The importance of contrail ice formation for mitigating the climate impact of aviation

Aircraft contrails and the cirrus clouds arising from them contribute substantially to aviation-induced climate forcing. The share of aviation in anthropogenic climate change can be reduced by avoiding contrail cirrus formation. The mitigation potential of altering the contrail formation stage is explored using a microphysical model to show how reductions in soot particle number emissions from jet engines, reductions in mean soot particle size, and a decrease in the supersaturation of aircraft exhaust plumes substantially lowers the optical depth of young contrails thereby decreasing the occurrence, lifetime, and radiative impact of contrail cirrus. The improved scientific understanding of initial ice formation processes allows atmospheric effects of mitigation options related to contrail cirrus to be investigated in unprecedented detail, especially those associated with the use of alternative aviation fuels. This study will enable a leap forward toward more reliable simulations addressing global climatic effects of contrail-induced cloudiness.