May 29, 2002
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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Contacts:
Krishna Ramanujan
AGU Press Room Washington Convention
Center
(Phone: #202-371-5016)
Cynthia O'Carroll
NASA Goddard Space Flight Center,
Greenbelt, Md.
(Phone: 301/614-5563)
Diane Noserale
U.S. Geological Survey, Reston, Va.
(Phone: 703/648-4333)
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Towns and Cities Affected By Melting Glaciers
This is a "Blue Marble" image from NASA,
"Earth at night" is superimposed on this
(NASA/GSFC), Using the lights as an
indication of population density. The squares
on the map highlight a representative number
of cities within the regions of glacier-fed areas.
All of these areas derive some benefit from
melting glaciers. The implication is that if the
glaciers melt away completely, or substantially,
these areas would be affected. Image:
Courtesy of NASA/GSFC, NOAA/NGDC,
DMSP, GLIMS
Glacial Lakes From Melting and Receding Glaciers
This image from the ASTER (Advanced
Spaceborne Thermal Emission and Reflection
Radiometer) instrument aboard NASA's Terra
Satellite shows the termini (the end) of the
glaciers in the Bhutan-Himalaya. Glacial lakes
have been rapidly forming on the surfaces of
debris-covered glaciers worldwide during the
last few decades.IMAGE COURTESY: Jeffrey
Kargel, USGS / NASA JPL / AGU
The Gangotri Glacier, India: Last 200 Years
This composite image from the ASTER
(Advanced Spaceborne Thermal Emission and
Reflection Radiometer) instrument aboard
NASA's Terra satellite shows how the Gangotri
Glacier terminus has retracted since 1780.
ASTER image courtesy of: NASA EROS Data
Center, Sept. 9, 2001
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