for National Geographic News
Soot emissions from U.S. coal burning may have significantly contributed to pre-1950 global warming in the Arctic, a new study suggests.
Soot, emitted naturally into the atmosphere by forest fires, is also a pollutant from human activities such as burning fossil fuels.
Winds carried soot from the United States and possibly other countries to the Arctic, where it fell on the snow. The darkened snow then absorbed more solar energy, warming the Arctic climate.
Because the sunlight is not reflected back into the atmosphere, the Arctic climate warmed.
(Related: "'Brown Clouds' Contribute to Himalaya Glacier Melt" [August 1, 2007].)
At its worst, U.S. soot pollution was eight times more powerful in warming the Arctic springtime than the soot from forest fires, said study lead author Joseph McConnell, a snow hydrologist at the Desert Research Institute in Nevada.
In 1900 the soot's effect on warming was about as strong as the effect of all of the carbon dioxide that the Industrial Age dumped into the atmosphere up until that time, McConnell said.
"This is much bigger than anybody would ever have expected," he said.
The research team measured soot deposits in a Greenland ice core, which contained snow that fell from 1788 to 2002.
To distinguish the effects of forest fires from those of coal burning, McConnell and colleagues measured not only the amount of soot the ice held, but also the amounts of sulfur and a chemical called vanillin.
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