Identifying appropriate climate metrics to predict climate effects of aviation

CO2

non-CO2

Clean Aviation Support for Impact Monitoring

Identifying appropriate climate metrics to predict climate effects of aviation

Aviation climate impact

3.2

2.2

3.1

3.4

2.4

2.3

3.3

WP2

WP3

Climate Impact Monitoring

Technology Impact Monitoring

A "technology watch" exercise in view to perform a theoretical preliminary performance assessment of two Clean Aviation aircraft concepts (SMR and HER).

Provide a review of state-of-the-art assessment climate metrics and aviation climate impact assessment methodologies.

Survey state-of-the-art advanced/disruptive aircraft concepts, architectures and technologies, as well as recent and on-going R&I in such aircraft concepts, architectures, and technologies, that aim to reduce the environmental and climate impact of aviation.

Identify knowledge gaps and research needs towards a climate neutral aviation.

Recommend assessment methodologies and climate metrics on the basis of the state-of-art assessment and gap analysis.

Conduct preliminary assessment of those concepts, architectures and technologies, in terms of greenhouse-gas emissions reductions.

Demonstrate the differences between simplified and detailed methods.

Climate Impact Monitoring [1/3]

Climate metrics

A climate metric represents a direct link between the emission and the impact, helping compare different emissions and mitigation strategies in a standardized way.

Why

How

Which

Existing metrics

GWP

RF

GTP

GWP*

Differences between advanced and simplified methods for calculating climate metrics

EGWP*

ATR

EGWP

Climate Impact Monitoring [2/3]

RF

GWP

EGWP

GTP

iGTP

ATR

GWP*

EGWP*

NEUTRALITY

STABILITY

COMPATIBILITY

SIMPLICITY

Evaluation of climate metrics vs requirements

Climate Impact Monitoring [3/3]

Differences between advanced and simplified methods for calculating climate metrics

Methodology

Compare total CO2 equivalents for our show cases vs. global aviation.

CO2 equivalent = Greenhouse gas emissions, including both CO2 and non-CO2 emissions

Climate Impact

Methodology Comparison

Regional aircraft

Long-range aircraft single-aisle

Long-range aircraft twin-aisle

Show cases

ATR100

GWP100

CO2 equivalent emissions for CO2, NOx, H2O & contrails

Multipliers

Pure kerosine

SAF

Fuel

ATR100

GWP100

CO2-equivalent emissions

ATR100

GWP100

Climate metrics

Recommendations

Advanced

Simplified

Method

Technology Impact Monitoring [1/4]

Technology Roadmaps

Based on a literature research on aviation technology strategies, pathways, roadmaps and projections from (inter)national authorities, non-governmental associations and research centres.

Collected Roadmaps

Technology Impact Monitoring [2/4]

Environmental Performance Improvements

New promising propulsion power concepts

Advanced and disruptive aircraft concepts and architectures

Advanced & purpose-built research facilities or test aircraft & demonstrators (worldwide)

New energy power sources with low-net emission

Advanced and disruptive aircraft concepts

Advanced and disruptive aircraft & system archtectures

Kerosene Fuel Burn

Focus on topics

CO2 reduction

Impact validation of technologies & operations

Possible synergies from other industrial sectors

NOX reduction

Technology Impact Monitoring [3/4]

Simplified Emission Sensitivity Study

Technological improvements that directly influence mission-based emission inventories, according to their proposed performance-improvement characteristics.

Performance analysis of aircraft concepts

HER

SMR

2035 Aircraft Performance Analysis​

Fully-iterated aircraft models, based on 2035 technologies, that serve as the basis for calculating mission-based emission inventories along representative trajectories​.

