Contrails, the white lines trailing from aircraft at high altitude, are more than a skyward curiosity. In cold, humid conditions they persist and spread into clouds that trap heat that would otherwise escape from the Earth, according to the BBC. To tackle this, a £5m UK trial will test whether artificial intelligence can predict where climate-warming contrails are likely to form and get planes to avoid those areas.
Why contrails matter
Contrails are formed when hot exhaust from aircraft engines meets cold air at high altitude, creating ice crystals. Many disappear quickly, but in particularly cold and humid conditions they can persist and spread, forming clouds that trap heat, the BBC explained.
Dr Paul Hodgson, Google’s technical lead for the operation, told the BBC’s Tech Life programme that contrail warming is “responsible for something like a third of all aviation climate warming”. He acknowledged there was uncertainty around the precise figure, but said scientists were confident it was “either quite a large problem or a very large problem”. He also noted his five-year-old has a more colourful description for the white lines: “sky graffiti”.
The trial will focus on the Shanwick Oceanic airspace in the eastern half of the North Atlantic corridor, which accounts for approximately 5% of global contrail warming.
How AI will reroute flights
The idea behind the trial, according to the BBC, is that if scientists can predict areas of the atmosphere where contrails are likely to form, aircraft could avoid them. The AI system works like this:
- Google uses satellite images and flight data to identify where planes have previously produced contrails.
- This is combined with weather patterns to forecast where conditions for new contrails are likely to occur.
- The information is passed to NATS, the UK air traffic control provider, where controllers can direct pilots to avoid those areas.
- Most adjustments involve changing an aircraft’s altitude by around 2,000ft — something that already happens routinely to avoid turbulence and bad weather.
According to the BBC, passengers are unlikely to notice the changes. Ian Jopson, director of sustainability at NATS, said it should be “pretty much business as usual using existing procedures for the operators on the North Atlantic”.
Operation Blue Skies partners and funding
The 30-month project, named Operation Blue Skies, brings together Google, the UK government, the Met Office, NATS, and researchers at the University of Cambridge and Imperial College London.
| Partner | Role | Contribution |
|---|---|---|
| AI research, engineering, computing infrastructure | £1.4m | |
| Department for Transport | Government funder | £2.65m |
| Met Office | Weather forecasting | Not stated |
| NATS | Air traffic control | Not stated |
| University of Cambridge | Research | Not stated |
| Imperial College London | Research | Not stated |
The BBC noted that the Department for Transport is providing £2.65m towards the programme, while Google is contributing £1.4m through AI research, engineering and computing infrastructure. The trial comes as the government backs expansion of UK airports, raising the question of whether tech solutions can sufficiently reduce aviation’s environmental impact as demand for flying grows. Google is also one of many big tech companies spending billions on new data centres, which environmentalists are concerned will contribute more to climate change. The BBC’s report also identifies Aviation Minister Keir Mather.
Trial scale and schedule
Testing will take place during selected evenings and nights in the winters of 2026-27 and 2027-28, when air traffic is lower. Around 10,000 flights are expected to pass through the airspace during the trial periods, although only a fraction will need to change altitude specifically to avoid contrails.
The central premise is that predicting contrail formation areas allows aircraft to make small, routine altitude changes that avoid the most warming clouds.
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