New Delhi, Jan. 27: Some Himalayan glaciers are melting, but others are stable and even growing, German scientists have said in a study that vindicates Indian glaciologists who had trashed predictions that most Himalayan glaciers would disappear by 2035.
The study, which used satellite images to analyse 286 Himalayan glaciers from 2000 to 2008, has found some glaciers losing ice, or retreating up to 80 metres a year, while others are accumulating snow at up to 40 metres per year.
Although retreating glaciers dominate, the retreat rates vary significantly, the researchers said, reporting their findings in the journal Nature Geoscience. More than half of the glaciers in the Karakoram are stable or advancing at about 8 metres per year while heavy rocky debris covers in the south central Himalayas as well as the Hindu Kush appear to be shielding the glaciers from melting.
“We see some dramatic differences in the response of the Himalayan glaciers to climate change,” said Dirk Scherler, a geologist at the University of Potsdam, and the first author of the study. “We find that debris covers can influence the melt rate of glacier.”
Rocky debris can change the amount of sunlight and heat delivered to the ice within the glacier. But most previous attempts to study impacts of climate change on glacial retreat have “largely ignored” the role of debris cover, Scherler told The Telegraph.
Scientists believe the thicker the debris cover, the greater the level of protection from melting. A thin layer of rocky debris — less than 2cm — increases the amount of sunlight absorbed and transmitted to the glacial ice. But a debris layer considerably thicker than 2cm is unable to transmit the absorbed heat to the glacial ice and thus serves as a shield against sunlight-driven melting.
Scherler and his colleagues found that in all regions except Karakoram, more than 65 per cent of the glaciers were retreating — the highest concentration of retreating glaciers was in the western and north central Himalayas with low debris covers. In the Hindu Kush and the central Himalayan region, with high levels of rocky debris covers, the glaciers are retreating at slower speeds.
In Karakoram, 58 per cent of the glaciers were stable or advancing at about 8 metres per year. Scherler said the accumulation of ice by the Karakoram glaciers is possibly because of more snowfall or greater cloudiness which can influence ice levels in the glaciers.
“These results highlight the importance of local factors in glacial response,” said Rajinder Ganjoo, director of the Institute of Himalayan Geology at the University of Jammu. “We’ve been arguing exactly this for more than two years.”
Ganjoo was among Indian glaciologists who questioned in 2009 a prediction by the Intergovernmental Panel on Climate Change (IPCC) — the UN climate change agency — that most Himalayan glaciers would disappear by 2035. India’s environment ministry had published their observations in a discussion paper that triggered a controversy that eventually led to the IPCC conceding that it had no evidence to support the prediction.
The German study has found greater debris in the rugged central Himalayas than in the relatively subdued landscapes of the Tibetan plateau, indicating that local topography can influence the response of glaciers to climate change.
