英文2024年驶向可持续天空：航空业低碳发展的挑战与策略分析报告

NavigatingSustainableSkies:ChallengesandStrategiesforGreenerAviation

NafisaLohawalaandZhiqing(Phoebe)Wen

Report24-07April2024

AbouttheAuthors

NafisaLohawalaisaFellowatResourcesfortheFuture(RFF).BeforejoiningRFF,sheearnedaPhDineconomicsattheUniversityofMichiganandaBS-MSdualdegreeineconomicswithaminorincomputerscienceandengineering(algorithms)fromthe

IndianInstituteofTechnology,Kanpur.Lohawala’sresearchliesattheintersectionofindustrialorganization,energyeconomics,andpublicfinance,focusingontheroleofgovernmentpoliciesonenvironmentalexternalitiesgeneratedbythetransportationsectoranddecarbonizationstrategiesformedium-andheavy-dutyvehiclesand

aviation.

Zhiqing(Phoebe)WenisaformerRFFinternandamaster’sstudentmajoringin

EnvironmentalHealthwithaspecializationinrisksciencesatHarvardT.H.ChanSchoolofPublicHealth.Beforethat,shegraduatedfromtheUniversityofWisconsin-MadisonwithaBSinEnvironmentalSciences.Sheisinterestedinairpollution,decarbonization,andhumanriskassessment.Herresearchfocusesontheenvironmentalandhealth

impactsoftheaviationsector.

Acknowledgements

WearegratefultoAnnaStratton,BeiaSpiller,BillyPizer,DanShawhan,DivyaSanghi,JingranZhang,MikeToman,SebastianEastham,XuanTeng,YongjoonPark,and

individualsatJobyAviationandUnitedAirlinesfortheirinvaluableinput,comments,andsuggestions.Allerrorsareourown.

ResourcesfortheFuturei

AboutRFF

ResourcesfortheFuture(RFF)isanindependent,nonprofitresearchinstitutionin

Washington,DC.Itsmissionistoimproveenvironmental,energy,andnaturalresourcedecisionsthroughimpartialeconomicresearchandpolicyengagement.RFFis

committedtobeingthemostwidelytrustedsourceofresearchinsightsandpolicysolutionsleadingtoahealthyenvironmentandathrivingeconomy.

TheviewsexpressedherearethoseoftheindividualauthorsandmaydifferfromthoseofotherRFFexperts,itsofficers,oritsdirectors.

SharingOurWork

OurworkisavailableforsharingandadaptationunderanAttribution-

NonCommercial-NoDerivatives4.0International(CCBY-NC-ND4.0)license.Youcancopyandredistributeourmaterialinanymediumorformat;youmustgive

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NavigatingSustainableSkies:ChallengesandStrategiesforGreenerAviationii

Abstract

Aviation,crucialforglobalconnectivity,significantlycontributestoclimatechange,

accountingfor2.5percentofhuman-inducedCO2emissionsand3.5percentofoverallhuman-madechangestotheenergybalanceintheEarth’satmosphere.Thesector’sCO2emissionshavedoubledsincethemid-1980s,withprojectionsindicatinga

potentialtriplingofdemandby2050,underscoringtheurgencyofgreenersolutionstobalanceeconomicbenefitswithenvironmentalimpacts.However,challengesabound,suchasthehighcostsandsustainabilityconcernsofsustainableaviationfuel,the

limitedcapabilitiesofalternativetechnologies,suchashydrogenandelectricaircraft,andtheneedforextensiveinfrastructureandinternationalcollaboration.Thereportoffersanoverviewofdifferentalternativesforgreeneraviationandtheassociated

challenges,discussespolicyapproaches,andhighlightsareasforfutureresearchtoeffectivelyreducethesector’senvironmentalfootprint.

