Aviation could become more environmentally friendly if airplanes choose flight paths that reduce the formation of their condensation trails, new research suggests.
Researchers from the University of Reading have shown that aircraft contribute less to global warming by avoiding the places where the thinly shaped clouds, called contrails, are produced – even if that means flying further and emitting more carbon dioxide.
Contrails only form in regions of the sky where the air is very cold and moist, which is often in the ascending air around high pressure systems. They can sometimes stay in the air for many hours, eventually spreading out to resemble natural, wispy clouds.
Just like natural clouds, contrails reflect some of the Sun’s incoming energy, resulting in a cooling effect, but also trap some of the infrared energy that radiates from Earth into space, therefore having a warming effect. Detailed calculations indicate that generally the warming effect wins over the cooling effect.
The findings suggest that policymakers need to consider more than carbon emissions in discussions about how to make aviation less environmentally damaging. Recent research has shown that the amount of global warming caused by contrails could be as large, or even larger, that the contribution from aviation CO2 emissions.
“If we can predict the regions where contrails will form, it may be possible to mitigate their effect be routing aircraft to avoid them,” said Dr. Emma Irvine, co-author of the study.
For example, for a small aircraft that is predicted to form a contrail 20 miles long, if an alternative route adds less than 200 miles onto the route (i.e. 10 times the length of contrail that would have been produced) then the alternative route would have a smaller climate impact. For larger aircraft, which emit more CO2 than smaller aircraft for each mile flown, the alternative route could still be preferable, but only if it added less than 60 miles (i.e. 3 times the contrail length) onto the route.
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