Could re-routing flights reduce climate change? Avoiding certain areas and weather conditions may help prevent global warming

  • Researchers from Reading University have shown that aircraft contribute less to global warming by avoiding places where contrails are made
  • This applies even if planes have to fly further and emit more carbon dioxide
  • Contrails only form in regions of the sky where air is very cold and moist
  • Findings suggest that policymakers need to consider more than carbon emissions when trying to make aviation less environmentally damaging

The aviation industry is under pressure to reduce the amount of carbon dioxide its aeroplanes emit.

And now a team of scientists has found that aircraft can become more environmentally friendly by choosing flight paths that reduce the formation of their distinctive condensation trails.

Researchers have shown that planes 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.

Researchers have shown that aircraft contribute less to global warming by avoiding the places where the thinly shaped clouds, called contrails (pictured) are produced - even if that means flying further and emitting more carbon dioxide

Researchers have shown that aircraft contribute less to global warming by avoiding the places where the thinly shaped clouds, called contrails (pictured) are produced - even if that means flying further and emitting more carbon dioxide

AEROPLANES AND CARBON DIOXIDE

Aviation carbon dioxide emissions accounted for 6 per cent of UK total greenhouse gas emissions in 2011.

Global Carbon dioxide emissions from aviation were estimated at 630 million tonnes of CO2 for 2005. This is 2.1 per cent of the global emissions of carbon dioxide in that year.

Previous research by scientists at the university has shown that, on average, 7 per cent of the total distance flown by aircraft is in cold, moist air where long-lasting contrails can form.

Aircraft engines emit a number of other gases and particles that can alter climate - such as oxides of nitrogen and sulphur gases - and their effects might also depend on the route taken.

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, experts from the University of Reading explained.

They can sometimes stay in the air for many hours, eventually spreading out to resemble natural, wispy clouds.

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 by routing aircraft to avoid them,’ Emma Irvine, of the university’s Department of Meteorology explained.

The findings suggest that policymakers need to consider more than carbon emissions in discussions about how to make aviation (illustrated) less environmentally damaging

The findings suggest that policymakers need to consider more than carbon emissions in discussions about how to make aviation (illustrated) less environmentally damaging

WHAT ARE CONTRAILS?

Researchers have shown that planes 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.

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.

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, to have a warming effect.

Detailed calculations indicate that generally the warming effect wins over the cooling effect.

‘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.’

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, to have a warming effect.

Detailed calculations indicate that generally the warming effect wins over the cooling effect.

In the study, which is published in IOP Publishing’s journal Environment Research Letters, the researchers estimate that smaller aircraft can fly much further to avoid forming contrails than larger aircraft.  

For example, for a small aircraft that is predicted to form a contrail 20 miles (32km) long, if an alternative route adds less than 200 miles (322km) onto the route - 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 carbon dioxide than smaller aircraft for each mile flown, the alternative route could still be preferable, but only if it added less than 60 miles (97km) which equates to three times the contrail length.

Just like natural clouds, contrails (pictured) 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, to have a warming effect

Just like natural clouds, contrails (pictured) 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, to have a warming effect

Dr Irvine said: ‘Comparing the relative climate impacts of carbon dioxide and contrails is not trivial. One complicating factor is their vastly differing lifetimes.

‘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.

‘The mitigation targets currently adopted by governments all around the world do not yet address the important non-CO2 climate impacts of aviation, such as contrails, which may cause a climate impact as large, or even larger, than the climate impact of aviation carbon dioxide emissions.

‘We believe it is important for scientists to assess the overall impact of aviation and the robustness of any proposed mitigation measures in order to inform policy decisions. Our work is one step along this road.’

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