Environmental News Network
Scientists
studying the Sahara Desert have found that dust particles absorb
much less heat from the sun than previously thought, possibly
reducing the amount of solar warming of the Earth's surface.
 Researchers
are confident that desert dust absorbs far less radiation than
previously thought. Pictured here, a satellite image of dust blowing
off the Sahara Desert.
Yoram Kaufman
of the National Aeronautics and Space Administration's (NASA)
Goddard Space Flight Center in Maryland, said, "Our new results,
produced with two independent sets of remote observations, found
dust absorption to be one to five percent."
This means
that the Earth's surface receives less warmth in areas where dust
lingers in the atmosphere since the dust particles reflect that
radiation back into space.
The results,
published in the April 15 issue of the American Geophysical Union's
Journal of Geophysical Research Letters, suggest that Saharan
dust absorption results could be representative of desert dust
properties around the world.
"The
new results strongly suggest that mineral dust from other regions
of the world will also be less absorbing than previously thought,"
says co-author Lorraine Remer. "So, more dust in the atmosphere
will lower current estimates of warming temperatures in those
areas."
Remer has
studied dust that reached the Channel Islands off the Southern
California coast from Asia and found similar levels of absorption.
Previous estimates
of the ability of dust to absorb the sun's radiation were 10 to
15 percent. The researchers are confident that desert dust absorbs
far less radiation than previously thought.
To arrive
at their findings, the scientists compared two images from NASA's
Landsat 5 Spacecraft of the coast of western Africa, taken two
weeks apart in 1987. One photo was taken during an intense dust
storm and the other was taken when dust levels were much lower.
 A
satellite image records one of the largest Saharan dust storms
ever documented. The photo was taken on Feb. 26, 2000.
The difference
in the brightness of solar radiation reflected by the land surface
and the heavy dust cloud showed that nearly all the sunlight in
the visible and near infrared part of the solar spectrum hitting
the dust cloud was reflected back into space. Very little heat
and light were absorbed by the iron-rich dust particles.
The U.S. Environmental
Protection Agency joins many scientists in saying on its global
warming Web site that determining the extent of global warming
is difficult and there are many complicating factors. For example,
as the ocean warms, evaporation will increase, leading to more
cloud formation.
Clouds play
a dual role in the atmosphere. They cool the Earth by reflecting
incoming radiation, and they warm the Earth by trapping outgoing
radiation underneath.
The amount
of cooling and warming depends on the type, amount and distribution
of clouds. Currently, they appear to cool more than they warm.
If more evaporation occurs, clouds may offset the warming.
Another complicating
factor is gas hydrates (frozen ice with about 90 percent methane)
trapped in the oceans. Warming of the oceans will release vast
amounts of hydrocarbon gases from melting gas hydrates, which
will increase global warming.
In an article
last year in the international science journal Nature, researchers
said that humans, plants and animals could also affect the rate
of global warming. As the global temperature rises and there is
more heat in the atmosphere, evaporation increases and respiration
rates for plants and animals will change. This will affect the
balance of gases in the atmosphere.
Currently
20,000 tons of greenhouse gases go into the atmosphere each year
worldwide. North America and Western Europe, which hold 10 percent
of the world's population, produce 40 percent of global greenhouse
gas emissions.
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