碳中和能源系统中的碳管理 Carbon Management in Net-Zero Energy Systems -White Paper

CarbonManagementinNet-ZeroEnergySystems

WhitePaper

MARCH2022

ABOUTTHISREPORT

EnvironmentalDefenseFundcommissionedEvolvedEnergyResearchtoadvanceunderstandingofhowcarbonmanagementinenergyandindustrycouldplayaroleinachievingnet-zerogreenhousegasemissionsintheU.S.by2050.TheBernardandAnneSpitzerCharitableTrustprovidedfinancialsupportforthisstudy.

PREPAREDBY

GabeKwok

BenHaley

RyanJones

ABOUTEVOLVEDENERGYRESEARCH

EvolvedEnergyResearch(EER)isaresearchandconsultingfirmfocusedonquestionsposedbytransformationoftheenergyeconomy.Theirconsultingworkandinsight,supportedbycomplextechnicalanalysesofenergysystems,aredesignedtosupportstrategicdecision-makingforpolicymakers,stakeholders,utilities,investors,andtechnologycompanies.

Copyright©2022EvolvedEnergyResearchLLC.Allrightsreserved.

CarbonManagementWhitePaper|EvolvedEnergyResearch

TableofContents

EXECUTIVESUMMARY 4

BACKGROUND 9

APPROACHANDASSUMPTIONS 11

CarbonManagementScope 11

StudyApproachandModelingFramework 12

GHGEmissionsAccounting 14

BaseAssumptions 16

SensitivityAnalysisAssumptions 18

CARBONMANAGEMENT’SROLE 25

Overview 25

RegionalInfrastructureImplications 33

CaseStudies 38

Non-CO2Considerations 41

CONCLUSIONSANDKEYFINDINGS 44

REFERENCES 51

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ExecutiveSummary

Background

Recentstudiesfromtheinternationalcommunitysuggestthatmeetingnet-zerogreenhousegas(GHG)emissionsbymid-centurywillrequiremanagingthecaptureofbillionsoftonsofcarbondioxide(CO2).Thetechnologiestodosoexisttoday,atleastattheprototypeordemonstrationstage,andmaybecrucialfordecarbonizingkeysectorsanddrawingdownatmosphericCO2.However,despiteitspotential,theroleofcarbonmanagementremainslargelynascent.

Thispapersetsouttoprovideadeeperunderstandingofcarbonmanagement’sroleinenergyandindustrythroughansweringkeyquestions:howmuchCO2captureisrequired?WhichtechnologiescapturesignificantquantitiesofCO2?WhenisCO2storedorutilized?Howsensitiveareoutcomestoalternativeassumptions?Howcouldstrategiesvaryregionally?

Approach

TheanalyticalapproachforthisstudyisbasedonourEnergyPATHWAYSandRegionalInvestmentandOperations(RIO)models.PairingbothmodelstosimulatetheU.S.energyandindustrialsystemisaframeworkthathasbeenappliedinrecentnet-zeroanalyses,includingCarbon-NeutralPathwaysfortheUnitedStates(Williamsetal.,2021)andPrincetonUniversity’sNet-ZeroAmericastudy(Larsonetal.,2021).

Thescopeofouranalysisincludestechnologicalcarbonmanagementsolutionsintheenergyandindustrialsystem,whilenon-technicalcarbonmanagement(e.g.,nature-basedsolutions)areoutsidethescope.WemodelasuiteofcarboncapturetechnologiesandCO2applications,includingretrofitsofexistingenergyinfrastructure,negativeemissionstechnologies(NETs),CO2storageingeologicformationsandCO2utilizationforsyntheticfuels.Weidentifytheircost-optimaldeploymentacrosssixteenU.S.regionstoachievedeepemissionsreductions.

WeconstructaCoreNetZero(CNZ)scenariowheretheU.S.economyachievesnet-zeroGHGemissionsby2050atleast-costusingbaselineenergytechnologycostandresourceavailabilityassumptions.Thisbaselineprovidesastartingpointtocompareagainstarangeofmodeleduncertaintiesthatcouldmateriallyaffectcarbonmanagementoutcomes.Weexplored

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alternative:fossilfuelcosts;geologicsequestrationcostandpotential;biomasscostandpotential;renewablescostandpotential;electrolysiscosts;andend-useelectrificationrates.

