Night flights under green scrutiny after study finds nocturnal contrails environmentally worse

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By Aimée Turner in London

Scientific study by UK university flags up increased impact of nocturnal contrails on global warming

The first study to look at the effects of aircraft condensation trails (contrails) at different times of the day and season suggests that aircraft flying at night can have a greater impact on the environment.

The study by the UK’s Reading University’s meteorology department shows that although night flights account for only a quarter of movements over the UK, they generate at least 60% of the climate warming associated with contrails.

Contrails both reflect some of the Sun’s energy back to space – cooling the Earth – while also increasing the greenhouse effect by trapping energy emitted from the Earth’s surface and atmosphere, leading to 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,” says principal researcher Dr Nicola Stuber.

Researchers combined high-resolution aircraft flight data supplied by Eurocontrol with routine weather balloon data to model the interaction of solar and infrared radiation with the atmosphere. The study focused on “persistent contrails” – contrails that remain for around an hour – in an entrance region to the North Atlantic flight corridor site over Herstmonceaux in south-east England. “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 the annual mean climate warming, even though they account for less than a quarter of annual air traffic,” Stuber says.

She says that the findings, which were based on four data sets of 6h periods, have implications beyond their pure scientific value and could be used if policy makers decided to modify flight-management procedures to reduce the climate impact of aviation. She suggests future studies could increase the precision of the early findings by using a 1h time resolution that would narrow the assessment window.

Project leader Dr Piers Forster says: “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 Airbus, Qinetiq, the UK Department of Trade and Industry, and the UK Department for Transport.