Without aggressive action to reduce soot emissions, the time table for carbon dioxide emission reductions may need to be significantly accelerated in order to achieve international climate policy goals such as those set forth in last December's Copenhagen Accord, according to "Assessing the climatic benefits of black carbon mitigation," a study published online June 21 in the Proceedings of the National Academy of Sciences (PNAS).
The Princeton University researchers assessed the climatic contribution of "carbonaceous aerosols," fine particulates emitted into the atmosphere and commonly known as soot. Soot is produced by the incomplete combustion of organic matter and comes from a variety of sources, ranging from diesel engines and coal combustion to biomass cook stoves, crop burning and wildfires.
Soot has complex effects on the global climate when airborne or deposited on snow. It has two main components: black carbon and organic carbon. Black carbon is dark and absorbs radiation, thus warming the atmosphere; organic carbon is light colored and reflective, so tends to have a cooling effect. Their effects on climate are complicated, in part because they depend on how they are mixed with other particles in the atmosphere, and in part because both types of aerosols can cool the climate through their effects on cloud formation. Black carbon also warms the Earth's surface when it is falls out of the atmosphere and lands on snow or ice, darkening it.
"Because of uncertainties in these many effects, and because of differences in whether and how these effects get incorporated into various models, past studies of soot's contribution to global warming have ranged widely," said Robert Kopp, a post-doctoral researcher jointly in Princeton's Woodrow Wilson School of Public & International Affairs and its
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Princeton University, Engineering School