【未来能源研究所】计算产品中的碳分子：解开不断增长的碳强度方法网-2025.11

CountingCarbonMoleculesinProducts:DisentanglingtheGrowingWebofCarbonIntensityMethods

MilanElkerbout,KatarinaNehrkorn,andBrandonHolmes

WorkingPaper25-27November2025

AbouttheAuthors

MilanElkerboutisafellowanddirectoroftheInternationalClimatePolicyInitiative

atResourcesfortheFuture(RFF),workingoninternationalclimatepolicyandonthe

interactionsbetweenclimateandtradepolicy.

KatarinaNehrkornisaresearchassociateatRFFwhoseresearchspansacross

internationalclimatepolicyandindustrialdecarbonization.NehrkornearnedherBA

ineconomicsfromtheUniversityofMichigan,afterwardsworkingatDeloitte’sRisk

andFinancialAdvisorydivisionfortwoyears.In2023,shecompletedherMScin

EnvironmentalEconomicsandClimateChangeattheLondonSchoolofEconomics.

BrandonHolmesisaresearchanalystatRFF.HolmesearnedhisMScinEnvironmental

andNaturalResourceEconomicsatDurhamUniversityintheUnitedKingdom.

AboutRFF

ResourcesfortheFuture(RFF)isanindependent,nonprofitresearchinstitutionin

Washington,DC.Itsmissionistoimproveenvironmental,energy,andnaturalresource

decisionsthroughimpartialeconomicresearchandpolicyengagement.RFFis

committedtobeingthemostwidelytrustedsourceofresearchinsightsandpolicy

solutionsleadingtoahealthyenvironmentandathrivingeconomy.

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informationanddiscussion.Theyhavenotnecessarilyundergoneformalpeerreview.

Theviewsexpressedherearethoseoftheindividualauthorsandmaydifferfromthose

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ResourcesfortheFuturei

ResourcesfortheFutureii

Abstract

ThisisthesecondResourcesfortheFuture(RFF)workingpaperoninteroperability

ofcarbonintensityquantificationmethods1Thispaperconnectstheongoingdebateoncarbonaccountingmethodswithexistingpracticesinlifecycleaccounting

andenvironmentalproductdeclarations.Acasestudycomparescarbonintensity

quantificationmethodsacrosstheEUcarbonborderadjustmentmechanisms,the

USEnvironmentalProtectionAgency’slabelingprogram,andanInternationalTrade

Commissionstudyonsteelandaluminumcarbonintensities.Thispaperfindsthat

theremaybelegitimateareaswhereproduct-levelcarbonintensityaccountingchoicesmaydiffer.Nevertheless,improvedinteroperabilitycouldstillbepossiblebydiscussingandrecognizingtrade-offsbetweenphysicalpropertiesandpolicyincentives.

1ToreadourfirstRFFpaperoninteroperability,see

/publications/

working-papers/trade-friendly-climate-policies-the-promise-of-interoperability/

.

CountingCarbonMoleculesinProducts:DisentanglingtheGrowingWebofCarbonIntensityMethodsiii

