"If you look at total aerosols (airborne particles), soot is only a small percentage," said Mark Jacobson, an atmospheric researcher at Stanford University in California. Since most aerosols cause dimming of sunlight at the surface, soot's importance is that it also warms the air around it — unlike other common aerosols, like sulfate.
The other chief concern about black carbon is its health effects as an air pollutant, said Jacobson.
The new study also estimates that during springtime, China's black carbon contributions to California's air are equivalent to 75 percent of the state's own black carbon emissions.
And although that's still not a lot, since California has strict controls on diesel use, the effects could still be strong enough to melt snow cover.
"When deposited on snow it has the effect of melting of the snow," said Jacobson.
The earlier mountain snows melt, the less time there is each year for the snowy ground to reflect sunlight back into space and keep things cool. Bare ground, on the other hand, absorbs sunlight and re-emits the light as heat — adding to global warming.
The good news is that unlike the greenhouse gas carbon dioxide, which can last a century in the atmosphere, black carbon lasts only a couple of weeks. So if China cleans up its emissions, this particular climate troublemaker could disappear just as quickly.