Assumptions

Reference Aircraft

Design of Experiment (DoE)

Generic Trajectories

Aircraft Concepts

Assumptions

Soot vs NOx for SMR & HER

CO2e breakdown for HER & SMR

SMR 2035

Influence of Climate Metric Selection on 2035 Aircraft Concepts

HER 2035

Exploration of Normalized Climate Impact Assessment Results for HER & SMR

Technology Impact Monitoring [4/4]

Energy carrier

Gaps regarding the CO2 and non-CO2 prediction for future aircraft

Propulsion level

Aircraft level

Improve current emission extrapolation methods and extend them for new energy carrier aspects

Key take-aways for non-CO2 assessment improvements

to enhance the accuracy of environmental performance predictions for the aircraft concepts from the early stages of conceptual design

Increase High-Fidelity modelling of complex propulsion systems

Integrate climate and Air Quality impacts into design KPIs

Implement uncertainty propagation throughout the design chain

The project is supported by the Clean Aviation Joint Undertaking and its members.​Funded by the European Union, under Grant Agreement No 101140632. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or Clean Aviation Joint Undertaking. Neither the European Union nor Clean Aviation JU can be held responsible for them.

Copyright © 2025, CLAIM Consortium, all rights reserved.Designed by EASN-TIS

Outcomes for SMR-2035

• Overall climate impact reduction for SMR-2035
• achieves significant CO₂ and NOₓ reductions
• Operational & technological effects:
• SMR-2035 (could) operate on higher flight altitudes
• H2O effect is higher, due to operations and SAF
• F25 (no SAF) contrail effect higher due to better propulsive efficiency
• Results depend highly on selected reference and network

Note: This use case is an academic exercise. Results depend on the study setup (aircraft, engines, scenarios, networks, operations), and variations can strongly influence the effectiveness of mitigation strategies.

Big data & data processing

Artificial & computational intelligence

Possible synergies from other industrial sectors

Machine learning & deep learning

Open databases & business models

Innovative materials, devices & IoT

Transversal promotion, multi-sector cooperation

Aircraft level

• Aircraft-level environmental assessments —particularly for non-CO₂ effects— are often missing or simplified in early design stages
• New aircraft architectures introduce additional uncertainties in emissions modeling due to integration requirements, often assessed with low-fidelity methods
• Engine integration can significantly affect contrail formation, suggesting conventional contrail models may not apply to advanced aircraft concepts with altered engine placements

Climate metric transparency

For climate metrics to be accepted, they should be as easy to understand and transparent as possible.

• Endpoint climate metrics (RF and GTP) are the easiest to understand and implement.
• Integrated climate metrics (GWP, EGWP, iGTP and ATR) are more complex and can sometimes be difficult to ascertain the impacts of individual species.
• Least transparent and simple are the GWP* and EGWP*. Use of these climate metrics requires in-depth understanding of the equivalency between SLCP emission rates and CO2 pulses.

CO2 reduction

• Compared to traditional reference aircraft (EIS<2015)
• Compared to state-of-the-art reference aircraft (2015<EIS<2025)
• Compared to future reference aircraft (EIS>2025)

Design of Experiment (DoE)

The DoE is structured into four parts, each representing a specific area of improvement targeted by Clean Aviation: aerodynamic and airframe optimization, propulsion improvements, combined enhancements, and combined enhancements with Sustainable Aviation Fuel (SAF). For each area, three levels of emissions reduction are defined for CO₂, H₂O, NOₓ, and soot.

Hybrid-Electric Regional Architecture

SMR Open-Fan Engine Architecture

Advanced & disruptive aircraft and system architectures

Integrated High Voltage Electrical Distribution

Primary Power Distribution

Primary & Secondary Power Distribution

Hydrogen-enabled integrated airframe

Operational effects strongly influence climate impact

• Cruise altitude, geographical operation and aircraft design directly affect non-CO₂ impact and FEI results
• Especially for NOx and contrail contributions, operational profiles play a decisive role

SMR segment highly sensitive to non-CO₂ effects

• NOₓ and contrails dominate climate impact at higher altitudes
• Effect of NOx reduction denominates over equal soot reduction
• Technologies targeting these contributors show highest mitigation potential in SMR

F25 achieves notable but limited FEI reductions

• Up to 28% FEI reduction with SAF & high soot reduction
• NOₓ reductions remain insufficient to fully meet DoE upper-range targets

HER segment mainly driven by CO₂ improvements

• Lower cruise altitudes reduce relevance of non-CO₂ species
• CO₂ and fuel burn reductions remain most effective for HER
• Uncertainties in emission prediction and sizing methodology

Recommendations

We propose a four-layer approach, based on the advance calculation method of climate metrics that accounts for emission location, as a best practice for climate impact assessment of new aviation technologies, which may be an entire aircraft or specific components, such as a new engine. This approach allows for incorporation of uncertainties to translate them into robustness metrics.

