Contrails, short for condensation trails, are the white streaks often seen in the sky behind aircraft. The international cloud atlas, which classifies clouds, has a category just for them: cirrus homogenitus, an example of man-made clouds.
Contrails contribute to climate change, adding to the warming by the carbon dioxide emitted by aviation. Although the exact amount of warming caused by these wispy-looking clouds is uncertain, what is understood now suggests that reducing the number of contrails has the potential to reduce the climate impact of flights.
