The world is cloudier and warmer because of aviation. Jet condensation trails – contrails – can spread into high-altitude cirrus clouds. These have a greater warming effect than aviation’s carbon dioxide emissions, claim a team of German atmospheric physicists.
Water vapour in jet engine exhaust condenses into contrails criss-crossing the sky. These contrails have their own warming impact, but it is small because the straight-line clouds only cover a tiny fraction of the earth’s surface.