Air traffic performance will increase significantly in the coming years. Compared to 2019 pre-Covid levels, passenger kilometres flown are expected to more than double. Admittedly, fuel consumption per passenger-kilometre has fallen by 33 percent internationally and 43 percent in Germany over the past 30 years. However, the climate change impact of these increased total passenger-kilometres is greater than could be compensated for by gains in aircraft engine efficiency. Regarding the goal of climate neutrality by 2050, aviation also faces a particular problem: CO2 emissions only account for one third of aviation’s climate impact. Non-CO2 effects, i.e. the formation of contrails and the emission of nitrogen oxides and aerosols, contribute twice as much to global warming. This means hydrogen can help defossilise air traffic, especially using climate-neutral synthetic fuel, but the non-CO2 climate impacts will remain. Achieving climate neutrality in aviation solely through hydrogen-based synthetic kerosene is not possible.