Contrails from airplanes impact temperatures at Earth's surface. But do they raise or lower them?
They usually appear above 26,000 feet where the air is less than -40 C (also -40 F.) But factors besides altitude also play a role in their formation. Depending on how much moisture is in air, for example, contrails last shorter or longer. Moisture availability also dictates whether they form at all, and how much they grow after formation.
As it turns out, they also impact temperatures at Earth's surface, although by how much and in which direction — up or down — is still being worked out. Read more.