December 22, 2003
Black Soot and Snow: A Warmer Combination
New research from NASA scientists suggests emissions of black soot alter
the way sunlight reflects off snow. According to a computer simulation,
black soot may be responsible for 25 percent of observed global warming
over the past century.
Soot in the higher latitudes of the Earth, where ice is more common,
absorbs more of the sun’s energy and warmth than an icy, white
background. Dark-colored black carbon, or soot, absorbs sunlight, while
lighter colored ice reflects sunlight.
Soot in areas with snow and ice may play an important role in climate
change. Also, if snow- and ice-covered areas begin melting, the warming
effect increases, as the soot becomes more concentrated on the snow surface. “This
provides a positive feedback (i.e. warming); as glaciers and ice sheets
melt, they tend to get even dirtier,” said Dr. James Hansen, a
researcher at NASA’s Goddard Institute for Space Studies, New York.
Hansen and Larissa Nazarenko, both of the Goddard Institute and Columbia
University’s Earth Institute, found soot’s effect on snow
albedo (solar energy reflected back to space), which has been neglected
in previous studies, may be contributing to trends toward early springs
in the Northern Hemisphere, thinning Arctic sea ice, melting glaciers
and permafrost. Soot also is believed to play a role in changes in the
atmosphere above the oceans and land.
“Black carbon reduces the amount of energy reflected by snow back
into space, thus heating the snow surface more than if there were no
black carbon,” Hansen said.
Soot’s increased absorption of solar energy is especially effective
in warming the world’s climate. “This forcing is unusually
effective, causing twice as much global warming as a carbon-dioxide forcing
of the same magnitude,” Hansen noted.
Hansen cautioned, although the role of soot in altering global climate
is substantial, it does not alter the fact greenhouse gases are the primary
cause of climate warming during the past century. Such gases are expected
to be the largest climate forcing for the rest of this century.
The researchers found that observed warming in the Northern Hemisphere
was large in the winter and spring at middle and high latitudes. These
observations were consistent with the researchers’ climate model
simulations, which showed some of the largest warming effects occurred
when there was heavy snow cover and sufficient sunlight.
Hansen and Nazarenko used a leading worldwide-climate computer model
to simulate effects of greenhouse gases and other factors on world climate.
The model incorporated data from NASA spacecraft that monitor the Earth’s
surface, vegetation, oceans and atmospheric qualities. The calculated
global warming from soot in snow and ice, by itself in an 1880-2000 simulation,
accounted for 25 percent of observed global warming. NASA’s Terra
and Aqua satellites are observing snow cover and reflectivity at multiple
wavelengths, which allows quantitative monitoring of changing snow cover
and effects of soot on snow.
The research is in the paper “Soot Climate Forcing via Snow and
Ice Albedos,” appearing online this week in the Proceedings of
the National Academy of Sciences.
This research 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/2003/1223blacksoot.html
A previous, related NASA release, “NASA Finds Soot Has Impact
on Global Climate,” is at:
http://www.gsfc.nasa.gov/topstory/2003/0509pollution.html
###
Contacts:
David E. Steitz
Headquarters, Washington
Phone: 202/358-1730
Rob Gutro/Krishna Ramanujan
Goddard Space Flight Center, Greenbelt, Md.
Phone: 301/286-4044; 607/273-2561
Mary Tobin
Columbia University, New York
Phone: 845/365-8607 |
|
Soot’s Effect on Ice Melt
This is a conceptual animation showing how polar ice reflects light from
the sun. As this ice begins to melt, less sunlight gets reflected into
space. It is instead absorbed into the oceans and land, raising the overall
temperature, and fueling further melting. Darker, soot-covered ice reflects
less light as well, part of the warming effect. Credit: NASA
High-Resolution Top Image
High-Resolution Bottom Image
Ice Melt’s Effect on Land and Sea
This is a conceptual animation showing how melting ice on land and at
sea, can affect the surrounding ocean water, changing both the chemistry
and relative sea level. Credit: NASA
Soot Density
Some climate computer models indicate soot by using colors, such as yellow
and orange. Darker colors indicate more soot. Credit: NASA
Soot’s Effect on Glaciers
Soot also affects melting of alpine glaciers. Some scientists believe
the snow cap of Mount Kilimanjaro will be gone in two decades. Researchers
say the ice fields on Africa’s highest mountain shrank by 80 percent
in the past century. The snow cap formed some 11,000 years ago. The Landsat
satellite captured these images of Kilimanjaro February 17, 1993 and
February 21, 2000. Credit: NASA/USG
Soot Particle Under a Microscope
Credit: D.M. Smith, University of Denver
Snowflake Under a Microscope
This is a hexagonal plate shape with dendritic extensions. Credit: USDA
Beltsville Agricultural Research Center in the Electron Microscopy Unit,
Bld. 177-B, Beltsville Maryland 20705
Pseudo-Color Snow Cristals
Credit: USDA Beltsville Agricultural Research Center in the Electron
Microscopy Unit, Bld. 177-B, Beltsville Maryland 20705
|