The white streaks that sometimes trail behind airplanes have long been a familiar sight, and scientists say they are largely frozen water vapor — not evidence of a secret chemical spraying operation.
That everyday sight later became one of the internet's most persistent conspiracy theories, in part because of an old military paper on weather modification.
What happened?
The thoroughly debunked "chemtrails" claim later drew on a 1996 U.S. Air Force research paper that explored possible future military uses of weather modification and referred to releasing energy or chemicals into atmospheric processes, according to The Telegraph.
In reality, the visible lines behind planes are contrails, short for condensation trails. While aircraft do release pollution — including carbon dioxide, nitrogen oxides, soot, and other byproducts from burning jet fuel — the streak itself is a cloud composed mainly of ice crystals, forming only when the air is cold and humid enough.
Marc Stettler, a transport and environment professor at Imperial College London, said: "Contrails are a type of high-altitude ice cloud, or cirrus cloud."
He added: "The conditions must be just right," which helps explain why some planes leave no visible trail while others do.
TCD Picks » Good Store Spotlight
Get 10% off your next purchase with code TCD10
Why does it matter?
Misinformation can draw attention away from legitimate environmental concerns. The chemtrails theory is not backed by evidence, but contrails and aircraft pollution do have measurable effects on the climate.
Stettler estimates contrails account for roughly half of aviation's climate impact and about 1% of overall human-caused warming. During the pandemic, when many flights were grounded, the drop in contrails contributed to slight global surface cooling.
"A simple explanation is often not very appealing," Karen Douglas, a social psychology professor at the University of Kent, said, according to The Telegraph. "People assume that there must somehow be a bigger explanation, or more going on than people know about."
Real weather modification efforts — including cloud seeding and climate-cooling experiments — do exist and carry scientific risks and benefits.
What's being done?
Researchers are exploring ways to reduce the warming effects of contrails without waiting for a complete transformation of the aviation industry. Stettler's work suggests airlines may be able to avoid especially cold and humid areas of the atmosphere where contrails are most likely to form, potentially cutting a meaningful share of flying's climate impact.
At the same time, governments are continuing to experiment with weather-related interventions. The Telegraph noted that China and the United Arab Emirates have used cloud seeding in attempts to increase rainfall, while Israel ended a decades-long program after determining it delivered little benefit.
In the United Kingdom, the Advanced Research and Invention Agency has announced funding for "climate cooling" projects, including field trials designed to reflect more sunlight away from Earth.
Dr. Valérie Masson-Delmotte, who leads the Climate Society Centre at France's Institut Pierre Simon Laplace, warned that aerosol-based climate interventions "could deplete ozone and could disrupt climate patterns," potentially affecting health, agriculture, and energy production.
Get TCD's free newsletters for easy tips, smart advice, and a chance to earn $5,000 toward home upgrades. To see more stories like this one, change your Google preferences here.
