Chemtrails, which have gripped the internet of late, regularly feature high in any list of the top conspiracy theories. 

Chemtrail conspiracy theorists “vary in their claims”, says the BBC. But some of the most popular include the belief that the white lines in the sky trailing planes are actually some kind of chemical sprayed by the government to control the weather; that scientists carrying out research about how to counteract climate change through a process called geo-engineering are secretly poisoning us; or even that secret powerful groups are spraying us with chemicals to make us pliant and easy to control. 

Suzanne Maher, the founder of Bye Bye Blue Sky - a group established to raise awareness of chemtrails – dismissed suggestions they were a conspiracy theory. She claims the trails from planes have only existed for 20 or 30 years, a claim rubbished by the BBC, which says you can clearly see condensation trails left behind aircraft in images from the Battle of Britain during the Second World War. 

So if they are not mind-controlling spray trails, what are they really? Cosmopolitan says they are just condensation trails, or ”contrails“, the result of what happens when the chemistry of burning jet fuel meets the chemistry of air. 

Scientists from the University of California, Irvine, and the Carnegie Institute have even got together and researched the topic, in an effort to debunk the myth. 

They surveyed hundreds of experts in contrails as well as those who study atmospheric deposition (how various chemicals fall to the ground from the air), presenting them with the so-called evidence provided on various chemtrail websites asking them to evaluate it. 

In the end, 77 scientists reported back, “and the results were not terribly surprising” says New Scientist, with 98.7% (76 out of 77) of the scientists saying they had encountered no evidence of a secret large-scale atmospheric programme. 

However, that still leaves one expert who did not agree with the majority consensus – and that may be enough for conspiracy theorists.