国际航空运输协会：2024航空业净零碳转型路径比较报告（英文版）

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ExecutiveSummary

Transitioningtowardsnet-zerocarbondioxide(CO2)emissionsby2050isthegreatestchallengefortheairtransportindustry.TheaviationindustrytookthemomentousdecisiontoreachnetzeroCO2emissionsin2021,followedbyICAOmemberstatesin2022.Toachievethisambition,abasketofmeasuresthatcoversaviationenergytransition,aircrafttechnologybreakthrough,operationalimprovements,market-basedmeasures,andpolicysupportisrequired.Giventhesignificantuncertaintiesassociatedwiththisjourney,therewillnotbeasingleuniversalpathwayforthesectortoreachnetzeroby2050.Hence,variousorganizationshavedevelopednet-zeroCO2pathwaysforairtransport,includingtheInternationalAirTransportAssociation(IATA),theInternationalEnergyAgency(IEA),theInternationalCivilAviationOrganization(ICAO),theAirTransportActionGroup(ATAG),theInternationalCouncilonCleanTransportation(ICCT),MissionPossiblePartnership(MPP),DESTINATION2050,andtheU.S.FederalAviationAdministration(FAA).Meanwhile,numerousacademicstudiesonaviationnet-zerotransitionhavealsobeenpublishedinleadingscientificjournals.

Thisreportprovidesthefirstcomprehensivereviewoffourteenleadingnet-zerotransitionroadmapsfortheaviationsector.Bybreakingdownthemassiveamountofinformationdiscussedinthoseroadmapsintovariousaspectsforcomparison,thereportaimstohelpairlinesandstakeholdersbetterunderstandtheircriticaldifferencesandsimilarities.Specifically,thereportcomparestheselectedroadmapsintermsoftheirscope,keyinputassumptions,modeledaviationenergydemand,respectiveCO2emissions,andtheemissionsreductionpotentialbydifferentmitigationlevers.

Somekeyfindingsfromthisanalysisinclude:

1)Possiblepathwaystonet-zeroemissionsby2050differsignificantlyacrosstheroadmaps,dependingonthemainvisionaroadmapaimstoconveyonhowaviationdecarbonizationtechnologiesandsolutionsmayevolve.Giventhedifferentpurposesoftheroadmaps,oneroadmapmayputgreaterimportanceoncertainmitigationleversthanothers.

2)AllroadmapsassumethatSAFwillberesponsibleforthehighestamountofCO2reductionsby2050,contributingto24%-70%(withamedianvalueof53%)oftheCO2emissionsreductionscompared

tothecorrespondingbaselineemissionslevels.However,thiswiderangeofpossiblecontributionsfromSAFalsosuggestsuncertaintyinitsglobalsupply,whichdependsonfeedstockavailability,productioncosts,aswellassupportiveactionfromgovernmentsandfinanciers.

3)Technologyandoperationefficiencyimprovementareexpectedtohavearelativelyconsistentroleinthenet-zerotransitionprocess,togethercontributingtoabout30%oftheemissionsreductionin2050.

4)Theemissionssavingsbyhydrogen-andbattery-poweredaircraftarealsohighlyuncertainacrosstheroadmaps,dependingonwhetherastrongpro-hydrogenpolicyisadoptedaswellasarapiddeclineofrenewableenergyprices,whichenablesthefastuptakeoftheelectricity-basedtechnologies.

5)ThebaselineemissionsmodeledintheroadmapshaveadirectimpactontheamountofCO2emissionsthatneedtobeabatedby2050.Thus,apartfromthedemandgrowthratesusedinagivenroadmap’sbaseline,itisalsoimportanttounderstandwhatisandisnotincludedinthebaseline(e.g.,energyefficiencyimprovementinthepipelineversusafrozentechnologyin2019).

6)Thedemandimpactofnet-zerotransitiononaviationemissionsismodeledonlyinahandfulofroadmaps,wherealimitedemissionsreductioncontributionbylessthan10%isexpected.However,astrongdemandmanagementpolicywoulddoublethisimpactaccordingtotheIEANetZero2050roadmap.

