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CLIMATECHANGE,MITIGATIONANDADAPTATIONWITHUNCERTAINTYANDLEARNINGAlanIngham1Thispaperisproducedaspartofaprojecton“TheEconomicAnalysisofAdaptationandMitigation”andisbasedonpapersproducedforthatprojectseeIngham,Ma,Ulph(2005).IamgratefultotheTyndallCentreforClimateChangeResearchforsupportforthisproject.1DivisionofEconomics,SchoolofSocialSciences,UniversityofSouthampton,SouthamptonSO171BJ,UK:ai@soton.ac.uk1IntroductionHowdoesthepossibilityofadaptationtoclimatechangeaffecthowmuchmitigationshouldbedone?Thisshortnotelooksatsomeoftheissuesthatareinvolvedinaddressingthisquestion.Ifitisthecasethatadaptationisanalternativetomitigationthencurrentpolicychoicesabouthowmuchmitigationshouldtakeplacewillbedeterminedbyastraightforwardanalysisoftherelativecostsandbenefitsofadaptationandmitigationandtherelationbetweenthetwo.Atatechnicaleconomiclevelthiswillhingeonwhetheradaptationandmitigationarecomplementsorsubstitutes.Iftheyaresubstitutesthenbasicallytheamountofeachactivitywillbedrivenbytherelativepricesofthetwotypesofactivities,andsoifadaptationbecomesacheaperactivitythenmoreofitwillbedonewithaconsequentreductionintheamountofmitigationthatwouldbedone.Ontheotherhandiftheseactivitiesarecomplements,thenitwillnotbedesirabletoattempttoreplaceonewiththeother.Ifpriceschangeinsuchawaythatmoremitigationshouldbedone,thenmoreadaptationshouldbedonealso.However,morecomplexissuesariseonceweincludetheeffectsofuncertaintyandlearningabouttheClimateChangeprocess.Then,thequestionofthetimingofactionsrelatedtoClimateChangebecomesmuchlessstraightforward.WeconsiderfivepropositionsconcerningadaptationtoClimateChange.Theseare1.Thatmitigationandadaptation,ingeneral,tobesubstitutesintheeconomicsenseandthisisaresultrobusttomanyassumptions.Onlyinthecasewheremitigationbuystimeforadaptationtotakeplacecantheybecomplementaryactivities.2.Whenuncertainty,thatarisesfromlearningandirreversibility,isintroducedintotheeconomicmodelresultschangefundamentally.3.Whenbothmitigationandadaptationareavailablestrategies,theconsequencesofirreversibilityareweakened4.Ingeneral,learningaboutwhattheclimatefuturemaybewillalwaysbemoreimportantthanirreversibility.5.Forthewaterindustrythereisanimportantlearningeffectconcerningfutureclimatechange;ifthereisthepossibilitythatinvestmentdecisionscantakeaccountofthis,costscouldbereducedbybetween10%and30%comparedtowhennolearningtakesplace.2MitigationandAdaptation-ComplementsorSubstitutes?Toanalyzethelinksbetweenadaptationandmitigationwebeginwiththesimplestcasewhereweignoredynamicaspectsanduncertainties,sothereisaknownrelationshipwhichshowshowmitigationandadaptationreducethedamagecostscausedbyclimatechange,andknowncostsofadaptationandofmitigation.Asinglesocialplannercanchoosetheoptimalmixofadaptationandmitigationtominimizetotalsocialcosts.Itisstraightforwardtoshowthatingeneraltheoptimalcombinationofmitigationandadaptationwillrequiretheuseofbothstrategies.Thisjustreflectstherathermildassumptionthatthefirstbitofmitigationoradaptationischeaprelativetothemarginalreductionindamagecoststheybringabout.Thisconfirmstheviewthatweneedtohaveanintegratedapproachtoadaptationandmitigation,andwecannotrelyoneithermitigationaloneoradaptationalonetodealwithclimatechange.Itissometimeclaimedthatthisjointdeterminationofmitigationandadaptationmeansthatadaptationandmitigationarecomplementary(IPCC(1996),Pielke(1998)).Thus,anincreaseindamagecostswouldbeexpectedtoleadtoanincreaseinbothadaptationandmitigation1.Butinthiscontextwehavesketchedsofar,intechnicaleconomicterms,adaptationandmitigationaresubstitutes,inthesensethatif,say,thecostofadaptationfell,theoptimalresponsewouldbetodomoreadaptationbutlessmitigation2.Thisjustreflectsthefactthatthesearetwodifferentwaysofreducingdamagecosts,soifonebecomesmoreexpensiveweshouldmakemoreuseoftheother.Thishasobviouslyimportantpolicyimplications.Forexample,earlygenerationsofmodelsoftheeconomicresponsetoclimate1Thisislikeanincomeeffectwithnormalgoods.2Inthiscontextweareessentiallytreatingmitigationasasingleactivityandadaptationasasingleactivity.Ofcoursetherearemanydifferentmethodsofmitigationandadaptation,andwedonotclaimthateveryformofmitigationisasubstituteforeveryformofadaptation(oreventhateveryformofmitigationisasubstituteforeveryotherformofmitigation,andsimilarlyforadaptation).Thisclaimonlyappliesinanaggregatesense.changetendedtofocusonlyonmitigationstrategies,socanbeconsideredastreatingthecostsofadaptationasinfinite.Latermodelshavegivenmoreattentiontoadaptationoptionsandfoundthemtoberelativelycheapandsohaveconcludedthatthereisratherlessneedformitigation(seeforexamplesurveysbyMendelsohn(2003)andTol(2003)).Theaboveargumentisbasedonasimplepartialeconomicanalysis,anditisconceivableinprinciplethatwithgeneralequilibriumeffectsadaptationandmitigationmightbecomecomplements.Forexample,ifincreasedmitigationcausedenergypricestofallthiscouldmakeitmoreattractivetousesomeformsofadaptation,butsuchgeneralequilibriumeffectswouldneedtobequitepowerfultooutweighthedirectpartialeffect,andwearenotawareofevidencewhichshowssuchresults.Thereisanother
本文标题:CLIMATE CHANGE, MITIGATION AND ADAPTATION WITH UNC
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