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Black Carbon – Hot Topic
The aerosol haze has long plagued the Arctic, but scientists are only now taking stock of a different and potentially uglier dimension of soot. As its name would suggest, black carbon absorbs sunlight. These particles heat the atmosphere while aloft; when they settle on the snow, they hasten its melting. This exposes the dark land and water, which absorb more of the sun’s energy and thereby drive up the region’s temperature. Recent research suggests that black carbon could be responsible for a large fraction of the Arctic warming. Soot also takes a toll elsewhere. In southeast Asia, studies suggest that it is choking the moisture supply for the Indian monsoons and contributing to the retreat of mountain glaciers that provide fresh water for more than a billion people.
These dark particles, the major constituents of soot, are the legacy of incomplete combustion in diesel engines, coal power plants, agricultural burning and wildfires far to the south. Prevailing winds sweep black carbon and other pollutants into the Arctic, where they circulate in a dirty yellow haze until storms wash them out of the air.
At this point, scientists lack enough data to definitively conclude how strongly black carbon is affecting the climate.
Drew Shindell, a modeller at the Goddard Institute, recently used a coupled ocean–atmosphere climate model to reconstruct twentieth-century influences on climate, or forcings, with and without black carbon. His results suggest that increases in black carbon from Asia and reductions in sulphate pollution have caused about 45% of the observed warming in the Arctic. In Ramanathan’s global assessment, the forcing from black carbon equals 0.9 watts per square metre, which is more than the forcing from methane and 55% of that from CO2.
Jacobson estimates that altogether, the climate has warmed 0.75–0.85°C and black carbon is responsible for 0.25°C of that.
“In other words, you could control up to 30% of global warming if you could control soot,” he says. Given that black carbon has its strongest effect in the Arctic, he suggests that such a strategy could slow sea-ice retreat until international controls on greenhouse gases kick in.
Extracts taken from the Nature News Feature: ‘Atmospheric science: Climate’s smoky spectre’
July 3rd, 2009 at 5:17 am
And Black Carbon is a technological problem, rather than a regulatory problem, so much cheaper and less unpleasant to deal with!