Contents

1.IntroductionandPolicyContext1

2.FromCountingtoAccounting2

2.1.InternationalvsCorporateAccounting3

3.RelevantPoliciesWeConsider5

4.WhatIsProduct-LevelAccounting?7

4.1.WhatIsaProduct?8

4.2.WhenAreProductsSubstitutes?9

5.AllocatingEmissionsfromFacilitiestoProducts10

5.1.IsAllocationAlwaysNecessary?10

5.2.Definitions11

5.3.FourFormsofAllocation11

5.4.OtherAllocationChallenges12

Box1.Recycling:HowtoTreatIt–ModuleDImplications13

Box2.AlternativeFuels15

6.CaseStudy:ComparingtheEUCBAM,EPALabelingProgram,

andUSITCStudy15

6.1.ProgramGoals17

6.2.EmissionTypes18

6.3.SystemBoundaries18

6.4.Facility-LevelQuantificationMethodologies19

6.5.Allocation19

6.6.LocationversusMarket-BasedAccountingforScope219

6.7.InteroperabilitywithDifferentStandards20

7.KeyTakeawaysandDiscussion20

References24

Appendix1.Life-CycleStagesinEPDs28

ResourcesfortheFutureiv

Appendix2.ISOStandards29

A2.1.ISO14067:Greenhousegases—Carbonfootprintofproducts—

Requirementsandguidelinesforquantification29

A2.2.ISO14025:EnvironmentalLabelsandDeclarations—TypeIII

EnvironmentalDeclarations—PrinciplesandProcedures29

A2.3.ISO14027:Environmentallabelsanddeclarations–development

ofproductcategoryrulesISO1402730

A2.4.ISO14044:Environmentalmanagement–lifecycleassessment–

Requirementsandguidelines30

A2.5.ISO14040:EnvironmentalManagement—LifeCycleAssessment

—PrinciplesandFramework31

A2.6.ISO21930:SustainabilityinBuildingsandCivilEngineeringWorks

—CoreRulesforEnvironmentalProductDeclarationsofConstruction

ProductsandServices32

A2.7.ISO/TR14069:GreenhouseGases—QuantificationandReporting

ofGreenhouseGasEmissionsforOrganizations—Guidanceforthe

ApplicationofISO14064-132

A2.8.ISO14064-1:ISO14064-1:2018,GreenhouseGases—Part1:Specification

withGuidanceattheOrganizationLevelforQuantificationandReportingof

GreenhouseGasEmissionsandRemovals33

A2.9.ISO14064-2:GreenhouseGases—Part2:SpecificationwithGuidanceat

theProjectLevelforQuantification,MonitoringandReportingofGreenhouse

GasEmissionReductionsorRemovalEnhancements33

A2.10.ISO14064-3:GreenhouseGases—Part3:SpecificationwithGuidance

fortheVerificationandValidationofGreenhouseGasStatements34

CountingCarbonMoleculesinProducts:DisentanglingtheGrowingWebofCarbonIntensityMethods1

1.IntroductionandPolicyContext

Countingcarbon—includinghowandwhytodoit—isgarneringmoreattentionin

climatepolicy.Newpoliciesthatintersectclimate,trade,sustainablefinance,and

domesticmanufacturingrequirecarbonintensitymetrics.Evenassomecountries

reappraisethepaceatwhichclimatepolicyshouldevolve,knowinghowmany

metrictonsofgreenhousegasesareassociatedwithaproduct,service,company,

orcountryremainscriticaltomanydecarbonizationpolicies.Whenmanycountries

aroundtheworldstartadoptingsuchpolicies,thepotentialforfrictionincreasesifthemethodologiesforcountingcarbondiffer.

Inaworkingpaperlastyear,wediscussedthisconceptofinteroperability(Elkerbout

andNehrkorn2024).TheOrganisationforEconomicCo-operationandDevelopment’sInclusiveForumonCarbonMitigationApproacheshasalsodonesignificantwork

toidentifychallengesandpotentialsolutionstocalculatingproduct-levelcarbon

intensitymetrics,includingrecentworkcomparingavailabledatasetsoncarbon

intensity(OECD2024,2025).Inthissecondpaper,weextendtheanalysistotheswiftlychangingdebateonwhatconstitutesappropriatecarbonaccounting,howitdiffers

fromgreenhousegasreporting,andhowcarbonintensityquantificationeffortsfor

climate-and-tradepoliciesrelatetolong-standingpracticesinenvironmentalproductdeclarationsandlife-cycleaccounting.

