The chemtrail conspiracy theory is the wrong idea that long-lasting condensation trails left in the sky by high-flying planes are actually "chemtrails" made of chemicals or biological substances sprayed for bad reasons not shared with the public. People who believe this theory say that normal contrails disappear quickly, but contrails that stay in the sky longer must contain other substances. Supporters of the theory think these substances might be used for purposes like controlling the weather, changing how much sunlight reaches Earth, influencing people's thoughts, controlling population numbers, or testing harmful agents. They also claim these trails cause health problems like breathing difficulties.
The chemtrail theory began in the late 1990s after a 1996 United States Air Force (USAF) report about weather modification was published. The Air Force was accused of secretly spraying substances from planes. The theory spread online and was promoted by radio host Art Bell starting in 1999.
Scientists have dismissed the chemtrail theory. There is no proof that so-called chemtrails are different from regular water-based contrails created by planes in certain weather conditions. Supporters have tried to show that chemical spraying happens, but their research has had mistakes or was based on incorrect ideas. Because the theory continues and questions about government actions remain, scientists and government groups worldwide have repeatedly explained that the supposed chemtrails are actually normal contrails.
History
Chemtrail conspiracy theories started spreading after the United States Air Force (USAF) released a 1996 report about weather modification. In the late 1990s, the USAF was accused of spraying the U.S. population with unknown substances from planes, which created unusual contrail patterns. People like Richard Finke and William Thomas shared these theories on internet forums. The theories became popular through late-night radio host Art Bell, beginning in 1999. As the ideas spread, federal officials received many angry calls and letters.
In 2000, a group of agencies, including 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), worked together to explain the rumors. Many chemtrail believers thought these official fact sheets proved a government cover-up. The EPA updated its information in 2015.
In the early 2000s, the USAF released a fact sheet stating that the conspiracy theories were false. The theories were partly fueled by a 1996 strategy paper from the USAF’s Air University titled Weather as a Force Multiplier: Owning the Weather in 2025. This paper was created in response to a military request to plan a future weather modification system to help the U.S. maintain military strength in 2025. The paper was labeled as "fictional representations of future situations." The USAF clarified in 2005 that the paper did not reflect current military policies and that no weather modification experiments were being conducted or planned. The USAF also said that the "chemtrail" hoax had been studied and disproven by many universities, scientific groups, and major media outlets.
Mainstream media rarely covers these theories, and when they do, they often describe them as examples of anti-government distrust. For instance, in 2013, when the CIA, NASA, and NOAA announced plans to fund research on geoengineering to fight global warming, an article in the International Business Times predicted that government efforts to control weather would face suspicion and fear, mentioning chemtrail theories as an example. In 2024, Robert F. Kennedy Jr., who became the U.S. Secretary of Health and Human Services in 2025, began supporting the conspiracy theory.
The chemtrail theory has led to attempts to pass laws in some U.S. states. For example, Florida passed such a law. In 2020, the Missouri Law Review discussed possible ways to legally regulate chemtrail misinformation.
Description
People who believe in the chemtrail conspiracy theory use sky events, videos online, and reports about government activities to support their ideas. They also have beliefs about the goals of the conspiracy and the effects of its actions, and they often take steps based on these beliefs.
The word "chemtrail" is made by combining "chemical" and "trail," similar to how "contrail" combines "condensation" and "trail."
Supporters of the chemtrail theory claim that chemtrails can be told apart from contrails because they last longer. They say chemtrails are the trails left by planes that stay in the sky for up to half a day or turn into clouds that look like cirrus clouds. They also claim that after 1995, contrails had a different chemical makeup and lasted longer, but they ignore evidence from World War II photos showing long-lasting contrails.
Supporters describe contrails as long, visible lines that form patterns in the sky and eventually become large clouds. They believe that seeing colors in the trails, unusual numbers of tracks in one area, or trails from planes that are not marked or are flying in unusual ways are signs of chemtrails.
Some photos show empty barrels on planes used for testing. These barrels are filled with water to simulate the weight of passengers or cargo. Water is moved between barrels to test how the plane balances during flight.
Edward Snowden, a former CIA employee, said he looked through U.S. government secrets for evidence of chemtrails. He stated that he found no proof and said, "Chemtrails are not a thing."
Jim Marrs cited a 2007 Louisiana TV report that claimed unsafe levels of barium were found under chemtrails. Later tests showed the equipment was used incorrectly, and the actual barium levels were normal and safe.
