Glacier melting a key clue to tracking climate change
Glaciers now occupy the center stage in the debate over causes and impacts of climate change.
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Part of the problem is that glaciers are fickle things to measure, said Allison, and requires legwork and lots of bamboo stakes.
These are placed in holes top to bottom, a potentially dangerous job, although satellites and lasers fitted to aircraft are changing this.
After a year or so, stakes placed up high will have had snow build up on them, so you can estimate how much snow fell there.Those down low will have lost mass due to melt and evaporation, so there would be more of the canes sticking out.
"So you can measure how much height is lowered down below, how much it's gained up top. You'll need to know the density of the snow and ice as well," Allison said.
But he said glaciers in one region can all apparently behave differently in response to the same climate signal.
"Because the fluctuations that occur in the front depend on how long it takes to transfer the mass from the top of the glacier to the bottom."
"You might have an area where all the small glaciers are all rapidly retreating but big glaciers still coming forward because they are still integrating changes that happened maybe 50 years ago," he added.
For the millions that live downstream, it is the impacts that are of most concern and among them is the threat of sudden bursting of lakes created as glaciers retreat.
About 14 of the estimated 3,200 glaciers in Nepal are at risk of bursting their dams.Ang Tshering Sherpa, from Khumjung village in the shadows of Mount Everest, said the Imja glacial lake could burst its dam anytime and wash away villages.
"When I was a child I used to take our yaks and mountain goats for grazing on grassy flat land overlooking Everest," Sherpa said."What was a grazing ground for yaks in 1960 has now turned into the Imja due to melting of snow," Sherpa, now a trekking and climbing entrepreneur, said in Kathmandu.
A glacial lake broke its dam 25 years ago destroying trekking trails, bridges and a hydroelectric plant in the region. Neighbouring Bhutan also faces the threat of bursting dams.
Just how much water melting glaciers contribute to major rivers such as the Ganges and Brahmaputra, though, remains unknown.
Richard Armstrong, a senior scientist of the National Snow and Ice Data Center in Boulder, Colorado, said it was nonsense to think that if glaciers melted there would be no water in the Ganges, a lifeline for millions in northern India.
"Even if the glaciers disappeared tomorrow it wouldn't have a huge impact on the water supply. The rest of the river flow comes from rain and melting seasonal snow."
He said the center has put in a proposal to NASA to use satellite data to build a better picture of the area and altitude of glaciers in the Himalayas.
"What we want to look at is what's the contribution of melting glacier ice to the downstream hydrology," Armstrong said. "It's really what's of primary importance to the socio-economic impacts of retreating glaciers."
Allison and Armstrong and many other scientists have dismissed the row over the U.N. climate panel error as overblown but said it served as a useful reminder of the gaps in global glacier monitoring and the need for a far better picture."It certainly brought attention to the problem," said Armstrong.