ResourcesfortheFutureiii

Contents

ExecutiveSummary1

EnvironmentalImpactsoftheAviationIndustry1

Challenges1

PolicySolutions4

OpenQuestions5

1.Introduction7

2.EnvironmentalImpactsoftheAviationIndustry9

3.Challenge1:ScalingSustainableAviationTechnologies12

3.1.SustainableAviationFuel13

3.2.HydrogenAircraft18

3.3.ElectricAircraft21

3.4.Hybrid-ElectricAircraft23

4.Challenge2:VoluntaryChangesinPassengerBehavior24

5.Challenge3:OperationsandManagement26

6.Challenge4:UnclearNationalResponsibilities27

7.WhatDifferentStakeholdersCanDo29

8.PolicySolutions30

8.1.PoliciestoPromotetheProductionandUsageofSAF30

8.2.PoliciestoAdvanceAircraftTechnologies36

8.3.PoliciestoChangeConsumerBehavior40

8.4.ChangesinCorporateTravelPolicies43

8.5.PoliciestoBuildSustainableAirports43

NavigatingSustainableSkies:ChallengesandStrategiesforGreenerAviationiv

9.OpenQuestions45

9.1.QuestionsRelatedtoSustainableAviationTechnologies45

9.2.QuestionsRelatedtoConsumerBehaviors50

9.3.QuestionsRelatedtoAirportEmissions52

9.4.QuestionsRelatedtoCountries’Responsibilities53

10.Conclusion53

References55

ResourcesfortheFuturev

ExecutiveSummary

Thisreportoffersanoverviewofsustainableaviation,focusingprimarilyoncommercialaviationwhilealsoaddressingawiderangeofotheraviationoperations.Itoutlines

challenges,strategies,andpolicyeffortsforgreeneraviationintheUnitedStatesandglobally.Importantly,itidentifieskeyresearchareasforpolicydevelopment,servingasanintroductoryguideforresearchersinterestedinaviationsustainability.

EnvironmentalImpactsoftheAviationIndustry

Commercialaviationisestimatedtoaccountforabout3.5percentoftheoverall

human-madechangestotheenergybalanceintheEarth’satmosphere.One-third

ofthisimpactisestimatedtocomefromCO2emissionsandtherestfromnon-CO2factors,suchasnitrogenoxides(NOx)andcontrails—thelong,thincloudsthatoftenformbehindanairplaneincoldandhumidconditionsthattrapatmosphericheat.

Alarmingly,CO2emissionsfromaviationhavedoubledsincethemid-1980sandcouldaccountforaquarteroftheCO2budgettolimitwarmingto1.5°Cby2050.Near

airports,aircraftoperationselevatepollutants,suchasNOxandozone,adversely

affectingairqualityandhumanhealth.Moreover,airportoperationsandexpansionsoftenincreasenoisepollutioninnearbyneighborhoods.Finally,leademissionsfromolder,smallpiston-engineaircraftusedinsmallernon-commercialoperationsarethelargestleadsourceinUSairandpresentsignificanthealthrisks.

Challenges

Scalingsustainableaviationtechnologies:Inconventionalaircraft,fueleconomycanbeimprovedthroughtechnologicalmeans,suchasaerodynamicdesign,advanced

engines,andweightreduction.Airlineoperationsalsocontributetoefficiencythroughoptimizedflightroutes,altitudeandspeedmanagement,andreducedrunwayidling.However,despitetheseimprovements,emissionsfromconventionalaircraftarerisingduetoincreasingairtraffic.

Intheneartomediumterm,sustainableaviationfuel(SAF)offersaviablegreener

alternativetotraditionaljetfuel.Itiscompatiblewithcurrentaircraftandcanreducegreenhousegasemissionsbyupto100percentandcontrailformationsby50–70

percentwhilealsoimprovingairqualitycomparedtotraditionaljetfuel.SAFis

producedfromvariousrawmaterials,suchasfats,oils,sugars,municipalwaste,and

capturedCO2,employingdistinctpathwayssuchashydroprocessedestersandfattyacids(HEFA),Fischer-Tropsch(FT),alcohol-to-jet(ATJ),andpower-to-liquid(PtL).

