Soot—also known as black carbon—heats up the atmosphere because it absorbs sunlight… On January 15th, the fifth day that smog-darkened Beijing’s air-quality index was registering “hazardous” , the most comprehensive study of black carbon yet conducted was published in the Journal of Geophysical Research: Atmospheres. It concluded that the stuff was the second-most-damaging greenhouse agent after CO2 and about twice as bad for the climate as had been thought until now. ..The biggest impact of soot, though, is not on the climate but on health—through lung and other diseases. The UNEP study reckoned that controlling emissions of black carbon could save 2.4m lives a year, regardless of any effects on the climate.
It might seem that the new study is one more item of bad environmental news. Not so. It should be easier to deal with black carbon than with carbon dioxide. Whereas CO2 is long-lasting and an inevitable by-product of burning fossil fuels, soot drops out of the atmosphere within weeks. Stop putting it there and it will rapidly go away—a potentially easy win. That win is made easier still by the fact that about 70% of emissions in Europe and the Americas come from diesel engines. Better exhausts, to trap carbon particles before they are emitted, and the scrapping of old, highly polluting vehicles could make an immediate impact. In other countries the problem is more often inefficient stoves and dirty fuel—again, things that are easy to deal with, at least in principle.
Excerpt, Global warming: The new black, Economist, Jan. 19, 2012, at 79