Contrails Make Clouds Say Researchers
No, this is not a ChemTrail airticle, but the UK's Met Office has concluded that high level contrails do have a global and localized effect ... on sunshine levels. One contrail studied by the office turned into a high level cirrus cloud that, at the peak of its formation, "covered an area of more than 20,000 square miles," Met Office Research Manager, Jim Haywood, told the UK's Times Online. According to the study, vapor trails laid down by aircraft along high traffic flight paths can reduce sunshine levels by as much as 10 percent whereas a lone contrail reduces light by less than one percent. Atmospheric conditions dictate how long the contrails remain in the sky and most dissipate quickly, said Hawyood. But some can last much longer, stimulating reactions in the surrounding stratosphere, "because the extra ice and soot act as 'nuclei' around which more water can condense," wrote the Times. Cloud cover aside, researchers say that the aviation-induced cloud cover can have other effects.
Intuitively, shade reduces heat, but researchers believe that high level cloud cover like that sometimes produced by contrails overall trap more heat than they reject. The overall effect then is a positive warming effect, which may be added to the three percent of greenhouse gas emissions that aviation is thought to contribute.