Operation Blue Skies is putting artificial intelligence to work on one of aviation’s less visible climate problems: warming contrails. Google and the UK government launched a 30-month trial on Tuesday to predict where persistent contrails are likely to form over the North Atlantic and help aircraft avoid those areas. The programme will focus on Shanwick Oceanic airspace, which covers the eastern half of the North Atlantic flight corridor and accounts for an estimated 5% of global contrail warming. Google estimates contrails contribute around one-third of aviation’s overall climate impact.

The project brings together Google UK, air traffic control provider NATS, the UK’s Met Office, Contrails.org, Imperial College London and the University of Cambridge.

Why Contrails Matter

Contrails form when hot aircraft exhaust encounters very cold, humid air at cruising altitude. Water vapour can freeze around particles in the exhaust, producing ice crystals. Under the right atmospheric conditions, those crystals can persist and spread into thin cloud layers.

Unlike short-lived contrails that disappear quickly, persistent ones can trap heat in the atmosphere. Their climate effect varies significantly depending on where and when they form, which is why identifying high-risk areas before aircraft reach them is central to the trial.

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AI Will Predict High-Risk Zones

Google plans to combine historical flight information and satellite imagery showing where contrails have formed with atmospheric and weather data.

The system will use those patterns to forecast locations where aircraft are more likely to create persistent warming contrails. Those predictions will then be provided to NATS controllers, who can advise pilots to make small altitude changes.

Small Altitude Changes Instead of Major Detours

The trial is not expected to involve large-scale changes to flight routes.

• Controllers will primarily request vertical adjustments of around 2,000 feet, a type of manoeuvre pilots already use when avoiding turbulence.
• Testing will take place on selected evenings and nights during the next two winter seasons, when traffic levels are lower.
• Around 20 to 40 nights of testing are planned in each winter period.
• Across the designated test windows, approximately 10,000 flights are expected to pass through the trial area.
• Only around 1% to 5% are expected to receive requests to change altitude.

The limited number of adjustments is deliberate. Researchers want enough observations to determine whether targeted avoidance can measurably reduce contrail formation without creating unnecessary disruption.

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The Fuel Penalty Remains a Key Question

Changing altitude can increase fuel consumption, potentially offsetting some of the climate benefit. That is one of the issues the trial will examine closely.

Google’s technical lead Paul Hodgson said earlier testing suggested the additional fuel use would be outweighed by the climate benefit of preventing warming contrails. Modelling cited by the BBC estimates that completely rerouting through Shanwick could require around 100 kilograms of additional fuel per diverted aircraft, although the actual trial is expected to rely mainly on smaller altitude changes.

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A £5 Million Climate Experiment

The Operation Blue Skies has a total budget of £5 million. The UK’s Department for Transport is contributing £2.65 million, while Google UK is providing £1.4 million through AI research, engineering expertise and computing resources on a pro bono basis.

The results are expected to be published in academic research, potentially providing evidence on whether AI-based contrail avoidance can work at the scale of a major oceanic flight corridor.

For aviation, the significance goes beyond saving fuel or changing routes. If accurate forecasts can identify only the flights and atmospheric conditions that create substantial warming, airlines and air traffic controllers could target interventions rather than making broad changes to every flight. That could make contrail avoidance a more practical part of aviation’s wider effort to reduce its climate impact.

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