When ice turns to water

Glacial melting poses potentially costly problems for Peru and Bolivia

FOR centuries, the run-off from the glaciers atop the spectacular snow-capped mountains of the Carabaya range has watered the pastures where alpacas graze around the small town of Macusani. More recently, the mountains have provided the town with drinking water and hydroelectricity, as well as hopes of attracting tourists to one of Peru's poorest areas. But in Carabaya, as across the Andes, the glaciers are melting fast. Their impending disappearance has large, and possibly catastrophic, implications for the country's economy and for human life.

Peru is home to the world's biggest expanse of tropical glaciers. Of the 2,500 square kilometres (965 square miles) of glaciers in the four countries of the tropical Andes—Bolivia, Colombia, Ecuador and Peru—70% are in Peru and 20% in Bolivia. The last comprehensive satellite survey by Peru's National Environmental Council, carried out in 1997, found that the area covered by glaciers had shrunk by 22% since the early 1960s. In the Carabaya range, they had receded by 32%.

Partial surveys by geologists suggest that the rate at which the glaciers are melting has speeded up over the past decade. The glacier at Pastoruri, in the Cordillera Blanca range north of Lima, shrank by more than 40% between 1995 and 2006, with the loss of ice caves popular with tourists, according to Marco Zapata, a glaciologist at the government's Natural Resources Institute. He reckons it will be gone by 2015. That is the fate that has already overtaken many smaller glaciers in Bolivia, and that of Cotacachi in Ecuador. Chacaltaya, above Bolivia's capital, La Paz, has almost disappeared; it is the site of the country's only ski resort, whose future is now uncertain.
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