Passengers flying across the North Atlantic this winter may experience slight altitude adjustments during their journeys, as air traffic controllers launch a landmark trial to curb one of aviation's largest climate impacts: condensation trails.
Starting in November, controllers managing the Shanwick airspace on the eastern side of the North Atlantic will advise transatlantic flights to alter their altitude to avoid atmospheric zones where contrails easily form. Contrails occur when soot particles from jet engines trigger the creation of ice crystals, producing white streaks across the sky that can persist for hours. Although daytime contrails reflect some sunlight back into space, overnight contrails trap significant amounts of heat below them, accounting for roughly one-third of aviation's total global warming impact.
The Shanwick corridor is a major transatlantic flight path and a known contrail hotspot, generating about 5 per cent of global contrail warming, mostly during winter. Under the £5 million "Operation Blue Skies" initiative, controllers will use AI-generated forecasts developed by Google to predict contrail formation. During evening and night flights, when warming impacts are highest, pilots will be instructed to adjust their altitude by up to 2,000 feet (600 metres) to navigate around these sensitive atmospheric layers.
While changing altitude requires planes to burn roughly 100 additional kilograms of fuel—releasing a few hundred kilograms of extra carbon dioxide—experts note that the trade-off is overwhelmingly positive. The contrail warming avoided on a single flight is measured in tonnes or tens of tonnes of equivalent CO2, far outweighing the slight increase in engine emissions. Previous smaller-scale tests showed that targeted re-routing could reduce contrail formation by 50 to 60 per cent.
Unlike earlier trials where participation was voluntary, this airspace-scale project makes altitude adjustments mandatory for all aircraft passing through the region. Running across two consecutive winter seasons through early 2028, researchers from the University of Cambridge and Imperial College London will analyze data from thousands of flights to evaluate the project's environmental effectiveness.