IPCC-AR6气候变化综合报告2023-Report（2023-03-27）

Adopted

IPCCAR6SYR

LongerReport

SubjecttoCopyeditp.1

SYNTHESISREPORT

OFTHEIPCCSIXTHASSESSMENTREPORT(AR6)

LongerReport

CoreWritingTeam:HoesungLee(Chair),KatherineCalvin(USA),DipakDasgupta(India/USA),GerhardKrinner(France/Germany),AditiMukherji(India),PeterThorne(Ireland/UnitedKingdom),ChristopherTrisos(SouthAfrica),JoséRomero(Switzerland),PaulinaAldunce(Chile),KoBarrett(USA),GabrielBlanco(Argentina),WilliamW.L.Cheung(Canada),SarahL.Connors(France/UnitedKingdom),FatimaDenton(TheGambia),AïdaDiongue-Niang(Senegal),DavidDodman(Jamaica/UnitedKingdom/Netherlands),MatthiasGarschagen(Germany),OliverGeden(Germany),BronwynHayward(NewZealand),ChristopherJones(UnitedKingdom),FrankJotzo(Australia),ThelmaKrug(Brazil),RodelLasco(Philippines),June-YiLee(RepublicofKorea),ValérieMasson-Delmotte(France),MalteMeinshausen(Australia/Germany),KatjaMintenbeck(Germany),AbdalahMokssit(Morocco),FriederikeE.L.Otto(UnitedKingdom/Germany),MinalPathak(India),AnnaPirani(Italy),ElviraPoloczanska(UK/Australia),Hans-OttoPörtner(Germany),AromarRevi(India),DebraC.Roberts(SouthAfrica),JoyashreeRoy(India/Thailand),AlexC.Ruane(USA),JimSkea(UnitedKingdom),PriyadarshiR.Shukla(India),RaphaelSlade(UnitedKingdom),AiméeSlangen(TheNetherlands),YoubaSokona(Mali),AnnaA.Sörensson(Argentina),MelindaTignor(USA/Germany),DetlefvanVuuren(TheNetherlands),Yi-MingWei(China),HaraldWinkler(SouthAfrica),PanmaoZhai(China),ZintaZommers(Latvia)

ExtendedWritingTeam:Jean-CharlesHourcade(France),FrancisX.Johnson(Thailand/Sweden),ShonaliPachauri(Austria/India),NicholasP.Simpson(SouthAfrica/Zimbabwe),ChandniSingh(India),AdelleThomas(Bahamas),EdmondTotin(Benin)

ContributingAuthors:AndrésAlegría(Germany/Honduras),KyleArmour(USA),BirgitBednar-Friedl

(Austria),KornelisBlok(TheNetherlands)GuéladioCissé(Switzerland/Mauritania/France),FrankDentener(EU/Netherlands),SiriEriksen(Norway),ErichFischer(Switzerland),GregoryGarner(USA),CélineGuivarch(France),MarjolijnHaasnoot(TheNetherlands),GerritHansen(Germany),MatthiasHauser(Switzerland),EdHawkins(UK),TimHermans(TheNetherlands),RobertKopp(USA),NoëmieLeprince-Ringuet(France),DeboraLey(Mexico/Guatemala),JaredLewis(Australia/NewZealand),ChloéLudden(Germany/France),ZebedeeNicholls(Australia),LeilaNiamir(Iran/TheNetherlands/Austria),ShreyaSome(India/Thailand),SophieSzopa(France),BlairTrewin(Australia),Kaj-IvarvanderWijst(TheNetherlands),GundulaWinter(TheNetherlands/Germany),MaximilianWitting(Germany)

ReviewEditors:PaolaArias(Colombia),MercedesBustamante(Brazil),IsmailElgizouli(Sudan),GregoryFlato(Canada),MarkHowden(Australia),CarlosMéndez(Venezuela),JoyPereira(Malaysia),RamónPichs-Madruga(Cuba),StevenKRose(USA),YaminaSaheb(Algeria/France),RobertoSánchez(Mexico),DianaÜrge-Vorsatz(Hungary),CundeXiao(China),NoureddineYassaa(Algeria)

