Glaciers high in the Himalayas are dwindling faster than anyone thought, putting nearly a billion people living in South Asia in peril of losing their water supply.
Throughout India, China, and Nepal, some 15,000 glaciers speckle the Tibetan Plateau, some of the highest land in the world. There, perched in thin, frigid air up to 7,200 meters (23,622 feet) above sea level, the ice might seem secluded from the effects of global warming.
But just the opposite is proving true, according to new research published last week in the journal Geophysical Research Letters.
Lonnie Thompson of Ohio State University and a team of researchers traveled to central Himalayas in 2006 to study the Naimona'nyi glacier, expecting to find some melting. Mountain glaciers have been receding all over the world since the 1990s and there was no reason this one, which provides water to the mighty Ganges, Indus, and Brahmaputra Rivers, should be any different.
But when the team analyzed samples of glacier, what they found stunned them. Glaciers around the planet are usually dated by looking for two pulses of radioactivity buried in the ice. These are the leftovers from American and Russian atomic bomb testing in the 1950's and 1960's.
In the Naimona'nyi samples, there was no sign of the tests. In fact, the glacier had melted so much that the exposed surface of the glacier dated to 1944.
"We were very surprised not to find the 1962-1963 horizon, and even more surprised not to find the 1951-1952 signal," Thompson said. In more than twenty years of sampling glaciers all over the world, this was the first time both markers were missing.
He suspects the reason for this is that high-altitude glaciers, despite residing in colder temperatures, are more sensitive to climate change. As more heat is trapped in the atmosphere, he said, it holds more water vapor. And when the water vapor rises to high altitudes it condenses, releasing the heat into the upper atmosphere, where high mountain landscapes feel the brunt of warming.
"At the highest elevations, we're seeing something like an average of 0.3 degrees Centigrade warming per decade," Thompson said. "The Intergovernmental Panel on Climate Change (IPCC) projects 3 degrees of warming by 2100. But that's at the surface; up at the elevations where these glaciers are there could be almost twice as much, almost 6 degrees."
"I have not seen much as compelling as this to demonstrate how some glaciers are just being decapitated," Shawn Marshall of the University of Calgary said.
Marshall, who studies glaciers in North America, said it's striking how much worse glaciers near the equator are than those in the Canadian Rocky and Cascade mountain ranges.
The finding has ominous implications for the hundreds of millions of people who depend on the waters of the Naimona'nyi and other glaciers for their livelihoods. Across the region, no one know just how much water the Himalayas have left, but Thompson said it's dwindling fast.
"You can think of glaciers kind of like water towers, " he said. "They collect water from the monsoon in the wet season, and release it in the dry season. But how effective they are depends on how much water is in the towers."