The same view, photographed 88 years apart, affords a striking contrast -- and a much diminished glacier.

David Breashears/Royal Geographic Society



Bolivia's famed Chacaltaya glacier has lost 80 percent of its surface area since 1982, and Peruvian glaciers have lost more than one-fifth of their mass in the past 35 years, reducing by 12 percent the water flow to the country's coastal region, home to 60 percent of Peru's population. And if warming trends continue, the study concluded, many of the Andes' tropical glaciers will disappear within 20 years, not only threatening the water supplies of 77 million people in the region, but also reducing hydropower production, which accounts for roughly half of the electricity generated in Bolivia, Peru, and Ecuador... So far this melting has brought temporary increases in stream flow and contributed to massive Amazonian floods that forced several hundred thousand people from their homes last year.



But within the next decade, scientists predict that this torrent of melt-water will turn into a trickle as glaciers shrink, meaning that the age-old source of water during the dry season will steadily dwindle. Some highland farmers near La Paz already report decreased water supplies.



Before the famed English mountaineer George Mallory died on Mount Everest, he was asked why he wanted to climb it, and his response, perhaps apocryphal, would become the three most famous words in mountaineering: "Because it's there." Something like that impulse had gripped Mallory years prior, when he joined the British Mount Everest Reconnaissance Team in its mission to explore the Himalayas and map a route to the summit now widely known as The Top of the World. Standing in Tibet in 1921, Mallory photographed the north face of the mountain that would claim his life three years later, no doubt marveling at its grandeur. He could scarcely imagine how another mountaineer would use his photograph almost nine decades hence.That mountaineer is David Breashears, who told his story Wednesday at the Aspen Ideas Festival. Undaunted by the scores who've died scaling Mt. Everest across the decades, Breashears summited there five times in three decades. He got to know the sherpas that help climbers ascend its slopes. They spoke of changes -- about less snow around the mountain, and more heat.But he didn't grasp how fast things were changing until 2007.Trekking in Tibet that year, he took out a reproduction of the old George Mallory photograph. "It showed the ice-encrusted north face of Everest and, below it, the great river of ice known as the Main Rongbuk Glacier, flowing in a sweeping, S-shaped curve down a broad, stony valley," he wrote in a magazine article about his efforts. "Eighty-six years after Mallory took that photograph, I sat in the exact spot where he had snapped his iconic picture. Pulling out his photo, I was stunned by the changes that had swept over this region. The wide river of ice had retreated more than half a mile, leaving a field of separated ice pinnacles melting into the rocky ground. In the distance, the ice streams on Everest's flank also had shrunk, exposing more of the mountain's dark face."The juxtaposition struck him so powerfully that he's been trying to reproduce the same experience ever since. As it turns out, a lot of early mountaineers photographed Mt. Everest, it being there and all. They took other photographs in the Himalayas too. What they captured on film are now the "before" images that The Glacier Research Imaging Project juxtaposes with "after" photos of the same spot today. Breashears helped found the project, and held forth Wednesday about the sophisticated "after" images it is producing (the one above is the Kyetrak glacier in the Cho Oyu region).He acknowledges that two data points captured many years apart do not tell us anything conclusive. But having observed the Himalayas over many years, and after studying them intensely in recent years, he is alarmed at the loss of ice. "The loss of these frozen reservoirs of water will have a huge impact, as the glaciers provide seasonal flows to nearly every major river system in Asia. From the Indus, Ganges, and Brahmaputra in South Asia, to the Yellow and Yangtze Rivers in China, hundreds of millions of people are partially dependent on this vast arc of high-altitude glaciers for water," he recently wrote. "As the glaciers recede and release stored water, flows will temporarily increase. But once these ice reservoirs are spent, the water supply for an overpopulated continent will be threatened, and the impacts on water resources and food security could be dire."It's a warning with echoes elsewhere. As Carolyn Kormann put it in a 2009 feature on the retreat of Andean glaciers:In his Wednesday talk, Breashears predicted that the images he's producing will have a huge impact on the next generation and its attitudes toward climate change. "The data doesn't resonate. There is no imagery that corresponds to what we see in the charts," he said. But detailed, high resolution imagery of faraway glaciers and the ways that they're losing ice over time?He believes they'll prove uniquely persuasive.