Ourbaseassumptionforachievingnet-zeroGHGemissionsby2050is:(a)modeledenergyandindustry(E&I)CO2decreasesto0.0Gt;and(b)thecombinationofnon-CO2emissionsandthelandsinksumtozerousingcarbondioxideequivalentswithGWP100(acommonsimplificationforeconomy-widenetzeroanalyses).Sincethetrajectoriesfornon-CO2mitigationandlanksinkenhancementarebothhighlyuncertainandaffecttheneedforcarbonmanagementintheenergysystemtomaintainnet-zeroGHGemissions,wefurthermodeled2050E&ICO2targetsof-0.5Gtand0.5Gt.

However,itisbecomingincreasinglyclearthatshort-livednon-CO2gases,suchasmethane,aredisproportionatelyresponsibleforglobalwarmingimpactsonshortertimeframes.Thissuggeststhatnon-CO2gasesarebothagreatliabilitytonet-zeroobjectives(becausetheycausewarming)andagreatopportunity(becausemitigationoftheirproductionandleakagepresentsanefficientpathwaytoreducewarming).ThiscaveatemphasizestheimportanceofresearchwearecurrentlyundertakingtodevelopimprovedmethodsthatcanadequatelyconsidertheclimateimpactsofallGHGsovermultipletimescales.

Keyfindings

Carbonmanagementisapillarofaleast-costpathwaytonet-zero

Wefindthatcarboncapturedeploymentinenergyandindustryisnecessarybymid-centuryevenassumingsuccessacrossallothermitigationstrategies,includinghighlyaggressiveenergyefficiency,electrification,electricitydecarbonization,enhancementofthelandsinkandmitigationofnon-CO2emissions.IntheCNZscenario,nearly700MtCO2iscapturedbymid-century,whichisequivalenttoabout10%oftoday’sU.S.grossGHGemissionsorallenergyCO2emissionsinTexas.Accountingforavarietyofuncertainties,totalCO2capturerangesfrom400to1,100MtCO2.Ifthecurrentlandsinkshrinksand/ornon-CO2emissionsprovemoredifficulttoabate,theimportanceofcarbonmanagementinenergyandindustryisfurtherincreased.

BothCO2storageandutilizationforsyntheticfuelproductionareimportantapplications.Storagerangesfrom300to900MtCO2,whichiswellbelowestimatedgeologicsequestrationpotential,whileCO2utilizationrangesfrom100to400MtCO2acrossmostcircumstances.CapturedCO2isoverwhelminglysuppliedfromNETs(250to950MtCO2),includingbioenergywithcarboncapture,

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utilization,andstorage(BECCUS)forfuelproductionanddirectaircapture(DAC).Near-neutraltechnologies,wherefossilfuelisaninputand90%to100%ofemissionsarecaptured,provideamuchsmallershareofCO2supply.

CarbonManagementMetricsin2050withModeledUncertainties

Note:rangereflectsmodeleduncertaintiesandlinerepresentsbaselineprojection(CoreNetZeroscenario).

Negativeemissionstechnologiesarewell-suitedfornet-zeroGHGemissions

Asemissionsreductionsacceleratefrom2030to2050,CO2captureshiftstowardsNETsandthesetechnologiessupplythree-quartersoftotalcarboncaptureintheCNZscenario.BECCUSforfuelproductionisgenerallythelowest-costoptionforsupplyingnegativeemissionsdueto:(1)itscarboncaptureefficiency(e.g.,approximately70-140MtCO2iscapturedper100milliontonsofbiomass);and(2)itsversatilitytodisplacefossilfuels.However,itsdeploymentisconstrainedbyanuncertainsupplyofsustainablebiomass.AlthoughDACisnotdeployedintheCNZscenario,itisanimportanttechnologytosupplynegativeemissionsunderveryplausiblecircumstancesthatmayariseonthepathtonet-zero,suchasslowerconsumeruptakeofelectricvehiclesorlowerbiomassavailability.OuranalysisconfirmsthatNETsdeploymentdoesnotdelayoravoidothermitigationstrategiessolongasastrongnet-zerotargetisinplace.

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Fossil-basedcarboncapturefaceshurdlesinanet-zerocontext

Carboncaptureatfossil-basedpowergenerationandhydrogenproductionfacilitieshavecharacteristicsthatdisadvantagetheirdeployment.First,theelectricitysectorshiftstowardsveryhighlevelsofvariablerenewableenergy(>70%ofgeneration),whichencouragesinvestmentinelectrolysis,acompetitorofbluehydrogen,anddiscouragesthermalpowergeneration.Second,large-scaledeploymentrequiressignificantlyscalingupCO2storageinfrastructure.Forexample,ifthesetechnologiessuppliedone-thirdofend-useelectricityandhydrogendemand,thenapproximately1,200MtCO2ofannualstoragewouldberequired.Finally,carboncaptureinthesetwosectorscanonlyaddresstheirownemissions,whereasNETscanflexiblyaddressresidualemissionsfromanysectorintheeconomy.