Identify the most sensitive parameters and establish a good understanding of the impact of uncertainties on the final outcome in all four steps of the approach.

Include a framework for uncertainties that supports risk analysis.

Cross-check the outcome of climate metrics with time series of the effects and evaluate them using higher-fidelity models on a sample basis.

Allow updates to the climate metrics in line with the latest and more consolidated research

Allow updates to the climate metrics in line with the latest and more consolidated research.

Advanced method

An alternative approach to assess climate effects of aviation considers spatial and temporal distributions of emissions with the use of climate response models. For an advanced method to calculate the climate impact of a given emission using various climate metrics, we use the climate response model AirClim.

Long-term climate warming

Focus on topics

Climate forecast needs

Climate valuable initiatives

Applicative research activities

Mapping of the relevant enablers

Technologies funded within CA

Optimised flight operations in SESAR

Efficacy-weighted Global Warming Potential starred (EGWP*) is a derivative of the GWP* metric calculated the same way as GWP* except replacing RF_i with RF_i r_i.

Climate metric neutrality

The first requirement is the neutral evaluation of the climate metric, meaning that the difference in the climate impact between two aircraft concepts assessed with climate metrics should have the same sign as the difference assessed with a scenario calculation. In other words, it should not be biased towards a specific technology, hence being neutral in this way.

A Monte Carlo simulation was carried out in which the following parameters were randomly varied within the specified limits to mimic different technologies: Fuel consumption, NOx emission, flight altitude, contrail distance, fuel, year of fleet introduction and background concentration.

Clean Aviation Target translated into FEI Target for HER & SMR

• SMR segment shows higher climate mitigation potential
• Non-CO₂ technologies are critical for SMR
• Clean Aviation targets achievable with propulsion and combined technologies
• HER: CO2 = -25%, H2O = -15%, NOx = -40% & Soot= -40%
• SMR: CO2 = -15%, H2O = -15%, NOx = -40% & Soot= -40%
• CO₂ and fuel burn improvements remain key for HER

Implement uncertainty propagation throughout the design chain

Uncertainty propagation should be implemented early in aircraft design to capture the effects of unknowns (fuel properties, emission levels, and component performance—especially for complex systems like batteries and hydrogen combustion) to enable more robust environmental assessment decisions.

Aviation climate impact

Aviation contributes to climate change via emissions of CO2 and non-CO2 emissions and effects. Non-CO2 effects comprise changes in atmospheric abundances of greenhouse gases (e.g. water vapour, ozone and methane), particulates (e.g. soot and sulphates) and changes in cloudiness (contrail-cirrus and changes in natural clouds). They are short-lived in comparison to CO2 and therefore often also called short-lived climate pollutants (SLCP). In order to reduce the climate impact of aviation, besides CO2 emissions, also those non-CO2 effects have to be considered.

CO2

O3S

CH4

O3pm

CiC

H2O

NOX

Lifetime

Up to a thousand years

Weeks

Hours

Weeks

Years

Years

Carbon Dioxide

Shortlived Ozone

Methane

Primary Mode Ozone

Contrail Cirrus

Water vapor

Climate Metrics

Average Temperature Response (ATR100) & Efficacy-weighted Global Warming Potential (EGWP100)

• Non-CO₂ agents (H₂O, NOₓ, CiC) show slightly lower contributions under EGWP100 compared to ATR100.
• Reductions in individual contributors (CO₂, H₂O, NOₓ, CiC) remain consistent across both metrics.
• Both metrics capture similar mitigation when advanced technologies or SAF (80% soot reduction) are applied.
• Overall climate impact reductions are nearly identical (<1% variation), confirming robust and comparable trends for both Climate Metrics.

Note: This use case is an academic exercise. Results depend on the study setup (aircraft, engines, scenarios, networks, operations), and variations can strongly influence the effectiveness of mitigation strategies.

