Glacial Melt Rates Accelerating Across Tibetan Plateau

June 6 issue - "The Chinese ask river gods for protection against floods. Each year tens of millions of Indian Hindus make pilgrimages to the Ganges to seek spiritual cleansing. In impoverished villages from Nepal to Bangladesh, waterways are the lifeblood of society, relied on for everything from drinking water to industry to burial. The veneration that Asians hold for rivers was on Chu Duo's mind as he fiddled with his instruments—a bevy of thermometers, barometers, solar-radiation meters, rainfall gauges—in a small, flat field near Lhasa's Jokhang Temple, Tibet's holiest Buddhist monastery. For the past five years, Chu, a 36-year-old meteorologist at the Tibet Institute of Plateau Atmospheric and Environmental Sciences in Lhasa, has been trying to measure changes in the local climate. He found that temperatures have risen more than 1 degree Celsius since the 1960s, while rainfall has increased. The results aren't out of line with what climate scientists have been finding for other parts of the world. But for the three fifths of the world's people who live in Asia, the prognosis is especially dire.

million-square-kilometer Tibetan Plateau, which stretches from Kazakhstan in the northwest to India in the south, is the main source of Asia's big rivers—the Yangtze, Yellow, Mekong, Indus and Ganges. For hundreds of thousands of years, more than 46,000 glaciers on the plateau have provided a steady flow of water to the lowlands. Each winter the glaciers have grown as snow has piled onto them. In May and June they begin to retreat as some of the ice and snow melt. Until recently, they've stayed pretty much the same size. But during the last several decades, glaciologists have recorded more melting in the summer than gets replaced in the winter. According to Yao Tandong, the director of China's Institute of Tibetan Plateau Research, glaciers on the plateau have retreated an average 7 percent during the past 40 years, and the rate at which they are melting is increasing. For glaciologists, the change has been abrupt: "By nature, glaciers are slow movers," says Yao. "The glacial retreat has happened very suddenly."

Because the glaciers are melting faster than usual, more water is pouring out of the mountains and into the rivers. According to Yao, annual glacial runoff on the Tibetan Plateau and surrounding areas is now equal to the total yearly discharge of the Yellow River, roughly 20 percent more than 40 years ago. Some of that water is making its way into Asia's rivers, increasing floods and spreading waterborne diseases. More of it is pouring into valleys, enlarging old lakes and creating new ones. This glacial melting is expected to continue at least at the present rate for many decades. In the process, it will transform Asia, creating a host of new environmental problems.

The increased melting has already begun to change the region's geography. One lake in northern Tibet, Fuqilin Lake, has risen 20 centimeters a year since 1997, spreading over local pastures and towns, and forcing residents to move to higher ground. Occasionally the lakes break their embankments, emptying tons of water into rivers and even dry valleys and causing devastating flash floods. In Nepal, a series of landslides and flash floods killed more than 350 people and left some 10,000 families homeless in 2003."

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