7)Toachievenetzeroin2050,almostalltheglobalroadmapssuggestthattheaviationsectorwillneedhelpfrommarket-basedmeasuresandcarbonremovalstobridgethegap(rangingfrom

95MtCO2to370MtCO2)betweentheirresidualemissionsandnetzeroemissionsin2050.Evenifcarbonremovaltechnologiesareconsideredan‘out-of-sector’mitigationmeasure,itisstillcriticaltodevelopthesetechnologiesastheywillplayakeyroleinsupplyingCO2asthefeedstockforproducingpower-to-liquid(PtL)fuels.

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1.Background

Owingtoitsalmostexclusivedependenceonpetroleum-basedjetfuelastheenergysourcetoday,theaviationsectorfacesagreatchallengetotransitiontowardsnet-zerocarbondioxide(CO2)emissionsby2050.However,theairlineindustryiscommittedtothisambitiousgoalfollowingtheircollectiveannouncementatthe77thInternationalAirTransportAssociation(IATA)AnnualGeneralMeetingin2021.MemberStatesoftheInternationalCivilAviationOrganization(ICAO)alsoagreedtoalong-

termaspirationalgoal(LTAG)ofnet-zeroCO2emissionsby2050in2022.ReachingthisambitioustargetwillrequirerapidCO2emissionsreductionintheaviationsectorwhilethedemandisexpectedtocontinuetogrow,particularlystronglyinemergingeconomies.Underthissetting,numerousorganizationsandresearchershavedevelopedtheirnet-zeroroadmapsfortheaviationsectorwithdifferentpossiblepathways,plans,andtransitionoptions.

Table1:Listofnet-zeroroadmapsandscenariosreviewedinthisstudy.

ID

ScenarioName

Organization

PublishedYear

1

Net-ZeroRoadmapS2

InternationalAirTransportAssociation(IATA)

2023

2

Net-Zero2050Roadmap(2023update)

InternationalEnergyAgency(IEA)

2023

3

Long-TermAspirationalGoal(LTAG)

IntegratedS2:Increased/furtherambitionscenario,mediumtrafficgrowth

InternationalCivilAviationOrganization(ICAO)

2022

4

Long-TermAspirationalGoal(LTAG)

IntegratedS3:Aggressive/speculativescenario,mediumtrafficgrowth

InternationalCivilAviationOrganization(ICAO)

2022

5

Vision2050BreakthroughScenario

InternationalCouncilonCleanTransportation(ICCT)

2022

6

Prudent(PRU)Scenario

MissionPossiblePartnership(MPP)

2022

7

OptimisticRenewableElectricity(ORE)Scenario

MissionPossiblePartnership(MPP)

2022

8

Biofuel+PtLscenario,middledemandscenario

Drayetal.(2022)publishedinNatureClimateChange

2022

9

Biofuel+Hydrogenscenario,middledemandscenario

Drayetal.(2022)publishedinNatureClimateChange

2022

10

Waypoint2050S1:pushingtechnologyandoperations

AirTransportActionGroup(ATAG)

2021

11

Waypoint2050S2:aggressivesustainablefueldeployment

AirTransportActionGroup(ATAG)

2021

12

Waypoint2050S3:aspirationalandaggressivetechnologyperspective

AirTransportActionGroup(ATAG)

2021

13

DESTINATION2050netzeroscenarioforEuropeanaviation

RoyalNetherlandsAerospaceCentre(NLR)andSEOAmsterdamEconomics(SEO)

2021

14

TheUSAviationClimateActionPlanscenario

TheUnitedStatesFederalAviationAdministration(FAA)

2021

Thesepathwaysprovidevaluableinsightsfortheaviationsectortomakenet-zerotransitionplans.However,itremainschallengingfortheaviationcommunitytomeaningfullycompareacrosstheexistingnet-zerotransitionpathwaysforseveralreasons.Firstly,eachscenariomayhavedifferentbackgroundassumptionsaboutfactorsoutsidetheaviationsector,suchassocio-economicdriversofair

transportdemand,fuelprices,geopoliticaldevelopments,andthelevelofprioritytheaviationsectorgetsforscarceresources.Secondly,theexistingnet-zeropathwaysdifferinpurposeandscope.Forexample,somemayfocusonwhatwouldbeneededfortheaviationsectortoreachnetzeroby2050,combiningCO2emissionsreducedbyboththewithin-sectormitigationmeasuresaswellastheout-

