Definitions and implications of climate-neutral aviation

To meet ambitious climate targets, the aviation sector needs to neutralize CO₂ emissions and reduce non-CO₂ climatic effects. Despite being responsible for approximately two-thirds of aviation’s impacts on the climate, most aviation non-CO₂ species are currently excluded from climate mitigation efforts. Here we identify three plausible definitions of climate-neutral aviation that include non-CO₂ forcing and assess their implications considering future demand uncertainty, technological innovation, and CO₂ removal. We use empirical relationships to translate aviation emissions to climate forcing and a reduced-complexity climate model to assess the impacts of these climate neutrality frameworks, including the needed CO₂ removal, on global temperature in the context of the different demand and technology scenarios. We demonstrate that simply neutralizing aviation’s CO₂ emissions, if nothing is done to reduce non-CO₂ forcing, causes up to 0.4 °C additional warming, thus compromising the 1.5 °C target. We further show that substantial rates of CO₂ removal are needed to achieve climate-neutral aviation in scenarios with little mitigation, yet cleaner-flying technologies can drastically reduce them. Our work provides policymakers with consistent definitions of climate-neutral aviation and highlights the beneficial side effects of moving to aircraft types and fuels with lower indirect climate effects.