The ReFuelEU Aviation regulation, passed by the European Union (EU) in 2023, introduces new blending requirements for alternative aviation fuels (AAF). As of January 2025, fuel suppliers at EU airports must include at least 2 % AAF in their kerosene mix. This share will gradually rise over the next few decades: 6 % in 2030, 20 % in 2035, 35 % in 2040, 50 % in 2045, and eventually 70 % by 2050.
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To meet these targets, the regulation accepts a range of cleaner fuel options, including sustainable aviation fuels (SAF) made from biomass, synthetic e-fuels produced using captured carbon dioxide (CO2), and green and liquid hydrogen. But the actual question is whether these supply chains can scale up fast enough and whether the emission cuts they deliver will be sufficient to help aviation meet Europe’s long-term climate goals.
Modeling the Impact of ReFuelEU Aviation
A detailed scenario study published in Communications Earth & Environment offers an open-data assessment of how ReFuelEU Aviation could influence Europe’s aviation system through 2070.1
The authors combine EUROCONTROL traffic projections (seven-year forecast up to 2031 and long-term forecast up to 2050) with a stock-and-flow model of the aircraft fleet and prospective life-cycle inventories covering fuels, aircraft, and hydrogen production.
They assess nine scenarios, created by pairing three traffic pathways with three fuel strategies:
Traffic pathways
- High growth, with demand rising 2.2 % per year
- Low growth, increasing by 0.7 % per year
- Managed decline, with demand falling to 70 % of 2019 levels by 2035
Fuel configurations
- A fossil-fuel baseline
- A transition relying entirely on synthetic e-fuels
- A mixed pathway introducing both e-fuels and liquid-hydrogen aircraft from 2035
Together, these combinations provide a broad view of possible futures and help identify the opportunities and the limitations embedded within the ReFuelEU regulation.
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Hydrogen Demand and Fleet Uptake
If Europe were to rely entirely on synthetic e-fuels to meet its alternative aviation fuel targets, the demand for hydrogen would skyrocket. By 2050, the aviation sector alone would need 44–64 million tons of green hydrogen, which represents 15–45 % of the EU’s expected domestic hydrogen production under net-zero plans. Introducing hydrogen-powered narrow-body aircraft helps ease this pressure, as burning hydrogen directly is more energy-efficient than converting it into e-fuel. This shift could reduce the sector’s 2050 hydrogen requirement by 13–26 %. This is not a game-changing reduction, but it is still significant, particularly considering aviation is competing with steelmaking, ammonia production, and heavy road transport sectors for the same pool of renewable electricity.
However, the pace of hydrogen aircraft adoption is limited by the realities of fleet turnover. New technologies only enter service when airlines order new aircraft, and with today’s 22-year retirement cycle, the transition is inevitably slow. Even if airlines switched immediately to hydrogen-powered planes for all new orders, hydrogen aircraft would make up approximately 10 % of intra-European traffic by 2040, rising to just above 60 % by 2070.
Meanwhile, hydrogen-powered wide-body aircraft for long-haul flights are still in early conceptual stages, meaning international routes will continue to depend on e-fuels, or even fossil kerosene, for the foreseeable future.
Aviation Emissions: CO2 vs Non-CO2 Effects
Europe can meet the ReFuelEU fuel-blending timelines and push aviation toward near-zero CO2, but the real climate challenge lies beyond carbon.
By 2060, all compliance pathways cut net CO2 emissions to roughly 20 % of today’s levels. Adding hydrogen aircraft brings an extra 23–32 % CO2 reduction in 2050, but the overall benefit is small because most of the decarbonization is already achieved by switching from fossil kerosene to synthetic e-fuels.
If the electricity used for hydrogen production and e-fuel synthesis is low-carbon, aviation can technically approach net-zero CO2 emissions without relying on offsets.
