Despite the lower carbon emissions of modern planes compared to older models, their contrails may have a greater impact on climate change. This research, led by scientists at Imperial College London, underscores the significant challenges the aviation industry faces in reducing its environmental impact. Additionally, the study indicates that private jets produce more contrails than previously understood, exacerbating their climate impact.
Contrails, or condensation trails, are cloud-like streaks formed by aircraft exhaust. These trails trap heat in the atmosphere, contributing to global warming. Although the exact warming effect of contrails is still uncertain, it is believed to surpass the warming caused by carbon emissions from jet fuel.
Published in Environmental Research Letters, the study utilized machine learning to analyze satellite data on over 64,000 contrails from various aircraft flying over the North Atlantic Ocean. The findings show that modern aircraft, such as the Airbus A350 and Boeing 787, which fly above 38,000 feet (about 12km), generate more contrails than older commercial aircraft.
Modern aircraft are designed to fly at higher altitudes to reduce jet fuel consumption due to thinner air and less aerodynamic drag, compared to older aircraft flying at slightly lower altitudes (around 35,000 feet or 11km). This design reduces carbon emissions per passenger but results in contrails that persist longer, thus prolonging their warming effect-a complex issue for the aviation industry.
Dr. Edward Gryspeerdt, the lead author and a Royal Society University Research Fellow at the Grantham Institute - Climate Change and the Environment, commented, "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.
"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.
"This doesn't mean that more efficient aircraft are a bad thing - 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."
The study also identified a straightforward method to reduce contrail longevity: minimizing soot emissions from aircraft engines, which occur when fuel burns inefficiently. Modern aircraft engines, designed to be cleaner, typically emit fewer soot particles, thereby shortening the lifespan of contrails.
While other studies have predicted this phenomenon through models, this research is the first to confirm it using real-world observations.
Dr. Marc Stettler, a co-author and a Reader in Transport and the Environment in the Department of Civil and Environmental Engineering at Imperial College London, explained, "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.
"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."
The research also found that private jets, despite being smaller and using less fuel, create contrails as frequently as larger commercial aircraft. This is particularly concerning given the high altitudes at which private jets fly, typically over 40,000 feet, where there is less air traffic. The high altitude contributes to longer-lasting contrails.
Dr. Gryspeerdt noted, "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.
"Our finding adds to concerns about the climate impact caused by private jets as poor countries continue to get battered by extreme weather events."
Research Report:Operational differences lead to longer lifetimes of satellite detectable contrails from more fuel efficient aircraft
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