Arctic snow was dirtier in early 1900s.

The amount of soot wafting to the Arctic has increased significantly since the beginning of the Industrial Revolution but isn't nearly as high now as it was a century ago, an ice core from Greenland suggests.

Greenland has always received some soot from Canadian wildfires, says Joseph R. McConnell, a hydrologist at the Desert Research Institute in Reno, Nev. But the load increased around 1850, when mills and power plants in Canada and elsewhere in the Northern Hemisphere began burning coal in large quantities.

Industrial soot fell at its greatest rate between 1906 and 1910, McConnell reports. During the months of 24-hour Arctic sunshine, the darkened snow at that time probably absorbed about eight times as much solar radiation as it would have if it had been free of coal soot, says McConnell. That change in energy balance during the summer, in turn, warmed the snow and influenced climate in the region, he notes.

The team's data came from an ice core collected in west-central Greenland. However, the entire Arctic region probably received soot from coal-fired industrial activity throughout the Northern Hemisphere.

In the past few decades, regulations and improved technology have significantly decreased emissions of industrial soot. Over that period, nevertheless, Arctic snow has on average absorbed about 40 percent more of the sun's energy during summer months than it did before the Industrial Revolution began tainting the snow, the team estimates in the Sept. 9 Science.