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of-sectorcarbonremovaltechnologiesandmarket-basedmeasures.Incontrast,otherroadmapsmayfocusonwhatlevelofCO2emissionsreductiontheaviationsectoriscapableofachievingby2050basedonthemaximumpotentialofthewithin-sectormitigationmeasures.Lastly,theexistingroadmapsadopteddifferentdemandmodelingapproaches.Someuseatop-downapproachwithpre-determineddemandgrowthrates,andthetransitionmeasuresareappliedontopofthisgrowthas‘gapfillers’toreducetheemissionstonetzeroby2050,whilesomeuseabottom-upapproachwhereaviationdemandgrowthismodeledtoreflecttheimpactsofdifferenttransitionmeasuresondemand.

Withoutcomprehensivelyassessingthecriticaldifferencesmentionedabove,itisdifficultforstakeholderstocomparethesenet-zerotransitionpathwaysandtheleversofactiontheyrelyupon.However,thereisnosuchanalysisthusfarinthisregard.Tofillthisgap,thisreportaimstoprovideaholisticreviewoffourteenmajorglobalandregionalnet-zeroCO2pathways,withafocusonwhatmodelingapproachestheseroadmapsadoptedintheiranalysis,whatmitigationoptionsareconsidered,whatdevelopmentswouldbeneededintheseoptionsfortheaviationsectortostayontrackwiththenet-zerotransition,andhowmuchCO2emissionsreductionthesetransitionmeasureswouldcollectivelycontributetomakingtheaviationsectorgeneratezeroCO2emissionsby2050.Table1showsthefourteenroadmapsreviewedinthisreport.

2.RoadmapScope

Thenet-zeroroadmapsselectedinthisreportallhavetheirownscope(Table2).Intermsofregionalcoverage,tenroadmapscovertheglobalaviationmarket,twofocusoninternationalaviation,andtwolookatacertainregionalmarketspecifically.Theroadmapsalsodifferintheiraviationactivitycoverage.TheIATA,ATAG,IEA,andDESTINATION2050roadmapsfocusoncommercialpassengertrafficonly,whileDrayetal.(2022)andICCTcovercommercialpassengerandcargotraffic.RoadmapsdevelopedbyICAO,theUSFAA,andMPPcoverawiderscope,wheresomeevencoveralltypesofairtraffic,includingmilitaryandgovernmentflightsandgeneralaviation.

Inaddition,theboundaryconditionforthelifecycleofaviationfuelsisdifferentacrosstheroadmaps.Forexample,eightofthefourteenroadmapsconsiderjusttheTank-to-Wake(TTW)portionoftheemissionsofconventionaljetfuel,whichonlycoverstheemissionsgeneratedfromthecombustionofthefuelontheaircraft.TheremainingsixroadmapsusetheWell-to-Wake(WTW),orfulllifecycleofconventionalfuel,whichcoversemissionsfromboththefuelproductionandthecombustionofconventionaljetfuel.Alltheroadmaps,however,considerthelifecycleemissionsofSustainableAviationFuel(SAF),giventhatthereductionsinCO2ofSAFaregainedduringtheWell-to-Tank(WTT)

portion,whichcoverstheemissionsgeneratedinthefuelproductionphases.Forthisportionofthelifecycle(WTT),allreportsconsiderCO2e,i.e.,theCO2plusanyotheremissionsgeneratedduringtheproductionofthefuelorcollectionofthefeedstock.FiveroadmapsapplyaCO2emetrictotheTTWportionofthelifecycle,accountingforaviation’snon-CO2emissionsduringtheflightoperationphase.

Table2alsoshowsifmarket-basedmeasures(MBMs)andcarbonremovalshavearoleasthe‘out-of-sector’mitigationmeasuresintheselectedroadmaps.MBMsincludetheEUEmissionsTradingSchemes(ETS)andtheICAO’sCarbonOffsettingandReductionSchemeforInternationalAviation(CORSIA).Carbonremovalstypicallyconsidertechnologiessuchascarboncaptureandstorage(CCS)anddirectaircapture(DAC)toabsorbCO2emissionsgeneratedfromindustrialprocessesorevenfromatmosphericair.EightroadmapsreviewedinthisstudyrelyonMBMsandcarbonremovalsascritical‘out-of-sector’measurestohelptheaviationsectorreachnetzeroby2050.Notably,whennotconsideredastandaloneemissionsmitigationoption,CCSandDACareoftenassumedtoplayakeyroleinsupplyingCO2asthefeedstockforproducingpower-to-liquid(PtL)fuels;therefore,developingcarbonremovaltechnologiesiscriticalforallnet-zerotransitionscenariosreviewed.

