A study by a team of scientists from Reno's Desert Research Institute has found that around the middle of the 19th century, the Arctic took a sooty turn for the worse.
Soot can darken the snow, causing it to absorb sunlight, warm up and melt. That, in turn, can add to local climate warming by exposing darker ground which absorbs energy from the sun that the white snow would have reflected.
Ice cores from before about 1850 show most soot came from forest fires. But since then, black soot in the snow has increased several times over and most now comes from industrial activities.
The soot study was done by a team led by Joseph McConnell of the
Desert Research Institute in Reno, Nevada. It appears in this week's online edition of the journal Science.
The researchers analyzed black carbon levels in ice from Greenland, covering the last 215 years.
They found that the older soot samples contained vanillic acid, an indicator of burning conifer trees.
In the more recent years the soot was seven times more common and contained a larger concentration of non-ocean sulfur, an indicator of industrial emissions.
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