Achievingnet-zerowithoutcarbonmanagementhassignificanttrade-offs

Excludingcarbonmanagementasastrategyis"technicallyfeasible”butentailsscalingbiomassandrenewableresourcestopotentiallyproblematiclevels(e.g.,morethanonebilliontonsofbiomass).Givenuncertaintyaboutthesupplyofsustainablebiomassandthechallengesofsitingrenewables,takingcarbonmanagementoffthetableamplifiestheriskofmissingnet-zero.

Prioritizecarbonmanagement’slong-termrole

Today’sresearchandfundingislargelyfocusedon:(a)deployingpoint-sourcecarboncaptureatexistingfossil-basedfacilities(e.g.,retrofitsoffossilpowerplants);and(b)usingCO2forenhancedoilrecovery(EOR),whichoftenrequireslong-distanceCO2pipelinenetworks.However,muchofthisinfrastructurethatisaretrofitcandidatefacesdecliningutilizationand/orlimitedremainingoperatinglifetimesinthecontextofnet-zero.Incontrast,ouranalysisshowscarboncapturetechnologyisalmostexclusivelyappliedtonewenergyinfrastructureandthatsignificantcapture(>100MtCO2/yr)occurs20to30yearsfromtoday.Asaresult,webelievefocusshouldbeexpandedtowardsareasthatbetteralignwithachievingnet-zerointhelong-term,including:(1)fosteringthedevelopmentofNETs;(2)placingvalueonbothCO2storageandbeneficialCO2utilizationinlow-carbonfuels;and(3)identifyinganddevelopingregionalintegratedcarbonmanagementhubswithsharedinfrastructure.

CO2ismanageddifferentlyacrosstheU.S.andisprimarilyusedintra-regionally

WefindsignificantvariationsinthesourcesofcapturedCO2anditsapplicationacrossU.S.regionsduetodifferencesinbiomass,renewablesandgeologicsequestrationpotential.Nearly

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allcapturedCO2isstoredorutilizedwithinseveralhundredmilesofthepointofcaptureandnottypicallytransportedlongdistancesacrosstheU.S.Furthermore,sinceCO2utilizationtoproducesyntheticfuelcanbeaccomplishedintra-regionally,thereislittleneedtotransportCO2long-distancestooil-producingregionsforEOR.

Innovationacrossthecarbonmanagementsupplychainisneeded

Carbonmanagement’sabilitytocontributetowardsnet-zeroGHGemissionsdependsoninnovationacrossachainofCO2capture,transportation,utilizationandstorageinfrastructure.Inouranalysis,nearlyallcapturedCO2in2050isfromtechnologiescurrentlyinthedemonstrationorprotypestage,andtechnologiesthatutilizeCO2areatasimilarstageofdevelopment.Thissuggeststhatsignificantresearch,development,anddemonstration(RD&D)isnecessarytoensurethetechnologiesmostcompatiblewithaleast-costnet-zeroenergysystem(e.g.,NETsandsyntheticfuelproduction)aredeployedinatimelymanner.

Theriskofcarboncaptureextendingthelifeoffossilfuelsislowifweareonapathtonet-zero

Onekeyconcernaboutcarbonmanagementisthatitfacilitatescontinuedfossilfueluse,butournet-zeroanalysisfindslargereductionsinfossilfuelconsumption(80-90%below2005levelsby2050).However,carbonmanagementtechnologiescouldenablesomefossilfueluse,suchasheatorfeedstocksforindustrialapplicationsthatarechallengingorveryexpensivetoabate.Sincecarbonmanagementdoesnotinherentlyaddressnon-CO2pollution,suchasmethane,itwillbeimportantforpolicymakerstomonitorandaddressco-pollutantsassociatedwithcarbonmanagement,lesttheynegateitsnear-andlong-termclimatebenefits.

