The massive glaciers of the Himalayas, which hold one of Earth's largest reserves of snow and ice, have dwindled by one-fifth in the past 4 decades. A team of Indian geologists and remote sensing experts published the alarming news this week--a grim warning that if the trend continues, it could jeopardize the fresh water supply of more than 500 million people in India.
The study, reported 10 January in Current Science, compared data from the oldest known glacial maps of the region (the 1962 Survey of India) to recent data from Indian remote sensing satellites. Anil Kulkarni of the Indian Space Research Organization in Ahmedabad and his team estimated glacial retreat for 466 glaciers in three major river basins, the Chenab, Parbati, and Baspa. They found that glacial extent had declined from 2077 square km in 1962 to 1628 square km at present, or about 21%. At the same time, the number of glaciers increased due to fragmentation. Ice fields and small structures known as glaciarates have shown more extensive deglaciation. For example, 127 glaciarates and ice fields less than 1 sq. km retreated 38% from 1962. "Small glaciers are more sensitive to global warming," Kulkarni notes. The results indicate that glacial fragmentation, higher retreat of small glaciers, and climate change are all influencing the sustainability of Himalayan glaciers.
For India, the crucial question is, how long will it be before the glaciers fade away? A veteran Himalayan geologist, John Shroder of the University of Nebraska at Omaha suggests it won't happen soon. "Overall, the larger Himalayan glaciers are going to last a fairly long time because the mountains are so high." Westerly winds and the monsoon will continue to replenish the snow on top, he says. "But if the monsoon starts to fail in any significant way in the lowlands," a dramatic decline could occur. The dwindling of smaller glaciers is already reducing irrigation water elsewhere in the region, most significantly in central parts of Afghanistan's Hindu Kush. "There you will already see profound drought stress to crops and people," says Shroder, and "this will only add to the political uncertainty in the region."