorinvestmentislimited.Thequalityofacountry’senablingenvironmentincludestheeffective-nessofitsinstitutions,regulationsandguidelinesregardingthepri-vatesector,securityofpropertyrights,credibilityofpoliciesandotherfactorsthathaveasubstantialimpactonwhetherprivatefirmsinvestinnewtechnologiesandinfrastructures.Dedicatedpolicyinstrumentsandfinancialarrangements,forexample,creditinsurance,feed-intar-iffs,concessionalfinanceorrebatesprovideanincentiveformitigation111Topic4AdaptationandMitigation4.5Trade-offs,synergiesandAnintegratedapproachtoenergyplanningandimplementationintegratedresponsesthatexplicitlyassessesthepotentialforco-benefitsandthepresenceofadversesideeffectscancapturecomplementaritiesTherearemanyopportunitiestolinkmitigation,adap-acrossmultipleclimate,socialandenvironmentalobjectivestationandthepursuitofothersocietalobjectives(mediumconfidence).Therearestronginteractiveeffectsacrossthroughintegratedresponses(highconfidence).Suc-variousenergypolicyobjectives,suchasenergysecurity,airquality,cessfulimplementationreliesonrelevanttools,suit-healthandenergyaccess(seeFigure3.5)andbetweenarangeofablegovernancestructuresandenhancedcapacitytosocialandenvironmentalobjectivesandclimatemitigationobjectivesrespond(mediumconfidence).(seeTable4.5).Anintegratedapproachcanbeassistedbytoolssuchascost-benefitanalysis,cost-effectivenessanalysis,multi-criteriaanalysisandexpectedutilitytheory.Italsorequiresappropriatecoordinatinginstitutions.{WGIIIFigureSPM.6,TS.1,TS.3}Agrowingevidencebaseindicatescloselinksbetweenadaptationandmitigation,theirco-benefitsandadversesideeffects,andrecognizesExplicitconsiderationofinteractionsamongwater,food,energysustainabledevelopmentastheoverarchingcontextforclimatepolicyandbiologicalcarbonsequestrationplaysanimportantrolein(seeSections3.5,4.1,4.2and4.3).Developingtoolstoaddressthesesupportingeffectivedecisionsforclimateresilientpathwayslinkagesiscriticaltothesuccessofclimatepolicyinthecontextof(mediumevidence,highagreement).Bothbiofuel-basedpowersustainabledevelopment(seealsoSections4.4and3.5).Thissectiongenerationandlarge-scaleafforestationdesignedtomitigateclimatepresentsexamplesofintegratedresponsesinspecificpolicyarenas,aschangecanreducecatchmentrun-off,whichmayconflictwithalter-wellassomeofthefactorsthatpromoteorimpedepoliciesaimedatnativewaterusesforfoodproduction,humanconsumptionorthemultipleobjectives.maintenanceofecosystemfunctionandservices(seealsoBox3.4).Conversely,irrigationcanincreasetheclimateresilienceoffoodandIncreasingeffortstomitigateandadapttoclimatechangefibreproductionbutreduceswateravailabilityforotheruses.{WGIIimplyanincreasingcomplexityofinteractions,encompassingBoxCC-WE,BoxTS.9}connectionsamonghumanhealth,water,energy,landuseandbiodiversity(veryhighconfidence).MitigationcansupporttheAnintegratedresponsetourbanizationprovidessubstantialachievementofothersocietalgoals,suchasthoserelatedtohumanopportunitiesforenhancedresilience,reducedemissionsandhealth,foodsecurity,environmentalquality,energyaccess,livelihoodsmoresustainabledevelopment(mediumconfidence).Urbanandsustainabledevelopment,althoughtherecanalsobenegativeareasaccountformorethanhalfofglobalprimaryenergyuseandeffects.Adaptationmeasuresalsohavethepotentialtodelivermiti-energy-relatedCO2emissions(mediumevidence,highagreement)andgationco-benefits,andviceversa,andsupportothersocietalgoals,containahighproportionofthepopulationandeconomicactivitiesatthoughtrade-offscanalsoarise.{WGIISPMC-1,SPMC-2,8.4,9.3–9.4,riskfromclimatechange.Inrapidlygrowingandurbanizingregions,11.9,BoxCC-WE,WGIIITableTS.3,TableTS.4,TableTS.5,TableTS.6,mitigationstrategiesbasedonspatialplanningandefficientinfrastruc-TableTS.7}turesupplycanavoidthelock-inofhighemissionpatterns.Mixed-usezoning,transport-orienteddevelopment,increaseddensityandco-lo-Integrationofadaptationandmitigationintoplanningandcatedjobsandhomescanreducedirectandindirectenergyuseacrossdecision-makingcancreatesynergieswithsustainabledevelop-sectors.Compactdevelopmentofurbanspacesandintelligentdensi-ment(highconfidence).Synergiesandtrade-offsamongmitigationficationcanpreservelandcarbonstocksandlandforagricultureandandadaptationpoliciesandpoliciesadvancingothersocietalgoalsbioenergy.Reducedenergyandwaterconsumptioninurbanareas4canbesubstantial,althoughsometimesdifficulttoquantifyespeciallythroughgreeningcitiesandrecyclingwaterareexamplesofmitigationinwelfareterms(seealsoSection3.5).Amulti-objectiveapproachtoactionswithadaptationbenefits.Buildingresilientinfrastructuresys-policy-makingcanhelpmanagethesesynergiesandtrade-offs.Poli-temscanreducevulnerabilityofurbansettlementsandcitiestocoastalciesadvancingmultiplegoalsmayalsoattractgreatersupport.{WGIIflooding,sealevelriseandotherclimate-inducedstresses.{WGIISPMC-1,SPMC-2,20.3,WGIII1.2.1,3.6.3,4.3,4.6,4.8,6.6.1}SPMB-2,SPMC-1,TSB-2,TSC-1,TSC-2,WGIIISPM.4.2.5,TS.3}Effectiveintegratedresponsesdependonsuitabletoolsandgov-ernancestructures,aswellasadequatecapacity(mediumconfi-dence).Managingtrade-offsandsynergiesischallengingandrequirestoolstohelpunderstandinteractionsandsupportdecision-makingatlocalandregionalscales.Integratedresponsesalsodependongovernancethatenablescoordinationacrossscalesandsectors,sup-portedbyappropriateinstitutions.Developingandimplementingsuitabletoolsandgovernancestructuresoftenrequiresupgradingthehumanandinstitutionalcapacitytodesignanddeployintegratedresponses.{WGIISPMC-1,SPMC-2,2.2,2.4,15.4,15.5,16.3,Table14-1,Table16-1,WGIIITS.1,TS.3,15.2}112AnnexesANNEXIUserGuide115AnnexIUserGuideUserGuideAsdefinedintheIPCCProcedures,theSynthesisReport(SYR)synthesisesandintegratesmaterialcontainedwithinIPCCAssessmentReportsandSpecialReports.ThescopeoftheSYRoftheFifthAssessmentReport(AR5)includesmaterialcontainedinthethreeWorkingGroupcontributionstotheAR5,anditdrawsoninformationcontainedinotherIPCCReportsasrequired.TheSYRisbasedexclusivelyonassessmentsbytheIPCCIWorkingGroups;itdoesnotrefertoorassesstheprimaryscientificliteratureitself.TheSYRisaself-contained,condensedsummaryofthemuchricherinformationcontainedintheunderlyingWorkingGroupReports.Usersmaywishtoaccessrelevantmaterialattherequiredlevelofdetailinthefollowingmanner:thereportcontainsaSummaryforPolicymakers(SPM)thatprovidesthemostcondensedsummaryofthecurrentunderstandingofscientific,technicalandsocio-economicaspectsofclimatechange.AllreferencesincurlybracketsinthisSPMrefertosectionsinthelongerreport.ThelongerreportconsistsofanIntroductionandfourTopics.ThenumbersoftheSPMsectionslargelycorrespondwiththesectionnumbersoftheTopics.Attheendofeachparagraph,referencesareprovidedinitalicsbetweencurlybrackets.TheserefertotheSummariesforPolicymakers(SPMs),TechnicalSummaries(TSs),ExecutiveSummariesofchapters(ESs)andchapters(withchapterandsectionnumbers)oftheunderlyingWorkingGroupcontributionstotheAR5andSpecialReportsoftheAR5.ReferencestotheIPCCFourthAssessmentReport(AR4)in2007areidentifiedbyadding“AR4”tothereference.UserswhowishtogainabetterunderstandingofscientificdetailsoraccesstheprimaryscientificliteratureonwhichtheSYRisbasedshouldrefertochaptersectionsoftheunderlyingWorkingGroupreportsthatarecitedinthelongerreportoftheSYR.TheindividualchaptersoftheWorkingGroupreportsprovidereferencestotheprimaryscientificliteratureonwhichIPCCassessmentsarebased,andalsoofferthemostdetailedregion-andsector-specificinformation.Aglossary,alistofacronyms,listsofauthorsandreviewers,alistofIPCCpublications(annexes)andanindexareprovidedtofurtherfacilitatetheuseofthisreport.116ANNEXIIGlossaryGlossaryEditorsKatharineJ.Mach(USA),SergePlanton(France),ChristophvonStechow(Germany)GlossaryContributorsMylesR.Allen(UnitedKingdom),JohnBroome(UnitedKingdom),JohnA.Church(Australia),LeonClarke(USA),PiersForster(UnitedKingdom),PierreFriedlingstein(UnitedKingdom/Belgium),JanFuglestvedt(Norway),GabrieleHegerl(UnitedKingdom/Germany),BlancaJiménezCisneros(Mexico/UNESCO),VladimirKattsov(RussianFederation),HowardKunreuther(USA),LeoMeyer(TheNetherlands),JanMinx(Germany),YacobMulugetta(Ethiopia),KarenO’Brien(Norway),MichaelOppenheimer(USA),Gian-KasperPlattner(Switzerland),AndyReisinger(NewZealand),RobertScholes(SouthAfrica),MelindaTignor(Switzerland/USA),DetlefvanVuuren(TheNetherlands)TSUFacilitationNoëmieLeprince-Ringuet(France)Thisannexshouldbecitedas:IPCC,2014:AnnexII:Glossary[Mach,K.J.,S.PlantonandC.vonStechow(eds.)].In:Cli-mateChange2014:SynthesisReport.ContributionofWorkingGroupsI,IIandIIItotheFifthAssessmentReportoftheIntergovernmentalPanelonClimateChange[CoreWritingTeam,R.K.PachauriandL.A.Meyer(eds.)].IPCC,Geneva,Switzerland,pp.117-130.117AnnexIIGlossaryThisglossarydefinessomespecifictermsastheCoreWritingAfforestationTeamoftheSynthesisReportintendsthemtobeinterpretedPlantingofnewforestsonlandsthathistoricallyhavenotcontainedinthecontextofthisreport.Red,italicizedwordsindicateforests.Foradiscussionofthetermforestandrelatedtermssuchasthatthetermisdefinedintheglossary.Thereferencestoafforestation,reforestationanddeforestation,seetheIPCCSpecialWorkingGroups(WG)I,IIandIIIinitalicsattheendofeachReportonLandUse,Land-UseChange,andForestry(IPCC,2000b).terminthisglossaryrefertotheAR5WGglossariesandSeealsoinformationprovidedbytheUnitedNationsFrameworkCon-shouldbereadas:WGI(IPCC,2013a),WGII(IPCC,2014a),ventiononClimateChange(UNFCCC,2013)andthereportonDefini-andWGIII(IPCC,2014b).tionsandMethodologicalOptionstoInventoryEmissionsfromDirectHuman-inducedDegradationofForestsandDevegetationofOtherVegetationTypes(IPCC,2003).{WGI,III}Abruptchange/abruptclimatechangeAgriculture,ForestryandOtherLandUse(AFOLUandFOLU/AbruptchangereferstoachangethatissubstantiallyfasterthantheLULUCF)rateofchangeintherecenthistoryoftheaffectedcomponentsofaAFOLUplaysacentralroleforfoodsecurityandsustainabledevel-IIscylismteamte.sAybstreumpttchlaimttaatkeecshpalnacgeeorveeferrasfteowadleacragdee-sscoarlelecshs,apnegresisintst(hoerompomreenotf.thThreeemstaraintegmieitsig:parteiovnenotipotnioonfsewmiitshsiinonAsFtOoLtUheiantvmolovsephoenreeboyrisanticipatedtopersist)foratleastafewdecadesandcausessubstan-conservingexistingcarbonpoolsinsoilsorvegetationorbyreducingtialdisruptionsinhumanandnaturalsystems.{WGI,II,III}emissionsofmethaneandnitrousoxide;sequestration—increasingthesizeofexistingcarbonpoolsandtherebyextractingcarbondioxideAdaptation(CO2)fromtheatmosphere;andsubstitution—substitutingbiologicalTheprocessofadjustmenttoactualorexpectedclimateanditseffects.productsforfossilfuelsorenergy-intensiveproducts,therebyreduc-Inhumansystems,adaptationseekstomoderateoravoidharmoringCO2emissions.Demand-sidemeasures(e.g.,reducinglossesandexploitbeneficialopportunities.Insomenaturalsystems,humaninter-wastesoffood,changesinhumandiet,orchangesinwoodconsump-ventionmayfacilitateadjustmenttoexpectedclimateanditseffects1.tion)mayalsoplayarole.{WGII,III}FOLU(ForestryandOtherLandUse)—alsoreferredtoasLULUCFAdaptationdeficit(LandUse,Land-UseChange,andForestry)—isthesubsetofAFOLUThegapbetweenthecurrentstateofasystemandastatethatmini-emissionsandremovalsofgreenhousegases(GHGs)resultingfrommizesadverseimpactsfromexistingclimateconditionsandvariability.directhuman-inducedlanduse,land-usechange,andforestryactivi-{WGII}tiesexcludingagriculturalemissions.{WGIII}AdaptationlimitAlbedoThepointatwhichanactor’sobjectives(orsystemneeds)cannotbeThefractionofsolarradiationreflectedbyasurfaceorobject,oftensecuredfromintolerablerisksthroughadaptiveactions.{WGII}expressedasapercentage.Snow-coveredsurfaceshaveahighalbedo,thealbedoofsoilsrangesfromhightolowandvegetation-coveredHardadaptationlimitsurfacesandoceanshavealowalbedo.TheEarth’splanetaryalbedoNoadaptiveactionsarepossibletoavoidintolerablerisks.variesmainlythroughvaryingcloudiness,snow,ice,leafareaandlandcoverchanges.{WGI,III}SoftadaptationlimitOptionsarecurrentlynotavailabletoavoidintolerablerisksAltimetrythroughadaptiveaction.AtechniqueformeasuringtheheightoftheEarth’ssurfacewithrespecttothegeocentreoftheEarthwithinadefinedterrestrialrefer-Adaptivecapacityenceframe(geocentricsealevel).{WGI}Theabilityofsystems,institutions,humansandotherorganismstoadjusttopotentialdamage,totakeadvantageofopportunities,ortoAncillarybenefitsrespondtoconsequences2.{WGII,III}SeeCo-benefits.{WGII,III}AdversesideeffectsAttributionThenegativeeffectsthatapolicyormeasureaimedatoneobjec-SeeDetectionandattribution.{WGI,II}.tivemighthaveonotherobjectives,irrespectiveoftheneteffectonoverallsocialwelfare.AdversesideeffectsareoftensubjecttoBaseline/referenceuncertaintyanddependonlocalcircumstancesandimplementa-Thebaseline(orreference)isthestateagainstwhichchangeismeas-tionpractices,amongotherfactors.SeealsoCo-benefitsandRisk.ured.Abaselineperiodistheperiodrelativetowhichanomaliesare{WGIII}computed.Inthecontextoftransformationpathways,thetermbaseline1Reflectingprogressinscience,thisglossaryentrydiffersinbreadthandfocusfromtheentryusedintheFourthAssessmentReportandotherIPCCreports.2ThisglossaryentrybuildsfromdefinitionsusedinpreviousIPCCreportsandtheMillenniumEcosystemAssessment(MEA,2005).118GlossaryAnnexIIscenariosreferstoscenariosthatarebasedontheassumptionthatnodevelopingcountriesproposedwaystolimittheirgrowthofemissionsmitigationpoliciesormeasureswillbeimplementedbeyondthosethatintheshapeofplansofaction.