This is Scientific American's 60-second Science, I'm Susanne Bard.Airplanes account for about 3 percent of the climate-altering carbon dioxide emissions we add to the atmosphere.But planes are warming the planet in another way."So if you look up in the sky, you probably see, at some point, an aircraft.And behind that aircraft are white, fluffy streaks. And that's what we call a contrail."Imperial College London engineer Marc Stettler.Contrails are made up of ice crystals that form when aircraft engines emit exhaust that hits the cold air.The ice crystals reflect incoming light from the sun back into space, which has a cooling effect on the atmosphere.But the contrails also stop heat coming up from the ground from escaping into space."It's reflected back down toward the ground. And so that's a warming effect."Stettler says, on balance, contrails warm the atmosphere more than they cool it."And that's primarily because the cooling effect due to reflecting of sunlight can only happen during the day, when the sun's shining,whereas the warming effect due to trapping of outgoing heat happens all of the time."Some contrails can form clouds that last for up to 18 hours.During that time, they spread out, trapping even more heat.This process allows contrails to warm the planet about as much as the carbon dioxide emissions from aircraft.But when Stettler and his team analyzed flight data they obtained of Japan airspace,
