Air pollution warming up Arctic

The Arctic region is 2 degrees to 3 degrees warmer during the winter than it would be without air pollution drifting in from elsewhere, according to a study by two University of Utah scientists.

The report, by Tim Garrett, assistant professor of meteorology, and Chuanfeng Zhao, a graduate student in the same field, was printed in the April 6 issue of Nature, the "international weekly journal of science" based in London.

Garrett and Zhao studied the impacts of inversions similar to those experienced by valley areas in northern Utah during the winter. They used readings from instruments maintained at two sites near Barrow, Alaska, by the U.S. Department of Energy and the National Oceanic and Atmospheric Administration.

In Utah, winter air inversions can cause icy conditions beneath the haze layer. Sunlight reflects from the particles so that less solar radiation reaches the valleys. Meanwhile, at mountain resorts above the pollution layer, snowboarders are "catching air" that is much warmer.

Garrett began wondering about the effects of air pollution on the Arctic when he was a Ph.D. student, flying over the region in an aircraft to measure pollution in the clouds.

"It really surprised me," he recalled. "Even in summer, it was clean at the surface, but flying above the cloud levels, we'd see these layers of gunk.

"It was just extremely polluted," with thin layers of haze. "You don't think that the Arctic should be polluted."

Attempting to find out what this global pollution would do to the Arctic, the researchers used data from the Barrow sites. One site measured the amount of infrared radiation reaching the surface while the other checked pollution in the air.

An instrument in the project could be described as seeing "many different colors in the infrared ... with extreme precision," he said. This data helped determine the size of droplets of moisture in the clouds overhead.

Polluting haze could cause more and smaller droplets to form as the moisture collects around tiny particles.

One might think that winter air pollution in the Arctic would cause cooling just as it happens in the Salt Lake Valley. But that turned out not to be true.

Winter inversions happen when the Arctic has little sunlight — the sun is below the horizon much of the winter. As a result, sunlight isn't bouncing off the high haze to cause cooling at the surface. Pollution wraps the region like a blanket, trapping heat.

"It turned out we found this effect was quite substantial," Garrett said.

"Under typical polluted conditions in the Arctic winter and spring, the surface warming ... is probably somewhere between, I would guess, 2 and 3 degrees Fahrenheit. It's not huge but it is significant."