Forpoliciesatthenexusofclimateandtrade,measuringproduct-levelcarbonintensityasawaytodifferentiateamongproducerscanhaveimportantenvironmentaland

economicmotivationsandimplications,withloweraveragecarbonintensitiesusedtojustifysafeguardingmeasuresvis-à-vismorecarbon-intensiveproducers.Consider,

forexample,suchcarbonborderpoliciesastheEUandUKCarbonBorderAdjustmentMechanisms(CBAM)andtheproposedUSForeignPollutionFeeAct(FPFA)andCleanCompetitionAct(EuropeanCommission2023a;UKHMRCandHMTreasury2024;USCongress2025).Especiallybecausecountriesarestillfiguringouthowtoimplementthesenascentpolicies—andwithcompetitivenesshighonpolicymakers’minds—theinterestinunderstandingcarbonfootprintsatdifferentlevelsofgranularityisonly

increasing.

Procurementpoliciesareanotherexamplewherecarbonfootprintsmatter.Theycan

beaneffectivewaytosteerdemandtowarddomesticproducers,therebycontributingtodemandformoreprotectionoflocalindustries.Ifdomesticindustriesarelower-

carbon,orifacertaincarbonperformanceismandatedforenvironmentalreasons,thencountingcarbonbecomesimportantonceagain.

Forsustainablefinancepolicies,countingcarboncanincreasetransparencyandaccountabilityaroundagivenentity’sexposureorcontributiontoclimatechange.

Butaccountabilityisonlyoneofmanyreasonscountingcarbonisbecomingmore

important.Withanincreasingmixofvoluntaryandmandatorypoliciesacrossdifferent(sub)-nationaljurisdictions,howdifferentwaysofcountingcarbonmeasureupagainst

ResourcesfortheFuture2

eachotherbecomesmoresalient.Companiesmaybesubjecttomultiplepolicies

simultaneously,makinginteroperabilityofmethodologies,reporting,andverificationcritical.Withoutinteroperability,firms—especiallysmallerones—facehightransactioncosts.

Thesenewpoliciesareemergingagainstthebackgroundofarapidlychangingglobaltradesystemthatincreasinglyemphasizesprotectionofdomesticmanufacturing

industries—thesameindustriesforwhichcarbonaccountingisbothcriticaland

challenging.TheexampleoftheFPFAshowshowevenpoliciesthataimtosupport

domesticindustrycanrequirecarbonintensitynumbersforimplementation.When

manycountriesaroundtheworldstartadoptingsuchpolicies,thepotentialforfrictionincreasesifthemethodologiesforcarbonintensityquantificationdiffer.

Thisraisesseveralquestionsthatlieattheheartofthispaper:atwhatpointdoes

countingcarbonbecomeaccountingforcarbon,andisthereapolicyrelevant

difference?Isanew(global)approachtocarbonreportingandaccountingnecessarytoenablefurtherclimatepolicyimplementation,andtowhatextentissuchasystemcompatiblewithexistingcarbonreportingpractices?Anddospecificclimatepolicygoalsrequirespecificcarboncounting/accountingapproaches,oraretheypotentiallycompatiblewithamoreextensive,generallyappliedcarbonaccountingsystem?

Beforeturningtothesequestions,wediscussthedifferencebetweengreenhouse

gasreporting,focusedonemissionssourcesandproduction,andcarbonaccounting,focusedonproductsandtransactions.Bothareimportant,butwhiletheformerhasbeenputintopracticefordecades,thelatterissettobecomemoreimportantin

comingdecadesasclimatepoliciesthattargetcarbon-intensiveandtradedgoodsgrowinnumber.

Wethencontrastdifferenttypesofpoliciesthatrequireknowledgeaboutthecarbonmoleculesassociatedwithaproduct,whichinturnmeritsdiscussiononwhatismeantbya“product.”Wediscussrelatedpracticesandstandardsinlife-cycleaccounting,

environmentalproductdeclarations,andassociatedinternationalstandards.We

thenpresentthreepolicycases—theEUCBAM,aUSEnvironmentalProtection

Agency(EPA)carbon-intensitylabelingprogram,anda2025USInternationalTradeCommission(ITC)studytobenchmarkUSsteelandaluminumproduct-levelcarbonintensities—tohighlightwhereexistingpracticesandmethodsrelatedtocarbon

intensityquantificationmaygiverisetodifferencesofopinionorinterpretationandhowthiscouldaffectinteroperability.

