A post on Instagram claims to show “what happens when the trails are put into the sky”, with a collage of pictures appearing to show a blue sky with white lines across it turning cloudy over the course of a morning with the word “chemtrails” written on it.
The instagram page that shared the post describes itself as sharing 'images, videos and other evidence of Geoengineering (chemtrails)/Climate Engineering and Weather Modification in OUR skies today”.
‘Chemtrails’ refers to a conspiracy theory which claims that the white lines in the sky which sometimes follow planes are evidence of a plot to either spread poison or control the weather by spraying chemicals from the aircraft.
There is no evidence to support claims that chemicals or weather-altering tools are being dispersed from aeroplanes. What the Instagram images actually show are contrails, formed when water vapour from aircraft engines freezes at high altitudes.
The frozen vapour leaves a trail of tiny ice crystals behind the aeroplane’s engines which, depending on the humidity of the air, either change directly from a solid to a gas—becoming invisible after a few minutes—or remain as water droplets or ice crystals, creating the white lines often seen in the sky.
These can last for many hours, and may eventually mix with cirrus clouds.
We have fact checked many similar claims about chemtrails in the past, with the frequency of posts we were seeing on social media increasing over the summer.
The Instagram post also adds: “The UK [...] has been clear, cold for weeks. Not one trail in the sky but lots of flights. I thought these “trails” are formed when the air temperature is very cold? Yes [sic] we see a lot more in the Spring and Summer months?”
One reason that there may be fewer visible contrails in the winter months is that the atmosphere is less humid than in the warm summer months.
The Met Office says: “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.”
As the BBC reports, contrails disappear quickly in clear, cloudless air as the ice particles sublimate, which means they pass from a solid to a gas. If the atmosphere is humid, however, the ice particles can’t sublimate which means they remain visible as trails for much longer.