Global Warming of 1.5 ºC — - IPCC

An IPCC special report on the impacts of global warming of 1.5 °C above pre-industrial levels and related global greenhouse gas emission pathways, ... AnIPCCspecialreportontheimpactsofglobalwarmingof1.5°Cabovepre-industriallevelsandrelatedglobalgreenhousegasemissionpathways,inthecontextofstrengtheningtheglobalresponsetothethreatofclimatechange,sustainabledevelopment,andeffortstoeradicatepoverty.ThetranslationsoftheSPMandothermaterialcanbedownloadedfromthis link  ”Pourcequiestdel’avenir,ilnes’agitpasdeleprévoir,maisdelerendrepossible.“ –AntoinedeSaintExupéry,Citadelle,1948   SummaryforPolicymakers View View Download ExploreGraphics Chapter1 Understandingtheimpactsof1.5°Cglobalwarmingabovepre-industriallevelsandrelatedglobalemissionpathwaysinthecontextofstrengtheningtheresponsetothethreatofclimatechange,sustainabledevelopmentandeffortstoeradicatepoverty. ExecutiveSummary View Download ExploreGraphics Thischapterframesthecontext,knowledge-baseandassessmentapproachesusedtounderstandtheimpactsof1.5°Cglobalwarmingabovepre-industriallevelsandrelatedglobalgreenhousegasemissionpathways,buildingontheIPCCFifthAssessmentReport(AR5),inthecontextofstrengtheningtheglobalresponsetothethreatofclimatechange,sustainabledevelopmentandeffortstoeradicatepoverty. Human-inducedwarmingreachedapproximately1°C(likelybetween0.8°Cand1.2°C)abovepre-industriallevelsin2017,increasingat0.2°C(likelybetween0.1°Cand0.3°C)perdecade(highconfidence).Globalwarmingisdefinedinthisreportasanincreaseincombinedsurfaceairandseasurfacetemperaturesaveragedovertheglobeandovera30-yearperiod.Unlessotherwisespecified,warmingisexpressedrelativetotheperiod1850–1900,usedasanapproximationofpre-industrialtemperaturesinAR5.Forperiodsshorterthan30years,warmingreferstotheestimatedaveragetemperatureoverthe30yearscentredonthatshorterperiod,accountingfortheimpactofanytemperaturefluctuationsortrendwithinthose30years.Accordingly,warmingfrompre-industriallevelstothedecade2006–2015isassessedtobe0.87°C(likelybetween0.75°Cand0.99°C).Since2000,theestimatedlevelofhuman-inducedwarminghasbeenequaltothelevelofobservedwarmingwithalikelyrangeof±20%accountingforuncertaintyduetocontributionsfromsolarandvolcanicactivityoverthehistoricalperiod(highconfidence).{1.2.1} Warminggreaterthantheglobalaveragehasalreadybeenexperiencedinmanyregionsandseasons,withhigheraveragewarmingoverlandthanovertheocean(highconfidence).Mostlandregionsareexperiencinggreaterwarmingthantheglobalaverage,whilemostoceanregionsarewarmingataslowerrate.Dependingonthetemperaturedatasetconsidered,20–40%oftheglobalhumanpopulationliveinregionsthat,bythedecade2006–2015,hadalreadyexperiencedwarmingofmorethan1.5°Cabovepre-industrialinatleastoneseason(mediumconfidence).{1.2.1,1.2.2} Pastemissionsaloneareunlikelytoraiseglobal-meantemperatureto1.5°Cabovepre-industriallevels(mediumconfidence),butpastemissionsdocommittootherchanges,suchasfurthersealevelrise(highconfidence).Ifallanthropogenicemissions(includingaerosol-related)werereducedtozeroimmediately,anyfurtherwarmingbeyondthe1°Calreadyexperiencedwouldlikelybelessthan0.5°Coverthenexttwotothreedecades(highconfidence),andlikelylessthan0.5°Conacenturytimescale(mediumconfidence),duetotheopposingeffectsofdifferentclimateprocessesanddrivers.Awarminggreaterthan1.5°Cisthereforenotgeophysicallyunavoidable:whetheritwilloccurdependsonfutureratesofemissionreductions.{1.2.3,1.2.4} 1.5°Cemissionpathwaysaredefinedasthosethat,givencurrentknowledgeoftheclimateresponse,provideaone-in-twototwo-in-threechanceofwarmingeitherremainingbelow1.5°Correturningto1.5°Cbyaround2100followinganovershoot.Overshootpathwaysarecharacterizedbythepeakmagnitudeoftheovershoot,whichmayhaveimplicationsforimpacts.All1.5°Cpathwaysinvolvelimitingcumulativeemissionsoflong-livedgreenhousegases,includingcarbondioxideandnitrousoxide,andsubstantialreductionsinotherclimateforcers(highconfidence).Limitingcumulativeemissionsrequireseitherreducingnetglobalemissionsoflong-livedgreenhousegasestozerobeforethecumulativelimitisreached,ornetnegativeglobalemissions(anthropogenicremovals)afterthelimitisexceeded.{1.2.3,1.2.4,Cross-ChapterBoxes1and2} Thisreportassessesprojectedimpactsataglobalaveragewarmingof1.5°Candhigherlevelsofwarming.Globalwarmingof1.5°Cisassociatedwithglobalaveragesurfacetemperaturesfluctuatingnaturallyoneithersideof1.5°C,togetherwithwarmingsubstantiallygreaterthan1.5°Cinmanyregionsandseasons(highconfidence),allofwhichmustbeconsideredintheassessmentofimpacts.Impactsat1.5°Cofwarmingalsodependontheemissionpathwayto1.5°C.Verydifferentimpactsresultfrompathwaysthatremainbelow1.5°Cversuspathwaysthatreturnto1.5°Cafterasubstantialovershoot,andwhentemperaturesstabilizeat1.5°Cversusatransientwarmingpast1.5°C(mediumconfidence).{1.2.3,1.3} Ethicalconsiderations,andtheprincipleofequityinparticular,arecentraltothisreport,recognizingthatmanyoftheimpactsofwarminguptoandbeyond1.5°C,andsomepotentialimpactsofmitigationactionsrequiredtolimitwarmingto1.5°C,falldisproportionatelyonthepoorandvulnerable(highconfidence).Equityhasproceduralanddistributivedimensionsandrequiresfairnessinburdensharingbothbetweengenerationsandbetweenandwithinnations.Inframingtheobjectiveofholdingtheincreaseintheglobalaveragetemperaturerisetowellbelow2°Cabovepre-industriallevels,andtopursueeffortstolimitwarmingto1.5°C,theParisAgreementassociatestheprincipleofequitywiththebroadergoalsofpovertyeradicationandsustainabledevelopment,recognisingthateffectiveresponsestoclimatechangerequireaglobalcollectiveeffortthatmaybeguidedbythe2015UnitedNationsSustainableDevelopmentGoals.{1.1.1} Climateadaptationreferstotheactionstakentomanageimpactsofclimatechangebyreducingvulnerabilityandexposuretoitsharmfuleffectsandexploitinganypotentialbenefits.Adaptationtakesplaceatinternational,nationalandlocallevels.Subnationaljurisdictionsandentities,includingurbanandruralmunicipalities,arekeytodevelopingandreinforcingmeasuresforreducingweather-andclimate-relatedrisks.Adaptationimplementationfacesseveralbarriersincludinglackofup-to-dateandlocallyrelevantinformation,lackoffinanceandtechnology,socialvaluesandattitudes,andinstitutionalconstraints(highconfidence).Adaptationismorelikelytocontributetosustainabledevelopmentwhenpoliciesalignwithmitigationandpovertyeradicationgoals(mediumconfidence).{1.1,1.4} Ambitiousmitigationactionsareindispensabletolimitwarmingto1.5°Cwhileachievingsustainabledevelopmentandpovertyeradication(highconfidence).Ill-designedresponses,however,couldposechallengesespecially–butnotexclusively–forcountriesandregionscontendingwithpovertyandthoserequiringsignificanttransformationoftheirenergysystems.Thisreportfocuseson‘climate-resilientdevelopmentpathways’,whichaimtomeetthegoalsofsustainabledevelopment,includingclimateadaptationandmitigation,povertyeradicationandreducinginequalities.Butanyfeasiblepathwaythatremainswithin1.5°Cinvolvessynergiesandtrade-offs(highconfidence).Significantuncertaintyremainsastowhichpathwaysaremoreconsistentwiththeprincipleofequity. {1.1.1,1.4} Multipleformsofknowledge,includingscientificevidence,narrativescenariosandprospectivepathways,informtheunderstandingof1.5°C.Thisreportisinformedbytraditionalevidenceofthephysicalclimatesystemandassociatedimpactsandvulnerabilitiesofclimatechange,togetherwithknowledgedrawnfromtheperceptionsofriskandtheexperiencesofclimateimpactsandgovernancesystems.Scenariosandpathwaysareusedtoexploreconditionsenablinggoal-orientedfutureswhilerecognizingthesignificanceofethicalconsiderations,theprincipleofequity,andthesocietaltransformationneeded.{1.2.3,1.5.2} Thereisnosingleanswertothequestionofwhetheritisfeasibletolimitwarmingto1.5°Candadapttotheconsequences.Feasibilityisconsideredinthisreportasthecapacityofasystemasawholetoachieveaspecificoutcome.Theglobaltransformationthatwouldbeneededtolimitwarmingto1.5°Crequiresenablingconditionsthatreflectthelinks,synergiesandtrade-offsbetweenmitigation,adaptationandsustainabledevelopment.Theseenablingconditionsareassessedacrossmanydimensionsoffeasibility–geophysical,environmental-ecological,technological,economic,socio-culturalandinstitutional–thatmaybeconsideredthroughtheunifyinglensoftheAnthropocene,acknowledgingprofound,differentialbutincreasinglygeologicallysignificanthumaninfluencesontheEarthsystemasawhole.Thisframingalsoemphasisestheglobalinterconnectivityofpast,presentandfuturehuman–environmentrelations,highlightingtheneedandopportunitiesforintegratedresponsestoachievethegoalsoftheParisAgreement.{1.1,Cross-ChapterBox1} Chapter2 Showinghowemissionscanbebroughttozerobymid-centurystaywithinthesmallremainingcarbonbudgetforlimitingglobalwarmingto1.5°C. ExecutiveSummary View Download ExploreGraphics Thischapterassessesmitigationpathwaysconsistentwithlimitingwarmingto1.5°Cabovepre-industriallevels.Indoingso,itexploresthefollowingkeyquestions:WhatroledoCO2andnon-CO2emissionsplay?{2.2,2.3,2.4,2.6}Towhatextentdo1.5°Cpathwaysinvolveovershootingandreturningbelow1.5°Cduringthe21stcentury?{2.2,2.3}Whataretheimplicationsfortransitionsinenergy,landuseandsustainabledevelopment?{2.3,2.4,2.5}Howdopolicyframeworksaffecttheabilitytolimitwarmingto1.5°C?{2.3,2.5}Whataretheassociatedknowledgegaps?{2.6} Theassessedpathwaysdescribeintegrated,quantitativeevolutionsofallemissionsoverthe21stcenturyassociatedwithglobalenergyandlanduseandtheworldeconomy.Theassessmentiscontingentuponavailableintegratedassessmentliteratureandmodelassumptions,andiscomplementedbyotherstudieswithdifferentscope,forexample,thosefocusingonindividualsectors.Inrecentyears,integratedmitigationstudieshaveimprovedthecharacterizationsofmitigationpathways.However,limitationsremain,asclimatedamages,avoidedimpacts,orsocietalco-benefitsofthemodelledtransformationsremainlargelyunaccountedfor,whileconcurrentrapidtechnologicalchanges,behaviouralaspects,anduncertaintiesaboutinputdatapresentcontinuouschallenges.(highconfidence){2.1.3,2.3,2.5.1,2.6,TechnicalAnnex2} TheChancesofLimitingWarmingto1.5°CandtheRequirementsforUrgentAction Pathwaysconsistentwith1.5°Cofwarmingabovepre-industriallevelscanbeidentifiedunderarangeofassumptionsabouteconomicgrowth,technologydevelopmentsandlifestyles.However,lackofglobalcooperation,lackofgovernanceoftherequiredenergyandlandtransformation,andincreasesinresource-intensiveconsumptionarekeyimpedimentstoachieving1.5°Cpathways.Governancechallengeshavebeenrelatedtoscenarioswithhighinequalityandhighpopulationgrowthinthe1.5°Cpathwayliterature.{2.3.1,2.3.2,2.5} UnderemissionsinlinewithcurrentpledgesundertheParisAgreement(knownasNationallyDeterminedContributions,orNDCs),globalwarmingisexpectedtosurpass1.5°Cabovepre-industriallevels,evenifthesepledgesaresupplementedwithverychallengingincreasesinthescaleandambitionofmitigationafter2030(highconfidence).ThisincreasedactionwouldneedtoachievenetzeroCO2emissionsinlessthan15years.Evenifthisisachieved,temperatureswouldonlybeexpectedtoremainbelowthe1.5°Cthresholdiftheactualgeophysicalresponseendsupbeingtowardsthelowendofthecurrentlyestimateduncertaintyrange.Transitionchallengesaswellasidentifiedtrade-offscanbereducedifglobalemissionspeakbefore2030andmarkedemissionsreductionscomparedtotodayarealreadyachievedby2030{2.2,2.3.5,Cross-ChapterBox11inChapter4}. Limitingwarmingto1.5°Cdependsongreenhousegas(GHG)emissionsoverthenextdecades,wherelowerGHGemissionsin2030leadtoahigherchanceofkeepingpeakwarmingto1.5°C(highconfidence).Availablepathwaysthataimfornoorlimited(lessthan0.1°C)overshootof1.5°CkeepGHGemissionsin2030to25–30GtCO2eyr−1in2030(interquartilerange).ThiscontrastswithmedianestimatesforcurrentunconditionalNDCsof52–58GtCO2eyr−1in2030.Pathwaysthataimforlimitingwarmingto1.5°Cby2100afteratemporarytemperatureovershootrelyonlarge-scaledeploymentofcarbondioxideremoval(CDR)measures,whichareuncertainandentailclearrisks.Inmodelpathwayswithnoorlimitedovershootof1.5°C,globalnetanthropogenicCO2emissionsdeclinebyabout45%from2010levelsby2030(40–60%interquartilerange),reachingnetzeroaround2050(2045–2055interquartilerange).1Forlimitingglobalwarmingtobelow2°Cwithatleast66%probabilityCO2emissionsareprojectedtodeclinebyabout25%by2030inmostpathways(10–30%interquartilerange)andreachnetzeroaround2070(2065–2080interquartilerange).