Contrails can last for hours

28 October 2022
What was claimed

Contrails disappear from the sky quickly, so lines of cloud which last for hours are chemtrails.

Our verdict

False. Contrails can last in the sky for many hours depending on atmospheric conditions. There’s no good evidence chemtrails, as they are often described, are real.

A Facebook post claims to show evidence of “chemtrails” in the sky, and says that while contrails disappear quickly, chemtrails linger for many hours.

Contrails are thin clouds which form when water vapour, a by-product of jet engines burning fuel, freezes as it is released into cold air surrounding an aircraft.

“Chemtrails” refers to the conspiracy theory that some of the trails spotted in the sky consist not of frozen water vapour trails but of other chemicals, and are evidence of malign forces controlling the environment, or spreading poison. 

While aircraft have been used to spread chemicals like herbicides (for example, the US Air Force during the Vietnam War, and in agricultural applications), there’s no evidence that the widespread phenomenon of contrails is anything but clouds of frozen water vapour. 

This post specifically cites as evidence the fact that contrails disappear quickly and so lines of clouds which do not are in fact chemtrails.

But this isn’t true. 

The Met Office describes what happens after a contrail is formed. It says: “What happens next depends on how dry or how humid the air is. If the air is very dry, the ice crystals will sublime (change phase directly from solid to gas) and become invisible. If the air is humid, the water droplets or ice crystals will stay where they are, often spreading out, leaving a fluffy trail where the aircraft has passed. Trails may last for many hours leaving the sky criss-crossed with lines, and mixing with cirrus cloud.”

NASA says: “Satellites have observed clusters of contrails lasting as long as 14 hours, though most remain visible for four to six hours.”

There is some evidence that contrails may contribute to global warming. But there just isn’t evidence that they are ‘chemtrails’. 

Claims about chemtrails are a widespread form of online misinformation Full Fact has written about many times before. None of the posts we have looked at have contained any compelling evidence of chemtrails.

For example, some have shown water tanks on board planes which are used to fight wildfires. Others have shown agricultural aircraft fitted with equipment to apply pesticides to fields.  

We’ve also seen hoax “#teamchemtrail” merchandise, sported by pilots as a running joke against the conspiracy theory, cited as evidence for the theory. 

Image courtesy of Michael C

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