When do contrails cool the atmosphere?

One of the main causes of aviation-induced climate change is the formation of contrails. To quantify how much of an impact contrails in general have on global warming, lots of thorough research has been done. Individual contrails might even decide on a cooling and a warming effect. This effect can be in the same order of magnitude as the climate impact of aviation-emitted carbon dioxides and nitrogen oxides. Therefore, three-dimensional optical and meteorological investigations of individual contrails have been performed. This paper focuses on conditions of contrails with a cooling effect on global warming. We found, that a flat sun position during sunrise and sunset increases the possibility of a solar cooling effect dominating the terrestrial heating effect. Individual contrails additionally benefit from flight paths between East and West due to an increased travelling distance of photons through the contrail. On a small scale, the outcomes can be applied to arbitrary trajectory optimization tools with a focus on environmental optimization. On a large scale, the results can be used in environmentally optimized Air Traffic Flow Management.