A study by the Meteorology Department at the University of Reading suggests that a widespread adoption of night-flying restrictions could help minimise the impact of aviation on our climate.
The study, published in Nature this week, shows that even though only one in four flights over the UK occur during the night, these flights are responsible for at least 60% of the climate warming associated with aircraft condensation trails (contrails). For countries without night-flying restrictions the contribution of these flights to the contrail warming can be even larger.
Contrails affect the climate by reflecting some of the sun’s energy back to space, which cools the earth. At the same time they enhance the natural greenhouse effect by trapping energy emitted from the Earth’s surface and atmosphere, leading to a warming. On average the greenhouse effect prevails and the climate warms. The contribution that night-time flying makes to climate warming is so high because the cooling effect only happens when the sun is up, whereas the warming effect occurs both day and night.
Researchers combined high resolution aircraft flight data and routine weather balloon data in a sophisticated computer programme that models the interaction of solar and infrared radiation with the atmosphere.
Principal researcher Dr. Nicola Stuber said, ‘We conducted our study for a site in southeast England, located in the entrance region to the North Atlantic flight corridor. For this investigation, we concentrated on ‘persistent contrails’ – contrails which remain for an hour or so after the aircraft have gone. As well as discovering that this small proportion of night-time flights contributes in such a significant way to climate warming, we also found that flights between December and February contribute half of the annual mean climate warming even though they account for less than a quarter of annual air traffic.’
‘The findings have implications beyond their pure scientific value; they could be used if policy makers decided to modify flight management systems in order to reduce the climate impact of aviation.’
Project leader Dr Piers Forster, now at the University of Leeds, said, ‘Aircraft currently only have a small effect on climate. However, the fact that the volume of air traffic is set to rapidly grow in coming years makes it important to investigate the effects of contrails on our climate.’
The study was supported by the Department of Transport, the Department of Trade and Industry, Airbus and Chris Eyers at QinetiQ.