ScientificSteeringCommittee:HoesungLee(Chair,IPCC),AmjadAbdulla(Maldives),EdvinAldrian(Indonesia),KoBarrett(UnitedStatesofAmerica),EduardoCalvo(Peru),CarloCarraro(Italy),FatimaDriouech(Morocco),AndreasFischlin(Switzerland),JanFuglestvedt(Norway),DiribaKorechaDadi(Ethiopia),ThelmaKrug(Brazil),NagmeldinG.E.Mahmoud(Sudan),ValérieMasson-Delmotte(France),CarlosMéndez(Venezuela),JoyJacquelinePereira(Malaysia),RamónPichs-Madruga(Cuba),Hans-OttoPörtner(Germany),AndyReisinger(NewZealand),DebraRoberts(SouthAfrica),SergeySemenov(RussianFederation),PriyadarshiShukla(India),JimSkea(UnitedKingdom),YoubaSokona(Mali),KiyotoTanabe(Japan),MuhammadTariq(Pakistan),DianaÜrge-Vorsatz(Hungary),CarolinaVera(Argentina),PiusYanda(UnitedRepublicofTanzania),NoureddineYassaa(Algeria),TahaM.Zatari(SaudiArabia),PanmaoZhai(China)

VisualConceptionandInformationDesign:ArleneBirt(USA),MeeyoungHa(RepublicofKorea)

Notes:SFsCompiledVersion

SubjecttoCopyeditp.2

TableofContents

Section1:Introduction4

Section2:CurrentStatusandTrends6

2.1ObservedChanges,ImpactsandAttribution6

2.1.1ObservedWarminganditsCauses6

2.1.2ObservedClimateSystemChangesandImpactstoDate11

2.2ResponsesUndertakentoDate18

2.2.1GlobalPolicySetting18

2.2.2MitigationActionstoDate19

2.2.3AdaptationActionstoDate21

2.3CurrentMitigationandAdaptationActionsandPoliciesarenotSufficient23

2.3.1TheGapBetweenMitigationPolicies,PledgesandPathwaysthatLimitWarmingto1.5or

Below2°C23

Cross-SectionBox.1:UnderstandingNetZeroCO2andNetZeroGHGEmissions26

2.3.2AdaptationGapsandBarriers27

2.3.3LackofFinanceasaBarriertoClimateAction28

Cross-SectionBox.2:Scenarios,GlobalWarmingLevels,andRisks29

Section3:Long-TermClimateandDevelopmentFutures33

3.1Long-TermClimateChange,ImpactsandRelatedRisks33

3.1.1Long-termClimateChange33

3.1.2ImpactsandRelatedRisks36

3.1.3TheLikelihoodandRisksofAbruptandIrreversibleChange42

3.2Long-termAdaptationOptionsandLimits43

3.3MitigationPathways46

3.3.1RemainingCarbonBudgets46

3.3.2NetZeroEmissions:TimingandImplications50

3.3.3SectoralContributionstoMitigation51

3.3.4OvershootPathways:IncreasedRisksandOtherImplications53

3.4Long-TermInteractionsBetweenAdaptation,MitigationandSustainableDevelopment53

3.4.1Synergiesandtrade-offs,costsandbenefits53

3.4.2AdvancingIntegratedClimateActionforSustainableDevelopment55

Section4:Near-TermResponsesinaChangingClimate56

4.1TheTimingandUrgencyofClimateAction56

4.2BenefitsofStrengtheningNear-TermAction59

4.3Near-TermRisks62

4.4EquityandInclusioninClimateChangeAction66

4.5Near-TermMitigationandAdaptationActions68

4.5.1EnergySystems70

4.5.2Industry71

4.5.3Cities,SettlementsandInfrastructure72

SubjecttoCopyeditp.3

4.5.4Land,Ocean,Food,andWater73

4.5.5HealthandNutrition74

4.5.6Society,Livelihoods,andEconomies74

4.6Co-BenefitsofAdaptationandMitigationforSustainableDevelopmentGoals75

4.7GovernanceandPolicyforNear-TermClimateChangeAction78

4.8StrengtheningtheResponse:Finance,InternationalCooperationandTechnology80

4.8.1FinanceforMitigationandAdaptationActions80

4.8.2InternationalCooperationandCoordination82

4.8.3TechnologyInnovation,Adoption,DiffusionandTransfer83

4.9IntegrationofNear-TermActionsAcrossSectorsandSystems84

Subject

1ThethreeWorkingGroupcontributionstoAR6are:ClimateChange2021:ThePhysicalScienceBasis;ClimateChange2022:Impacts,AdaptationandVulnerability;andClimateChange2022:MitigationofClimateChange,respectively.Theirassessmentscoverscientificliteratureacceptedforpublicationrespectivelyby31January2021,1September2021and11October2021.

