For years, the buzz on the Web has been that contrails -- or "chemtrails," in conspiracy-theorist lingo -- are part of some top-secret government project to control the weather. The National Oceanic and Atmospheric Administration, however, explains that that they're simply long, wispy streams of condensation, created when hot, humid air in the exhaust from jet aircraft engines mixes with extremely cold (-40 F and below) air at high altitudes that has a lower vapor pressure.
Far from being a malevolent portent of the New World Order, they're basically water vapor -- just another mundane, harmless curiosity of the modern technological age.
Or maybe not. As it turns out, contrails aren't really so benign. Researchers have discovered that, combined with the carbon dioxide spewed by jet exhaust, they actually contribute significantly to global warming.
Contrails can spread and combine to form ice-filled artificial cirrus clouds that trap reflected solar energy and keep it from going back into space. Contrails also block sunlight, too, but the heat-trapping effect is greater.