Black-carbon soot is the No. 2 global warming agent released into the atmosphere by human activities. A landmark study in California shows some success in controlling it.
Between 1989 and 2008, clean-air rules in California virtually halved the concentrations of black-carbon soot in the state's skies, in effect reducing the state's carbon footprint by the equivalent of cutting carbon dioxide emissions by 21 million tons a year, according to new analysis.
That would represent about 5 percent of the state's CO2 emissions in 2009, according to the report. Though the data have yet to be fed into global climate models to see if California's results can be replicated elsewhere, they bolster the hope that focusing on black-carbon soot could be an effective way to begin to address global warming.
During the past decade, atmospheric scientists have focused increasing attention on black-carbon soot, the tiny particles found in Diesel exhaust as well as the emissions from wood and dung fires. The soot, which absorbs sunlight and re-radiates it as heat, has edged out methane as the second most-abundant greenhouse-agent released into the atmosphere by human activities. But unlike carbon dioxide or methane, soot takes only days or weeks to settle out of the atmosphere, compared with decades to centuries for methane and CO2.
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