IMF-氣候轉型期間的公共債務動態(tài)（英）

PublicDebtDynamicsduringtheClimateTransition

DanielGarcia-Macia,W.RaphaelLam,andAnhDinhMinhNguyen

WP/24/71

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2024

MAR

?2024InternationalMonetaryFund

WP/24/71

IMFWorkingPaper

FiscalAffairsDepartment

PublicDebtDynamicsDuringtheClimateTransition

PreparedbyDanielGarcia-Macia,W.RaphaelLam,andAnhDinhMinhNguyen1

AuthorizedfordistributionbyW.RaphaelLam

March2024

IMFWorkingPapersdescriberesearchinprogressbytheauthor(s)andarepublishedtoelicit

commentsandtoencouragedebate.TheviewsexpressedinIMFWorkingPapersarethoseofthe

author(s)anddonotnecessarilyrepresenttheviewsoftheIMF,itsExecutiveBoard,orIMFmanagement.

ABSTRACT:Managingtheclimatetransitionpresentspolicymakerswithatradeoffbetween

achievingclimategoals,fiscalsustainability,andpoliticalfeasibility,whichcallsforafiscalbalancingactwiththerightmixofpolicies.Thispaperdevelopsatractabledynamicgeneralequilibriummodeltoquantifythefiscalimpactsofvariousclimatepolicypackagesaimedatreachingnetzero

emissionsbymid-century.Oursimulationsshowthatrelyingprimarilyonspendingmeasuresto

deliveronclimateambitionswillbecostly,possiblyraisingdebtby45-50percentofGDPby2050.

However,abalancedmixofcarbon-pricingandspending-basedpoliciescandeliveronnetzerowithamuchsmallerfiscalcost,limitingtheincreaseinpublicdebtto10-15percentofGDPby2050.

Carbonpricingiscentralnotonlyasaneffectivetoolforemissionsreductionbutalsoasarevenuesource.Delayingcarbonpricingactioncouldincreasecosts,especiallyiflesseffectivemeasuresarescaleduptomeetclimatetargets.Technologyspilloverscanreducethecostsbutbottlenecksin

greeninvestmentcouldunwindthegainsandslowthetransition.

RECOMMENDEDCITATION:DanielGarcia-Macia,W.RaphaelLam,andAnhDinhMinhNguyen.2024.“PublicDebtDynamicsduringtheClimateTransition”,InternationalMonetaryFundWorkingPaperNo.

2024/71.

JELClassificationNumbers:E10,H30,H50,H60,Q54

Keywords:

Climatechange;mitigation;publicdebt;carbonpricing;subsidies;publicinvestment;industrialpolicies;dynamicgeneralequilibrium.

Author’sE-MailAddress:dgarciamacia@;wlam@;anguyen3@.

1WearegratefulforthecommentsanddiscussionfromSimonBlack,BenjaminCarton,EraDabla-Norris,RuuddeMooij,Vitor

Gaspar,FlorenceJaumotte,IanParry,ChristineRichmond,GregorSchwerhoff,andKarlygashZhunussova,andparticipantsfromtheIMFFiscalMonitorworkshopandfrominternaldiscussionsattheIMF’sFiscalAffairsdepartment.

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WORKINGPAPERS

PublicDebtDynamicsduringthe

ClimateTransition

PreparedbyDanielGarcia-Macia,W.RaphaelLam,andAnhDinhMinhNguyen

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Contents

I.Introduction

4

II.RelatedLiterature

6

III.ModelFrameworkandCalibration

6

IV.Results

10

A.Scenario1:Scalingupspendingtomeetclimategoals

10

B.Scenario2:Relyingprimarilyoncarbonpricing

12

C.Scenario3:CombinationofWell-SequencedPolicyInstruments

13

AdvancedEconomies

14

EmergingMarketandDevelopingEconomies

16

D.Scenario4:DelaysinCarbonPricing

18

E.Scenarios5and6:TechnologySpilloversandInvestmentBottlenecks

18

F.AdditionalSensitivityAnalysisandRobustness

20

V.PolicyImplicationsandConclusions

21

References

23

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I.Introduction

Theyear2023wasthewarmestonrecord.Thelikelihoodofclimatic“tippingpoints”increaseswithglobalwarming,bringingpotentiallycatastrophicconsequences(IPCC2021;McKayandothers2022;