{2.2,2.3.3,2.3.5,2.5.3,Cross-ChapterBoxes6inChapter3and9inChapter4,4.3.7} Limitingwarmingto1.5°CimpliesreachingnetzeroCO2emissionsgloballyaround2050andconcurrentdeepreductionsinemissionsofnon-CO2forcers,particularlymethane(highconfidence).Suchmitigationpathwaysarecharacterizedbyenergy-demandreductions,decarbonizationofelectricityandotherfuels,electrificationofenergyenduse,deepreductionsinagriculturalemissions,andsomeformofCDRwithcarbonstorageonlandorsequestrationingeologicalreservoirs.Lowenergydemandandlowdemandforland-andGHG-intensiveconsumptiongoodsfacilitatelimitingwarmingtoascloseaspossibleto1.5°C.{2.2.2,2.3.1,2.3.5,2.5.1,Cross-ChapterBox9inChapter4}. Incomparisontoa2°Climit,thetransformationsrequiredtolimitwarmingto1.5°Carequalitativelysimilarbutmorepronouncedandrapidoverthenextdecades(highconfidence).1.5°Cimpliesveryambitious,internationallycooperativepolicyenvironmentsthattransformbothsupplyanddemand(highconfidence).{2.3,2.4,2.5} Policiesreflectingahighpriceonemissionsarenecessaryinmodelstoachievecost-effective1.5°Cpathways(highconfidence).Otherthingsbeingequal,modellingstudiessuggesttheglobalaveragediscountedmarginalabatementcostsforlimitingwarmingto1.5°Cbeingabout3–4timeshighercomparedto2°Coverthe21stcentury,withlargevariationsacrossmodelsandsocio-economicandpolicyassumptions.Carbonpricingcanbeimposeddirectlyorimplicitlybyregulatorypolicies.Policyinstruments,liketechnologypoliciesorperformancestandards,cancomplementexplicitcarbonpricinginspecificareas.{2.5.1,2.5.2,4.4.5} Limitingwarmingto1.5°Crequiresamarkedshiftininvestmentpatterns(mediumconfidence).Additionalannualaverageenergy-relatedinvestmentsfortheperiod2016to2050inpathwayslimitingwarmingto1.5°Ccomparedtopathwayswithoutnewclimatepoliciesbeyondthoseinplacetoday(i.e.,baseline)areestimatedtobearound830billionUSD2010(rangeof150billionto1700billionUSD2010acrosssixmodels).Totalenergy-relatedinvestmentsincreasebyabout12%(rangeof3%to24%)in1.5°Cpathwaysrelativeto2°Cpathways. Averageannualinvestmentinlow-carbonenergytechnologiesandenergyefficiencyareupscaledbyroughlyafactorofsix(rangeoffactorof4to10)by2050comparedto2015,overtakingfossilinvestmentsgloballybyaround2025(mediumconfidence).Uncertaintiesandstrategicmitigationportfoliochoicesaffectthemagnitudeandfocusofrequiredinvestments.{2.5.2} FutureEmissionsin1.5°CPathways  MitigationrequirementscanbequantifiedusingcarbonbudgetapproachesthatrelatecumulativeCO2emissionstoglobalmeantemperatureincrease.Robustphysicalunderstandingunderpinsthisrelationship,butuncertaintiesbecomeincreasinglyrelevantasaspecifictemperaturelimitisapproached.Theseuncertaintiesrelatetothetransientclimateresponsetocumulativecarbonemissions(TCRE),non-CO2emissions,radiativeforcingandresponse,potentialadditionalEarthsystemfeedbacks(suchaspermafrostthawing),andhistoricalemissionsandtemperature.{2.2.2,2.6.1} CumulativeCO2emissionsarekeptwithinabudgetbyreducingglobalannualCO2emissionstonetzero.Thisassessmentsuggestsaremainingbudgetofabout420GtCO2foratwo-thirdschanceoflimitingwarmingto1.5°C,andofabout580GtCO2foranevenchance(mediumconfidence).TheremainingcarbonbudgetisdefinedhereascumulativeCO2emissionsfromthestartof2018untilthetimeofnetzeroglobalemissionsforglobalwarmingdefinedasachangeinglobalnear-surfaceairtemperatures.Remainingbudgetsapplicableto2100wouldbeapproximately100GtCO2lowerthanthistoaccountforpermafrostthawingandpotentialmethanereleasefromwetlandsinthefuture,andmorethereafter.Theseestimatescomewithanadditionalgeophysicaluncertaintyofatleast±400GtCO2,relatedtonon-CO2responseandTCREdistribution.Uncertaintiesinthelevelofhistoricwarmingcontribute±250GtCO2.Inaddition,theseestimatescanvaryby±250GtCO2dependingonnon-CO2mitigationstrategiesasfoundinavailablepathways.{2.2.2,2.6.1} Stayingwithinaremainingcarbonbudgetof580GtCO2impliesthatCO2emissionsreachcarbonneutralityinabout30years,reducedto20yearsfora420GtCO2remainingcarbonbudget(highconfidence).The±400GtCO2geophysicaluncertaintyrangesurroundingacarbonbudgettranslatesintoavariationofthistimingofcarbonneutralityofroughly±15–20years.Ifemissionsdonotstartdeclininginthenextdecade,thepointofcarbonneutralitywouldneedtobereachedatleasttwodecadesearliertoremainwithinthesamecarbonbudget.{2.2.2,2.3.5} Non-CO2emissionscontributetopeakwarmingandthusaffecttheremainingcarbonbudget.Theevolutionofmethaneandsulphurdioxideemissionsstronglyinfluencesthechancesoflimitingwarmingto1.5°C.Inthenear-term,aweakeningofaerosolcoolingwouldaddtofuturewarming,butcanbetemperedbyreductionsinmethaneemissions(highconfidence).Uncertaintyinradiativeforcingestimates(particularlyaerosol)affectscarbonbudgetsandthecertaintyofpathwaycategorizations.Somenon-CO2forcersareemittedalongsideCO2,particularlyintheenergyandtransportsectors,andcanbelargelyaddressedthroughCO2mitigation.Othersrequirespecificmeasures,forexample,totargetagriculturalnitrousoxide(N2O)andmethane(CH4),somesourcesofblackcarbon,orhydrofluorocarbons(highconfidence).Inmanycases,non-CO2emissionsreductionsaresimilarin2°Cpathways,indicatingreductionsneartheirassumedmaximumpotentialbyintegratedassessmentmodels.EmissionsofN2OandNH3increaseinsomepathwayswithstronglyincreasedbioenergydemand.{2.2.2,2.3.1,2.4.2,2.5.3}  TheRoleofCarbonDioxideRemoval(CDR) Allanalysedpathwayslimitingwarmingto1.5°CwithnoorlimitedovershootuseCDRtosomeextenttoneutralizeemissionsfromsourcesforwhichnomitigationmeasureshavebeenidentifiedand,inmostcases,alsotoachievenetnegativeemissionstoreturnglobalwarmingto1.5°Cfollowingapeak(highconfidence).ThelongerthedelayinreducingCO2emissionstowardszero,thelargerthelikelihoodofexceeding1.5°C,andtheheaviertheimpliedrelianceonnetnegativeemissionsaftermid-centurytoreturnwarmingto1.5°C(highconfidence).ThefasterreductionofnetCO2emissionsin1.5°Ccomparedto2°CpathwaysispredominantlyachievedbymeasuresthatresultinlessCO2beingproducedandemitted,andonlytoasmallerdegreethroughadditionalCDR.Limitationsonthespeed,scaleandsocietalacceptabilityofCDRdeploymentalsolimittheconceivableextentoftemperatureovershoot.LimitstoourunderstandingofhowthecarboncyclerespondstonetnegativeemissionsincreasetheuncertaintyabouttheeffectivenessofCDRtodeclinetemperaturesafterapeak.{2.2,2.3,2.6,4.3.7} CDRdeployedatscaleisunproven,andrelianceonsuchtechnologyisamajorriskintheabilitytolimitwarmingto1.5°C.CDRisneededlessinpathwayswithparticularlystrongemphasisonenergyefficiencyandlowdemand.ThescaleandtypeofCDRdeploymentvarieswidelyacross1.5°Cpathways,withdifferentconsequencesforachievingsustainabledevelopmentobjectives(highconfidence).Somepathwaysrelymoreonbioenergywithcarboncaptureandstorage(BECCS),whileothersrelymoreonafforestation,whicharethetwoCDRmethodsmostoftenincludedinintegratedpathways.Trade-offswithothersustainabilityobjectivesoccurpredominantlythroughincreasedland,energy,waterandinvestmentdemand.Bioenergyuseissubstantialin1.5°CpathwayswithorwithoutBECCSduetoitsmultiplerolesindecarbonizingenergyuse.{2.3.1,2.5.3,2.6.3,4.3.7}  PropertiesofEnergyandLandTransitionsin1.5°CPathways Theshareofprimaryenergyfromrenewablesincreaseswhilecoalusagedecreasesacrosspathwayslimitingwarmingto1.5°Cwithnoorlimitedovershoot(highconfidence).By2050,renewables(includingbioenergy,hydro,wind,andsolar,withdirect-equivalencemethod)supplyashareof52–67%(interquartilerange)ofprimaryenergyin1.5°Cpathwayswithnoorlimitedovershoot;whilethesharefromcoaldecreasesto1–7%(interquartilerange),withalargefractionofthiscoalusecombinedwithcarboncaptureandstorage(CCS).From2020to2050theprimaryenergysuppliedbyoildeclinesinmostpathways(−39to−77%interquartilerange).Naturalgaschangesby−13%to−62%(interquartilerange),butsomepathwaysshowamarkedincreasealbeitwithwidespreaddeploymentofCCS.TheoveralldeploymentofCCSvarieswidelyacross1.5°Cpathwayswithnoorlimitedovershoot,withcumulativeCO2storedthrough2050rangingfromzeroupto300GtCO2(minimum–maximumrange),ofwhichzeroupto140GtCO2isstoredfrombiomass.Primaryenergysuppliedbybioenergyrangesfrom40–310EJyr−1in2050(minimum-maximumrange),andnuclearfrom3–66EJyr−1(minimum–maximumrange).Theserangesreflectbothuncertaintiesintechnologicaldevelopmentandstrategicmitigationportfoliochoices.{2.4.2} 1.5°Cpathwayswithnoorlimitedovershootincludearapiddeclineinthecarbonintensityofelectricityandanincreaseinelectrificationofenergyenduse(highconfidence).By2050,thecarbonintensityofelectricitydecreasesto−92to+11gCO2MJ−1(minimum–maximumrange)fromabout140gCO2MJ−1in2020,andelectricitycovers34–71%(minimum–maximumrange)offinalenergyacross1.5°Cpathwayswithnoorlimitedovershootfromabout20%in2020.By2050,theshareofelectricitysuppliedbyrenewablesincreasesto59–97%(minimum-maximumrange)across1.5°Cpathwayswithnoorlimitedovershoot.Pathwayswithhigherchancesofholdingwarmingtobelow1.5°Cgenerallyshowafasterdeclineinthecarbonintensityofelectricityby2030thanpathwaysthattemporarilyovershoot1.5°C.{2.4.1,2.4.2,2.4.3} Transitionsinglobalandregionallandusearefoundinallpathwayslimitingglobalwarmingto1.5°Cwithnoorlimitedovershoot,buttheirscaledependsonthepursuedmitigationportfolio(highconfidence).Pathwaysthatlimitglobalwarmingto1.5°Cwithnoorlimitedovershootprojecta4millionkm2reductiontoa2.5millionkm2increaseofnon-pastureagriculturallandforfoodandfeedcropsanda0.5–11millionkm2reductionofpastureland,tobeconvertedinto0-6millionkm2ofagriculturallandforenergycropsanda2millionkm2reductionto9.5millionkm2increaseinforestsby2050relativeto2010(mediumconfidence).Land-usetransitionsofsimilarmagnitudecanbeobservedinmodelled2°Cpathways(mediumconfidence).Suchlargetransitionsposeprofoundchallengesforsustainablemanagementofthevariousdemandsonlandforhumansettlements,food,livestockfeed,fibre,bioenergy,carbonstorage,biodiversityandotherecosystemservices(highconfidence).{2.3.4,2.4.4}  Demand-SideMitigationandBehaviouralChanges Demand-sidemeasuresarekeyelementsof1.5°Cpathways.Lifestylechoicesloweringenergydemandandtheland-andGHG-intensityoffoodconsumptioncanfurthersupportachievementof1.5°Cpathways(highconfidence).By2030and2050,allend-usesectors(includingbuilding,transport,andindustry)showmarkedenergydemandreductionsinmodelled1.5°Cpathways,comparableandbeyondthoseprojectedin2°Cpathways.Sectoralmodelssupportthescaleofthesereductions.{2.3.4,2.4.3,2.5.1}  Linksbetween1.5°CPathwaysandSustainableDevelopment Choicesaboutmitigationportfoliosforlimitingwarmingto1.5°Ccanpositivelyornegativelyimpacttheachievementofothersocietalobjectives,suchassustainabledevelopment(highconfidence).Inparticular,demand-sideandefficiencymeasures,andlifestylechoicesthatlimitenergy,resource,andGHG-intensivefooddemandsupportsustainabledevelopment(mediumconfidence).Limitingwarmingto1.5°Ccanbeachievedsynergisticallywithpovertyalleviationandimprovedenergysecurityandcanprovidelargepublichealthbenefitsthroughimprovedairquality,preventingmillionsofprematuredeaths.However,specificmitigationmeasures,suchasbioenergy,mayresultintrade-offsthatrequireconsideration.{2.5.1,2.5.2,2.5.3}   Chapter3 Whyisitnecessaryandevenvitaltomaintaintheglobaltemperatureincreasebelow1.5°Cversushigherlevels?Adaptationwillbelessdifficult.Ourworldwillsufferlessnegativeimpactsonintensityandfrequencyofextremeevents,onresources,ecosystems,biodiversity,foodsecurity,cities,tourism,andcarbonremoval. ExecutiveSummary View Download ExploreGraphics ThischapterbuildsonfindingsofAR5andassessesnewscientificevidenceofchangesintheclimatesystemandtheassociatedimpactsonnaturalandhumansystems,withaspecificfocusonthemagnitudeandpatternofriskslinkedforglobalwarmingof1.5°Cabovetemperaturesinthepre-industrialperiod.Chapter3exploresobservedimpactsandprojectedriskstoarangeofnaturalandhumansystems,withafocusonhowrisklevelschangefrom1.5°Cto2°Cofglobalwarming.Thechapteralsorevisitsmajorcategoriesofrisk(ReasonsforConcern,RFC)basedontheassessmentofnewknowledgethathasbecomeavailablesinceAR5.  1.5°Cand2°CWarmerWorlds Theglobalclimatehaschangedrelativetothepre-industrialperiod,andtherearemultiplelinesofevidencethatthesechangeshavehadimpactsonorganismsandecosystems,aswellasonhumansystemsandwell-being(highconfidence).Theincreaseinglobalmeansurfacetemperature(GMST),whichreached0.87°Cin2006–2015relativeto1850–1900,hasincreasedthefrequencyandmagnitudeofimpacts(highconfidence),strengtheningevidenceofhowanincreaseinGMSTof1.5°Cormorecouldimpactnaturalandhumansystems(1.5°Cversus2°C).