Contrail is a contraction of the two words “condensation trails.” Contrails are those long, thin, artificial clouds that can form behind aircraft.  At high altitudes, generally 25,000 feet or more, the warm exhaust from aircraft engines mixes with the moisture laden air at low temperature. The invisible water vapor condenses on the exhaust particles, essentially forming a momentary cloud.

We see the same phenomena taking place on the ground when we go outside in cold winter weather and notice a cloud formed by our breath.

Contrails were noticed back in the 1940’s, especially when the United States Eighth Air Force send hundreds of B-17 bombers from England to hit targets in Nazi Germany. Americans saw the contrails on Movietone News Reels seen in movie theatres.

The length of time that the contrails persist depends on the altitude, temperature, water vapor content, and sheer winds. If the winds aloft are calm, the contrail will keep its shape and be seen from horizon to horizon.

Sometimes, strong winds will spread out the contrail, so it looks like those high-altitude cirrus clouds, often referred to as “mare’s tails.”

Cloud seeding has been in operation in various locations around the globe since the 1950’s. Shooting silver iodine crystals into clouds causes the clouds to give up their water content. Cloud seeding has been used to relieve drought, increase snowfall, dissipate hurricanes, and suppress hail.

The Chinese government promised clear skies for the August 8 opening of the 2008 Summer Olympics. They launched 1,100 rain dispersal rockets from 21 sites around Beijing. Sure enough, no rain fell on their parade.

People in rural areas tend to pay close attention to the skies. They generally report seeing more contrails these days compared to decades ago. That is no doubt true, as there has been a large increase in jet traffic, both civilian and military.

In addition, much of that air traffic has been at higher altitudes, some as high as 40,000 feet, where winds aloft are less likely to disperse the contrails quickly.

There have been those stories, held by conspiracy theorists, that chemicals are being spread from planes for a certain purpose. They call them “chemtrails” rather than “contrails”.

Some of the chemtrail conspiracy stories that float around the Internet claim that barium, aluminum salts, thorium, and silicon carbide are being released. Other accounts have the skies being seeded with electrically conductive materials as part of a super weapons program. Other stated reasons are population control and alleviating global warming.

Studies done in the United States, Canada, and Great Britain found no scientific evidence to support the allegation that high altitude spraying is being conducted.

These operations may very well be going on, but thus far nobody has brought forth any proof or evidence. They remain, for now, just conspiracy theories.