1. 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. 2. 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. 3. Soot in areas with snow and ice may play all
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, as glaciers and ice sheet
smelt, they tend to get even dirtier," said Dr. James Hansen, a researcher at
NASA's Goddard Institute for Space Studies, New York. 4. Hansen
found soot's effect on snow albedo (solar energy reflected back to space), which
may be contributing to trends toward early springs in the Northern Hemisphere,
such as 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. 5. "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. 6. Hansen cautioned,
although the role of soot in altering global climate is substantial, it does not
alter the fact that greenhouse gases are the primary cause of climate warming
during the past century. Such gases are expected to be the largest climate
forcing of the rest of this century. 7. 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 were heavy snow cover and sufficient
sunlight. A. Soot's Role in Changes in the Climate and the
Atmosphere B. Observations of Warming in the Northern
Hemisphere C. Explanation of Increased Warming Effect Caused by
Soot D. Effort to Reduce Snow Albedo E. Ways
to Reduce Soot Emission F. Greenhouse Gases as the Main Factor
of Global Warming
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Paragraph 3 ______
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Paragraph 4 ______
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Paragraph 6 ______
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A. produces much more global warming than a carbon-dioxide forcing of the same magnitude
B. contributed to 25 percent of observed global warming
C. can produce greenhouse gases
D. absorb more of sun's energy and warmth than white background
E. still surpass soot in warming the world's climate during the last century
F. can be seen mostly in the Northern Hemisphere
In the twentieth century, soot ______.
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Hansen cautioned that greenhouse gases ______.
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Black soot covered snow and ice ______.
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A soot forcing is unusually effective, which ______