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CarbonManagement

Technical

(energy&industry)

Fossil-basedpointsourcecarboncapture

Negativeemissiontechnologies(“NETs”)

or

Carbondioxide

removal(“CDR”)

Non-technical

(natural)

Background

U.S.andinternationaldeepdecarbonizationstudieshaveidentifiedenergysystemstrategiesthatarenecessaryforachievingemissionsreductionsconsistentwithclimatestabilizationtargets.Energyefficiency,end-useelectrification,andelectricitydecarbonization,commonlyreferredtoasthe“threepillars”,featureconsistentlyacrossalargebodyoftechnicalworkdemonstratinglow-carbonenergysystemsalignedwith“80%by2050”targets.1Analysesconsistentwithmoreaggressivegreenhousegas(GHG)ambition,suchas“net-zeroby2050”,haveidentifiedcarbonmanagementasafourthpillarofdeepdecarbonization.2

Asshownin

Figure1

,carbonmanagementconsistsoftwoapproaches:(1)technicalsolutionsin

energyandindustry;and(2)non-technicalornaturalsolutionsoutsideoftheenergysystem,suchasafforestation/reforestationandocean-basedcarbondioxideremoval(CDR).Inthispaper,weassesstechnicalcarbonmanagementoptions,includingcarboncaptureatfossil-basedpowerplantsandindustrialfacilities,aswellasnegativeemissionstechnologiessuchasdirectaircaptureandbio-energywithcarboncapture.

Figure1CarbonManagementApproachesandTechnologies

Powerplants

Industrialfacilities

Directaircapture

Bio-energywithcarboncapture

Afforestation/Reforestation

Soilcarbonsequestration

Enhancedmineralization

Ocean-basedCDR

1SeeWilliamsetal.(2014)

2SeeHaleyetal.(2018)andWilliamsetal.(2020).

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Technologicalcarbonmanagementresearchhasprimarilyfocusedonitsroletodecarbonizespecificsectors(e.g.,electricpower)orfuels(e.g.,hydrogen),aswellasindividualtechnologyassessments.IntheU.S.,recentstudieshaveconsideredtheroleofcarboncaptureretrofitsatexistingfacilities,theuseofcapturedCO2inenhancedoilrecovery(EOR)andthedevelopmentoflong-distanceCO2transportationtoaddressspatialmismatchesbetweenexistingemissionssourcesandgeologicsequestrationsites.3Net-zeroenergysystem-widestudiesshowawiderangeofresultsforthetotalquantityofCO2captured,thesourcesofcapturedCO2(e.g.,fossilfuelorbiomass)anditsapplication(e.g.,sequestrationorutilization).

Thegoalofthiswhitepaperistoadvanceunderstandingofhowcarbonmanagementinenergyandindustrycouldplayaroleinachievingnet-zeroGHGemissionsintheU.S.Thetechnologies,sectors,andapplicationswherecarbonmanagementcouldbeimplementedtosupportnet-zeroisvast.Ouranalysisincorporatesawiderangeofuncertaintiestofurtherunderstandwhatdrivesalternativecarbonmanagementoutcomesandwhichtechnologiesarerobustinthelongrun.

Theremainderofthispaperisorganizedasfollows.Section2providesanoverviewofthescopeofcarbonmanagementtechnologiesandapplicationsconsideredinthisworkandourmodelingapproachandassumptions.Section3presentsanalyticalresultsforcarbonmanagementinthecontextofanet-zeroGHGemissions,andSection4summarizeskeyfindingsandconclusions.

3Forexample,seeEdwardsandCelia(2018)andGreatPlainsInstitute(2020).

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ApproachandAssumptions

CarbonManagementScope

Tounderstandthecontributionofcarbonmanagementtomeetnet-zeroGHGemissions,we

evaluatedasuiteofcarboncapturetechnologiesandapplicationsofCO2acrosstheenergyand

industrialsectors,asshownin

Figure2

.Werepresentretrofitsofexistingenergyinfrastructure

suchasfossilpowerplants,cornethanolfacilitiesandcementproduction,aswellasnewfuelproductionfacilitiesthatcouldplayameaningfulroleinadeeplydecarbonizedenergysystem.

Wecategorizecarboncaptureatpowergeneration,bluehydrogenandindustrialfacilitiesasnear-neutralemissionstechnologiessincetheirenergyinputisfossilfuelandcaptureratesrangefrom90%to100%.ThisdesignationreferstocombustionandprocessemissionsatthefacilitiesanddoesnotaccountforpotentialupstreamordownstreamGHGemissionsleakage,animportantconsiderationthatwediscusslaterinthispaper.Intheelectricpowersector,wemodelretrofitsofexistingfossilresources,aswellasnewgas-firedresourceswithcaptureratesof90%and100%(i.e.,AllamCycle).Wemodelcarboncaptureinthecementindustrydueitshighlevelofemissionsandlackofalternativedecarbonizationoptions,andwenotethatotherindustrialsectors(e.g.,ironandsteel)couldapplycarboncapture.

