Satellite imagery being presented today shows that the great majority of the world's glaciers are melting at rates equal to or greater than long-established trends, including some that are receding at alarming and accelerating paces.
If the climate warms at an accelerated rate over the next century, as some scientists predict, the glaciers would be adversely affected, scientists said.
Though most glaciers are receding, the joint study by NASA and the United States Geological Survey (USGS) found that a small minority of them are increasing their bulk. Early results of the project are being discussed today by Jeff Kargel, a USGS scientist, at the American Geophysical Union Spring Meeting in Washington, D.C.
The project, which involves scientists from 23 countries, uses satellites to map and examine glaciers throughout the world during the middle to latter part of the melt season when permanent ice is exposed. Current images are compared with older topographical maps and other records.
"Glaciers in most areas of the world are known to be receding," said Kargel, who heads up the project. "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."
When ice melts and pools, the melt rate can increase dramatically. 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 1.4C to 5.8C 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, the research team predicts. 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 more than 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, the researchers say. 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 project primarily draws 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.
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