Despitethisdiversity,SAFproductioncurrentlyfallsshortofglobaldemand.Amajorchallengeforagriculturalfeedstockisindirectlandusechange(ILUC),withconcernsofdeforestationandhabitatdestructionassociatedwithcultivation.Ediblecrops

likecorncouldfurtherinfluencefoodprices.AccuratelyassessingtheenvironmentalimpactoffeedstocksandproductionmethodsisalsochallengingduetodifferencesinmodelssuchastheInternationalCivilAviationOrganization(ICAO)CarbonOffsetting

NavigatingSustainableSkies:ChallengesandStrategiesforGreenerAviation

1

andReductionSchemeforInternationalAviation(CORSIA)andArgonneGreenhousegases,RegulatedEmissions,andEnergyuseinTransportation(GREET).

Feedstockavailabilityisasignificanthurdle,especiallyforHEFAfeedstockssuch

aswasteoils,whichareinherentlylimited.Whileagriculturalfeedstockscould

theoreticallybeexpanded,competitionfromsectorslikerenewabledieselposes

challenges.EmergingPtLtechnology—utilizingabundantwaterandCO2—offersa

solution.However,theearly-stageandenergy-intensivenatureoftheproduction

processleadstohighproductioncosts.Moreover,itsenvironmentalbenefitshingeonsustainablesourcing(e.g.,renewableelectricityfortheelectrolysisofwater).

ThefinanciallandscapeforSAFischallenging,withhighproductioncostsandmarketrisksdeterringprivateinvestmentandmakingrenewabledieselmoreappealingfor

producers.Governmentsupportandclearincentivesarecrucialforitseconomic

viability.Additionally,theinfrastructurefordistributionandblendingwithconventionaljetfuelrequiresfurtherdevelopment.Finally,thelowaromatichydrocarboncontentinSAFpresentsadualaspect:itisanopportunityforreducingemissions,asignificant

environmentalbenefit,butsimultaneouslyachallenge,asitcancompromisesealintegrityinolderaircraftengines,necessitatingnew,compatiblesealtechnologies.

Inthelongerterm,hydrogenandelectricaircraftmayalsohelpmeettheaviation

industry’ssustainabilityandenvironmentalgoals.However,bothfacedistinct

challenges.Mostimportantly,theyhavelowerpassengercapacityandrangethan

conventionalaircraftduetothelowerenergydensityofalternativefuelscomparedtokerosene,thoughhydrogenaircrafthaveanedgeoverelectriccounterparts.

Usinghydrogen,incombustionenginesorfuelcells,significantlyreducescarbon

emissionsandotherairpollutants.Forstorage,aircraftrelyonliquidhydrogen,whichisspaceefficientbutrequiresadvancedcryogenictechnology,orcompressedhydrogengas,whichislessefficientandrequireshigh-pressuresystems.TheInternational

CouncilonCleanTransportation(ICCT)estimatesindicatethatby2035,liquid

hydrogencouldenablenarrow-bodyplanestocarry165passengersover3,400kmandturboprops70passengersover1,400km,makinghydrogen-poweredflights

commerciallyfeasible.In2018,aboutone-thirdofaviationCO2emissionsoriginatedfromflightsunder1500km;ICCT’sprojectionssuggestthathydrogenaircraftcouldpotentiallyreplacetheseemissionslong-term.

Keychallengesintheirdeploymentincludesafetyconcerns,mixedpublicperceptionduetohistoricalrisks,andextensiveinfrastructureneedsforhydrogenstorageandhandling.Refuelingwithpassengersonboardmaynotbefeasible,addingtoairport

operationalcosts.Producinganddeliveringhydrogenisalsocostlyandcomplex,

withhighercostsforcleanerhydrogen.Moreover,ensuringenvironmentaljusticeindeployinghydrogensolutionsisessentialtoaddressdisparitiesinthehydrogenvaluechain.Hydrogenaircraftcouldalsoincreasecontrailformation,impactingclimate

change.Finally,scalinguprequirescollaborationacrossvarioussectors.

ResourcesfortheFuture2

Electricaircraft,ontheotherhand,havezeroin-flightemissionsandlower

maintenanceneedsbutareseverelyconstrainedbybatterytechnology.Thislimitationaffectstheirrangeandpayload,confiningthemtoveryshortflights.ICCTestimatesindicatethatevenifbatterytechnologyimprovedtodoubleitscurrentefficiency,

electricplanesseatingaround90passengersmayonlycoverdistancesupto280km.

