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Contrails - the white lines in the sky created by planes - have a net warming effect on the planet, at least as important as the one caused by aviation’s CO2 emissions. But only a minority of flights (3%) generate 80% of contrail warming. Tweaking the flight paths of these very few flights can reduce global contrail warming by more than half before 2040. T&E warns that, while avoiding contrails would lead to significant climate benefits, it does not make it any less urgent to reduce the CO2 emissions of the aviation sector, whose impact on the climate remains as significant as before.
Changing flight paths to avoid contrails will only happen on a very small number of flights and only for a small part of the journey. The extra fuel burnt to avoid contrails would be less than 0.5% on the whole fleet over a year. And on those few flights where rerouting will happen, 80% of the contrail warming of the flight can be avoided, with an extra fuel burn of 5% or less.
The climate benefits from avoiding the most warming contrails would always be larger than the climate penalty from the extra CO2 emissions, the analysis finds. Assuming extra CO2 emissions and accuracy levels which are already being achieved today in flight tests, climate benefits from contrail avoidance would still be 15 to 40 times larger than the CO2 penalty. These benefits are expected to go up as technology advances.
Geography and flight latitude have a strong influence on whether a contrail is warming. Flights over North America, Europe and the North Atlantic region accounted for more than half of global contrail warming in 2019. Time of day also influences the climate effects of contrails. Those formed by evening and night flights have the largest warming contribution. Seasonality is also important: the most warming contrails tend to occur in winter.
As a climate solution, contrail avoidance is particularly cheap. Using a conservative estimate, the study finds that on a flight from Paris to New York, it would cost less than £3.35 per ticket to re-route the flight to avoid the contrail. This price accounts for the extra fuel and all technologies associated with contrail avoidance (humidity sensors, satellites, etc.). Per tonne of CO2 equivalent abated, this is more than 15 times cheaper than other climate solutions like carbon capture and storage (CCS). Contrail avoidance is also a solution that could be deployed at scale in the next decade, provided decisive action is taken.
Airlines, start-ups and other actors are already putting contrail avoidance in practice. In 2023, a trial took place over 70 flights where 54% of contrail formation was mitigated, with an estimated 2% fuel burn penalty at fleet level. To ensure contrail avoidance is deployed at scale, T&E recommends that contrails also be monitored on all flights departing from and arriving to the EU as of 2027 and that regulators prepare the European airspace for inclusion of contrail avoidance. The EU should prioritize funding for contrail avoidance research and offer incentives to early mover airlines and manufacturers, until these technologies become standard.
Non-CO2 effects of aviation, such as nitrogen oxides and contrails, warm the planet at least as much as aviation’s CO2. Contrails - created by aircraft flying through cold and humid air - are the most significant of aviation’s non-CO2 effects. Most contrails dissolve within a few minutes, but in certain conditions, they can persist in the atmosphere, spread out, and become artificial cirrus clouds with a net warming effect. In the year 2018, a landmark study estimated that the effective radiative forcing from contrails was larger than the ERF from the historic CO2 emitted by the sector since 1940.
Anna Krajinska, UK Director at Transport & Environment said:
“The aviation industry is being offered a simple and cheap way to reduce its climate impact. Some industry actors overstate the scientific uncertainty of warming contrails, but the climate benefits of contrail avoidance are huge and solutions are improving by the day. By identifying the very few flights which cause warming contrails and tweaking their flight paths, we can have an immediate effect on contrails warming. So let's no longer discuss whether we have to do it, but how to do it.
There are very few climate solutions that can be implemented so quickly, at so little cost and with little impact to industry and consumers. But this can only happen if we include contrail mitigation in our climate targets and adopt groundbreaking policies to monitor, avoid contrails and mandate solutions. We can and must make our skies free of warming contrails in the next 10 years, for the sake of the planet. Policy makers and the industry cannot afford to lose the climate opportunity of this decade.”
ENDS
Note to editors:
A series of conservative assumptions have been made for this study. These assumptions result in estimated contrail avoidance costs 3-10 times larger than other sources, and lower climate benefits. With less conservative assumptions, the costs would be lower, and the climate benefits larger, creating an ever stronger case to deploy contrail avoidance.