{WGIII}arealreadyinforceand/orarelegislatedorplannedtobeadopted.Baselinescenariosarenotintendedtobepredictionsofthefuture,CarboncyclebutrathercounterfactualconstructionsthatcanservetohighlighttheThetermusedtodescribetheflowofcarbon(invariousforms,e.g.,aslevelofemissionsthatwouldoccurwithoutfurtherpolicyeffort.Typ-carbondioxide(CO2))throughtheatmosphere,ocean,terrestrialandically,baselinescenariosarethencomparedtomitigationscenariosmarinebiosphereandlithosphere.Inthisreport,thereferenceunitforthatareconstructedtomeetdifferentgoalsforgreenhousegas(GHG)theglobalcarboncycleisGtCO2orGtC(Gigatonneofcarbon=1GtCemissions,atmosphericconcentrationsortemperaturechange.The=1015gramsofcarbon.Thiscorrespondsto3.667GtCO2).{WGI,II,III}termbaselinescenarioisusedinterchangeablywithreferencescenarioandnopolicyscenario.Inmuchoftheliteraturethetermisalsosynon-CarbonDioxideCaptureandStorage(CCS)ymouswiththetermbusiness-as-usual(BAU)scenario,althoughtheAprocessinwhicharelativelypurestreamofcarbondioxide(CO2)termBAUhasfallenoutoffavourbecausetheideaofbusinessasfromindustrialandenergy-relatedsourcesisseparated(captured),con-usualincentury-longsocio-economicprojectionsishardtofathom.ditioned,compressedandtransportedtoastoragelocationforlong-S(ReCePas)lsaondEmSRisEsSiosncesnceanriaorsi.o{,WRGeIp,rIeI,sIeInI}tativeConcentrationPathwaystDeiromxidiseoClaatpiotunrefroamndtShteoraatgmeo(sBpEhCeCreS.)SaenedaSlesqouBesiotreanteiorgny.{WanGdIICI}arbonIIBiodiversityCarbonDioxideRemoval(CDR)Thevariabilityamonglivingorganismsfromterrestrial,marineandCarbonDioxideRemovalmethodsrefertoasetoftechniquesthataimotherecosystems.Biodiversityincludesvariabilityatthegenetic,spe-toremoveCO2directlyfromtheatmospherebyeither(1)increasingciesandecosystemlevels3.{WGII,III}naturalsinksforcarbonor(2)usingchemicalengineeringtoremovetheCO2,withtheintentofreducingtheatmosphericCO2concentration.BioenergyandCarbonDioxideCaptureandStorage(BECCS)CDRmethodsinvolvetheocean,landandtechnicalsystems,includingTheapplicationofCarbonDioxideCaptureandStorage(CCS)technol-suchmethodsasironfertilization,large-scaleafforestationanddirectogytobioenergyconversionprocesses.Dependingonthetotallife-captureofCO2fromtheatmosphereusingengineeredchemicalmeans.cycleemissions,includingtotalmarginalconsequentialeffects(fromSomeCDRmethodsfallunderthecategoryofgeoengineering,thoughindirectland-usechange(iLUC)andotherprocesses),BECCShasthethismaynotbethecaseforothers,withthedistinctionbeingbasedonpotentialfornetcarbondioxide(CO2)removalfromtheatmosphere.themagnitude,scaleandimpactoftheparticularCDRactivities.TheSeealsoSequestration.{WGIII}boundarybetweenCDRandmitigationisnotclearandtherecouldbesomeoverlapbetweenthetwogivencurrentdefinitions(IPCC,2012b,Burdensharing/effortsharingp.2).SeealsoSolarRadiationManagement(SRM).{WGI,III}Inthecontextofmitigation,burdensharingreferstosharingtheeffortofreducingthesourcesorenhancingthesinksofgreenhousegasesCarbonintensity(GHGs)fromhistoricalorprojectedlevels,usuallyallocatedbysomeTheamountofemissionsofcarbondioxide(CO2)releasedperunitofcriteria,aswellassharingthecostburdenacrosscountries.{WGIII}anothervariablesuchasGrossDomesticProduct(GDP),outputenergyuseortransport.{WGIII}CancúnAgreementsAsetofdecisionsadoptedatthe16thSessionoftheConferenceoftheCarbonpriceParties(COP)totheUnitedNationsFrameworkConventiononClimateThepriceforavoidedorreleasedcarbondioxide(CO2)orCO2-equivalentChange(UNFCCC),includingthefollowing,amongothers:thenewlyemissions.Thismayrefertotherateofacarbontax,orthepriceofestablishedGreenClimateFund(GCF),anewlyestablishedtechnol-emissionpermits.Inmanymodelsthatareusedtoassesstheeconomicogymechanism,aprocessforadvancingdiscussionsonadaptation,acostsofmitigation,carbonpricesareusedasaproxytorepresenttheformalprocessforreportingmitigationcommitments,agoaloflimitinglevelofeffortinmitigationpolicies.{WGIII}globalmeansurfacetemperatureincreaseto2°CandanagreementonMRV—Measurement,ReportingandVerificationforthosecountriesCarbontaxthatreceiveinternationalsupportfortheirmitigationefforts.{WGIII}Alevyonthecarboncontentoffossilfuels.Becausevirtuallyallofthecarboninfossilfuelsisultimatelyemittedascarbondioxide(CO2),aCancúnPledgescarbontaxisequivalenttoanemissiontaxonCO2emissions.{WGIII}During2010,manycountriessubmittedtheirexistingplansforcon-trollinggreenhousegas(GHG)emissionstotheClimateChangeSec-ClimateretariatandtheseproposalshavenowbeenformallyacknowledgedClimateinanarrowsenseisusuallydefinedastheaverageweather,orundertheUnitedNationsFrameworkConventiononClimateChangemorerigorously,asthestatisticaldescriptionintermsofthemeanandvar-(UNFCCC).Developedcountriespresentedtheirplansintheshapeofiabilityofrelevantquantitiesoveraperiodoftimerangingfrommonthseconomy-widetargetstoreduceemissions,mainlyupto2020,whiletothousandsormillionsofyears.Theclassicalperiodforaveragingthese3ThisglossaryentrybuildsfromdefinitionsusedintheGlobalBiodiversityAssessment(Heywood,1995)andtheMillenniumEcosystemAssessment(MEA,2005).119AnnexIIGlossaryvariablesis30years,asdefinedbytheWorldMeteorologicalOrganiza-coversprivateandpublicfunds,domesticandinternationalflowstion.Therelevantquantitiesaremostoftensurfacevariablessuchastem-andexpendituresformitigationandadaptationtocurrentclimateperature,precipitationandwind.Climateinawidersenseisthestate,variabilityaswellasfutureclimatechange.includingastatisticaldescription,oftheclimatesystem.{WGI,II,III}TotalclimatefinanceflowingtodevelopingcountriesClimatechangeTheamountofthetotalclimatefinanceinvestedindevelopingClimatechangereferstoachangeinthestateoftheclimatethatcancountriesthatcomesfromdevelopedcountries.Thiscoversprivatebeidentified(e.g.,byusingstatisticaltests)bychangesinthemeanandpublicfunds.and/orthevariabilityofitspropertiesandthatpersistsforanextendedperiod,typicallydecadesorlonger.Climatechangemaybeduetonat-PrivateclimatefinanceflowingtodevelopingcountriesuralinternalprocessesorexternalforcingssuchasmodulationsoftheFinanceandinvestmentbyprivateactorsin/fromdevelopedcoun-solarcycles,volcaniceruptionsandpersistentanthropogenicchangestriesformitigationandadaptationactivitiesindevelopingcountries.inthecompositionoftheatmosphereorinlanduse.NotethattheFrameworkConventiononClimateChange(UNFCCC),initsArticle1,PublicclimatefinanceflowingtodevelopingcountriesIIddeirfeinctelysoclriminadtierecchtlayntgoehausm:‘aancahcatnivgiteyothfactlimaltaetreswthheicchomispaotstirtiibounteodfFinanceprovidedbydevelopedcountries’governmentsandbilateralinstitutionsaswellasbymultilateralinstitutionsformitigationandtheglobalatmosphereandwhichisinadditiontonaturalclimatevaria-adaptationactivitiesindevelopingcountries.Mostofthefundsbilityobservedovercomparabletimeperiods’.TheUNFCCCthusmakesprovidedareconcessionalloansandgrants.adistinctionbetweenclimatechangeattributabletohumanactivitiesalteringtheatmosphericcompositionandclimatevariabilityattributa-Climatemodel(spectrumorhierarchy)bletonaturalcauses.SeealsoDetectionandAttribution.{WGI,II,III}Anumericalrepresentationoftheclimatesystembasedonthephys-ical,chemicalandbiologicalpropertiesofitscomponents,theirinter-Climateextreme(extremeweatherorclimateevent)actionsandfeedbackprocessesandaccountingforsomeofitsknownSeeExtremeweatherevent.{WGI,II}properties.Theclimatesystemcanberepresentedbymodelsofvaryingcomplexity;thatis,foranyonecomponentorcombinationofcompo-Climatefeedbacknentsaspectrumorhierarchyofmodelscanbeidentified,differinginAninteractioninwhichaperturbationinoneclimatequantitycausessuchaspectsasthenumberofspatialdimensions,theextenttowhichachangeinasecondandthechangeinthesecondquantityultimatelyphysical,chemicalorbiologicalprocessesareexplicitlyrepresented,orleadstoanadditionalchangeinthefirst.Anegativefeedbackisoneinthelevelatwhichempiricalparametrizationsareinvolved.Coupledwhichtheinitialperturbationisweakenedbythechangesitcauses;aAtmosphere–OceanGeneralCirculationModels(AOGCMs)provideapositivefeedbackisoneinwhichtheinitialperturbationisenhanced.representationoftheclimatesystemthatisnearoratthemostcom-IntheFifthAssessmentReport,asomewhatnarrowerdefinitionisprehensiveendofthespectrumcurrentlyavailable.Thereisanevo-oftenusedinwhichtheclimatequantitythatisperturbedisthegloballutiontowardsmorecomplexmodelswithinteractivechemistryandmeansurfacetemperature,whichinturncauseschangesintheglobalbiology.Climatemodelsareappliedasaresearchtooltostudyandradiationbudget.Ineithercase,theinitialperturbationcaneitherbesimulatetheclimateandforoperationalpurposes,includingmonthly,externallyforcedorariseaspartofinternalvariability.{WGI,II,III}seasonalandinterannualclimatepredictions.{WGI,II,III}ClimatefinanceClimateprojectionThereisnoagreeddefinitionofclimatefinance.ThetermclimatefinanceAclimateprojectionisthesimulatedresponseoftheclimatesystemisappliedbothtothefinancialresourcesdevotedtoaddressingclimatetoascenariooffutureemissionorconcentrationofgreenhousegaseschangegloballyandtofinancialflowstodevelopingcountriestoassist(GHGs)andaerosols,generallyderivedusingclimatemodels.Climatetheminaddressingclimatechange.Theliteratureincludesseveralconceptsprojectionsaredistinguishedfromclimatepredictionsbytheirdepend-inthesecategories,amongwhichthemostcommonlyusedinclude:{WGIII}enceontheemission/concentration/radiativeforcingscenarioused,whichisinturnbasedonassumptionsconcerning,forexample,futureIncrementalcostssocio-economicandtechnologicaldevelopmentsthatmayormaynotThecostofcapitaloftheincrementalinvestmentandthechangeberealized.{WGI,II,III}ofoperatingandmaintenancecostsforamitigationoradaptationprojectincomparisontoareferenceproject.ItcanbecalculatedasClimate-resilientpathwaysthedifferenceofthenetpresentvaluesofthetwoprojects.IterativeprocessesformanagingchangewithincomplexsystemsinordertoreducedisruptionsandenhanceopportunitiesassociatedwithIncrementalinvestmentclimatechange.{WGII}Theextracapitalrequiredfortheinitialinvestmentforamitigationoradaptationprojectincomparisontoareferenceproject.ClimateresponseSeeClimatesensitivity.{WGI}TotalclimatefinanceAllfinancialflowswhoseexpectedeffectistoreducenetgreen-Climatesensitivityhousegas(GHG)emissionsand/ortoenhanceresiliencetotheInIPCCreports,equilibriumclimatesensitivity(units:°C)referstotheimpactsofclimatevariabilityandtheprojectedclimatechange.Thisequilibrium(steadystate)changeintheannualglobalmeansurface120GlossaryAnnexIItemperaturefollowingadoublingoftheatmosphericequivalentcarbonTheCO2-equivalentemissionisobtainedbymultiplyingtheemissiondioxide(CO2)concentration.Owingtocomputationalconstraints,theofaGHGbyitsGlobalWarmingPotential(GWP)forthegiventimeequilibriumclimatesensitivityinaclimatemodelissometimesesti-horizon(seeWGIChapter8,Table8.A.1andWGIIIAnnexII.9.1formatedbyrunninganatmosphericgeneralcirculationmodelcoupledGWPvaluesofthedifferentGHGsusedhere).ForamixofGHGsittoamixed-layeroceanmodel,becauseequilibriumclimatesensitivityisobtainedbysummingtheCO2-equivalentemissionsofeachgas.islargelydeterminedbyatmosphericprocesses.EfficientmodelscanCO2-equivalentemissionisacommonscaleforcomparingemissionsberuntoequilibriumwithadynamicocean.TheclimatesensitivityofdifferentGHGsbutdoesnotimplyequivalenceofthecorrespondingparameter(units:°C(Wm–2)–1)referstotheequilibriumchangeintheclimatechangeresponses.ThereisgenerallynoconnectionbetweenannualglobalmeansurfacetemperaturefollowingaunitchangeinCO2-equivalentemissionsandresultingCO2-equivalentconcentrations.radiativeforcing.{WGI,III}Theeffectiveclimatesensitivity(units:°C)isanestimateoftheglobalCo-benefitsmeansurfacetemperatureresponsetodoubledCO2concentrationThepositiveeffectsthatapolicyormeasureaimedatoneobjectivethatisevaluatedfrommodeloutputorobservationsforevolvingnon-mighthaveonotherobjectives,irrespectiveoftheneteffectonoverallefeqeudilbibarcikusmatcoanpdaitritoicnusl.aIrttiimseaamnedamsuaryevoafrythweitshtrfeonrgcitnhgshoifsttohreyaclnimdactlie-sooncilaolcwalelcfiarrceu.mCsot-abnecneesfitasnadreimofptleenmseunbtjaetcitotnopurnaccetrictaeisn,tyamanodngdeoptehnedrIImatestateandthereforemaydifferfromequilibriumclimatesensitivity.factors.Co-benefitsarealsoreferredtoasancillarybenefits.{WGII,III}Thetransientclimateresponse(units:°C)isthechangeintheglobalConfidencemeansurfacetemperature,averagedovera20-yearperiod,centeredThevalidityofafindingbasedonthetype,amount,qualityandcon-atthetimeofatmosphericCO2doubling,inaclimatemodelsimulationsistencyofevidence(e.g.,mechanisticunderstanding,theory,data,inwhichCO2increasesat1%/yr.Itisameasureofthestrengthandmodels,expertjudgment)andonthedegreeofagreement.Inthisrapidityofthesurfacetemperatureresponsetogreenhousegas(GHG)report,confidenceisexpressedqualitatively(Mastrandreaetal.,2010).forcing.{WGI,II,III}SeeWGIAR5Figure1.11forthelevelsofconfidence;seeWGIAR5Table1.2forthelistoflikelihoodqualifiers;seeWGIIAR5Box1-1.SeeClimatesystemalsoUncertainty.