Table2:Roadmapscope,jetfuellifecycleemissionsboundary,andtheroleofMBMs/carbonremovals.

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ScenarioName

RegionCoverage

AviationActivityCoverage

TTW

EmissionsScope

Aviationfuel

lifecycleboundary

Reachingnetzeroby2050throughMBMs/Carbon

Removals(Y/N)

IATARoadmapS2

Global

Commercialpassenger

CO2only

TTW

Y

IEANet-Zero2050Roadmap

Global

Commercialpassenger

CO2only

TTW1

Y

ICAOLTAGS2

(International),Mid

Internationalaviation

Commercialpassenger+cargo+businessjet

CO2only

TTW

N

ICAOLTAGS3

(International),Mid

Internationalaviation

Commercialpassenger+cargo+businessjet

CO2only

TTW

N

ATAGWaypointS1

Global

Commercialpassenger

CO2only

TTW

Y

ATAGWaypointS2

Global

Commercialpassenger

CO2only

TTW

Y

ATAGWaypointS3

Global

Commercialpassenger

CO2only

TTW

Y

DESTINATION2050(EU+)

Europe(allflightswithinand

departingfromtheEU+region3)

Commercialpassenger

CO2only

TTW

Y

ICCTBreakthrough

Global

Commercialpassenger+cargo

CO2only

WTW2

N

MPPPRU

Global

Commercialpassenger+cargo,publicsector(e.g.,military,government),

andgeneralaviation

CO2+non-CO2

WTW

Y

MPPORE

Global

Commercialpassenger+cargo,publicsector(e.g.,military,government),

andgeneralaviation

CO2+non-CO2

WTW

Y

Drayetal.(2022)Biofuel+PtL,Mid

Global

Commercialpassenger+cargo

CO2+non-CO2

WTW

N

Drayetal.(2022)

Biofuel+Hydrogen,Mid

Global

Commercialpassenger+cargo

CO2+non-CO2

WTW

N

USAviationClimateActionPlan

DomesticUS+allinternational

flightsdepartingfromUSairports

Commercialpassenger+cargo,businessjet,andgeneralaviation

CO2+non-CO2

WTW

N

Note:

1AlthoughonlyTTWisconsideredintheIEAaviationmodel,theemissionsrelatedtofuelextraction,refining,etc.,intheWTTphaseareaccountedforinthe

IEA’sglobalenergyandclimatemodel(GEC),

ofwhichaviationisapart.

2Onaverage,WTWemissionsoffossiljetAfuelareabout20%higherthantheTTWemissions.

3EU+regioncoversEU27,theUnitedKingdom(UK),andtheEuropeanFreeTradeAssociation(EFTA).

3.ComparingModelInput,Assumptions,andModelOutputoftheRoadmaps

Theforward-lookingnatureoftheroadmapsmeansthatregardlessofwhatnet-zeropathwaysaroadmapfollows,itwouldrequireamodeltoprojectCO2emissionsfromtheaviationsectorbasedondifferenttechnological,operational,fuel,andeconomicassumptions.Alltheroadmapsreviewedinthispaperuseamodelingapproachtodifferent

extentsandmakedifferentassumptionsintheirmodelstoprojectCO2emissionsoftheaviationsectorto2050.Thissectioncomparesthemodelinputsandkeyassumptionsoftheselectedroadmapsandthendiscussesdifferencesinthecorrespondingmodeloutputsindetail.

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3.1ModelInputandKeyAssumptions

Trafficdemandforairtransportisakeydriveroftheindustry’semissions.Howfastthedemandwillgrowfromthecurrentleveldirectlyimpactstheamountof

CO2emissionstheindustryneedstoabateby2050.Theselectedroadmapsadopteddifferentapproachestoprojectthedemand(Table3).

Table3:Airtrafficdemandprojectionsintheselectedroadmaps.

