According to the chemtrail conspiracy theory, long-lasting trails left in the sky by high-flying aircraft are chemical or biological agents deliberately sprayed for sinister purposes undisclosed to the general public. Believers in the theory argue that normal contrails dissipate relatively quickly, and contrails that do not dissipate must contain additional substances. These arguments have been dismissed by the scientific community: such trails are normal water-based contrails (condensation trails) that are routinely left by high-flying aircraft under certain atmospheric conditions. Although proponents have attempted to prove that the claimed chemical spraying does take place, their analyses have been flawed or based on misconceptions.

Because of the widespread popularity of the conspiracy theory, official agencies have received many inquiries from people demanding an explanation. Scientists and government officials around the world have repeatedly needed to confirm that supposed chemtrails are in fact normal contrails.

The term chemtrail is a portmanteau of the words “chemical” and “trail,” just as contrail is a contraction of “condensation trail.” Believers in the conspiracy theory speculate that the purpose of the claimed chemical release may be for solar radiation management, psychological manipulation, human population control, weather modification, or biological or chemical warfare, and that the trails are causing respiratory illnesses and other health problems. Contrails are formed at high altitudes (5–10 miles or 8–16 kilometers) and if any chemicals were released at such altitude they would disperse harmlessly and fall many hundreds of miles away, or degrade before touching the ground.

Has Winnipeg been targeted? There has been a lot of chemtrails, or contrails, over the city in the past few months. Some recent photos from my apartment balcony:

In 1996, a chemtrail conspiracy theory began to circulate when the United States Air Force (USAF) was accused of “spraying the U.S. population with mysterious substances” from aircraft “generating unusual contrail patterns.” The USAF says these accusations were a hoax fueled in part by citations to a strategy paper drafted within their Air University entitled Weather as a Force Multiplier: Owning the Weather in 2025. The paper was presented in response to a military directive to outline a future strategic weather modification system for the purpose of maintaining the United States’ military dominance in the year 2025, and identified as “fictional representations of future situations/scenarios.” The USAF further clarified that the paper “does not reflect current military policy, practice, or capability,” and that it is “not conducting any weather modification experiments or programs and has no plans to do so in the future.” Additionally, the USAF states that the “‘Chemtrail’ hoax has been investigated and refuted by many established and accredited universities, scientific organizations, and major media publications.”

An article in the Skeptical Inquirer said that the conspiracy theory was first started in the 1990s by “investigative journalists” such as William Thomas, and then promoted on the late-night radio shows of Art Bell. The conspiracy theory is seldom covered by the mainstream media, and when it is, it is usually cast as an example of anti-government paranoia.

Photographs of barrels installed in the passenger space of an aircraft for flight test purposes have been claimed to show aerosol dispersion systems. The real purpose of the barrels is to simulate the weight of passengers or cargo. The barrels are filled with water, and the water can be pumped from barrel to barrel in order to test different centers of gravity while the aircraft is in flight.

Jim Marrs has cited a 2007 Louisiana television station report as evidence for chemtrails. In the report the air underneath a crosshatch of supposed chemtrails was measured and apparently found to contain unsafe levels of barium: at 6.8 parts per million, three times the US nationally recommended limit. A subsequent analysis of the footage showed, however, that the equipment had been misused, and the reading exaggerated by a factor of 100—the true level of barium measured was both usual and safe.

Astronomer Bob Berman has characterized the chemtrail conspiracy theory as a classic example of failure to apply Occam’s razor (among competing hypotheses, the one with the fewest assumptions should be selected), since instead of adopting the long-established “simple solution” that the trails consist of frozen water vapour, “the conspiracy web sites think the phenomenon started only a decade ago and involves an evil scheme in which 40,000 commercial pilots and air traffic controllers are in on the plot to poison their own children”.