Chemtrails
The persistent white trails left by aircraft at high altitude are condensation trails (contrails) made of ice crystals formed when hot exhaust meets cold, humid air. There is no scientific evidence of any covert large-scale atmospheric spraying program.
What we know
Contrails, short for condensation trails, are well-understood atmospheric phenomena rather than a mystery requiring alternative explanation. Jet exhaust contains water vapor from fuel combustion, which freezes rapidly at the low temperatures found at cruising altitude, typically below minus 39 degrees Celsius. Under conditions of high atmospheric humidity, these ice crystal trails persist rather than dissipating quickly, and can spread laterally over time into cirrus-like clouds that may remain visible for hours. This behavior was documented and studied as early as the Second World War, well before any modern conspiracy theory existed. NASA, NOAA, the EPA, and the FAA jointly published a fact sheet in 2000 explaining contrail science in direct response to public concerns that had already begun circulating at the time.
A 2016 survey published in Environmental Research Letters asked 77 atmospheric scientists and geochemists specializing in contrails and atmospheric deposition whether they had encountered any evidence of a secret large-scale atmospheric spraying program. Seventy-six of the 77 specialists, or 98.7 percent, said they had not, and explained that the data commonly cited as evidence, including persistent contrails and detections of barium or aluminum in soil or rainwater, could be fully explained by ordinary atmospheric chemistry, contrail physics, and pre-existing environmental background levels of those elements.
The "chemtrails" theory typically claims that visible trails are composed of chemical or biological agents deliberately dispersed for purposes ranging from weather modification to population control or mind control. No credible physical evidence, whistleblower testimony, or peer-reviewed study has ever substantiated any of these claims. The U.S. Air Force has stated explicitly that the theory "has been investigated and refuted by many established and accredited universities, scientific organizations, and major media publications." The EPA similarly states it is not aware of any scientific evidence supporting claims of nefarious activity connected to ordinary aircraft contrails.
Some legitimate, openly published academic research into solar geoengineering, meaning deliberately reflecting a small fraction of sunlight to slow warming, does exist at universities and research institutions. This research is conducted transparently, is subject to peer review and public debate, and is entirely distinct from a covert, unacknowledged spraying program of the kind described in chemtrail claims. The visible trails observed in everyday skies remain, overwhelmingly, ordinary ice and water vapor whose persistence varies predictably with local humidity and temperature, exactly as contrail science predicts.
The belief also persists partly because of pattern misperception, people rarely track ordinary contrails on clear, dry days when they dissipate within seconds, but they do notice and remember the trails that persist on humid days, creating a skewed impression of unusual or increasing activity. Increased air traffic over the past several decades has also genuinely increased the frequency with which any given observer sees a contrail-covered sky, another mundane factor sometimes mistaken for evidence of a coordinated program.
Common claims
- Persistent contrails are proof of secret chemical sprayingNot supported, contrail persistence is explained by atmospheric humidity levels
- Barium and aluminum found in soil/water prove chemtrailsNot supported, these elements occur naturally; cited analyses have contained errors
- Governments are poisoning the population through chemtrailsNo evidence, no regulatory agency, whistleblower, or confirmed sample has supported this
- Contrails never used to last this longFalse, long-lasting contrails are documented in photographs dating to WWII
Evidence hierarchy
All sources
- Atmospheric science experts agree chemtrails is a fantasyScience / AAAS · 2016
- Information on Contrails from AircraftU.S. Environmental Protection Agency · 2025
- Aircraft Contrails, NASA Earth ObservatoryNASA · 2004
- Coordinated Approach to Contrails Research, National AcademiesNational Academies of Sciences, Engineering, and Medicine · 2025
- Understanding and addressing chemtrails, Salata InstituteHarvard Salata Institute · 2025