Recent insights into the non-CO2 effects of aviation

The non-CO2 effects of aviation on climate have received much attention recently from the aviation industry and European policymakers, and several research consortia are working on the topic. Focus is especially on the non-CO2 effects that are both most uncertain and potentially associated with sizeable radiative forcings compared to aviation CO2: contrail formation, the perturbation of atmospheric chemistry by aviation nitrogen oxides (NOx) emissions, and the interactions between aviation aerosols and clouds.This talk will present recent insights into understanding and quantifying the radiative forcing of the non-CO2 effects of aviation obtained by the ACACIA and Climaviation research projects. Those projects involve several types of models, including computational fluid dynamics, large eddy simulation, and global climate models, and ground-, aircraft- and satellite-based observations. Key insights are (1) improved understanding of the influence of the near field for contrail formation and evolution, (2) a new estimate of global contrail radiative forcing and its adjustments in the LMDZ climate model, (3) quantification of the benefits and risks of contrail avoidance for a given flight, (4) improved understanding of the response of ozone and methane chemistry to aviation NOx perturbations, (5) new results on aviation aerosol-cirrus interactions.Together, these results inform mitigation options aimed at reducing the climate impact of aviation non-CO2 effects.