Poster for presentation at the Transportation Research Board 2024 Annual meeting, discussing results of UC Davis Policy Institute research on policies to support the deployment of sustainable aviation fuels (SAF)

1. Findings
Fuel Technologies
• Zero-emission technologies may power regional flights; longer haul will require energy-dense liquid fuels – e.g.
alternative jet fuel (AJF) – for some time.
• Of 9 currently certified AJF technologies, all require blending with fossil jet at present, though some may be able to
work as neat fuels with further development.
• Only 1 technology, hydrotreated lipid (HEFA) alternative jet fuel, has a demonstrated ability to scale.
• Two technologies – HEFA and alcohol-to-jet – have analogues in wide use on road: renewable diesel and ethanol.
• “E-fuels” synthesized using electricity hold promise.
• Need lots of zero carbon electricity for GHG benefits.
• Two-track approach: Deploy pilot plants to help mature tech, but delay scale-up until grid is closer to zero carbon.
• Technologies using cellulosic (low carbon) feedstocks remain expensive and technically unproven at scale after
commercialization failures as on-road fuels in the 2010s.
• Supplies of sustainable and cost-effective biomass are likely limited.
• Land use change is still a risk.
Getting to Scale: Transition Issues
• Alternative aviation fuel market volumes are growing fast, but still low. Global aviation fuel demand exceeds total (on-
road and non-road) alternative fuel production capacity.
• Resource allocation of feedstocks and fuels to different technologies and end uses requires attention to specifics like
fuel delivery systems, blending potential, and spatial distribution of production/demand centers.
• Transition timing raises issues like syncing e-fuel roll-out with decarbonized grids, or deploying technologies first in
the sector (on-road vs. aviation) where they scale more readily to realize learning and cost reductions.
Aviation Fuels – Low Carbon Options Under Current Policy (US Focus)
Julie Witcover, PhD; Colin Murphy, PhD
UC Davis Policy Institute for Energy, Environment & the Economy; UC Davis Low Carbon Fuel Policy Research Initiative
January 2024
Contacting the Authors:
Julie Witcover (jwitcover@ucdavis.edu), Colin Murphy (cwmurphy@ucdavis.edu)
Research Question
Research Questions
• Are current policies adequate to develop
enough low carbon aviation fuels to meet
climate goals?
• If not, what are the key barriers?
• What are the policy implications?
• How are different jurisdictions and
stakeholders approaching decarbonizing
aviation?
Background
• Low carbon aviation fuels are critical for
global aviation decarbonization due to the
need for energy-dense fuels.
• Current aviation decarbonization strategies
rely on carbon offsets, which have often
struggled to deliver verifiable, permanent,
and additional emissions benefits, and are
a temporary solution at best.
• Given projected increases in long-distance
air travel, displacing fossil jet fuel is critical.
Study Methods
Approach
• Literature review
• Focused on:
• Alternative jet fuel technologies
• Transition issues in getting to scale
• Current policy landscape
• Synthesis White Paper draws out, among findings, key areas of uncertainty for policymakers
Select References
• Witcover, J., & Murphy, C. W. (2023). Aviation Fuels – Exploring Low Carbon Options Under Current Policy. UC Office of the
President: University of California Institute of Transportation Studies. http://dx.doi.org/10.7922/G2D21VXJ
• Cazzola, P., & Murphy, C. W. (2023). Low-Carbon Fuels for Aviation and Maritime Transport: Insights from Two Mirroring Workshops
Held in the US and Europe. UC Davis: European Transport and Energy Research Centre. http://dx.doi.org/10.7922/G2SB442Z
• ICAO (2022). “Report on the Feasibility of a Long-Term Aspirational Goal (LTAG) for International Civil Aviation CO2 Emissions
Reductions.” Committee on Aviation Environmental Protection. International Civil Aviation Organization.
https://www.icao.int/environmental-protection/LTAG/Documents/REPORT%20ON%20THE%20FEASIBILITY%20OF%20A%20LONG-
TERM%20ASPIRATIONAL%20GOAL_en.pdf
Acknowledgment: Made possible through funding received by UC-ITS from the State of
California through the Road Repair and Accountability Act of 2017 (Senate Bill 1).
Adapted from ICAO 2022 Long-Term Aspirational Goal, most ambitious emissions savings scenario (Witcover & Murphy).
Policy Discussion
Policy Landscape
• Policy has focused on on-road alternative fuels to date, but aviation is quickly getting more policy attention.
• Policies targeting very low carbon fuels will be needed to spark technology development and deployment.
• Overlapping jurisdictions for international, regional, national and subnational policies complicates policy.
• State policies like California’s Low Carbon Fuel Standard, which incentivizes alternative jet fuel alongside on-road
low carbon fuels, play an outsize role in initial commercial deployment, stacking on federal incentives.
• Policy safeguards against land use change emissions due to biofuel use are insufficient to protect the environment
as biomass feedstock demand grows.
Key Areas of Uncertainty for Policymakers
• Investing in portfolio of technologies with no clear winner. Avoiding overinvesting in current
technologies with a potential link to land use change.
• Hydrogen likely to play a large, but as-yet undetermined role in future energy and fuel systems.
• How and when to build infrastructure -- airport and fuel system – to accommodate low carbon jet fuel.
• How to assign limited biomass feedstock to hard-to-electrify sectors, including aviation. Link to paper.