contrails
noun

- streaks of condensed water vapor created in the air by an airplane or rocket at high altitudes.

Merriam-Webster

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ORIGIN

Derived from "CONdensation TRAIL" this term was first recorded in 1943, probably as a result of high-frequency of high-altitude flights in military operations.

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Contrails are also known to conspiracy theorists as “chemtrails.” Despite government efforts to deny any threat to human health, some people still hold the view that jets routinely spray behaviour-altering chemicals in the air.

There is more serious speculation that contrails may be implicated in climate change. Originally it was believed that they have a cooling effect, but more recent research suggests that contrails actually contribute to global warming.

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INTERESTING NUMBERS

- 14,000: Average number of planes in the air at any given time

- 39 million: Estimated number of commercial flights in 2019

- 6.5%: Increase in global air traffic in 2018, according to the International Air Transport Association

- -40°c: Atmospheric temperature conducive to contrail formation

- 26,000 ft and above: Altitude at which contrails typically form

- 900 million metric tons: Estimated global airline CO2 emissions in 2018

- 0.6%: Portion of the sky typically covered by contrail cirrus clouds

Source: Quartz