Re-Routing Flights Could Reduce Climate Impact: Contrails Contribute to Global Warming

It turns out that aircraft could become a little more environmentally friendly just by changing their flight paths. Scientists have found that if aircraft choose flight paths that reduce the formation of their distinctive condensation trails, they can also reduce their impact on global warming.

Contrails, which are the condensation trails that follow in the wake of aircraft, only form in regions of the sky where the air is very cold and moist. These conditions usually occur around high pressure systems. These contrails can stay within the air for many hours before eventually spreading out to resemble natural, wispy clouds.

Unfortunately, researchers have found in the past that these contrails can be a large contributor to global warming. In fact, they may be an even larger contributor that aircraft CO2 emissions. Like natural clouds, contrails reflect some of the sun's energy and cause a cooling effect. Yet they also trap some of that infrared energy and therefore having a warming effect. For contrails, this warming effect prevails and thus can contribute to warmer temperatures.

"If we can predict the regions where contrails will form, it may be possible to mitigate their effect by routing aircraft to avoid them," said Emma Irvine, one of the researchers, in a news release. "Our work shows that for a rounded assessment of the environmental impact of aviation, more needs to be considered than just the carbon emissions of aircraft."

In fact, the researchers estimate that if smaller aircraft fly further to avoid former contrails, then they have a reduced environmental impact-despite the increased carbon dioxide emissions. However, that's only if the alternative route adds less than 200 miles. The same is true for larger aircraft, though only if the added route is less than 60 miles.

"Comparing the relative climate impacts of CO2 and contrails is not trivial," said Irvine in a news release. "One complicating factor is their vastly differing lifetimes. Contrails may last for several hours, whilst CO2 can last for decades. In terms of mitigating these impacts, air traffic control agencies would need to consider whether such flight-by-flight re-routing is feasible and safe, and weather forecasters would need to establish if they can reliably predict when and where contrails are likely to form."

The findings are published in the journal Environmental Research Letters.