Regional and Seasonal Variability in Decreasing Contrail Cirrus Cloudiness Using Sustainable Aviation Fuel

Abstract The impact of aviation induced contrail cirrus on Earth's radiation budget depends on the optical depth (OD) and the life time of these clouds. Their tendency to enhance global warming may be mitigated by replacing conventional kerosene with fuels that form fewer soot particles, such as sustainable aviation fuels (SAF). The resulting reduction in ice nucleation leads to lower contrail OD, shorter contrail life times and, hence, a lower radiative effect (RE). Here we investigate the regional and seasonal variability in the relationship between the reduction in soot number emissions and the associated reduction in the contrail cirrus RE. We use the atmospheric general circulation model ECHAM5‐CCMod to study the impact of replacing kerosene with SAF. The resulting reduction in contrail ice nucleation is largest in winter, when contrails form at ambient temperatures well below the contrail formation threshold. The reduction in contrail cirrus OD and RE, however, is small in winter. Hence, a large reduction in the initial ice crystal number cannot be directly translated into a large reduction of the RE. Instead, reducing ice nucleation is most effectively lowering the RE in seasons and areas in which contrails attain a large ice water content. Our model indicates, that the largest decline in the contrail cirrus RE per used SAF can be achieved over Europe or the North Atlantic flight corridor in autumn and over USA‐Mexico and the North Atlantic in summer.