In a very positive move, You tube has added a link to the Encyclopedia Britannica article on Contrails to most of the videos that promote the "chemtrails" conspiracy theory.
It's a great article to use as the initial excerpt directly addresses the most common misconceptions about contrails - the idea that they always quickly dissipate.
It's also a great quote because the Encyclopedia Britannica exists in print, where it says the same thing. here's a clip from the 1983 editionContrail, also called condensation trail or vapour trail, streamer of cloud sometimes observed behind an airplane flying in clear cold humid air. It forms upon condensation of water vapour produced by the combustion of fuel in airplane engines. When the ambient relative humidity is high, the resulting ice-crystal plume may last several hours. The trail may be distorted by the winds, and sometimes it spreads outward to form a layer of cirrus cloud.
(If someone can find a better image of this, I'd greatly appreciate it!)
And of course there are many other books that say the same thing, as I described in this thread, and video
(which ALSO has the EB Contrail article linked)
While this might elicit cries of "propaganda" or "censorship", the information provided is both accurate and verifiable. I think the addition of neutral factual information to an otherwise highly misleading video is a good thing.