Thislimitedrangemeanstheywouldhaveaminimaleffectonaviation’sclimateimpact.However,theycouldstillimproveairqualitybyreducingthenumberofjet-fueled

flightdepartures.Widespreadadoptionrequiresadvancedcharginginfrastructure

andpotentiallymajorpowergridupgrades.Theirenvironmentalbenefitsalsorely

onwhethertheenergyforchargingthemcomesfromrenewablesources.Recent

advancementsaremakingshort-rangeurbanflightsfeasible,withstudiessuggestingelectricverticaltakeoffandlandingaircraftcouldreduceemissionsmoreeffectivelythanelectriccarsforshortdistances.

Hybridaircrafttechnologies,whichutilizeacombinationofenergysourcesinflightareemergingasapromisingsolution.Moredevelopedthansolelyelectricorhydrogen-

poweredalternatives,thesetechnologiescanbemorereadilyadaptedtofitcurrentaircraftdesigns.

Voluntarychangesinpassengerbehaviors:Anotherchallengeispersuading

passengerstomakesustainablechoices,suchasrail,carbonoffsetprograms,orflightswithloweremissions.Manypreferairtravelforitsspeedandconvenience,evenfor

shortdistances,despitetheavailabilityofgreeneralternatives.Encouragingashift

torailforshortertripsinvolvesimprovingitsinfrastructure,competitivepricing,andraisingpublicawareness,whichcanbecostlyandcomplex.Carbonoffsetsprovide

analternative,buttheireffectivenessisdebatableduetovalidationchallengesand

potentialcommunityimpacts.Moreover,gettingpassengerstochooselower-emissionflightsiscomplicatedbyinconsistentinformationfromvariousflightcomparisonsitesandthelackofastandardizedemissionscalculationmethod.

Operationsandmanagement:Effortstoimproveaviationoperations,suchas

optimizingflightschedulesandenginesettings,canfurtherhelpreduceemissions

butrequireadelicatebalancebetweenminimizingairqualityimpacts,cuttingCO2

emissions,andmaintainingpassengersatisfaction.Researchshowsthatreducing

CO2emissionscansometimesincreasepopulationexposuretootherpollutants.

Additionally,effortstoreduceCO2emissionsbyflyingslowercanleadtolongerflighttimes,potentiallyimpactingpassengerexperience.Finally,decarbonizingairport

groundoperations,suchasbyelectrifyinggroundsupportequipmentandshuttle

busesandimprovingtheenergyefficiencyofairportbuildings,canfurtherhelpreducethisindustry’simpactbutrequirescomprehensivegridinfrastructureupgrades,

financialinvestment,technologicalinnovation,sustainableenergysources,operationalchanges,training,andsupportivepolicies.

Unclearnationalresponsibilities:UndertheUnitedNationsFrameworkConventiononClimateChange(UNFCCC),emissionsfrominternationalflightsarerecorded

separatelyfromindividualcountries’nationaltotals.Instead,theyareclassifiedunder“bunkerfuels”duetotheiroccurrenceininternationalwatersorairspace,complicatingeffortstoholdspecificnationsaccountable.Duringthedevelopmentofthe1997Kyoto

NavigatingSustainableSkies:ChallengesandStrategiesforGreenerAviation3

Protocol,countriesagreedtoaddressemissionsfromthesebunkersthroughthe

ICAOnegotiationsandnotthroughtheUNFCCC.Whethercausalornot,thisallowedcountrieslistedasAnnexIPartiestoincreasetheiremissionsfromthesesectors

withoutimpactingtheiremissionreductioncommitments.Forexample,USaviationbunkerfuelemissionsdoubledfrom1990to2019.

Althoughthe2015ParisAgreementencompassesallanthropogenicemissions,itslackofspecificityhasresultedinnationallydeterminedcontributions(NDCs)submitted

bypartiesprimarilyfocusingondomesticemissions,leavinginternationaltransportlargelyunaddressed.

