Air traffic growth jeopardises European aviation’s climate mitigation efforts despite the substantial potential of hydrogen

The European Union recently adopted ReFuelEU Aviation as a regulation to stimulate the use of alternative aviation fuels. We explore how this affects the climate impact of European aviation and its alignment with notions of successful climate change mitigation. Using stock-and-flow modelling and lifecycle assessment, we analyse the role of hydrogen in decarbonising the aviation system. We find that the adoption of alternative fuels alone does not guarantee successful mitigation, since the resulting temperature change can vary widely (2.2-8.9 millikelvin estimated by 2070) and most scenarios exceed CO ₂ -based targets. Although alternative fuels can greatly reduce CO ₂ emissions and non-CO ₂ impacts—with hydrogen-powered aircraft yielding the largest reductions—persistent air traffic growth drives the near-term use of fossil resources and the long-term scale of non-CO ₂ effects. Therefore, we recommend reassessing aviation climate targets, including the consideration of non-CO ₂ effects in budget-based targets and stronger incentives to reduce near-term fossil kerosene use.