Contrails, the ice crystal clouds formed when an aircraft’s exhaust fumes mix with cold air, have a significant warming effect on the planet, according to a new study by the campaign group Transport Energy. The study argues that the warming caused by contrails could be as important as the impact of carbon dioxide emissions from aviation fuel.
Contrails are created when warm, moist exhaust gases from aircraft meet cold air at high altitudes, forming ice crystals that trail behind planes. While these trails typically dissipate, in humid conditions, they can spread and linger, trapping heat near the Earth’s surface, much like cirrus clouds. This effect, the study suggests, could be contributing to global warming in ways that are often overlooked.
According to Transport Energy’s research, just 3% of flights are responsible for 80% of contrail-induced warming. The study proposes that by slightly adjusting flight paths—particularly in regions where contrails are more likely to form—this warming effect could be reduced by over 50% by 2040.
Flights operating at higher latitudes, such as those over North America, Europe, and the North Atlantic, are more prone to producing warming contrails, making them prime candidates for adjustments. Additionally, evening and night flights contribute the most to this warming effect.
The study’s authors suggest that the climate benefits of avoiding contrail formation would far outweigh the costs associated with reducing emissions from aviation. Even with added fuel costs and new technology such as humidity sensors to prevent contrail formation, the cost per passenger could be minimal—under €4 (£3.30) for a flight from Paris to New York, and just €1.20 (£1) for a route from Barcelona to Berlin.
A 2021 study found that contrails, in terms of their contribution to global warming, could be even more significant than CO2 emissions from aviation, especially between 2000 and 2018.
The issue of contrail-induced warming will be a key topic at the upcoming COP29 climate summit, where the University of Cambridge’s institute will co-host an event discussing the climate impact of aviation. The new findings suggest that, with small adjustments, the aviation industry could play a significant role in mitigating its environmental impact while also helping to combat global warming.