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, but their arguments have been dismissed by the scientific community: such trails are simply normal water-based contrails (condensation trails) which 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 misconception.
Experts on atmospheric phenomena say chemtrails do not exist, and that the characteristics attributed to them are simply features of contrails responding differently in diverse conditions in terms of the sunlight, temperature, horizontal and vertical wind shear, and humidity levels present at the aircraft’s altitude. In the US, the gridlike nature of the National Airspace System’s flight lanes tends to cause crosshatched contrails, and in general it is hard to discern from the ground whether overlapping contrails are at similar altitudes or not. The jointly published fact sheet produced by NASA, the EPA, the FAA, and NOAA in 2000 in response to alarms over chemtrails details the science of contrail formation, and outlines both the known and potential impacts contrails have on temperature and climate. The USAF produced a fact sheet as well that described these contrail phenomena as observed and analyzed since at least 1953. It also rebutted chemtrail theories more directly by identifying the theories as a hoax and denying the existence of chemtrails.
Contrail testing being carried out on an Airbus A340 and much older Boeing 707[
Patrick Minnis, an atmospheric scientist with NASA’s Langley Research Center in Hampton, Virginia, is quoted in USA Today as saying that logic does not dissuade most chemtrail proponents: “If you try to pin these people down and refute things, it’s, ‘Well, you’re just part of the conspiracy’,” he said.
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 kilometres) 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.
An article in the Skeptical Inquirer said that the conspiracy theory was first started in the 1990s by “investigative journalists” like William Thomas, and then promoted in the late-night radio shows of Art Bell. The proponents claim that after 1995 contrails had a different chemical composition and lasted a lot longer on the sky; they never acknowledge the photographs of long-lasting contrails dating as far back as World War II.
In the United Kingdom, when the Secretary of State for Environment, Food and Rural Affairs was asked “what research her Department has undertaken into the polluting effects of chemtrails for aircraft,” the response was that “the Department is not researching into chemtrails from aircraft as they are not scientifically recognized phenomena,” and that work was being conducted to understand “how contrails are formed and what effects they have on the atmosphere.”
In a response to a petition by concerned Canadian citizens regarding “chemicals used in aerial spraying are adversely affecting the health of Canadians,” the Government House Leader responded by stating, “There is no substantiated evidence, scientific or otherwise, to support the allegation that there is high altitude spraying conducted in Canadian airspace. The term ‘chemtrails’ is a popularized expression, and there is no scientific evidence to support their existence.” The house leader goes on to say that “it is our belief that the petitioners are seeing regular airplane condensation trails, or contrails.”
Official statements on the non-existence of chemtrails have not discouraged the conspiracy theorists. Various versions of the chemtrail conspiracy theory have propagated via the internet and radio programs. There are web sites dedicated to the conspiracy theory, and it is particularly favored by right-wing groups since it fits well with deep suspicion of government. In some of the accounts, the chemicals are described as barium and aluminum salts, polymer fibers, thorium, or silicon carbide. Other accounts allege that the skies are being seeded with electrically conductive materials as part of a massive electromagnetic superweapons program based around the High Frequency Active Auroral Research Program (HAARP). Those who believe in the conspiracy say the chemtrails are toxic, but the reasons given by those who believe in the conspiracy vary widely, ranging from military weapons testing to chemical population control to climate control. Scientists and federal agencies have consistently denied that chemtrails exist, insisting the sky tracks are simply persistent contrails. As the chemtrail conspiracy theory spread, federal officials were flooded with angry calls and letters. A multi-agency response to dispel the rumors was published in a 2000 fact sheet by the Environmental Protection Agency (EPA), the Federal Aviation Administration (FAA), the National Aeronautics and Space Administration (NASA) and the National Oceanic and Atmospheric Administration (NOAA), a step many chemtrail believers have interpreted as further evidence of the existence of a government cover-up.
It is well established by atmospheric scientists that contrails can not only persist for hours, but it is a perfectly normal characteristic for them to spread out into cirrus sheets. The different sized ice crystals in contrails descend at different rates, which spreads the contrail vertically. Then the differential in wind speeds between altitudes (wind shear) results in the spreading of the contrail across many miles in the sky. This mechanism is similar to the formation of cirrus uncinus clouds. Contrails between 25,000 and 40,000 feet can often merge into an “almost solid” interlaced sheet. Contrails can have a lateral spread of several kilometers, and given sufficient air traffic it is possible for contrails to create an entirely overcast sky which increases the ice budget of individual contrails and persists for hours.