Rerouting Aviation: Climate Benefits of Contrail Avoidance

As the aviation industry seeks to mitigate its environmental impact, the formation of contrails—those wispy trails left behind by aircraft—has emerged as a significant area of concern. A recent study conducted by researchers from Sorbonne University and the University of Reading sheds light on a promising strategy: rerouting flights to avoid contrail formation. The findings not only provide reassurance that this practice is unlikely to worsen climate outcomes but also offer a nuanced understanding of the ongoing battle against climate change in the realm of air travel.

Contrails form when water vapor from an aircraft’s exhaust mixes with the cold ambient air at high altitudes, resulting in ice crystals that create visible streaks across the sky. While they may seem innocuous, contrails can significantly affect the climate by trapping heat in the atmosphere, exacerbating global warming. Prior to this research, it was uncertain whether rerouting flights to avoid creating these contrails would be an effective means of reducing aviation’s overall climate impact. Concerns existed that the additional carbon dioxide (CO2) emissions resulting from longer flight paths could counteract any potential benefits.

Research into the climate effects of aviation is intricate, often involving the calculation of CO2 equivalence—a method of quantifying the warming potential of both CO2 and contrails. This measurement is fraught with political implications, as the definition and weighting of these effects can lead to varying conclusions. The study aimed to clarify these complexities by analyzing a substantial dataset of flights to determine the relative climate impacts of rerouting.

The results of this research, published on September 15 in Atmospheric Chemistry and Physics, indicated a clear trend. For a significant majority of flights traversing the North Atlantic on contrail-prone routes, the climate benefits of avoiding contrails outweigh the added emissions generated by flying longer paths. The researchers analyzed nearly half a million flights conducted in 2019, measuring the warming attributable to both contrails and CO2 emissions.

Their projections revealed that by 2039, warming caused by emissions from these flights is expected to escalate, with estimates suggesting an increase of about 17 microKelvins (μK). However, should flights be rerouted effectively to prevent contrail formation—requiring only 1% additional fuel burn—the total warming potential could diminish significantly. By 2039, the projection drops to about 5 μK, reflecting a 29% reduction in warming from contrail-free flight paths. This trend continues into the next century, with warming expected to decrease to roughly 2 μK, translating to a 14% reduction by 2119.

Professor Nicolas Bellouin, one of the study’s co-authors, expressed optimism regarding these findings, highlighting that they could pave the way for more sustainable aviation practices. The data suggests that rerouting flights to avoid contrails is a viable strategy for enhancing the sustainability of air travel. However, the study also underscores a critical caveat: the precision of contrail formation forecasting must improve to maximize the benefits of this approach.

The research team employed nine different assessment methodologies to analyze the climate impacts. Remarkably, all methods concurred that controlled rerouting could yield positive climate outcomes, provided that contrails are effectively avoided. This consistency reinforces the importance of scientifically informed flight planning in achieving environmental objectives.

The aviation industry’s intersection with climate science presents both challenges and opportunities. This study illuminates a practical approach to mitigating one of aviation’s most significant environmental concerns—contrail formation. While there are still hurdles to overcome in forecasting and implementation, the findings instigate a shift towards more environmentally conscious flight operations. By prioritizing rerouting for flights most likely to generate warming contrails, the aviation sector can take decisive steps toward reducing its impact on climate change, demonstrating that innovation and sustainability can indeed soar together.