CORSIA,introducedbyICAOin2016,aimstomanageemissionsfrominternationalaviation,focusingmainlyonairlines.However,effectiveemissionreductionrequiresstakeholderinvolvementbeyondjustairlines,underscoringtheneedforcountriestoberesponsiblefortheseemissions.

PolicySolutions

PoliciestopromotetheproductionandusageofSAF:Financialincentives,suchasgrantsandtaxcredits,canreducehighproductionandusagecosts,supportingfeedstockcultivation,infrastructure,andresearchanddevelopment(R&D).

ExamplesofsuchsupportincludetheUSDepartmentofEnergy’sloanguaranteesforcommercial-scaleSAFprojectsandthetaxcreditsforSAFundertheInflationReductionAct(IRA).

Market-basedstrategies,suchastheEuropeanUnion’semissionstradingsystemandICAO’sCORSIA,canencourageairlinestouseSAF.Thisapproachcanalsoindirectlypromotedevelopingmorefuel-efficientaircraftbyincreasingdemand.

GovernmentinvestmentinR&DcanfosterSAFinnovation,efficiency,andscalability,makingitmoreviablefortheindustry.AnotableexampleisthegovernmentwideSAFGrandChallengebytheUSDepartmentsofEnergy,Transportation,andAgricultureandotherfederalagencieslaunchedin2021tohelpreducecostsandexpand

productionanduseofSAF.

MandatesthatrequireblendingSAFwithconventionalfuelscanboostits

attractivenessforairlines.AnexampleistheEUSAFmandateapprovedin2023undertheReFuelEUAviationinitiative.ImposingtaxesonfossilfuelscanfurtherincentivizetheshifttowardSAF.

Policiestoadvanceaircrafttechnologies:Strictstandardsforaircraftemissions,suchasthoseintroducedbytheICAOforCO2andnonvolatileparticulatematter(nvPM)

emissions,canencourageaircraftmanufacturerstoinvestinR&Dtomeetorexceedthesebenchmarks.Concurrently,governmentinvestmentinR&D,throughinitiativessuchastheUSFederaiAviationAdministration’s(FAA)ContinuousLowerEnergy,EmissionsandNoiseandEliminateAviationGasolineLeadEmissionsPrograms,canadvanceaircraftperformanceandreduceemissions.

ResourcesfortheFuture4

Furthermore,governmentsubsidiesforR&D,demonstration,anddeploymentof

emergingtechnologies,suchashydrogenandelectricaircraft,canhelpbringthesetechnologiestothemarketandimprovetheirrangeandpassengercapacity.Theycouldbeviableforshort-haultravelandoffersignificantenvironmentalbenefitsandreducednoiselevels.Duetotheirearly-stagedevelopment,theyarelikelytoreceiveinadequateprivateinvestment,makinggovernmentsupportessential.Yet,currentUSincentivesforthemlagbehindthoseforgroundvehicles,indicatinganeedfor

increasedsupportinthissector.

Policiestochangeconsumerbehavior:Investinginhigh-speedrailcanreduceair

traveldependencyforshort-haultravel,provideditiscompetitivelypriced.Taxingairpassengers,suchastheUKAirPassengerDuty,canalsoencourageshiftstoother

transportmodes.Furthermore,regulatingtheVoluntaryCarbonOffset(VCO)marketcanhelpvalidatetheauthenticityandenvironmentalbenefitsofcarbonoffsetprojectsandaidbuyersincomparingandunderstandingdifferentcarbonoffsetoptions.Finally,corporatepolicychanges,suchasencouragingvirtualmeetings,optingforlower-

emissiontransport,andlimitingnonessentialtravel,cansignificantlyreducebusinesstravel’senvironmentalimpact.

Policiestobuildsustainableairports:Financialincentivesforrenewableenergy,

electricgroundserviceequipment,andhydrogenandelectricaircraftinfrastructurecanencourageairportstoembracesustainableinfrastructureandpractices,reducingcarbonandnoisepollutionandimprovingairquality.Overthelongerterm,policy

reformscouldstreamlineenvironmentalreviewsundertheNationalEnvironmentalPolicyActtoaccelerateairportelectricandhydrogenaviationinfrastructure

development.

