Google Reroutes Hundreds of Flights to Reduce Climate-Warming Contrails

A recent extensive study involving thousands of flights between the United States and Europe revealed that contrails form less frequently when aircraft follow AI-recommended flight paths aimed at minimizing their global warming impact.

Contrails, the condensation streaks produced by soot particles from aircraft engines, are believed to contribute significantly to global warming—potentially more than the carbon dioxide emissions from planes. Recent research indicates that specific icy regions of the upper atmosphere are more prone to contrail formation, and AI can effectively leverage detailed weather forecasts to predict these locations.

Preliminary trials have demonstrated that directing planes away from these contrail-prone areas effectively reduces their formation. However, this strategy has yet to be widely implemented in commercial aviation.

According to Dinesh Sanekom and his team at Google, an AI-based contrail prediction tool was employed to offer route guidance in a randomized controlled trial encompassing over 2,400 real-world American Airlines flights.

The trial featured a one-way eastbound route from the U.S. to Europe, conducted over approximately 17 weeks from January to May 2025. These flights were scheduled at night when contrails are known to have a more intensive warming effect, contrasting with daytime flights, which tend to reflect sunlight and create a cooling effect.

Each flight path between two cities was randomly divided into two groups. The first group had the choice of an AI-optimized route designed to produce fewer contrails, while the second group received no alternative routing suggestions.

In the first group, air traffic controllers had the opportunity to select a contrail-reducing route; however, only 112 out of 1,232 flights actually opted for this alternative due to cost, safety, and operational concerns, as mentioned by Sanekom.

Analysis of satellite imagery showed that flights opting for contrail-optimized routes experienced a remarkable 62% reduction in visible contrails. Overall, when considering all flights offered a contrail-optimized option, the reduction in contrail formation was approximately 11.6% compared to the control group.

“This validates our hypothesis that this is a scalable method for minimizing contrail formation across numerous flights if we find a way to safely and accurately incorporate it into the flight planning process,” states Sanekom.

The researchers project that the overall global warming impact from flights was diminished by 13.7% for the entire group using the recommended route, and by 69.3% for those employing the optimized route. Notably, there were no significant differences in fuel consumption between the groups.

“This approach could be the optimal solution, at least given our current resources,” says Edward Grisspeed from Imperial College London. “The 62% contrail reduction observed via satellite is unlikely to be coincidental.”

However, due to the complexities involved in flight planning, Grisspeed noted the real-world scalability of the 11.6% reduction remains uncertain. “It’s not guaranteed that we can achieve a 60% reduction in contrails for every flight, but even a 10% decrease would have a significant impact.”