Contrails from winter night flights may be most responsible for the global warming caused by air traffic, even though they comprise a fraction of commercial flights, meteorologists at the United Kingdom’s University of Reading reported Wednesday.
While there would be enormous practical problems, airlines could markedly reduce aviation’s effect on the climate by changing schedules to restrict night flying, the researchers said in the journal Nature.
“We get one-half of the climate effect from one-quarter of the year, from less than one-quarter of the air traffic,” said meteorologist Nicola Stuber who led the English research team. “If you get rid of the night flights, you can reduce the climate warming effect of the contrails.”
Overall, aviation accounts for a relatively small portion of the emissions involved in rising global temperatures, but international commercial air travel is among the fastest growing unregulated sources of greenhouse gases and a growing topic of concern among climate regulators.
By its accounting, the International Air Transport Association says air traffic accounts for 2 percent of global carbon dioxide emissions. Jet exhaust, however, injected at high altitude can have two or three times the warming effect of carbon dioxide alone, researchers concluded.
In particular, climate experts have worried about the effect of the trails of ice particles that quickly 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, to cause slight cooling. At the same time, they also block heat rising from the Earth below, to enhance the greenhouse effect. At night, that warming is especially pronounced, the researchers determined.
Stuber determined that night flights account for 25 percent of the daily air traffic but contributed 60 percent to 80 percent of the climate effect. Moreover, winter flights accounted for only 22 percent of the annual total but contributed half of the annual warming.
“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,” said atmosphere expert Joyce Penner at the University of Michigan.
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