Jun 19, 2014 04:47 AM EDT By Staff Reporter, UniversityHerald Reporter

Aircrafts can become more environment-friendly by selecting flight paths that decrease the formation of condensation trails in the sky, according to a University of Reading study.

Researchers said that planes contribute less to global warming by staying away from places where the thinly shaped clouds - contrails - are formed. Contrails are produced in regions where the air is very cold and moist. The vapour trails can sometimes remain in the air for several hours and eventually start to resemble natural clouds.

Previous studies showed that the amount of global warming caused by contrails could be as large, or even larger, than the aviation carbon dioxide emissions.

"If we can predict the regions where contrails will form, it may be possible to mitigate their effect by routing aircraft to avoid them," Emma Irvine of the Department of Meteorology said in a press 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."

Researchers said that similar to natural clouds, contrails reflect some of the sun's incoming energy which results in a cooling effect. But, they also lock in some of the infra-red energy that radiates from Earth into space to have a warming effect.  Detailed calculations suggest that the warming effect occurs at a greater rate than the cooling effect.

The researchers believe that smaller aircrafts can travel much further to avert contrail formation than larger aircrafts. For example, if a small aircraft that is predicted to produce a contrail 20 miles (32km) long in one route and less than 200 miles (322km) in an alternative route, the second path clearly has a smaller climate impact.

On the other hand, larger aircrafts release more carbon dioxide than smaller aircraft for each mile flown. The alternative route can still be applicable, provided it adds less than 60 miles (i.e. 3 times the contrail length) onto the route.

"Contrails may last for several hours, while carbon dioxide 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," Irvine said.

The finding is published in the journal Environmental Research Letters.

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