As I sat on the train coming into London this morning, I was stuck by the number of aircraft trails lingering in the sky. It was a beautiful clear morning, but there were probably about a dozen trails visible, some of which had spread out to a considerable width.
I was wondering to what extent, if any, aircraft trails are increasing cloud cover. I tried a few Google searches and there seems to be a lot of info out there, but much of it seems to be infected by the “chemtrail” tinfoil crowd.
North American got to do some real science on this topic in 2001.
After 9/11 air travel was non-existant for several days, and severely curtailed for a slightly longer period, meaning vritually no contrails* over the US for several days. Scienticists took advantage of the situation to make some observations and compared the data to more normal times with abundant air traffic. There was a whole bunch of really complicated technical stuff involved which I’m not even going to try to explain.
Verdict: yes, contrails do affect cloud cover, serving at the source of a certain amount of high-altitude clouds.
Since it has been a few years since that time I don’t have an exact recollection of where I read about all that, but it was from sources I consider realiable. If I can remember where the information was I’ll post it here.
Air Force One, some military flights, and some emergency medical flights did occur, however, the medical flights and a substantial portion of the military flights were at relatively low altitudes and did not form contrails.
When you search on Google, got to “Advanced Search” and under the part where it says “without the words” put “chemtrail, chemtrails” to eliminate some of the tinfoil hat sites.
BrieflyEmpty Skies Offer Climate Clues is an article that I read after 9/11 that described the study done of contrails as the skies emptied and it has some interesting information about contrails and cloud cover.