First if you're not familiar with the "chemtrail" believer maybe watch this video:
If you do a quick YouTube search, you'll find hundreds and hundreds of videos with people filming the contrail lines from commercial flights. The chemtrail conspiracists claim that the Canadian/USA governments are purposefully altering the climate by spraying poisonous chemicals throughout the troposphere
First, what causes a contrail?
An airplanes engine makes lots and lots of hot water vapour with their combustible engines, which condenses once it mixes with the cold air.
Boom. Instant cloud under the right conditions.
I'm sure you've noticed that some days the skies are filled with them, and other days lack the atmospheric conditions to have cloud formation. Since most flights are at 10-12km above the surface, the temperatures are very, very cold!
Cold air isn't great at holding much moisture, compared to warm air. For contrails to form you need to reach the saturation point, so on days where the upper atmosphere is dry, you won't get many contrails.
The few days following September 11th, 2001 there was an unprecedented ban on commercial aircraft; therefore, a huge lack of contrails in the skies above.
Findings showed that contrails really weren't increasing the temperature by much, and in fact helped to keep temperature swings to a minimum, but there's still no verdict.
More info can be found in this BBC article on the study: http://www.bbc.co.uk/blogs/climatechange/2009/05/911_contrails_study_challenged.html
So if those conspiracists would simply read up on some high school chemistry and download this app...
...they would be able to see Air Canada flight 293 or West Jet flight 136, for example, leaving contrails above their heads.
I'll have a full blog post tomorrow about the first fall storm of 2013 approaching the coast Thursday/Thursday Night. It's looking like the strong winds and heavier rain will hit Haidi Gwaii and Northern Vancouver Island, sparing Vancouver.