2.FromCountingtoAccounting

Intheworldoffinance,“accounting”hasaspecificmeaningandextensivehistory.Oneofitscriticalfeaturesisdouble-entrybookkeeping,goingbackatleasttofifteenth-

century

Medici-eraFlorence

,whereanytransactionisrecordedonbothacreditanddebitsideoftheledger—hencethedoubleentry(Devlin2019).Notablehereistheemphasisontransactionsasthekeyeventtokeeptrackof,incontrasttoproductionitself.

CountingCarbonMoleculesinProducts:DisentanglingtheGrowingWebofCarbonIntensityMethods3

InstitutionalizedglobalclimatepolicycooperationgoesbacktotheestablishmentoftheIntergovernmentalPanelonClimateChange(IPCC)in1988andtheUnitedNationsFrameworkConventiononClimateChange(UNFCCC)in1992.Countinggreenhousegasemissionshasbeenacriticalmetricunderpinningmultilateralnegotiations.

Knowinghowmanymetrictonshavebeenandcontinuetobeemittedbydifferent

countriesisvaluablenotjusttoestimateandforecastevenmorefoundationalclimatesciencemetrics(suchascarbondioxide,orCO2,concentrationsintheatmosphere)butalsobecausedifferentiatedresponsibilitiesandequitybetweencountriesaresomeofthemostcontestedelementsofclimatediplomacy.

Countriestodaycontinuetomaintainso-calledgreenhousegasinventoriesandreporttheirannualemissionsaccordingtoIPCCstandardstotheUNFCCC(UNFCCC2014;UNFCCCn.d.a;Goodwinetal.2006).Themethodologyforthisreportingisbased

onIPCCguidelinesfrom2006(Egglestonetal.2006).Thisreportingfocuseson

sourcesandsinksandisnottheclimatepolicyversionoffinancialaccounting—i.e.,

carbonaccounting—butratherlikesimplecounting.Insteadoftransactions,reportingemissionssourcesandsinksfocusesonman-made(production)processesand/

ornaturalprocessesaddingorremovinggreenhousegasestotheatmosphere.

InteractionsamongcountriesusingcarbonunitsarealsoafeatureofArticle6ofthe

ParisAgreement,whichsetsupinternationalcarbontrading(UNFCCC2025).AlthoughArticle6introducesconceptssuchasindirectemissionsandprecursors,byand

largetheseguidelinesdealwithemissionssources.Thusclimatepolicy,globallyanddomestic,hasevolvedwithoutafully-fledgedmandatorycarbonaccountingsystem,evenascarbon-differentiatedtransactionsaregrowing.

Anaccountingframeworkmightsupportdifferentpolicygoalsdependingonhow

theinformationisused.Inconsistencyinunderlyingaccountingmethodscanreducecredibilityandcreateperverseincentives—particularlyifemissionsareunderreportedordouble-counted.Furthermore,alackofclearguidancemayencourage“method

shopping”inwhichapproachesarecombinedtoreporttheleastemissionspossible.

Inaninteroperablesystem,acarbonaccountingframeworkshouldstillbeabletoaccommodatedifferentpolicies,withdifferentincentives.Oncethepoliciesand

incentivesarealigned,it’sarguablymoreaccuratetospeakofharmonization,whichgoesbeyondinteroperability.

2.1.InternationalvsCorporateAccounting

Meanwhile,oneofthemostwidelyusedsystemstoquantifycarbonfootprintsinthebusinessworldistheGreenhouseGas(GHG)Protocol’sEmissionsScopes1,2,and3.(Bhatiaetal.2011).Scope1coversdirectemissionsandcorrespondsmorecloselytowhatisreportedasemissionsfromsourcesingreenhousegasinventories.Scope2emissionsareemissionsassociatedwithconsumedpowerorheatand,outside

oftheGHGProtocol,arereferredtoasindirectemissions.Scope3emissionsaretheemissionsinasupplychain(upstream)orassociatedwiththeuseofaproduct(downstream).Inprinciple,Scope2emissionscouldbeseenasanexampleof

upstreamScope3emissions,inthattheyareemissionsrelatedtoaninput—itjusthappenstobeahighlycommontypeofindirect,inducedemissions.

