Industrial black carbon—particularly in the period around 1900—left a dirty, harmful human smudge on the Arctic, researchers say.
Black carbon absorbs a wide spectrum of light radiation, so a little soot retains a lot of heat. “Even the tiniest amount of black carbon will change quite dramatically the reflectance properties of the snow,” says Joe McConnell of the Desert Research Institute in Reno, Nevada. “That means that the snow will absorb more energy and therefore melt faster.” If the snow melts early, he adds, the ground below it is even less reflective, heating the surroundings still more.
Studying ice cores from central Greenland, McConnell and his colleagues measured black carbon levels from 1788 to 2002. At their peak, in 1908, the concentrations were 10 times their preindustrial levels, the researchers reported in September. Concentrations of two other chemicals in the ice cores, vanillic acid (a chemical formed when conifer forests burn) and non–sea salt sulfur (a primary component in acid rain), helped distinguish between soot from natural sources and that from industrial pollution. Forest fires produced much of the Arctic soot before 1850, but between the late 1880s and 1950, industrial black carbon pollution predominated.
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