The Kyoto Protocol, an international agreement, mandates cutbacks in such emissions, but the reductions are small and the United States, the biggest emitter, is not a party, arguing that the mandates will set back the U.S. economy.

As that pact takes effect Feb. 16, the impact of climate change is already apparent.

An international study concluded in November that winter temperatures have risen as much as 7 degrees Fahrenheit over 50 years in the Arctic, where permafrost is thawing and sea ice is shrinking. Pacific islands are losing land to encroaching seas, oceans expanding as they warm and as they receive runoff from the Greenland ice cap and other sources.

Those sources include at least one gushing new river of meltwater in western China, where thousands of Himalayan and other glaciers are shrinking. In the Italian Alps, 10 percent of the ice melted away in the European heat wave of 2003 and experts fear all will be gone in 20 to 30 years.

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.

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 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 17,500-foot-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.