# Aircraft contrails and cloud cover **URL:** \ **Category:** Factual Questions\ **Created:** [September 16, 2004, 10:36am UTC](https://boards.straightdope.com/t/aircraft-contrails-and-cloud-cover/264668 "2004-09-16T10:36:21Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\ **Post date:** [September 16, 2004, 10:36am UTC](https://boards.straightdope.com/t/aircraft-contrails-and-cloud-cover/264668/1 "2004-09-16T10:36:21Z")
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. Anyone got the Bacofoil-free skinny? ---
**Author:** ![Broomstick](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/broomstick/32/246_2.png) [@Broomstick](https://boards.straightdope.com/u/Broomstick)\ **Post date:** [September 16, 2004, 10:50am UTC](https://boards.straightdope.com/t/aircraft-contrails-and-cloud-cover/264668/2 "2004-09-16T10:50:09Z")
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. ---
**Author:** ![Broomstick](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/broomstick/32/246_2.png) [@Broomstick](https://boards.straightdope.com/u/Broomstick)\ **Post date:** [September 16, 2004, 10:56am UTC](https://boards.straightdope.com/t/aircraft-contrails-and-cloud-cover/264668/3 "2004-09-16T10:56:04Z")
Here we go - if I can get the link to work properly - is a document from NASA, an organization usually considered pretty level-headed and scientific: [Spreading of Isolated Contrails During the 2001Air Traffic Shutdown](http://64.233.167.104/search?q=cache:S8gNFeJudCMJ:www-pm.larc.nasa.gov/sass/pub/conference/Minnis.abs.ARAMS.02.pdf+meteorology+contrails+cloud+formation+-chemtrail,+-chemtrails&hl=en) 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. ---
**Author:** ![Lsura](https://avatars.discourse-cdn.com/v4/letter/l/7993a0/32.png) [@Lsura](https://boards.straightdope.com/u/Lsura)\ **Post date:** [September 16, 2004, 10:56am UTC](https://boards.straightdope.com/t/aircraft-contrails-and-cloud-cover/264668/4 "2004-09-16T10:56:55Z")
[BrieflyEmpty Skies Offer Climate Clues](http://cartome.org/9-11climatology.htm) 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. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [September 16, 2004, 10:56am UTC](https://boards.straightdope.com/t/aircraft-contrails-and-cloud-cover/264668/5 "2004-09-16T10:56:59Z")
[Cecil’s (somewhat tangential) article on the subject](http://www.straightdope.com/columns/000616.html)