A 2014 video showed a plane landing in fog and was claimed to be emitting chemtrails. Experts explained that passengers would see any spraying, which would not be secret, and the visible lines were caused by the plane's wings, not chemicals. In the same year, photos of German leader Angela Merkel at an air show showed water tanks next to her, which were wrongly called toxic chemicals.
In 2014, a video of a plane dumping fuel for an emergency landing was shared online as evidence of chemtrails. The person who made the video later said it was a joke.
Some people describe the chemicals in chemtrails as barium, aluminum salts, polymer fibers, thorium, or silicon carbide. Supporters of the theory see cloud seeding programs and climate research as proof of the conspiracy.
The chemtrail idea is spread online and on radio. Websites and far-right groups often support it because they distrust the government. A 2014 study of 20 chemtrail websites found that believers use science in some arguments but ignore what scientists and government experts say. Scientists and agencies have said that chemtrails do not exist and that sky tracks are just long-lasting contrails. Believers often claim chemtrails are part of a global conspiracy, with goals like profit, population control, or weapons testing. One idea is that clouds are seeded with materials for a secret electromagnetic weapon program.
Believers say chemtrails are harmful. A 2011 study found that 2.6% of people in the U.S., Canada, and the UK fully believed in the theory, and 14% believed it partly. A 2016 study found that 9% of 36,000 people thought the government uses planes to spray harmful chemicals, and 19% thought it was somewhat true.
Some believers say discovering chemtrails feels like a religious experience. They often attend events about weather control and have sent threats to scientists. Some use a device called a "cloudbuster," created by Wilhelm Reich, filled with crystals and metal, to try to clear the sky of chemtrails.
Believers sometimes collect samples and test them, but their methods are not scientific. For example, using jars with metal lids can contaminate samples.
In 2001, a U.S. law called the Space Preservation Act was proposed, which mentioned chemtrails as a banned "exotic weapon." Supporters said this was proof the government acknowledged chemtrails, but skeptics noted the bill also mentioned other weapons like "extraterrestrial weapons." The bill was not passed and was not about chemtrails.
In 2003, the Canadian government said there was no evidence that chemicals sprayed from planes harm people's health.
Contrails
Contrails, or condensation trails, are "lines of water vapor that form in the air when an airplane or rocket flies at high altitudes." Burning fuel in engines produces carbon dioxide, water vapor, and tiny particles that help water vapor form clouds. At high altitudes, the air is very cold. Hot, moist air from the engine mixes with the colder air around it, causing water vapor to form droplets or ice crystals that create visible clouds. How quickly contrails disappear depends on weather conditions. If the air is nearly full of moisture, contrails may last for a long time. If the air is dry, contrails will fade quickly.
Scientists agree that contrails can remain visible for hours and often spread into large, sheet-like clouds. Ice crystals of different sizes fall at different speeds, causing the contrail to spread upward. Differences in wind speed at different heights (wind shear) cause the contrail to spread sideways. This process is similar to how certain types of clouds form. Contrails between 25,000 and 40,000 feet (7,600 and 12,200 meters) can sometimes merge into thick, interwoven sheets. Contrails can spread several kilometers wide, and with many planes flying, they may cover the sky completely, increasing the amount of ice in the clouds and lasting for hours.
Experts say that features often linked to "chemtrails" are actually normal parts of contrail behavior, influenced by sunlight, temperature, wind, and humidity at the plane's altitude. In the United States, the grid-like flight paths of the National Airspace System often create crosshatched contrails. From the ground, it is hard to tell if overlapping contrails are at the same height. A fact sheet created by NASA, the EPA, the FAA, and NOAA in 2000 explained how contrails form and their effects on temperature and climate. The USAF also produced a fact sheet in 1953 that described contrail behavior and rejected chemtrail theories as false.
Patrick Minnis, a scientist at NASA, said that many people who believe in chemtrails do not change their views, even when given evidence. Studies show that using commercial planes for climate engineering is generally not practical. Astronomer Bob Berman said the chemtrail idea is an example of failing to use Occam's razor, a principle that suggests the simplest explanation is often correct. He noted that websites promoting chemtrails claim the phenomenon began only 10 years ago, despite evidence showing contrails have existed for decades.
A 2016 survey of 77 atmospheric scientists found that 76 of them said they had no evidence of secret large-scale atmospheric programs. They stated that data presented as proof of such programs could be explained by normal contrail formation or issues with how data was collected.