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Contrails, white trails formed by the condensation of water vapor emitted by an aircraft engine at very high altitude, from aircraft reflect sunlight overErcé-près-Liffré, western France on Oct. 2, 2023.DAMIEN MEYER/Getty Images

The American Airlines jet roared out of the Belize airport and climbed through the tropical skies on its way to Dallas. The Boeing 737 levelled out at 32,000 feet – below the typical altitude – before ascending to a higher-than-usual 38,000 feet.

It was an unusual route, but this was not a typical flight.

The deviations allowed the aircraft to avoid leaving cloud-like vapour streams known as contrails, a small step in reducing the major impact aviation has on climate change.

The flight was one of 70 flown by the airline earlier this year on which the pilots were armed with contrail forecasts. That data, compiled by researchers at Google, pinpointed the location of the moist, cool atmospheric conditions in which ice and water vapour cling to an aircraft’s sooty emissions and form the clouds that can trail an aircraft.

Contrails are major contributors to climate change, forming long-lasting clouds that spread and trap the Earth’s heat. Contrails boost aviation’s share of global CO2 emissions to 3.5 per cent from 2.5 per cent, according to the United Nations’ Intergovernmental Panel on Climate Change. The effect is most pronounced at night, when they do not reflect sunlight and only trap heat.

American Airlines, Delta Airlines and others have teamed up with researchers at Massachusetts Institute of Technology and Google to reduce aviation’s climate impact by conducting studies and flying at altitudes that do not create contrails, adopting different flight plans in pilot projects.

Experts say contrail reduction is the only tool the aviation industry has today to make meaningful cuts in its carbon emissions.

Airlines are taking steps to reduce their outsized impact on climate change, but these moves are mostly limited to buying planes that are more efficient, reducing speeds and selecting paths that save fuel. Any savings in pollution or consumption are outpaced by the rapid growth of commercial aviation.

Electric planes that can replace jetliners are many years away. The use of sustainable aviation fuel, made with old cooking oil and plants, has hurdles that include cost and availability. Hydrogen, mostly made from hydrocarbons, is not green at all. And paper straws and biodegradable plates won’t do it.

That leaves contrail reduction.

Atmospheric conditions are constantly changing, but contrails are known to form over certain regions, including the North Atlantic, and parts of North America and Europe. Cool, wet air and night-time are all conditions that foster the streams.

Paul Parker, professor emeritus at University of Waterloo in Ontario, said widespread adoption of flight paths that reduce or eliminate contrails offers an immediate way to limit the harm to the planet from flying. “We don’t need to wait for the silver bullet of non-fossil fuel aviation. This is something that can be done today,” said Prof. Parker, a pilot and former associate director of the Waterloo Institute for Sustainable Aeronautics. “You just change your altitude or change your location.”

Flying the paths Google created, American Airlines’s aircraft reduced the number of contrails the planes left by 54 per cent, while fuel consumption rose by about 2 per cent.

“Contrail mitigation is quite possible and can be done at a relatively low cost,” said Joey Cathcart, a senior associate at RMI, the non-profit environmental organization that convened the studies with Google, American Airlines and other airlines (none Canadian), Airbus and Boeing.

Building the model that predicted contrails required assembling mountains of flight data, satellite imagery and atmospheric forecasts. Researchers at Google tackled the project because it presented a chance to use big data to confront a problem, said Dinesh Sanekommu, a product manager at Google Research, which makes all the work freely available to the public.

“Our team overall is focused on accelerating climate positive action by leveraging our capabilities in artificial intelligence and data processing,” Mr. Sanekommu said from Mountain View, Calif. “Contrails felt like one of those projects that was at the intersection of a big data problem and a big climate opportunity.”

Studies have shown 80 per cent of contrails are created by 2- to 12-per-cent of all flights, Mr. Sanekommu said, meaning actions on small number would have a large impact.

A United Nations panel on climate change has warned the rate at which the Earth is warming must be capped at 1.5 C by the end of the century. Failure will mean more severe heat, drought and flooding. To reach this goal, emissions must peak before 2025 and fall by 43 per cent by 2030, the UN group says.

Air Canada spokesman Peter Fitzpatrick said the Montreal-based airline’s environmental team is watching the various studies on contrail reduction, “with an eye to incorporating the findings in future flight planning.”

Nav Canada, the air traffic controller for domestic airspace and much of the busy North Atlantic region, takes part in industry discussions led by the United Nations’s civil aviation agency and is working with Transport Canada on ways to reduce the impact of aviation. This includes studying contrails, said Vanessa Adams, a Nav Canada spokeswoman.

Jill Blickstein, as American Airlines’s chief sustainability officer, is driving the Texas-based carrier’s plan to reduce harmful emissions. She knows this is not an easy route for one of the world’s biggest airlines, and the tools to get there are at least a decade away.

“All of our climate solutions are not yet developed,” she said from New York City. “When you look at our pathway to net zero [emissions] by 2050, we’re relying on things that barely exist now, like [sustainable aviation fuel], or don’t really exist yet, like hydrogen propulsion. All of these things have a 10- to 15-year runway.”

The airline is no longer flying routes that avoid creating contrails – that experiment is finished, she said. She believes the 2-per-cent added burn in fuel is too great. Still, scientists she works with tell her now is the time to be ready to trigger that tactic once more. “As we learn and become better at targeting the most warming contrails, we’ll have those strategies in place,” she said.

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