{WGI,II,III}Theclimatesystemisthehighlycomplexsystemconsistingoffivemajorcomponents:theatmosphere,thehydrosphere,thecryosphere,Cost-effectivenessthelithosphereandthebiosphereandtheinteractionsbetweenthem.Apolicyismorecost-effectiveifitachievesagivenpolicygoalatlowerTheclimatesystemevolvesintimeundertheinfluenceofitsowninter-cost.Integratedmodelsapproximatecost‐effectivesolutions,unlessnaldynamicsandbecauseofexternalforcingssuchasvolcanicerup-theyarespecificallyconstrainedtobehaveotherwise.Cost-effectivetions,solarvariationsandanthropogenicforcingssuchasthechangingmitigationscenariosarethosebasedonastylizedimplementationcompositionoftheatmosphereandland-usechange.{WGI,II,III}approachinwhichasinglepriceoncarbondioxide(CO2)andothergreenhousegases(GHGs)isappliedacrosstheglobeineverysectorClimatevariabilityofeverycountryandthatrisesovertimeinawaythatachieveslowestClimatevariabilityreferstovariationsinthemeanstateandothersta-globaldiscountedcosts.{WGIII}tistics(suchasstandarddeviations,theoccurrenceofextremes,etc.)oftheclimateonallspatialandtemporalscalesbeyondthatofindividualDecarbonizationweatherevents.VariabilitymaybeduetonaturalinternalprocessesTheprocessbywhichcountriesorotherentitiesaimtoachieveawithintheclimatesystem(internalvariability),ortovariationsinnat-low-carboneconomy,orbywhichindividualsaimtoreducetheircon-uraloranthropogenicexternalforcing(externalvariability).Seealsosumptionofcarbon.{WGII,III}Climatechange.{WGI,II,III}DeforestationCO2-equivalent(CO2-eq)concentrationConversionofforesttonon-forest.ForadiscussionofthetermforestTheconcentrationofcarbondioxide(CO2)thatwouldcausethesameandrelatedtermssuchasafforestation,reforestationanddeforesta-radiativeforcingasagivenmixtureofCO2andotherforcingcomponents.tion,seetheIPCCSpecialReportonLandUse,Land-UseChange,andThosevaluesmayconsideronlygreenhousegases(GHGs),oracom-Forestry(IPCC,2000b).SeealsoinformationprovidedbytheUnitedbinationofGHGs,aerosolsandsurfacealbedochange.CO2-equivalentNationsFrameworkConventiononClimateChange(UNFCCC,2013)concentrationisametricforcomparingradiativeforcingofamixofandthereportonDefinitionsandMethodologicalOptionstoInvento-differentforcingcomponentsataparticulartimebutdoesnotimplyryEmissionsfromDirectHuman-inducedDegradationofForestsandequivalenceofthecorrespondingclimatechangeresponsesnorfutureDevegetationofOtherVegetationTypes(IPCC,2003).{WGI,II}forcing.ThereisgenerallynoconnectionbetweenCO2-equivalentemissionsandresultingCO2-equivalentconcentrations.{WGI,III}DetectionandattributionDetectionofchangeisdefinedastheprocessofdemonstratingthatCO2-equivalent(CO2-eq)emissionclimateorasystemaffectedbyclimatehaschangedinsomedefinedTheamountofcarbondioxide(CO2)emissionthatwouldcausethestatisticalsense,withoutprovidingareasonforthatchange.Aniden-sameintegratedradiativeforcing,overagiventimehorizon,asantifiedchangeisdetectedinobservationsifitslikelihoodofoccurrenceemittedamountofagreenhousegas(GHG)oramixtureofGHGs.bychanceduetointernalvariabilityaloneisdeterminedtobesmall,121AnnexIIGlossaryforexample,<10%.Attributionisdefinedastheprocessofevaluat-EcosystemingtherelativecontributionsofmultiplecausalfactorstoachangeAnecosystemisafunctionalunitconsistingoflivingorganisms,theiroreventwithanassignmentofstatisticalconfidence(Hegerletal.,non-livingenvironmentandtheinteractionswithinandbetweenthem.2010).{WGI,II}Thecomponentsincludedinagivenecosystemanditsspatialboun-dariesdependonthepurposeforwhichtheecosystemisdefined:inDetectionofimpactsofclimatechangesomecasestheyarerelativelysharp,whileinotherstheyarediffuse.Foranatural,humanormanagedsystem,identificationofachangeEcosystemboundariescanchangeovertime.Ecosystemsarenestedfromaspecifiedbaseline.Thebaselinecharacterizesbehaviorinthewithinotherecosystemsandtheirscalecanrangefromverysmalltoabsenceofclimatechangeandmaybestationaryornon-stationarytheentirebiosphere.Inthecurrentera,mostecosystemseithercontain(e.g.,duetoland-usechange).{WGII}peopleaskeyorganisms,orareinfluencedbytheeffectsofhumanactivitiesintheirenvironment.{WGI,II,III}DisasterSeverealterationsinthenormalfunctioningofacommunityorasoci-EcosystemservicesetyduetohazardousphysicaleventsinteractingwithvulnerablesocialEcologicalprocessesorfunctionshavingmonetaryornon-monetaryIIcoornednivtiioronns,mleeandtainlgeftfoecwtsidtehsaptrereaqduairdeviemrsmeehduimataene,mmeartgeerniacl,yerceosnpoomnsiecvaaslu(1e)tsoupinpdoirvtiidnugaslserovricseoscsieutcyhaatslaprrgoed.uTchteivsietyaorerfbrieoqduiveenrtslyityclmasasiinfiteed-tosatisfycriticalhumanneedsandthatmayrequireexternalsupportnance,(2)provisioningservicessuchasfood,fiberorfish,(3)regulat-forrecovery.{WGII}ingservicessuchasclimateregulationorcarbonsequestrationand(4)culturalservicessuchastourismorspiritualandaestheticapprecia-Discountingtion.{WGII,III}Amathematicaloperationmakingmonetary(orother)amountsreceivedorexpendedatdifferenttimes(years)comparableacrosstime.Thedis-ElNiño-SouthernOscillation(ENSO)counterusesafixedorpossiblytime‐varyingdiscountrate(>0)fromThetermElNiñowasinitiallyusedtodescribeawarm-watercurrentyeartoyearthatmakesfuturevalueworthlesstoday.{WGII,III}thatperiodicallyflowsalongthecoastofEcuadorandPeru,disrupt-ingthelocalfishery.Ithassincebecomeidentifiedwithabasin-wideDroughtwarmingofthetropicalPacificOceaneastofthedateline.ThisoceanicAperiodofabnormallydryweatherlongenoughtocauseaseriouseventisassociatedwithafluctuationofaglobal-scaletropicalandhydrologicalimbalance.Droughtisarelativeterm;thereforeanydis-subtropicalsurfacepressurepatterncalledtheSouthernOscillation.cussionintermsofprecipitationdeficitmustrefertotheparticularThiscoupledatmosphere–oceanphenomenon,withpreferredtimeprecipitation-relatedactivitythatisunderdiscussion.Forexample,scalesoftwotoaboutsevenyears,isknownastheElNiño-SouthernshortageofprecipitationduringthegrowingseasonimpingesonOscillation(ENSO).Itisoftenmeasuredbythesurfacepressureanom-cropproductionorecosystemfunctioningeneral(duetosoilmois-alydifferencebetweenTahitiandDarwinortheseasurfacetemper-turedrought,alsotermedagriculturaldrought)andduringtherunoffaturesinthecentralandeasternequatorialPacific.DuringanENSOandpercolationseasonprimarilyaffectswatersupplies(hydrologicalevent,theprevailingtradewindsweaken,reducingupwellinganddrought).Storagechangesinsoilmoistureandgroundwaterarealsoalteringoceancurrentssuchthattheseasurfacetemperatureswarm,affectedbyincreasesinactualevapotranspirationinadditiontoreduc-furtherweakeningthetradewinds.Thiseventhasagreatimpactontionsinprecipitation.Aperiodwithanabnormalprecipitationdeficitisthewind,seasurfacetemperatureandprecipitationpatternsinthedefinedasameteorologicaldrought.AmegadroughtisaverylengthytropicalPacific.IthasclimaticeffectsthroughoutthePacificregionandandpervasivedrought,lastingmuchlongerthannormal,usuallyainmanyotherpartsoftheworld,throughglobalteleconnections.Thedecadeormore.Forthecorrespondingindices,seeWGIAR5Box2.4.coldphaseofENSOiscalledLaNiña.Forthecorrespondingindices,see{WGI,II}WGIAR5Box2.5.{WGI,II}EarlywarningsystemEmissionscenarioThesetofcapacitiesneededtogenerateanddisseminatetimelyandAplausiblerepresentationofthefuturedevelopmentofemissionsofmeaningfulwarninginformationtoenableindividuals,communitiessubstancesthatarepotentiallyradiativelyactive(e.g.,greenhouseandorganizationsthreatenedbyahazardtopreparetoactpromptlygases(GHGs),aerosols)basedonacoherentandinternallyconsist-andappropriatelytoreducethepossibilityofharmorloss4.{WGII}entsetofassumptionsaboutdrivingforces(suchasdemographicandsocio-economicdevelopment,technologicalchange,energyandlandEarthSystemModel(ESM)use)andtheirkeyrelationships.Concentrationscenarios,derivedfromAcoupledatmosphere–oceangeneralcirculationmodelinwhichaemissionscenarios,areusedasinputtoaclimatemodeltocomputerepresentationofthecarboncycleisincluded,allowingforinteractiveclimateprojections.InIPCC(1992)asetofemissionscenarioswaspre-calculationofatmosphericCO2orcompatibleemissions.AdditionalsentedwhichwereusedasabasisfortheclimateprojectionsinIPCCcomponents(e.g.,atmosphericchemistry,icesheets,dynamicvegeta-(1996).TheseemissionscenariosarereferredtoastheIS92scenarios.tion,nitrogencycle,butalsourbanorcropmodels)maybeincluded.IntheIPCCSpecialReportonEmissionsScenarios(IPCC,2000a)emis-SeealsoClimatemodel.{WGI,II}sionscenarios,theso-calledSRESscenarios,werepublished,someof4ThisglossaryentrybuildsfromthedefinitionsusedinUNISDR(2009)andIPCC(2012a).122GlossaryAnnexIIwhichwereused,amongothers,asabasisfortheclimateprojectionsExtremeweathereventpresentedinChapters9to11ofIPCCWGITAR(IPCC,2001a)andAnextremeweathereventisaneventthatisrareataparticularplaceChapters10and11ofIPCCWGIAR4(IPCC,2007)aswellasintheandtimeofyear.Definitionsofrarevary,butanextremeweathereventIPCCWGIAR5(IPCC,2013b).Newemissionscenariosforclimatewouldnormallybeasrareasorrarerthanthe10thor90thpercentilechange,thefourRepresentativeConcentrationPathways,weredevel-ofaprobabilitydensityfunctionestimatedfromobservations.Bydefi-opedfor,butindependentlyof,thepresentIPCCassessment.Seealsonition,thecharacteristicsofwhatiscalledextremeweathermayvaryBaseline/reference,MitigationscenarioandTransformationpathway.fromplacetoplaceinanabsolutesense.Whenapatternofextreme{WGI,II,III}weatherpersistsforsometime,suchasaseason,itmaybeclassedasanextremeclimateevent,especiallyifityieldsanaverageortotalthatEnergyaccessisitselfextreme(e.g.,droughtorheavyrainfalloveraseason).{WGI,II}Accesstoclean,reliableandaffordableenergyservicesforcookingandheating,lighting,communicationsandproductiveuses(AGECC,Feedback2010).{WGIII}SeeClimatefeedback.{WGI,II}EnergyintensityFThloeoodverflowingofthenormalconfinesofastreamorotherbodyofwater,IITheratioofenergyusetoeconomicorphysicaloutput.{WGIII}ortheaccumulationofwateroverareasnotnormallysubmerged.FloodsEnergysecurityincluderiver(fluvial)floods,flashfloods,urbanfloods,pluvialfloods,Thegoalofagivencountry,ortheglobalcommunityasawhole,tosewerfloods,coastalfloodsandglaciallakeoutburstfloods.{WGII}maintainanadequate,stableandpredictableenergysupply.MeasuresencompasssafeguardingthesufficiencyofenergyresourcestomeetFoodsecuritynationalenergydemandatcompetitiveandstablepricesandtheresil-Astatethatprevailswhenpeoplehavesecureaccesstosufficientienceoftheenergysupply;enablingdevelopmentanddeploymentofamountsofsafeandnutritiousfoodfornormalgrowth,developmenttechnologies;buildingsufficientinfrastructuretogenerate,storeandandanactiveandhealthylife.{WGII,III}transmitenergysuppliesandensuringenforceablecontractsofdeliv-ery.{WGIII}ForestAvegetationtypedominatedbytrees.ManydefinitionsofthetermEnsembleforestareinusethroughouttheworld,reflectingwidedifferencesinAcollectionofmodelsimulationscharacterizingaclimatepredictionbiogeophysicalconditions,socialstructureandeconomics.Foradis-orprojection.Differencesininitialconditionsandmodelformulationcussionofthetermforestandrelatedtermssuchasafforestation,resultindifferentevolutionsofthemodeledsystemandmaygivereforestationanddeforestation,seetheIPCCSpecialReportonLandinformationonuncertaintyassociatedwithmodelerroranderrorinUse,Land-UseChange,andForestry(IPCC,2000b).Seealsoinforma-initialconditionsinthecaseofclimateforecastsandonuncertaintytionprovidedbytheUnitedNationsFrameworkConventiononClimateassociatedwithmodelerrorandwithinternallygeneratedclimatevar-Change(UNFCCC,2013)andtheReportonDefinitionsandMethod-iabilityinthecaseofclimateprojections.{WGI,II}ologicalOptionstoInventoryEmissionsfromDirectHuman-inducedDegradationofForestsandDevegetationofOtherVegetationTypesEquilibriumclimatesensitivity(IPCC,2003).{WGI,III}SeeClimatesensitivity.{WGI}FuelpovertyEutrophicationAconditioninwhichahouseholdisunabletoguaranteeacertainlevelOver-enrichmentofwaterbynutrientssuchasnitrogenandphospho-ofconsumptionofdomesticenergyservices(especiallyheating)orrus.Itisoneoftheleadingcausesofwaterqualityimpairment.Thesuffersdisproportionateexpenditureburdenstomeettheseneeds.twomostacutesymptomsofeutrophicationarehypoxia(oroxygen{WGIII}depletion)andharmfulalgalblooms.{WGII}GeoengineeringExposureGeoengineeringreferstoabroadsetofmethodsandtechnologiesthatThepresenceofpeople,livelihoods,speciesorecosystems,environ-aimtodeliberatelyaltertheclimatesysteminordertoalleviatethementalfunctions,services,andresources,infrastructure,oreconomic,impactsofclimatechange.Most,butnotall,methodsseektoeithersocial,orculturalassetsinplacesandsettingsthatcouldbeadversely(1)reducetheamountofabsorbedsolarenergyintheclimatesystemaffected.{WGII}(SolarRadiationManagement)or(2)increasenetcarbonsinksfromtheatmosphereatascalesufficientlylargetoalterclimate(CarbonExternalforcingDioxideRemoval).Scaleandintentareofcentralimportance.TwokeyExternalforcingreferstoaforcingagentoutsidetheclimatesystemcharacteristicsofgeoengineeringmethodsofparticularconcernarecausingachangeintheclimatesystem.Volcaniceruptions,solarvar-thattheyuseoraffecttheclimatesystem(e.g.,atmosphere,landoriationsandanthropogenicchangesinthecompositionoftheatmos-ocean)globallyorregionallyand/orcouldhavesubstantiveunintendedphereandland-usechangeareexternalforcings.Orbitalforcingisalsoeffectsthatcrossnationalboundaries.Geoengineeringisdifferentanexternalforcingastheinsolationchangeswithorbitalparametersfromweathermodificationandecologicalengineering,butthebound-eccentricity,tiltandprecessionoftheequinox.