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:
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the Internet, visit:
