Re: Black Soot and Snow: A Warmer Combination
- The key conclusion of the study is this: "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."
--- In ClimateArchive@yahoogroups.com, npat1@j... wrote:
> 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
> 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