Policiestopromotecountries’accountability:CORSIAandICAO’slong-termglobalaspirationalgoalforinternationalaviationarestepsforwardinmanaginginternationalairtravel’senvironmentalimpactbutdonotassignemissionsresponsibilityfrom

internationalflightstocountries.IncludingtheseemissionsintheNDCsunderthe

ParisAgreementisbeingdiscussedasastrategyforcomprehensiveaccounting.TheEUandits27memberstatesalreadyincludeemissionsfromoutgoingflightsintheirNDCs.EnvironmentaladvocacygroupsarepushingcountriestorevisetheirNDCstocoverallaviationemissions,althoughaccuratelyattributingcarbonemissionsfrominternationalaviationtospecificcountriesisacomplexchallenge.

OpenQuestions

Questionsrelatedtosustainableaviationtechnologies:Researchcanhelpdeterminethecost-effectivenessofmodernizingversusretrofittingolderaircraftandtheoptimaltimingforfleetreplacement,weighingtheeconomicandenvironmentalbenefitsof

newaircraftagainsttheimpactsofproductionanddisposal.Itisalsonecessarytofullyunderstandtheeffectsofvariousemissions,includingNOx,CO2,andparticulates,theeffectivenessofemissionreductiontechnologies,howaircraftmanufacturersrespondtoregulations(suchasICAO’sstandards),andthetrueimpactofpoliciesonaircraft

fuelefficiency.

NavigatingSustainableSkies:ChallengesandStrategiesforGreenerAviation5

ResearchisalsoessentialinansweringquestionscenteredaroundSAF.Itcanhelp

identifyandresolvebottlenecksinmaintainingaconsistentfeedstocksupply.A

keyareaisoptimizingresourceallocation,giventhecompetitionforfeedstockand

biorefinerycapacitybetweenrenewabledieselandSAF.ItisalsocrucialtounderstandtheinfrastructureandfinancingrequirementsforintegratingSAFintoaviationand

analyzehowinternationalandnationalregulations,incentives,andmandatesaffect

SAFpricing,adoption,production,andticketprices.Researchisneededtoinvestigatetheholisticenvironmentalimpacts,includingILUC,ofvariousfeedstockandpathways.

Researchcanalsodevelopstrategiesfordeployingandscalinghydrogenandelectricaviationbyhelpingimproveproduction,storage,andtransportation;assessing

competitionforhydrogenacrosssectorsandstrategiesforefficientdistribution;

assessingenvironmentaljusticeissuesacrosshydrogenvaluechain;andexploringinfrastructureneeds,includingflightpatterns,refuelingstrategies,networkdesign,andtheviabilityofhub-and-spokesystems.Itcanalsoevaluatethelife-cycle

environmentaleffectsofdifferenttechnologiesandcomparethecostsandbenefitswithalternativessuchashigh-speedrail.Asregulatorybodies,suchastheFederalAviationAdministrationandEuropeanAviationSafetyAgency,developguidelinesonnewtechnologies,researchcanplayacrucialroleinshapingthem.Finally,researchcanhelpassessconsumerattitudestowardnewaviationtechnologiestosteertheirdevelopment.

Questionsrelatedtoconsumerbehavior:Understandingconsumerbehavioris

crucialforshapingsustainabletransportationpolicies.Researchcanhighlighthow

factorssuchaspricing,comfort,anddemographicsinfluencetransportchoices

andwillingnesstopayforsustainableaviation.Theseinsightsarevitalfordevising

strategiesthatencourageconsumers’shifttowardgreeneraviationandalternative

transportation.Researchcanalsohelpassesstheeffectsofpoliciessuchasaviation

taxesandlimitsonshort-haulflightsonpassengerbehavior,ticketprices,andairtraveldemand;understandtheroleofloyaltyprogramsininfluencingflyingfrequency;and

identifytheimpactofstrategies,suchasfrequent-flyertaxes,onthetravelhabitsoffrequentflyers.Moreover,furtherresearchisneededtoregulateVCOsto