ScenarioName

Demand

modellingapproach

Demandresponse

Multipledemandscenarios

CAGR1

(2019-50)

Demandmetric

Demandin2030

(trillions)2

Demandin2050

(trillions)2

IATARoadmapS2

Bottom-up3

No

N

2.9%

RPK

12.71

21.55

IEANet-Zero

2050Roadmap

Bottom-up

Yes

N

2.1%

PKM

(sameasRPK)

10.97

16.55

ICAOLTAGS2(International),Mid

Top-down

No

Y,Mid

3.8%

RPK

8.10

13.12

ICAOLTAGS3(International),Mid

Top-down

No

Y,Mid

3.8%

RPK

8.10

13.12

ICCT

Breakthrough

Top-down

Yes

Y,Central

2.7%

RPK

11.73

19.96

MPPPRU

Top-down

No4

N

2.5%

RPK

10.64

19.22

MPPORE

Top-down

No

N

2.5%

RPK

10.64

19.22

Drayetal.

(2022)Biofuel+PtL,Mid

Bottom-up

Yes

Y,Mid

3.4%

RPK

13.10

24.24

Drayetal.

(2022)Biofuel+Hydrogen,Mid

Bottom-up

Yes

Y,Mid

3.3%

RPK

13.10

23.26

ATAGWaypointS1

Top-down

No

Y,Central

3.1%

RPK

12.39

22.35

ATAGWaypointS2

Top-down

No

Y,Central

3.1%

RPK

12.39

22.35

ATAGWaypointS3

Top-down

No

Y,Central

3.1%

RPK

12.39

22.35

DESTINATION2050(EU+)

Top-down

Yes

N

2.0%

Passengers

Enplanements

0.9billion

1.4billion

USAviation

ClimateActionPlan

Top-down

No

N

3.3%

RPM

1.31

(2.11inRPK)

2.90

(4.67inRPK)

Notes:1ICAOLTAGroadmapsCAGRcovers2018-2050;DESTINATION2050roadmapCAGRalsocovers2018-2050.

2Thereporteddemandisfordifferentgeographiccoverage;seeTable2Regioncoverage.

3AlthoughtheIATAroadmapusestheAIMmodel,thedemandforecastsarealignedwiththeIATApassengerforecast.

4Demandchangesduetovideoconferencing,modeshifts,etc.,arenotmodeledinMPP’smainscenariosbutassensitivityanalysis.

Atop-downapproachusesapre-determinedcompoundannualgrowthrate(CAGR)betweenthebaseyearand2050toextrapolateairtrafficdemandby2050.Underthisapproach,demandgrowthisamodelinput.Withthispre-determineddemandgrowthrate,CO2emissionsassociatedwiththe

demandunderthebusiness-as-usualcase(i.e.energyforaviationisstill100%providedbypetroleum-basedjetfuelby2050)areestimatedasthebaseline.Then,differentmitigationoptionsareappliedtoreduceemissionsfromthebaselineleveluntiltheindustryreachesnetzeroby2050.

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Asaresult,thetransitionmeasuresarethe‘gapfillers’betweenthebaselineCO2emissionsandthenet-zeroemissions.Somestudiesassumeanenergyefficiencygainthroughtechnologyembeddedintothisgrowth,sothebaselineemissionsgrowslowerthanthedemand(IATAS2,forexample).Otheranalysesfreezetechnologyatagivenyearandextrapolateemissionsatthesamegrowthrateasthetrafficgrowth(USAviationClimateActionPlan).

Incomparison,someroadmapsadoptabottom-upapproachthatprojectsthedemandusingeconometricmodels,wheredemandgrowthmeasuredbyCAGRisamodeloutputratherthanapre-determinedvalue.Hence,thebottom-upmodelsenableroadmapstoadjustthedemandgrowthbasedontheimpactsofvariousfactorsondemandduringthenet-zerotransition.Factorsthatmayaffectaviationdemandincludethehigherpriceofairtravelduetoeconomicmeasuresonsustainability(e.g.theEUEmissionsTradingSchemes),thehigherpriceofairtravelduetoincreasedcostoftheenergytransitioninaviation(e.g.highercostsofusingSAF),thechangingconsumerbehavior(e.g.moreteleconferencingratherthanbusinesstravel),anddemandmanagementpolicymeasures(e.g.banningshort-haulflights).Withthisbottom-upapproach,aviationdemandgrowthanditscorrespondingtotalCO2emissionscouldchangewiththeimpactofthenet-zerotransitionondemandaswellastheemissionsreductionfromthetransitionmeasuresapplied.