{3.3,3.4,3.5,3.6,Cross-ChapterBoxes6,7and8inthischapter} Human-inducedglobalwarminghasalreadycausedmultipleobservedchangesintheclimatesystem(highconfidence).Changesincludeincreasesinbothlandandoceantemperatures,aswellasmorefrequentheatwavesinmostlandregions(highconfidence).Thereisalso(highconfidence)globalwarminghasresultedinanincreaseinthefrequencyanddurationofmarineheatwaves.Further,thereissubstantialevidencethathuman-inducedglobalwarminghasledtoanincreaseinthefrequency,intensityand/oramountofheavyprecipitationeventsattheglobalscale(mediumconfidence),aswellasanincreasedriskofdroughtintheMediterraneanregion(mediumconfidence).{3.3.1,3.3.2,3.3.3,3.3.4,Box3.4} Trendsinintensityandfrequencyofsomeclimateandweatherextremeshavebeendetectedovertimespansduringwhichabout0.5°Cofglobalwarmingoccurred(mediumconfidence).Thisassessmentisbasedonseverallinesofevidence,includingattributionstudiesforchangesinextremessince1950.{3.2,3.3.1,3.3.2,3.3.3,3.3.4} Severalregionalchangesinclimateareassessedtooccurwithglobalwarmingupto1.5°Cascomparedtopre-industriallevels,includingwarmingofextremetemperaturesinmanyregions(highconfidence),increasesinfrequency,intensityand/oramountofheavyprecipitationinseveralregions(highconfidence),andanincreaseinintensityorfrequencyofdroughtsinsomeregions(mediumconfidence).{3.3.1,3.3.2,3.3.3,3.3.4,Table3.2} Thereisnosingle‘1.5°Cwarmerworld’(highconfidence).InadditiontotheoverallincreaseinGMST,itisimportanttoconsiderthesizeanddurationofpotentialovershootsintemperature.Furthermore,therearequestionsonhowthestabilizationofanincreaseinGMSTof1.5°Ccanbeachieved,andhowpoliciesmightbeabletoinfluencetheresilienceofhumanandnaturalsystems,andthenatureofregionalandsubregionalrisks.Overshootingposeslargerisksfornaturalandhumansystems,especiallyifthetemperatureatpeakwarmingishigh,becausesomerisksmaybelong-lastingandirreversible,suchasthelossofsomeecosystems(highconfidence).Therateofchangeforseveraltypesofrisksmayalsohaverelevance,withpotentiallylargerisksinthecaseofarapidrisetoovershootingtemperatures,evenifadecreaseto1.5°Ccanbeachievedattheendofthe21stcenturyorlater(mediumconfidence).Ifovershootistobeminimized,theremainingequivalentCO2budgetavailableforemissionsisverysmall,whichimpliesthatlarge,immediateandunprecedentedglobaleffortstomitigategreenhousegasesarerequired(highconfidence).{3.2,3.6.2,Cross-ChapterBox8inthischapter} Robust1 globaldifferencesintemperaturemeansandextremesareexpectedifglobalwarmingreaches1.5°Cversus2°Cabovethepre-industriallevels(highconfidence).Foroceans,regionalsurfacetemperaturemeansandextremesareprojectedtobehigherat2°Ccomparedto1.5°Cofglobalwarming(highconfidence).Temperaturemeansandextremesarealsoprojectedtobehigherat2°Ccomparedto1.5°Cinmostlandregions,withincreasesbeing2–3timesgreaterthantheincreaseinGMSTprojectedforsomeregions(highconfidence).Robustincreasesintemperaturemeansandextremesarealsoprojectedat1.5°Ccomparedtopresent-dayvalues(highconfidence){3.3.1,3.3.2}.Therearedecreasesintheoccurrenceofcoldextremes,butsubstantialincreasesintheirtemperature,inparticularinregionswithsnoworicecover(highconfidence){3.3.1}. Climatemodelsprojectrobust2differencesinregionalclimatebetweenpresent-dayandglobalwarmingupto1.5°C3,andbetween1.5°Cand2°C4(highconfidence),dependingonthevariableandregioninquestion(highconfidence).Large,robustandwidespreaddifferencesareexpectedfortemperatureextremes(highconfidence).Regardinghotextremes,thestrongestwarmingisexpectedtooccuratmid-latitudesinthewarmseason(withincreasesofupto3°Cfor1.5°Cofglobalwarming,i.e.,afactoroftwo)andathighlatitudesinthecoldseason(withincreasesofupto4.5°Cat1.5°Cofglobalwarming,i.e.,afactorofthree)(highconfidence).ThestrongestwarmingofhotextremesisprojectedtooccurincentralandeasternNorthAmerica,centralandsouthernEurope,theMediterraneanregion(includingsouthernEurope,northernAfricaandtheNearEast),westernandcentralAsia,andsouthernAfrica(mediumconfidence).Thenumberofexceptionallyhotdaysareexpectedtoincreasethemostinthetropics,whereinterannualtemperaturevariabilityislowest;extremeheatwavesarethusprojectedtoemergeearliestintheseregions,andtheyareexpectedtoalreadybecomewidespreadthereat1.5°Cglobalwarming(highconfidence).Limitingglobalwarmingto1.5°Cinsteadof2°Ccouldresultinaround420millionfewerpeoplebeingfrequentlyexposedtoextremeheatwaves,andabout65millionfewerpeoplebeingexposedtoexceptionalheatwaves,assumingconstantvulnerability(mediumconfidence).{3.3.1,3.3.2,Cross-ChapterBox8inthischapter} Limitingglobalwarmingto1.5°Cwouldlimitrisksofincreasesinheavyprecipitationeventsonaglobalscaleandinseveralregionscomparedtoconditionsat2°Cglobalwarming(mediumconfidence).Theregionswiththelargestincreasesinheavyprecipitationeventsfor1.5°Cto2°Cglobalwarminginclude:severalhigh-latituderegions(e.g.Alaska/westernCanada,easternCanada/Greenland/Iceland,northernEuropeandnorthernAsia);mountainousregions(e.g.,TibetanPlateau);easternAsia(includingChinaandJapan);andeasternNorthAmerica(mediumconfidence).Tropicalcyclonesareprojectedtodecreaseinfrequencybutwithanincreaseinthenumberofveryintensecyclones(limitedevidence,lowconfidence).Heavyprecipitationassociatedwithtropicalcyclonesisprojectedtobehigherat2°Ccomparedto1.5°Cofglobalwarming(mediumconfidence).Heavyprecipitation,whenaggregatedataglobalscale,isprojectedtobehigherat2°Cthanat1.5°Cofglobalwarming(mediumconfidence){3.3.3,3.3.6} Limitingglobalwarmingto1.5°Cisexpectedtosubstantiallyreducetheprobabilityofextremedrought,precipitationdeficits,andrisksassociatedwithwateravailability(i.e.,waterstress)insomeregions(mediumconfidence).Inparticular,risksassociatedwithincreasesindroughtfrequencyandmagnitudeareprojectedtobesubstantiallylargerat2°Cthanat1.5°CintheMediterraneanregion(includingsouthernEurope,northernAfricaandtheNearEast)andsouthernAfrica(mediumconfidence).{3.3.3,3.3.4,Box3.1,Box3.2} Riskstonaturalandhumansystemsareexpectedtobelowerat1.5°Cthanat2°Cofglobalwarming(highconfidence).Thisdifferenceisduetothesmallerratesandmagnitudesofclimatechangeassociatedwitha1.5°Ctemperatureincrease,includinglowerfrequenciesandintensitiesoftemperature-relatedextremes.Lowerratesofchangeenhancetheabilityofnaturalandhumansystemstoadapt,withsubstantialbenefitsforawiderangeofterrestrial,freshwater,wetland,coastalandoceanecosystems(includingcoralreefs)(highconfidence),aswellasfoodproductionsystems,humanhealth,andtourism(mediumconfidence),togetherwithenergysystemsandtransportation(lowconfidence).{3.3.1,3.4} Exposuretomultipleandcompoundclimate-relatedrisksisprojectedtoincreasebetween1.5°Cand2°CofglobalwarmingwithgreaterproportionsofpeoplebothexposedandsusceptibletopovertyinAfricaandAsia(highconfidence).Forglobalwarmingfrom1.5°Cto2°C,risksacrossenergy,food,andwatersectorscouldoverlapspatiallyandtemporally,creatingnew–andexacerbatingcurrent–hazards,exposures,andvulnerabilitiesthatcouldaffectincreasingnumbersofpeopleandregions(mediumconfidence).Smallislandstatesandeconomicallydisadvantagedpopulationsareparticularlyatrisk(highconfidence).{3.3.1,3.4.5.3,3.4.5.6,3.4.11,3.5.4.9,Box3.5} Globalwarmingof2°Cwouldleadtoanexpansionofareaswithsignificantincreasesinrunoff,aswellasthoseaffectedbyfloodhazard,comparedtoconditionsat1.5°C(mediumconfidence).Globalwarmingof1.5°Cwouldalsoleadtoanexpansionofthegloballandareawithsignificantincreasesinrunoff(mediumconfidence)andanincreaseinfloodhazardinsomeregions(mediumconfidence)comparedtopresent-dayconditions.{3.3.5} Theprobabilityofasea-ice-freeArcticOcean5 duringsummerissubstantiallyhigherat2°Ccomparedto1.5°Cofglobalwarming(mediumconfidence).Modelsimulationssuggestthatatleastonesea-ice-freeArcticsummerisexpectedevery10yearsforglobalwarmingof2°C,withthefrequencydecreasingtoonesea-ice-freeArcticsummerevery100yearsunder1.5°C(mediumconfidence).Anintermediatetemperatureovershootwillhavenolong-termconsequencesforArcticseaicecoverage,andhysteresisisnotexpected(highconfidence).{3.3.8,3.4.4.7} Globalmeansealevelrise(GMSLR)isprojectedtobearound0.1m(0.04–0.16m)lessbytheendofthe21stcenturyina1.5°Cwarmerworldcomparedtoa2°Cwarmerworld(mediumconfidence).ProjectedGMSLRfor1.5°Cofglobalwarminghasanindicativerangeof0.26–0.77m,relativeto1986–2005,(mediumconfidence).Asmallersealevelrisecouldmeanthatupto10.4millionfewerpeople(basedonthe2010globalpopulationandassumingnoadaptation)wouldbeexposedtotheimpactsofsealevelrisegloballyin2100at1.5°Ccomparedtoat2°C.Aslowerrateofsealevelriseenablesgreateropportunitiesforadaptation(mediumconfidence).Thereishighconfidencethatsealevelrisewillcontinuebeyond2100.InstabilitiesexistforboththeGreenlandandAntarcticicesheets,whichcouldresultinmulti-meterrisesinsealevelontimescalesofcenturytomillennia.Thereis(mediumconfidence)thattheseinstabilitiescouldbetriggeredataround1.5°Cto2°Cofglobalwarming.{3.3.9,3.4.5,3.6.3} Theoceanhasabsorbedabout30%oftheanthropogeniccarbondioxide,resultinginoceanacidificationandchangestocarbonatechemistrythatareunprecedentedforatleastthelast65millionyears(highconfidence).Riskshavebeenidentifiedforthesurvival,calcification,growth,developmentandabundanceofabroadrangeofmarinetaxonomicgroups,rangingfromalgaetofish,withsubstantialevidenceofpredictabletrait-basedsensitivities(highconfidence).Therearemultiplelinesofevidencethatoceanwarmingandacidificationcorrespondingto1.5°Cofglobalwarmingwouldimpactawiderangeofmarineorganismsandecosystems,aswellassectorssuchasaquacultureandfisheries(highconfidence).{3.3.10,3.4.4} Largerrisksareexpectedformanyregionsandsystemsforglobalwarmingat1.5°C,ascomparedtotoday,withadaptationrequirednowandupto1.5°C.However,riskswouldbelargerat2°Cofwarmingandanevengreatereffortwouldbeneededforadaptationtoatemperatureincreaseofthatmagnitude(highconfidence).{3.4,Box3.4,Box3.5,Cross-ChapterBox6inthischapter} Futurerisksat1.5°Cofglobalwarmingwilldependonthemitigationpathwayandonthepossibleoccurrenceofatransientovershoot(highconfidence).Theimpactsonnaturalandhumansystemswouldbegreaterifmitigationpathwaystemporarilyovershoot1.5°Candreturnto1.5°Claterinthecentury,ascomparedtopathwaysthatstabilizeat1.5°Cwithoutanovershoot(highconfidence).Thesizeanddurationofanovershootwouldalsoaffectfutureimpacts(e.g.,irreversiblelossofsomeecosystems)(highconfidence).Changesinlanduseresultingfrommitigationchoicescouldhaveimpactsonfoodproductionandecosystemdiversity.{3.6.1,3.6.2,Cross-ChapterBoxes7and8inthischapter} ClimateChangeRisksforNaturalandHumansystems TerrestrialandWetlandEcosystems Risksoflocalspecieslossesand,consequently,risksofextinctionaremuchlessina1.5°Cversusa2°Cwarmerworld(highconfidence).Thenumberofspeciesprojectedtoloseoverhalfoftheirclimaticallydeterminedgeographicrangeat2°Cglobalwarming(18%ofinsects,16%ofplants,8%ofvertebrates)isprojectedtobereducedto6%ofinsects,8%ofplantsand4%ofvertebratesat1.5°Cwarming(mediumconfidence).Risksassociatedwithotherbiodiversity-relatedfactors,suchasforestfires,extremeweatherevents,andthespreadofinvasivespecies,pestsanddiseases,wouldalsobelowerat1.5°Cthanat2°Cofwarming(highconfidence),supportingagreaterpersistenceofecosystemservices. {3.4.3,3.5.2} Constrainingglobalwarmingto1.5°C,ratherthanto2°Candhigher,isprojectedtohavemanybenefitsforterrestrialandwetlandecosystemsandforthepreservationoftheirservicestohumans(highconfidence).Risksfornaturalandmanagedecosystemsarehigherondrylandscomparedtohumidlands.Theglobalterrestriallandareaprojectedtobeaffectedbyecosystemtransformations(13%,interquartilerange8–20%)at2°Cisapproximatelyhalvedat1.5°Cglobalwarmingto4%(interquartilerange2–7%)(mediumconfidence).Above1.5°C,anexpansionofdesertterrainandvegetationwouldoccurintheMediterraneanbiome(mediumconfidence),causingchangesunparalleledinthelast10,000years(mediumconfidence).{3.3.2.2,3.4.3.2,3.4.3.5,3.4.6.1,3.5.5.10,Box4.2} Manyimpactsareprojectedtobelargerathigherlatitudes,owingtomeanandcold-seasonwarmingratesabovetheglobalaverage(mediumconfidence).High-latitudetundraandborealforestareparticularlyatrisk,andwoodyshrubsarealreadyencroachingintotundra(highconfidence)andwillproceedwithfurtherwarming.Constrainingwarmingto1.5°Cwouldpreventthethawingofanestimatedpermafrostareaof1.5to2.5millionkm2overcenturiescomparedtothawingunder2°C(mediumconfidence).