While scientists and politicians focus mostly on carbon dioxide, cutting a lesser-known culprit—soot—might offer a more efficient way to slow global warming within the next few decades. Mark Jacobson, an atmospheric scientist at Stanford University, modeled the climate effects of soot and found it to be the second leading cause of warming, right behind carbon dioxide.
Carbon dioxide and other greenhouse gases warm the lower atmosphere by absorbing heat from the earth that would otherwise escape into space. Soot particles do this, too, but they also soak up visible and ultraviolet light from the sun, converting the energy to heat, much as a black dress does on a summer day. Diesel engines, coal-fired generators, forest fires, and wood stoves contribute to the soot problem. Fortunately, the particles have a short life in air, just weeks or months. Eliminating fossil-fuel soot, such as the burnoff from a Canadian oil well, could reduce net global warming by 40 percent within three to five years, Jacobson says, and would improve health. Soot particles lodge deep in the lungs, where they can cause asthma and other diseases. "It's an easy target. But you still can't neglect carbon dioxide. It has a lifetime of 50 to a thousand years," Jacobson says.