Cost effectiveness of synthetic fuel and CO2 removal for net-zero aviation

Aviation is one of the fastest-growing sources of greenhouse gas emissions. The sector's climate impacts extend beyond carbon dioxide (CO 2 ), as non-CO 2 climate effects such as contrail cirrus further increase warming. Yet most decarbonization policies, including the European Union's ReFuelEU, focus narrowly on CO 2 and promote sustainable aviation fuels (SAFs), including synthetic fuels (synfuels), as solutions, overlooking permanent carbon removal. Here, we show that this policy approach is not cost effective, as we project that median abatement costs of direct air carbon capture and storage (DACCS) are 80% lower when considering CO 2 alone. When considering all climate effects, DACCS costs are 49%–69% lower ($312/tCO 2 e versus $1,014/tCO 2 e for global warming potential [GWP]100; $312/tCO 2 e versus $607/tCO 2 e for GWP20). Combining DACCS with rerouting reduces costs by 21%–33%. Allowing DACCS to fulfill synfuel quotas under the ReFuelEU mandate could cut compliance costs by 62%–80%. These findings strongly support a technology-open approach to aviation decarbonization.