A new study shows that while some glaciers in the Karakoram region of the northwestern Himalayas, which feed the River Indus, are stable, more than 65 percent of the glaciers fed by monsoons in the central Himalayas are melting.
"Our study shows that there is no uniform response of the Himalayan glaciers to climate change," said Dirk Scherler, one of three researchers who produced the study published in the current edition of Nature Geoscience, a monthly journal.
Scherler and one of his co-researchers, Manfred Strecker, are at the Institute of Earth and Environmental Science at the University Potsdam, Germany, while the third, Bodo Bookhagen, is at the University of California.
"The glaciers [in the Karakoram] might not be melting for a number of reasons… precipitation, cloudiness - it is difficult to say." Moisture brought by the monsoon falls as snow and forms ice, building the glaciers.
The three-year study, one of the first to cover a large area of the Hindu Kush-Himalaya region - sometimes referred to as the Third Pole because it has the largest expanse of frozen water outside of the Polar Regions - looked at remotely sensed changes at the front of the glaciers, and their surface velocities between 2000 and 2008.
Information on the state and behaviour of the region’s glaciers is critical because they feed 10 rivers that provide water to 20 percent of the world's population. Changes in glacier ice or snow-melt affect the glacier’s storage capacity, and the flow of water downstream.
Most scientists acknowledge that rising global temperatures mean more work needs to be done on the Third Pole region, as not enough is known about glaciers.
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A joint study from 1999 to 2003 by the International Centre for Integrated Mountain Development (ICIMOD), a Nepal-based research centre supported by eight governments in the region, the UN Environment Programme (UNEP), and the Asia-Pacific Network for Global Change Research (APN), documented about 15,000 glaciers and 9,000 glacial lakes in Bhutan, Nepal, Pakistan and selected basins in China and India.
Scherler said they had studied 40 glaciers in an area of about 3,000sq km in the Karakoram. "It is a small area if you consider the fact that the entire ice-covered area, according to one estimate, in the Karakoram region is about 16,000 square kilometres."
Monsoon-influenced glaciers have been retreating in the central rugged Himalayan region. The researchers found that debris from the mountains was choking the flow of water into a number of glaciers, which was not a good sign. Scherler said there was a need to study the debris so as to understand the demise of glaciers.
A number of studies between 1999 and 2001 have backed the link between climate change and glacier melting. "The Himalayan glaciers have retreated by approximately a kilometre since the Little Ice Age [from 1350 to 1900]," said a joint study by ICIMOD and UNEP.
"Himalayan glaciers are retreating at rates ranging from 10m to 60m per year, and many small glaciers (less than 0.2sq km) have already disappeared."
A sustained glacier retreat will increase the volume of water in rivers, and also sediments, which can choke water supply, affecting agriculture.
When glaciers retreat, lakes commonly form behind the newly exposed debris - soil and rock called a moraine - carried along by the front edge of the ice wall. The ICIMOD/UNEP study said the rapid accumulation of water in these lakes could lead to a sudden breach of the moraine dam, causing a possibly catastrophic glacial lake outburst flood (GLOF).
In the recent past, Nepal alone has been affected by 21 GLOF events, and 200 potentially dangerous glacial lakes have been documented across the Himalayan region.