New Scientist News - Night flights give bigger boost to global warming

THE romance of night flight has inspired all kinds of artists, from writers to rock musicians. Rather less romantic is the impact of night-time flights on global warming revealed by an analysis of aircraft movements over England.
Aircraft contrails - the streams of water droplets and ice that form when hot exhaust meets cold, moist air - can persist for many hours, spreading to an average width of 2 kilometres before dispersing. They are known to contribute to global warming by trapping the infrared radiation emitted from the Earth's surface (New Scientist, 19 October 2002, p 6).
Nicola Stuber of the University of Reading, UK, and her colleagues used computer models to study the warming effect of contrails created by aircraft entering the North Atlantic flight corridor over south-east England. This showed, as expected, that winter flights make a disproportionate contribution to warming because winter weather favours the formation of contrails.
More striking was the difference between night and day. While night flights accounted for only 25 per cent of air traffic at the monitored site, their contrails contributed up to 80 per cent of the warming in cloud-free conditions. That's because daytime contrails partly offset the overall warming effect by blocking incoming sunlight (Nature, vol 441, p 864).
The team also showed that the 36 per cent of flights over the US east coast that occur during the night account for 53 per cent of the warming. The 48 per cent of all flights in the North Atlantic corridor that are at night account for 58 per cent of the warming. The simplest way to minimise the warming effect of contrails would be to reschedule flights for the daytime, Stuber says.
Bob Noland of Imperial College London, who also works on contrail-induced warming, says this research should help persuade a sceptical aviation industry to address the issue. "They've done a fine job, using well-established data," he says of Stuber's team.
But shifting all night traffic to the daytime would be unrealistic, he says. Instead, he suggests planes should be manoeuvred around regions where contrails would form, just as they avoid thunderstorms. However, Stuber says it is difficult to forecast conditions that favour the formation of contrails.
From issue 2556 of New Scientist magazine, 14 June 2006, page 19