Modern fuel-efficient jets can contribute more to global warming than older planes.
Airplanes flying at higher altitudes can produce longer-lasting vapor trails, which are likely to contribute more to global warming. Because private jets and modern fuel-efficient aircraft typically fly higher than other passenger planes, they may be causing more warming than previously estimated.
Under certain conditions, soot particles emitted by jet engines can trigger the formation of ice particles in the aircraft's wake, leading to the creation of clouds known as contrails, which have a net warming effect. It is estimated that up to half of aviation's warming impact comes from contrails rather than carbon dioxide emissions.
The duration of contrails largely determines their warming potential, but studying their persistence is challenging. Gryspeerdt's team combined flight data and satellite observations to match specific aircraft with their contrails and examine how the type of aircraft influences contrail persistence.
Previously, this kind of analysis was done on a small scale manually. However, by utilizing artificial intelligence, the team analyzed 64,000 flights, revealing that private jets and more fuel-efficient jets, which typically cruise at around 12 kilometers (38,000 feet)—a kilometer higher than other planes—are more likely to create longer-lasting contrails. "This was unexpected," says Gryspeerdt.
Not all soot particles emitted by an aircraft become ice particles, but the team believes that at higher altitudes, a larger proportion of soot particles seed ice particles, though the overall size of these ice particles is smaller.
Smaller ice particles descend more slowly, taking longer to reach warmer regions where they sublimate back into water vapor. As a result, contrails persist longer and cause more warming.
However, because the properties of these higher-altitude contrails differ, the team cannot yet determine exactly how much additional warming they cause. It remains unclear whether the extra warming from longer-lasting contrails outweighs the reduced warming from the lower fuel consumption of modern planes.
What is clear is that the climate impact of private jets is being underestimated.
Since contrails are more visible over oceans, and the team only had data from a single geostationary satellite, they focused on flights over the western Atlantic, near Bermuda.
“The study highlights the significant non-CO2 climate impact of aircraft operating at high altitudes, primarily due to the persistent contrails they produce,” says Krisztina Hencz of Transport & Environment, a European environmental advocacy organization.
Hencz points out that high altitudes are mainly used by long-haul flights, which have been excluded from a European Union scheme aimed at reducing non-CO2 warming.
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