A brown haze was first observed in the Arctic in the 1950s, co-author Katherine Law noted.

With global warming already occurring twice as fast in the Arctic as elsewhere, the region is highly sensitive to future increases in greenhouse gases including tropospheric ozone, Law said in e-mailed answers to questions.

The pollution lofted from the temperate zone to the Arctic can set in motion a chain of events that could accelerate climate change in the far north, said Law of the Universite Pierre et Marie Curie in Paris.

"The surface temperature response to these increases is higher at high latitudes even though the gases are emitted largely in temperate regions," she said. "This can lead to melting of sea ice, which in turn leads to enhanced warming."

Sea ice is a powerful reflector of the sun's rays. Less sea ice means less solar radiation is reflected and more is absorbed, increasing heating at the Earth's surface.

"Observations already show a 3 percent per decade decline in Arctic sea ice cover and models predict that summer sea ice might disappear by the middle of this century," Law wrote.

VANISHING SEA ICE

If the Arctic sea ice goes away, scientists predict more pollution and even stronger climate change because of the expected increase in shipping and oil drilling in the area.

Warming in the Arctic and Antarctic can have wide-ranging impact on the world's climate system, according to experts meeting in Hanover, New Hampshire, for a summit on Arctic science this week.

Climate change also affects the great ice sheets that cover Greenland and Antarctica.

Another Science study estimated the two areas are losing a combined mass of 125 gigatons a year, enough to add another sliver -- 0.013 of an inch (0.33 mm) -- to the annual rise in global sea levels of 0.1 of an inch (2.54 mm).

A third Science article maintained that predicting what will happen to the big ice sheets is difficult because scientists are only now learning what is going on underneath the surface.

The focus on polar research in this edition of the journal was a nod to International Polar Year. That is actually a two-year period beginning this month with study focused on the poles, including the disproportionate impact global warming has on the polar regions.

"By now, most people know that the poles are the ideal places to study the effects of global climate change," Science's executive publisher, Alan Leshner, wrote in an editorial.