DitlevsenandDitlevsen2023).Countrieshaverecognizedtheneedforurgentactiontoaddress

globalwarming.Inadditiontothe2015ParisAgreement,countrieshavealsocommittedtolonger-termtargetsfornet-zeroemissions—cuttinggreenhousegasemissionstoasclosetozeroas

possiblebyaboutmidcentury.Despiteprogressinmanycountries,includingthelargestemitters,largegapsinambitionandimplementationremain(Figure1).1

Achievingtemperaturegoalswillrequirea

fundamentaltransformationofproduction,

consumption,andinvestmentbyhouseholds,

firms,andgovernmentsoverthecomingyears.Ongoingdevelopmentsingreensectorscould

resultinnewproductsandprocesseswithlowergreenhousegasemissions(GHG)(Aghionand

Howitt2005;SternandValero2021).Butthe

transitioncostscouldbespreadunevenlyacrosspeopleandfirms(Mercureandothers2018;

Gourinchas,Schwerhoff,andSpilimbergo,2023).Atthesametime,adaptingtoclimatechange

willrequirepublicinvestmentingreen

technologies,addingtoothersustainable

developmentgoals(SDGs)andputtingpressureonmanyfiscally-constraineddeveloping

countries.

Suchtransformationnecessitatescareful

managementofpublicfinances.Ontheone

hand,governmentsneedtodesignappropriate

Figure1.AnnualGlobalGreenhouseGas

Emissions,1990–2050

(Billionsoftonsofcarbondioxideemissions

equivalence)

Sources:IntergovernmentalPanelonClimateChange(2022);Blackandothers(2023).

Note:ThefigureshowsestimatesfromprojectionusingusingtheIMF–WorldBankClimatePolicyAssessmentTool.NDC=nationallydeterminedcontributions.

fiscalpoliciestoincentivizedecarbonizationandfacilitatethegreentransition.Ontheotherhand,

theyneedtobalancepolicytradeoffsandensureequitableburdensharingoftransitioncostsacrosshouseholds,whilesafeguardingfiscalsustainability.Akeyquestionishowgovernmentscan

encouragefirmsandhouseholdstodecarbonizewhilerespectinggovernmentbudgetconstraints.Atthesametime,manycountries—notablylow-incomecountriesandsmalldevelopingstates—have

multiplecompetingdevelopmentneedsalongsidetheimperativetoadapttoclimatechange.

1Thecurrentlargestemitters,includingChina,theEuropeanUnion,India,andtheUnitedStates,togetheraccountformorethan60percentofglobalemissionsby2030.Theshareofemergingmarketeconomiesisexpectedtoreach

almost70percentby2035,signifyingtheirimportanceforglobalmitigationefforts.Thesetofcountriesclassifiedasthelargestemittersandrespectivesharewouldvarydependingonthetimeframe.

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Therefore,assessingthefiscalimplicationsofpoliciestoachieveclimateobjectivesiscrucial.

Furthermore,long-standingtradeoffsintacklingclimatechangeareamplifiedatatimewhenmanycountriesfaceelevateddebtlevels,highinflation,andweakgrowthprospectsfollowingthe

pandemicandenergycrisis.Apushforenergysecurityispromptingcountriestopursueafaster,but

likelybumpy,greentransition.Protectionistmeasuresalsoexacerbatetherisksofgeopoliticalfragmentationandcouldimpedetechnologydiffusionacrossborders.

Againstthisbackdrop,thispaperdevelopsadynamicgeneralequilibriummodeltoinvestigatethefiscalimpactsofenvironmentalpolicychoicesduringtheclimatetransition.Ourmaincontributionsaretwofold.First,wequantifythedynamicimplicationsfordeficitsandpublicdebtofvariouspolicypackagestoachievenetzeroemissionsfortwocountrygroups—advancedandemergingmarket

economies.Second,weassesstheevolvingdesirablemixofclimateinstrumentsfromamacro-fiscalperspective.

Specifically,weanalyzesixscenarioswherepoliciesachievenetzeroemissionsbyaround

midcentury:(i)Scaled-upsending:countriesprimarilyscaleupspendingthrough,forinstance,greensubsidiesandpublicinvestmenttoreachclimategoals;(ii)Relianceoncarbonpricing:climate

policiesrelyprimarilyoncarbonpricing;(iii)Balancedpolicymix:abalancedmixofrevenueand

expendituremeasuresisadopted,consideringbothclimatetargetsandpublicdebtsustainability;(iv)Costofdelayingcarbonpricing;(v)Technologyspillovers;and(vi)InvestmentBottlenecks.