ResourcesfortheFuture4

TheGHGProtocolisanongovernmentalinitiativeandismostlyusedforcorporate

andvoluntaryclimateaction(Sotos2015).Theprotocolisnotubiquitouslyusedfor

compliancepolicies.Nevertheless,ithasbecomesowidelyusedthatlegislatorshavebegunreferringtoitinlegislationoftheirown.Forexample,California’sdisclosurelawsSB253andSB261repeatedlyrefertoemissionsscopesandstate,“TheGreenhouse

GasProtocolisthegloballyrecognizedGHGemissionsaccountingandreportingstandard”(CaliforniaStateLegislature2023a,2023b).

Itisneverthelessachoicemadebythelegislatortoadoptanexistingnon-

governmentalaccounting/reportingframework,ratherthantodraftanewsetof

rules.TheIPCC2006guidelinesfornationalGHGreportingdonotrefertoemissionsscopes,althoughconceptssuchasindirectemissionsandprecursors(aninputinto

anotherproductionprocess–anexampleofScope3emissions)areused.Byandlarge,however,theseguidelinesdealwithsourcesofemissions;whatintheGHGProtocol

wouldbeScope1emissions.

Inrecentyears,theE-ledgersInstitute,theEFIFoundation,andothershaveled

discussionsaboutnewcarbonaccountingframeworksthatcontrastwiththeGHG

Protocol(E-ledgersInstituten.d.;Monizetal.2025).AcommoncritiqueisthatundertheGHGProtocol,emissionscanbecountedmorethanonce.Indeed,allemissions

haveasourceandwillbecountedassomeentity’sdirect,Scope1emissions,eveniftheyalsocountasindirectemissionsoremissionsinotherentities’supplychains.ForproponentsoftheGHGProtocol,countingemissionsmorethanonceisfeature,notabug,asithighlightsdispersedresponsibilitiesforbothproducersandconsumers.

Ifemissionscanonlybecountedonce,eitheronlydirectemissionssourcesshouldbecounted,oramoreextensivesystemaccountingforcertaintransactionsisneeded.

Thisstatementshouldnotbeseenasendorsing(ordenying)theneedforanew

carbonaccountingsystem.TheexampleofnationalGHGinventoriesshowsthatsomeformsofreportingonlyemissionssourcescanbeanimportantunderpinningofclimatepolicy.Indeed,internationalclimatepolicyhasevolvedfornearlyfourdecadeswithoutasystemofcarbonaccountingofequivalentdepthtomodernfinancialaccounting

practices.

Thiscaneitherbeseenasevidencethatnosuchsystemisnecessarytomake

progressondecarbonization,orasproofthatfurtherdecarbonizationdependsonnewcarbonaccountingsystems.

Perhapsthemostcriticalchallengeinthecontextofvariousindustrialdecarbonizationpoliciesistheneedtoquantifythecarbonfootprintofvariousindustrialproducts,

whichrequiresgoingfromthefacilitylevel(whicharesourcesofdirectemissions)totheproductlevel.Dependingontheproduct,itmayalsoinvolveaccountingfortheemissionsfromseveralinputs,andthereforepossiblyfromseveralfacilities.

CountingCarbonMoleculesinProducts:DisentanglingtheGrowingWebofCarbonIntensityMethods5

3.RelevantPoliciesWeConsider

Publicprocurement,bordermeasures,andreportingdependonreliablecarbon

accountingmethodologiesbutmayentaildifferentpoliticalchoicesandrequirements.ThreecaseswediscussinmoredepthinSection6exemplifythesedifferences:

theEPAbegana

labelingprogram

toaidthe(nowdefunct)US

BuyClean

publicprocurementprogramforcleanerconstructionmaterials,whiletheEUCBAM

willrequireimporterstopayapricebasedonthecarbonintensityofarangeof

products(USEPA2025b;CEQn.d.).Andinthecaseofthe

USInternationalTrade

Commission’s(ITC’s)SteelandAluminum

study,policymakersaresimplytryingto

betterunderstandproduct-levelcarbonemissionsthroughreportingmandates(Petersetal.2025).

