世界银行-气候变化适应：证据说明了什么？（英）-2024.3_市场营销策划_2024年市场报告-3月.docx

PaUO1.nnValnsoosQ.2-qndPolicyResearchWorkingPaper10729ClimateChangeAdaptationWhatDoestheEvidenceSay?PZ'OfnValnsoosQ.2-qndJonahRexerSiddharthSharmaworldBankgroupSouthAsiaRegionOfficeoftheChiefEconomistMarch2024Poi.icyRESEARCHWorkingPaper10729AbstractAdaPtingtoclimatechangeisanincreasinglyurgentpolicypriorityinlower-andmiddle-incomecountries.Thissystematicreviewsummarizesthecurrentstateoftheliteratureonadaptationtoclimatechange,andconductsaquantitativemcta-analysisoftheeffectivenessofclimateadaptation.ThCmcta-analysisrevealsthatObSCrVCdadaptationsoffset46percentofclimatelossesonaverage,withfirmsusingmoreeffectiveadaptationstrategicsthanhouseholdsandfarmers.Thereviewidentifiesseveralkeylessons.First,purelyprivateadaptationstoclimateshockstendtobelesseffectivethanthosefrompublicinfrastructureandservices,althoughneitherbyitselfisgenerallysufficienttofullyoffsettheeffectsofclimatechange.Second,someadaptationsmayreduceclimatelossesinthepresent,butinthelong-run,households,firms,andfarmersmightbebcttcr-sencdbyreducingtheirclimateexposure.Third,theliteraturetendstofocusonadaptationbyhouseholdsandfarmers,neglectingfirms.Finally,productivitylossesfromclimateshocksmaybeoffsetifcapitalandlaborcanadjustacrosssectorsandlocations,butconstraintsonthesereallocationshavenotbeensufficientlystudied.ThispaperisaproductoftheOfficeoftheChiefEconomist,SouthAsiaRegion.ItispartofalargereffortbytheWorldBanktoprovideopenaccesstoitsresearchandmakeacontributiontodevelopmentpolicydiscussionsaroundtheworld.PolicyResearchWorkingPapersarealsopostedontheWebatTheauthorsmaybecontactedatssharmalworldbank.organdjrexerworldbank.org.TIjcPoiityRese<rcbWorkingPaperSeriesdisseminatestf)efindingofn>ork.hiprogresstoencouragetbcexcbanofideasaboutdetvfofimentissues.Anoecthfeoftheseriesisto*/tbtfindingoutquickfy,evNif'thepresentationsarelessthanfullypolished.Thepaperscanythenawtsoftbeauthorsandshouldbecited(ccorditty.Thefinding,interpretations,andconclusionsexpressedinthisp(rareentirrlyt!wse可theauthors.TheydonotnecrssarilyrrprvstrnttheviewsoftheInleniationalbankforReconstructionandDevtiopMenl/WorldBankanditsaffiliatedorganisations,orthoseoftheVlxecuihvDincforsoflbeWorldBankortheavmmentstheyrepresent.ProducedbytheResearchSupportTeamClimatechangeadaptation:Whatdoestheevidencesay?JonahRexer*1SiddharthSharma1Keywords:Climatechangeadaptation,Meta-analysis,SouthAsia,Technologyadoption,Publicgoods,Reallocation,Transfers,Diversification.JE1.codes,.Q50,Q54,Q55,Q561. IntroductionClimatechangeisleadingtohighersurfacetemperatures,acidifyingoceans,andarisingglobalmeansealevel.Theconsensusestimateisthattheaverageglobalsurfacetemperaturehasincreasedby0.85degreeCelsiussincetheindustrialrevolution,withestimatesoffutureincreaserangingfrom0.9to5.4degreesCelsiusbytheendofthiscentury(HsiangandKopp2018,IPCC2014).Withlong-termprecipitationpatternschangingincomplexways,somepartsoftheworldareexpectedtogetdrier,whileothersgetwetter(HsiangandKopp2018).Droughtsareexpectedtobecomemorecommonindrierpartsoftheworld(Collinsetal.2014).Climatechangeisalsoincreasingthefrequencyandintensityofextremeweatherevents.Forinstance,theprevalenceofintensetropicalcyclonesisexpectedtoincrease(Kossinetal.2017).Thesechangesintheearth,sclimateareprojectedtoreduceaggregateeconomicoutputbecauseoftheiradverseeffectsonagriculturalyields,industrialoutput,laborsupply,productivity,andhumancapital,amongothermechanisms(Auffhammer2018,CarletonandHsiang2016,Dell,Jones,andOlken2014,InternationalMonetaryFund2020).RecenteconometricstudiessuggestthatwarminghasasizableadverseimpactonGDP(Burke,Hsiang,andMiguel2015,Dell,Jones,andOlken2012,Hsiang2010).Basedonareviewofsuchstudies,CarletonandHsiang(2016)estimatethatfuturewarmingwillreducetheglobalGDPgrowthrateby0.28percentagepointsperyearduringthecomingcentury.SuchestimatesofaggregateGDPimpactsaresubjecttouncertaintyaboutthefuturepathofclimatechange.However,whentheeconomicimpactsofbothclimatetrends(suchasrisingtemperatures)andclimate-change-relatedextremeeventrisks(suchasmorefrequentcyclones)aretakenintoaccount,evenmoderatefutureclimatechangescenariosimplysizableeffectsonGDP(Fernando,1.iu,andMcKibbin2021).Majorstormshavesizablenegativeimpactsonsucheconomicoutcomesasper-capitaincomeandoutput(Anttila-HughesandHsiang2013,Cachon,Gallino,andOlivares2012,Nordhaus2010,Yang2008).Stormsalsodamageproductiveassets:inIndia,forexample,theaveragecyclonedestroys2.2percentofafirm'sfixedassets(Pcllietal.2023).Cyclonesanddroughtsalsoincreaseinfantmortalityandworsenotherhealthoutcomes(Anttila-HughesandHsiang2013,CurrieandRossin-Slater2013,Kudamatsu2016,Schmitt,Graham,andWhite2016).Asaresult,extremeweathereventsnotonlyreduceoutputintheshortrun,butalsoharmlong-runeconomicgrowth:a90th-percentilecycloneeventisestimatedtoreduceper-capitaincomesby7.4percenttwodecadeslater(HsiangandJina2014).Theeconomicimpactsofclimatetrends,suchasrisingtemperatures,arealsocomplexandsizable.Abnormaltemperaturesareassociatedwithdamagestoagriculturalyields(Guiteras2009,1.obell,Schlenker,andCosta-Roberts2011,Schlenkerand1.obell2010,SchlenkerandRoberts2009).Forexample,Guiteras(2009)estimatesthatinthelongrun(2070-2099),climatechangewillreducefarmyieldsinIndiabyatleastby25percent.Temperaturealsoaffectsindustrialoutput(Cachon,Gallino,andOlivares2012,Dell,Jones,andOlken2012,Hsiang2010,Somanathan2021,Zhangetal.2018).Annualoutputisestimatedtofallbyabout2percentperdegreeCelsiusofwarminginIndianmanufacturingplants(Somanathanetal.2021).Heatalsoreduceslaborproductivity(Niemelaetal.2002)andlaborsupply(ZivinandNeidell2014).Inadditiontotheseimpactsoneconomicoutcomes,exposuretoabnormaltemperatureshasnegativehealthconsequences,forexample,reducedbirthweightandincreasedmortalityamonginfants(Barreca2012,Burgessetal.2013,DeschenesandGreenstone2011).Exposureofchildrentoabnormalheatorrainfallatallstagesofearlydevelopment-in-utero,duringinfancyandatschool-age-canhavelong-termimpactsonhumancapital(Fishmanetal.2019,Gargetal.2020,MacciniandYang2009).Becauseprojectionsoftheadverseeconomicimpactsofclimatechangearesolarge,itisimportanttobetterunderstandhowfirmsandhouseholdsadapttoachangingclimate,andtheextenttowhichadjustmentscanmakeeconomicactivitymoreresilienttoclimatechange.Householdsandfirmscanreducetheirvulnerabilitytoextremeweatherinmanyways.Forexample,farmerscanadoptcropvarietiesbettersuitedtoadversegrowingconditions,buyinsurance,anddiversifyintononfarmactivitiesthatarelessvulnerabletoachangingclimate.Theycanalsomigrateawayfromvulnerablelocations.Understandingthedriversandimpactsofsuchresponsescanhelpauthoritiesdevisemoreeffectivepoliciestoaddressclimatechange.Agrowingbodyofeconomicliteratureexploreswhethersuchadaptationoccurs,howitoccurs,andtheextenttowhichitissuccessfulinmakingeconomicactivitylessvulnerabletoclimatechange.Thepurposeofthisreviewistogeneratearepositoryofthisevidencebase,withthegoalofdescribingtrendsinthefieldandidentifyinggapsintheliterature.Thereviewisglobalandnotrestrictedtoanyareaoftheworld.However,becauseitispartofaregionalworkprogramonclimatechangeadaptationattheWorldBank'sOfficeoftheChiefEconomistforSouthAsia,itpaysparticularattentiontoassessingtheevidenceonSouthAsia.First,itbuildsacomprehensivedatabaseofstudiesonclimatechangeadaptation.Afterfilteringforrelevanceandquality,adatabasewasbuiltthatconsistsof324studiesfromhigh-incomecountriesandemergingmarketanddevelopingeconomies(EMDEs).Second,thereviewsystematicallyassessesthesestudiesintermsofregionalcoverage,typesofclimateshockconsidered,typeofadaptationmechanismbeinganalyzed,andtheagentwhoseadaptationbehaviorisbeingstudied(firms,farmersandhouseholds).Third,itstandardizesthequantitativeestimatespresentedin80ofthereviewedpapersthosethatpermitsuchstandardization一andconductsametaregressionanalysisoftheimpactofadaptation.Finally,toinformpolicydialogueandhelpsetanagendaforpolicy-relevantresearch,thereviewidentifiesthemainemergingmessagesandknowledgegapsinunderstandingwhenadaptationoccurs,howitoccurs,theconstraintsonit,anditseffects.Thereareseveralkeypointsaboutthestateoftheliteratureonclimateadaptation.Thisliteratureislargebutshrinkssubstantiallywhenjournalqualityisaccountedfor,becausethetopjournalsineconomicshaveonlyrecentlybeguntocoverthesubject.Althoughstudiesonagricultureandhouseholdbehaviorarewell-represented,therearefewerstudiesonfirmresponses.Perhapsbecauseofitshighexposuretoclimateshocks,theSouthAsiaregioniswell-representedintheliterature.Themoststudiedadaptationmechanismsdifferbytypeofagent,butreallocations,technologyadoption,andmigrationtopthelist.Thereviewfindsthatneitherindividual-leveladaptationnorpublicinvestmentsinadaptationontheirownareenoughtorecoupthefullcostofclimateshocks.Somecommonlyseenindividualleveladaptations,suchascropdiversification,arecostlyandlimitedintheirimpacts.Thismeansthereisaroleforpolicytofacilitatemoreeffectivetypesofadaptations.Furthermore,whilecertainnecessaryadaptationscanonlyoccurthroughpolicyforexample,largeinfrastructureinvestmentsinseawalls(Husbyetal.2014)orirrigationcanals,theimpactofsuchpolicyinterventionsisnotwell-studied.Aquantitativemeta-analysisof118estimatesoftheimpactofadaptationshowsthat,onaverage,climateadaptationoffsets46percentofthecostofclimateshocks.Adaptationsthatinvolvepublicgoodsortechnologyadoptiontendtobemoreeffectivethanpurelyprivateadjustmentstrategiesunaidedbypublicgoodsornewtechnologies.Theeffectivenessofadaptationishigherforfirmsthanhouseholdsorfarmers.Thisdifferenceisprimarilytheresultofthegreateradoptionoftechnologybyfirms.Householdsandfarmersgenerallyemploylesseffectivestrategies,suchaslabororlandmarketadjustments.Thereviewalsofindsthatthereareimportanttradeoffsacrossadaptivemechanisms.Forexample,theadoptionofcertainpracticesortechnologies,suchasdrought-resistantcropvarieties,mightreduceclimatelossesinthepresent,butinthelong-run,farming-dependenthouseholdsinseverelyclimate-exposedareasmightbebetter-servedbymigratingtolessexposedareasorworkinginlessclimate-sensitivesectors.Macro-leveladjustmentssuchasspatialreallocationandstructuralchangetowardlessclimate-exposedsectorscanbeefficiency-enhancingbecauseclimate-exposedsectorslikeagriculturetendtobelessproductive.Anothermessageemergingfromthisreviewisthatthereislimitedunderstandingofthefactorsthatconstrainindividuals'andfirms,choiceofadaptationmechanisms,especiallythelatter.Similarly,littleisknownabouttheconstraintsonsectoralandspatialreallocation,suchastheroleofintegratedmarketsandfactormobility.Therestofthispaperisorganizedasfollows.Section2describesthemethodologyofthesystematicreviewandasummarydescriptionofthereviewedstudies.Section3summarizesthemainmechanismsofadaptationexaminedinthereviewedstudiesandkeyfindingsaboutadaptationresponsesbyagenttype.Section4presentsthemethodologyandresultsofameta-analysisoftheestimatesoftheeffectivenessofadaptationresponsesreportedinthereviewedstudies.Section5concludes.2. Methodologyandstudysampledescription2.1. SamplingmethodologyThegoalofthisreviewistwofold:tobuildarepositoryofstudiesontheeconomicsofclimatechangeadaptation,andtoreviewandcategorizethesestudiesalongasetofrelevantcharacteristics.Inaddition,Section4conductsaquantitativemeta-analysisoftheimpactofadaptationonclimatelosses.Thisreviewdefinesstudiespertainingto“adaptation”asthosethatconsideranyhumanbehavioralresponsetoclimateorweathershocksthatcouldbeconstruedasattemptingtomitigatelossesfromtheseshocks.Importantly,thereviewexcludesstudiesthatattemptsolelytoquantifytheeconomiclossesofclimatechangewithoutconsideringbehavioralresponses.Togeneratethesampleofacademicarticles,thereviewfirstidentifiedasetof147workscitedinarecentreviewarticleonclimatechangeadaptation(Balbonietal.2023).Ofthese,58studieswereidentifiedaspertainingtoadaptationaccordingtothecriteria.Theseserveasthebasisforthesamplingprocedure.Thereviewthenconductedforwardandbackwardcitationchasingonthese58studies,collectingallarticlescitingorcitedbythesestudies.Thisgeneratedasetof5,881studies.Restrictingthesampletostudiespublishedaftertheyear2000yields5,340studies.Asetofkeywordrestrictionswasthenimposedonthetitlesandabstractstoensurethepapersarerelevanttoclimatechange,broadlyconstrued,furthernarrowingthesampleto3,074.Theseare:environment;climate;adaptation;temperature;disaster;flood;rainfall;drought;weathershock;heat;groundwater.Finally,aqualityconstraint一inwhichonlythe250top-rankedeconomicsjournalsonResearchPapersinEconomics(RePEc)wereused-furthernarrowedthepoolto946studies.Theseremainingstudiesweremanuallyreviewedtoidentifytheirrelevancetoclimateadaptation.Intotal,324studieswerefoundrelevantandcomprisethefinalsample.Someanalysesthatfollowimposetheadditionalrestrictionthatthestudiesmustbepublishedinatopeconomicsjournal,whichreducesthesampleto101studies.Thetopjournalsare:theAmericanEconomicReview,theJournalofPoliticalEconomy,theQuarterlyJournalofEconomics,Econometrica,theReviewofEconomicStudies(theTop5);JournaloftheEuropeanEconomicAssociation,theReviewofEconomicsandStatistics,theAmericanEconomicJournals,theEconomicJournal(theTop10);theJournalofEnvironmentalEconomicsandManagement,theJournalofDevelopmentEconomics,theJournalofPublicEconomics,ManagementScience,andtheReviewofFinancialStudies(theTopFields).The324relevantclimatechangeadaptationstudiesweregroupedinareviewmatrixacrossseveralstudycharacteristics.Agentsweregroupedintothreecategories:firms,households,andfarmers.Climateshocksweregroupedintorainfallanomalies,temperature(includingextremeheat),drought,flooding,andothernaturaldisasters.Studyoutcomesrangesubstantiallygiventhesignificantheterogeneityintopicsstudied.Someexamplesincludecropyield,landuse,floodinsurancetake-up,householdincome,firmsales,migration,andmortality.ThematrixalsoincludestheWorldBankregionofthestudy,andtheempiricalmethodology-experimental,quasi-experimental,observational,orstructural.Importantly,thereviewmatrixclassifiestheprimaryadaptationmechanismbywhichagentsinthestudycopewithclimatechangeintothefollowinggroups:financialmarkets,publicpolicy,transfers,infrastructure,labormarkets,migration,technologyadoption,reallocation,andgeneraladaptation.2.2. CharacteristicsofthereviewedstudiesThefieldofclimatechangeadaptationhasgrownsubstantiallyoverthepasttwodecades.Figure1(left)plotsthecumulativenumberofclimatechangeadaptationarticlesovertime,byjournalranking.Mostoftheincreaseintheliteratureisconcentratedinlower-rankedjournals;coverageinthemostselectiveeconomicspublicationsremainsrelativelylow.Therightpanelfocusesonthesubsetof101studiespublishedinatopeconomicsjournal,plottingthetrendoverlimebysubject.Themajority,54percent,ofthestudiesfocusonhouseholds,followedbyfarmers,34percents,andfirms,22percent.Notethatthesecategoriesarenotmutuallyexclusive,andsotheirsharessumtomorethan100percent.Notonlyarefirmstheleast-representedinstudiesamongtopjournalpublications,theyareevenlessrepresentedoverall,thesubjectofjust9percentofstudiesinthenon-topjournalpublications.Studiesonfirmsappearneglectedintheaggregate,butthatvariesb