The white, feathery lines behind airplanes that look like bits of harmless cloud are anything but, warn experts, who say they could have a greater environmental impact than the aviation sector's CO2 emissions. The condensation trails - contrails, for short - are being increasingly studied as scientists work with the industry to find technological solutions to the problem. Classified as non-CO2 emissions from aircraft, in September they were the subject of a symposium in Montreal organized by the International Civil Aviation Organization, a UN agency. Contrails are clouds that form at high altitudes in cold, humid areas called ice supersaturated regions (ISSRs). When jet fuel is burned by engines, water vapor condenses on to soot particles to form ice crystals. Enough ice crystals, and they begin to form cirrus clouds - high-altitude, wispy white filaments that, when created this way, trail out behind planes as they cross the sky. These trails trap some of the heat that rises from the Earth at night, preventing it from radiating back out of the atmosphere - thus acting as a greenhouse gas, causing warming, explains Donald Wuebbles, a professor at the University of Illinois. Contrails that stay in the sky for a few minutes are not very worrisome, he says. "But if they form at night, they'll maybe last a little longer, and at night they can cause a warming effect," he adds. Non-CO2 emissions could account for up to two-thirds of aviation's impact on global warming, which "gives you an idea of how important they are to consider," Wuebbles said. And contrails could form up to 57 percent of that impact - far more than the C02 emissions from burning fuel, according to a 2021 study. However, such emissions are short-lived compared to carbon dioxide and their impact on global warming could be quickly eroded if solutions were found to avoid them, experts say. Not all flights create contrails - it... |