According to Space.com, these human-made clouds form between 32,000 and 42,000 feet. You may not see a contrail behind every plane that you see due to the environment that is always changing.

The clouds you are seeing are caused by aircraft and are composed primarily of water in the form of ice crystals, according to the EPA. The EPA also said the clouds do not pose any health risks.

An airplane speeds through the clouds, a trail of technicolor contrails following behind, illuminating the sky in dazzling rainbow shades. This incredible moment was captured on film by Brisbane ...

TEHRAN (Tasnim) - The climate impact of airplane contrails - the white ice clouds that sometimes seen behind planes as they cross the sky - is expected to triple by 2050 compared to 2006 levels.

In cold and damp conditions, aircraft condensation trails and the cirrus clouds that develop from them can remain in the sky for many hours. Their impact on the global climate system has not yet been ...

Unanswered questions about the formation of clouds and their impact on the climate are currently setting limitations on the validity of global climate forecasts. To make a detailed analysis of the ...

NASA Cirrus clouds, in contrast to low-level water clouds, consist of ice crystals. But aircraft passing though them can be expected to have an effect all the same.

D.G. in San Francisco sent another photo with a number of cloud trails over the City. You can see an airplane leaving behind one vapor trail.