But CO2 is not the main driver of aviation’s warming today; non-CO2 effects matter more. Nitrogen oxides and persistent contrails create almost five times the warming of aviation’s CO2 in 2024. Hydrogen combustion sharply cuts NOx (around 90 %) and synthetic fuels produce less soot, so fewer contrails form. As a result, introducing hydrogen-powered aircraft could reduce aviation-induced temperature change by 13–16 % by 2070.
Still, even the most optimistic hydrogen and e-fuel deployment cannot stop aviation’s warming impact from rising unless demand is controlled. Under high traffic growth, the temperature contribution begins increasing again after 2060. In other words, technology can reduce the harm, but it cannot deliver “climate-neutral” flight if demand keeps surging.
Climate Budget and Demand Management
According to a 2024 analysis by CE Delft, Europe's aviation sector would have a carbon budget of roughly 2.4 Gt CO2 from 2024 to 2070 to align with the Paris Agreement's 1.5 °C goal.2
Modeling shows that both high-growth and low-growth traffic scenarios would exhaust this budget by around 2040–2043. Only a managed decline - or “degrowth” - pathway keeps cumulative CO2 within limits while also maintaining the total radiative-forcing consistent with the Paris Agreement’s 1.5?°C goal.
The study concludes that the ReFuelEU fuel mandate alone is not enough; it must be paired with measures that limit near-term fossil kerosene use, such as ticket taxes, frequent-flyer levies, or capacity caps at busy airports, to truly stay on track with climate targets.
Biomass is Not a Silver Bullet
Under ReFuelEU, bio-based sustainable aviation fuels (bio-SAF) can account for up to 50 % of the quota until 2030, decreasing to 25 % by 2050.
The study focuses on hydrogen and deliberately excludes bio-based pathways, but it notes that sustainable biomass supply chains face limitations due to land-use and biodiversity concerns. Adding biomass could reduce the need for hydrogen, but the overall climate benefit would remain largely the same, as long as the same proportion of fossil kerosene is replaced.
Key Takeaways for Industry and Policy
- ReFuelEU sets a clear investment signal: by 2050 three-quarters of all fuel uplifted at EU airports must be AAF.
- Delivering the mandate requires a hydrogen supply chain comparable in size to today’s entire European chlorine industry, plus carbon-delivery infrastructure for e-fuel.
- Even perfect compliance does not guarantee Paris-compatibility unless growth in passenger kilometers is moderated before 2035.
- Hydrogen aircraft help, mainly by reducing hydrogen demand and non-CO2 warming, but they arrive too late and in too small numbers to remove the need for demand-side measures.
The regulation is best viewed as a supply-side enabler, not a standalone solution. Without additional policies that price carbon across all phases of flight and that manage demand, Europe’s skies will still overshoot their fair share of the remaining global carbon budget.
Outlook for Decarbonizing the Aviation Industry
Europe’s success in decarbonizing aviation will depend on how quickly the supporting ecosystem develops. The pace at which green hydrogen production scales up, low-carbon electricity becomes widely available, and e-fuel plants are deployed will determine whether ReFuelEU’s targets remain achievable goals or merely aspirational benchmarks.
Technology alone won’t be enough. Clear policies, predictable carbon pricing, and coordinated investment across airports, energy suppliers, and aircraft manufacturers are equally crucial.
The next decade will be decisive. If infrastructure, energy capacity, and demand-management measures come together early, Europe could become a global leader in climate-aligned aviation. If not, even the most advanced fuels and aircraft may struggle to offset rising demand and constrained carbon budgets.
References and Further Reading
- Arblaster, T., Thonemann, N. & Steubing, B. Air traffic growth jeopardises European aviation’s climate mitigation efforts despite the substantial potential of hydrogen. Commun Earth Environ 6, 976 (2025). https://www.nature.com/articles/s43247-025-02935-5
- CE Delft. (2023). Carbon budget of aviation: Definition and method (Report No. 230219). https://assets.ctfassets.net/biom0eqyyi6b/cO085ZE3mTsi4qJFgkfEh/fbf4cadd73cedc7a7b94117b0d0e120f/CE_Delft_230219_Carbon_budget_aviation_Def.pdf
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