Astronomical, Atmospheric, and Lifetime-specific Requirements for Cooling Contrails

The radiative impact of contrails has posed challenges for both scientists and regulators for decades, as this metric is essential to quantify the influence of air traffic on the greenhouse effect. However, it is clear that, depending on the sun’s position and the contrail’s lifetime, individual contrails can have a cooling effect on the Earth’s atmospheric radiation balance. This study focuses on astronomical conditions with optimal sun positions (preferably during sunrise and sunset), the resulting requirements for contrail lifetimes (two to seven hours), and identifies atmospheric conditions (such as slight updrafts and thin ice-supersaturated layers) that enable the required lifetimes. Analyses of real historical weather data suggest that these conditions occur approximately during 30 % of the year. Consequently, cooling contrails regularly happen, and their radiative impact is likely overestimated. The results of this study can provide valuable insights for predicting and internalizing contrails.