Small changes to aircraft flight paths to avoid the atmospheric conditions that create condensation trails – known as contrails – could reduce aviation’s global warming impact by nearly half, a new study suggests.

The study, led by researchers at the University of Cambridge, suggests that changing cruising altitude by a few thousand feet, either up or down, could prevent contrails from forming. Reducing or avoiding contrail formation in this way would also be faster and cheaper than other climate mitigation measures for the aviation industry, since the practice can be adopted with existing aircraft and fuel.

However, the researchers say that time is of the essence and that the sooner airlines adopt contrail avoidance policies, the bigger the positive climate impact will be. Their results are reported in the journal Nature Communications.

Contrails are the thin white streaks seen behind aircraft flying at high altitude, and form when hot exhaust gases mix with cold, humid air at cruising altitude. Under the right conditions, the water vapour freezes into ice crystals, forming clouds that can persist for hours.

Contrails also trap heat in the atmosphere. Aviation contributes around 2–3% of global carbon dioxide emissions, but its total climate impact is larger because of non-CO₂ effects such as contrails. Interest in contrail avoidance has grown rapidly in recent years as governments and airlines search for ways to reduce aviation’s climate impact while the sector transitions to lower-carbon fuels.

“Contrail avoidance can often be as simple as changing the flight paths,” said lead author Dr Jessie Smith, from Cambridge’s Department of Engineering. “Often it’s even simpler than that – just moving slightly to a higher or lower altitude to avoid the areas of the atmosphere where contrails form.”

Smith and her colleagues modelled how altitude adjustments for contrail avoidance could affect aviation’s overall climate footprint. They found that such a programme, phased in between 2035 and 2045, could recover around 9% of the temperature budget the world has left before breaching the Paris Agreement’s 2°C limit.

However, they also found that if no action is taken, by 2050 aviation contrails will have added around 0.054°C of warming — 36% more than the warming attributable to aviation CO₂ over the same period.

“What surprised me was how quickly the temperature saving could be made,” said Smith. “Over a decade, you can take a really big chunk of aviation’s warming impact out very rapidly. That's unusual in climate science, where most changes take a very long time.”

The researchers also found that while rerouting aircraft can increase fuel use slightly, the reduction in warming from fewer contrails would more than offset the extra carbon dioxide emissions.

Implementing contrail avoidance would require airlines and air traffic controllers to adjust routes dynamically based on atmospheric conditions. Some aviation experts have raised concerns about whether such changes could increase workload for air traffic management systems, but the researchers say the adjustments required may be relatively modest.

Flights already alter their routes or altitude to avoid turbulence or bad weather, meaning similar systems could potentially be used to avoid contrail-forming regions.

“It's an operational change, not a technological one,” said Smith. “You don't need to modify aircraft. You just need to work out how it will operate, and then the system is already built for it — pilots do these manoeuvres all the time. That’s why we have more hope for this than for other interventions like sustainable aviation fuels, which face enormous infrastructure and supply-chain hurdles.”

Using a climate model that tracks temperature responses across 10,000 simulated scenarios, the researchers found that beginning contrail avoidance in 2035 rather than 2045 produces a temperature reduction at 2050 that is equivalent to roughly a 78% improvement in effectiveness. “In other words, waiting a decade has roughly the same effect as making the programme almost five times less efficient,” said Smith.

While more work is needed to improve forecasts of the atmospheric conditions that cause contrails and to better understand their climate effects, the researchers say that imperfect avoidance — even at 25% effectiveness — still delivers a meaningful climate benefit, and that starting early matters more than waiting for the technology to be perfected.

Scaling up contrail avoidance will require coordination from pilots, air traffic controllers, weather forecasters and policymakers, however. “The first step is demonstrating this works on a large scale through testing,” said Smith. “Once that's done, the policy can follow. But the modelling shows clearly that you do not want to wait for perfect conditions before you begin.”

Smith said the findings show the approach could play a major role in aviation’s climate strategy. “We’re not saying it solves everything,” she said. “But it could make a very big difference.”

Reference:
Jessie R Smith et al. ‘The climate opportunities and risks of contrail avoidance.’ Nature Communications (2026). DOI: 10.1038/s41467-026-68784-8