A long-debunked conspiracy theory claiming that aircraft leave behind toxic 'chemtrails' as part of a secret government plot has gained renewed attention in the United States. The resurgence comes amid confusion over proposals to use geoengineering to combat climate change, with state-level legislation to ban chemtrails introduced in Tennessee and Florida.
Robert F. Kennedy Jr., a prominent figure in the incoming Trump administration as nominee for health secretary, has amplified the theory. He wrote on X in August, 'We are going to stop this crime,' and stated on his podcast that it was 'frightening to think that somebody may be putting large amounts of bioavailable aluminum into the environment.' Scientists have repeatedly found no evidence for such claims.
The white lines seen behind aircraft are condensation trails, or contrails, formed when water vapor from engine exhaust freezes into ice crystals at high altitudes. A 2016 survey of leading atmospheric scientists concluded there was no secret spraying program. Ken Caldeira, who led the study, said he received death threats from conspiracy theorists.
David Fahey of the National Oceanic and Atmospheric Administration noted that interest in chemtrails 'bubbles up every once in a while' and is often linked to weather events. He dismissed claims of government weather modification, stating that even experimenting with such measures would be a 'big step' for the agency.
While contrails are harmless, they can contribute to global warming by forming cirrus clouds that trap heat. Caldeira emphasised that this is an unintended consequence of fossil fuel use, not a secret plot. The confusion between actual weather modification techniques, such as cloud seeding, and conspiracy theories continues to fuel misinformation.
