American Airlines and Google said Thursday that they significantly reduced the climate impact of some of the airline's flights using an AI-based forecasting tool to help prevent contrails.
When airplanes fly through cold and humid areas, ice crystals can form around the soot particles emitted from the engine, creating clouds that trap heat and warm the planet. Google is using artificial intelligence to predict where these condensation trails, or contrails, are likely to form if planes pass through. American Airlines added the forecasts to its flight planning system on a trial basis to show where pilots could safely shift altitude or use optional routes to avoid those areas.
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American Airlines and Google said the tool could be one of the most cost-effective, scalable climate solutions available in aviation now.
The aviation industry is under growing pressure to take action on climate change. And while those thin, white lines that form behind airplanes may look wispy, they're responsible for a surprising amount of Earth’s warming — 1% to 2%, according to Contrails.org, a nonprofit research organization dedicated to reducing aviation’s climate impact through contrail management, as part of the Breakthrough Energy group founded by Bill Gates. The group was among the collaborators in the trial.
Switching to cleaner fuels, such as sustainable aviation fuel, can significantly reduce emissions and contrails, though that’s far more expensive than slightly altering a flight route.
Many contrails are short-lived, but some may persist for hours or even days if it's extremely humid. Research on the subject suggested that minor adjustments to flight altitudes or routes to avoid these regions could eliminate a significant portion of this warming using a minimal amount of additional fuel — a theory tested through this trial.
Testing on flights from the U.S. to Europe
The trial involved 2,400 flights from the U.S. to Europe. In research shared in a blog post Thursday, Google said half were given a route option to avoid creating contrails and the other half were the control group.
For the 112 flights that flew that option, they formed 62% fewer contrails compared to the control group, the paper said. The researchers estimated that reduced the climatological warming from those flights by about 69%.
The trial started in January 2025 and ended in May. Flightkeys, the flight planning service used by American Airlines, joined the airline, Google and Contrails.org in the collaborative work.
“We know that aviation is one of the hardest, most difficult sectors to decarbonize,” Dinesh Sanekommu, who leads Google’s work on contrails, said in an interview. “We think there’s a way that AI can help make that a reality. And the hope is, whether it’s these AI-based forecasts, whether it is doing these operational scientific demonstrations together, they all add a little bit of evidence and generate a bit of data that helps make the right decisions in the long run.”
This built on earlier work by Google, American Airlines and Breakthrough Energy. They partnered in 2023 to reduce the warming effects of contrails and did a smaller test where the flights were identified manually versus integrated into the flight planning system.
As for what's next, Sanekommu said they need to do a larger trial and they want to work with all the other flight planning software providers to build contrail forecasts and avoidance features into their products.
Showing the way for other airlines
One of the biggest deterrents for airlines in adjusting a route is the potential cost of extra fuel, but the trial found no statistically significant difference in fuel usage observed between the two groups.
It’s also a challenge to coordinate among pilots and air traffic controllers over different airspace regions internationally, said Thomas Walker, who researches aviation climate impacts at the Boston-based Clean Air Task Force. CATF has been talking with other major airlines about avoiding contrails, Walker said, and “there’s been a little bit of pushback.”
Jill Blickstein, vice president of sustainability at American Airlines, said the trial showed it wasn't difficult for dispatchers and pilots to file and fly alternative plans to avoid contrails.
The North Atlantic region is a hot spot for contrails, making attempts to avoid creating them there particularly effective, added Walker, CATF’s senior transportation technology manager.
Walker said there have been trials in Europe to adjust routes, and this is the largest one he has heard of in the United States, which is “a pretty big step in the right direction.” He said he hoped American Airlines' positive results will encourage other airlines to participate.
American Airlines said it's not yet making contrail avoidance a routine part of its regular flight planning process. The airline said it hopes to continue working with its partners on additional studies, potentially involving different flight routes and times of day, that could help answer important scientific questions.
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