Contrails: Surprising dual impact on Earth's climate revealed

Airplanes leaving contrails can influence the Earth's climate in surprising ways. Research indicates that these white lines in the sky act on our planet in two ways. They cool its surface during the day while impeding the emission of heat at night. This information comes from the "arXiv" service.

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

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

"The results suggest that contrails produced by airplanes have a net cooling effect during the day by reflecting sunlight back into space," state the study's authors.

At the same time, they also have a drawback concerning climate warming—they hinder the emission of heat into space. However, this has little significance during the day as they significantly limit the Sun's heat intake.

The situation looks worse at night. When the Sun is not shining, contrails hinder the emission of heat from the Earth's surface, contributing to global warming. The study also noted that 62 percent of the observed contrails formed at night, so the net impact 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 climate impact by limiting the Sun's heat intake. Although, it must be noted, they will not eliminate carbon dioxide emissions, which also contribute to global warming. Contrails persist on average from 2.5 to 3.5 hours, but some can last even 14 hours or longer. For this reason, contrails formed in the afternoon and persisting at night may have a net warming effect.

One solution could be to direct airplanes to avoid areas with humid air where contrails form most easily. This could be accomplished, among other ways, by flying higher or lower. However, this approach would be associated with lengthening the flight route and/or increasing fuel consumption. The research team plans to repeat the study at other times of the year to see if and how the overall impact of contrails on the climate changes.