Study shows that preventing contrails is less likely to inadvertently harm the climate than previously thought

Researchers at Sorbonne University and Reading University have found that for most flights that create contrails over the North Atlantic, the climate benefit of avoiding these contrails outweighs the additional carbon dioxide emissions caused by flying a different route.

To avoid contrails, a comparison of the climate impacts of carbon dioxide and contrails, called CO, is necessary.₂ Equivalence. Various methods have been proposed, the choice of which has been largely politically motivated. Scientists feared that some options could be misleading, making avoidance appear beneficial to the climate when in fact it is harmful.

The study published today (Sunday, September 15) Atmospheric chemistry and physics, concludes that for a large majority of North Atlantic flights, avoiding contrails would benefit the climate, regardless of the choice of CO₂ Equivalence.

Contrails explained

Contrails – the white lines left by airplanes in the sky – can trap heat in the atmosphere and contribute to global warming.

The new study builds on previous research that suggested that aircraft could be rerouted to avoid the formation of contrails, potentially reducing climate impacts. However, the benefits of avoiding contrails are outweighed by the disadvantages of additional CO₂ -Emissions were unclear.

Prof Nicolas Bellouin, co-author at the University of Reading, said: “Rerouting flights to avoid contrails could, in theory, reduce the climate impact of air travel and make flying more sustainable. Our results remove a major obstacle to implementing contrail avoidance, but we now need better predictions and real-world trials to put this into practice.”

The new findings show that regardless of the trade-off between avoiding contrails and increasing CO₂ emissions are measured, diversions rarely inadvertently worsen climate effects. The study looked at nearly half a million flights over the North Atlantic in 2019 to estimate how much warming was caused by the carbon dioxide emissions from those flights and the contrails they created.

The researchers first examined how current flight routes would affect the Earth over time. They estimate that CO₂ The emissions and contrails from these flights will have warmed the climate by about 17 microkelvins (µK) in 2039, 20 years later, and by 14 µK in 2119, 100 years later. A microkelvin is a very small unit of temperature change.

The researchers then imagined a situation in which airplanes could avoid all contrails by burning just 1% more fuel. In this case, the overall warming would decrease significantly. By 2039, warming would be reduced by about 5 μK, which is 29% less than without diversion. By 2119, it would be about 2 μK (14%) less.

The researchers used nine different methods to measure climate impacts. In most cases, all methods agreed that rerouting flights would be good for the climate, as long as the planes successfully avoided contrails as predicted.

The researchers stress that there are still large uncertainties in predicting exactly where contrails form and how much warming they cause. They suggest focusing diversion efforts initially on flights that form the warmest contrails, as that is where the climate benefit is most evident.