Rerouting the flight paths of commercial aircraft to minimize the condensation trails, or contrails, they leave behind would help slow global warming, even if the new flight path is longer, according to research published today.
Contrails, thin clouds composed of ice crystals condensed from an aircraft’s exhaust, can persist for 17 hours or more and are likely the single largest contributor to climate change associated with aviation. They form when a plane passes through parts of the atmosphere that are very cold and moist, usually near high pressure systems.
This map illustrates typical distances added to a flight between New York (NY) and London (LON), in order to avoid areas where contrails are likely to form. For a flight in still air, the shortest route is the dashed line. The shortest alternative routes that avoid contrail formation are labeled A and B, and they each add roughly 14 miles (23 kilometers). (Image credit: Irvine et al., 2014, Environ. Res. Lett.)
The new research shows that avoiding contrail formation has greater climate benefits than avoiding additional carbon dioxide emissions associated with slightly longer flight routes. For example, for a small aircraft that is predicted to form a contrail 20 miles long, an alternative path that adds less than 200 miles will have a smaller climate impact than the contrail.
For a larger aircraft, which emits more CO2 per mile than a smaller plane, the alternative route is preferable if it adds less than 60 miles, according to researchers from the University of Reading. Many governments have adopted plans to reduce aviation’s climate impacts, but those plans only account for CO2 emissions, the researchers note. Understanding the climate impacts of contrails and how to avoid them is important for guiding such policies, they say.