Night Flights Boost Global Warming - A study

Condensation trails (sometimes vapour trails) from winter night flights may be most responsible for the global warming caused by air traffic, even though they constitute a fraction of commercial flights, meteorologists at the University of Reading in UK reported Wednesday.

According to the British research, which published in the journal Nature, the aircraft exhausts produce their largest contrails-an artificial cirrus clouds made by the exhaust of aircraft engines or wingtip vortices which precipitate a stream of tiny ice crystals in moist, frigid upper air, at night-time and especially during the short and cold winter days.

Researchers have suggested in their report that a nationwide ban on night flights would significantly reduce the aviation industry's impact on the climate. However, there would be enormous practical problems but airlines could markedly reduce aviation's impact on climate by changing schedules to restrict night flying, the researchers said.

Nicola Stuber-a meteorologist at Reading University, who led the English research team said, “We get one-half of the climate effect from one-quarter of the year, from less than one-quarter of the air traffic,” emphasizing on the warming effect of aircraft, Stuber added “If you get rid of the night flights, you can reduce the climate warming effect of the contrails.”

Generally, aviation accounts for a relatively small portion of the diffusion involved in rising global temperatures, but international commercial air travel is among the fastest growing unregulated sources of greenhouse gases and a topic of concern among climate regulators.

Piers Forster, an environmental scientist at the England’s University of Leeds, who headed the project, said: “Night flights are twice as bad for the environment. If the government wanted to reduce the likely impact of aviation on climate then it could ensure that more flew during the day.”

Stressing on, shifting all British night flights to the daytime would save the equivalent of 2.5% of the UK's annual carbon dioxide emissions, Dr Forster said, “Aircraft currently only have a small effect on climate. However, the fact that the volume of air traffic is set to grow rapidly in coming years makes it important to investigate the effects of contrails on our climate.”

Scientist are especially worried about the impact of the trails of ice particles that swiftly condense in the wake of jet exhaust, which can spread in hours from a few yards wide to thousands of square miles. These shining clouds are mirrors in the sky. From their upper surface, they reflect solar radiation, causing a moderate cooling. At the same time, they block any heat rising from the earth below, intensifying the greenhouse effect. At night, that warming is especially pronounced, the researchers ascertained.

To explore the climate effects of contrails, Stuber and her fellow researchers studied the airspace over the south of England at the entrance to the North Atlantic flight corridor, possibly the world's busiest skyway, with as many as 36,000 flights per month.

They watched only at information on condensation trails that persisted for an hour or more, combining aircraft flight data with weather balloon recordings of temperature and humidity. Condensation trails were nearly twice as likely to form in winter as in summer.

After monitoring air traffic over the UK, they determined that, although one in four flights occurred between 6pm and 6am, they contributed 60-80% of the warming that could be attributed to contrails. Furthermore, winter flights had more effect than those in the summer, contributing 50% of the warming despite providing only 22% of traffic.

Agreed to the new research, Joyce E. Penner-atmosphere expert at the University of Michigan said, “If we control emissions from other sources and don't do something about aircraft, then in the future they are going to become a dominant source," on the recent discovery that warming effect of aircraft is much greater when they fly in the dark, Penner said, “Maybe there are ways to avoid such a high climate impact by scheduling different routings.”