Definitions and implications of climate-neutral aviation

Abstract

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.