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“The sky is Falling”

We’ve all heard the story of Chicken Little—a fanciful tale about panic and jumping to conclusions. But how would it feel to truly believe that the sky is out to get you?

For believers in one strange conspiracy theory, it’s scary to see a blue sky crossed by wispy white contrail lines from passing jet planes. They claim some of those contrails are not clouds or exhaust from jet engines as they appear, but sinister “chemtrails.” Supposedly, an evil government conspiracy uses jet planes to secretly spread poison across skies worldwide. Is there any possibility this paranoid claim could be true?

Let’s Find out!


Before we dig into the chemtrails legend, let’s learn about ordinary, well-understood, non-evil contrails. These have been a familiar, common sight for several decades. But what are contrails, exactly?

They’re line-shaped clouds of tiny ice crystals. “Contrail” is short for “condensation trail.” They’re created when airplanes disturb air that is cold enough and moist enough. Jet engine exhaust includes gases, water vapor, and microscopic particles of metal and soot. These cause tiny water droplets to condense from moisture that is already present in the outside air, and these drops immediately freeze.

Passenger jets fly incredibly high—usually above 30,000 feet. That’s higher than the top of Mount Everest. At that altitude the air is always thin and cold. Those are good conditions for creating contrails. Planes flying at lower altitudes rarely leave contrails because the air is warmer closer to the ground.

Even when flying in the frigid air above 30,000 feet, jets sometimes create contrails and sometimes do not. It depends on the humidity— the amount of moisture in the air. If the air is too dry, there isn’t enough water to condense into a cloud.


When you watch planes soar overhead, you’ll notice that some contrails are quite short and fade away quickly. Others stretch far across the sky and last a long time. Once again it’s humidity that makes the difference.

In a fact sheet about contrails, the United States Environmental Protection Agency (EPA) explains why this happens:

After the initial formation of ice, a contrail evolves in one of two ways…. If the humidity is low…the contrail will be short-lived.

Newly formed ice particles will quickly evaporate…. The resulting line-shaped contrail will extend only a short distance behind the aircraft.

But if the humidity in the air is high enough, the contrail’s ice crystals don’t evaporate. Instead, explains the EPA,

Newly formed ice particles will continue to grow in size by taking water from the surrounding atmosphere. The resulting line-shaped contrail extends for large distances behind an aircraft. Persistent contrails can last for hours while growing to several kilometers in width….

If several planes cross the sky while conditions are suitable for forming persistent contrails, all of them are likely to leave lingering, expanding white trails behind them. Depending on the winds, these contrails may spread out so much that they blend together and create a thin hazy cloud layer across most of the sky.

So many planes crisscrossing the globe every day add up to a lot of manmade clouds—and a big environmental impact. (We’ll come back to that later in our story.)


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About Skeptic

ARTIFICIAL INTELLIGENCE DANGER ARTICLES: Why We Should Be Concerned About Artificial Superintelligence; Is Artificial Intelligence an Existential Threat?; Artificial Intelligence: Simulation, Not Synthesis; The Rise of the Alt-Right and the Politics of Polarization in America; Delusions of the Imagination: Debunking an Early 19th Century Medical Quack Device — The “Tractor”; Area 51: What is Really Going on There?; Is Race a Useful Concept?; The Three Shades of Atheism; COLUMNS: pH Mythology: Separating pHacts from pHiction; Are You An Unconscious Racist? REVIEWS of: Rethink: The Surprising History of New Ideas; How Men Age: What Evolution Reveals About Male Health and Mortality; Not a Scientist: How Politicians Mistake, Misrepresent, and Utterly Mangle Science; Big Con: Great Hoaxes, Frauds, Grifts, and and Swindles in American History by Nate Hendley; Fraud: An American History from Barnum to Madoff; Homo Deus: A Brief History of Tomorrow JUNIOR SKEPTIC: Chemtrails