Cathay Pacific and Google Cut Contrail Climate Impact by 40 Percent

Cathay Pacific and Google have announced an expansion of their joint program testing artificial intelligence designed to help pilots avoid zones prone to forming contrails. In the first testing phase, which began in late 2025, more than 80 flights flew routes with adjusted cruising altitudes, cutting the estimated warming impact of their contrails by about 40 percent.

Cathay Pacific is the first commercial carrier in the Asia-Pacific region to test the technology in live flight operations, and the first in the world to trial contrail avoidance on ultra-long-haul routes. The nonprofit Contrails.org has also joined the collaboration, providing scientific backing for the program.

How the system works

Google's technology combines AI-based predictive models with satellite and weather data to identify areas where thin bands of humid air turn engine exhaust into heat-trapping clouds. The forecasts feed into the Electronic Flight Folder, used by dispatchers and pilots to decide whether to adjust cruising altitude.

Contrails only form under specific atmospheric conditions, but according to Google data they account for roughly one-third of the entire aviation sector's total climate impact, more than the carbon dioxide emissions from burning fuel alone. That's why identifying and avoiding these zones, even at the cost of a small route adjustment, can produce a disproportionately large climate benefit.

The Hong Kong-Singapore corridor

Most of the data was gathered on the route linking Hong Kong with Singapore, one of the most frequently tested in the program. According to Google, this single corridor accounted for half of the total emissions reduction achieved in the first testing phase, showing that the program's effect depends heavily on the specific geography and weather conditions of a given route.

Those results formed the basis for the decision to move into a second, much larger phase of the collaboration. The new tests are set to cover more than 100 flights and focus on ultra-long-haul routes connecting Asia with North America, where flights last more than ten hours and cross numerous different climate zones.

Randomized controlled trials

In the second phase, the companies plan to apply a randomized controlled trial methodology, known mainly from medical and clinical research. Some flights on the same route will have their altitude adjusted to avoid contrails, while others will serve as a control group flying a standard altitude profile, providing more reliable data on the method's real-world effectiveness across different operating conditions.

Contrails.org, a nonprofit focused on researching contrails' climate impact, has joined the effort to help verify the methodology and translate the test results into broader recommendations for the aviation industry that extend beyond Cathay Pacific alone.

Aviation needs solutions to address climate change, and AI is accelerating that progress - Lawrence Fong, Chief Digital and Information Officer, Cathay Pacific

The cost of route adjustments

Avoiding contrails requires changing cruising altitude, which typically means slightly higher fuel consumption on a given leg. Google and Cathay Pacific emphasize that the goal of the second phase is to find economically viable and scalable ways to limit this effect, meaning route adjustments that deliver a measurable climate benefit without a disproportionate increase in the carrier's operating costs.

That distinction matters for the entire industry, since previous efforts to reduce aviation's climate footprint have focused mainly on alternative fuels and new engines, which require large infrastructure investments. Route adjustment based on AI forecasts requires no fleet replacement or new ground infrastructure, making it a relatively cheap tool that can be deployed right away.

For Polish airlines and airports, the program points to the direction climate regulation for the sector could take in Europe, where the European Union has spent years working to bring aviation's non-CO2 impact, including contrails, into the ETS emissions trading system. Predictive tools similar to those being tested by Google could eventually reach routes operated by European carriers as well.