{WGI,II}arycanbefuzzy(IPCC,2012b,p.2).{WGI,II,III}123AnnexIIGlossaryGlobalclimatemodel(alsoreferredtoasgeneralcirculationImpacts(consequences,outcomes)model,bothabbreviatedasGCM)Effectsonnaturalandhumansystems.Inthisreport,thetermimpactsSeeClimatemodel.{WGI,II}isusedprimarilytorefertotheeffectsonnaturalandhumansystemsofextremeweatherandclimateeventsandofclimatechange.ImpactsGlobalTemperaturechangePotential(GTP)generallyrefertoeffectsonlives,livelihoods,health,ecosystems,econo-Anindexmeasuringthechangeinglobalmeansurfacetemperatureatmies,societies,cultures,servicesandinfrastructureduetotheinteractionachosenpointintimefollowinganemissionofaunitmassofagivenofclimatechangesorhazardousclimateeventsoccurringwithinaspe-substance,relativetothatofthereferencesubstance,carbondioxidecifictimeperiodandthevulnerabilityofanexposedsocietyorsystem.(CO2).TheGlobalTemperaturechangePotential(GTP)thusrepresentsImpactsarealsoreferredtoasconsequencesandoutcomes.Theimpactsthecombinedeffectofthedifferingtimesthesesubstancesremaininofclimatechangeongeophysicalsystems,includingfloods,droughtstheatmosphere,theireffectivenessincausingradiativeforcingandandsealevelrise,areasubsetofimpactscalledphysicalimpacts.{WGII}theresponseoftheclimatesystem.TheGTPhasbeendefinedintwodifferentways:Indirectemissions•FixedGTP:basedonafixedtimehorizoninthefuture(suchEmissionsthatareaconsequenceoftheactivitieswithinwell-definedII•aDsynGaTmP1ic00GfoTrPa:btiamseedhoornizaontaorfg1et00yeyaera(rssu)chastheyearwhenboorupnrdoacreisess,obfu,tfowrihniscthanoccec,uarroeugtiosind,eantheecosnpoemcifiicedsecbtoour,nadacroiems.paFnoyrglobalmeantemperatureisexpectedtoreachatargetexample,emissionsaredescribedasindirectiftheyrelatetotheuseoflevel).InthedynamicGTP,thetimehorizonreducesovertimeheatbutphysicallyariseoutsidetheboundariesoftheheatuser,ortoasthetargetyearisapproachedandhencetheGTPvalueelectricityproductionbutphysicallyariseoutsideoftheboundariesofchangesforemissionsoccurringfurtherinthefuture.{WGIthepowersupplysector.{WGIII}Chapter8}IndustrialRevolutionGlobalwarmingAperiodofrapidindustrialgrowthwithfar-reachingsocialandeco-Globalwarmingreferstothegradualincrease,observedorprojected,nomicconsequences,beginninginBritainduringthesecondhalfofinglobalsurfacetemperature,asoneoftheconsequencesofradiativethe18thcenturyandspreadingtoEuropeandlatertoothercountriesforcingcausedbyanthropogenicemissions.{WGIII}includingtheUnitedStates.Theinventionofthesteamenginewasanimportanttriggerofthisdevelopment.TheindustrialrevolutionmarksGlobalWarmingPotential(GWP)thebeginningofastrongincreaseintheuseoffossilfuelsandemis-Anindexmeasuringtheradiativeforcingfollowinganemissionofasionof,inparticular,fossilcarbondioxide(CO2).Inthisreportthetermsunitmassofagivensubstance,accumulatedoverachosentimehori-pre-industrialandindustrialrefer,somewhatarbitrarily,totheperiodszon,relativetothatofthereferencesubstance,carbondioxide(CO2).beforeandafter1750,respectively.{WGI,II,III}TheGWPthusrepresentsthecombinedeffectofthedifferingtimesthesesubstancesremainintheatmosphereandtheireffectivenessinIntegratedassessmentcausingradiativeforcing.(WGI,III}Amethodofanalysisthatcombinesresultsandmodelsfromthephysical,biological,economicandsocialsciencesandtheinteractionsHazardamongthesecomponentsinaconsistentframeworktoevaluatetheThepotentialoccurrenceofanaturalorhuman-inducedphysicaleventstatusandtheconsequencesofenvironmentalchangeandthepolicyortrendorphysicalimpactthatmaycauselossoflife,injury,orotherresponsestoit.SeealsoIntegratedmodels.{WGII,III}healthimpacts,aswellasdamageandlosstoproperty,infrastructure,livelihoods,serviceprovision,ecosystemsandenvironmentalresources.IntegratedCoastalZoneManagement(ICZM)Inthisreport,thetermhazardusuallyreferstoclimate-relatedphysicalAnintegratedapproachforsustainablymanagingcoastalareas,takingeventsortrendsortheirphysicalimpacts.{WGII}intoaccountallcoastalhabitatsanduses.{WGII}HeatwaveIntegratedmodelsAperiodofabnormallyanduncomfortablyhotweather.{WGI,II}Integratedmodelsexploretheinteractionsbetweenmultiplesectorsoftheeconomyorcomponentsofparticularsystems,suchastheHydrologicalcycleenergysystem.Inthecontextoftransformationpathways,theyrefertoThecycleinwhichwaterevaporatesfromtheoceansandthelandmodelsthat,ataminimum,includefullanddisaggregatedrepresenta-surface,iscarriedovertheEarthinatmosphericcirculationaswatertionsoftheenergysystemanditslinkagetotheoveralleconomythatvapour,condensestoformclouds,precipitatesoveroceanandlandaswillallowforconsiderationofinteractionsamongdifferentelementsrainorsnow,whichonlandcanbeinterceptedbytreesandvegeta-ofthatsystem.Integratedmodelsmayalsoincluderepresentationsoftion,providesrunoffonthelandsurface,infiltratesintosoils,recharg-thefulleconomy,landuseandland-usechange(LUC)andtheclimateesgroundwater,dischargesintostreamsandultimatelyflowsoutintosystem.SeealsoIntegratedassessment.{WGIII}theoceans,fromwhichitwilleventuallyevaporateagain.ThevarioussystemsinvolvedinthehydrologicalcycleareusuallyreferredtoasInternalvariabilityhydrologicalsystems.{WGI,II}SeeClimatevariability.{WGI}124GlossaryAnnexIIIrreversibilityTable1.2andWGIIAR5Box1-1.SeealsoConfidenceandUncertainty.Aperturbedstateofadynamicalsystemisdefinedasirreversibleona{WGI,II,III}giventimescale,iftherecoverytimescalefromthisstateduetonaturalprocessesissubstantiallylongerthanthetimeittakesforthesystemtoLock-inreachthisperturbedstate.Inthecontextofthisreport,thetimescaleLock-inoccurswhenamarketisstuckwithastandardeventhoughofinterestiscentennialtomillennial.SeealsoTippingpoint.{WGI}participantswouldbebetteroffwithanalternative.Inthisreport,lock-inisusedmorebroadlyaspathdependence,whichisthegenericLanduseandland-usechangesituationwheredecisions,eventsoroutcomesatonepointintimeLandusereferstothetotalofarrangements,activitiesandinputsconstrainadaptation,mitigationorotheractionsoroptionsatalaterundertakeninacertainlandcovertype(asetofhumanactions).Thepointintime.{WGII,III}termlanduseisalsousedinthesenseofthesocialandeconomicpurposesforwhichlandismanaged(e.g.,grazing,timberextractionLowregretspolicyandconservation).InurbansettlementsitisrelatedtolanduseswithinApolicythatwouldgeneratenetsocialand/oreconomicbenefitsundercitiesandtheirhinterlands.Urbanlandusehasimplicationsoncitycurrentclimateandarangeoffutureclimatechangescenarios.{WGII}mhoaunsaeggeamse(nGt,HsGtr)uecmtuirsesiaonndsafonrdmmaonbdilitthyu,samononegneortghyedreamspaencdts,.g{rWeeGnI-,Marine-basedicesheetIIII,III}Anicesheetcontainingasubstantialregionthatrestsonabedlyingbelowsealevelandwhoseperimeterisincontactwiththeocean.TheLand-usechange(LUC)bestknownexampleistheWestAntarcticicesheet.{WGI}Land-usechangereferstoachangeintheuseormanagementoflandbyhumans,whichmayleadtoachangeinlandcover.LandMeridionalOverturningCirculation(MOC)coverandland-usechangemayhaveanimpactonthesurfaceMeridional(north–south)overturningcirculationintheoceanquanti-albedo,evapotranspiration,sourcesandsinksofgreenhousegasesfiedbyzonal(east–west)sumsofmasstransportsindepthordensity(GHGs),orotherpropertiesoftheclimatesystemandmaythusgivelayers.IntheNorthAtlantic,awayfromthesubpolarregions,theMOCrisetoradiativeforcingand/orotherimpactsonclimate,locallyor(whichisinprincipleanobservablequantity)isoftenidentifiedwithglobally.SeealsotheIPCCSpecialReportonLandUse,Land-Usethethermohalinecirculation(THC),whichisaconceptualandincom-Change,andForestry(IPCC,2000b).pleteinterpretation.ItmustbeborneinmindthattheMOCisalsodrivenbywindandcanalsoincludeshalloweroverturningcellssuchasIndirectland-usechange(iLUC)occurintheupperoceaninthetropicsandsubtropics,inwhichwarmIndirectland-usechangereferstoshiftsinlanduseinducedbya(light)watersmovingpolewardaretransformedtoslightlydenserchangeintheproductionlevelofanagriculturalproductelsewhere,watersandsubductedequatorwardatdeeperlevels.{WGI,II}oftenmediatedbymarketsordrivenbypolicies.Forexample,ifagriculturallandisdivertedtofuelproduction,forestclearancemayMitigation(ofclimatechange)occurelsewheretoreplacetheformeragriculturalproduction.SeeAhumaninterventiontoreducethesourcesorenhancethesinksofalsoAgriculture,ForestryandOtherLandUse(AFOLU),Afforesta-greenhousegases(GHGs).Thisreportalsoassesseshumaninterven-tion,DeforestationandReforestation.tionstoreducethesourcesofothersubstanceswhichmaycontributedirectlyorindirectlytolimitingclimatechange,including,forexample,LeakagethereductionofparticulatematteremissionsthatcandirectlyalterPhenomenawherebythereductioninemissions(relativetoabaseline)theradiationbalance(e.g.,blackcarbon)ormeasuresthatcontrolinajurisdiction/sectorassociatedwiththeimplementationofmitiga-emissionsofcarbonmonoxide,nitrogenoxides,VolatileOrganicCom-tionpolicyisoffsettosomedegreebyanincreaseoutsidethejuris-poundsandotherpollutantsthatcanaltertheconcentrationoftropo-diction/sectorthroughinducedchangesinconsumption,production,sphericozonewhichhasanindirecteffectontheclimate.{WGI,II,III}prices,landuseand/ortradeacrossthejurisdictions/sectors.Leakagecanoccuratanumberoflevels,beitaproject,state,province,nationMitigationscenarioorworldregion.Aplausibledescriptionofthefuturethatdescribeshowthe(studied)systemrespondstotheimplementationofmitigationpoliciesandInthecontextofCarbonDioxideCaptureandStorage(CCS),CO2measures.SeealsoBaseline/reference,Emissionscenario,Represent-leakagereferstotheescapeofinjectedcarbondioxide(CO2)fromtheativeConcentrationPathways(RCPs),SRESscenariosandTransforma-storagelocationandeventualreleasetotheatmosphere.Inthecon-tionpathway.{WGIII}textofothersubstances,thetermisusedmoregenerically,suchasformethane(CH4)leakage(e.g.,fromfossilfuelextractionactivities)Netnegativeemissionsandhydrofluorocarbon(HFC)leakage(e.g.,fromrefrigerationandair-Asituationofnetnegativeemissionsisachievedwhen,asresultofconditioningsystems).{WGIII}humanactivities,moregreenhousegases(GHGs)aresequesteredorstoredthanarereleasedintotheatmosphere.{SYRBox2.2,footnote29}LikelihoodThechanceofaspecificoutcomeoccurring,wherethismightbeesti-Oceanacidificationmatedprobabilistically.LikelihoodisexpressedinthisreportusingaOceanacidificationreferstoareductioninthepHoftheoceanoveranstandardterminology(Mastrandreaetal.,2010),definedinWGIAR5extendedperiod,typicallydecadesorlonger,whichiscausedprimarily125AnnexIIGlossarybyuptakeofcarbondioxide(CO2)fromtheatmosphere,butcanalsothechangeinenergyfluxcausedbyadriverandiscalculatedatthebecausedbyotherchemicaladditionsorsubtractionsfromtheocean.tropopauseoratthetopoftheatmosphere.{WGI}AnthropogenicoceanacidificationreferstothecomponentofpHreductionthatiscausedbyhumanactivity(IPCC,2011,p.37).{WGI,II}ReasonsForConcern(RFCs)Elementsofaclassificationframework,firstdevelopedintheIPCCOvershootpathwaysThirdAssessmentReport(IPCC,2001b),whichaimstofacilitatejudg-Emissions,concentrationortemperaturepathwaysinwhichthemetricmentsaboutwhatlevelofclimatechangemaybedangerous(intheofinteresttemporarilyexceeds,orovershootsthelong-termgoal.languageofArticle2oftheUnitedNationsFrameworkConventionon{WGIII}ClimateChange(UNFCCC))byaggregatingimpacts,risksandvulner-abilities.{WGII}OxygenMinimumZone(OMZ)Themidwaterlayer(200–1000m)intheopenoceaninwhichoxygenReducingEmissionsfromDeforestationandForestDegradationsaturationisthelowestintheocean.Thedegreeofoxygendepletion(REDD)dependsonthelargelybacterialconsumptionoforganicmatterandAnefforttocreatefinancialvalueforthecarbonstoredinforests,IItthioend.Iinstcriobausttiaolnoocfetahnes,OOMMZZssisexinteflnudentocetdhebsyhlealrvgees-sacnadlemoacyeaanlsociracfufelac-tofoffreersitnegdilnacnednstivaensdfoinrvdeestveinloploinwg-ccaorubnotnriepsattohsretdouscuesetaminisasbiolensdefrvoeml-benthicecosystems.{WGII}opment(SD).Itisthereforeamechanismformitigationthatresultsfromavoidingdeforestation.REDD+goesbeyondreforestationandPermafrostforestdegradationandincludestheroleofconservation,sustainableGround(soilorrockandincludediceandorganicmaterial)thatmanagementofforestsandenhancementofforestcarbonstocks.Theremainsatorbelow0°Cforatleasttwoconsecutiveyears.{WGI,II}conceptwasfirstintroducedin2005inthe11thSessionoftheCon-ferenceoftheParties(COP)inMontrealandlatergivengreaterrecog-pHnitioninthe13thSessionoftheCOPin2007atBaliandinclusioninpHisadimensionlessmeasureoftheacidityofwater(oranysolution)theBaliActionPlanwhichcalledfor‘policyapproachesandpositivegivenbyitsconcentrationofhydrogenions(H+).pHismeasuredonincentivesonissuesrelatingtoreducingemissionsfromdeforestationalogarithmicscalewherepH=–log10(H+).Thus,apHdecreaseofandforestdegradationindevelopingcountries(REDD)andtheroleof1unitcorrespondstoa10-foldincreaseintheconcentrationofH+,orconservation,sustainablemanagementofforestsandenhancementofacidity.