Jacobson said the sum of warming caused by all anthropogenic greenhouse gases CO2, methane, nitrous oxide, chlorofluorocarbons and some others plus the warming caused by black and brown carbon will yield a planetary warming effect of 2 degrees Celsius over the 20-year period simulated by the computer. But light-colored particles white and gray particles primarily reflect sunlight and enhance cloudiness, causing more light to reflect.
"The cooling effect of these light-colored particles amounts to slightly more than 1 C," Jacobson said, "so you end up with a total net warming gain of 0.9 C or so. Of that net gain, we've calculated that biomass burning accounts for about 0.4 C."
Jacobson's model also tracks the impact of the direct heat produced by combusting biomass.
"The direct heat generated by burning biomass is significant and contributes to cloud evaporation by decreasing relative humidity," Jacobson said. "We've determined that 7 percent of the total net warming caused by biomass burning that is, 7 percent of the 0.4 C net warming gain can be attributed to the direct heat caused by the fires."
Biomass burning also includes the combustion of agricultural and lumber waste for energy production. Such power generation often is promoted as a "sustainable" alternative to burning fossil fuels. And that's partly true as far as it goes. It is sustainable, in the sense that the fuel can be grown, processed and converted to energy on a cyclic basis. But the thermal and pollution effects of its combustion in any form can't be discounted, Jacobson said.
"The bottom li
|Contact: Tom Abate|
Stanford School of Engineering