Currently,publicprocurementpoliciesandclimate-and-tradepoliciesusedifferent

frameworksforemissionsreporting.Publicprocurementpoliciestypicallydepend

ontheuseofEnvironmentalProductDeclarations(EPDs),whichreporttheresults

ofalife-cycleanalysis(LCA)tocalculatetheglobalwarmingpotential(GWP)1LCAs

areinformedbyproductcategoryrules(PCRs)whichsettherulesforconducting

anLCAandaregenerallynotstandardizedandcanvaryinquality.TheInternational

OrganizationforStandardization(ISO)2hasdoneworktostandardizetherulesand

processesforthedevelopmentofEPDs,LCAs,andPCRs;however,guidelinesare

relativelygeneric,andthereforeareasforpotentialdisagreementremain.ThesegapshavespurredtheIndustrialDeepDecarbonisationInitiative(IDDI),aspecializedUnitedNationsagencyfocusedonacceleratingindustrialdevelopment,tobeginworkonPCRharmonizationandpromotecomparabilityofEPDsacrossproductsandjurisdictions,thereforepromotinginteroperability(UNIDO2024).

Meanwhile,theEUCBAMisapolicydesignedtomirrortheEU’semissionstrading

system.Therefore,theEUisdesigningitsownmethodologiestotranslatefacility-

levelemissionstotheproductlevel.Thiscreatesanumberofrestraintsandpoliticalchoices,whichmaybedifferentthantheexistingrequirementsfromEPDs3,suchassystemboundaries,allocationmethods,anddataqualityrequirement.WewilldiscussthesechoicesandcompareapproachesinSection6.

1Inthiscontext,GWPrepresentsthecarbondioxideequivalent(CO2e)perunitofprod-uct/material(USEPA2024b).WediscussthisfurtherinSection6.

2SeeAppendix2foradescriptionofrelevantISOstandards.

3SeealsoE-ledgersInstitute(2024)foradiscussionofhowEPDscanbeastartingpointformoregranularproduct-levelcarbonaccountingbutarenotsufficientthemselves.

ResourcesfortheFuture6

Figure1.EnvironmentalProductDeclarationProcessand

RelationtoCarbon-IntensityQuantification

EPDCreationProcess

Rules:ProductCategoryRule(PCR)

ISO14027:providesprinciples,requirementsandguidelinesfordeveloping,reviewing,registeringandupdatingthePCR.

Ozonedepletion

Eutrophication

Wateruse

3

Calculation:LifeCycleAssessment(LCA)

ISO14067:specifiesprinciples,requirementsandguidelinesforthequantificationandreportingofthecarbonfootprintofaproduct.

A

ISO14040:describestheprinciplesandframeworkforanLCA

+

ISO14044:coversLCAstudiesandlifecycleinventorystudies

Reporting:EnvironmentProductDeclaration(EPD)

ISO21930:providestheprinciples,specificationsandrequirementstodevelopanenvironmentalproductdeclaration.

ISO14025:establishestheprinciplesandspecifiestheproceduresfordevelopingTypeIIIenvironmentaldeclarationprogrammesandTypeIIIenvironmental

declarations.

GlobalWarming

Potential(GWP)

Chemicalregulation

Water

conservationregulation

Public

Border

Waterqualityregulation

measures

procurement

Note:ISO21930andISO14025arelistedseparatelyintheEPDreportingprocess,asISO21930givesconstructionsectorspecificruleswhereasISO14025givesgeneralframeworkforEPDs.ForacompleteexpansionoftheISOs,pleaserefertoAppendix2.

Theabovefigureshowstherelationshipbetweeninternationalstandards,product

categoryrules,life-cycleassessments,environmentalproductdeclarations,andpolicy.PCRssettherulesfor