Nucleation and Contrail Formation

Abstract

Condensation trails, or contrails, are aircraft-induced cirrus clouds. They come from the formation of water droplets, later converting to ice crystals as a result of water vapor condensing on aerosols either emitted by the aircraft engines or already present in the upper atmosphere. While there is ongoing debate about their true impact, contrails are estimated to be a major contributor to climate forcing from aviation. We remind that air transportation currently accounts for about 5 % of the global anthropogenic climate forcing, and that it is anticipated that air traffic will double in the coming decade or two. The expected growth reinforces the urgency of the need to develop a plan to better understand contrail formation and persistence, and deploy means to reduce or avoid contrail formation, or greatly mitigate their impact. It is evident that contrails should be part of the picture when developing a plan to make the aviation sector sustainable.