Such rapid runoff would do more than feed rising seas. It would end centuries of reliable flows through populated lands, jeopardizing water supplies for human consumption, agriculture and electricity.
In Peru, endowed with vast Andean ice caps and glaciers, 70 percent of the power comes from hydroelectric dams catching runoff, but officials fear much of it could be gone within a decade. Meanwhile, new mountainside lakes are bulging from the melt, threatening to break their banks and devastate nearby towns.
Here in impoverished Bolivia, the government has barely begun to plan for climate change.
Water Assessments
Tomas Quisbert, a hydrological engineer with the water company serving the 2 million people of the La Paz region, said 95 percent of its supplies come from the mountains, either from rain runoff or glacier melt.
"But we can't say precisely how much comes from the glaciers," he said.
Ramirez and fellow scientists are seeking government support to do a complete assessment of water in the La Paz basin, linked to computer modeling of future regional climate and its impact.
They'll soon move on from 5,300m-high Chacaltaya -- "Cold Road" in the native Aymara language -- as it shrinks toward oblivion. But in 13 years of intense study of the glacier, the scientists have gathered a rich lode of data representative of countless small glaciers across the region.
A rugged hour's drive up from La Paz, with a simple mountain lodge beside it, Chacaltaya was once the world's highest ski slope. But no one has skied down its tongue of snow-coated ice since 1998. The melt has exposed rock right across its midsection, splitting the glacier in two.
It covers an area of less than six hectares, with ice less than 7.8m thick. Ramirez said it lost two-thirds of its mass in the 1990s alone, and is now probably 2 percent the size it once was.
Chacaltaya and other Andean glaciers had been retreating since the 18th century, when the "Little Ice Age" ended locally, but the rate has picked up dramatically in recent decades, melting three times faster since the 1980s than in the mid-20th century.
Although rising temperatures are an underlying factor, glaciologists find a complex cycle at work: A warming Pacific Ocean has created disruptive El Nino climate periods more frequently and powerfully, reducing precipitation, including snows to replenish glaciers. Less snow also means glaciers that are less white, more gray, absorbing more heat. Newly exposed rock walls then act like an oven to further speed melting.
Whatever the regional wrinkles, "it's a global view," said Lonnie Thompson, one of the world's foremost glaciologists.
"What we see in the Andes is happening in Kilimanjaro and in the Himalayas. We've just been in southeast Alaska, and 1,987 out of 2,000 glaciers are retreating there," the Ohio State University scientist said in a telephone interview from Columbus.
"It's a very compelling story," he said. The glaciers -- "water towers of the world" -- are the most visible indicators that we are now in the first phase of global warming, Thompson said.
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