[NEW DELHI] The "glacier row" that erupted last week over a claim that the Himalayan glaciers will disappear by 2035 has highlighted important gaps in scientists' understanding.
There is consensus among most experts that many Himalayan glaciers are retreating, with serious implications for the water supply of the millions who live below.
But scientists say that research is too narrow, with insufficient work spanning the whole Himalayan region. Meanwhile some measurement methods are controversial, and the relationship between glaciers and water supply remains unclear.
The controversy arose because of a prediction in the UN Intergovernmental Panel on Climate Change's 2007 report that Himalayan glaciers could disappear by 2035 because of climate change. The prediction was based on one scientist's conversation with a journalist that the former now terms "speculative".
"It may be incorrect to state that Himalayan glaciers will disappear by 2035," said Anil Kulkarni, project coordinator of the snow and glaciers project at India's Space Applications Centre, part of the Indian Space Research Organisation. "But still the larger point should not be missed that many are receding."
Kulkarni's team combined data from two Indian remote sensing satellites with field observations. Their analysis of 1,317 glaciers in the Indian Himalayas, published in a February 2009 issue of a space department bulletin, said the Himalayan glacier area has decreased from 5,866 square kilometres in 1962 to 4,921 square kilometres in 2004 — a 'deglaciation' of 16 per cent.
But while the Himalayan glaciers span eight countries, scientists' work is usually confined to their specific country, said Kang Shichang, a glaciologist at the Institute of Tibetan Plateau Research in China.
"The  dispute comes from researchers who are only focusing on small or limited regions. As the Himalayas extend several thousand kilometres from the west to the east, the climate conditions are quite different."
"It is not [a] surprise that there are differences for glacier changes, even within the Himalayas themselves."
Much glacier research, meanwhile, is simplistic because it studies the movement of the "snout" of the glacier. Although snouts in general have been found to be retreating, snout data reveals little about the overall mass of water.
"Some glaciers can lose a massive amount of ice through lowering of the ice surface while the glacier snout remains more or less stagnant," said Arun Shreshtha, climate change specialist at the International Centre for Integrated Mountain Development (ICIMOD), whose work spans eight countries.
A more sophisticated approach, say scientists, is "mass-balance" studies. But these are still uncommon so that, "ultimately, there is no systematic data", according Andreas Schild, director of ICIMOD, in an interview with SciDev.Net (see Q&A: Andreas Schild and the glacial retreat debate).
Even the consequences of glacier retreat are poorly understood.
Richard Taylor, a hydrologist and hydrogeologist at the United Kingdom's University College London, said: "Actually figuring out the contribution of [retreating] glaciers to river discharge is something where one needs to go over the evidence in detail."
"For the Peruvian Andes it has been overestimated how much of the river discharge actually derives from the glacial meltwaters."
He added that he has not seen clear evidence of how much glaciers contribute to river flow in comparison with groundwater.