DECLINE
OF WORLD'S GLACIERS EXPECTED TO HAVE GLOBAL IMPACTS OVER THIS CENTURY The
great majority of the world's glaciers appear to be declining at rates equal to
or greater than long-established trends, according to early results from a joint
NASA and United States Geological Survey (USGS) project designed to provide a
global assessment of glaciers. At the same time, a small minority of glaciers
are advancing. Jeff
Kargel, a USGS scientist who will discuss glacier changes and their potential
political and economic impacts at the American Geophysical Union (AGU) Spring
Meeting in Washington, suggests that accelerating climate change over the next
century will directly impact the rate that glaciers retreat. The
research is part of an international effort by glaciologists, coordinated by the
USGS, which uses NASA satellite imagery to map and assess glaciers throughout
the world during the middle to latter part of the melt season when permanent ice
is exposed. Current
glacier satellite images are being compared with topographical maps and other
records of glaciers from the 20th century. The project, called the Global Land
Ice Measurements from Space (GLIMS), includes more than 100 collaborators in 23
countries. "Glaciers
in most areas of the world are known to be receding," said Kargel, who is
also the international coordinator for GLIMS. "But glaciers in the Himalaya
are wasting at alarming and accelerating rates, as indicated by comparisons of
satellite and historic data, and as shown by the widespread, rapid growth of lakes
on the glacier surfaces." While
ice reflects the sun's rays, lake water absorbs and transmits heat more efficiently
to the underlying ice, kicking off a feedback that creates further melting. According
to a 2001 report by the Intergovernmental Panel on Climate Change, scientists
estimate that surface temperatures could rise by 1.4°C to 5.8°C by the
end of the century. The researchers have found a strong correlation between increasing
temperatures and glacier retreat. Glacier
changes in the next 100 years could significantly affect agriculture, water supplies,
hydroelectric power, transportation, mining, coastlines, and ecological habitats.
Melting ice may cause both serious problems and, for the short term in some regions,
helpful increases in water availability, but all these impacts will change with
time, Kargel said. For
example, the Gangotri glacier between Kashmir and Nepal is retreating at an accelerated
rate that cannot be accounted for by lingering effects from warming after the
little ice age over 200 years ago. The Gangotri glacier-and many others-feed the
Ganges River Basin, upon which hundreds of millions of people, including those
in New Delhi and Calcutta, depend for fresh water. Kargel
finds that over one percent of water in the Ganges and Indus Basins (South Asia)
is currently due to runoff from wasting of permanent ice from glaciers. This contribution
is expected to increase as melting rates accelerate, though ultimately the added
runoff is predicted to disappear as glaciers decline many decades from now. Such
changes are important since water use in these basins is already approaching capacity
as populations continue to grow. In drier parts of Asia, like in arid Western
China, wasting glaciers currently account for over ten percent of fresh water
supplies. But
the research finds positive aspects to glacier changes as well. "It's
not all doom and gloom," Kargel said. "Glaciers are wastelands, but
as they recede the land underneath may become available for use." The
net loss or benefit of receding glaciers has not been calculated, but Kargel suspects
the overall impacts will be negative. GLIMS
is designed to monitor the world's glaciers primarily using data from the ASTER
(Advanced Spaceborne Thermal Emission and reflection Radiometer) instrument aboard
the NASA's Earth Observing System (EOS) Terra spacecraft, launched in December
1999. "A
World of Changing Glaciers: Hazards, Opportunities, and Measures of Global Climate
Change," at the AGU Spring Meeting in Washington, D.C., is scheduled on Wednesday,
May 29, session U31A, 9:45 a.m., Washington Convention Center Room WCC30.
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