Soldato
There was some quite interesting reports post 9/11 about how the reduced Air Travel for those few days in 2001 did have some kind of measurable affect on the environment. Will dig out links when I get home!
A bad affect if i remember correctly.
3. Airplanes' contrails may also play a role in climate change. Contrails are high-altitude vapor trails. They form when water vapor in the atmosphere condenses and freezes around tiny, cooled particles of engine exhaust.
The three-day grounding of all American air traffic after September 11, 2001 created a natural experiment for studying contrails' effects. Researchers discovered that the absence of contrails expanded the difference between daytime and nighttime temperatures by a full degree Celsius, compared with the average of the last three decades. The difference was even greater in Cascadia and other heavy-air-traffic, mid-latitude regions (see endnote 5). Apparently, contrails dampen natural temperature variations.
Source: http://www.sightline.org/research/energy/res_pubs/rel_air_travel_aug04
Mega PDF original source document
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