Notably,atop-downmodelcouldstillexogenouslycapturethepotentialpriceimpactondemandbyadjustingitspre-determinedCAGRtoalowervaluebasedontheirassumedpriceelasticities(e.g.theICCTBreakthroughandDESTINATION2050).Similarly,abottom-upmodelmayturnoffthedemandresponsemechanismtopricechangesinitsdemandforecasts,suchastheIATARoadmap.Therefore,thedemandmodelingapproachandthedemandresponsemechanismshowninTable3couldbe

decoupledfeaturesdependingonthespecificusecase.

AsshowninTable3,themajorityoftheroadmapsusethetop-downapproach,whereapre-determinedCAGRofdemandisusedasamodelinput.Incomparison,thefourtransitionpathwaysdevelopedbyIATA,IEA,andDray,etal.(2022)projectedthedemandinabottom-upmanner,wheretheyallusedtheopen-source,econometric-basedUCLAviationIntegratedModel(AIM2015)intheirdemandforecasting(althoughtheIATAroadmapdoesnotusethedemandresponsefunctionintheAIMmodel).Thedemandgrowthis,therefore,oneofthemodeloutputsintheseroadmaps.AnexampleonthispointisDrayetal.(2022),wherethedemandgrowth(middledemandscenario)forthebio-SAFbridgingpower-to-liquid(PtL)scenariois3.4%peryearwhiledemandgrowthforthebio-SAFbridgingliquidhydrogen(LH2)scenariois3.3%,despitebothusingthesame‘middledemand’setofexternalsocioeconomicdemanddrivers.

Tobetterreflecttheuncertaintiesinfutureaviation

demand,eightroadmapshavemultiplescenarioson

thedemandgrowthrates.However,onlyDrayetal.

(2022)andICAOLTAGprovidedpossibletransition

pathwaysunderallthreedemandscenarios.The

remainingsixroadmapsonlyusedtheircentral

demandgrowthscenariosthroughouttheanalysesor

conductedseparatesensitivityanalysesforother

demandscenarios.Table3showsthedemandgrowth

rates(CAGR)usedintheselectedroadmaps.Notably,

alltheglobalroadmaps(seeTable2)producecomparabledemandintheircorrespondingcentral

demandscenariosby2030andby2050,exceptfor

theIEANetZero2050roadmap.Thisisbecausethe

IEAroadmapreliesheavilyonavoideddemand(by20%in2050comparedwiththebaseline)fromdemand

managementandeconomicmeasures,makingitsdemandgrowthover2019-2050thelowestat2.1%peryearamongallthescenarios.

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Table4:Comparisonofthekeyassumptionsontransitionmeasuresintheroadmaps.

ScenarioName

Technologyefficiency

improvement(MJ/RPKp.a.)

Operationalefficiency

improvement(MJ/RPKp.a.)

SAF

shareby20301

AverageSAFcost($/tonne)by20302

SAF

shareby20501

AverageSAFcost($/tonne)by20502

PtL

entryyear

Hydrogenaircraftentryyear

Electricaircraftentryyear

Hydrogen/Electricshareby20501

IATARoadmapS2

2019-2050:-1.1%2019-2050:-0.2%

6%

N/A

90%

N/A

2021

2030

N/A

5%

IEANet-Zero2050Roadmap

2019-2050:-2.0%

11%

N/A

70%

N/A

2030

By2040

By2040

11%

ICAOLTAGS2

(International),Mid

2018-2050:-0.9%2018-2050:-0.3%

13%

1432

(1.79$/L)

72%3

1440

(1.80$/L)

2021

N/A

N/A

N/A

ICAOLTAGS3

(International),Mid

2018-2050:-0.2%2018-2050:-0.4%

21%

1360

(1.70$/L)

98%

1336

(1.67$/L)

2021

2045

N/A

2%

ICCTBreakthrough

2019-2034:-1.1%2035-2050:-2.2%

2019-2050:-0.6%

15%

1464

(1.83$/L)