{WGI}forestcarbonstockindevelopingcountries’.Sincethen,supportforREDDhasincreasedandhasslowlybecomeaframeworkforactionPovertysupportedbyanumberofcountries.{WGIII}Povertyisacomplexconceptwithseveraldefinitionsstemmingfromdifferentschoolsofthought.ItcanrefertomaterialcircumstancesReforestation(suchasneed,patternofdeprivationorlimitedresources),economicPlantingofforestsonlandsthathavepreviouslycontainedforestsconditions(suchasstandardofliving,inequalityoreconomicposition)butthathavebeenconvertedtosomeotheruse.Foradiscussionofand/orsocialrelationships(suchassocialclass,dependency,exclusion,thetermforestandrelatedtermssuchasafforestation,reforestationlackofbasicsecurityorlackofentitlement).{WGII}anddeforestation,seetheIPCCSpecialReportonLandUse,Land-UseChange,andForestry(IPCC,2000b).SeealsoinformationprovidedPre-industrialbytheUnitedNationsFrameworkConventiononClimateChangeSeeIndustrialRevolution.{WGI,II,III}(UNFCCC,2013).SeealsotheReportonDefinitionsandMethodolog-icalOptionstoInventoryEmissionsfromDirectHuman-inducedDeg-PrivatecostsradationofForestsandDevegetationofOtherVegetationTypes(IPCC,Privatecostsarecarriedbyindividuals,companiesorotherprivate2003).{WGI,II,III}entitiesthatundertakeanaction,whereassocialcostsincludeaddi-tionallytheexternalcostsontheenvironmentandonsocietyasaRepresentativeConcentrationPathways(RCPs)whole.QuantitativeestimatesofbothprivateandsocialcostsmaybeScenariosthatincludetimeseriesofemissionsandconcentrationsincomplete,becauseofdifficultiesinmeasuringallrelevanteffects.ofthefullsuiteofgreenhousegases(GHGs)andaerosolsand{WGIII}chemicallyactivegases,aswellaslanduse/landcover(Mossetal.,2008).ThewordrepresentativesignifiesthateachRCPprovidesProjectiononlyoneofmanypossiblescenariosthatwouldleadtothespecificAprojectionisapotentialfutureevolutionofaquantityorsetofradiativeforcingcharacteristics.Thetermpathwayemphasizesthatquantities,oftencomputedwiththeaidofamodel.Unlikepredictions,notonlythelong-termconcentrationlevelsareofinterest,butalsoprojectionsareconditionalonassumptionsconcerning,forexample,thetrajectorytakenovertimetoreachthatoutcome(Mossetal.,futuresocio-economicandtechnologicaldevelopmentsthatmayor2010).maynotberealized.SeealsoClimateprojection.{WGI,II}RCPsusuallyrefertotheportionoftheconcentrationpathwayextend-Radiativeforcingingupto2100,forwhichIntegratedAssessmentModelsproducedThestrengthofdriversisquantifiedasRadiativeForcing(RF)inunitscorrespondingemissionscenarios.ExtendedConcentrationPathwayswattspersquaremeter(W/m2)asinpreviousIPCCassessments.RFis(ECPs)describeextensionsoftheRCPsfrom2100to2500thatwere126GlossaryAnnexIIcalculatedusingsimplerulesgeneratedbystakeholderconsultationsandpracticesthatenhancesoilcarboninagriculture(croplandman-anddonotrepresentfullyconsistentscenarios.agement,grazinglandmanagement).Inpartsoftheliterature,butnotinthisreport,(carbon)sequestrationisusedtorefertoCarbonDioxideFourRCPsproducedfromIntegratedAssessmentModelswereselectedCaptureandStorage(CCS).{WGIII}fromthepublishedliteratureandareusedinthepresentIPCCAssess-mentasabasisfortheclimatepredictionsandprojectionspresentedSinkinWGIAR5Chapters11to14(IPCC,2013b):Anyprocess,activityormechanismthatremovesagreenhousegas(GHG),anaerosoloraprecursorofaGHGoraerosolfromtheatmos-RCP2.6phere.{WGI,II,III}Onepathwaywhereradiativeforcingpeaksatapproximately3W/m2before2100andthendeclines(thecorrespondingECPSocialcostofcarbonassumingconstantemissionsafter2100).Thenetpresentvalueofclimatedamages(withharmfuldamagesexpressedasapositivenumber)fromonemoretonneofcarboninRCP4.5andRCP6.0theformofcarbondioxide(CO2),conditionalonaglobalemissionsTiswsotaibnitleizremdeadtiaatpepsrotaxbimiliaztaetliyon4.p5aWth/mwa2yasndin6w.0hWic/hmr2aadfitaetriv2e1f0o0rc(tinhgetrajectoryovertime.{WGII,III}IIcorrespondingECPsassumingconstantconcentrationsafter2150).SocialcostsSeePrivatecosts.{WGIII}RCP8.5Onehighpathwayforwhichradiativeforcingreaches>8.5W/m2SolarRadiationManagement(SRM)by2100andcontinuestoriseforsomeamountoftime(thecorre-SolarRadiationManagementreferstotheintentionalmodificationofspondingECPassumingconstantemissionsafter2100andcon-theEarth’sshortwaveradiativebudgetwiththeaimtoreduceclimatestantconcentrationsafter2250).changeaccordingtoagivenmetric(e.g.,surfacetemperature,pre-cipitation,regionalimpacts,etc.).ArtificialinjectionofstratosphericForfurtherdescriptionoffuturescenarios,seeWGIAR5Box1.1.SeeaerosolsandcloudbrighteningaretwoexamplesofSRMtechniques.alsovanVuurenetal.,2011.{WGI,II,III}Methodstomodifysomefast-respondingelementsofthelongwaveradiativebudget(suchascirrusclouds),althoughnotstrictlyspeakingResilienceSRM,canberelatedtoSRM.SRMtechniquesdonotfallwithintheThecapacityofsocial,economicandenvironmentalsystemstocopeusualdefinitionsofmitigationandadaptation(IPCC,2012b,p.2).Seewithahazardouseventortrendordisturbance,respondingorreor-alsoCarbonDioxideRemoval(CDR)andGeoengineering.{WGI,III}ganizinginwaysthatmaintaintheiressentialfunction,identityandstructure,whilealsomaintainingthecapacityforadaptation,learningSRESscenariosandtransformation5.{WGII,III}SRESscenariosareemissionscenariosdevelopedbyIPCC(2000a)andused,amongothers,asabasisforsomeoftheclimateprojectionsRiskshowninChapters9to11ofIPCCWGITAR(IPCC,2001a),Chapters10Thepotentialforconsequenceswheresomethingofvalueisatstakeand11ofIPCCWGIAR4(IPCC,2007),aswellasintheIPCCWGIAR5andwheretheoutcomeisuncertain,recognizingthediversityofvalues.(IPCC,2013b).{WGI,II,III}RiskisoftenrepresentedasprobabilityorlikelihoodofoccurrenceofhazardouseventsortrendsmultipliedbytheimpactsiftheseeventsStormsurgeortrendsoccur.Inthisreport,thetermriskisoftenusedtorefertotheThetemporaryincrease,ataparticularlocality,intheheightoftheseapotential,whentheoutcomeisuncertain,foradverseconsequencesonduetoextrememeteorologicalconditions(lowatmosphericpressurelives,livelihoods,health,ecosystemsandspecies,economic,socialandand/orstrongwinds).Thestormsurgeisdefinedasbeingtheexcessculturalassets,services(includingenvironmentalservices)andinfra-abovethelevelexpectedfromthetidalvariationaloneatthattimestructure.{WGII,III}andplace.{WGI,II}RiskmanagementStructuralchangeTheplans,actionsorpoliciestoreducethelikelihoodand/orconse-Changes,forexample,intherelativeshareofgrossdomesticproductquencesofrisksortorespondtoconsequences.{WGII}(GDP)producedbytheindustrial,agricultural,orservicessectorsofaneconomy,ormoregenerally,systemstransformationswherebysomeSequestrationcomponentsareeitherreplacedorpotentiallysubstitutedbyotherTheuptake(i.e.,theadditionofasubstanceofconcerntoareservoir)components.{WGIII}ofcarboncontainingsubstances,inparticularcarbondioxide(CO2),interrestrialormarinereservoirs.BiologicalsequestrationincludesdirectSustainabilityremovalofCO2fromtheatmospherethroughland-usechange(LUC),Adynamicprocessthatguaranteesthepersistenceofnaturalandafforestation,reforestation,revegetation,carbonstorageinlandfillshumansystemsinanequitablemanner.{WGII,III}5ThisdefinitionbuildsfromthedefinitionusedinArcticCouncil(2013).127AnnexIIGlossarySustainabledevelopmentenergyandinfrastructureareusedandproduced,naturalresourcesDevelopmentthatmeetstheneedsofthepresentwithoutcompromis-aremanagedandinstitutionsaresetupandinthepaceanddirectioningtheabilityoffuturegenerationstomeettheirownneeds(WCED,oftechnologicalchange(TC).SeealsoBaseline/reference,Emission1987).{WGII,III}scenario,Mitigationscenario,RepresentativeConcentrationPathways(RCPs)andSRESscenarios.{WGIII}ThermalexpansionInconnectionwithsealevel,thisreferstotheincreaseinvolume(andTransientClimateResponsetoCumulativeCO2Emissions(TCRE)decreaseindensity)thatresultsfromwarmingwater.AwarmingofThetransientglobalaveragesurfacetemperaturechangeperunittheoceanleadstoanexpansionoftheoceanvolumeandhenceancumulatedCO2emissions,usually1000PgC.TCREcombinesbothincreaseinsealevel.{WGI,II}informationontheairbornefractionofcumulatedCO2emissions(thefractionofthetotalCO2emittedthatremainsintheatmosphere)andTippingpointonthetransientclimateresponse(TCR).{WGI}Alevelofchangeinsystempropertiesbeyondwhichasystemreorgan-izes,oftenabruptly,anddoesnotreturntotheinitialstateeveniftheUncertaintyIIdcrriitviecarslothfrtehsehochldanwgheeanreglaobbaatleodr.Froergitohneacllicmlimataetesycshteamng,eitsrefrfoemrstoonaeAmasttiaotneoorffirnocmomdpislaegterekenmoewnltedagbeoutthawthcaatnisreksnuolwtfnroomreavelanckknoofwinabfoler-.stablestatetoanotherstablestate.ThetippingpointeventmaybeItmayhavemanytypesofsources,fromimprecisioninthedatatoirreversible.SeealsoIrreversibility.{WGI,II,III}ambiguouslydefinedconceptsorterminology,oruncertainprojec-tionsofhumanbehaviour.UncertaintycanthereforeberepresentedbyTransformationquantitativemeasures(e.g.,aprobabilitydensityfunction)orbyqual-Achangeinthefundamentalattributesofnaturalandhumansystems.itativestatements(e.g.,reflectingthejudgmentofateamofexperts){WGII}(seeMossandSchneider,2000;Manningetal.,2004;Mastrandreaetal.,2010).SeealsoConfidenceandLikelihood.{WGI,II,III}TransformationpathwayThetrajectorytakenovertimetomeetdifferentgoalsforgreenhouseVulnerabilitygas(GHG)emissions,atmosphericconcentrations,orglobalmeansur-Thepropensityorpredispositiontobeadverselyaffected.Vulnerabilityfacetemperaturechangethatimpliesasetofeconomic,technologi-encompassesavarietyofconceptsandelementsincludingsensitivitycalandbehaviouralchanges.Thiscanencompasschangesinthewayorsusceptibilitytoharmandlackofcapacitytocopeandadapt.{WGII}ReferencesAGECC,2010:EnergyforaSustainableFuture.UnitedNationsSecretaryGeneral’sPanelonClimateChange[Houghton,J.T.,L.G.Meira,A.Callander,N.Harris,A.AdvisoryGrouponEnergyandClimate(AGECC),NewYork,NY,USA,24pp.KattenbergandK.Maskell(eds.)].CambridgeUniversityPress,Cambridge,UnitedKingdomandNewYork,NY,USA,572pp.ArcticCouncil,2013:Glossaryofterms.In:ArcticResilienceInterimReport2013.StockholmEnvironmentInstituteandStockholmResilienceCentre,Stockholm,IPCC,2000a:EmissionsScenarios.SpecialReportofWorkingGroupIIIoftheInter-Sweden,p.viii.governmentalPanelonClimateChange[Nakićenović,N.andR.Swart(eds.)].CambridgeUniversityPress,Cambridge,UnitedKingdomandNewYork,NY,Hegerl,G.C.,O.Hoegh-Guldberg,G.Casassa,M.P.Hoerling,R.S.Kovats,C.Parmesan,USA,599pp.D.W.PierceandP.A.Stott,2010:Goodpracticeguidancepaperondetectionandattributionrelatedtoanthropogenicclimatechange.In:MeetingReportoftheIPCC,2000b:LandUse,Land-UseChange,andForestry.SpecialReportoftheInter-IntergovernmentalPanelonClimateChangeExpertMeetingonDetectionandgovernmentalPanelonClimateChange[Watson,R.T.,I.R.Noble,B.Bolin,N.H.AttributionofAnthropogenicClimateChange[StockerT.F.,C.B.Field,D.Qin,V.Ravindranath,D.J.VerardoandD.J.Dokken(eds.)].CambridgeUniversityPress,Barros,G.-K.Plattner,M.Tignor,P.M.MidgleyandK.L.Ebi(eds.)].IPCCWorkingCambridge,UnitedKingdomandNewYork,NY,USA,377pp.GroupITechnicalSupportUnit,UniversityofBern,Bern,Switzerland,8pp.IPCC,2001a:ClimateChange2001:TheScientificBasis.ContributionofWorkingHeywood,V.H.(ed.),1995:TheGlobalBiodiversityAssessment.UnitedNationsGroupItotheThirdAssessmentReportoftheIntergovernmentalPanelonCli-EnvironmentProgramme,CambridgeUniversityPress,Cambridge,UnitedKing-mateChange[Houghton,J.T.,Y.Ding,D.J.Griggs,M.Noquer,P.J.vanderLinden,dom,1152pp.X.Dai,K.MaskellandC.A.Johnson(eds.)].CambridgeUniversityPress,Cam-bridge,UnitedKingdomandNewYork,NY,USA,881pp.IPCC,1992:ClimateChange1992:TheSupplementaryReporttotheIPCCScientificAssessment[Houghton,J.T.,B.A.CallanderandS.K.Varney(eds.)].CambridgeIPCC,2001b:ClimateChange2001:Impacts,Adaptation,andVulnerability.Contri-UniversityPress,Cambridge,UnitedKingdomandNewYork,NY,USA,116pp.butionofWorkingGroupIItotheThirdAssessmentReportoftheIntergovern-mentalPanelonClimateChange[McCarthy,J.,O.Canziani,N.Leary,D.DokkenIPCC,1996:ClimateChange1995:TheScienceofClimateChange.ContributionofandK.White(eds.)],CambridgeUniversityPress,Cambridge,UnitedKingdomWorkingGroupItotheSecondAssessmentReportoftheIntergovernmentalandNewYork,NY,USA,1032pp.128GlossaryAnnexIIIPCC,2003:DefinitionsandMethodologicalOptionstoInventoryEmissionsfromChange2014:MitigationofClimateChange.ContributionofWorkingDirectHuman-InducedDegradationofForestsandDevegetationofOtherVege-GroupIIItotheFifthAssessmentReportoftheIntergovernmentalPanelontationTypes[Penman,J.,M.Gytarsky,T.Hiraishi,T.Krug,D.Kruger,R.Pipatti,L.ClimateChange[Edenhofer,O.,R.Pichs-Madruga,Y.Sokona,E.Farahani,Buendia,K.Miwa,T.Ngara,K.TanabeandF.Wagner(eds.)].TheInstituteforS.Kadner,K.Seyboth,A.Adler,I.Baum,S.Brunner,P.Eickemeier,B.Kriemann,GlobalEnvironmentalStrategies(IGES),Japan,32pp.J.Savolainen,S.Schlömer,C.vonStechow,T.ZwickelandJ.C.Minx(eds.)].Cam-bridgeUniversityPress,Cambridge,UnitedKingdomandNewYork,NY,USA,pp.IPCC,2007:ClimateChange2007:ThePhysicalScienceBasis.ContributionofWor-1251–1274.kingGroupItotheFourthAssessmentReportoftheIntergovernmentalPanelonClimateChange.[Solomon,S.,D.Qin,M.Manning,Z.Chen,M.Marquis,K.B.Manning,M.R.,M.Petit,D.Easterling,J.Murphy,A.Patwardhan,H.