What are “chemtrails”?
“Chemtrail” combines the English words “chemical” and “contrail.” It refers to the conspiracy theory that “contrails that linger in the sky are not ordinary clouds but traces of chemicals sprayed from planes by governments or secret organizations.” What is supposedly being sprayed varies by story: chemicals to control the weather, poisons to harm people’s health, drugs to make people obedient and so on.
How it spread
This conspiracy theory spread in the United States from the late 1990s. A 1996 report by U.S. Air Force researchers considering the future possibility of weather modification was even cited as evidence. As the internet spread, photos of contrails crisscrossing in grid patterns and claims that “clouds didn’t linger like this in the past” circulated.
Why contrails linger
Contrails form when water vapor in engine exhaust is cooled by the cold air high up and turns into ice crystals. If the air aloft is dry, they disappear quickly, but if it is humid, the ice crystals do not evaporate and linger, spreading sideways into cloud-like shapes. The increase in the number of flights, and differences in altitude and weather, explain most “contrails that don’t disappear.”
Scientists’ investigation
In 2016, American researchers asked 77 experts in atmospheric chemistry and contrails to examine data presented as evidence of chemtrails. Of these, 76 answered that there was “no evidence of a secret spraying program.” Even so, the conspiracy theory continues to be told around the world and is often linked with theories such as weather control by HAARP.
