Preventing the formation of contrails, the white lines left by airplanes in the sky, on a small share of flights could delay global warming attributed to aviation by about ten years, according to a study.
According to a study prepared by Klima Consulting, commissioned by the environmental organization Transport & Environment (T&E) and signed by former IPCC scientist Olivier Boucher, this measure would reduce the projected temperature increase for 2050 by up to 0.025 degrees.
The report released on Tuesday estimates that if warming generated by these contrails were reduced by half from 2030 onward, aviation’s contribution to the increase in global temperature would reach 0.08 degrees in 2050, instead of reaching that level a decade earlier, in 2040.
By 2070, the accumulated reduction would be about 0.049 degrees, according to the study, which estimates that avoiding contrails would free between 3 and 5 percentage points of the global warming margin available between 2025 and 2050 to limit the temperature increase to 2 degrees.
Contrails form when the water vapor emitted by the engines condenses and freezes under certain humidity and temperature conditions at high altitudes, potentially giving rise to clouds that trap heat in the atmosphere.
Moreover, their climatic effect is concentrated on a small number of routes.
In 2019, only 3% of flights were responsible for 80% of the warming associated with contrails, according to research cited by T&E, with particular impact on overnight flights and during winter.
Therefore, the authors of the report consider that slightly modifying routes or the schedules of certain flights to avoid atmospheric zones conducive to their formation could be one of the most economical ways to reduce, in the short term, the climate impact of aviation.
At current levels of air traffic, reducing by half the warming caused by contrails would amount to avoiding, each year, between 67 and 225 million tonnes of CO2 equivalent — which represents between 7% and 23% of aviation’s global CO2 emissions projected for 2025.
“Diverting or rebooking only a few flights could delay by ten years the aviation industry’s contribution to global warming,” stressed Diane Vitry, the Aviation Director at T&E, describing contrails as one of the most accessible opportunities to reduce the sector’s climate impact.
The European Union began, in 2025, to regulate aviation emissions that are not CO2, with the European Commission proposing, as part of the revision of the European carbon market, to grant free emission allowances to airlines that successfully avoid the formation of contrails.
Moreover, this winter, in the North Atlantic, the first large-scale test of the oceanic airspace to reduce this phenomenon is planned, in an initiative that involves, among others, the British government and air traffic control services.
The authors of the study, however, stressed that the temperature benefit lasts only as long as the measures to avoid contrails are maintained, and that acting on them does not replace the reduction of CO2 emissions from aviation.
