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U.S.A.:BlackSoot Increases Global Warming 

(published by ENS, 15 may 2003)

New York, 15 May 2003 (ENS) – Black carbon particles of soot are more plentiful in theworld’s atmosphere and contribute more to climate change than was previouslyassumed by the Intergovernmental Panel of Climate Change (IPCC), a team ofuniversity and government researchers has found. They conclude that sootcontributes about twice as much to warming the climate than had been estimatedby the IPCC.

The researchers, led byscientists from Columbia University and the National Aeronautics and SpaceAdministration (NASA), concluded if these microscopic soot particles are notreduced at least as quickly as light colored pollutants, the world could warmmore quickly. Both soot and the light colored particles, most of which aresulfates, pose problems for air quality around the world.

The findings appear in thelatest issue of the “Proceedings of the National Academy of Sciences.”The study is authored by James Hansen, Makiko Sato, and others from NASA’sGoddard Institute for Space Studies (GISS) and Columbia University, New York;Oleg Dubovik, Brent Holben and Mian Chin of NASA’s Goddard Space Flight Center,Greenbelt, Maryland; and Tica Novakov, Lawrence Berkeley National Laboratory,Berkeley, California.

“There is a pitfall,however, in reducing sulfate emissions without simultaneously reducing blackcarbon emissions,” Hansen said. Since soot is black, it absorbs heat andcauses warming, he explains. Sulfate aerosols are white, reflect sunlight, andcause cooling. At present, the warming and cooling effects of the dark and lightparticles partially balance.

Sato, Hansen andcolleagues used global atmospheric measurements taken by the Aerosol RoboticNetwork, a global network of more than 100 sun photometers that measure theamount of sunlight absorbed by aerosols, fine particles in the air, atwavelengths from ultraviolet to infrared.

The scientists comparedthe network data with Chin’s global aerosol computer model and a GISS climatemodel, both of which included sources of soot aerosols consistent with theestimates of the Intergovernmental Panel of Climate Change, a group of some2,500 scientists from around the world.

The researchers found theamount of sunlight absorbed by soot was up to four times larger than previouslyassumed. This larger absorption is due in part to the way the tiny carbonparticles are incorporated inside other larger particles – absorption isincreased by light rays bouncing around inside the larger particle, thescientists said.

The larger absorption isattributable also to previous underestimates of the amount of soot in theatmosphere.

Black carbon or soot isgenerated from traffic, industrial pollution, outdoor fires and householdburning of coal and biomass fuels. Soot is a product of incomplete combustion,especially of diesel fuels, biofuels, coal and outdoor biomass burning.

Emissions are large inareas where cooking and heating are done with wood, field residue, cow dung andcoal, at a low temperature that does not allow for complete combustion. Theresulting soot particles absorb sunlight, just as dark pavement becomes hotterthan light pavement, the research team explains.

The research was funded byNASA’s Earth Science Enterprise which is working to understand the Earth as anintegrated system and to apply science to improve the prediction of climate,weather, and natural hazards using the unique vantage point of space.


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