{3.3.2,3.4.3,3.4.4} OceanEcosystems Oceanecosystemsarealreadyexperiencinglarge-scalechanges,andcriticalthresholdsareexpectedtobereachedat1.5°Candhigherlevelsofglobalwarming(highconfidence).Inthetransitionto1.5°Cofwarming,changestowatertemperaturesareexpectedtodrivesomespecies(e.g.,plankton,fish)torelocatetohigherlatitudesandcausenovelecosystemstoassemble(highconfidence).Otherecosystems(e.g.,kelpforests,coralreefs)arerelativelylessabletomove,however,andareprojectedtoexperiencehighratesofmortalityandloss(veryhighconfidence).Forexample,multiplelinesofevidenceindicatethatthemajority(70–90%)ofwarmwater(tropical)coralreefsthatexisttodaywilldisappearevenifglobalwarmingisconstrainedto1.5°C(veryhighconfidence).{3.4.4,Box3.4} Currentecosystemservicesfromtheoceanareexpectedtobereducedat1.5°Cofglobalwarming,withlossesbeingevengreaterat2°Cofglobalwarming(highconfidence).Therisksofdecliningoceanproductivity,shiftsofspeciestohigherlatitudes,damagetoecosystems(e.g.,coralreefs,andmangroves,seagrassandotherwetlandecosystems),lossoffisheriesproductivity(atlowlatitudes),andchangestooceanchemistry(e.g.,acidification,hypoxiaanddeadzones)areprojectedtobesubstantiallylowerwhenglobalwarmingislimitedto1.5°C(highconfidence).{3.4.4,Box3.4} WaterResources Theprojectedfrequencyandmagnitudeoffloodsanddroughtsinsomeregionsaresmallerunder1.5°Cthanunder2°Cofwarming(mediumconfidence).Humanexposuretoincreasedfloodingisprojectedtobesubstantiallylowerat1.5°Ccomparedto2°Cofglobalwarming,althoughprojectedchangescreateregionallydifferentiatedrisks(mediumconfidence).Thedifferencesintherisksamongregionsarestronglyinfluencedbylocalsocio-economicconditions(mediumconfidence).{3.3.4,3.3.5,3.4.2} Risksofwaterscarcityareprojectedtobegreaterat2°Cthanat1.5°Cofglobalwarminginsomeregions(mediumconfidence).Dependingonfuturesocio-economicconditions,limitingglobalwarmingto1.5°C,comparedto2°C,mayreducetheproportionoftheworldpopulationexposedtoaclimatechange-inducedincreaseinwaterstressbyupto50%,althoughthereisconsiderablevariabilitybetweenregions(mediumconfidence).RegionswithparticularlylargebenefitscouldincludetheMediterraneanandtheCaribbean(mediumconfidence).Socio-economicdrivers,however,areexpectedtohaveagreaterinfluenceontheserisksthanthechangesinclimate(mediumconfidence).{3.3.5,3.4.2,Box3.5} LandUse,FoodSecurityandFoodProductionSystems Limitingglobalwarmingto1.5°C,comparedwith2°C,isprojectedtoresultinsmallernetreductionsinyieldsofmaize,rice,wheat,andpotentiallyothercerealcrops,particularlyinsub-SaharanAfrica,SoutheastAsia,andCentralandSouthAmerica;andintheCO2-dependentnutritionalqualityofriceandwheat(highconfidence).Alossof7–10%ofrangelandlivestockgloballyisprojectedforapproximately2°Cofwarming,withconsiderableeconomicconsequencesformanycommunitiesandregions(mediumconfidence).{3.4.6,3.6,Box3.1,Cross-ChapterBox6inthischapter} Reductionsinprojectedfoodavailabilityarelargerat2°Cthanat1.5°CofglobalwarmingintheSahel,southernAfrica,theMediterranean,centralEuropeandtheAmazon(mediumconfidence).Thissuggestsatransitionfrommediumtohighriskofregionallydifferentiatedimpactsonfoodsecuritybetween1.5°Cand2°C(mediumconfidence).Futureeconomicandtradeenvironmentsandtheirresponsetochangingfoodavailability(mediumconfidence)areimportantpotentialadaptationoptionsforreducinghungerriskinlow-andmiddle-incomecountries.{Cross-ChapterBox6inthischapter} Fisheriesandaquacultureareimportanttoglobalfoodsecuritybutarealreadyfacingincreasingrisksfromoceanwarmingandacidification(mediumconfidence).Theserisksareprojectedtoincreaseat1.5°Cofglobalwarmingandimpactkeyorganismssuchasfinfishandbivalves(e.g.,oysters),especiallyatlowlatitudes(mediumconfidence).Small-scalefisheriesintropicalregions,whichareverydependentonhabitatprovidedbycoastalecosystemssuchascoralreefs,mangroves,seagrassandkelpforests,areexpectedtofacegrowingrisksat1.5°Cofwarmingbecauseoflossofhabitat(mediumconfidence).Risksofimpactsanddecreasingfoodsecurityareprojectedtobecomegreaterasglobalwarmingreachesbeyond1.5°Candbothoceanwarmingandacidificationincrease,withsubstantiallosseslikelyforcoastallivelihoodsandindustries(e.g.,fisheriesandaquaculture)(mediumtohighconfidence).{3.4.4,3.4.5,3.4.6,Box3.1,Box3.4,Box3.5,Cross-ChapterBox6inthischapter} Landuseandland-usechangeemergeascriticalfeaturesofvirtuallyallmitigationpathwaysthatseektolimitglobalwarmingto1.5°C(highconfidence).Mostleast-costmitigationpathwaystolimitpeakorend-of-centurywarmingto1.5°Cmakeuseofcarbondioxideremoval(CDR),predominantlyemployingsignificantlevelsofbioenergywithcarboncaptureandstorage(BECCS)and/orafforestationandreforestation(AR)intheirportfolioofmitigationmeasures(highconfidence).{Cross-ChapterBox7inthischapter} Large-scaledeploymentofBECCSand/orARwouldhaveafar-reachinglandandwaterfootprint(highconfidence).Whetherthisfootprintwouldresultinadverseimpacts,forexampleonbiodiversityorfoodproduction,dependsontheexistenceandeffectivenessofmeasurestoconservelandcarbonstocks,measurestolimitagriculturalexpansioninordertoprotectnaturalecosystems,andthepotentialtoincreaseagriculturalproductivity(mediumagreement).Inaddition,BECCSand/orARwouldhavesubstantialdirecteffectsonregionalclimatethroughbiophysicalfeedbacks,whicharegenerallynotincludedinIntegratedAssessmentsModels(highconfidence).{3.6.2,Cross-ChapterBoxes7and8inthischapter} Theimpactsoflarge-scaleCDRdeploymentcouldbegreatlyreducedifawiderportfolioofCDRoptionsweredeployed,ifaholisticpolicyforsustainablelandmanagementwereadopted,andifincreasedmitigationeffortswereemployedtostronglylimitthedemandforland,energyandmaterialresources,includingthroughlifestyleanddietarychanges(mediumconfidence).Inparticular,reforestationcouldbeassociatedwithsignificantco-benefitsifimplementedinamannerthanhelpsrestorenaturalecosystems(highconfidence).{Cross-ChapterBox7inthischapter} HumanHealth,Well-Being,CitiesandPoverty Anyincreaseinglobaltemperature(e.g.,+0.5°C)isprojectedtoaffecthumanhealth,withprimarilynegativeconsequences(highconfidence).Lowerrisksareprojectedat1.5°Cthanat2°Cforheat-relatedmorbidityandmortality(veryhighconfidence),andforozone-relatedmortalityifemissionsneededforozoneformationremainhigh(highconfidence).Urbanheatislandsoftenamplifytheimpactsofheatwavesincities(highconfidence).Risksforsomevector-bornediseases,suchasmalariaanddenguefeverareprojectedtoincreasewithwarmingfrom1.5°Cto2°C,includingpotentialshiftsintheirgeographicrange(highconfidence).Overallforvector-bornediseases,whetherprojectionsarepositiveornegativedependsonthedisease,regionandextentofchange(highconfidence).Lowerrisksofundernutritionareprojectedat1.5°Cthanat2°C(mediumconfidence).Incorporatingestimatesofadaptationintoprojectionsreducesthemagnitudeofrisks(highconfidence).{3.4.7,3.4.7.1,3.4.8,3.5.5.8} Globalwarmingof2°Cisexpectedtoposegreaterriskstourbanareasthanglobalwarmingof1.5°C(mediumconfidence).Theextentofriskdependsonhumanvulnerabilityandtheeffectivenessofadaptationforregions(coastalandnon-coastal),informalsettlementsandinfrastructuresectors(suchasenergy,waterandtransport)(highconfidence).{3.4.5,3.4.8} Povertyanddisadvantagehaveincreasedwithrecentwarming(about1°C)andareexpectedtoincreaseformanypopulationsasaverageglobaltemperaturesincreasefrom1°Cto1.5°Candhigher(mediumconfidence).Outmigrationinagricultural-dependentcommunitiesispositivelyandstatisticallysignificantlyassociatedwithglobaltemperature(mediumconfidence).Ourunderstandingofthelinksof1.5°Cand2°Cofglobalwarmingtohumanmigrationarelimitedandrepresentanimportantknowledgegap.{3.4.10,3.4.11,5.2.2,Table3.5} KeyEconomicSectorsandServices Riskstoglobalaggregatedeconomicgrowthduetoclimatechangeimpactsareprojectedtobelowerat1.5°Cthanat2°Cbytheendofthiscentury(mediumconfidence).{3.5.2,3.5.3}Thelargestreductionsineconomicgrowthat2°Ccomparedto1.5°Cofwarmingareprojectedforlow-andmiddle-incomecountriesandregions(theAfricancontinent,SoutheastAsia,India,BrazilandMexico)(lowtomediumconfidence).CountriesinthetropicsandSouthernHemispheresubtropicsareprojectedtoexperiencethelargestimpactsoneconomicgrowthduetoclimatechangeshouldglobalwarmingincreasefrom1.5°Cto2°C(mediumconfidence).{3.5}Globalwarminghasalreadyaffectedtourism,withincreasedrisksprojectedunder1.5°Cofwarminginspecificgeographicregionsandforseasonaltourismincludingsun,beachandsnowsportsdestinations(veryhighconfidence).Riskswillbelowerfortourismmarketsthatarelessclimatesensitive,suchasgamingandlargehotel-basedactivities(highconfidence).Risksforcoastaltourism,particularlyinsubtropicalandtropicalregions,willincreasewithtemperature-relateddegradation(e.g.,heatextremes,storms)orlossofbeachandcoralreefassets(highconfidence).{3.3.6,3.4.4.12,3.4.9.1,Box3.4} SmallIslands,andCoastalandLow-lyingareas Smallislandsareprojectedtoexperiencemultipleinter-relatedrisksat1.5°Cofglobalwarmingthatwillincreasewithwarmingof2°Candhigherlevels(highconfidence).Climatehazardsat1.5°Careprojectedtobelowercomparedtothoseat2°C(highconfidence).Long-termrisksofcoastalfloodingandimpactsonpopulations,infrastructuresandassets(highconfidence),freshwaterstress(mediumconfidence),andrisksacrossmarineecosystems(highconfidence)andcriticalsectors(mediumconfidence)areprojectedtoincreaseat1.5°Ccomparedtopresent-daylevelsandincreasefurtherat2°C,limitingadaptationopportunitiesandincreasinglossanddamage(mediumconfidence).Migrationinsmallislands(internallyandinternationally)occursformultiplereasonsandpurposes,mostlyforbetterlivelihoodopportunities(highconfidence)andincreasinglyowingtosealevelrise(mediumconfidence).{3.3.2.2,3.3.6–9,3.4.3.2,3.4.4.2,3.4.4.5,3.4.4.12,3.4.5.3,3.4.7.1,3.4.9.1,3.5.4.9,Box3.4,Box3.5} Impactsassociatedwithsealevelriseandchangestothesalinityofcoastalgroundwater,increasedfloodinganddamagetoinfrastructure,areprojectedtobecriticallyimportantinvulnerableenvironments,suchassmallislands,low-lyingcoastsanddeltas,atglobalwarmingof1.5°Cand2°C(highconfidence).Localizedsubsidenceandchangestoriverdischargecanpotentiallyexacerbatetheseeffects.Adaptationisalreadyhappening(highconfidence)andwillremainimportantovermulti-centennialtimescales.{3.4.5.3,3.4.5.4,3.4.5.7,5.4.5.4,Box 3.5} Existingandrestorednaturalcoastalecosystemsmaybeeffectiveinreducingtheadverseimpactsofrisingsealevelsandintensifyingstormsbyprotectingcoastalanddeltaicregions(mediumconfidence).Naturalsedimentationratesareexpectedtobeabletooffsettheeffectofrisingsealevels,giventheslowerratesofsealevelriseassociatedwith1.5°Cofwarming(mediumconfidence).Otherfeedbacks,suchaslandwardmigrationofwetlandsandtheadaptationofinfrastructure,remainimportant(mediumconfidence).{3.4.4.12,3.4.5.4,3.4.5.7} IncreasedReasonsforConcern TherearemultiplelinesofevidencethatsinceAR5theassessedlevelsofriskincreasedforfourofthefiveReasonsforConcern(RFCs)forglobalwarminglevelsofupto2°C(highconfidence).Therisktransitionsbydegreesofglobalwarmingarenow:fromhightoveryhighbetween1.5°Cand2°CforRFC1(Uniqueandthreatenedsystems)(highconfidence);frommoderatetohighriskbetween1°Cand1.5°CforRFC2(Extremeweatherevents)(mediumconfidence);frommoderatetohighriskbetween1.5°Cand2°CforRFC3(Distributionofimpacts)(highconfidence);frommoderatetohighriskbetween1.5°Cand2.5°CforRFC4(Globalaggregateimpacts)(mediumconfidence);andfrommoderatetohighriskbetween1°Cand2.5°CforRFC5(Large-scalesingularevents)(mediumconfidence).{3.5.2} Thecategory‘Uniqueandthreatenedsystems’(RFC1)displayatransitionfromhightoveryhighriskwhichisnowlocatedbetween1.5°Cand2°Cofglobalwarmingasopposedtoat2.6°CofglobalwarminginAR5,owingtonewandmultiplelinesofevidenceforchangingrisksforcoralreefs,theArcticandbiodiversityingeneral(highconfidence).{3.5.2.1} In‘Extremeweatherevents’(RFC2),thetransitionfrommoderatetohighriskisnowlocatedbetween1.0°Cand1.5°Cofglobalwarming,whichisverysimilartotheAR5assessmentbutisprojectedwithgreaterconfidence(mediumconfidence).Theimpactliteraturecontainslittleinformationaboutthepotentialforhumansocietytoadapttoextremeweatherevents,andhenceithasnotbeenpossibletolocatethetransitionfrom‘high’to‘veryhigh’riskwithinthecontextofassessingimpactsat1.5°Cversus2°Cofglobalwarming.Thereisthuslowconfidenceinthelevelatwhichglobalwarmingcouldleadtoveryhighrisksassociatedwithextremeweathereventsinthecontextofthisreport.{3.5} Withrespecttothe‘Distributionofimpacts’(RFC3)atransitionfrommoderatetohighriskisnowlocatedbetween1.5°Cand2°Cofglobalwarming,comparedwithbetween1.6°Cand2.6°CglobalwarminginAR5,owingtonewevidenceaboutregionallydifferentiatedriskstofoodsecurity,waterresources,drought,heatexposureandcoastalsubmergence(highconfidence).