Contrails, the fluffy white patterns one sees left behind an airplane in the sky, may account for more than 57% of climate impact by aviation. The condensed water vapors trap and absorb heat that otherwise escapes into outer space. Dr. Marc Stettler, an environment lecturer at Imperial College London, says the impact of contrails can be significantly reduced by 59% simply by changing the altitudes of fewer than 2% of flights. Professor Keith Hayward from Royal Aeronautical Society says the cost to adjust the flight software is minimal compared to an engine change, which can cost $12 million. "A relatively small proportion of flights contribute to the majority of climate impact, " says Dr. Stettler. "So if we can alter these flights, we can significantly reduce the climate impact."