Sunday, August 19, 2012
What's going on in the Himalayas? Are the glaciers receding or advancing?
There has been much speculation over the past decade that the melting of the glaciers in the Himalayas might cause the rivers that nurture a huge land mass to decline, causing water supply stress for 200,000,000 people in India and China. Recent work has led to the realization that such generalizations cannot, and should not, be made because of the Himalayas are so huge extent and the climate and weather vary considerably along their length.
There is little controversy over the fact that the climate is warming in the Himalayas, and that some glaciers are suffering, particularly in the east. On the other hand, some western glaciers in the Karakoram are growing. The Karakoram is part of the greater Himalaya (which includes the Hindu Kush and other ranges), north of the actual Himalaya Range. The Karakoram includes K2, the second highest peak in the world, at least 20 other peaks over 7,000 meters, and more than 100 peaks over 6100 meters (20,000 feet).
In 2005, Kenneth Hewitt documented evidence that many glaciers in the central Karakoram region were expanding.** These glaciers were "almost exclusively" in basins at the highest elevations. They had been diminishing in size through the mid-1990's and suddenly started expanding, which is a puzzle not yet solved. The flows in the Indus and Yarkand rivers in the western Himalayas have been declining in spite of the glacier expansion, indicating that the extra ice is being stored in the glaciers rather than providing water to the rivers.
Glaciers in the Karakoram generally start in steep tributaries typically between 4500 and 5500 meters, where they consist of icefalls and avalanches that coalesce to form the main ice mass in the drainages. The ice is fairly thin and highly cravassed. Conversion from snow to glacier ice occurs on the time-scale of years or decades rather than centuries as occurs in other places around the world. Much of the movement occurs by collapse of unstable sections rather than by gradual slip along the base of the glacier. Because of the fragmented nature of the ice, more of it is exposed to ambient atmospheric conditions and to meltwater than glaciers which are less heavily fractured.
In the Karakoram, there are three distinct weather systems. Two thirds of snow accumulation on glaciers here occurs in the winter when a westerly circulation and cyclonic storms provide moisture. The remaining 1/3 accumulation occurs during summer snowfall. Solar radiation during the two other weather systems when clear weather occurs accounts for most of the glacier ablation. Since the early 1960's winter precipitation has increased and summer mean and minimum temperatures have declined.
Hewitt strongly warns that the expansion of the Karakoram glaciers does not refute the case for climate change or for atmospheric warming. Rather, warming is the only way to explain these changes with the warming causing the transportation of moisture to higher altitudes than before, thus explaining the growth of the high-altitude glaciers.
**Hewitt, Kenneth. "The Karakoram Anomaly? Glacier expansion and the 'elevation effect,' Karakoram, Himalay, Mountain Research and Development, November 2005, 332-340. This paper gives an excellent general discussion of the dynamics of glaciers.