{3.5} In‘globalaggregateimpacts’(RFC4)atransitionfrommoderatetohighlevelsofriskisnowlocatedbetween1.5°Cand2.5°Cofglobalwarming,asopposedtoat3.6°CofwarminginAR5,owingtonewevidenceaboutglobalaggregateeconomicimpactsandriskstoEarth’sbiodiversity(mediumconfidence).{3.5} Finally,‘large-scalesingularevents’(RFC5),moderateriskisnowlocatedat1°Cofglobalwarmingandhighriskislocatedat2.5°Cofglobalwarming,asopposedtoat1.6°C(moderaterisk)andaround4°C(highrisk)inAR5,becauseofnewobservationsandmodelsoftheWestAntarcticicesheet(mediumconfidence).{3.3.9,3.5.2,3.6.3} Chapter4 Theglobalresponsetowarmingof1.5°Ccomprisestransitionsinlandandecosystem,energy,urbanandinfrastructure,andindustrialsystems.Thefeasibilityofmitigationandadaptationoptions,andtheenablingconditionsforstrengtheningandimplementingthesystemicchanges,areassessedinthischapter. ExecutiveSummary View Download ExploreGraphics Limitingwarmingto1.5°Cabovepre-industriallevelswouldrequiretransformativesystemicchange,integratedwithsustainabledevelopment.Suchchangewouldrequiretheupscalingandaccelerationoftheimplementationoffar-reaching,multilevelandcross-sectoralclimatemitigationandaddressingbarriers.Suchsystemicchangewouldneedtobelinkedtocomplementaryadaptationactions,includingtransformationaladaptation,especiallyforpathwaysthattemporarilyovershoot1.5°C(mediumevidence,highagreement){Chapter2,Chapter3,4.2.1,4.4.5,4.5}.CurrentnationalpledgesonmitigationandadaptationarenotenoughtostaybelowtheParisAgreementtemperaturelimitsandachieveitsadaptationgoals.Whiletransitionsinenergyefficiency,carbonintensityoffuels,electrificationandland-usechangeareunderwayinvariouscountries,limitingwarmingto1.5°Cwillrequireagreaterscaleandpaceofchangetotransformenergy,land,urbanandindustrialsystemsglobally.{4.3,4.4,Cross-ChapterBox9inthisChapter} Althoughmultiplecommunitiesaroundtheworldaredemonstratingthepossibilityofimplementationconsistentwith1.5°Cpathways{Boxes4.1-4.10},veryfewcountries,regions,cities,communitiesorbusinessescancurrentlymakesuchaclaim(highconfidence).Tostrengthentheglobalresponse,almostallcountrieswouldneedtosignificantlyraisetheirlevelofambition.Implementationofthisraisedambitionwouldrequireenhancedinstitutionalcapabilitiesinallcountries,includingbuildingthecapabilitytoutilizeindigenousandlocalknowledge(mediumevidence,highagreement).Indevelopingcountriesandforpoorandvulnerablepeople,implementingtheresponsewouldrequirefinancial,technologicalandotherformsofsupporttobuildcapacity,forwhichadditionallocal,nationalandinternationalresourceswouldneedtobemobilized(highconfidence).However,public,financial,institutionalandinnovationcapabilitiescurrentlyfallshortofimplementingfar-reachingmeasuresatscaleinallcountries(highconfidence).Transnationalnetworksthatsupportmultilevelclimateactionaregrowing,butchallengesintheirscale-upremain.{4.4.1,4.4.2,4.4.4,4.4.5,Box4.1,Box4.2,Box4.7} Adaptationneedswillbelowerina1.5°Cworldcomparedtoa2°Cworld(highconfidence){Chapter3;Cross-ChapterBox11inthischapter}.Learningfromcurrentadaptationpracticesandstrengtheningthemthroughadaptivegovernance{4.4.1},lifestyleandbehaviouralchange{4.4.3}andinnovativefinancingmechanisms{4.4.5}canhelptheirmainstreamingwithinsustainabledevelopmentpractices.Preventingmaladaptation,drawingonbottom-upapproaches {Box4.6}andusingindigenousknowledge{Box4.3}wouldeffectivelyengageandprotectvulnerablepeopleandcommunities.Whileadaptationfinancehasincreasedquantitatively,significantfurtherexpansionwouldbeneededtoadaptto1.5°C.Qualitativegapsinthedistributionofadaptationfinance,readinesstoabsorbresources,andmonitoringmechanismsunderminethepotentialofadaptationfinancetoreduceimpacts.{Chapter3,4.4.2,4.4.5,4.6} SystemTransitions Theenergysystemtransitionthatwouldberequiredtolimitglobalwarmingto1.5°Cabovepre-industrialconditionsisunderwayinmanysectorsandregionsaroundtheworld(mediumevidence,highagreement).Thepolitical,economic,socialandtechnicalfeasibilityofsolarenergy,windenergyandelectricitystoragetechnologieshasimproveddramaticallyoverthepastfewyears,whilethatofnuclearenergyandcarbondioxidecaptureandstorage(CCS)intheelectricitysectorhavenotshownsimilarimprovements.{4.3.1} Electrification,hydrogen,bio-basedfeedstocksandsubstitution,and,inseveralcases,carbondioxidecapture,utilizationandstorage(CCUS),wouldleadtothedeepemissionsreductionsrequiredinenergy-intensiveindustriestolimitwarmingto1.5°C.However,thoseoptionsarelimitedbyinstitutional,economicandtechnicalconstraints,whichincreasefinancialriskstomanyincumbentfirms(mediumevidence,highagreement).Energyefficiencyinindustryismoreeconomicallyfeasibleandhelpsenableindustrialsystemtransitionsbutwouldhavetobecomplementedwithgreenhousegas(GHG)-neutralprocessesorcarbondioxideremoval(CDR)tomakeenergy-intensiveindustriesconsistentwith1.5°C(highconfidence). {4.3.1,4.3.4} Globalandregionalland-useandecosystemstransitionsandassociatedchangesinbehaviourthatwouldberequiredtolimitwarmingto1.5°Ccanenhancefutureadaptationandland-basedagriculturalandforestrymitigationpotential.Suchtransitionscould,however,carryconsequencesforlivelihoodsthatdependonagricultureandnaturalresources{4.3.2,Cross-ChapterBox6inChapter3}.Alterationsofagricultureandforestsystemstoachievemitigationgoalscouldaffectcurrentecosystemsandtheirservicesandpotentiallythreatenfood,waterandlivelihoodsecurity.Whilethiscouldlimitthesocialandenvironmentalfeasibilityofland-basedmitigationoptions,carefuldesignandimplementationcouldenhancetheiracceptabilityandsupportsustainabledevelopmentobjectives(mediumevidence,mediumagreement).{4.3.2,4.5.3} Changingagriculturalpracticescanbeaneffectiveclimateadaptationstrategy.Adiversityofadaptationoptionsexists,includingmixedcrop-livestockproductionsystemswhichcanbeacost-effectiveadaptationstrategyinmanyglobalagriculturesystems(robustevidence,mediumagreement).Improvingirrigationefficiencycouldeffectivelydealwithchangingglobalwaterendowments,especiallyifachievedviafarmersadoptingnewbehavioursandwater-efficientpracticesratherthanthroughlarge-scaleinfrastructuralinterventions(mediumevidence,mediumagreement).Well-designedadaptationprocessessuchascommunity-basedadaptationcanbeeffectivedependinguponcontextandlevelsofvulnerability.{4.3.2,4.5.3} Improvingtheefficiencyoffoodproductionandclosingyieldgapshavethepotentialtoreduceemissionsfromagriculture,reducepressureonland,andenhancefoodsecurityandfuturemitigationpotential(highconfidence).Improvingproductivityofexistingagriculturalsystemsgenerallyreducestheemissionsintensityoffoodproductionandoffersstrongsynergieswithruraldevelopment,povertyreductionandfoodsecurityobjectives,butoptionstoreduceabsoluteemissionsarelimitedunlesspairedwithdemand-sidemeasures.Technologicalinnovationincludingbiotechnology,withadequatesafeguards,couldcontributetoresolvingcurrentfeasibilityconstraintsandexpandthefuturemitigationpotentialofagriculture. {4.3.2,4.4.4} Shiftsindietarychoicestowardsfoodswithloweremissionsandrequirementsforland,alongwithreducedfoodlossandwaste,couldreduceemissionsandincreaseadaptationoptions(highconfidence).Decreasingfoodlossandwasteandchangingdietarybehaviourcouldresultinmitigationandadaptation(highconfidence)byreducingbothemissionsandpressureonland,withsignificantco-benefitsforfoodsecurity,humanhealthandsustainabledevelopment{4.3.2,4.4.5,4.5.2,4.5.3,5.4.2},butevidenceofsuccessfulpoliciestomodifydietarychoicesremainslimited. MitigationandAdaptationOptionsandOtherMeasures Amixofmitigationandadaptationoptionsimplementedinaparticipatoryandintegratedmannercanenablerapid,systemictransitions–inurbanandruralareas–thatarenecessaryelementsofanacceleratedtransitionconsistentwithlimitingwarmingto1.5°C.Suchoptionsandchangesaremosteffectivewhenalignedwitheconomicandsustainabledevelopment,andwhenlocalandregionalgovernmentsaresupportedbynationalgovernments{4.3.3,4.4.1,4.4.3}.Variousmitigationoptionsareexpandingrapidlyacrossmanygeographies.Althoughmanyhavedevelopmentsynergies,notallincomegroupshavesofarbenefitedfromthem.Electrification,end-useenergyefficiencyandincreasedshareofrenewables,amongstotheroptions,areloweringenergyuseanddecarbonizingenergysupplyinthebuiltenvironment,especiallyinbuildings.Otherrapidchangesneededinurbanenvironmentsincludedemotorizationanddecarbonizationoftransport,includingtheexpansionofelectricvehicles,andgreateruseofenergy-efficientappliances(mediumevidence,highagreement).Technologicalandsocialinnovationscancontributetolimitingwarmingto1.5°C,forexample,byenablingtheuseofsmartgrids,energystoragetechnologiesandgeneral-purposetechnologies,suchasinformationandcommunicationtechnology(ICT)thatcanbedeployedtohelpreduceemissions.Feasibleadaptationoptionsincludegreeninfrastructure,resilientwaterandurbanecosystemservices,urbanandperi-urbanagriculture,andadaptingbuildingsandlandusethroughregulationandplanning(mediumevidence,mediumtohighagreement).{4.3.3,4.4.3,4.4.4} Synergiescanbeachievedacrosssystemictransitionsthroughseveraloverarchingadaptationoptionsinruralandurbanareas.Investmentsinhealth,socialsecurityandrisksharingandspreadingarecost-effectiveadaptationmeasureswithhighpotentialforscalingup(mediumevidence,mediumtohighagreement).Disasterriskmanagementandeducation-basedadaptationhavelowerprospectsofscalabilityandcost-effectiveness(mediumevidence,highagreement)butarecriticalforbuildingadaptivecapacity.{4.3.5,4.5.3} Convergingadaptationandmitigationoptionscanleadtosynergiesandpotentiallyincreasecost-effectiveness,butmultipletrade-offscanlimitthespeedofandpotentialforscalingup.Manyexamplesofsynergiesandtrade-offsexistinallsectorsandsystemtransitions.Forinstance,sustainablewatermanagement(highevidence,mediumagreement)andinvestmentingreeninfrastructure(mediumevidence,highagreement)todeliversustainablewaterandenvironmentalservicesandtosupporturbanagriculturearelesscost-effectivethanotheradaptationoptionsbutcanhelpbuildclimateresilience.Achievingthegovernance,financeandsocialsupportrequiredtoenablethesesynergiesandtoavoidtrade-offsisoftenchallenging,especiallywhenaddressingmultipleobjectives,andattemptingappropriatesequencingandtimingofinterventions.{4.3.2,4.3.4,4.4.1,4.5.2,4.5.3,4.5.4} ThoughCO2dominateslong-termwarming,thereductionofwarmingshort-livedclimateforcers(SLCFs),suchasmethaneandblackcarbon,canintheshorttermcontributesignificantlytolimitingwarmingto1.5°Cabovepre-industriallevels.Reductionsofblackcarbonandmethanewouldhavesubstantialco-benefits(highconfidence),includingimprovedhealthduetoreducedairpollution.This,inturn,enhancestheinstitutionalandsocio-culturalfeasibilityofsuchactions.ReductionsofseveralwarmingSLCFsareconstrainedbyeconomicandsocialfeasibility(lowevidence,highagreement).Astheyareoftenco-emittedwithCO2,achievingtheenergy,landandurbantransitionsnecessarytolimitwarmingto1.5°CwouldseeemissionsofwarmingSLCFsgreatlyreduced.{2.3.3.2,4.3.6} MostCDRoptionsfacemultiplefeasibilityconstraints,whichdifferbetweenoptions,limitingthepotentialforanysingleoptiontosustainablyachievethelarge-scaledeploymentrequiredinthe1.5°C-consistentpathwaysdescribedinChapter2(highconfidence).Those1.5°Cpathwaystypicallyrelyonbioenergywithcarboncaptureandstorage(BECCS),afforestationandreforestation(AR),orboth,toneutralizeemissionsthatareexpensivetoavoid,ortodrawdownCO2emissionsinexcessofthecarbonbudget{Chapter2}.ThoughBECCSandARmaybetechnicallyandgeophysicallyfeasible,theyfacepartiallyoverlappingyetdifferentconstraintsrelatedtolanduse.ThelandfootprintpertonneofCO2removedishigherforARthanforBECCS,butgiventhelowlevelsofcurrentdeployment,thespeedandscalesrequiredforlimitingwarmingto1.5°Cposeaconsiderableimplementationchallenge,eveniftheissuesofpublicacceptanceandabsenceofeconomicincentivesweretoberesolved(highagreement,mediumevidence).Thelargepotentialofafforestationandtheco-benefitsifimplementedappropriately(e.g.,onbiodiversityandsoilquality)willdiminishovertime,asforestssaturate(highconfidence).Theenergyrequirementsandeconomiccostsofdirectaircarboncaptureandstorage(DACCS)andenhancedweatheringremainhigh(mediumevidence,mediumagreement).Atthelocalscale,soilcarbonsequestrationhasco-benefitswithagricultureandiscost-effectiveevenwithoutclimatepolicy(highconfidence).Itspotentialfeasibilityandcost-effectivenessattheglobalscaleappearstobemorelimited.