2ThethreeSpecialReportsare:GlobalWarmingof1.5°C(2018):anIPCCSpecialReportontheimpactsofglobalwarmingof1.5°Cabovepre-industriallevelsandrelatedglobalgreenhousegasemissionpathways,inthecontextofstrengtheningtheglobalresponsetothethreatofclimatechange,sustainabledevelopment,andeffortstoeradicatepoverty(SR1.5);ClimateChangeandLand(2019):anIPCCSpecialReportonclimatechange,desertification,landdegradation,sustainablelandmanagement,foodsecurity,andgreenhousegasfluxesinterrestrialecosystems(SRCCL);andTheOceanandCryosphereinaChangingClimate(2019)(SROCC).TheSpecialReportscoverscientificliteratureacceptedforpublicationrespectivelyby15May2018,7April2019and15May2019.

3TheGlossary(AnnexI)includesdefinitionsofthese,andothertermsandconceptsusedinthisreportdrawnfromtheAR6jointWorkingGroupGlossary.

4Dependingontheclimateinformationcontext,geographicalregionsinAR6mayrefertolargerareas,suchassub-continentsandoceanicregions,ortotypologicalregions,suchasmonsoonregions,coastlines,mountainrangesorcities.AnewsetofstandardAR6WGIreferencelandandoceanregionshavebeendefined{1.4.5,10.1,11.9,12.1–12.4,Atlas.1.3.3–1.3.4}.WGIIIallocatescountriestogeographicalregions,basedontheUNStatisticsDivisionClassification{AnnexII,WGIII}.

5Eachfindingisgroundedinanevaluationofunderlyingevidenceandagreement.Alevelofconfidenceisexpressedusingfivequalifiers:verylow,low,medium,highandveryhigh,andtypesetinitalics,forexample,mediumconfidence.Thefollowingtermshavebeenusedtoindicatetheassessedlikelihoodofanoutcomeorresult:virtuallycertain99–100%probability;verylikely90–100%;likely66–100%;morelikelythannot>50-100%;aboutaslikelyasnot33–66%;unlikely0–33%;veryunlikely0–10%;andexceptionallyunlikely0–1%.Additionalterms(extremelylikely95–100%;morelikelythannot>50–100%;andextremelyunlikely0–5%)arealsousedwhenappropriate.Assessedlikelihoodalsoistypesetinitalics:forexample,verylikely.ThisisconsistentwithAR5.InthisReport,unlessstatedotherwise,squarebrackets[xtoy]areusedtoprovidetheassessedverylikelyrange,or90%interval.

toCopyeditp.4

Section1:Introduction

1.Introduction

ThisSynthesisReport(SYR)oftheIPCCSixthAssessmentReport(AR6)summarisesthestateofknowledgeofclimatechange,itswidespreadimpactsandrisks,andclimatechangemitigationandadaptation,basedonthepeer-reviewedscientific,technicalandsocio-economicliteraturesincethepublicationoftheIPCC’sFifthAssessmentReport(AR5)in2014.

Theassessmentisundertakenwithinthecontextoftheevolvinginternationallandscape,inparticular,developmentsintheUNFrameworkConventiononClimateChange(UNFCCC)process,includingtheoutcomesoftheKyotoProtocolandtheadoptionoftheParisAgreement.Itreflectstheincreasingdiversityofthoseinvolvedinclimateaction.

ThisreportintegratesthemainfindingsoftheAR6WorkingGroupreports

1

andthethreeAR6SpecialReports

2

.Itrecognizestheinterdependenceofclimate,ecosystemsandbiodiversity,andhumansocieties;thevalueofdiverseformsofknowledge;andthecloselinkagesbetweenclimatechangeadaptation,mitigation,ecosystemhealth,humanwell-beingandsustainabledevelopment.Buildingonmultipleanalyticalframeworks,includingthosefromthephysicalandsocialsciences,thisreportidentifiesopportunitiesfortransformativeactionwhichareeffective,feasible,justandequitableusingconceptsofsystemstransitionsandresilientdevelopmentpathways

3

.Differentregionalclassificationschemes

4

areusedforphysical,socialandeconomicaspects,reflectingtheunderlyingliterature.

Afterthisintroduction,Section2,‘CurrentStatusandTrends’,openswiththeassessmentofobservationalevidenceforourchangingclimate,historicalandcurrentdriversofhuman-inducedclimatechange,anditsimpacts.Itassessesthecurrentimplementationofadaptationandmitigationresponseoptions.Section3,‘Long-TermClimateandDevelopmentFutures’,providesalong-termassessmentofclimatechangeto2100andbeyondinabroadrangeofsocio-economicfutures.Itconsiderslong-termcharacteristics,impacts,risksandcostsinadaptationandmitigationpathwaysinthecontextofsustainabledevelopment.Section4,‘Near-TermResponsesinaChangingClimate’,assessesopportunitiesforscalingupeffectiveactionintheperiodupto2040,inthecontextofclimatepledges,andcommitments,andthepursuitofsustainabledevelopment.