Wefindthatheavilyrelyingonspendingmeasurestoachieveclimategoalswillbecostly,potentiallyincreasingdebtby45-50percentofGDPbymid-century.Incontrast,abalancedapproach

combiningcarbonpricingwithspending-basedpoliciescanachievenet-zerogoalsatasignificantlylowerfiscalcost,limitingtheriseinpublicdebtto10-15percentofGDPby2050.Inthisbalanced

policymix,carbonpricingplaysanessentialrolenotonlyasaneffectivemeansofreducing

emissionsbutalsoasasourceofrevenue.Postponingactiononcarbonpricingiscostly.While

technologyspilloverscanhelpreducethecosts,investmentbottleneckscouldhinderthetransitionandcausedebt-to-GDPratiostorisefurther.

Thepaperisstructuredasfollows.SectionIIdiscussesourcontributionsinrelationtotheliterature.

SectionIIIpresentsthemainfeaturesofmodelframeworkandcalibration.SectionIVillustratesthe

implicationsforpublicfinancesifcountrieseithera)scaleupspendingmostly,orb)relyprimarilyoncarbonpricestoreachclimategoals.Thenthepaperpresentssimulationsofanappropriatepolicy

mixthatreducesfiscalcostsandimprovesmacroeconomicoutcomesandpoliticalfeasibility.2The

sectionalsodiscussestheimplicationsfordebtdynamicsunderalternativescenarios:delayedclimateaction,consideringtechnologicalspillovers,andwithbottlenecksingreeninvestment.Sensitivity

analysesareprovidedtoillustratetheuncertaintysurroundingtheestimates.SectionVconcludeswithpolicyimplicationsfromthesequantitativeresults.

2Politicalfeasibilitycouldvaryovertimeandacrosscountries.Anumberofcountrieshaveadoptedcarbonpricing,butwithcarbon pricesonaverageatlowlevelsandcoveringrelativelylimitedsectors(seeIMF2023).Theadoptionofcarbonpricinginonecountrymakesiteasierforotherstoadoptit(Linsenmeier,Mohommad,andSchwerhoff2023).Nevertheless,overcomingpoliticalhurdlesisstillchallenging,makingitdifficulttoraisecarbonpricessignificantlyorexpandcoveragetobroadereconomicactivity.

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II.RelatedLiterature

Ourpaperaimstobuildabridgebetweentwodifferentstreamsoftheliterature.First,itcontributestotheextensivebodyofresearchonmodellingfiscalpolicyusingNew-Keynesianmodels.SimilartoTraumandYang(2015),ourmodelincorporatesacomprehensivesetoffiscalinstruments,bothonrevenueandexpendituresides,aswellastheevolutionofpublicdebt.Themodelalsodifferentiatestwotypesofhouseholds:saversandnon-savers(alsoknownasliquidity-constrainedhouseholds),

whichallowstomodeloftargetedtransferstothelattergroup.Additionally,wefollowMian,Straub,andSufi(2022)tomodelthefeedbackeffectofpublicdebtoninterestrate,particularlyrelevantforcountrieswheretheborrowingcostissensitivetodebtdynamics.

Second,ourpaperiscloselyrelatedtotheclimate-macroliterature,particularlystudiesusing

dynamicgeneral-equilibriummodelstoexaminetheeffectsofenvironmentalpolicies.Forinstance,FischerandSpringborn(2011)andHeutel(2012)exploretheinteractionbetweenenvironmental

policyandeconomicresponsestoproductivityshocksinarealbusinesscyclemodelwithapollutionexternality.AnnicchiaricoandDiDio(2014)investigatetheconditioningroleofdifferent

environmentalpolicyregimesontheresponsetonominalandrealshocksinaNewKeynesian

model.Barrage(2019)quantifiesoptimalcarbontaxesinadynamicgeneralequilibriumclimate-

economymodelwithdistortionaryfiscalpolicy.FerrariandLandi(2020)studytheeffectsofgreen

quantitativeeasinginaDSGEmodelthatdistinguishesbetweentwoproductionsectors(similartowithAcemogluandothers(2012,2016)):apollutingbrownsectorandanon-pollutinggreensector.

