Hydrogen-based fuels for European aviation

Abstract

Through exploratory scenario development, this study delves into the environmental impacts of European commercial aviation. Climate targets and the adoption of alternative aviation fuels (AAF) following ReFuelEU Aviation are assessed, considering e-fuel produced from direct air capture (DAC) and hydrogen aircraft. A novel method is applied, combining the generation of prospective life cycle inventories based on integrated assessment models with technology forecasting, system dynamics, and scenario development. This enables reflection on not only aircraft performance, but also fuel production, aircraft manufacturing, and fleet dynamics. Although there are limitations, including the relatively simple approach to system dynamics and limited data availability, clear conclusions can be drawn. Even for high-growth trajectories of air traffic, the total fuel demand of aviation could stagnate by 2035 under highly ambitious circumstances. Lower air traffic would require less ambitious circumstances. Combined with the reduced impact of AAF on aviation-induced cloudiness modelled here, the radiative forcing associated with aviation could reach a peak by 2050. However, the current scope of ReFuelEU Aviation does not prevent this peak from being eclipsed again by 2070. To prevent this, the mandate for a 70% share of AAF by 2050 should be followed up with a mandate for a 100% share. Thereby, warming neutrality is within reach – provided the necessary technologies can be implemented at scale. Hydrogen propulsion makes more efficient use of resources than e-fuel does, which is relevant for some impact categories, but less so for climate change as assessed here. When considering the magnitude of radiative forcing, present projections fall short. Estimating a budget of CO2 emissions through a grandfathering approach of the targets set by ICAO and IATA, the budget is exceeded by 2070, even with the most optimistic technological advancements. Critical here is the high use of fossil fuel leading up to 2035, for which there are no timely technological solutions. Lacking offsetting opportunities that are reliable, large-scale, and long-term, the only option is to restrict the volume of air traffic. Reducing traffic to 70% of the 2019 passenger-kilometers can be sufficient to respect the CO2 limit, even without optimistic developments in aircraft technology. This challenges conventional narratives, which advocate against demand management, claiming this would limit technological innovation. Thereby, evidence is created in support of the degrowth discourse which has gained momentum in recent decades. To ensure that aviation can provide long-term societal benefits, near-future flight activity must be redistributed to future generations. Given the boundaries and uncertainties of the presented scenarios, a much-needed discussion is encouraged: what share of global environmental limits is aviation – and within that, European aviation – entitled to?