The white streaks you often see trailing behind airplanes in the sky are known as contrails, short for condensation trails. They form when hot, humid air from jet engine exhaust mixes with the much colder air at high altitudes usually above 8,000 meters (around 26,000 feet).
This drastic temperature difference causes the water vapor in the exhaust to cool rapidly, condense, and then freeze into tiny ice crystals, which is what creates the long, white streaks you see.
Contrails can vary in appearance depending on atmospheric conditions. If the air at that altitude is very dry, the contrail may disappear quickly. But if the atmosphere is humid, the ice crystals can linger and even spread out, forming larger cloud-like formations...READ FULL; FROM THE SOURCE.
In fact, persistent contrails can sometimes contribute to cloud cover and even have a small impact on local climate conditions.
Many people mistakenly believe these streaks are pollution or “chemtrails,” but scientifically, they’re mostly water vapor and are a normal part of high-altitude flight. While jet engines do release some carbon emissions, the white trails themselves are primarily a natural physical reaction to flying in cold upper-atmosphere conditions.
