1 August 2007 - Scientists
have concluded that the global warming trend
caused by the buildup of greenhouse gases
is a major contributor to the melting of Himalayan
and other tropical glaciers. Now a new analysis
of pollution-filled "brown clouds"
over south Asia by researchers at Scripps
Institution of Oceanography at UC San Diego
offers hope that the region may be able to
arrest some of the alarming retreat of such
glaciers by reducing its air pollution.
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 Indus. These rivers in
turn comprise the chief water supply for billions
of people in China, India and other south
Asian countries.
"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
Asia," the Nature article concluded.
"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 Indonesia this December. For it
is likely that in curbing greenhouse gases
we can tackle the twin challenges of climate
change and brown clouds and in doing so, reap
wider benefits from reduced air pollution
to improved agricultural yields," Steiner
added.
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 Maldives, an island nation in the
Indian Ocean south of India. The Maldives
Autonomous unmanned aerial vehicle Campaign
(MAC) took place during the region's dry season
when polluted air masses travel south from
the continent to the Indian Ocean. The air
typically contains particles released from
industrial and vehicle emissions as well as
through biomass burning.
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 aircraft, flying in stacked formations,
made nearly simultaneous measurements of the
brown clouds from different altitudes, creating
a profile of soot concentrations and light
absorption that was unprecedented in its level
of vertical detail.
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 Himalayas. The amount of heating corresponds
to observed levels of glacial retreat.
"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 Asia's warming trend is more pronounced
at higher altitudes than closer to sea level.
"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 Asia, the soot
particles in the brown clouds are intensifying
the atmospheric warming trend caused by greenhouse
gases by as much as 50 percent."
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 National Ocean
and Atmospheric Administration (NOAA) and
NASA provided support as did the UNEP, which
sponsors the Atmospheric Brown Clouds (ABC)
project and operates the Maldives ABC observatory
in collaboration with Scripps.
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Scripps Institution of Oceanography, at the
University of California, San Diego, is one
of the oldest, largest, and most important
centers for global science research and graduate
training in the world. The National Research
Council has ranked Scripps first in faculty
quality among oceanography programs nationwide.
The scientific scope of the institution has
grown since its founding in 1903 to include
biological, physical, chemical, geological,
geophysical, and atmospheric studies of the
earth as a system. Hundreds of research programs
covering a wide range of scientific areas
are under way today in 65 countries. The institution
has a staff of about 1,300, and annual expenditures
of approximately $140 million from federal,
state, and private sources. Scripps operates
one of the largest U.S. academic fleets with
four oceanographic research ships and one
research platform for worldwide exploration.
Source: Nature - International weekly journal
of science