Are contrails harmful to the environment?
Based on Science
Some contrails can contribute to global warming. Contrails—pure ice clouds (“cirrus”) that form from aircraft exhaust under specific cold conditions—can trap heat in the atmosphere, sometimes creating as much warming as the carbon dioxide released by burning jet fuel.
Last update August, 22 2025
Contrails form when hot, humid air from aircraft engines mixes with cold air at high altitudes, condensing and freezing into a line of ice crystals in the sky. Most contrails fade quickly, but under certain conditions, some persist for minutes to hours and spread into cirrus-like clouds.
Some contrails warm the planet
Contrails form when hot, humid air from aircraft engines mixes with cold air at high altitudes, condensing and freezing into a line of ice crystals in the sky. Most contrails fade quickly, but under certain conditions, some persist for minutes to hours and spread into cirrus-like clouds. These persistent contrails trap heat in the atmosphere, especially at night or over dark surfaces, creating a net warming effect.
Contrail clouds (like natural cirrus ice clouds) both reflect sunlight (a cooling effect) and trap Earth’s heat (a warming effect). On average, the warming outweighs the cooling, particularly when contrails continue for hours and grow into wider cloud coverage.
Studies estimate that the warming from these contrails is about as large as—or even larger than—the warming from aviation’s CO₂ emissions.
Not all flights cause warming contrails
While the aviation sector generates millions of flights each year, only a small fraction of those produce contrails that significantly affect climate. In fact, most flights have little or no contrail impact. The majority of the warming effect from contrails comes from a small percentage of flights that pass through parts of the upper atmosphere called ice-supersaturated regions (ISSRs) which are cold and have high humidity (water vapor).
Researchers are studying ways to predict when and where these regions form, so pilots might one day be able to avoid them. Even small altitude changes may help prevent the most climate-impactful contrails.
Scientists are still working to reduce the uncertainty
Although the warming effect of contrails is well supported, there is still uncertainty about how strong the effect is. Scientists estimate there is around 70% uncertainty in how much warming contrails contribute, but they agree the net effect is warming.
That is why better measurements of humidity and temperature at flight altitudes are a top research priority. New technologies such as improved water vapor sensors and satellite imaging could help forecast contrail conditions more accurately and support real-time contrail avoidance.
Why reducing contrails matters for the U.S. economy
Addressing contrail-related climate impacts is not just an environmental issue—it also has economic implications. The U.S. aviation industry risks falling behind if it does not invest in contrail mitigation research and technology as other countries may start regulating contrails. Supporting this work helps U.S. airlines, aircraft manufacturers, and fuel producers stay competitive in a global market that is increasingly focused on climate performance.
Why reducing contrails matters for the U.S. economy
Several strategies could help lessen the environmental impact of contrails:
Avoiding high-risk airspaces: Rerouting flights to avoid ISSRs can reduce the number of persistent contrails formed.
Using cleaner fuels: Sustainable aviation fuels that produce fewer particles may lower the chances of contrail formation.
Improving aircraft engines: New technologies that emit fewer particulates can make a difference.
ADDITIONAL RESOURCES
Disclaimer: Initial brainstorming and outlining for articles in this series, produced in 2025, may include input generated with the assistance of ChatGPT. Human experts review all AI-supported content to ensure factual accuracy, relevancy and the appropriate context.
