What Is the Chemtrails Conspiracy Theory?

Jet engines spew out very hot air, and because water vapor is also one of the byproducts of the exhaust, the air is also very humid [source: Ackerman]. However, high in the atmosphere where these jets fly, the air is typically very cold — often below minus 40 degrees Fahrenheit (minus 40 degrees Celsius). Additionally, the atmosphere at that height has low vapor pressure, or the force exerted by a gas on the surrounding environment.

When a jet engine emits hot, humid air into an atmosphere that is so cold and has low vapor pressure, the result is condensation. The water vapor coming out of the engine quickly condenses into water droplets and then crystallizes into ice. The ice crystals are the clouds that we see forming behind the engine. That is why we call these streaks contrails, short for "condensation trails."

To help explain it, scientists liken it to seeing your breath on cold days. You may have noticed that puffs of breath dissipate quickly on drier days. The same is true of contrails: When the atmosphere is more humid, the contrails linger longer, but when the atmosphere is dry, the contrails disappear more quickly. Normal contrails can last for hours and cover great distances [source: FAA].

This explanation makes sense. But, as author and airline pilot Patrick Smith wrote, the contrails consist of not just ice crystals and water vapor, but also of other byproducts of engine exhaust, including carbon dioxide, nitrogen oxides, sulfate particles and soot [source: Smith].

Some point out that these, in addition to the extra cloud cover, can have negative environmental effects. And conspiracy theorists have nicknamed contrails "chemtrails" because they suspect that governments are taking advantage of this scientific phenomenon to secretly release chemical or biological agents into the atmosphere.

Contrails and Chemtrail Theories

While people accept that contrails are natural byproducts of jet engines, their suspicion is that the government has since used that excuse to put harmful substances in those trails, thereby creating chemtrails. In addition, conspiracy theorists latch on to anecdotal evidence that connect epidemics of flu-like symptoms to instances of contrails.

Those who believe that there's something fishy about contrails have come up with several theories to explain what governments might be covering up.

One extreme conspiracy theory says that the government is intentionally spraying people with harmful substances in order to experiment with the effects — or even to "weed out" the sick and elderly. Other conspiracy theories suggest the chemtrails are an attempt by the government at mind control and even sterilization.

However, many reputable scientists dismiss these theories on the grounds that such experiments would be of no real use.

"We have not seen any credible evidence that chemtrails exist. If we did see any evidence that governments were endangering their own citizens in the manner alleged in the chemtrails conspiracy, we would be eager to expose and stop any such activities," writes a group of Harvard engineers under the leadership of David Keith, professor of Applied Physics at the Harvard John A. Paulson School of Engineering and Applied Sciences.

How the Chemtrails Conspiracy Theory Began

The chemtrails conspiracy theory dates back to the mid-1990s. A 1996 U.S. Air Force report, titled "Weather as a Force Multiplier: Owning the Weather in 2025" helped fuel the conspiracy. However, the report was purely speculative.

Chemtrail Bill

Despite the lack of scientific evidence, the chemtrail conspiracy theory persists. Tennessee legislators proposed banning federal geoengineering. The bill cites concerns over potential health and environmental impacts from large-scale geoengineering projects, like the release of particles intended to reflect sunlight and slow climate change. Supporters connect it to a 2022 federal initiative for climate intervention research, while critics, such as Sierra Club lobbyist Scott Banbury, call the bill “nonsense.”

For one thing, the chemtrails would be released so high in the atmosphere that unpredictable winds would move them around significantly, making such experiments worthless and unreliable [source: Hodapp]. Others speculate that the government is dumping barium salt aerosol on the land in order to assist in radar mapping for defense purposes [source: Knight].

Still, others believe that the government could be experimenting with weather manipulation for defense purposes. This actually isn't as much of a stretch as it may seem. In the 1950s, the British successfully "seeded" clouds with salt, dry ice and silver iodide to make rain (see "Operation Cumulus" below).

It seems that weather manipulation, then, is very possible. Conspiracy theorists believe it might have connections to HAARP, the High Frequency Active Auroral Research Program, which studies the ionosphere to advance communication and navigation systems [source: HAARP].

Albedo Modification

Another popular theory is that chemtrails are well-intentioned attempts by the government to combat global warming or the depletion of the ozone layer by spraying particles into the atmosphere to deflect the sun's radiation — so-called albedo modification, sometimes called solar geoengineering.

Albedo refers to the amount of light radiation that is reflected back into space. Research on albedo modification is no secret and has been going on for years.

"We are confident that there is no currently active program to actually test or implement albedo modification outdoors. We are not now involved in outdoor experimentation, though we are indeed actively developing proposals for field experiments. This experiment will proceed only if it is conducted in a fully transparent and public manner, and only if it passes a comprehensive independent safety review. The experimental plans, operations and results will be publicly available and freely usable (no patenting)," writes Harvard's Keith.

Operation Cumulus

The British cloud-seeding experiment in the 1950s was far more effective than planned. On Aug. 15, 1952, they resulted in deadly flash floods in Lynmouth, a village in Devon, England.

After dozens of people died in the floods, "Operation Cumulus" was put on hold. The British Ministry of Defense denied involvement in cloud seeding until 2001, when documents exposing it were declassified.

Cloudseeding Today

Cloud seeding is currently an operational technology that several regions worldwide use to enhance precipitation, mitigate drought, and reduce the severity of hailstorms. Countries including the United States, China, Russia, the United Arab Emirates and India use cloud seeding techniques, especially in water-scarce or drought-prone areas.

The technology typically involves dispersing substances like silver iodide, potassium iodide, or sodium chloride from aircraft or ground-based generators to encourage ice crystal formation within clouds, leading to increased precipitation.

While cloud seeding has shown promise, it remains somewhat limited in efficacy, with results varying based on cloud conditions and atmospheric factors. It is also still controversial. Julie Gondzar, previously the program manager for Wyoming's Weather Modification Progam, would receive calls criticizing the state's efforts. They would say, "You're playing God" or "You are stealing moisture from the storm."

Let's be clear: Many studies show that contrails can have a negative impact on the environment, but not for the reasons spouted by conspiracy theorists.

For one thing, contrails can spread into cirrus clouds, reducing the amount of sunlight reaching Earth's surface and lowering temperatures. Moreover, studies have shown that contrails also trap heat. NASA scientists found that between 1975 and 1994, there was an increase in temperature of the United States that corresponded with the increase in the amount of contrails. Most studies suggest that contrails have a net warming effect on the planet.

So, whether you consider the conspiracy hype healthy skepticism or paranoia, contrails (along with the fuel consumption and energy use of the air traffic industry that cause them) are certainly an area of concern for the environment.

This article was updated in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.