High in the sky where the cirrus ice crystal clouds form, jet contrails draw their crisscross patterns. Now researchers have found that these elevated ice cloud trails can influence temperatures on the ground and affect local climate.

For contrails to form, the atmosphere at the level the jet is flying must be cold enough that the moisture from the jet exhaust freezes into ice crystals. There also must be enough moisture in the air that the clouds that form remain in the sky for at least a few hours as persisting contrails.

The researchers found that contrails depress the difference between daytime and nighttime temperatures, typically decreasing the maximum temperature and raising the minimum temperature. In this respect, the contrail clouds mimic the effect of ordinary clouds.