Increase High-Fidelity modelling of complex propulsion systems

Hydrogen combustion and hybrid-electric propulsion systems require integration of high-fidelity modeling to capture complex, multidisciplinary interactions between electrical, thermal, aerodynamic, and structural subsystems.

Kerosene fuel burn

• Compared to traditional reference aircraft (EIS<2015)
• Compared to state-of-the-art reference aircraft (2015<EIS<2025)
• Compared to future reference aircraft (EIS>2025)

United States 2021 Aviation Climate Action Plan, 2021

Destination 2050 – A Route to net zero European Aviation, February 2021

Clean Sky 2 – Technology Evaluator First Global Assessment 2020 Technical Report, May 2021

Waypoint 2050, September 2021

Towards emission free aviation - DLR Strategy for European Green Deal, December 2021

Clean Aviation – Strategic Research and Innovation Agenda, December 2021

European Aviation Environmental Report 2022, 2022

Destination Zero - The Technology Journey to 2050, 2022

Vision 2050 – Aligning Aviation with the Paris Agreement, 2022

Report on the feasibility of a long-term aspirational goal (LTAG) for international civil aviation CO2 emission reductions, March 2022

10

Roadmap to climate neutral aviation in Europe, March 2022

11

Making Net-Zero Aviation Possible – An industry-backed 1.5°C-aligned transition strategy, July 2022

12

Roadmap to True Zero – A path-breaking approach to bring down aviation’s total climate impact, August 2022

13

TRANSCEND D3.2: Novel propulsion and alternative fuels for aviation towards 2050, September 2022

14

Aircraft Technology – Net Zero Roadmap, 2023

15

Net zero and the UK aviation sector, December 2023

16

Non-CO2 Technologies Roadmap, April 2024

17

HER Assumptions

SMRAssumptions

CO2 reduction

• Compared to traditional reference aircraft (EIS<2015)
• Compared to state-of-the-art reference aircraft (2015<EIS<2025)
• Compared to future reference aircraft (EIS>2025)

Temporal stability

Another requirement for a climate metric is stability over time, which refers to whether its ability to accurately represent climate impacts remains consistent over different time periods. The analysis focused on how the CO2 equivalents of two different scenarios (CORSIA and FP2050) change over time.

Flight demonstrators

Impact validation of technologies and operations by means of...

Ground test rig

Life cycle assessment

Flight operational assessment

Propulsion level

• The ICAO Engine Emissions Databank has no data for turboprops, turboshafts, and new energy carriers
• Extrapolation methods have limited reliability for lean-burn and hydrogen
• Emission predictions for low-soot fuels and advanced combustors are uncertain
• Hydrogen combustion presents new modeling challenges
• Existing models are inadequate for hybrid-electric aircraft

Short-Medium Range Aircraft

Advanced & disruptive aircraft concepts

Ultra Efficient Regional Aircraft

Electric Regional Aircraft

More Electric Aircraft

Exploration of Normalized Climate Impact Assessment Results for HER & SMR

• The SMR segment exhibits a higher climate mitigation potential under equivalent mission-level emission reduction scenarios
• Non-CO₂ technologies are critical for SMR
• A 30% reduction in climate impact relative to the baseline is achievable with propulsion and combined technologies
• HER: CO2 = -25%, H2O = -15%, NOx = -40% & Soot= -40%
• SMR: CO2 = -15%, H2O = -15%, NOx = -40% & Soot= -40%
• CO₂ and fuel burn improvements remain key for HER

Note: This use case is an academic exercise. Results depend on the study setup (aircraft, engines, scenarios, networks, operations), and variations can strongly influence the effectiveness of mitigation strategies.

Compatibility with climate policy

It is important that climate metrics are compatible with current climate policy framework. While this is the case for all conventional metrics, it is not the case for GWP* and EGWP*, as these metrics effectively have a second time horizon

Simplified method

The GWP of a pulse emission over time horizon of 100 years is a generally accepted metric to evaluate the equivalents (IPCC AR4). In the simplified method, the total climate impact of an aviation technology is estimated by summing CO2 emissions with the CO2 equivalents of non-CO2 emissions, which are derived by multiplying the emissions by their respective GWPs.

