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Contrails are created by jet exhaust mixing warm, humid air with cooler air, resulting in condensation. They were first observed during World War I and can indicate weather conditions. Persistent contrails can create man-made cloud cover, which may affect Earth’s climate. Some speculate they are part of government conspiracies, but these allegations are baseless.
A contrail is the trail of condensation that is created and left behind when a jet moves through cold air with low vapor pressure. At high altitudes, temperatures are cold enough that only a small amount of moisture is required to create condensation. The jet exhaust delivers the moisture in the warm, humid air. The turbulence also created by the exhaust jet mixes that warm air with cooler air from the atmosphere, resulting in condensation. It is the same process that creates a “cloud” when warm breath is exhaled on a cold day.
Contrails were first observed during World War I, but it wasn’t until World War II that they became a concern, for two reasons. Firstly, they made it possible to detect aircraft, and secondly, they sometimes impeded visibility so much that it was impossible for pilots to keep an eye on enemy aircraft during combat. Today, due to the increase in air traffic over the last half century, contrails have been observed in almost all areas of the world.
They’re made of condensed liquid, so contrails stay in areas of higher humidity longer than they do in drier skies. In fact, they won’t form at all if the atmosphere is too dry. Sailors sometimes observe these patterns to make plausible predictions about the weather. If the trails are invisible or disappear quickly, it indicates drier air and stable weather conditions. On days when they persist, higher humidity and lower atmospheric stability are likely, so weather changes may occur.
If contrails persist long enough, they can spread across the sky, creating what amounts to man-made cloud cover. Scientists and environmentalists share concerns about the effect this could have on Earth’s climate, as some estimates report an increase of up to 20% in cloud cover in areas of heavy air traffic. This additional cloud cover acts as cirrus clouds, reflecting incoming sunlight and inhibiting heat loss from the planet. It can also alter the balance of sunlight and infrared energy in the atmosphere. In the United States, the National Aeronautics and Space Administration (NASA) and the Department of Energy (DOE) are sponsoring a research project to study the impact this has on atmospheric chemistry, weather and climate, and further studies to examine how jet exhaust affects the water vapor content and chemistry of the upper troposphere.
Some contrails are speculated to be part of government conspiracies. It is suggested that they are being used to “spray” the general population with chemical or biological agents for undisclosed purposes. Governments around the world deny these allegations and they remain baseless.
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