‐H.Rogner,R.Averyt,M.TignorandH.L.Miller(eds.)].CambridgeUniversityPress,Cambridge,SwartandG.Yohe(eds.),2004:IPCCWorkshoponDescribingScientificUncer-UnitedKingdomandNewYork,NY,USA,996pp.taintiesinClimateChangetoSupportAnalysisofRiskofOptions.WorkshopReport.IntergovernmentalPanelonClimateChange,Geneva,Switzerland,138IPCC,2011:WorkshopReportoftheIntergovernmentalPanelonClimateChangepp.WorkshoponImpactsofOceanAcidificationonMarineBiologyandEcosystems[rFeiae,ldM,.CT.iBg.n,Vo.rBaanrdroKs.,TL..FE.bStio(eckdes.r,)]D..IPQCinC,KW.oJ.rMkinagchG,rGo.u-Kp.IPIlTaetctnhenri,cMal.SDu.pMpaosrttrUanndit-,MasEtr.aKnrdiergelae,r,MK..DJ..,MCa.cBh.,FiPe.lRd.,TM.Fa.tSstcohcoksesr,,GO..-EKd.ePnlahtotnfeerr,,KG..LW.E.bYoi,hDe.Ja.nFrdaFm.We,.HZ.wHieelrds,,IICarnegieInstitution,Stanford,CA,USA,164pp.2010:GuidanceNoteforLeadAuthorsoftheIPCCFifthAssessmentReportonConsistentTreatmentofUncertainties.IntergovernmentalPanelonClimateIPCC,2012a:ManagingtheRisksofExtremeEventsandDisasterstoAdvanceClima-Change(IPCC),Geneva,Switzerland,4pp.teChangeAdaptation.ASpecialReportofWorkingGroupsIandIIoftheInter-governmentalPanelonClimateChange[Field,C.B.,V.Barros,T.F.Stocker,D.Qin,MEA,2005:AppendixD:Glossary.In:EcosystemsandHumanWell-being:CurrentD.J.Dokken,K.L.Ebi,M.D.Mastrandrea,K.J.Mach,G.-K.Plattner,S.K.Allen,M.StatesandTrends.FindingsoftheConditionandTrendsWorkingGroup,Vol.1TignorandP.M.Midgley(eds.)].CambridgeUniversityPress,Cambridge,UKand[Hassan,R.,R.Scholes,andN.Ash(eds.)].MillenniumEcosystemAssessmentNewYork,NY,USA,582pp.(MEA),IslandPress,Washington,DC,USA,pp.893-900.IPCC,2012b:MeetingReportoftheIntergovernmentalPanelonClimateChangeMoss,R.andS.Schneider,2000:UncertaintiesintheIPCCTAR:RecommendationstoExpertMeetingonGeoengineering[Edenhofer,O.,R.Pichs-Madruga,Y.Sokona,C.LeadAuthorsforMoreConsistentAssessmentandReporting.In:IPCCSuppor-Field,V.Barros,T.F.Stocker,Q.Dahe,J.Minx,K.J.Mach,G.-K.Plattner,S.Schlömer,tingMaterial:GuidancePapersonCrossCuttingIssuesintheThirdAssessmentG.HansenandM.Mastrandrea(eds.)].IPCCWorkingGroupIIITechnicalSupportReportoftheIPCC[Pachauri,R.,T.TaniguchiandK.Tanaka(eds.)].Intergovern-Unit,PotsdamInstituteforClimateImpactResearch,Potsdam,Germany,99pp.mentalPanelonClimateChange,Geneva,Switzerland,pp.33–51.IPCC,2013a:AnnexIII:Glossary[Planton,S.(ed.)].In:ClimateChange2013:TheMoss,R.,M.Babiker,S.Brinkman,E.Calvo,T.Carter,J.Edmonds,I.Elgizouli,S.Emori,PhysicalScienceBasis.ContributionofWorkingGroupItotheFifthAssessmentL.Erda,K.Hibbard,R.Jones,M.Kainuma,J.Kelleher,J.F.Lamarque,M.Manning,ReportoftheIntergovernmentalPanelonClimateChange[Stocker,T.F.,D.Qin,B.Matthews,J.Meehl,L.Meyer,J.Mitchell,N.Nakicenovic,B.O’Neill,R.Pichs,G.-K.Plattner,M.Tignor,S.K.Allen,J.Boschung,A.Nauels,Y.Xia,V.BexandP.M.K.Riahi,S.Rose,P.Runci,R.Stouffer,D.vanVuuren,J.Weyant,T.Wilbanks,J.P.vanMidgley(eds.)].CambridgeUniversityPress,Cambridge,UnitedKingdomandYperseleandM.Zurek,2008:Towardsnewscenariosforanalysisofemissions,NewYork,NY,USA,pp.1447–1466,doi:10.1017/CBO9781107415324.031.climatechange,impactsandresponsestrategies.IPCCExpertMeetingReport,19-21September,2007,Noordwijkerhout,Netherlands,IntergovernmentalPanelIPCC,2013b:ClimateChange2013:ThePhysicalScienceBasis.ContributionofWor-onClimateChange(IPCC),Geneva,Switzerland,132pp.kingGroupItotheFifthAssessmentReportoftheIntergovernmentalPanelonClimateChange[Stocker,T.F.,D.Qin,G.-K.Plattner,M.Tignor,S.K.Allen,J.Moss,R.,J.A.,Edmonds,K.A.Hibbard,M.R.Manning,S.K.Rose,D.P.vanVuuren,Boschung,A.Nauels,Y.Xia,V.BexandP.M.Midgley(eds.)].CambridgeUniver-T.R.Carter,S.Emori,M.Kainuma,T.Kram,G.A.Meehl,J.F.B.Mitchell,sityPress,Cambridge,UnitedKingdomandNewYork,NY,USA,1535pp.,N.Nakicenovic,K.Riahi,S.J.Smith,R.J.Stouffer,A.M.Thomson,J.P.Weyantanddoi:10.1017/CBO9781107415324.T.J.Wilbanks,2010:Thenextgenerationofscenariosforclimatechangeresearchandassessment.Nature,463,747–756.IPCC,2014a:AnnexII:Glossary[Agard,J.,E.L.F.Schipper,J.Birkmann,M.Campos,C.Dubeux,Y.Nojiri,L.Olsson,B.Osman-Elasha,M.Pelling,M.J.Prather,M.G.UNFCCC,2013:ReportingandaccountingofLULUCFactivitiesundertheKyotoPro-Rivera-Ferre,O.C.Ruppel,A.Sallenger,K.R.Smith,A.L.St.Clair,K.J.Mach,M.D.tocol.UnitedNationsFrameworkConventiononClimaticChange(UNFCCC),MastrandreaandT.E.Bilir(eds.)].In:ClimateChange2014:Impacts,Adaptation,Bonn,Germany.Availableat:http://unfccc.int/methods/lulucf/items/4129.phpandVulnerability.PartB:RegionalAspects.ContributionofWorkingGroupIItotheFifthAssessmentReportoftheIntergovernmentalPanelonClimateChangeUNISDR,2009:2009UNISDRTerminologyonDisasterRiskReduction.UnitedNati-[Barros,V.R.,C.B.Field,D.J.Dokken,M.D.Mastrandrea,K.J.Mach,T.E.Bilir,M.onsInternationalStrategyforDisasterReduction(UNISDR),UnitedNations,Chatterjee,K.L.Ebi,Y.O.Estrada,R.C.Genova,B.Girma,E.S.Kissel,A.N.Levy,S.Geneva,Switzerland,30pp.MacCracken,P.R.MastrandreaandL.L.White(eds.)].CambridgeUniversityPress,Cambridge,UnitedKingdomandNewYork,NY,USA,pp.1757–1776.vanVuuren,D.P.,J.Edmonds,M.Kainuma,K.Riahi,A.Thomson,K.Hibbard,G.C.Hurtt,T.Kram,V.Krey,J.F.Lamarque,T.Masui,M.Meinshausen,N.Nakicenovic,IPCC,2014b:AnnexI:Glossary,AcronymsandChemicalSymbols[Allwood,J.M.,V.S.J.SmithandS.K.Rose,2011:TheRepresentativeConcentrationPathways:anBosetti,N.K.Dubash,L.Gómez‐EcheverriandC.vonStechow(eds.)].In:Climateoverview.ClimaticChange,109,pp.5–31.129AnnexIIGlossaryWCED,1987:OurCommonFuture.WorldCommissiononEnvironmentandDevelop-ment(WCED),OxfordUniversityPress,Oxford,UK,300pp.2130ANNEXIIIAcronyms,ChemicalSymbolsandScientificUnits131AnnexIIIAcronyms,ChemicalSymbolsandScientificUnitsμatmMicroatmosphereFARFirstAssessmentReportAFOLUAgriculture,ForestryandOtherLandUseAMOCAtlanticMeridionalOverturningCirculationFITFeed-inTariffAR4FourthAssessmentReportAR5FifthAssessmentReportFOLUForestryandOtherLandUseBATBestAvailableTechniqueBAUBusinessAsUsualGCMGlobalClimateModelBECCSBioenergywithCarbonDioxideCaptureandStorageGDPGrossDomesticProductCCSCarbonCaptureandStorageCDMCleanDevelopmentMechanismGHGGreenhouseGasCDRCarbonDioxideRemovalPerfluoromethaneGMIGlobalMethaneInitiativeIIICF4MethaneCombinedHeatandPowerGtGigatonnesCH4CoupledModelIntercomparisonProjectPhase5CHPCarbonDioxideGTPGlobalTemperaturechangePotentialCMIP5CarbonDioxideEquivalentCO2ConcentratingSolarPowerGWPGlobalWarmingPotentialCO2-eqDevelopingCountryCSPEquilibriumClimateSensitivityH2HydrogenDCEmissionDatabaseforGlobalAtmosphericResearchECSExajouleHadCRUT4HadleyCentreClimaticResearchEDGAREarthSystemModelofIntermediateComplexityUnitGriddedSurfaceTemperatureDataSet4EJElNiño-SouthernOscillationEMICExecutiveSummaryHDVHeavy-DutyVehiclesENSOEarthSystemModelESEmissionsTradingSystemHFCHydrofluorocarbonESMFluorinatedgasesETSFrequentlyAskedQuestionHFC-152aHydrofluorocarbon-152a,F-gasesDifluoroethaneFAQ132IAMIntegratedAssessmentModelICAOInternationalCivilAviationOrganizationIMOInternationalMaritimeOrganizationIOInternationalOrganizationLDVLight-DutyVehiclesLULUCFLandUse,Land-UseChangeandForestryMAGICCModelfortheAssessmentofGreenhouseGasInducedClimateChangeMEFMajorEconomiesForumMRVMonitoring,ReportingandVerificationN2ONitrousOxideNAMANationallyAppropriateMitigationActionNAPNationalAdaptationPlanNAPANationalAdaptationProgrammesofActionAcronyms,ChemicalSymbolsandScientificUnitsAnnexIIINGONon-GovernmentalOrganizationTCRETransientClimateResponsetoCumulativeO2OxygenCO2EmissionsOAOceanAcidificationTFEThematicFocusElementOECDOrganisationforEconomicCo-operationTSTechnicalSummaryandDevelopmentUHIUrbanHeatIslandPFCPerfluorocarbonUNFCCCUnitedNationsFrameworkppbpartsperbillionConventiononClimateChangeppmpartspermillionWWattPVPhotovoltaicWGWorkingGroupR&DResearchandDevelopmentWMGHGWell-MixedGreenhouseGasRCPRepresentativeConcentrationPathwayRERenewableEnergyIIIREDDReducingEmissionsfromDeforestationandForestDegradation133REEEPRenewableEnergyandEnergyEfficiencyPartnershipRESRenewableEnergySystemRFCReasonForConcernRPSRenewablePortfolioStandardSARSecondAssessmentReportSMSupplementaryMaterialSO2SulfurDioxideSPMSummaryforPolicymakersSRESSpecialReportonEmissionsScenariosSREXSpecialReportonManagingtheRisksofExtremeEventsandDisasterstoAdvanceSRMClimateChangeAdaptationSRRENSolarRadiationManagementSpecialReportonRenewableEnergySYRSourcesandClimateChangeMitigationTCRSynthesisReportTransientClimateResponseANNEXIV1AuthorsandReviewEditors135AnnexIVAuthorsandReviewEditorsCoreWritingTeamMembersFORSTER,PiersUniversityofLeedsALLEN,MylesR.UKUniversityofOxfordUKFRIEDLINGSTEIN,PierreUniversityofExeterBARROS,VicenteR.UKIPCCWGIICo-ChairUniversityofBuenosAiresFUGLESTVEDT,JanArgentinaCenterforInternationalClimateandEnvironmentalResearch(CICERO)BROOME,JohnNorwayUniversityofOxfordUKGOMEZ-ECHEVERRI,LuisInternationalInstituteforAppliedSystemsAnalysis(IIASA)CHRIST,RenateAustriaSecretaryoftheIPCCIPCCSecretariat,WorldMeteorologicalOrganization(WMO)HALLEGATTE,StephaneSwitzerlandWorldBankUSACHURCH,JohnA.CommonwealthScientificandIndustrialHEGERL,GabrieleC.ResearchOrganisation(CSIRO)UniversityofEdinburghAustraliaUKCLARKE,LeonHOWDEN,MarkPacificNorthwestNationalLaboratoryCommonwealthScientificandIndustrialUSAResearchOrganisation(CSIRO)AustraliaCRAMER,WolfgangJIMÉNEZCISNEROS,BlancaIVPotsdamInstituteforClimateImpactResearch/InstitutUniversidadNacionalAutónomadeMéxico/UnitedNationsEducational,ScientificandCulturalOrganization(UNESCO)MéditerranéendeBiodiversitéetd’EcologiemarineetcontinentaleMexico/France(IMBE)Germany/FranceKATTSOV,VladimirVoeikovMainGeophysicalObservatoryDASGUPTA,PurnamitaRussianFederationUniversityofDelhiEnclaveIndiaKEJUN,JiangEnergyResearchInstituteDUBASH,NavrozChinaCentreforPolicyResearch,NewDelhiIndiaLEE,HoesungIPCCVice-ChairEDENHOFER,OttmarKeimyungUniversityIPCCWGIIICo-ChairRepublicofKoreaPotsdamInstituteforClimateImpactResearchGermanyMACH,KatharineJ.IPCCWGIITechnicalSupportUnitELGIZOULI,IsmailUSAIPCCVice-ChairSudanMAROTZKE,JochemMaxPlanckInstituteforMeteorologyFIELD,ChristopherB.GermanyIPCCWGIICo-ChairCarnegieInstitutionforScienceUSA136AuthorsandReviewEditorsAnnexIVMASTRANDREA,MichaelD.RAVINDRANATH,N.H.IPCCWGIITechnicalSupportUnitIndianInstituteofScienceUSAIndiaMEYER,LeoREISINGER,AndyIPCCSynthesisReportTechnicalSupportUnitNZAgriculturalGreenhouseGasResearchCentreTheNetherlandsNewZealandMINX,JanRIAHI,KeywanIPCCWGIIITechnicalSupportUnitInternationalInstituteforAppliedSystemsAnalysis(IIASA)GermanyAustriaMULUGETTA,YacobRUSTICUCCI,MatildeUniversityofSurreyUniversidaddeBuenosAiresUKArgentinaO’BRIEN,KarenSCHOLES,RobertUniversityofOsloCouncilforScientificandIndustrialResearch(CSIR)NorwaySouthAfricaOPPENHEIMER,MichaelSEYBOTH,KristinPrincetonUniversityIPCCWGIIITechnicalSupportUnitUSAUSAPACHAURI,R.K.SOKONA,YoubaIPCCChairIPCCWGIIICo-ChairTheEnergyandResourcesInstitute(TERI)SouthCentreIndiaSwitzerlandPEREIRA,JoyJ.STAVINS,RobertUniversitiKebangsaanMalaysiaMalaysiaHarvardUniversityPICHS-MADRUGA,RamónUSAIVIPCCWGIIICo-ChairCentrodeInvestigacionesdelaEconomíaMundialSTOCKER,ThomasF.CubaIPCCWGICo-ChairUniversityofBernPLATTNER,Gian-KasperSwitzerlandIPCCWGITechnicalSupportUnitSwitzerlandTSCHAKERT,PetraPennsylvaniaStateUniversityPÖRTNER,Hans-OttoUSAAlfred-Wegener-InstituteGermanyVANVUUREN,DetlefNetherlandsEnvironmentalAssessmentAgency(PBL)POWER,ScottB.TheNetherlandsBureauofMeteorologyAustraliaVANYPERSELE,Jean-PascalIPCCVice-ChairPRESTON,BenjaminUniversityofLouvainOakRidgeNationalLaboratoryBelgiumUSAQIN,DaheIPCCWGICo-ChairChinaMeteorologicalAdministrationChina137AnnexIVAuthorsandReviewEditorsExtendedWritingTeamMembersYOHE,GaryWesleyanUniversityBLANCO,GabrielUSAUniversidadNacionaldelCentrodelaProvinciadeBuenosAiresArgentinaReviewEditorsEBY,MichaelALDUNCE,PaulinaUniversityofVictoriaUniversityofChileCanadaChileEDMONDS,JaeCHEN,WenyingUniversityofMarylandTsinghuaUniversityUSAChinaFLEURBAEY,MarcDOWNING,ThomasPrincetonUniversityGlobalClimateAdaptationPartnershipUSAUKGERLAGH,ReyerJOUSSAUME,SylvieTilburgUniversityLaboratoiredesSciencesduClimatetdel’Environnement(LSCE)TheNetherlandsInstitutPierreSimonLaplaceFranceKARTHA,SivanStockholmEnvironmentInstituteKUNDZEWICZ,ZbigniewUSAPolishAcademyofSciencesPolandKUNREUTHER,HowardTheWhartonSchooloftheUniversityofPennsylvaniaPALUTIKOF,JeanUSAGriffithUniversityAustraliaROGELJ,JoeriSKEA,JimIVInternationalInstituteforAppliedSystemsAnalysis(IIASA)ImperialCollegeLondonUKAustriaTANAKA,KanakoSCHAEFFER,MichielJapanScienceandTechnologyAgencyWageningenUniversityJapanGermany/TheNetherlandsTANGANG,FredolinSEDLÁČEK,JanNationalUniversityofMalaysiaETHZurichMalaysiaSwitzerlandZHANG,Xiao-YeSIMS,RalphChinaMeteorologicalAdministrationMasseyUniversityChinaNewZealandÜRGE-VORSATZ,DianaCentralEuropeanUniversityHungaryVICTOR,DavidG.UniversityofCaliforniaSanDiegoUSA138ANNEXV1ExpertReviewers139AnnexVExpertReviewersAKIMOTO,KeigoCONVERSI,AlessandraResearchInstituteofInnovativeTechnologyfortheEarthNationalResearchCouncilofItalyJapanItalyALCAMO,JosephDING,YihuiUniversityofKasselNationalClimateCenter,MeteorologicalAdministrationGermanyChinaALEXANDER,LisaV.DIXON,TimUniversityofNewSouthWalesInternationalEnergyAgencyGreenhouseGasR&DProgrammeAustralia(IEAGHG)UKAMESZ,BertTheNetherlandsDONG,WenjieBejingNormalUniversityARAKI,MakotoChinaForestryandForestProductsResearchInstituteJapanEKHOLM,TommiTechnicalResearchCentreofFinland(VTT)ARROYOCURRÁS,TabaréFinlandWWFInternationalMexicoESASHI,KeiTheFederationofElectricPowerCompaniesBINDOFF,NathanielL.JapanUniversityofTasmaniaAustraliaFISCHLIN,AndreasETHZurichBORGESLANDÁEZ,PedroAlfredoSwitzerlandMinistryofScienceandTechnologyVenezuelaFITZSIMMONS,JasonCharteredInstitutionofBuildingServicesEngineers(CIBSE)BRAGHIERE,RenatoUKUniversityofReadingUKGALE,DavidRoyalInstituteofBritishArchitectsBRUNO,JohnUKTheUniversityofNorthCarolinaatChapelHillUSAHABERL,HelmutAlpen-AdriaUniversitätKlagenfurt,Wien,GrazCARTER,PeterAustriaVClimateEmergencyInstituteHARNISCH,JochenKfWBankengruppeCanadaGermanyCASEY,MichaelHOUSE,JoannaCarbonVirginBristolUniversityIrelandUKCHOI,Young-JuneJU,HuiSeoulMetropolitanGovernmentChineseAcademyofAgriculturalScienceRepublicofKoreaChinaCOHEN,StewartKAINUMA,MikikoEnvironmentCanadaNationalInstituteforEnvironmentalStudiesCanadaJapan140ExpertReviewersAnnexVKATBEHBADER,NedalMURATA,AkihikoEnvironmentQualityAuthorityResearchandDevelopmentCenterforGlobalChangePalestineJapanKAZUNO,HirofumiNDIONE,JacquesAndreTheKansaiElectricPowerCo.,Inc.CentredeSuiviEcologiqueJapanSenegalKHESHGI,HaroonOZDEMIR,ErayExxonMobilResearchandEngineeringCompanyGeneralDirectorateofForestryUSATurkeyKOSONEN,KaisaPALTSEV,SergeyGreenpeaceMassachusettsInstituteofTechnologyFinlandUSALEFFERTSTRA,HaroldPLANTON,SergeNorwegianEnvironmentAgency(retired)Météo-FranceNorwayFranceLIU,QiyongPLATTNER,Gian-KasperNationalInstituteforCommunicableDiseaseControlandPreventionIPCCWGITechnicalSupportUnitChinaSwitzerlandLLASAT,Maria-CarmenPOLOCZANSKA,ElviraUniversityofBarcelonaCommonwealthScientificandIndustrialResearchOrganisationSpain(CSIRO)AustraliaLYNN,JonathanIPCCSecretariat,WorldMeteorologicalOrganization(WMO)PORTER,JohnSwitzerlandUniversityofCopenhagenDenmarkMA,ShimingChineseAcademyofAgriculturalSciencesPOWER,ScottB.ChinaBureauofMeteorologyAustraliaMASUDA,KooitiJapanAgencyforMarine-EarthScienceandTechnologyRAHOLIJAO,NirivololonaJapanNationalMeteorologicalOfficeMÉNDEZ,CarlosMadagascarVInstitutoVenezolanodeInvestigacionesCientíficasVenezuelaRAMASWAMY,VenkatachalamNationalOceanicandAtmosphericAdministration(NOAA)MENZEL,LenaUSAAlfredWegenerInstituteGermanyRHEIN,MonikaUniversityofBremenMOJTAHED,VahidGermanyUniversitàCa’FoscaridiVeneziaItalyROGNER,Hans-HolgerInstituteforAppliedSystemsAnalysis(IIASA)(retired)MOLINA,TomasAustriaUniversitatdeBarcelonaSpainSCHEI,TormodAndreStatkraftASNorway141AnnexVExpertReviewersSCHLEUSSNER,Carl-FriedrichWARD,RobertPotsdamInstituteforClimateImpactResearchLondonSchoolofEconomics(LSE)GermanyUKSHINE,KeithWARREN,RachelUniversityofReadingUniversityofEastAngliaUKUKSOUTHWELL,CarlWEIR,TonyRiskandPolicyInstituteUniversityoftheSouthPacificUSAAustraliaSTOTT,PeterA.WRATT,DavidMetOfficeHadleyCentreNationalInstituteofWaterandAtmosphericResearch(NIWA)UKNewZealandSU,MingshanWU,JianGuoNationalCenterforClimateChangeStrategyandInternationalChineseResearchAcademyofEnvironmentalSciencesCooperationChinaChinaWUEBBLES,DonaldSUAREZRODRIGUEZ,AvelinoG.UniversityofIllinoisInstituteofEcologyandSystematicsUSACubaXIA,ChaozongSUGIYAMA,TaishiChinaTheCentralResearchInstituteofElectricPowerIndustry(CRIEPI)JapanYAMIN,FarhanaUniversityCollegeLondon(UCL)TAKAHASHI,KiyoshiUKNationalInstituteforEnvironmentalStudiesJapanYUTA,SasakiTohokuElectricPowerCo.,Inc.TAKASHI,HongoJapanMitsuiGlobalStrategicStudiesInstituteJapanZHANG,ChengyiNationalClimateCenterTAKEMURA,ToshihikoChinaKyushuUniversityJapanZHANG,GuobinStateForestryAdministration(SFA)VTATTERSHALL,DavidChinaUSAZHAO,Zong-CiChinaMeteorologicalAdministration(CMA)THORNE,PeterW.ChinaNansenEnvironmentalandRemoteSensingCenter(NERSC)NorwayZHOU,GuomoZhejiangA&FUniversityTOL,RichardChinaAIUniversityofSussexZHU,SongliUKEnergyResearchInstituteChinaTSUTSUI,JunichiTheCentralResearchInstituteofElectricPowerIndustry(CRIEPI)JapanURGE-VORSATZ,DianaCentralEuropeanUniversityHungary142ANNEXVIPublicationsbytheIntergovernmentalPanelonClimateChange143AnnexVIPublicationsbytheIntergovernmentalPanelonClimateChangeAssessmentReportsClimateChange1995:SynthesisofScientific-TechnicalInforma-tionRelevanttoInterpretingArticle2oftheUNFrameworkFifthAssessmentReportConventiononClimateChangeClimateChange2013:ThePhysicalScienceBasisAReportoftheIntergovernmentalPanelonClimateChangeContributionofWorkingGroupItotheFifthAssessmentReportClimateChange2014:Impacts,Adaptation,andVulnerabilitySupplementaryReportstotheFirstAssessmentReportContributionofWorkingGroupIItotheFifthAssessmentReportClimateChange1992:TheSupplementaryReporttotheIPCCScientificAssessmentClimateChange2014:MitigationofClimateChangeSupplementaryreportoftheIPCCScientificAssessmentWorkingContributionofWorkingGroupIIItotheFifthAssessmentReportGroupIClimateChange2014:SynthesisReportClimateChange1992:TheSupplementaryReporttotheIPCCAReportoftheIntergovernmentalPanelonClimateChangeImpactsAssessmentSupplementaryreportoftheIPCCImpactsAssessmentWorkingGroupIIFourthAssessmentReportClimateChange:TheIPCC1990and1992AssessmentsClimateChange2007:ThePhysicalScienceBasisIPCCFirstAssessmentReportOverviewandPolicymakerSummariesContributionofWorkingGroupItotheFourthAssessmentReportand1992IPCCSupplementClimateChange2007:Impacts,AdaptationandVulnerabilityFirstAssessmentReportContributionofWorkingGroupIItotheFourthAssessmentReportClimateChange:TheScientificAssessmentReportoftheIPCCScientificAssessmentWorkingGroupI,1990ClimateChange2007:MitigationofClimateChangeContributionofWorkingGroupIIItotheFourthAssessmentReportClimateChange:TheIPCCImpactsAssessmentReportoftheIPCCImpactsAssessmentWorkingGroupII,1990ClimateChange2007:SynthesisReportAReportoftheIntergovernmentalPanelonClimateChangeClimateChange:TheIPCCResponseStrategiesReportoftheIPCCResponseStrategiesWorkingGroupIII,1990ThirdAssessmentReportClimateChange2001:TheScientificBasisSpecialReportsContributionofWorkingGroupItotheThirdAssessmentReportClimateChange2001:Impacts,Adaptation,andVulnerabilityManagingtheRisksofExtremeEventsandDisasterstoAdvanceContributionofWorkingGroupIItotheThirdAssessmentReportClimateChangeAdaptation(SREX)2012ClimateChange2001:MitigationRenewableEnergySourcesandClimateChangeMitigationContributionofWorkingGroupIIItotheThirdAssessmentReport(SRREN)2011ClimateChange2001:SynthesisReportCarbonDioxideCaptureandStorage2005ContributionofWorkingGroupsI,IIandIIItotheThirdAssessmentReportSafeguardingtheOzoneLayerandtheGlobalClimateSystem:IssuesRelatedtoHydrofluorocarbonsandPerfluorocarbons(IPCC/TEAPjointreport)2005SecondAssessmentReportClimateChange1995:ScienceofClimateChangeLandUse,Land-UseChange,andForestry2000ContributionofWorkingGroupItotheSecondAssessmentReportEmissionsScenarios2000VIClimateChange1995:Scientific-TechnicalAnalysesofImpacts,AdaptationsandMitigationofClimateChangeMethodologicalandTechnologicalIssuesinTechnologyTransferContributionofWorkingGroupIItotheSecondAssessmentReport2000ClimateChange1995:EconomicandSocialDimensionsofAviationandtheGlobalAtmosphere1999ClimateChangeContributionofWorkingGroupIIItotheSecondAssessmentReportTheRegionalImpactsofClimateChange:AnAssessmentofVul-nerability1997144PublicationsbytheIntergovernmentalPanelonClimateChangeAnnexVIClimateChange1994:RadiativeForcingofClimateChangeandTechnologies,PoliciesandMeasuresforMitigatingClimateanEvaluationoftheIPCCIS92EmissionScenarios1994ChangeIPCCTechnicalPaperI,1996MethodologyReportsandTechnicalGuidelinesForalistofSupportingMaterialpublishedbytheIPCC(workshopandmeetingreports),pleaseseewww.ipcc.ch2013RevisedSupplementaryMethodsandGoodPracticeGuid-orcontacttheIPCCSecretariat,c/oWorldMeteorologicalanceArisingfromtheKyotoProtocol(KPSupplement)2014Organization,7bisAvenuedelaPaix,CasePostale2300,Ch-1211Geneva2,Switzerland2013Supplementtothe2006IPCCGuidelinesforNationalGreenhouseGasInventories:Wetlands(WetlandsSupplement)20142006IPCCGuidelinesforNationalGreenhouseGasInventories(5Volumes)2006DefinitionsandMethodologicalOptionstoInventoryEmissionsfromDirectHuman-inducedDegradationofForestsandDeveg-etationofOtherVegetationTypes2003GoodPracticeGuidanceforLandUse,Land-useChangeandFor-estry2003GoodPracticeGuidanceandUncertaintyManagementinNationalGreenhouseGasInventories2000Revised1996IPCCGuidelinesforNationalGreenhouseGasInventories(3volumes)1996IPCCTechnicalGuidelinesforAssessingClimateChangeImpactsandAdaptations1994IPCCGuidelinesforNationalGreenhouseGasInventories(3vol-umes)1994PreliminaryGuidelinesforAssessingImpactsofClimateChange1992TechnicalPapersVIClimateChangeandWater145IPCCTechnicalPaperVI,2008ClimateChangeandBiodiversityIPCCTechnicalPaperV,2002ImplicationsofProposedCO2EmissionsLimitationsIPCCTechnicalPaperIV,1997StabilizationofAtmosphericGreenhouseGases:Physical,Bio-logicalandSocio-EconomicImplicationsIPCCTechnicalPaperIII,1997AnIntroductiontoSimpleClimateModelsUsedintheIPCCSecondAssessmentReportIPCCTechnicalPaperII,1997VI1Index147IndexIndexNote:Anasterisk()indicatesthetermalsoAnthropogenicemissions,3,4‑5,5,8,16,18,20,causesof,4‑5,44‑51appearsintheGlossary.Pagenumbersinbold44,45‑47,45‑47,54,63‑64,73‑74,74,78comprehensivestrategiesfor,91indicatepagespansforthefourTopics.Pagenum-decisionmakingabout,17,76‑77,107bersinitalicsdenotefigures,tablesandboxedAnthropogenicforcings,5,6,44‑47,45,48,48driversof,4,5‑96,8‑10,9,44‑47,47,56‑58,62,material.Arcticregion,rapidwarmingin,4,10,6070‑71,81,84Arcticseaice,4,12,48,62emissionsreductions,effectson,17‑19,18,20,A56,84‑85anthropogenicinfluenceson,5,48,49futurechanges,8‑16,56‑74Abruptclimatechange,13,16,65,73‑74observedchanges,4,41,42,48,49futurerisksandimpacts,13‑16,17‑19,18,77‑79,Adaptation,17‑31,76‑112projectedchanges,12,62,7478AtlanticMeridionalOverturningCirculationimpactsattributedto,6,7,49‑51,50‑52approaches,varietyof,27,94,95,96(AMOC),60‑62,74irreversibleorabruptchanges,13,16,65,73‑74characteristicsof,19‑20,79‑81Atmosphere,2,3,40,41,42,47,58‑60,82limiting,8,17,20,56,65,84‑85co-benefits,17,20,26,80‑81,90,91,98Attribution.SeeDetectionandattributionriskamplificationby,13,16,64,66,77,78cooperativeactionin,17,26,29,76,94,102,105,timescales,13,16,62‑63,63,73‑74,77106BClimateextreme.SeeExtremeweathereventsemissionsreductionsand,17,76Climatefinance,95,109‑110,111enablingfactorsandconstraints,19‑20,26,80,Biodiversity,13,64,65,67,98,109,112Climatemodels,12,43,56‑58,56,5894,95,111Bioenergy,25,82,85,86,102confidenceanduncertaintyin,56equityandfairnessin,17,76‑77,95BioenergyandCarbonCaptureandStorageClimate-resilientpathways,17,31,76,77,90finance,30‑31,97,107,110‑111,110‑111Climatesensitivity,48,49,62firststepin,19,80(BECCS),22,23,24,28,81,82,85,89,100Climatesystemfundinggap,31,111Biogeochemistry,62driversofchangesin,4‑5,8‑10,44‑47,56‑58,81,futurepathways,17‑26,76‑9184interactionswithmitigation,17‑18,20,26,76,77,Chumaninfluenceon,2,4‑5,5,8,9,44,48‑49,51,80‑81,90,98,11263‑64maladaptation,20,77,80CancúnPledges,23,24,84,85observedchangesin,2‑4,3,12,40‑44,41‑43,near-termdecisions,77,79Capandtrade,30,10749‑51,50‑52place-andcontext-specificityof,79‑80Carboncycle,45,56,56,62projectedchangesin,10‑13,16,56,58‑64,59‑61,planningandimplementation,19‑20,26,29‑30,Carbondioxide(CO2)63‑6431,54,80,94,95‑97,96,98,106,107,112responsesof,62‑63policyapproachesfor,26,29‑31,94,96,102‑111CO2-equivalents,5,20‑23,21‑24,28,45‑46,46,timescalesofchange,62‑63,63riskmanagement/reductionby,14,17‑19,18,47,81,82‑87,84‑85,99‑100,99,101warmingof,2‑4,3,62‑6365‑67,65,70‑71,76,77‑79,79,94,108emissions,driversof,4,46‑47,47,81CO2.SeeCarbondioxiderisks/sideeffectsof,17,76,91emissions,increasein,3,4‑5,5,44,44,45‑47,Coastalsystems,13,15,66,67,97,98riskscomparedwithrisksfromclimatechange,45‑47Co-benefits,17,20,26,30,77,78‑79,80‑81,90,17,19,77emissionsscenarios,8,18‑19,18,20‑24,21‑23,90‑91,98,102,103‑104,107,109sustainabledevelopmentand,17,19,31,76,79,28,28,57,81‑86,82‑86,99,101Confidence,2,37,5695emissions,warmingand,8‑10,9,18‑19,18,20,Cooperation,17,26,29,76,89,94,102,105,106transformationand,20,27,76,80,9621,62‑63,63‑64,78Coralreefs,13,67,68,72,74,97Adaptationdeficit,91,95projections,8,9,16,63‑64,73‑74,74Cost-effectiveness,24,24‑25,28‑30,77,84‑86,Adaptationexperience,26,54,106‑107,106radiativeforcingand,43,44,4585‑86,98,99,102,107,112Adaptationlimits,19‑20,72,79removalfromatmosphere,16,62‑63,74Costsexceedanceof,20,67,77,80SeealsoEmissionsofmitigation,17,24‑25,24‑25,28‑30,84‑86,Adaptationoptions,26,27,76,94,95‑98,96CarbonDioxideRemoval(CDR),21,23,24,81,85‑86,98,99,102bysectors,95‑97,9882,89ofmitigationdelays,19,24,25,79,85,86Adaptationpathways,17‑26,76‑91Carbondioxidecaptureandstorage(CCS),22,SeealsoClimatefinancecharacteristicsof,19‑20,79‑8124,25,28,82,85,109,110Cropyields,13,15,51,69,69,98Adaptationpotentials,65,70‑71Carbonprice,24,25,30,106,107,108,109Cryosphere,2,42,47,52,62Adaptivecapacity,26,77,80,94Carbonsequestration,31,101,112Aerosols,44,90Carbonsinks,20,28,45,67