Contrail Concerns Heat Up

Contrails are a factor in global warming, according to a new study by researchers at the Norwegian Institute for Air Research in Kjeller. Atmospheric scientists Gunnar Myhre and Frode Stordal have found that when jets produce the water vapour exhausts during the day, the ice crystals trap more of the heat rising from the earth than they reflect back into space, creating a small but significant increase in temperature. A previous 1999 study found that over areas with dense air traffic, such as Europe and North America, contrails could warm up the atmosphere by up to 0.l C.

Myhre and Stordal noted that when jets fly at dawn or dusk, the contrails bounce incoming sunlight back into space, thus having a cooling effect. The key, they said, lies in the low angle of the sun in the sky at those times. Although the net warming effect of contrails is currently about 75 times less than that of synthetic carbon dioxide, there is a predicted fivefold increase in air traffic for the next 50 years. The researchers of this study concluded that increasing the air traffic volume around dawn and dusk might decrease the impact on contrails on the environment.

< nature.com > August 15, 2001