CHACALTAYA GLACIER, Bolivia — Up and down the icy spine of South America, the glaciers are melting, the white mantle of the Andes Mountains washing away at an ever faster rate.

"Look. You can see. Chacaltaya has split in two," scientist Edson Ramirez said as he led a visitor up toward a once-grand ice flow high in the thin air of the Bolivian cordillera.

In the distance below, beneath drifting clouds, sprawled two-mile-high La Paz, a growing city that survives on the water running off the shoulders of these treeless peaks.

Chacaltaya, a frozen storehouse of such water, will be gone in seven to eight years, said Ramirez, a Bolivian glaciologist, or ice specialist.

"Some small glaciers like this have already disappeared," he said as melting icicles dripped on nearby rock, exposed for the first time in millennia. "In the next 10 years, many more will."

They'll disappear far beyond Bolivia. From Alaska in the north, to Montana's Glacier National Park, to the great ice fields of wild Patagonia at this continent's southern tip, the "rivers of ice" that have marked landscapes from prehistory are liquefying, shrinking, retreating.

In east Africa, the storied snows of Mount Kilimanjaro are vanishing. In the icebound Alps and Himalayas of Europe and Asia, the change has been stunning. From South America to south Asia, new glacial lakes threaten to overflow and drown villages below.

In the past few years, space satellites have helped measure the global trend, but scientists such as Rajendra K. Pachauri, a native of north India, have long seen what was happening on the ground.

"I know from observation," Pachauri told a reporter at an international climate conference in Argentina. "If you go to the Himalayan peaks, the rate at which the glaciers are retreating is alarming. And this is not an isolated example. I've seen photographs of Mount Kilimanjaro 50 years ago and now. The evidence is visible."

"Ample" evidence indicates that global warming is causing glaciers to retreat worldwide, reports the Intergovernmental Panel on Climate Change, a U.N.-sponsored network of climate scientists led by Pachauri.

Global temperatures rose about 1 degree Fahrenheit in the 20th century. French glaciologists working with Ramirez and other scientists at La Paz's San Andres University estimate that the Bolivian Andes are warming even faster, currently at a half-degree Fahrenheit per decade.

The warming will continue as long as "greenhouse gases," primarily carbon dioxide from the burning of fossil fuels, accumulate in the atmosphere, say the U.N. panel and other authoritative scientific organizations.