{4.3.7} Uncertaintiessurroundingsolarradiationmodification(SRM)measuresconstraintheirpotentialdeployment.Theseuncertaintiesinclude:technologicalimmaturity;limitedphysicalunderstandingabouttheireffectivenesstolimitglobalwarming;andaweakcapacitytogovern,legitimize,andscalesuchmeasures.Somerecentmodel-basedanalysissuggestsSRMwouldbeeffectivebutthatitistooearlytoevaluateitsfeasibility.Evenintheuncertaincasethatthemostadverseside-effectsofSRMcanbeavoided,publicresistance,ethicalconcernsandpotentialimpactsonsustainabledevelopmentcouldrenderSRMeconomically,sociallyandinstitutionallyundesirable(lowagreement,mediumevidence).{4.3.8,Cross-ChapterBox10inthischapter} EnablingRapidandFar-ReachingChange Thespeedoftransitionsandoftechnologicalchangerequiredtolimitwarmingto1.5°Cabovepre-industriallevelshasbeenobservedinthepastwithinspecificsectorsandtechnologies{4.2.2.1}.Butthegeographicalandeconomicscalesatwhichtherequiredratesofchangeintheenergy,land,urban,infrastructureandindustrialsystemswouldneedtotakeplacearelargerandhavenodocumentedhistoricprecedent(limitedevidence,mediumagreement).Toreduceinequalityandalleviatepoverty,suchtransformationswouldrequiremoreplanningandstrongerinstitutions(includinginclusivemarkets)thanobservedinthepast,aswellasstrongercoordinationanddisruptiveinnovationacrossactorsandscalesofgovernance.{4.3,4.4} Governanceconsistentwithlimitingwarmingto1.5°Candthepoliticaleconomyofadaptationandmitigationcanenableandacceleratesystemstransitions,behaviouralchange,innovationandtechnologydeployment(mediumevidence,mediumagreement).For1.5°C-consistentactions,aneffectivegovernanceframeworkwouldinclude:accountablemultilevelgovernancethatincludesnon-stateactors,suchasindustry,civilsocietyandscientificinstitutions;coordinatedsectoralandcross-sectoralpoliciesthatenablecollaborativemulti-stakeholderpartnerships;strengthenedglobal-to-localfinancialarchitecturethatenablesgreateraccesstofinanceandtechnology;addressingclimate-relatedtradebarriers;improvedclimateeducationandgreaterpublicawareness;arrangementstoenableacceleratedbehaviourchange;strengthenedclimatemonitoringandevaluationsystems;andreciprocalinternationalagreementsthataresensitivetoequityandtheSustainableDevelopmentGoals(SDGs).Systemtransitionscanbeenabledbyenhancingthecapacitiesofpublic,privateandfinancialinstitutionstoaccelerateclimatechangepolicyplanningandimplementation,alongwithacceleratedtechnologicalinnovation,deploymentandupkeep.{4.4.1,4.4.2,4.4.3,4.4.4} Behaviourchangeanddemand-sidemanagementcansignificantlyreduceemissions,substantiallylimitingtherelianceonCDRtolimitwarmingto1.5°C{Chapter2,4.4.3}.Politicalandfinancialstakeholdersmayfindclimateactionsmorecost-effectiveandsociallyacceptableifmultiplefactorsaffectingbehaviourareconsidered,includingaligningtheseactionswithpeople’scorevalues(mediumevidence,highagreement).Behaviour-andlifestyle-relatedmeasuresanddemand-sidemanagementhavealreadyledtoemissionreductionsaroundtheworldandcanenablesignificantfuturereductions(highconfidence).Socialinnovationthroughbottom-upinitiativescanresultingreaterparticipationinthegovernanceofsystemstransitionsandincreasesupportfortechnologies,practicesandpoliciesthatarepartoftheglobalresponsetolimitwarmingto1.5°C.{Chapter2,4.4.1,4.4.3,Figure4.3} Thisrapidandfar-reachingresponserequiredtokeepwarmingbelow1.5°Candenhancethecapacitytoadapttoclimateriskswouldrequirelargeincreasesofinvestmentsinlow-emissioninfrastructureandbuildings,alongwitharedirectionoffinancialflowstowardslow-emissioninvestments(robustevidence,highagreement).Anestimatedmeanannualincrementalinvestmentofaround1.5%ofglobalgrossfixedcapitalformation(GFCF)fortheenergysectorisindicatedbetween2016and2035,aswellasabout2.5%ofglobalGFCFforotherdevelopmentinfrastructurethatcouldalsoaddressSDGimplementation.Thoughqualitypolicydesignandeffectiveimplementationmayenhanceefficiency,theycannotfullysubstitutefortheseinvestments.{2.5.2,4.2.1,4.4.5} Enablingthisinvestmentrequiresthemobilizationandbetterintegrationofarangeofpolicyinstrumentsthatincludethereductionofsociallyinefficientfossilfuelsubsidyregimesandinnovativepriceandnon-pricenationalandinternationalpolicyinstruments.Thesewouldneedtobecomplementedbyde-riskingfinancialinstrumentsandtheemergenceoflong-termlow-emissionassets.Theseinstrumentswouldaimtoreducethedemandforcarbon-intensiveservicesandshiftmarketpreferencesawayfromfossilfuel-basedtechnology.Evidenceandtheorysuggestthatcarbonpricingalone,intheabsenceofsufficienttransferstocompensatetheirunintendeddistributionalcross-sector,cross-nationeffects,cannotreachtheincentivelevelsneededtotriggersystemtransitions(robustevidence,mediumagreement).But,embeddedinconsistentpolicypackages,theycanhelpmobilizeincrementalresourcesandprovideflexiblemechanismsthathelpreducethesocialandeconomiccostsofthetriggeringphaseofthetransition(robustevidence,mediumagreement).{4.4.3,4.4.4,4.4.5} Increasingevidencesuggeststhataclimate-sensitiverealignmentofsavingsandexpendituretowardslow-emission,climate-resilientinfrastructureandservicesrequiresanevolutionofglobalandnationalfinancialsystems.Estimatessuggestthat,inadditiontoclimate-friendlyallocationofpublicinvestments,apotentialredirectionof5%to10%oftheannualcapitalrevenues1isnecessaryforlimitingwarmingto1.5°C{4.4.5,Table1inBox4.8}.Thiscouldbefacilitatedbyachangeofincentivesforprivateday-to-dayexpenditureandtheredirectionofsavingsfromspeculativeandprecautionaryinvestmentstowardslong-termproductivelow-emissionassetsandservices.Thisimpliesthemobilizationofinstitutionalinvestorsandmainstreamingofclimatefinancewithinfinancialandbankingsystemregulation.Accessbydevelopingcountriestolow-riskandlow-interestfinancethroughmultilateralandnationaldevelopmentbankswouldhavetobefacilitated(mediumevidence,highagreement).Newformsofpublic–privatepartnershipsmaybeneededwithmultilateral,sovereignandsub-sovereignguaranteestode-riskclimate-friendlyinvestments,supportnewbusinessmodelsforsmall-scaleenterprisesandhelphouseholdswithlimitedaccesstocapital.Ultimately,theaimistopromoteaportfolioshifttowardslong-termlow-emissionassetsthatwouldhelpredirectcapitalawayfrompotentiallystrandedassets(mediumevidence,mediumagreement).{4.4.5} Knowledgegapsaroundimplementingandstrengtheningtheglobalresponsetoclimatechangewouldneedtobeurgentlyresolvedifthetransitiontoa1.5°Cworldistobecomereality.Remainingquestionsinclude:howmuchcanberealisticallyexpectedfrominnovationandbehaviouralandsystemicpoliticalandeconomicchangesinimprovingresilience,enhancingadaptationandreducingGHGemissions?Howcanratesofchangesbeacceleratedandscaledup?Whatistheoutcomeofrealisticassessmentsofmitigationandadaptationlandtransitionsthatarecompliantwithsustainabledevelopment,povertyeradicationandaddressinginequality?Whatarelife-cycleemissionsandprospectsofearly-stageCDRoptions?Howcanclimateandsustainabledevelopmentpoliciesconverge,andhowcantheybeorganisedwithinaglobalgovernanceframeworkandfinancialsystem,basedonprinciplesofjusticeandethics(including‘commonbutdifferentiatedresponsibilitiesandrespectivecapabilities’(CBDR-RC)),reciprocityandpartnership?Towhatextentwouldlimitingwarmingto1.5°Crequireaharmonizationofmacro-financialandfiscalpolicies,whichcouldincludefinancialregulatorssuchascentralbanks?Howcandifferentactorsandprocessesinclimategovernancereinforceeachother,andhedgeagainstthefragmentationofinitiatives?{4.1,4.3.7,4.4.1,4.4.5,4.6} Chapter5 Theinteractionsofclimatechangeandclimateresponseswithsustainabledevelopmentincludingsustainabledevelopmentimpactsat1.5°Cand2°C,thesynergiesandtradeoffsofmitigationandadaptationwiththeSustainableDevelopmentGoals/SDGs,andthepossibilitiesforsustainableandequitablelowcarbon,climate-resilientdevelopmentpathways, ExecutiveSummary View Download ExploreGraphics Thischaptertakessustainabledevelopmentasthestartingpointandfocusforanalysis.Itconsidersthebroadandmultifacetedbi-directionalinterplaybetweensustainabledevelopment,includingitsfocusoneradicatingpovertyandreducinginequalityintheirmultidimensionalaspects,andclimateactionsina1.5°Cwarmerworld.ThesefundamentalconnectionsareembeddedintheSustainableDevelopmentGoals(SDGs).Thechapteralsoexaminessynergiesandtrade-offsofadaptationandmitigationoptionswithsustainabledevelopmentandtheSDGsandoffersinsightsintopossiblepathways,especiallyclimate-resilientdevelopmentpathwaystowardsa1.5°Cwarmerworld. SustainableDevelopment,PovertyandInequalityina1.5°CWarmerWorld Limitingglobalwarmingto1.5°Cratherthan2°Cabovepre-industriallevelswouldmakeitmarkedlyeasiertoachievemanyaspectsofsustainabledevelopment,withgreaterpotentialtoeradicatepovertyandreduceinequalities(mediumevidence,highagreement).Impactsavoidedwiththelowertemperaturelimitcouldreducethenumberofpeopleexposedtoclimaterisksandvulnerabletopovertyby62to457million,andlessentherisksofpoorpeopletoexperiencefoodandwaterinsecurity,adversehealthimpacts,andeconomiclosses,particularlyinregionsthatalreadyfacedevelopmentchallenges(mediumevidence,mediumagreement).{5.2.2,5.2.3}Avoidedimpactsexpectedtooccurbetween1.5°Cand2°CwarmingwouldalsomakeiteasiertoachievecertainSDGs,suchasthosethatrelatetopoverty,hunger,health,waterandsanitation,citiesandecosystems(SDGs1,2,3,6,11,14and15)(mediumevidence,highagreement).{5.2.3,Table5.2availableattheendofthechapter} Comparedtocurrentconditions,1.5°Cofglobalwarmingwouldnonethelessposeheightenedriskstoeradicatingpoverty,reducinginequalitiesandensuringhumanandecosystemwell-being(mediumevidence,highagreement).Warmingof1.5°Cisnotconsidered‘safe’formostnations,communities,ecosystemsandsectorsandposessignificantriskstonaturalandhumansystemsascomparedtothecurrentwarmingof1°C(highconfidence).{Cross-ChapterBox12inChapter5}Theimpactsof1.5°Cofwarmingwoulddisproportionatelyaffectdisadvantagedandvulnerablepopulationsthroughfoodinsecurity,higherfoodprices,incomelosses,lostlivelihoodopportunities,adversehealthimpactsandpopulationdisplacements(mediumevidence,highagreement).{5.2.1}Someoftheworstimpactsonsustainabledevelopmentareexpectedtobefeltamongagriculturalandcoastaldependentlivelihoods,indigenouspeople,childrenandtheelderly,poorlabourers,poorurbandwellersinAfricancities,andpeopleandecosystemsintheArcticandSmallIslandDevelopingStates(SIDS)(mediumevidence,highagreement).{5.2.1,Box5.3,Chapter3,Box3.5,Cross-ChapterBox9inChapter4} ClimateAdaptationandSustainableDevelopment PrioritizationofsustainabledevelopmentandmeetingtheSDGsisconsistentwitheffortstoadapttoclimatechange(high confidence).Manystrategiesforsustainabledevelopmentenabletransformationaladaptationfora1.5°Cwarmerworld,providedattentionispaidtoreducingpovertyinallitsformsandtopromotingequityandparticipationindecision-making(mediumevidence,highagreement).Assuch,sustainabledevelopmenthasthepotentialtosignificantlyreducesystemicvulnerability,enhanceadaptivecapacity,andpromotelivelihoodsecurityforpooranddisadvantagedpopulations(highconfidence).{5.3.1} SynergiesbetweenadaptationstrategiesandtheSDGsareexpectedtoholdtrueina1.5°Cwarmerworld,acrosssectors andcontexts(mediumevidence,mediumagreement).Synergiesbetweenadaptationandsustainabledevelopmentaresignificantforagricultureandhealth,advancingSDGs1(extremepoverty),2(hunger),3(healthylivesandwell-being)and6(cleanwater)(robustevidence,mediumagreement).{5.3.2}Ecosystem-andcommunity-basedadaptation,alongwiththeincorporationofindigenousandlocalknowledge,advancessynergieswithSDGs5(genderequality),10(reducinginequalities)and16(inclusivesocieties),asexemplifiedindrylandsandtheArctic(highevidence,mediumagreement).{5.3.2,Box5.1,Cross-ChapterBox10inChapter4} Adaptation strategies can resultin  trade-offs  with  andamongtheSDGs(mediumevidence,highagreement).StrategiesthatadvanceoneSDGmaycreatenegativeconsequencesforotherSDGs,forinstanceSDGs3(health)versus7(energyconsumption)andagriculturaladaptationandSDG2(foodsecurity)versusSDGs3(health),5(genderequality),6(cleanwater),10(reducinginequalities),14(lifebelowwater)and15(lifeontheland)(mediumevidence,mediumagreement).