Barrett(2021)arguesthatthemosteffectivepolicypackageinemissions-reducingregionsisaresearchsubsidyfundedbyacarbontax.Ourpaperdistinguishesitselffromthesestudiesby

analyzingtheimplicationsofclimatepoliciesonpublicdebtdynamicsusingadynamicgeneralequilibriummodelequippedwitharichsetoffiscalinstruments.

OurmodellingsetupdiffersfromotherclimatemodelssuchastheIMF-WBClimatePolicy

AssessmentToolsandcomputablegeneralequilibrium(CGE)modelsbyaccountingfor

intertemporalbehavioralresponsestoexpectedchangesinclimatepolicies.Theseareimportantforexaminingthedecisionsonconsumptionandinvestment,aswellastheimplicationsforpublicdebtdynamics.Pricerigiditiesarenecessarytogeneraterealistictransitiondynamicsfromshorttermto

longterm.However,ourmodelfocusesonaclosedeconomyandsoisnotequippedtoanalyze

cross-borderissuessuchascarbon-borderadjustmentsorinternationalspilloversofclimatepolicies,whichcanbecapturedinlarge-scalemodelssuchasGMMET(Cartonandothers,2023).Despitethislimitation,ourmodel'scomputationaltractabilityallowsustoretainpotentialnonlineardynamics,

whichcanbechallenginginsolvingmulti-countrymodels.

III.ModelFrameworkandCalibration

WedevelopamodelthatintegratesthestandardNewKeynesiandynamicgeneralequilibriummodelequippedwitharichsetoffiscalpoliciesasinTraumandYang(2015)withaclimatemodule,

featuringgreenenergyandbrownenergyinproduction,asmotivatedbyAcemogluandothers

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(2012,2016).Ouranalysisassumesperfectforesight,andsolvesthetransitiondynamicsnonlinearly,whichmattersgiventhelargemagnitudesofpotentialchangesintheenergysector.

Themodelinheritsstandardfeaturesofthetwo-agentNewKeynesianmodelwithafiscalblock,similartoTraumandYang(2015):

1.Therearetwotypesofhouseholds:saversandnon-savers.Thenon-saversdonothaveaccesstofinancialorcapitalmarketsandconsumealloftheirincome(wagesandtransfers)eachperiod.

Theforward-lookingsavershaveaccesstocompleteassetandcapitalmarket.

2.Thefinalgood'spriceissubjecttonominalrigidity(àlaquadraticadjustmentcosts).Also,investmentissubjecttoadjustmentcosts.

3.Thelargesetoffiscalinstrumentsincludesaconsumptiontax,laborandcapitalincometaxes,

governmentexpenditure,andtransfers.Debtisstabilizedbychangesinlump-sumtaxonsavers.

4.MonetarypolicyfollowsaTaylorrulerespondingtoinflationgapandoutputgap.

Giventhepurposeoftheexercise,weintegratetwofeaturesintothisstandardsetting.First,energyisusedintheproductionoffinalgoodsandgeneratedfrombothgreenandbrownsources.Each

energysourceemploysspecificprivatecapitalandlabor,aswellaspubliccapitalinthecaseofgreenenergy(forexample,electricitygrids)andprivateinvestmentsubjecttoadjustmentcosts.Second,

fiscalpolicytoolsareextendedtoincludecarbonpricing,greensubsidies,publicinvestment,andtargetedtransfers.

Thefollowingequationsfocusmainlyontheadditionalclimateandtechnologyfeaturesofthe

modelrelativetoTraumandYang(2015).Finalgoodsareproducedcombiningintermediateenergyyandnon-energyinputsywithaConstantElasticityofSubstitution(CES)functionwithelasticityηfandenergyshareCf:

yt=((1-C)1/ηf(y)(ηf-1)/ηf+C1/ηf(y)(ηf-1)/ηf)ηf/(ηf-1).

Thenon-energyinputyisproducedbyusinggenericcapitalandlaborinputsinastandardCobb-Douglasproductionfunction.EnergyitselfisalsoproducedwithaCESbundleofgreenandbrownsourcesofenergy,withelasticityηandbrownenergyshare幼:3

y=((1-幼)1/η(y)(η-1)/η+幼1/η(y)(η-1)/η)η/(η-1).

