Climate "double whammy" delivered by commercial high-flying aircraft
Modern commercial aircraft are delivering a 'double whammy' warming of the climate through their long-lived contrails, finds new research.
Chances are if you at look the sky on a warm, sunny day like today, it’ll be clear except for a few aircraft contrails streaking across the blue expanse. These thin traces of cloud are created by aircraft fumes, and trap heat in the atmosphere; a new study has found that although modern commercial planes flying at high altitudes emit less carbon than older aircraft, they also create longer-lived contrails.
The exact warming effect of contrails, or condensation trails, is uncertain, but scientists believe its greater than warming caused by carbon emissions from jet fuel, and their study emphasises the challenges the aviation faces in reducing its impact on the climate.
Spanner in the works
Researchers, led by Imperial College London, employed machine learning to analyse satellite data on over 64,000 contrails from a range of aircraft flying over the North Atlantic Ocean.
Modern aircraft, like the Airbus A350 and Boeing 787 Airliners, typically fly at above 38,000 feet, where the air is thinner with less aerodynamic drag, thus reducing jet fuel consumption. In comparison, passenger-carrying older commercial aircraft usually fly at slightly lower altitudes, around 35,000ft.
Data revealed that although higher-flying modern aircraft create less carbon emissions per passenger, they also create more contrails that take longer to disperse and a longer warming effect than older commercial aircraft.
“It's common knowledge that flying is not good for the climate. However, most people do not appreciate that contrails and jet fuel carbon emissions cause a double whammy warming of the climate,” explains Dr Edward Gryspeerdt, lead author, and a Royal Society University Research Fellow at the Grantham Institute – Climate Change and the Environment at Imperial.
“This study throws a spanner in the works for the aviation industry. Newer aircraft are flying higher and higher in the atmosphere to increase fuel efficiency and reduce carbon emissions. The unintended consequence of this is that these aircraft flying over the North Atlantic are now creating more, longer-lived, contrails, trapping additional heat in the atmosphere and increasing the climate impact of aviation.”
But that doesn’t mean that more efficient aircraft are a bad thing, Gryspeerdt adds: “far from it, as they have lower carbon emissions per passenger-mile. However, our finding reflects the challenges the aviation industry faces when reducing its climate impact.”
Simple step
Modern aircraft engines are intended to be cleaner and typically emit fewer soot particles, which this study confirms is a simple step to shortening the lifetime of contrails.
“From other studies, we know that the number of soot particles in aircraft exhaust plays a key role in the properties of newly formed contrails. We suspected that this would also affect how long contrails live for,” says co-author Dr Marc Stettler, a Reader in Transport and the Environment at the Department of Civil and Environmental Engineering at Imperial,
“Our study provides the first evidence that emitting fewer soot particles results in contrails that fall out of the sky faster compared to contrails formed on more numerous soot particles from older, dirtier engines.”
Rich, high-flyers
Private jets fly even higher, at over 40,000 feet above earth where there is less air traffic. Despite being smaller and using less fuel, they create contrails more often than previously thought – adding to concerns about the excessive use of these aircraft by the super-rich. These contrails were similar to much larger commercial aircraft, which surprised the researchers.
“Despite their smaller size, private jets create contrails as often as much larger aircraft. We already know that these aircraft create a huge amount of carbon emissions per passenger so the super-rich can fly in comfort,” Gryspeerdt says. “Our finding adds to concerns about the climate impact caused by private jets as poor countries continue to get battered by extreme weather events.”
News reference
Gryspeerdt, E. et al. (2024) Operational differences lead to longer lifetimes of satellite detectable contrails from more fuel efficient aircraft, Environmental Research Letters.