Directaircapture(DAC)andthecaptureofCO2intheproductionofbiofuels(alsoreferredtoasbioenergywithcarboncapture,utilization,andstorageor“BECCUS”)arecategorizedastechnicalnegativeemissionstechnologies(“techNETs”)sincetheyextractCO2directlyfromtheatmosphereorindirectlythroughtheCO2embodiedinbiomass.4Strategiesoutsideoftheenergysectorthatincreaseterrestrialcarbonsequestration(“landNETS”)arenotexplicitlymodeled,butweincludearangeofalternativelandsinkassumptionsinouranalysis,asdiscussedbelow.5

Oncecaptured,CO2followstwopossibleroutes:(1)sequestrationingeologicformations;or(2)utilizationintheproductionofsyntheticfuels,suchasliquidsandmethane.6Ourmodeling

4WerefertocapturedbiogenicandatmosphericCO2as“NETsCO2”.

5Technicalandnaturalnegativeemissionstechnologiesarecollectivelyreferredtoas“carbondioxideremoval”(CDR)inotherwork,whilelandNETSarefrequentlydescribedas“naturalclimatesolutions.”

6SeeIEA(2019)foranextensivereviewofCO2utilizationtechnologyoptions.

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approachidentifiesthecost-optimalcarboncapturetechnologydeploymentandapplicationofCO2tomeetnet-zeroemissionsaspartofthesolutionforthebroaderenergysystem.

Figure2ModeledCO2SourcesandApplications

StudyApproachandModelingFramework

Recognizingthatcarbonmanagementoutcomestoachievenet-zeroGHGemissionsaresensitivetoalternativeassumptions,weusedthefollowingapproach.First,weconstructaCoreNetZero(CNZ)scenarioreflectingourbaseassumptionsandthisisthestartingpointtocompareallothersensitivitiesagainst.Next,weimplementmultiplesensitivitiesofftheCNZscenariothatreflectuncertaintiesaffectingthecostandviabilityofvariouscarbonmanagementoptions.Thisprocessallowsustotesttherobustnessofourresultsanddrawadditionalinsights,includinginsightsforlawmakerslookingtopasspolicytoimprovecarbonmanagementtoolsandpractices.Weexplorearangeofuncertaintiesaroundfossilfuelprices;resourcepotential;technologycosts;end-useelectrificationrates;andenergyandindustrialCO2emissionsreductiontargets.Finally,weevaluatetopic-specificcasestudiestobetterunderstandtheroleoffossil-

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basedcarboncapturetechnologiesandtheimplicationsofnotpursuingtheinnovationneededforcarbonmanagementtobetechnologicallyready.

TheanalyticalapproachforthisstudyisbasedonourEnergyPATHWAYS(EP)andRegionalInvestmentandOperations(RIO)models.PairingbothmodelstosimulatetheoverallU.S.energyandindustrial(E&I)systemisaframeworkthathasbeenappliedinrecentU.S.net-zeroanalyses,includingCarbon-NeutralPathwaysfortheUnitedStatesandPrincetonUniversity’sNet-ZeroAmericastudy.7Thisframeworkincludestwosteps:(1)EPproducesabottom-upprojectionoffinalenergydemandforallend-usesacrosstheeconomybasedonuser-definedenergyefficiencyandfuelswitchinglevers;and(2)RIOdeterminesthecost-optimalenergysupplytomeetenergydemandprojectionsfromEP,whilemeetingannualemissionsandadditionalconstraints.

Optimalinvestmentsacrosstheelectricityandfuelssectorsaredeterminedsimultaneously.Thisuniqueframeworkiswell-suitedtoevaluatecarbonmanagementbecausethesupplyanddemandforcapturedCO2crossesmultiplesectorsanditcapturesdynamicinteractionsthatoccuraslinesbetweentraditionallydistinctsectorsbecomeblurredovertime.Forexample,aDACfacility:(a)isamajorelectricload;(b)cansupplyCO2forsyntheticfuelproduction;and(c)cansupplyCO2forsequestrationtoaddressresidualor“legacy”emissionsinanysector.