79%

1184

(1.34$/L)

2030

2035,regionalandNBupto3400km

2030,9-19seatcommutersonlyupto500km

21%

MPPPRU

2019-2030:-1.5%2030-2050:-2.0%

13%

1417

86%

1096

2025

2040,upto2500km

2040,upto

1000km

15%

MPPORE

2019-2030:-1.5%2030-2050:-2.0%

15%

1178

66%

765

2025

2035,norangelimitation

2035,upto

1000km

34%

Drayetal.(2022)Biofuel+PtL,Mid

ModeledModeled

10%

1000

(1.25$/L4)

100%

592

(0.74$/L)

2025

2035,uptolargeWBaircraft

2045,uptolargeNBaircraft

negligible

Drayetal.(2022)

Biofuel+Hydrogen,Mid

ModeledModeled

10%

1032

(1.29$/L4)

47%

904

(1.13$/L)

2025

2035,uptolargeWBaircraft,

2045,uptolargeNBaircraft

53%

ATAGWaypointS1

2019-2050:-1.1%2019-2050:-0.2%

N/A

1061

90%

878

2030

N/A

N/A

N/A

ATAGWaypointS2

2019-2050:-1.1%2019-2050:-0.1%

N/A

1061

90%

878

2030

N/A

N/A

N/A

ATAGWaypointS3

2019-2050:-1.1%2019-2050:-0.1%

N/A

1061

90%

878

2030

2035,100-210seatsNB

2025,upto19seats

10%

DESTINATION2050(EU+)

2018-2050:-1.2%2018-2050:-0.3%

6%

2686

(2274€/t)

66%

1949

(1650€/t)

2030

2035,NBintra-EU+only,upto2000

km,165seats

2030,smallclassaircraft

21%

USAviationClimateActionPlan

2019-2030:-1.1%2030-2050:NA

2019-2030:-0.4%2030-2050:NA

10%

N/A

88%

N/A

2025

N/A

N/A

N/A

Note:1Shareintotalflightphaseenergyuse.

2WeightedaverageSAFcostsbySAFvolumesofvariousSAFtypesifvolumesareavailable,ifnot,simpleaverageofallSAFtypes.

3Theremaining28%offuelsareprovidedbylowercarbonpetroleumfuels(LCAF)intheICAOS2scenario.

4Drayetal.provideSAFcostsintheearly2020sinsteadof2030.

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Besidesairtransportdemandgrowth,theselectedroadmapsalsomakeassumptionsaboutotherkeyinputvariablesthathavedirectimpactsonthefinalCO2emissionsby2050(Table4).Typically,assumptionsaremadeforvariousmitigationmeasures,includingtechnologyefficiencyimprovement,operationalefficiencyimprovement,theshareofSustainableAviationFuels(SAFs)inthetotalaviationenergydemandandtheexpectedSAFcosts,theshareofhydrogenandelectricityinthetotalaviationenergydemand,andtheentryintoserviceyearsofdifferentaircrafttechnologies.Table4providesasummaryoftheassumptionsmadeonthesecriticalmodelinputvariablesintheselectedroadmaps.

Emissionsreductionfromconventionalaircrafttechnologyefficiencyimprovementisaresultofreplacingoldaircraftwithnewerandmoreenergy-efficientaircraftinthefleet.Theimprovementisoftenmeasuredbyareductioninenergyuseinmegajoules(MJ)perrevenuepassengerkilometers(RPK).Giventhatcurrently,thereareonlyafewnewaircraftprojectsunderdevelopmentandthefleetreplacementrateisgenerallylow,mostoftheroadmapsassume,onaverage,about1.0%peryearimprovementinenergyefficiencyfromtodayto2050.However,someroadmapshavemoreaggressiveassumptionsontheannualfuelefficiencyimprovement,suchastheICCTBreakthroughroadmap,whichassumesa2.2%peryearfuelefficiencyimprovementfromnewtypesofaircraftintroducedsince2035.

Improvementsinaircraftoperationalefficiencycouldalsocontributetoemissionsreduction.Optionsinthistransitionmeasureincludeanincreaseinaircraftloadfactor,optimizedairtrafficmanagement,single-enginetaxi,etc.Notably,notallroadmapsprovidespecificemissionsreductionestimatesfromindividual