For years, efforts to study and reduce the impacts of climate change have focused on one very specific gas--carbon dioxide (C[O.sub.2]). But when it comes to global warming, other gases and atmospheric particles may play more than just a supporting role. Black carbon, a form of particulate air pollution produced mainly from burning biomass, cooking with solid fuels and diesel exhaust, has a warming potential in the atmosphere three to four times greater than scientists originally thought. Unlike C[O.sub.2], black carbon absorbs solar radiation, and current estimates show that black carbon could have up to 60% of the current global warming effect of carbon dioxide.
Black carbon is part of a category of emissions called "short-lived climate forcings" (SLCFs) that includes methane, hydrofluorocarbons and tropospheric ozone. These emissions are more powerful than C[O.sub.2] in terms of their warming potential, but they don't last anywhere near as long. Black carbon only remains in the atmosphere for a few weeks at most. "Black carbon is removed quickly by rain, whereas C[O.sub.2] has a lifetime of about 40 years," explains Mark Jacobson, Ph.D., a professor at Stanford University. But black carbon's short, concentrated lifespan offers major global warming reduction potential. Jacobson's research indicates that controlling soot could reduce warming above parts of the Arctic Circle by almost three degrees Fahrenheit within five years, equivalent to reversing virtually all warming that has occurred in the Arctic in the last 100 years.
Black carbon warms the climate in two ways. When it is suspended in the air it absorbs sunlight and generates heat which warms the air and affects cloud formation and precipitation patterns. It absorbs sunlight at all wavelengths and transfers that warmth to the atmosphere with almost a million times the heat-trapping power of C[O.sub.2]. Also, as black carbon falls out of the atmosphere with precipitation, it deposits on snow and ice where it accelerates melting.
More than three-quarters of the world's black carbon is believed to come from developing countries, discharged from wood-burning stoves, open pit burning and old diesel engines. Between 25% and 35% of black carbon in the atmosphere comes from China and India. North America and Europe contribute black carbon emissions mainly via diesel engines. And scientists have observed that North American emissions contribute to black carbon falling on Greenland's ice, while Europe's emissions reach the rest of the Arctic.
A study in Nature Geoscience suggested that black carbon …