This is how a glacier retreats.
At nearly 13,000 ft above sea level, in the shadow of a sharp Himalayan peak, a wall of black ice oozes in the sunshine. A tumbling stone breaks the silence of the mountains, or water gurgles under the ground, a sign that the glacier is melting from inside. Where it empties out—scientists call it the snout—a noisy, frothy stream rushes down to meet the Ganga river.
D.P. Dobhal, a glaciologist who has spent the last three years climbing and poking the Chorabari glacier, stands at the edge of the snout and points ahead. Three years ago, the snout was roughly 90 ft farther away. On a map drawn in 1962, it was plotted 860 ft from here. Dobhal marked the spot with a Stonehenge-like pile of rocks.
Dobhal’s steep and solitary quest—to measure the changes in the glacier's size and volume—points to a looming worldwide concern, with particularly serious repercussions for India and its neighbours. The thousands of glaciers studded across 1,500 miles of the Himalayas make up the savings account of South Asia's water supply, feeding more than a dozen major rivers and sustaining a billion people downstream. Their apparent retreat threatens to bear heavily on everything from the region’s drinking water supply to agricultural production to disease and floods.
According to Dobhal’s measurements, the Chorabari’s snout has retreated 29.5 ft every year for the last three years, and while that is too short a time to draw scientific conclusions about the glacier's health, it conforms to a disquieting pattern of glacial retreat across the Himalayas.
A recent study by the Indian Space Research Organization, using satellite imaging to gauge the changes to 466 glaciers, has found more than a 20% reduction in size from 1962 to 2001, with bigger glaciers breaking into smaller pieces, each one retreating faster than its parent.
A separate study found the Parbati glacier, one of the largest in the area, to be retreating by 170 ft a year during the 1990s. Another glacier that Dobhal has tracked, known as Dokriani, lost 20% of its size in three decades. Between 1991 and 1995, its snout inched back 55 ft each year.