Climate metrics recommendation

ATR

Average Temperature Response

Meets all four requirements with at least an “acceptable” result (three “0” and one “++”). The ATR, as a temperature-based climate metric, has the potential to include more climatic processes and be more relevant for temperature-based targets. However, the larger number of assumptions and uncertainties must also be considered.

CO2e breakdown for HER & SMR

• SMR shows higher climate impact reduction potential than HER
• HER segment dominated by CO₂ effects
• Non-CO₂ mitigation is more effective in SMR
• Contrail mitigation is the key driver in SAF scenarios

Outcomes for HER-2035

• Emissions, and therefore climate impact, heavily reduced:
• Up to 300nm fully electric operations
• From 300nm up to 1000nm hybrid electric operations (gas turbine as range extender)
• Reductions mainly on CO2, H2O and NOx contribution
• Lower contribution of non-CO2 to overall climate impact due to operation and network

Note: This use case is an academic exercise. Results depend on the study setup (aircraft, engines, scenarios, networks, operations), and variations can strongly influence the effectiveness of mitigation strategies.

NOX reduction

• Compared to traditional reference aircraft (EIS<2015)
• Compared to state-of-the-art reference aircraft (2015<EIS<2025)
• Compared to future reference aircraft (EIS>2025)

Short-Medium EIS 2035

• F25 operates significantly higher
• F25 achieves significant CO₂ and NOₓ reductions
• SAF scenarios provide rebounce effects on H2O emission

• Overall FEI reduction for F25
• H2O effect is higher, due to operations and SAF
• F25 (no SAF) contrail effect higher due to better propulsive efficiency
• With SAF & soot reduction, FEI reduction up to ~28%, near Clean Aviation target

Climate metrics recommendation

EGWP

Efficacy-weighted Global Warming Potential

Meets all four requirements with at least an “acceptable” result (three “0” and one “++”). The EGWP may be a useful compromise for policymakers, in that it can more accurately represent the climate impact of aviation whilst still using the GWP methodology.

CO2e breakdown for HER & SMR

• SMR shows higher climate impact reduction potential than HER
• HER segment dominated by CO₂ effects
• Non-CO₂ mitigation is more effective in SMR
• Contrail mitigation is the key driver in SAF scenarios

Note: This use case is an academic exercise. Results depend on the study setup (aircraft, engines, scenarios, networks, operations), and variations can strongly influence the effectiveness of mitigation strategies.

Soot vs NOx for SMR & HER

• NOₓ shows stronger reduction potential
• Initial advantage for soot curve due to DoE setup
• HER segment benefits initially from lower nonCO₂ sensitivity
• Reduction potential higher for SMR at higher improvement factors

Sustainable Aviation Fuels

New energy power sources with low-net emission

Innovative Electric Batteries

Fuel Cells & Liquid Hydrogen

NOX reduction

• Compared to traditional reference aircraft (EIS<2015)
• Compared to state-of-the-art reference aircraft (2015<EIS<2025)
• Compared to future reference aircraft (EIS>2025)

Overview of the Radiative Forcing concept and on the right various types of Radiative Forcing (instantaneous, adjusted, and effective radiative forcing)

Energy carrier

• Conventional jet fuel properties can vary and influence emissions
• SAFs introduce additional variability in emissions
• Secondary emission can play a growing role in low-soot scenarios
• For hydrogen, impurities such as sulfur or CO can affect fuel cell performance

Soot vs NOx for SMR & HER

• NOₓ shows stronger reduction potential
• Initial advantage for soot curve due to DoE setup
• HER segment benefits initially from lower nonCO₂ sensitivity
• Reduction potential higher for SMR at higher improvement factors

Note: This use case is an academic exercise. Results depend on the study setup (aircraft, engines, scenarios, networks, operations), and variations can strongly influence the effectiveness of mitigation strategies.

