FOR THE PAST FEW YEARS, MY FACEBOOK PAGE KEPT flagging strange websites that claimed that ordinary contrails formed by high-flying aircraft are "chemtrails," a special kind of chemical sprayed on the unwitting population for reasons too bizarre and illogical to take seriously. For a long time, I've ignored such wild Internet bafflegab, but in recent years it has gotten more and more pervasive, and I've encountered people who believe it. There are whole shows about it on the once-scientific Discovery Channel, and the History Channel as well--both seem to have sold their souls to commercialism. Now they seem to broadcast one pseudoscientific show after another. Soon there will be a low-budget Hollywood movie release, Poison Sky, that will further spread this idea. The chemtrail conspiracy mongers circulate their photos and videos among themselves, post hundreds of videos on YouTube, and on their own sites and forums. But with the way the Internet works as a giant echo chamber for weird ideas with no peer review, fact checking, or quality control, it is becoming ever more difficult to ignore them, so it's time to debunk this conspiracy theory.

The first few times I heard about "chemtrails" my reaction was "This can't be serious." But the people who spread this idea are serious. They are generally people who have already accepted the conspiracy theory mindset, where everything they don't like or don't understand is immediate proof of some nefarious government conspiracy. But there's an even bigger factor at work here: gross science illiteracy. The first thing that pops into my mind reading their strange ideas is "Didn't this person learn any science in school?" And my initial rebuttal is: "Do you even understand the first thing about our atmosphere? Do the math! Anything released at 30,000 feet will blow for miles away from where you see it, and has virtually no chance of settling straight down onto the people below. And it will be so diluted it would have no measurable amount of the chemical by the time it lands. That's why crop-dusting planes fly barely 30 feet off the ground--so their dust won't blow too far away from the crops!" As skeptic Kyle Hill describes it:

If the chemtrail conspiracy were true, millions of pilots would be needed to crop dust the American population. A typical crop duster might use seven ounces of agent diluted in seven gallons of water to cover one acre of land. Chemtrail "people dusters" would use a similar concentration to cover the entire United States, just to be safe. For 2.38 billion acres of land, the pilots would then need--for just one week of spraying--120 billion gallons of these cryptic chemicals. That's around the same volume as...