Contrails: Can Smarter Flight Paths Make Aviation Greener? 

Those thin, white trails behind planes might seem harmless—however, they account for nearly 35% of aviation’s total global warming impact. More surprisingly, just a small fraction of planes create the worst of these contrails. What if flying greener did not require redesigning any part of the plane, but simply changing where they fly?

Contrails, or condensation trails, form when hot exhaust gases mix with cold and humid air in the atmosphere. Under the right meteorological conditions, water vapor condenses and freezes around particles in the aircraft’s exhaust, forming ice crystals that can create clouds lasting for hours. These clouds can trap heat radiating from the Earth, creating a net warming effect. Aviation produces approximately 2–3% of global carbon dioxide emissions, and additional effects, like contrails, add even more to aviation’s climate impact.

Nevertheless, many researchers have found a simple solution to this issue. Only about 2–10% of flights are responsible for about 80% of estimated contrail warming, and simply rerouting these flights to avoid certain areas of the atmosphere could make a drastic difference. American Airlines worked with Breakthrough Energy and Google Research to analyze satellite imagery, weather data, software models, and AI prediction tools during 70 test flights. Over six months, these tools helped pilots steer above or below areas where contrails were likely to form, reducing contrail formation by 54%.

Moreover, Dr. Jessie Smith from the University of Cambridge’s Department of Engineering has stated that if this solution were implemented between 2035 and 2045, it could recover about 9% of the remaining temperature budget before global warming reaches 2 degrees Celsius above preindustrial levels. She also found that if no action is taken, contrails could contribute about 0.054 degrees Celsius of warming by 2050.

Additionally, rerouting flights away from these areas is a highly feasible and cost-friendly idea. It is comparable to rerouting due to turbulence and would primarily require additional preflight planning, atmospheric forecasts, route-planning software, and coordination with air-traffic control. Furthermore, this idea is easily scalable and could have a substantial impact on climate change in a short amount of time.

Unfortunately, like every solution, this has drawbacks as well. Rerouting aircraft uses extra fuel, which can increase operating costs and aviation’s impact on global warming. However, researchers have found that reducing the climate effect of contrails by 73% increased fleet-wide fuel consumption by as little as 0.11% and overall costs by 0.08%. These increases are minuscule compared with the costs of many current aviation sustainability ideas, such as sustainable aviation fuels, electric propulsion systems, and many more.

Another concern is that shifting weather conditions could make this idea more challenging. Quick rerouting and planning would be needed, which could cause unnecessary delays, especially in upcoming years with higher traffic levels in the sky. In addition, some daytime contrails can produce a cooling effect by reflecting shortwave radiation from the Sun. This would have to be accounted for when analyzing the net benefit of preventing additional contrails, although contrails produce a net warming effect overall.

Contrails may disappear within hours, but their effect on the climate can last far longer. Contrail-aware flight planning offers a promising way to reduce this impact by directing only the most climate-damaging flights around high-risk regions while limiting additional fuel use. Although better forecasting and further testing are still needed, this solution shows that making aviation more sustainable may not always require an entirely new aircraft or fuel. Sometimes, a greener future can begin by simply choosing a smarter path through the sky.

Image sourced via Cambridge University. Used for editorial purposes only. No commercial use. All rights belong to their respective owners.