Yale Environment 360: Flight paths that avoid forming contrails 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...