Basedonscientificunderstanding,keyfindingscanbeformulatedasstatementsoffactorassociatedwithanassessedlevelofconfidenceusingtheIPCCcalibratedlanguage

5

.ThescientificfindingsaredrawnfromtheunderlyingreportsandarisefromtheirSummaryforPolicymakers(hereafterSPM),TechnicalSummary(hereafterTS),andunderlyingchaptersandareindicatedby{}brackets.Figure1.1showstheSynthesisReportFiguresKey,aguidetovisualiconsthatareusedacrossmultiplefigureswithinthisreport.

SubjecttoCopyeditp.5

Figure1.1:TheSynthesisReportfigureskey.

Subject

toCopyeditp.6

CO2-X2007scaletobeconsistentwithWGI.OperationalCO2reportinghassincebeenupdatedtousetheWMO-CO2-X2019scale.

Section2:CurrentStatusandTrends

2.1ObservedChanges,ImpactsandAttribution

Humanactivities,principallythroughemissionsofgreenhousegases,haveunequivocallycausedglobalwarming,withglobalsurfacetemperaturereaching1.1°Cabove1850-1900in2011-2020.Globalgreenhousegasemissionshavecontinuedtoincreaseover2010-2019,withunequalhistoricalandongoingcontributionsarisingfromunsustainableenergyuse,landuseandland-usechange,lifestylesandpatternsofconsumptionandproductionacrossregions,betweenandwithincountries,andbetweenindividuals(highconfidence).Human-causedclimatechangeisalreadyaffectingmanyweatherandclimateextremesineveryregionacrosstheglobe.Thishasledtowidespreadadverseimpactsonfoodandwatersecurity,humanhealthandoneconomiesandsocietyandrelatedlossesanddamages

6

tonatureandpeople(highconfidence).Vulnerablecommunitieswhohavehistoricallycontributedtheleasttocurrentclimatechangearedisproportionatelyaffected(highconfidence).

2.1.1ObservedWarminganditsCauses

Globalsurfacetemperaturewasaround1.1°Cabove1850–1900in2011–2020(1.09°C[0.95°C–1.20°C])

7

,withlargerincreasesoverland(1.59[1.34to1.83]°C)thanovertheocean(0.88°C[0.68°C–1.01°C])

8

.Observedwarmingishuman-caused,withwarmingfromgreenhousegases(GHG),dominatedbyCO2andmethane(CH4),partlymaskedbyaerosolcooling(Figure2.1).Globalsurfacetemperatureinthefirsttwodecadesofthe21stcentury(2001-2020)was0.99[0.84to1.10]°Chigherthan1850-1900.Globalsurfacetemperaturehasincreasedfastersince1970thaninanyother50-yearperiodoveratleastthelast2000years(highconfidence).Thelikelyrangeoftotalhuman-causedglobalsurfacetemperatureincreasefrom1850–1900to2010–2019

9

is0.8°Cto1.3°C,withabestestimateof1.07°C.Itislikelythatwell-mixedGHGs

10

contributedawarmingof1.0°C–2.0°C,andotherhumandrivers(principallyaerosols)contributedacoolingof0.0°C–0.8°C,natural(solarandvolcanic)driverschangedglobalsurfacetemperatureby±0.1°Candinternalvariabilitychangeditby±0.2°C.{WGISPMA.1,WGISPMA.1.2,WGISPMA.1.3,WGISPMA.2.2,WGIFigureSPM.2;SRCCLTS.2}

Observedincreasesinwell-mixedGHGconcentrationssincearound1750areunequivocallycausedbyGHGemissionsfromhumanactivities.Landandoceansinkshavetakenupanear-constantproportion(globallyabout56%peryear)ofCO2emissionsfromhumanactivitiesoverthepastsixdecades,withregionaldifferences(highconfidence).In2019,atmosphericCO2concentrationsreached410partspermillion(ppm),CH4reached1866partsperbillion(ppb)andnitrousoxide(N2O)reached332ppb

