Contrails, short for condensation trails, are the long white streaks that form behind aircraft under certain weather conditions. Under the right conditions, contrails don’t just fade away. They can persist, spread, and evolve into thin, cirrus-like cloudiness that traps heat in the atmosphere. We estimate that contrails have already contributed about 2% of the global temperature increase since the Industrial Revolution. This is roughly comparable to the warming from all accumulated aviation CO₂ emissions since the beginning of the jet age.
As the world works to meet the Paris Agreement goal of limiting global temperature increase to well-below 2°C above preindustrial levels, all contributors to global warming, including contrails, need to be examined.
One potential solution relies on the fact that contrails persist only when aircraft fly through areas of humid, cold air called ice-supersaturated regions (ISSRs). These regions can be avoided by routing a flight higher, lower, or around a region, thereby preventing a contrail from persisting. This practice, called navigational contrail avoidance, is already being tested operationally by airlines. As this technology develops, we asked: how much climate benefit could navigational avoidance achieve, and what risks come with implementing it at a global scale?
Action on contrails could recover 9% of the remaining temperature budget
The world is already on track to reach 1.5°C of warming above preindustrial levels. If no action is taken on contrails, the combined warming from aviation CO2 and contrails could use up 19% of the remaining temperature budget, that is, the remaining warming "headroom" before crossing 2°C. If swift and effective action is taken on contrails, specifically if contrail warming is eliminated by rolling out navigational contrail avoidance over 10 years (2035 to 2045), we estimate the global temperature rise could be reduced by 0.044°C. This corresponds to recovering 9% of the remaining temperature budget for staying below the 2°C goal.
Since navigational contrail avoidance is still a developing technology, its real-world performance is uncertain. We explored three potential risks using multiple scenarios:
- Technology maturity: contrail avoidance is simulated to be 25% to 100% effective.
- Delay: contrail avoidance is rolled out starting in 2035, 2040, and 2045.
- Additional fuel burn: contrail avoidance increases global aviation fuel use by 0.35%, 5%, or 10%.
The biggest risk is delay
Our results show that delaying the rollout of navigational contrail avoidance by 10 years, from 2035 to 2045, is worse than deploying a timely solution that is only 25% effective in reducing contrail warming.
Delay also outweighs the risk of additional fuel burn. Rerouting flights for contrail avoidance can increase fuel use, and that extra CO₂ could, in principle, offset the climate benefit of avoiding contrails. However, our analysis indicates that, even in the most pessimistic case, 25% effectiveness of contrail avoidance and a 10% increase in fuel consumption, contrail avoidance is very likely (>90% probability) to deliver a net climate benefit. In the more realistic case of a 0.35% additional fuel use, a net climate benefit is virtually certain (>99% probability).
Implications for the adoption of contrail avoidance
Using reduced-order climate modeling, we find that navigational contrail avoidance can deliver meaningful, near-term reductions to global temperature change. The central risk is delay: even if we cannot eliminate contrail warming, adopting a less effective solution sooner is better for the climate than waiting to perfect the technology.