Scientists reveal surprising climate impact of airplane contrails

Airplanes leaving contrails may affect the Earth's climate in a surprising way. Research indicates that these white lines in the sky have a dual effect on our planet: they cool the surface during the day while simultaneously trapping heat at night. This is reported by the "arXiv" service.

During flights in humid air, soot particles emitted by jet engines lead to the formation of ice crystals, which turn into persistent contrails. These contrails can last in the atmosphere for many hours. Previous analyses suggested that they might have a greater impact on Earth's climate warming than carbon dioxide emissions from aviation fuel itself.

Research conducted by Irene Ortiz's team from Charles III University of Madrid aimed to determine the net effect of contrails over two winter periods – January 2023 and 2024. The authors of the study used tools that utilize artificial intelligence. These enabled the identification and analysis of the net warming effect for 700,000 contrails from satellite images covering Europe, North Africa, and surrounding oceans.

"These persistent contrails, as they are known, help to reflect solar radiation back to space, which has a cooling effect," the authors of the study state.

Simultaneously, they also have a downside in the context of climate warming: they impede the radiating of heat into space. However, this has little significance during the day since they significantly limit the incoming heat from the Sun.

The situation is worse at night. When the Sun is not shining, contrails hinder the radiating of heat from the Earth's surface, contributing to global warming. The study also noted that 62% of observed contrails formed at night; hence, the net effect of all contrails is warming. However, the study was limited to the northern hemisphere in winter, when nights are longer than days.

The study's authors suggest that daytime flights could reduce the impact on climate by limiting the incoming heat from the Sun. However, it must be acknowledged that this will not eliminate carbon dioxide emissions, which also contribute to global warming. Contrails last, on average, 2.5 to 3.5 hours, but some can persist for up to 14 hours or longer. Therefore, contrails formed in the afternoon and lasting into the night can have a net warming effect.

One solution could be to direct airplanes to avoid areas of humid air, where contrails form most easily. This could be achieved, among other things, by flying higher or lower. However, such an approach would involve lengthening the flight route and/or increasing fuel consumption. The research team plans to repeat the study in other seasons to see if and how the overall impact of contrails on the climate changes.