Chemtrails

Chemtrails
	FALSE
	"The long white trails left by aircraft are "chemtrails": chemicals or biological agents deliberately sprayed by governments or other groups to control the weather, the population or people's health."
Domain	Science & Environment
Tactic	Conspiracy Theory; False Context;
Era	Current
First seen	1996
Origin	Speculation following a 1996 US Air Force research paper on weather modification, spread by talk radio and early internet forums in the late 1990s
Last reviewed	2026-10-26
	Further reading: books on Science & Environment

The chemtrail conspiracy theory holds that the white trails left behind by high-flying aircraft are not ordinary condensation trails, or contrails, but chemicals deliberately sprayed for secret purposes, such as weather control, population control, mind control or poisoning. There is no evidence for any such program. Contrails are clouds formed when water vapor in hot engine exhaust condenses and freezes in cold, humid air, and their behavior is explained by basic atmospheric physics. A 2016 survey of 77 leading atmospheric chemists and geochemists found that 76 had encountered no evidence of a secret large-scale spraying program.

The claim

Believers point to trails that linger and spread across the sky, to grid-like patterns of trails, and to unusual weather, illnesses or residues on the ground as evidence of spraying. The purported purposes vary widely, from secret geoengineering to fight climate change, to weather warfare, to deliberately making people sick.

Origin

In 1996, a US Air Force research paper titled "Weather as a Force Multiplier: Owning the Weather in 2025" speculated about how the military might use weather modification in the future. It was a hypothetical exercise, not a description of an existing program. In the late 1990s, talk-radio hosts and early internet forums combined the paper with photographs of persistent contrails and claims about illnesses to suggest that a spraying program was already under way. The idea spread through websites, documentary-style videos and, later, social media.

What contrails are

Aircraft engines burn fuel, producing hot, humid exhaust that includes water vapor. At cruising altitudes, the air is often extremely cold, typically below minus 40 degrees Celsius. When the exhaust mixes with this air, the water vapor condenses and freezes into ice crystals, forming a visible trail, much as breath becomes visible on a cold day.

Whether a contrail disappears quickly or lingers depends on the humidity of the surrounding air. In dry air, the ice crystals quickly turn back into vapor and the trail vanishes. In air that is already close to saturation with respect to ice, the trail can persist for hours and spread into wide sheets resembling cirrus clouds. This explains why trails behave differently on different days and why one plane may leave a short trail while another at a different altitude leaves a long one. Grid patterns reflect busy flight routes. Scientists have studied contrails extensively, including their effect on climate: persistent contrails do trap some heat, and researchers are studying ways to reduce them.

What the evidence shows

In 2016, researchers at the Carnegie Institution for Science and the University of California, Irvine, surveyed 77 experts in atmospheric chemistry and geochemistry, asking them to evaluate the evidence chemtrail believers present, such as residues in soil and water samples and photographs of persistent trails. Seventy-six of the 77 said they had encountered no evidence of a secret large-scale atmospheric spraying program, and found that the data cited by believers could be explained by ordinary factors, including normal contrail formation, natural sources of the elements found in samples, and flawed sampling.

A covert program on the scale imagined, involving thousands of daily flights, the fuel and chemical supply chain, airline and military personnel and air traffic control around the world, would require cooperation by enormous numbers of people across many countries, with no credible leak, document or physical evidence.

Real weather modification exists but is limited and public. Cloud seeding, which typically disperses silver iodide from aircraft or ground generators to encourage rain or snow, has been used for decades in several countries, including in the western United States, in programs that are documented and disclosed. Proposals for solar geoengineering, which would involve spraying reflective particles in the upper atmosphere to cool the planet, are discussed openly by scientists and remain at the research stage; no large-scale deployment is known to have occurred.

Recent developments

The theory has moved from the fringe into politics. In 2024, Tennessee passed a law banning the intentional release of chemicals into the atmosphere to affect weather or sunlight, and similar bills have been proposed in other US states, reflecting public concern about geoengineering and chemtrails.

Lessons for readers

Ordinary explanations, such as water vapor and humidity, should be ruled out before extraordinary ones.
A research paper speculating about the future is not evidence of a current program.
Large secret operations requiring the silent cooperation of thousands of people are very difficult to sustain.
Real activities, such as cloud seeding and geoengineering research, are a better focus for concern than imagined ones.

Sources

Christine Shearer et al., "Quantifying expert consensus against the existence of a secret, large-scale atmospheric spraying program," Environmental Research Letters 11 (2016).
US Air Force, Weather as a Force Multiplier: Owning the Weather in 2025 (1996).
US Environmental Protection Agency and others, Aircraft Contrails Factsheet (2000).
US National Academies of Sciences, Engineering, and Medicine, Reflecting Sunlight: Recommendations for Solar Geoengineering Research and Research Governance (2021).