A conspiracy theory claiming that aircraft condensation trails are part of a secret government plot to release toxic chemicals has gained renewed attention in the United States. The theory, which has no supporting evidence, has been repeatedly debunked since the 1990s but continues to resurface amid confusion over proposals to use geoengineering to combat climate change.
State legislation to ban what some lawmakers call 'chemtrails' has been introduced in Tennessee and Florida. Robert F Kennedy Jr, who has expressed interest in the theory on social media and his podcast, is set to become health secretary under Donald Trump. In August, Kennedy wrote on X: 'We are going to stop this crime.' He has claimed that 'bioavailable aluminum' may be sprayed from aircraft.
Scientists say the white lines seen in the sky are condensation trails, or contrails, formed when water vapour from aircraft exhaust freezes into ice crystals at high altitudes. A 2016 survey of atmospheric scientists found no evidence of a secret spraying programme. Ken Caldeira, who led the study, said he received death threats from conspiracy theorists.
David Fahey of the National Oceanic and Atmospheric Administration (NOAA) noted that misinformation about weather modification often resurfaces after major hurricanes. He said NOAA does not conduct orchestrated weather modification and that such experiments would be a 'big step' the agency is not prepared to take.
While contrails are not part of a secret plot, they do contribute to climate change by forming cirrus clouds that trap heat. Caldeira said: 'As with many conspiracy theories, there is some truth to it in that aircraft are releasing particles and affecting the Earth’s climate system. But this is because of unintended consequences of the fossil fuel airline system, rather than some nefarious secret reason.'
