National Geographic : 2010 Apr
• Glacial melt plays its most vital role before and a er the rainy season, when it supplies a greater portion of the ow in every river from the Yang- tze (which irrigates more than half of China's rice) to the Ganges and the Indus (key to the agricultural heartlands of India and Pakistan). But over the past half century, the balance has been lost, perhaps irrevocably. Of the 680 gla- ciers Chinese scientists monitor closely on the Tibetan Plateau, 95 percent are shedding more ice than they're adding, with the heaviest losses on its southern and eastern edges. " ese gla- ciers are not simply retreating," ompson says. " ey're losing mass from the surface down." e ice cover in this portion of the plateau has shrunk more than 6 percent since the 1970s--- and the damage is still greater in Tajikistan and northern India, with 35 percent and 20 percent declines respectively over the past ve decades. The rate of melting is not uniform, and a number of glaciers in the Karakoram Range on the western edge of the plateau are actu- ally advancing. is anomaly may result from increases in snowfall in the higher latitude--- and therefore colder---Karakorams, where snow and ice are less vulnerable to small temperature increases. e gaps in scienti c knowledge are still great, and in the Tibetan Plateau they are deepened by the region's remoteness and politi- cal sensitivity---as well as by the inherent com- plexities of climate science. ough scientists argue about the rate and cause of glacial retreat, most don't deny that it's happening. And they believe the worst may be yet to come. e more dark areas that are exposed by melting, the more sunlight is absorbed than re ected, causing temperatures to rise faster. (Some climatologists believe this warming feed- back loop could intensify the Asian monsoon, triggering more violent storms and ooding in places such as Bangladesh and Myanmar.) If current trends hold, Chinese scientists believe that 40 percent of the plateau's glaciers could disappear by 2050. "Full-scale glacier shrinkage is inevitable," says Yao Tandong, a glaciologist at China's Institute of Tibetan Plateau Research. "And it will lead to ecological catastrophe." extend far beyond the glaciers. On the Tibetan Plateau, especially its dry northern ank, people are already a ected by a warmer climate. e grasslands and wet- lands are deteriorating, and the permafrost that feeds them with spring and summer melt is re- treating to higher elevations. ousands of lakes have dried up. Desert now covers about one- sixth of the plateau, and in places sand dunes lap across the highlands like waves in a yellow sea. e herders who once thrived here are run- ning out of options. Along the plateau's southern edge, by con- trast, many communities are coping with too much water. In alpine villages like Mingyong, the glacial melt has swelled rivers, with welcome side effects: expanded croplands and longer growing seasons. But such bene ts o en hide deeper costs. In Mingyong, surging meltwater has carried away topsoil; elsewhere, excess run- o has been blamed for more frequent ooding and landslides. In the mountains from Paki- stan to Bhutan, thousands of glacial lakes have formed, many potentially unstable. Among the more dangerous is Imja Tsho, at 16,400 feet on the trail to Nepal's Island Peak. Fi y years ago the lake didn't exist; today, swollen by melt, it is a mile long and 300 feet deep. If it ever burst through its loose wall of moraine, it would drown the Sherpa villages in the valley below. Brook Larmer wrote about Shanghai in the March issue. Jonas Bendiksen photographed the May 2007 story on Dharavi, a slum in Mumbai, India. Most scientists believe the worst may be yet to come. "Full-scale glacier shrinkage is inevitable, " says Yao Tandong of China's Institute of Tibetan Plateau Research. "It will lead to ecological catastrophe. "