On a day when many people are traveling for the holidays, I thought you might be interested in a recent story from Smithsonian magazine on the impact of contrails on local and regional climate.
Contrails are high-altitude clouds made of ice crystals and are formed by emissions from jet aircraft interacting with moisture high in the atmosphere. When there is a lot of moisture at these levels, you get many contrails. When there is little moisture, then contrails are short and can look almost nonexistent. The optical effects of these clouds differ depending on what kind of light is passing through them. Sunlight scatters from the ice crystals but the light may not appear to dim much from the icy clouds. At night contrails and natural cirrus clouds help to trap heat near the ground, keeping minimum temperatures higher than they would under a completely clear sky.
In climate models, these high-level clouds are not handled well by the computer simulations, leading to questions about how they will affect climate in the future. Climatologists know that in areas where there is a lot of jet traffic (for example, in northern Illinois west of O’Hare airport, daytime temperatures can be reduced and night-time temperatures increased by the persistent contrails on this major air route.