Carbonemissionsaredirectlyproportionaltothebrownenergyoutput,withunitelasticity.Each

energysourcei=fG,B}employsprivatecapitalkiandlaborhi,withproductivityAi,aswellas

publiccapitalkGiinthecaseofgreenenergy(forexample,electricitygrids).TheproductionfunctionforgreenenergysourceGisthus:

y=A(((1-WG)1/ηG(k-1)(ηG-1)/ηG+W/ηG(kG1)(ηG-1)/ηG)ηG/(ηG-1))1-rG(h)rG,

3Cartonandothers(2023)featureagranularmodellingofelectricitygeneration,transportation,andfossilfuelmining,therefore

increasingthelikelihoodofcapturingtheactualobstaclesoftheenergytransition.Thiscouldbeapotentialextensionforourmodel.

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wheretheshareofpubliccapitalissettozeroforbrownenergy—asimplifyingassumptionthatdoesnotaffectkeyresults.

Inaddition,productivityineachenergysourcebenefitsfromlearning-by-doingexternalities.Itgrowsinproportiontotheexistingcapitalstock:

log(A)=ailog(k-1/ks)+E,

whereksindicatesthesteady-statecapitallevelandEisanexogenoustrend.

Privateinvestmentissubjecttoadjustmentcosts,capturingpotentialbottlenecksforgreen

investment,suchasscarcityorsupplydisruptionsofcriticalminerals,includingfromrising

geopoliticalfragmentation,and/orbottlenecksindivestingstrandedbrownassets.Adjustmentcosts

growquadraticallyinproportiontothedeviationoftheinvestmentratioineachcapitalstocki/

k-1fromthedepreciationrate,thusimposingacostonbothsharpcapitalaccumulationand

divestment.Thecapitalaccumulationfunctionforeachcapitalstockj(privategreen,privatebrown,

publicgreen,orgeneric)is:

k(1+g)(1+n)=(1-δ)k-1+i--δ)2k-1,

wheregisthebalanced-growth-pathinoutputpercapita,nisthepopulationgrowth,δisthedepreciationrate,andYiistheadjustmentcostparameter.

Sovereigninterestratesareincreasinginthedebt-to-GDPratiotocapturethedownward-slopingdemandforsafeassets,whichisparticularlyrelevantforcountrieswithlessfiscalspace.Specifically,thefunctionalformfollowsMian,Straub,andSufi(2022),withtheconvenienceyieldofholding

governmentdebtequalto:

-

一bt-b

Cyt=-φ.

whereistheconvenienceyieldindeviationfromthesteadystate,φisthedebtelasticity,andbtisthelevelofdebt(inthesteadystate).Highergovernmentdebtincreasesinterestratesas

liquidityandsafetypremiumsongovernmentdebtdiminish(KrishnamurthyandVissing-Jorgensen2012).

DataandCalibration

Thesimulationscomparea“business-as-usual”baselinebasedoncurrentpolicieswithpolicy

scenariosthatreduceemissionsby80percentby2050inadvancedeconomiesandby2060in

emergingmarketeconomies.Thebaselinepathsforoutput,population,andgovernmentdebtarebasedonIMFWorldEconomicOutlookdatabaseprojections,long-termprojectionsbythe

OrganisationforEconomicCo-operationandDevelopment,andtheUNpopulationprojection,whiletheemissionspathandinitialcarbonpricesareconsistentwithanalysesusingtheClimatePolicy

AssessmentToolandinitialenergysharesfromtheUSEnergyInformationAdministrationand

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Table1.CalibrationofModelParameters

Parameters

Symbol

Value

Sources

Energy-relatedParameters

Elasticityofenergyinfinalgoods

ηf

0.21

Labandeira,Labeaga,and

production

López-Otero(2017)

Elasticitybetweengreenandbrownenergy

η

3.5

Acemogluandothers(2012)

Elasticitybetweenprivategreencapitalandpublicgreencapital

ηG

0.9

Seetextfordiscussion

Shareofenergyinfinalgoodsproduction

cf

0.07

K?nzig(2023)

Shareofbrownsourceinenergy

φ

0.8(AE)/0.9(EM)

IEA’sWorldEnergyBalances,

production

alsoseetextfordiscussion

Shareofpublicgreencapitalinthegreen

WG

0.16

BasedonTraumandYang

capital

(2015)