Conclusions

Significant efficiency improvements compared with traditional reference aircraft (EIS < 2015):

40-50% less kerosene fuel burn and CO2

70% less NOX

Promising technologies:

• Aircraft architectures: Several​
• Fuel/energy: H2 and batteries lead to -100% CO2 emissions (TTW)​
• Propulsion: Hybrid-electric fans, (BLI), UHBR turbofans, etc.
• Aerodynamics: High aspect ratio wings, drag reduction, some: laminar flow control​
• Structural: Composites lead to weight reductions​

Improve current emission extrapolation methods and extend them for new energy carrier aspects

Methods need to be extended to account for non-standard operating regimes and alternative energy carriers, supported by more detailed emission data and adapted models.

Hybrid Electric

New promising propulsion power concepts

Hydrogen for Aviation

More Electronic Systems

Regional EIS 2035

• HER operates on same flight level as the baseline
• HER concept shows significant emission increases
• Emission prediction for HER is highly uncertain

• HER concept leads to higher FEI than baseline
• NOₓ increase drives the largest FEI rise, exceeding CO₂-only impact
• HER-2035 exceeds baseline and DoE expectations
• Critical uncertainties for emission prediction identified for new concepts

Principle concept of GWP*. The blue line shows examples of SLCP emissions and the red line respective eq. CO2 emissions derived by using the climate matric GWP* with dt=20 years.

HER Trajectories

SMRTrajectories

Note: This use case is an academic exercise. Results depend on the study setup (aircraft, engines, scenarios, networks, operations), and variations can strongly influence the effectiveness of mitigation strategies.

Integrate climate and Air Quality impacts into design KPIs

Extend design tools to include 4D trajectories and weather data in order to integrate climate and air quality impacts—early aircraft design process.

Design of Experiment (DoE)

The DoE is structured into four parts, each representing a specific area of improvement targeted by Clean Aviation: aerodynamic and airframe optimization, propulsion improvements, combined enhancements, and combined enhancements with Sustainable Aviation Fuel (SAF). For each area, three levels of emissions reduction are defined for CO₂, H₂O, NOₓ, and soot.

2035 Aircraft Performance Analysis

Aircraft Concepts

Regional: HER-2035 - Plug-In Hybrid-Electric

• Distributed Electric Propulsion
• Fully Battery Electric up to 300nm
• Range Extender (gas turbine) operations 300-1000nm

Short-Medium Range: SMR-2035 - Public Research Baseline Aircraft

• High Aspect Ratio Wing
• UHBR engine
• CFRP materials

United States 2021 Aviation Climate Action Plan, 2021

Destination 2050 – A Route to net zero European Aviation, February 2021

Clean Sky 2 – Technology Evaluator First Global Assessment 2020 Technical Report, May 2021

Waypoint 2050, September 2021

Towards emission free aviation - DLR Strategy for European Green Deal, December 2021

Clean Aviation – Strategic Research and Innovation Agenda, December 2021

European Aviation Environmental Report 2022, 2022

Destination Zero - The Technology Journey to 2050, 2022

Vision 2050 – Aligning Aviation with the Paris Agreement, 2022

Report on the feasibility of a long-term aspirational goal (LTAG) for international civil aviation CO2 emission reductions, March 2022

10

Roadmap to climate neutral aviation in Europe, March 2022

11

Making Net-Zero Aviation Possible – An industry-backed 1.5°C-aligned transition strategy, July 2022

12

Roadmap to True Zero – A path-breaking approach to bring down aviation’s total climate impact, August 2022

13

TRANSCEND D3.2: Novel propulsion and alternative fuels for aviation towards 2050, September 2022

14

Aircraft Technology – Net Zero Roadmap, 2023

15

Net zero and the UK aviation sector, December 2023

16

Non-CO2 Technologies Roadmap, April 2024

17

Overview of the show cases

Kerosene fuel burn

• Compared to traditional reference aircraft (EIS<2015)
• Compared to state-of-the-art reference aircraft (2015<EIS<2025)
• Compared to future reference aircraft (EIS>2025)

2035 Aircraft Performance Analysis

Aircraft Concepts

Regional: HER-2035 - Plug-In Hybrid-Electric

• Distributed Electric Propulsion
• Fully Battery Electric up to 300nm
• Range Extender (gas turbine) operations 300-1000nm

Short-Medium Range: SMR-2035 - Public Research Baseline Aircraft

• High Aspect Ratio Wing
• UHBR engine
• CFRP materials

HER Trajectories

SMRTrajectories

Note: This use case is an academic exercise. Results depend on the study setup (aircraft, engines, scenarios, networks, operations), and variations can strongly influence the effectiveness of mitigation strategies.

