evidence: Water vapor is also a product of jet fuel consumption, making up about 30 percent of the exhaust. With its short lifespan in the atmosphere as part of the water cycle, water vapor from aircraft has a minimal direct warming impact. However, its presence in the exhaust plume has an indirect impact by contributing to the formation of contrails. Water vapor in the exhaust instantly freezes when the ambient temperature is cold enough, as particulates in the exhaust form the nucleus of ice crystals. When the ambient atmosphere is sufficiently humid and cold, the small ice crystals expand as they draw water vapor from the atmosphere and are sustained as contrails that can spread horizontally and vertically to form contrail-induced cirrus clouds. These lingering contrails and contrail-induced cirrus clouds trap infrared rays, producing a warming effect up to three times the impact of CO2. Even though these cirrus clouds have a relatively short life span, usually a matter of hours, their collective influence, produced by thousands of flights, have a serious warming effect. The effect is so large today that it exceeds the total warming influence of all the CO2 emitted by aircraft since the beginning of powered flight.