,81,98DAfforestation,28,29,81,102,112Cascadingimpacts,51,52AFOLU(Agriculture,ForestryandOtherLandCauses.SeeDetectionandattributionDecarbonization,5,78,81,98,99‑100Use),28,30,101,104,108Certainty,2,37Decisionmaking,17,19,29,76‑77,107Agriculture,16,29,69,81,98,102CleanDevelopmentMechanism(CDM),105‑106,Deforestation,28,29,67,83,102SeealsoCropyields108Delayinmitigation,effectsof,17,19,20,24,25,Antarcticicesheet,4,16,42,74Climatechange,2‑16,40‑74adaptationandmitigationand,17‑31,76‑11231,76,77,79,81,84‑85,86,90148attributionof,47‑51beyond2100,16,73‑74IndexDetectionandattribution,4‑8,7,45‑51,50‑51sea-levelriseand,16observedchanges,5,42,48IndexSeealsoHumansspecificsectorsandgases,28,46,47,99,99projectedchanges,12,62SRESscenarios,57,58Globalaggregateimpacts,18,18,72‑73,73,78Disasterriskmanagement,26,27,31,54,91,94,standardsetof,56‑58,57GlobalTemperaturechangePotential(GTP),95,96,97,106,111temperatureand,8‑10,9,16,18‑19,18,20‑24,87‑8822,62‑63,81GlobalWarmingPotential(GWP),87‑88Droughts,8,15,36,51,53,69,97,98Energyaccess,30,109Governments/governance,17,26,29‑30,31,89,Energyaccumulationinclimatesystem,4,42112EEnergydemand,29,99‑100adaptationand,19,26,54,80,94,95,106,107Energyefficiency,30,81,110SeealsoPoliciesEarlywarningsystems,27,95,96,97Energyintensity,47,47,94,98‑99Greenhousegasemissions.SeeEmissionsEconomicdiversification,19,27,30,31,80,96Energyprice.SeeCarbonpriceGreenlandicesheet,5,48Economicgrowthanddevelopment,64,94Energyproduction,28,28,30,31,81,99‑100,observedchanges,4,5,42,48100‑101,103,110projectedchanges,16,74emissionsand,4,8,20,44,46‑47,47,56,81decarbonizingof,28,98,99‑100Economicindicators,aggregate,78low-carbonenergy,21,23,28,30,82,84,85,94,HEconomicinstruments,30,107‑109,108100,100,110Economiclosses,53,73policyinstruments,108Heatwaves,7‑8,10,53,58,60,69Ecosystemservices,13,20,64,65,67,81Equity,17,76‑77,89,90,95,109Humanhealth,13,15,31,51,65,69,97,109Ecosystems,8,13,16,20,26,27,53,64,67,74,97Exposure,8,13,16,20,36,53,54,58,64,76,96Humansecurity,16,54,64,77,97reductionof,19,27,80Humanskeyrisks,65,65,66,67,74Extinctionrisk,13,19,51,65,67management,27,29,96,97Extremeweatherevents,7‑8,53anthropogenicforcings,5,6,44‑47,45,48,48ElNiñoSouthernOscillation(ENSO),4,40,56,economiclossesfrom,53anthropogenicgreenhousegasemissions,3,4‑5,60humaninfluences,8,535,8,9,16,18,20,44,45‑47,45‑47,54,63‑64,Emissionsobservedchanges,7‑8,5373‑74,74,78anthropogenic,3,4‑5,5,8,16,18,20,44,45‑47,precipitation,7,8,10,11,15,53,58,60humanactivities,constraintson,15,19,65,69,7745‑47,54,63‑64,73‑74,74,78projections,10,11,58influenceonclimatesystem,2,4‑5,5,8,9,44,CO2-equivalent,5,20‑23,21‑24,28,45‑46,46,asReasonforConcern,18,18,72‑73,7848‑49,51,63‑6447,81,82‑87,84‑85,99‑100,99,101risksdueto,19,65responsestoclimatechange(Seeadaptation;asdriverofclimatechange,4‑5,8‑10,9,18,19,sealevel,7,8,53mitigation)44,45‑47,45,56‑58,62,84temperature,7‑8,10,53,60driversof,4,8,20,44‑47,47,56,81Ieconomicassessmentand,30,79,85,86Ffuturerisksand,8‑16,17‑19,18,77‑79,78Icesheets,56metricsfor,23,87‑88Finance,29,30‑31,95,95,97,102,107,109‑110,observedlosses,4,5,42,48ofnon-CO2gases,23,28,84,87,99110‑111projectedlosses,16,74observedchanges,2,3,4‑5,5,44,44,45‑47,fundinggap,31,11145‑47,54Impacts,8‑16,56‑74projections(SeeEmissionsscenarios)Fisheries,13,15,67,68,97onallcontinentsandoceans,v,6,47,49reductions,8,17‑19,18,20‑24,28,30,56,76,86,Floods,8,15,53,67attributionof,47‑51,50‑5298‑100,99‑101Foodproduction,15,16,67,68‑69,69,97cascading,51,52reductions,challengesof,20,81Foodsecurity,13,16,19,64,65,69,109ofclimatechange,2,6,7,13‑16,49‑51,50‑52,reductions,substantial,8‑10,17‑19,18,19,20,Forests,29,52,67,81,10264‑7324,28,56,63,77‑78,81,110distributionof,18,18,72‑73,78relationshipwithclimatechanges,3,4,17,18,86afforestation,28,29,81,82‑83,102exposureandvulnerabilityand,58,58byspecificgases,5,46deforestation,28,29,67,83,102ofextremeevents,53temperature(warming)and,8‑10,9,18‑19,18,Futurechanges,risks,andimpacts,8‑16,56‑74future,8‑16,56‑7420‑24,56,58,62‑63,81‑86,83SeealsoProjectedchangesglobalaggregate,18,18,72‑73,73,78Emissionsscenarios,8,18‑19,18,20‑24,21‑24,Futurepathways,17‑26,76‑91high,severe,widespread,andirreversible,8,13,28,28,60‑61,63‑64,74,81‑86,82‑86adaptationpathways,19‑20,79‑8117,18‑19,56,62‑63,64,65,77,79baseline,8,20,21,22,24,24,28,28,82,85,99,decisionmakingand,17,19,76‑77,107modelsof,58,58110mitigationpathways,20‑26,81‑86ReasonforConcernand,18,18,72‑73climatechangerisksand,8,18‑19,18,73‑74riskreductionfor,65,65mitigationpathwaysand,18,20‑23,21‑23,78,Gtimescalesof,13,16,62‑63,7781‑86,98‑100,99‑101SeealsoObservedchangesovershootscenarios,20‑23,22,81,83,89Geoengineering,89overviewof,21‑23,83,83Glaciers,5,48,56Indigenouspeoples,19,26,27,80,95RCPs,8,9,10,11,16,21,22,56‑62,57,59‑61,Informationmeasures,30,95,108,10963‑64,74,74riskand,66149IndexIndexInfrastructure,15,26,29,69,79,94,95riskreductionby,14,17‑19,18,76,77‑79projections,10,12,16,58,59,62,66,74Institutions,26,27,29‑30,94,95,96,105,107risks/sideeffectsof,17,19,30,76,78‑79,91,102,risksassociated,13,65,66,67Integratedresponses,26,28,31,54,94,98,112103‑104,107,109timescaleof,16,74Internationalcooperation,17,29,76,102,105,riskscomparedwithrisksfromclimatechange,Overshootscenarios,20‑23,22,81,83,8917,19,77,78‑79106warminglevelswithoutadditionalmitigation,17,PInvestments,26,30‑31,94,108,109,110‑111,18‑19,18,77,81Mitigationcosts,17,24‑25,24‑25,28‑30,84‑86,Permafrost,4,12,16,42,62,74110‑11185‑86,98,99,102Policies,17,29‑31,91,94,102‑111Irreversibleimpacts,8,13,17,18‑19,56,62‑63,cost-effectiveness,24,24‑25,28‑30,84‑86,85‑86,98,99,102,107foradaptation,mitigation,technology,and64,77,79delaysand,19,24,25,79,85,86finance,26,29‑31,81,94,95,96,102‑111Irreversibleorabruptchanges,13,16,65,73‑74distributionof,86assessing,76economicassessments,79,85,86,111decisionmakingand,17,19,29,76‑77,107KMitigationoptions,26,28‑29,31,90,98‑102,emissionmetricsand,87‑8899‑101sectoralinstruments,30,107,108KyotoProtocol,29,84,105‑106bysectors,28,98‑99,99,101sustainabledevelopmentand,90,91Mitigationpathways,17‑26,76‑91,98‑100,Populationgrowth,4,8,20,44,46‑47,47,56,81L99‑101Poverty,16,17,27,31,54,73,76,90,96characteristicsof,20‑26,81‑86PrecipitationLanduseandland-usechange,27,31,56,96emissionmetricsand,23,87‑88extremeevents,7,8,10,11,15,53,58,60AFOLU,28,30,101,104,108Mitigationscenarios,18‑19,18,20‑25,21‑24,28,observedchanges,4,8,12,40,41,48,51,53,61RCPsand,5728,30,81‑86,82‑86,98‑100,99‑101,110projectedchanges,11,12,60,61Models.SeeClimatemodelsPrivatesector,19,29,30,80,95,97,106,107,111Large-scalesingularevents,18,18,72‑73,78,79Projectedchanges,10‑13,11,56‑74Likelihood.SeeConfidenceNbasisfor(models),56,58Livelihoods,26,27,64,65,67,90,94,96,97inclimatesystem,10‑13,16,56,58‑64,59‑61,Localgovernments,19,29,80,106,107Nationalgovernments,19,29,30,80,106‑10963‑64Low-carbonenergysupply,21,23,28,30,82,84,confidenceanduncertaintyin,56Oecosystemsandservices,66,6785,94,100,100,110emissionsscenariosand,8,9,18‑19,18,20‑24,Observedchanges,2‑8,40‑5421‑24,28,28,56,57,60‑61,63‑64,74,81‑86,Minclimatesystem,2‑4,3,12,40‑44,41‑43,47,82‑8649‑51,50‑52relativeto1986—2005,10,58Methane,4,44,44,57,84inemissions,2,3,4‑5,5,44,44,44‑48,45‑47,SeealsoTemperatureprojectionsMigration45‑47,54extremeevents,7‑8,53Rofhumanpopulations,16,73humaninfluenceand,2,5ofspecies(Seerangeshifts)impactsof,6,7,49‑51,50‑52Radiativeforcing,5,6,43,44,45,48,48Mitigation,17‑31,76‑112intemperature,2‑4,3,5,7‑8,12,40,41,43,47,Rangeshiftsofspecies,6,13,51,67behaviour,lifestyle,andcultureand,26,27,29,49,61ReasonsforConcern,18,18,72‑73,77‑78,7881,94,95‑96,98‑102Regionscharacteristicsof,20‑26,81‑86Ocean,40‑41,60‑62,97co-benefitsof,17,20,30,77,78‑79,80‑81,90,cascadingimpactsin,52adaptationexperience,106,10690‑91,98,102,103‑104,107,109energyaccumulationin,4,42impacts,7,50‑51cooperativeactionin,17,26,29,76,94,102,105heatcontent,5,45,48,49irreversiblechanges,16delay,effectsof,17,19,20,24,25,31,76,77,79,modeling,56keyrisks,13,14,65,6581,84‑85,86,90observedchanges,2,3,4,5,40‑41,41,42mitigationinitiatives,106emissionsincreasesdespite,54oxygencontent,13,41,51,62temperaturedata,49emissionsreductionsand,17,76,81‑86,98‑100,projectedchanges,10,11,16,60‑62,67Renewableenergy,22,28,30,11099‑101salinityof,4,40,48RepresentativeConcentrationPathways(RCPs),enablingfactorsandconstraints,26,94,95,111thermalexpansion,42,48,568,9,10,11,16,21,22,56‑62,59‑61,63‑64,74,equityandfairnessin,17,76‑77,109warmingof,2,3,4,5,10,11,40,41,45,47‑48,74futurepathways,17‑26,76‑9149,58,60,67descriptionof,57influenceonclimatechange,86Resilience,31,94integratedapproach,26,28,31,54,94,98,112Oceanacidificationclimate-resilientpathways,17,31,76,77,90interactionswithadaptation,17‑18,20,26,76,impactsof,51,67,7477,80‑81,90,98,112observedincrease,4,40‑41,45,48nationalandsub-national,106‑109near-termdecisions,17‑18,19,77,79policyapproachesfor,29‑31,102‑111150IndexRisk,8‑16,36,56‑74Seasonalactivities,6,51warmingtoabove2°Cabovepre-industrial,10,Indexofadaptation,17,76,91Sectors,97,9811,19,20‑21,22,24,60,60,74,77,81‑82,83causesof,58,64SeealsoEmissionsscenariosfromclimatechange,13‑16,17‑19,18,31,36,adaptationoptions,95‑97,98Thermalexpansion,42,48,5664‑73,66,76‑79,78GHGemissionsby,28,46,47,88,99,99,101Timescalesofclimatechangeandimpacts,13,estimating,58keyrisks,65,70‑7162‑63,73‑74,77future,8‑16,56‑74mitigationoptions,28,98‑99,99,101Trade-offs,20,26,31,80‑81,90,95,98,98,112ofgeoengineering,89policyinstruments,30,107,108Transformation,20,27,76,80,96withhightemperatures,15,16,18,66,73‑74,77,Snowcover,2,4,42,47,48,51,6278Solarirradiance,10,44,58Ukeyrisks,14,64‑65,65,70‑73Solarradiationmanagement(SRM),25‑26,89ofmitigation,17,19,30,76,78‑79,91,102,Speciesextinctions.SeeExtinctionriskUncertainty,17,20,36,37,56103‑104,107,109Speciesrangeshifts.SeeRangeshiftsSeealsoConfidencemodelsof,58,58SRESscenarios,57,58newrisks,duetoclimatechange,13,64Subsidies,30,107‑109,108UNFCCC(UnitedNationsFrameworkConventionperceptionof,17,19,77Sustainabledevelopment,17,31,76‑77onClimateChange),2,18,29,36,102,105quantificationof,36,58,79adaptationandmitigationand,17,19,31,76,79ReasonforConcernand,18,18,72‑73,77‑78,78climatechangeasthreatto,31,90Uniqueandthreatenedsystems,18,18,19,65,region-specific,13,14,65climatepolicyand,31,76,90,9172‑73,78unavoidable,19equityand,17,76‑77,109unevendistributionof,13,64futurepathways,17‑26,76‑91Urbanareas,15,31,69,97,112trade-offs,synergiesandinteractions,31,80‑81,Riskmanagement/reduction,8,13,14,17‑19,90,112V36,65transformationsand,20,80adaptationandmitigationand,14,17‑19,17‑25,Synergies,19,20,26,31,80‑81,90,109,112Valuesandvaluation,17,19,23,36,76‑77,9618,26,65‑67,65,70‑71,76,77‑79,79,94,108Violentconflicts,16,54,77substantialemissionsreductions,19,20,77‑78,TVolcanicaerosols,10,43,44,5681Vulnerability,8,13,26,36,53,54,94,96SeealsoDisasterriskmanagementTechnology,20,23,24,25,26,81,85,94,95,95,100estimatingandmodels,58Ruralareas,16,65,69,97policiesand,29,30,102,109reductionof,19,27,80risksand,58,58,64,76STemperatureemissionsand,8‑10,9,16,18‑19,18,20‑24,22,WScenarios,17‑26,56‑58,81‑86,82‑8656,58,62‑63,63‑64,78,83emissions,8,9,18‑19,18,20‑24,21‑24,28,28,extremes,7‑8,10,53,60Warming60‑61,63‑64,74,81‑86,82‑86globalmeansurfacetemperature,9,10,20,ofclimatesystem,2‑4,3,8,9,40‑44,43,47,48,overshoot,20‑23,22,81,83,8958‑60,59‑6149,62‑63RCPs,8,9,10,11,16,21,22,56‑62,57,59‑61,GlobalTemperaturechangePotential(GTP),87‑88CO2emissionsand,3,8‑10,9,18‑19,18,20‑24,63‑64,74,74humaninfluenceon,4,5,8,9,44,47‑48,48,63,21,56,62‑63,63,64,78SRES,57,5863‑64feedbacksand,62SeealsoEmissionsscenariosmortalityassociatedwith,8,51,53humancontributionto,4,5,8,9,44,47‑48,48,observedchanges,2‑4,3,5,7‑8,12,40,41,43,63,63‑64Seaice49,61irreversibilityof,62‑63anthropogenicinfluenceson,5,48,49observedchanges,contributionsto,48,48ofocean,2,3,4,5,10,11,40,41,45,47‑48,49,Arctic,4,5,12,41,42,48,49,62,74observedregionalchanges,4958,60,65,67observedchanges,4,5,41,42,48,49recenttrends,43,48projectionsof,9,10,11,12,16,20‑21,22,56,projectedchanges,12,59,62risksfromhightemperatures,15,16,18,66,58‑60,59‑61,63,7473‑74,77,78risksinhighwarmingscenarios,66,73‑74,77,78Sealeveltimescaleofchanges,62‑63,73‑74timescalesof,16,20,62‑63,73‑74extremes,7,8,53variabilityin,2‑4,3,40,41,43withoutadditionalmitigation,17,18‑19,18,77,observedchanges,2,3,42‑44,61SeealsoWarming81thermalexpansionand,42,48,56SeealsoTemperatureTemperatureprojections,8‑10,9,11‑12,16,20‑24,Sealevelrise56,58‑60,59‑61,63‑64,73‑74,74,83Wateranthropogenicinfluenceson,5,48indiscontinuanceofSRM,26management,27,31,96,97,98contributionsto,42,44,74globalmeanpeaksurfacetemperaturechange,62resourcesandquality,13,16,20,51,69,97,98observed,2,3,4,5,41,42‑44,48mitigationand,20‑25,21‑23,81security,13,67‑69projected,10,11,13,16,58,59‑61,62,74,74warmingto2°Cabovepre-industrial,8‑10,11,19,risksassociatedwith,65,65,66,67,7420,22,23‑24,60,60,62,63,74,77,81‑82,83,85Watercycle,4,5,47,48,60timescaleof,16,74variabilityin,13,62151

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