Soot vs NOx for SMR & HER

• NOₓ shows stronger reduction potential
• Initial advantage for soot curve due to DoE setup
• HER segment benefits initially from lower nonCO₂ sensitivity
• Reduction potential higher for SMR at higher improvement factors

Note: This use case is an academic exercise. Results depend on the study setup (aircraft, engines, scenarios, networks, operations), and variations can strongly influence the effectiveness of mitigation strategies.

CO2e breakdown for HER & SMR

• SMR shows higher climate impact reduction potential than HER
• HER segment dominated by CO₂ effects
• Non-CO₂ mitigation is more effective in SMR
• Contrail mitigation is the key driver in SAF scenarios

Note: This use case is an academic exercise. Results depend on the study setup (aircraft, engines, scenarios, networks, operations), and variations can strongly influence the effectiveness of mitigation strategies.

Outcomes for HER-2035

• Emissions, and therefore climate impact, heavily reduced:
• Up to 300nm fully electric operations
• From 300nm up to 1000nm hybrid electric operations (gas turbine as range extender)
• Reductions mainly on CO2, H2O and NOx contribution
• Lower contribution of non-CO2 to overall climate impact due to operation and network

Note: This use case is an academic exercise. Results depend on the study setup (aircraft, engines, scenarios, networks, operations), and variations can strongly influence the effectiveness of mitigation strategies.

Exploration of Normalized Climate Impact Assessment Results for HER & SMR

• The SMR segment exhibits a higher climate mitigation potential under equivalent mission-level emission reduction scenarios
• Non-CO₂ technologies are critical for SMR
• A 30% reduction in climate impact relative to the baseline is achievable with propulsion and combined technologies
• HER: CO2 = -25%, H2O = -15%, NOx = -40% & Soot= -40%
• SMR: CO2 = -15%, H2O = -15%, NOx = -40% & Soot= -40%
• CO₂ and fuel burn improvements remain key for HER

Note: This use case is an academic exercise. Results depend on the study setup (aircraft, engines, scenarios, networks, operations), and variations can strongly influence the effectiveness of mitigation strategies.

HER Assumptions

SMRAssumptions

Climate Metrics

Average Temperature Response (ATR100) & Efficacy-weighted Global Warming Potential (EGWP100)

• Non-CO₂ agents (H₂O, NOₓ, CiC) show slightly lower contributions under EGWP100 compared to ATR100.
• Reductions in individual contributors (CO₂, H₂O, NOₓ, CiC) remain consistent across both metrics.
• Both metrics capture similar mitigation when advanced technologies or SAF (80% soot reduction) are applied.
• Overall climate impact reductions are nearly identical (<1% variation), confirming robust and comparable trends for both Climate Metrics.

Note: This use case is an academic exercise. Results depend on the study setup (aircraft, engines, scenarios, networks, operations), and variations can strongly influence the effectiveness of mitigation strategies.

Design of Experiment (DoE)

The DoE is structured into four parts, each representing a specific area of improvement targeted by Clean Aviation: aerodynamic and airframe optimization, propulsion improvements, combined enhancements, and combined enhancements with Sustainable Aviation Fuel (SAF). For each area, three levels of emissions reduction are defined for CO₂, H₂O, NOₓ, and soot.

Outcomes for SMR-2035

• Overall climate impact reduction for SMR-2035
• achieves significant CO₂ and NOₓ reductions
• Operational & technological effects:
• SMR-2035 (could) operate on higher flight altitudes
• H2O effect is higher, due to operations and SAF
• F25 (no SAF) contrail effect higher due to better propulsive efficiency
• Results depend highly on selected reference and network

Note: This use case is an academic exercise. Results depend on the study setup (aircraft, engines, scenarios, networks, operations), and variations can strongly influence the effectiveness of mitigation strategies.