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August
1, 2007 The team led by
Scripps atmospheric chemistry
professor V. Ramanathan describes findings that atmospheric brown
clouds
enhanced solar heating of the lower atmosphere by about 50 percent in a
paper
to be released in the Aug. 2 edition of the journal Nature.
The combined heating effect of greenhouse gases and the
brown clouds, which contain soot, trace metals and other particles from
a
growing cadre of urban, industrial and agricultural sources, is enough
to
account for the retreat of Himalayan glaciers observed in the past half
century, the researchers concluded. The glaciers supply water to major
Asian
rivers including the Yangtze, Ganges and "The rapid melting
of these glaciers,
the third-largest ice mass on the planet, if it becomes widespread and
continues for several more decades, will have unprecedented downstream
effects
on southern and eastern "The main cause of
climate change is the
buildup of greenhouse gases from the burning of fossil fuels," said
Achim
Steiner, United Nations under-secretary general and executive director
of the
UN Environment Programme (UNEP), which helped support the research.
"But
brown clouds, whose environmental and economic impacts are beginning to
be
unraveled by scientists, are complicating and in some cases aggravating
their
effects. "The new findings
should spur the
international community to ever greater action, in particular at the
next
crucial climate change convention meeting in The scientists
based their conclusions in
large part on data gathered by a fleet of unmanned aircraft during a
landmark
field campaign conducted in March 2006 in the skies over the Such polluted air
has been demonstrated to
have a dual effect of warming the atmosphere as particles absorb
sunlight and
of cooling the earth's surface as the particles curb the amount of
sunlight
that reaches the ground. The net effect of the two forces remains
uncertain but
other research by Ramanathan has suggested that the surface dimming
might serve
to mask global warming, leading scientists and the public to
underappreciate
the full magnitude of anthropogenic climate change. The researchers
validated the data from the
aircraft with ground-based measurements taken at a station at the
Maldivian
island Hanimadhoo. When the
researchers fed both greenhouse gas
and brown cloud data into computer climate models, the simulations
yielded an estimate
that the region's atmosphere has warmed 0.25 degrees C (0.5 degrees F)
per
decade since 1950 at altitudes ranging from 2 to 5 kilometers (6,500 to
16,500
feet) above sea level. At those heights are found many of the glaciers
in the "In order to
understand the processes
that can throw the climate out of balance, Ramanathan and colleagues,
for the
first time ever, used small and inexpensive unmanned aircraft and their
miniaturized
instruments as a creative means of simultaneously sampling of clouds,
aerosols
and radiative fluxes in polluted environments, from within and from all
sides
of the clouds," said Jay Fein, program director in the National Science
Foundation (NSF)'s Division of Atmospheric Sciences. "These
measurements,
combined with routine environmental observations and a state-of-the
science
model, led to these remarkable results." The analysis
revealed that the effect of the
brown cloud was necessary to explain temperature changes that have been
observed in the region over the last half-century. It also indicated
that south
"The conventional
thinking is that brown
clouds have masked as much as 50 percent of the global warming by
greenhouse
gases through the so-called global dimming," said Ramanathan, who is
lead
author of the Nature paper. "While this is true globally, this study
reveals that over southern and eastern In addition to
Ramanathan, the report's
authors include Muvva Ramana, Gregory Roberts, Dohyeong Kim, Craig
Corrigan,
and Chul Chung from Scripps Oceanography and David Winker from the
National
Aeronautics and Space Administration's (NASA's) Langley Research
Center. The NSF provided
the main funding for the
research. Additionally, the ##
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