No need for the controversy of chemtrails-
"Contrails, by affecting the Earth’s radiation balance, act as a radiative forcing. Studies have found that contrails trap outgoing longwave radiation emitted by the Earth and atmosphere (positive radiative forcing) at a greater rate than they reflect incoming solar radiation (negative radiative forcing)."
http://www.eosnap.com/clouds/contrails-over-jutland-peninsula-denmark-and-germany/
Check it out, great photo(s) and a short, interesting read.
