A recent study addresses concerns that changing flight paths to prevent climate-warming contrails may unintentionally exacerbate global warming.
A recent study addresses concerns that changing flight paths to prevent climate-warming contrails may unintentionally exacerbate global warming.
Researchers from Sorbonne Universite and the University of Reading discovered that, for most flights producing contrails in the North Atlantic, the environmental advantages of avoiding these contrails surpass the additional carbon dioxide released by taking alternative routes.
To assess contrail avoidance, it’s essential to evaluate the environmental effects of carbon dioxide against those of contrails, known as CO2 equivalence. Various methods for this comparison have been proposed, influenced largely by political agendas. Scientists had concerns that some of these methods could create misleading conclusions, making contrail avoidance appear beneficial for the climate when it may be harmful.
The study, published today (Sunday, 15 September) in Atmospheric Chemistry and Physics, concludes that the majority of North Atlantic flights would benefit the environment from avoiding contrails, irrespective of how CO2 equivalence is measured.
Understanding Contrails
Contrails are the white streaks airplanes leave behind in the sky and can trap heat, contributing to global warming.
This new research builds on earlier studies indicating that rerouting flights to circumvent contrail formation could minimize climate impacts. However, the overall benefits of avoiding contrails compared to the drawbacks of increased CO2 emissions remained uncertain.
Prof. Nicolas Bellouin, a co-author from the University of Reading, stated, “Changing flight paths to prevent contrails could theoretically lessen aviation’s climate impact and promote sustainable air travel. Our findings eliminate a significant barrier to implementing contrail avoidance, but we still need improved forecasting and real-world tests to make it viable.”
The new results reveal that, regardless of how the balance between reducing contrails and increasing CO2 emissions is assessed, rerouting is unlikely to unintentionally worsen environmental consequences. The study analyzed nearly half a million flights over the North Atlantic in 2019 to determine the warming effects caused by the carbon dioxide emissions and any contrails produced by those flights.
The researchers started by evaluating how present flight paths would affect global warming over time. They predict that the CO2 and contrails from these flights would lead to an increase in temperature of around 17 microKelvins (μK) by 2039, 20 years later, and 14 μK by 2119, 100 years later. A microKelvin represents a minuscule change in temperature.
Next, they considered a scenario where aircraft could completely avoid contrails at the cost of using just 1% more fuel. In this case, the total warming effect would significantly diminish. By 2039, this approach would lower warming by roughly 5 μK, which accounts for a 29% reduction compared to not rerouting. By 2119, the reduction would be about 2 μK (14%).
The researchers evaluated the climate impact using nine different methods. In most instances, all the methods concurred that rerouting flights would benefit the climate, assuming the planes successfully avoid contrails as planned.
However, the researchers caution that there remains substantial uncertainty regarding precisely where contrails will develop and the extent of their warming effects. They recommend beginning rerouting efforts with flights that produce the most significant warming contrails, where the climate benefits are most apparent.