{5.3.2} Pursuing place-specific adaptation pathways  towards  a  1.5°Cwarmerworldhasthepotentialforsignificantpositiveoutcomesforwell-beingincountriesatalllevelsofdevelopment(mediumevidence,highagreement).Positiveoutcomesemergewhenadaptationpathways(i)ensureadiversityofadaptationoptionsbasedonpeople’svaluesandthetrade-offstheyconsideracceptable,(ii)maximizesynergieswithsustainabledevelopmentthroughinclusive,participatoryanddeliberativeprocesses,and(iii)facilitateequitabletransformation.Yetsuchpathwayswouldbedifficulttoachievewithoutredistributivemeasurestoovercomepathdependencies,unevenpowerstructures,andentrenchedsocialinequalities(mediumevidence,highagreement).{5.3.3} MitigationandSustainableDevelopment Thedeploymentofmitigationoptionsconsistentwith1.5°Cpathwaysleadstomultiplesynergiesacrossarangeofsustainabledevelopmentdimensions.At the same time, therapidpaceandmagnitudeofchangethatwouldberequiredtolimitwarmingto1.5°C,ifnotcarefullymanaged,wouldleadtotrade-offswithsomesustainabledevelopmentdimensions(highconfidence).Thenumberofsynergiesbetweenmitigationresponseoptionsandsustainabledevelopmentexceedsthenumberoftrade-offsinenergydemandandsupplysectors;agriculture,forestryandotherlanduse(AFOLU);andforoceans(veryhighconfidence).{Figure5.2,Table5.2availableattheendofthechapter}The1.5°Cpathwaysindicaterobustsynergies,particularlyfortheSDGs3(health),7(energy),12(responsibleconsumptionandproduction)and14(oceans)(veryhighconfidence).{5.4.2,Figure5.3}ForSDGs1(poverty),2(hunger),6(water)and7(energy),thereisariskoftrade-offsornegativesideeffectsfromstringentmitigationactionscompatiblewith1.5°Cofwarming(mediumevidence,highagreement).{5.4.2} AppropriatelydesignedmitigationactionstoreduceenergydemandcanadvancemultipleSDGssimultaneously.Pathwayscompatiblewith1.5°Cthatfeaturelowenergydemandshowthemostpronouncedsynergiesandthelowestnumberoftrade-offswithrespecttosustainabledevelopmentandtheSDGs(veryhighconfidence).AcceleratingenergyefficiencyinallsectorshassynergieswithSDGs7(energy),9(industry,innovationandinfrastructure),11(sustainablecitiesandcommunities),12(responsibleconsumptionandproduction),16(peace,justiceandstronginstitutions),and17(partnershipsforthegoals)(robustevidence,highagreement).{5.4.1,Figure5.2,Table5.2}Low-demandpathways,whichwouldreduceorcompletelyavoidtherelianceonbioenergywithcarboncaptureandstorage(BECCS)in1.5°Cpathways,wouldresultinsignificantlyreducedpressureonfoodsecurity,lowerfoodpricesandfewerpeopleatriskofhunger(mediumevidence,highagreement).{5.4.2,Figure5.3} TheimpactsofcarbondioxideremovaloptionsonSDGsdependonthetypeofoptionsandthescaleofdeployment(highconfidence).Ifpoorlyimplemented,carbondioxideremoval(CDR)optionssuchasbioenergy,BECCSandAFOLUwouldleadtotrade-offs.Appropriatedesignandimplementationrequiresconsideringlocalpeople’sneeds,biodiversityandothersustainabledevelopmentdimensions(veryhighconfidence).{5.4.1.3,Cross-ChapterBox7inChapter3} Thedesignofthemitigationportfoliosandpolicyinstruments    tolimitwarmingto1.5°Cwilllargelydeterminetheoverallsynergiesandtrade-offsbetweenmitigationandsustainabledevelopment(veryhighconfidence).Redistributivepoliciesthatshieldthepoorandvulnerablecanresolvetrade-offsforarangeofSDGs(mediumevidence,highagreement).IndividualmitigationoptionsareassociatedwithbothpositiveandnegativeinteractionswiththeSDGs(veryhighconfidence).{5.4.1}However,appropriatechoicesacrossthemitigationportfoliocanhelptomaximizepositivesideeffectswhileminimizingnegativesideeffects(highconfidence).{5.4.2,5.5.2}Investmentneedsforcomplementarypoliciesresolvingtrade-offswitharangeofSDGsareonlyasmallfractionoftheoverallmitigationinvestmentsin1.5°Cpathways(mediumevidence,highagreement).{5.4.2,Figure5.4}Integrationofmitigationwithadaptationandsustainabledevelopmentcompatiblewith1.5°Cwarmingrequiresasystemsperspective(highconfidence).{5.4.2,5.5.2} Mitigationconsistentwith1.5°Cofwarming create high risks forsustainabledevelopmentincountrieswithhighdependency onfossilfuelsforrevenueandemploymentgeneration(highconfidence).Theserisksarecausedbythereductionofglobaldemandaffectingminingactivityandexportrevenuesandchallengestorapidlydecreasehighcarbonintensityofthedomesticeconomy(robustevidence,highagreement).{5.4.1.2,Box5.2}Targetedpoliciesthatpromotediversificationoftheeconomyandtheenergysectorcouldeasethistransition(mediumevidence,highagreement).{5.4.1.2,Box5.2} SustainableDevelopmentPathwaysto1.5°C Sustainabledevelopmentbroadlysupportsandoften enables thefundamentalsocietalandsystems transformationsthat wouldberequiredforlimitingwarmingto1.5°Cabovepre-industriallevels(highconfidence).Simulatedpathwaysthatfeaturethemostsustainableworlds(e.g.,SharedSocio-EconomicPathways(SSP)1)areassociatedwithrelativelylowermitigationandadaptationchallengesandlimitwarmingto1.5°Catcomparativelylowermitigationcosts.Incontrast,developmentpathwayswithhighfragmentation,inequalityandpoverty(e.g.,SSP3)areassociatedwithcomparativelyhighermitigationandadaptationchallenges.Insuchpathways,itisnotpossibletolimitwarmingto1.5°Cforthevastmajorityoftheintegratedassessmentmodels(mediumevidence,highagreement).{5.5.2}InallSSPs,mitigationcostssubstantiallyincreasein1.5°Cpathwayscomparedto2°Cpathways.Nopathwayintheliteratureintegratesorachievesall17SDGs(highconfidence).{5.5.2}Real-worldexperiencesattheprojectlevelshowthattheactualintegrationbetweenadaptation,mitigationandsustainabledevelopmentischallengingasitrequiresreconcilingtrade-offsacrosssectorsandspatialscales(veryhighconfidence).{5.5.1} Without  societal  transformation  and   rapid   implementationof ambitious greenhouse gas  reduction  measures, pathwaystolimitingwarmingto1.5°Candachievingsustainabledevelopment will be exceedingly difficult, if  not  impossible,toachieve(highconfidence).Thepotentialforpursuingsuchpathwaysdiffersbetweenandwithinnationsandregions,duetodifferentdevelopmenttrajectories,opportunitiesandchallenges(veryhighconfidence).{5.5.3.2,Figure5.1}Limitingwarmingto1.5°Cwouldrequireallcountriesandnon-stateactorstostrengthentheircontributionswithoutdelay.Thiscouldbeachievedthroughsharingeffortsbasedonbolderandmorecommittedcooperation,withsupportforthosewiththeleastcapacitytoadapt,mitigateandtransform(mediumevidence,highagreement).{5.5.3.1,5.5.3.2}Currenteffortstowardsreconcilinglow-carbontrajectoriesandreducinginequalities,includingthosethatavoiddifficulttrade-offsassociatedwithtransformation,arepartiallysuccessfulyetdemonstratenotableobstacles(mediumevidence,mediumagreement).{5.5.3.3,Box5.3,Cross-ChapterBox13inthischapter} Socialjusticeandequityarecoreaspectsofclimate-resilientdevelopmentpathwaysfortransformationalsocialchange.Addressingchallenges and widening opportunities betweenand within countries and communities would be necessary  toachievesustainable development and limit warming to 1.5°C,withoutmakingthepooranddisadvantagedworse off(highconfidence).Identifyingandnavigatinginclusiveandsociallyacceptablepathwaystowardslow-carbon,climate-resilientfuturesisachallengingyetimportantendeavour,fraughtwithmoral,practicalandpoliticaldifficultiesandinevitabletrade-offs(veryhighconfidence).{5.5.2,5.5.3.3,Box5.3}Itentailsdeliberationand problem-solvingprocessestonegotiatesocietalvalues,well-being,risksandresilienceandtodeterminewhatisdesirableandfair,andtowhom(mediumevidence,highagreement).Pathwaysthatencompassjoint,iterativeplanningandtransformativevisions,forinstanceinPacificSIDSlikeVanuatuandinurbancontexts,showpotentialforliveableandsustainablefutures(highconfidence).{5.5.3.1,5.5.3.3,Figure5.5,Box5.3,Cross-ChapterBox13inthischapter} Thefundamentalsocietalandsystemicchangestoachievesustainabledevelopment,eradicatepovertyandreduceinequalitieswhilelimitingwarmingto1.5°Cwouldrequire meetingasetofinstitutional,social,cultural,economicandtechnologicalconditions(highconfidence).The coordinationandmonitoringofpolicyactionsacrosssectorsandspatialscalesisessentialtosupportsustainabledevelopmentin1.5°Cwarmerconditions(veryhighconfidence).{5.6.2,Box5.3}Externalfundingandtechnologytransferbettersupporttheseeffortswhentheyconsiderrecipients’context-specificneeds(mediumevidence,highagreement).{5.6.1}Inclusiveprocessescanfacilitatetransformationsbyensuringparticipation,transparency,capacitybuildinganditerativesociallearning(highconfidence).{5.5.3.3,Cross-ChapterBox13,5.6.3}Attentiontopowerasymmetriesandunequalopportunitiesfordevelopment,amongandwithincountries,iskeytoadopting1.5°C-compatibledevelopmentpathwaysthatbenefitallpopulations(highconfidence).{5.5.3,5.6.4,Box5.3}Re-examiningindividualandcollectivevaluescouldhelpspururgent,ambitiousandcooperativechange(mediumevidence,highagreement).{5.5.3,5.6.5} Glossary ThisglossarydefinessomespecifictermsastheLeadAuthorsintendthemtobeinterpretedinthecontextofthisreport.Blue,italicizedwordsindicatethatthetermisdefinedintheGlossary. Notethatsubtermsareinitalicsbeneathmainterms. View View Download ExploreGraphics SPM SummaryforPolicymakers 1 FramingandContext 2 Mitigationpathwayscompatiblewith1.5°Cinthecontextofsustainabledevelopment 3 Impactsof1.5ºCglobalwarmingonnaturalandhumansystems 4 Strengtheningandimplementingtheglobalresponse 5 SustainableDevelopment,PovertyEradicationandReducingInequalities G Glossary SPM Chapter1 Chapter2 Chapter3 Chapter4 Chapter5 Glossary SummaryforPolicymakers Viewchapter IIntroductionAUnderstandingGlobalWarmingof1.5°C*BProjectedClimateChange,PotentialImpactsandAssociatedRisksCEmissionPathwaysandSystemTransitionsConsistentwith1.5°CGlobalWarmingDStrengtheningtheGlobalResponseintheContextofSustainableDevelopmentandEffortstoEradicatePoverty+CoreConceptsCentraltothisSpecialReport+Acknowledgements+CitationSDSPMDownloads FramingandContext Viewchapter ESExecutiveSummaryXCitation1.1AssessingtheKnowledgeBasefora1.5°CWarmerWorld1.1.1Equityanda1.5°CWarmerWorld1.1.2EradicationofPoverty1.1.3SustainableDevelopmentanda1.5°CWarmerWorld1.2Understanding1.5°C:ReferenceLevels,Probability,Transience,Overshoot,andStabilization1.2.1WorkingDefinitionsof1.5°Cand2°CWarmingRelativetoPre-IndustrialLevels1.2.1.1Definitionofglobalaveragetemperature1.2.1.2Choiceofreferenceperiod1.2.1.3Totalversushuman-inducedwarmingandwarmingrates1.2.2GlobalversusRegionalandSeasonalWarming1.2.3Definitionof1.5°CPathways:Probability,Transience,StabilizationandOvershoot1.2.3.1Pathwaysremainingbelow1.5°C1.2.3.2Pathwaystemporarilyexceeding1.5°C1.2.3.3Impactsat1.5°Cwarmingassociatedwithdifferentpathways:transienceversusstabilisation1.2.4GeophysicalWarmingCommitment1.3Impactsat1.5°CandBeyond1.3.1Definitions1.3.2DriversofImpacts1.3.3UncertaintyandNon-LinearityofImpacts1.4StrengtheningtheGlobalResponse1.4.1ClassifyingResponseOptions1.4.2Governance,ImplementationandPolicies1.4.3Transformation,TransformationPathways,andTransition:EvaluatingTrade-OffsandSynergiesBetweenMitigation,AdaptationandSustainableDevelopmentGoals1.5AssessmentFrameworksandEmergingMethodologiesthatIntegrateClimateChangeMitigationandAdaptationwithSustainableDevelopment1.5.1KnowledgeSourcesandEvidenceUsedintheReport1.5.2AssessmentFrameworksandMethodologies1.6Confidence,UncertaintyandRisk1.7StorylineoftheReportFAQsFrequentlyAskedQuestionsSMSupplementaryMaterialCDChapterDownloads Mitigationpathwayscompatiblewith1.5°Cinthecontextofsustainabledevelopment Viewchapter ESExecutiveSummaryXCitation2.1IntroductiontoMitigationPathwaysandtheSustainableDevelopmentContext2.1.1MitigationPathwaysConsistentwith1.5°C2.1.2TheUseofScenarios2.1.3NewScenarioInformationsinceAR52.1.4UtilityofIntegratedAssessmentModels(IAMs)intheContextofthisReport2.2GeophysicalRelationshipsandConstraints2.2.1GeophysicalCharacteristicsofMitigationPathways2.2.1.1Geophysicaluncertainties:non-CO2forcingagents2.2.1.2Geophysicaluncertainties:climateandEarthsystemfeedbacks2.2.2TheRemaining1.5°CCarbonBudget2.2.2.1Carbonbudgetestimates2.2.2.2CO2andnon-CO2contributionstotheremainingcarbonbudget2.3Overviewof1.5°CMitigationPathways2.3.1RangeofAssumptionsUnderlying1.5°CPathways2.3.1.1Socio-economicdriversandthedemandforenergyandlandin1.5°Cpathways2.3.1.2Mitigationoptionsin1.5°Cpathways2.3.1.3Policyassumptionsin1.5°Cpathways2.3.2KeyCharacteristicsof1.5°CPathways2.3.2.1Variationinsystemtransformationsunderlying1.5°Cpathways2.3.2.2Pathwayskeepingwarmingbelow1.5°Cortemporarilyovershootingit2.3.3EmissionsEvolutionin1.5°CPathways2.3.3.1Emissionsoflong-livedclimateforcers2.3.3.2Emissionsofshort-livedclimateforcersandfluorinatedgases2.3.4CDRin1.5°CPathways2.3.4.1CDRtechnologiesanddeploymentlevelsin1.5°Cpathways2.3.4.2SustainabilityimplicationsofCDRdeploymentin1.5°Cpathways2.3.5ImplicationsofNear-TermActionin1.5°CPathways2.4DisentanglingtheWhole-SystemTransformation2.4.1EnergySystemTransformation2.4.2EnergySupply2.4.2.1Evolutionofprimaryenergycontributionsovertime2.4.2.2Evolutionofelectricitysupplyovertime2.4.2.3Deploymentofcarboncaptureandstorage2.4.3EnergyEnd-UseSectors2.4.3.1Industry2.4.3.2Buildings2.4.3.3Transport2.4.4Land-UseTransitionsandChangesintheAgriculturalSector2.5Challenges,OpportunitiesandCo-ImpactsofTransformativeMitigationPathways2.5.1PolicyFrameworksandEnablingConditions2.5.2EconomicandInvestmentImplicationsof1.5°CPathways2.5.2.1Priceofcarbonemissions2.5.2.2Investments2.5.3SustainableDevelopmentFeaturesof1.5°CPathways2.6KnowledgeGaps2.6.1GeophysicalUnderstanding2.6.2IntegratedAssessmentApproaches2.6.3CarbonDioxideRemoval(CDR)FAQsFrequentlyAskedQuestionsSMSupplementaryMaterialCDChapterDownloads Impactsof1.5ºCglobalwarmingonnaturalandhumansystems Viewchapter ESExecutiveSummaryXCitation3.1AbouttheChapter3.2HowareRisksat1.5°CandHigherLevelsofGlobalWarmingAssessedinthisChapter?3.2.1HowareChangesinClimateandWeatherat1.5°CversusHigherLevelsofWarmingAssessed?3.2.2HowarePotentialImpactsonEcosystemsAssessedat1.5°CversusHigherLevelsofWarming?3.3GlobalandRegionalClimateChangesandAssociatedHazards3.3.1GlobalChangesinClimate3.3.2RegionalTemperaturesonLand,IncludingExtremes3.3.2.1Observedandattributedchangesinregionaltemperaturemeansandextremes3.3.2.2Projectedchangesinregionaltemperaturemeansandextremesat1.5°Cversus2°Cofglobalwarming3.3.3RegionalPrecipitation,IncludingHeavyPrecipitationandMonsoons3.3.3.1Observedandattributedchangesinregionalprecipitation3.3.3.2Projectedchangesinregionalprecipitationat1.5°Cversus2°Cofglobalwarming3.3.4DroughtandDryness3.3.4.1Observedandattributedchanges3.3.4.2Projectedchangesindroughtanddrynessat1.5°Cversus2°C3.3.5RunoffandFluvialFlooding3.3.5.1Observedandattributedchangesinrunoffandriverflooding3.3.5.2Projectedchangesinrunoffandriverfloodingat1.5°Cversus2°Cofglobalwarming3.3.6TropicalCyclonesandExtratropicalStorms3.3.7OceanCirculationandTemperature3.3.8SeaIce3.3.9SeaLevel3.3.10OceanChemistry3.3.11GlobalSynthesis3.4ObservedImpactsandProjectedRisksinNaturalandHumanSystems3.4.1Introduction3.4.2FreshwaterResources(QuantityandQuality)3.4.2.1Wateravailability3.4.2.2Extremehydrologicalevents(floodsanddroughts)3.4.2.3Groundwater3.4.2.4Waterquality3.4.2.5Soilerosionandsedimentload3.4.3TerrestrialandWetlandEcosystems3.4.3.1Biomeshifts3.4.3.2Changesinphenology3.4.3.3Changesinspeciesrange,abundanceandextinction3.4.3.4Changesinecosystemfunction,biomassandcarbonstocks3.4.3.5Regionalandecosystem-specificrisks3.4.3.6Summaryofimplicationsforecosystemservices3.4.4OceanEcosystems3.4.4.1Observedimpacts3.4.4.2Warmingandstratificationofthesurfaceocean3.4.4.3Stormsandcoastalrunoff3.4.4.4Oceancirculation3.4.4.5Oceanacidification3.4.4.6Deoxygenation3.4.4.7Lossofseaice3.4.4.8Sealevelrise3.4.4.9Projectedrisksandadaptationoptionsforoceansunderglobalwarmingof1.5°Cor2°Cabovepre-industriallevels3.4.4.10Frameworkorganisms(tropicalcorals,mangrovesandseagrass)3.4.4.11Oceanfoodwebs(pteropods,bivalves,krillandfinfish)3.4.4.12Keyecosystemservices(e.g.,carbonuptake,coastalprotection,andtropicalcoralreefrecreation)3.4.5CoastalandLow-LyingAreas,andSeaLevelRise3.4.5.1Global/sub-globalscale3.4.5.2Cities3.4.5.3Smallislands3.4.5.4Deltasandestuaries3.4.5.5Wetlands3.4.5.6Othercoastalsettings3.4.5.7Adaptingtocoastalchange3.4.6Food,NutritionSecurityandFoodProductionSystems(IncludingFisheriesandAquaculture)3.4.6.1Cropproduction3.4.6.2Livestockproduction3.4.6.3Fisheriesandaquacultureproduction3.4.7HumanHealth3.4.7.1Projectedriskat1.5°Cand2°Cofglobalwarming3.4.8UrbanAreas3.4.9KeyEconomicSectorsandServices3.4.9.1Tourism3.4.9.2Energysystems3.4.9.3Transportation3.4.10LivelihoodsandPoverty,andtheChangingStructureofCommunities3.4.10.1Livelihoodsandpoverty3.4.10.2Thechangingstructureofcommunities:migration,displacementandconflict3.4.11InteractingandCascadingRisks3.4.12SummaryofProjectedRisksat1.5°Cand2°CofGlobalWarming3.4.13SynthesisofKeyElementsofRisk3.5AvoidedImpactsandReducedRisksat1.5°CComparedwith2°CofGlobalWarming3.5.1Introduction3.5.2 AggregatedAvoidedImpactsandReducedRisksat1.5°Cversus2°CofGlobalWarming3.5.2.1RFC1–Uniqueandthreatenedsystems3.5.2.2RFC2–Extremeweatherevents3.5.2.3RFC3–Distributionofimpacts3.5.2.4RFC4–Globalaggregateimpacts3.5.2.5RFC5–Large-scalesingularevents3.5.3 RegionalEconomicBenefitAnalysisforthe1.5°Cversus2°CGlobalGoals3.5.4 ReducingHotspotsofChangefor1.5°Cand2°CofGlobalWarming3.5.4.1Arcticseaice3.5.4.2Arcticlandregions3.5.4.3Alpineregions3.5.4.4SoutheastAsia3.5.4.5SouthernEuropeandtheMediterranean3.5.4.6WestAfricaandtheSahel3.5.4.7SouthernAfrica3.5.4.8Tropics3.5.4.9Smallislands3.5.4.10Fynbosandshrubbiomes3.5.5 AvoidingRegionalTippingPointsbyAchievingMoreAmbitiousGlobalTemperatureGoals3.5.5.1Arcticseaice3.5.5.2Tundra3.5.5.3Permafrost3.5.5.4Asianmonsoon3.5.5.5WestAfricanmonsoonandtheSahel3.5.5.6Rainforests3.5.5.7Borealforests3.5.5.8Heatwaves,unprecedentedheatandhumanhealth3.5.5.9Agriculturalsystems:keystaplecrops3.5.5.10Agriculturalsystems:livestockinthetropicsandsubtropics3.6ImplicationsofDifferent1.5°Cand2°CPathways3.6.1GradualversusOvershootin1.5°CScenarios3.6.2Non-CO2ImplicationsandProjectedRisksofMitigationPathways3.6.2.1Risksarisingfromland-usechangesinmitigationpathways3.6.2.2Biophysicalfeedbacksonregionalclimateassociatedwithland-usechanges3.6.2.3Atmosphericcompounds(aerosolsandmethane)3.6.3ImplicationsBeyondtheEndoftheCentury3.6.3.1Seaice3.6.3.2Sealevel3.6.3.3Permafrost3.7KnowledgeGaps3.7.1 GapsinMethodsandTools3.7.2 GapsinUnderstanding3.7.2.1Earthsystemsand1.5°Cofglobalwarming3.7.2.2Physicalandchemicalcharacteristicsofa1.5°Cwarmerworld3.7.2.3Terrestrialandfreshwatersystems3.7.2.4OceanSystems3.7.2.5HumansystemsFAQsFrequentlyAskedQuestionsSMSupplementaryMaterialCDChapterDownloads Strengtheningandimplementingtheglobalresponse Viewchapter ESExecutiveSummaryXCitation4.1AcceleratingtheGlobalResponsetoClimateChange4.2PathwaysCompatiblewith1.5°C:StartingPointsforStrengtheningImplementation4.2.1 ImplicationsforImplementationof1.5°C-ConsistentPathways4.2.1.1ChallengesandOpportunitiesforMitigationAlongtheReviewedPathways4.2.1.2 ImplicationsforAdaptationAlongtheReviewedPathways4.2.2SystemTransitionsandRatesofChange4.2.2.1Mitigation:historicalratesofchangeandstateofdecoupling4.2.2.2Transformationaladaptation4.2.2.3Disruptiveinnovation4.3SystemicChangesfor1.5°C-ConsistentPathways4.3.1EnergySystemTransitions4.3.1.1 Renewableelectricity:solarandwind4.3.1.2Bioenergyandbiofuels4.3.1.3Nuclearenergy4.3.1.4Energystorage4.3.1.5Optionsforadaptingelectricitysystemsto1.5°C4.3.1.6Carbondioxidecaptureandstorageinthepowersector4.3.2 LandandEcosystemTransitions4.3.2.1Agricultureandfood4.3.2.2Forestsandotherecosystems4.3.2.3Coastalsystems4.3.3 UrbanandInfrastructureSystemTransitions4.3.3.1Urbanenergysystems4.3.3.2Urbaninfrastructure,buildingsandappliances4.3.3.3Urbantransportandurbanplanning4.3.3.4Electrificationofcitiesandtransport4.3.3.5Shipping,freightandaviation4.3.3.6Climate-resilientlanduse4.3.3.8Sustainableurbanwaterandenvironmentalservices4.3.3.7Greenurbaninfrastructureandecosystemservices4.3.4IndustrialSystemsTransitions4.3.4.1Energyefficiency4.3.4.2Substitutionandcircularity4.3.4.3Bio-basedfeedstocks4.3.4.4Electrificationandhydrogen4.3.4.5CO2capture,utilizationandstorageinindustry4.3.5OverarchingAdaptationOptionsSupportingAdaptationTransitions4.3.5.1Disasterriskmanagement(DRM)4.3.5.2Risksharingandspreading4.3.5.3Educationandlearning4.3.5.4Populationhealthandhealthsystemadaptationoptions4.3.5.5Indigenousknowledge4.3.5.6Humanmigration4.3.5.7Climateservices4.3.6Short-LivedClimateForcers4.3.7 CarbonDioxideRemoval(CDR)4.3.7.1Bioenergywithcarboncaptureandstorage(BECCS)4.3.7.2 Afforestationandreforestation(AR)4.3.7.3 Soilcarbonsequestrationandbiochar4.3.7.4Enhancedweathering(EW)andoceanalkalinization4.3.7.5Directaircarbondioxidecaptureandstorage(DACCS)4.3.7.6Oceanfertilization4.3.8SolarRadiationModification(SRM)4.3.8.1Governanceandinstitutionalfeasibility4.3.8.2Economicandtechnologicalfeasibility4.3.8.3Socialacceptabilityandethics4.4ImplementingFar-ReachingandRapidChange4.4.1EnhancingMultilevelGovernance4.4.1.1Institutionsandtheircapacitytoinvokefar-reachingandrapidchange4.4.1.2Internationalgovernance4.4.1.3Sub-nationalgovernance4.4.1.4Interactionsandprocessesformultilevelgovernance4.4.2EnhancingInstitutionalCapacities4.4.2.1Capacityforpolicydesignandimplementation4.4.2.2Monitoring,reporting,andreviewinstitutions4.4.2.3Financialinstitutions4.4.2.4Co-operativeinstitutionsandsocialsafetynets4.4.3 EnablingLifestyleandBehaviouralChange4.4.3.1Factorsrelatedtoclimateactions4.4.3.2Strategiesandpoliciestopromoteactionsonclimatechange4.4.3.3Acceptabilityofpolicyandsystemchanges4.4.4EnablingTechnologicalInnovation4.4.4.1Thenatureoftechnologicalinnovations4.4.4.2Technologiesasenablersofclimateaction4.4.4.3Theroleofgovernmentin1.5°C-consistentclimatetechnologypolicy4.4.4.4TechnologytransferintheParisAgreement4.4.5StrengtheningPolicyInstrumentsandEnablingClimateFinance4.4.5.1Thecorechallenge:cost-efficiency,coordinationofexpectationsanddistributiveeffects4.4.5.2Carbonpricing:necessityandconstraints4.4.5.3Regulatorymeasuresandinformationflows4.4.5.4Scalingupclimatefinanceandde-riskinglow-emissioninvestments4.4.5.5Financialchallengeforbasicneedsandadaptationfinance4.4.5.6Towardsintegratedpolicypackagesandinnovativeformsoffinancialcooperation4.5IntegrationandEnablingTransformation4.5.1 AssessingFeasibilityofOptionsforAcceleratedTransitions4.5.2ImplementingMitigation4.5.2.1Assessingmitigationoptionsforlimitingwarmingto1.5˚CagainstfeasibilitydimensionsEnablingconditionsforimplementationofmitigationoptionstowards1.5˚C4.5.3ImplementingAdaptation4.5.3.1Feasibleadaptationoptions4.5.3.2Monitoringandevaluation4.5.4 SynergiesandTrade-OffsbetweenAdaptationandMitigation4.6KnowledgeGapsandKeyUncertaintiesFAQsFrequentlyAskedQuestionsSMSupplementaryMaterialCDChapterDownloads SustainableDevelopment,PovertyEradicationandReducingInequalities Viewchapter ESExecutiveSummaryXCitation5.1ScopeandDelineations5.1.1SustainableDevelopment,SDGs,PovertyEradicationandReducingInequalities5.1.2Pathwaysto1.5°C5.1.3TypesofEvidence5.2Poverty,EqualityandEquityImplicationsofa1.5°CWarmerWorld5.2.1ImpactsandRisksofa1.5°CWarmerWorld:ImplicationsforPovertyandLivelihoods5.2.2AvoidedImpactsof1.5°Cversus2°CWarmingforPovertyandInequality5.2.3Risksfrom1.5°Cversus2°CGlobalWarmingandtheSustainableDevelopmentGoals5.3ClimateAdaptationandSustainableDevelopment5.3.1SustainableDevelopmentinSupportofClimateAdaptation5.3.2SynergiesandTrade-OffsbetweenAdaptationOptionsandSustainableDevelopment5.3.3AdaptationPathwaystowardsa1.5°CWarmerWorldandImplicationsforInequalities5.4MitigationandSustainableDevelopment5.4.1SynergiesandTrade-OffsbetweenMitigationOptionsandSustainableDevelopment5.4.1.1EnergyDemand:MitigationOptionstoAccelerateReductioninEnergyUseandFuelSwitch5.4.1.2EnergySupply:AcceleratedDecarbonization5.4.1.3Land-basedagriculture,forestryandocean:mitigationresponseoptionsandcarbondioxideremoval5.4.2SustainableDevelopmentImplicationsof1.5°Cand2°CMitigationPathways5.4.2.1Airpollutionandhealth5.4.2.2Foodsecurityandhunger5.4.2.3Lackofenergyaccess/energypoverty5.4.2.4Watersecurity5.5SustainableDevelopmentPathwaysto1.5°C5.5.1IntegrationofAdaptation,MitigationandSustainableDevelopment5.5.2PathwaysforAdaptation,MitigationandSustainableDevelopment5.5.3Climate-ResilientDevelopmentPathways5.5.3.1Transformations,equityandwell-being5.5.3.2Developmenttrajectories,sharingofeffortsandcooperation5.5.3.3Countryandcommunitystrategiesandexperiences5.6ConditionsforAchievingSustainableDevelopment,EradicatingPovertyandReducingInequalitiesin1.5°CWarmerWorlds5.6.1FinanceandTechnologyAlignedwithLocalNeeds5.6.2IntegrationofInstitutions5.6.3InclusiveProcesses5.6.4AttentiontoIssuesofPowerandInequality5.6.5ReconsideringValues5.7SynthesisandResearchGapsFAQsFrequentlyAskedQuestionsCDChapterDownloads Glossary Viewchapter Citation123ABCDEFGHIJKLMNOPQRSTUVWXYZGDGlossaryDownloads