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Aviation is highly dependent on liquid fossil fuel, and the production of ‘sustainable aviation fuels’ (SAF) is being proposed as a solution to removing the fossil carbon component, especially for long-haul flights. An analysis of 12 aviation roadmaps for net zero 2050 reveals heavy reliance on biogenic SAF in the medium-term and synthetic e-kerosene in the longer term. Realising these roadmaps could require 9 % of global renewable electricity and 30 % of sustainably available biomass in 2050, with significant energy ‘losses’. The continued use of hydrocarbon fuel in the roadmaps generates 1.35 GtCO2 in 2050, of which 30 % are still from fossil fuel. The net carbon savings from the 70 % depend on the direct and indirect life cycle emissions of producing SAF. Additional effects that are omitted in most roadmaps relate to decadal time lags in re-sequestering biocarbon in the case of forest biomass and the impact of non-CO2 emissions. Both require greater scrutiny in fully understanding the climate impact of SAF substitution. The scaling up of SAF to not only maintain but grow global aviation is problematic as it competes for land needed for nature-based carbon removal, clean energy that could more effectively decarbonise other sectors, and captured CO2 to be stored permanently. As such, SAF production undermines global goals of limiting warming to 1.5 °C; a conflict that is neither recognised in the roadmaps nor in the public debate.
Becken et al. (Mon,) studied this question.