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David E. Steitz
Headquarters, Washington                         May 13, 2003
(Phone: 202/358-1730)

Robert J. Gutro                         Mary Tobin 
Goddard Space Flight Center             Columbia University
(Phone: 301/286-4044)                   (Phone: 845/365-8607)

Allan Chen
Lawrence Berkeley National Laboratory
(Phone: 510/486-4210)

RELEASE: 03-168

NASA FINDS SOOT HAS IMPACT ON GLOBAL CLIMATE 

     A team of researchers, led by NASA and Columbia
University scientists, found airborne, microscopic, black-
carbon (soot) particles are even more plentiful around the 
world, and contribute more to climate change, than was 
previously assumed by the Intergovernmental Panel of Climate 
Change (IPCC).

The researchers concluded if these soot particles are not 
reduced, at least as rapidly as light-colored pollutants, the 
world could warm more quickly.

The findings appear in the latest issue of the Proceedings of 
the National Academy of Sciences. It is authored by Makiko 
Sato, James Hansen and others from NASA's Goddard 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, Md.; and Tica Novakov, 
Lawrence Berkeley National Laboratory, Berkeley, Calif.

Sato, Hansen and colleagues used global atmospheric 
measurements taken by the Aerosol Robotic Network (AERONET). 
AERONET is a global network of more than 100 sun photometers 
that measure the amount of sunlight absorbed by aerosols 
(fine particles in the air) at wavelengths from ultraviolet 
to infrared. The scientists compared the AERONET data with 
Chin's global-aerosol computer model and GISS climate model, 
both of which included sources of soot aerosols consistent 
with the estimates of the IPCC.

The researchers found the amount of sunlight absorbed by soot 
was two-to-four times larger than previously assumed. This 
larger absorption is due in part to the way the tiny carbon 
particles are incorporated inside other larger particles: 
absorption is increased by light rays bouncing around inside 
the larger particle.

According to the researchers, the larger absorption is 
attributable also to previous underestimates of the amount of 
soot in the atmosphere. The net result is soot contributes 
about twice as much to warming the world as had been 
estimated by the IPCC.

Black carbon or soot is generated from traffic, industrial 
pollution, outdoor fires and household burning 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 in areas where cooking 
and heating are done with wood, field residue, cow dung and 
coal, at a low temperature that does not allow for complete 
combustion. The resulting soot particles absorb sunlight, 
just as dark pavement becomes hotter than light pavement.

Both soot and the light-colored tiny particles, most of which 
are sulfates, pose problems for air quality around the world. 
Efforts are beginning to reduce the sulfate aerosols to 
address air quality issues.

"There is a pitfall, however, in reducing sulfate emissions 
without simultaneously reducing black carbon emissions," 
Hansen said. Since soot is black, it absorbs heat and causes 
warming. Sulfate aerosols are white, reflect sunlight, and 
cause cooling. At present, the warming and cooling effects of 
the dark and light particles partially balance.

This research continues observations of global climate 
change. It was funded by NASA's Earth Science Enterprise. The 
Enterprise is dedicated to understanding the Earth as an 
integrated system and applying Earth System Science to 
improve prediction of climate, weather, and natural hazards 
using the unique vantage point of space.

For more information and images on the Internet, visit:

http://www.gsfc.nasa.gov/topstory/2003/0509pollution.html

For information the about the AERONET program on the 
Internet, visit:

http://aeronet.gsfc.nasa.gov/

For information about NASA and Earth Science initiatives on 
the Internet, visit:

http://www.nasa.gov

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