WerepresenttheU.S.E&Isystemacross16geographicregions,asdepictedinFigure3.Theseregionsarecharacterizedbyimportantdifferencesthataffecthowdeepdecarbonizationoccurs,including:(a)resourceendowmentssuchasrenewableresourcepotentialandquality,biomassfeedstocksupplyandgeologicsequestrationavailability;and(b)electrictransmissionconstraintsbetweenregions.Regionalcarbonmanagementimplicationsarestronglyinfluencedbyresourceendowments,whichwediscussindetailinsection3.2.

7SeeWilliamsetal.(2021)andLarsonetal.(2020).

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Figure3ModeledRegions

GHGEmissionsAccounting

Inthissection,wedescribe:(1)thescopeofemissionscoveredinourmodeling;(2)ourassumptionsaboutemissionsoutsidethescopeofourmodeling;and(3)adescriptionofaccountingconventionsastheyrelatetocarbonmanagement.Allscenariosevaluatedinthisstudyareinthecontextofachievingeconomy-widenet-zeroGHGemissionsby2050intheU.S.However,thescopeofourmodelingislimitedtoE&ICO2emissions,whichincludesfourcomponents:

1.Grossenergy:CO2emissionsfromfossilfuelconsumptionorfossilcarbonthatisextractedandembeddedinproducts.Itaccountsforfossilfuelusedinpowergeneration,transportation,hydrogenproductionanddirectlybyend-uses,suchasappliancesinbuildings.Emissionsareanoutputfromourmodeling.

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2.Grossindustry:CO2emissionsfromindustrialprocesses,suchascementproduction.Itstrajectoryisanexogenousinputbasedonprojectedindustrialactivity.

3.Productsequestration:CO2emissionssequesteredindurableproducts,suchasplastics.Itstrajectoryisanexogenousinputbasedonprojectedeconomicactivity.8

4.Geologicsequestration:CO2emissionssequesteredingeologicformations.Reflectsallsequestrationfrombothnear-neutralandnegativeemissionstechnologies.

NetE&ICO2,thesumofthefourcomponentsabove,istheprimaryemissionsconstraintappliedinourmodelingandourbaseinputassumptionis0.0Gtby2050.Reachingnet-zeroGHGemissionsalsorequireschangestonon-CO2GHGemissionsandthelandsink,whicharecurrently~1.3GtCO2eand-0.8GtCO2e,respectively.Basedonplausiblenon-CO2mitigationandlandsinkenhancementtrajectoriesfromtheliterature,weassumethatthelandsinkandnon-CO2GHGssumtozeroby2050.9Table1illustratestheGHGaccountingconventionsdescribedaboveusinganexamplecalculationofnet-zeroGHGby2050.

Table1ExampleofNet-ZeroGHGEmissionsAccountingandModelingMethods

Category

Sub-Category

ModelingMethod

LineItem

GtCO2e(2050)

E&ICO2

Grossenergy

OptimizedoutputfromRIO

[A]

0.6

Grossindustry

ExogenousassumptionusedasinputintoRIO

[B]

0.2

Productsequestration

ExogenousassumptionusedasinputintoRIO

[C]

-0.3

Geologicsequestration

OptimizedoutputfromRIO

[D]

-0.5

NetE&ICO2

InputconstraintusedinRIO

[E=A+B+C+D]

0.0

Non-CO2

CH4,N20&F-gases

Assumption

[F]

0.9

LandSink

NetLULUCF

Assumption

[G]

-0.9

GHG

NetGHG

[H=E+F+G]

0.0

8TheU.S.EPAalternativelyadjustsforcarbonstoredinproductsbysubtractingfromtotalfuelconsumption,whereaswealternativelytrackunadjustedfuelconsumptionsinceweallowfuelsupplydecarbonization.ForanoverviewoftheEPA’smethodology,seeSection3.2ofU.S.EPA(2021).

9SeeSection4.2fromWilliamsetal.(2020)foradetaileddiscussion.

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BaseAssumptions

Table2

summarizeskeyassumptionsfromtheCNZscenariothatareappliedconsistentlyacross

theanalysisunlessspecifiedotherwise.Allscenariosachievenet-zeroGHGemissionsbymid-century,whiledeliveringenergyservicesprojectedfromtheU.S.DepartmentofEnergy’s(DOE)AnnualEnergyOutlook2021(AEO).WeusepubliclyavailabledatafromU.S.governmentagenciesorlaboratoriestocharacterizefuelcostsandtechnologycostandperformance,andrelyonourexperiencemodelingnet-zeroU.S.energysystemstodevelopassumptionsforend-useefficiencyandelectrification.

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Table2KeyBaseAssumptions

Category

Assumption

Emissions

Tar