It covers an area of less than 15 acres, with ice less than 26 feet thick. Ramirez said it lost two-thirds of its mass in the 1990s alone, and is now probably a mere 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.