MacroeconomicParameters

Discountfactor

β

0.99

Standardvalue

Intertemporalelasticityofsubstitution

σ

1

Standardvalue

Depreciationrate

δ

0.025

Standardvalue

InverseFrischelasticity

2

Standardvalue

Shareoflaboringreen,brown,andnon-energyproduction

ai

0.68

Standardvalue

Debtelasticity

φ

0(AE)/0.003(EM)

Seetextfordiscussion

Priceelasticity

E

p

10

Standardvalue

Capitaladjustmentcost

Yi

4

Standardvalue,alsoseetextforfurtherdiscussion

Priceadjustmentcost

K

52.9

Matchtheaveragefrequencyofpricechanges(everythree

quarters)

Consumptiontaxrate

c

τ

12percent

Standardvalue

Laborincometaxrate

τw

20percent

Standardvalue

Capitalincometaxrate

k

τ

20percent

Standardvalue

Lump-sumtax:Responsetodebt-to-GDP

φB

0.01

Gomes,Jacquinot,andPisani

ratio

(2012),seetextfordiscussion

Taylorrule:smoothing

p

0.5

Standardvalue

Taylorrule:responsetoinflation

Yπ

2

Standardvalue

Taylorrule:responsetooutputgap

Yy

0.125

Standardvalue

Inflationtarget

π

2percent(AE)/4

percent(EM)

Standardvalue

Source:Authors’compilations.

Note:StandardvaluesarebasedonSmetsandWouters(2007),Christiano,Eichenbaum,andEvans(2005),Gomes,Jacquinot,andPisani(2012),andTraumandYang(2015).AE=advancedeconomies;EM=emergingmarketeconomies;IEA=

InternationalEnergyAgency.

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InternationalEnergyAgency.ThemodeliscalibratedtoarepresentativeadvancedeconomybasedontheGroupofSevenandarepresentativeemergingmarketisanaverageofcountriesincluding

Argentina,Brazil,China,India,Indonesia,Mexico,SouthAfrica,andTürkiye.Theinitialcarbonpriceissetto$40forarepresentativeadvancedeconomyand$5forarepresentativeemergingmarket.

Keyparametersofthemodelareinlinewiththeliterature(Table1).Theshareofpubliccapital(”G)

ingreencapitalissetto0.16,matchinggenericpubliccapitalinTraumandYang(2015).The

elasticitybetweenprivategreencapitalandpublicgreencapitalissetto0.9,closetobutslightlysmallerthantheunitelasticityusedinthecaseofgenericpublicinvestment,reflectingthespecificneedofpublicinvestmentingreenproduction.Theshareofliquidityconstraintshouseholdsis30percentinadvancedeconomies(Kaplan,Violante,andWeidner2014;Kumhofandothers2010;

Gomes,Jacquinot,andPisani2010)and50percentinemergingmarketeconomies(Kumhofandothers2010).

Thecapitaladjustmentcostissettothestandardvalueof4.Atthesteadystate,theadjustmentcostisalwayszeroregardlessoftheadjustmentcostparameter.Inthepreferrednetzeroemission

packageofadvancedeconomies,theexpostannualcostonoutputisverysmall,about0.03percentofGDPto2050onaverage(or0.8percentintotalbetween2023–50).

Thedebtelasticityoftheconvenienceyield(Ψ)issettozerofortheadvancedeconomies,while

representativeemergingmarketeconomiesarecalibratedsothattheequilibriuminterestrate

increasesby20basispointswhengovernmentdebtincreasesby10percent(Mian,Straub,andSufi2022).4

IV.Results

Thepaperpresentssimulationresultsacrossdifferentscenariosforarepresentativeadvanced

economyandarepresentativelargeemergingmarketeconomyasnotedabove.Wefirstexaminetheimpactonpublicfinancesifcountriesscaleupspendingtoreachclimategoalswithout

ambitiouscarbonpricingmeasures(Scenario1).Then,thesecondscenarioconsiderstheimpactonpublicfinancesandthemacroeconomyiftheprimaryinstrumenttoreachnetzeroemissionsby

midcenturyisalargeandrapidincreaseincarbonprices(Scenario2).Third,thepaperconsidersa

mixofclimateinstrumentsincludingbothrevenueandspendingmeasurestoreachthenetzero