11

.Othermajorcontributorstowarmingaretroposphericozone(O3)andhalogenatedgases.ConcentrationsofCH4andN2Ohaveincreasedtolevelsunprecedentedinatleast800,000years(veryhighconfidence),andthereishighconfidencethatcurrentCO2concentrationsarehigherthanatanytimeoveratleastthepasttwomillionyears.Since1750,increasesinCO2(47%)andCH4(156%)concentrationsfarexceed–andincreasesinN2O(23%)aresimilarto–thenaturalmulti-millennialchangesbetweenglacialandinterglacialperiodsoveratleastthepast800,000

6Inthisreport,theterm‘lossesanddamages’referstoadverseobservedimpactsand/orprojectedrisksandcanbeeconomicand/ornon-economic.(SeeAnnexI:Glossary)

7TheestimatedincreaseinglobalsurfacetemperaturesinceAR5isprincipallyduetofurtherwarmingsince2003–2012(+0.19[0.16to0.22]°C).Additionally,methodologicaladvancesandnewdatasetshaveprovidedamorecompletespatialrepresentationofchangesinsurfacetemperature,includingintheArctic.Theseandotherimprovementshavealsoincreasedtheestimateofglobalsurfacetemperaturechangebyapproximately0.1°C,butthisincreasedoesnotrepresentadditionalphysicalwarmingsinceAR5{WGISPMA1.2andfootnote10}

8For1850–1900to2013–2022theupdatedcalculationsare1.15°C[1.00°C–1.25°C]forglobalsurfacetemperature,1.65°C[1.36°C–1.90°C]forlandtemperaturesand0.93°C[0.73°C–1.04°C]foroceantemperaturesabove1850–1900usingtheexactsamedatasets(updatedby2years)andmethodsasemployedinWGI.

9Theperioddistinctionwiththeobservedassessmentarisesbecausetheattributionstudiesconsiderthisslightlyearlierperiod.Theobservedwarmingto2010–2019is1.06°C[0.88°C–1.21°C].{WGISPMfootnote11}

10Contributionsfromemissionstothe2010-2019warmingrelativeto1850-1900assessedfromradiativeforcingstudiesare:CO20.8[0.5to1.2]°C;methane0.5[0.3to0.8]°C;nitrousoxide0.1[0.0to0.2]°Candfluorinatedgases0.1[0.0to0.2]°C.

11For2021(themostrecentyearforwhichfinalnumbersareavailable)concentrationsusingthesameobservationalproductsandmethodsasinAR6WGIare:415ppmCO2;1896ppbCH4;and335ppbN2O.NotethattheCO2isreportedhereusingtheWMO-

Adopted

IPCCAR6SYR

LongerReport

SubjecttoCopyeditp.7

years(veryhighconfidence).Thenetcoolingeffectwhicharisesfromanthropogenicaerosolspeakedinthelate20thcentury(highconfidence).{WGISPMA1.1,WGISPMA1.3,WGISPMA.2.1,WGIFigureSPM.2,WGITS2.2,WGI2ES,WGIFigure6.1}

[STARTFIGURE2.1HERE]

Adopted

IPCCAR6SYR

LongerReport

Subject

12GHGemissionmetricsareusedtoexpressemissionsofdifferentGHGsinacommonunit.AggregatedGHGemissionsinthisreportarestatedinCO2-equivalents(CO2-eq)usingtheGlobalWarmingPotentialwithatimehorizonof100years(GWP100)withvaluesbasedonthecontributionofWorkingGroupItotheAR6.TheAR6WGIandWGIIIreportscontainupdatedemissionmetricvalues,evaluationsofdifferentmetricswithregardtomitigationobjectives,andassessnewapproachestoaggregatinggases.ThechoiceofmetricdependsonthepurposeoftheanalysisandallGHGemissionmetricshavelimitationsanduncertainties,giventhattheysimplifythecomplexityofthephysicalclimatesystemanditsresponsetopastandfutureGHGemissions.{WGISPMD.1.8,WGI7.6;WGIII SPMB.1,WGIIICross-ChapterBox2.2}(AnnexI:Glossary)

toCopyeditp.8

Figure2.1:Thecausalchainfromemissionstoresultingwarmingoftheclimatesystem.EmissionsofGHGhaveincreasedrapidlyoverrecentdecades(panel(a)).GlobalnetanthropogenicGHGemissionsincludeCO2fromfossilfuelcombustionandindustrialprocesses(CO2-FFI)(darkgreen);netCO2fromlanduse,land-usechangeandforestry(CO2-LULUCF)(green);CH4;N2O;andfluorinatedgases(HFCs,PFCs,SF6,NF3)(lightblue).Theseemissionshaveledtoincreasesinthe