Passenger Planes and Private Jets: Contributing More to Global Warming Than Estimated
Passenger planes and private jets that fly at higher altitudes can create longer-lasting contrails, meaning their contribution to global warming has been underestimated. Contrails are clouds produced by water vapor condensing on soot emitted by jet engines.
Higher Altitude Flights, Longer Lasting Contrails
Aeroplanes that fly at higher altitudes can create longer-lasting vapor trails that are likely to cause more global warming. Private jets and modern fuel-efficient jets fly higher than other passenger jets, so these aircraft may be causing even more warming than previously thought.
Challenges in Studying Contrail Persistence
How long contrails persist largely determines how much warming they cause, but their persistence is difficult to study. A research team at Imperial College London has combined flight data and satellite observations to match specific aircraft to contrails, and see how the type of aircraft relates to persistence.
Private Jets and Fuel-Efficient Jets: Higher Impact
The study revealed 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 generate longer-lasting contrails. “It was not what we expected,” says Edward Gryspeerdt, lead author of the study.
At higher altitudes, a higher proportion of soot particles emitted by aircraft seed ice particles, but the overall size of ice particles is smaller. Smaller ice particles fall more slowly, taking longer to reach warmer air where they sublimate back into water vapor. This means contrails persist for longer and cause more warming.
Uncertainties and Future Research
However, the exact warming caused by these higher-altitude contrails is still uncertain. It is not clear if the additional warming caused by longer-lasting contrails outweighs the avoided warming due to the lower fuel use of modern planes.
The study also highlights the need to consider the impact of private jets, which have an even more significant impact on the climate per passenger than previously thought.
Policy Implications
“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 at Transport & Environment, an environmental advocacy organization.
High altitudes are mainly used by long-haul flights, but long-haul flights have been excluded from a European Union scheme that aims to reduce the non-CO2 warming. This study emphasizes the importance of switching to fuels that generate fewer soot particles.