South America's glaciers melting faster than in past
Sunday, December 21, 2003
BUENOS AIRES, Argentina -- When Borge Ousland and Thomas Ulrich trekked across the vast and wild Patagonian glaciers, they braved heavy snows and bitterly cold temperatures -- nothing to make them think the ice was melting beneath their feet.
"We got a meter of snow in one night," said Ousland after the pair completed the 54-day crossing of the icefield.
While the two European adventurers became the first to cross the icefields unaided earlier this year, the glaciers made news of their own: A study published in the journal Science found that the Patagonian glaciers melted at twice the rate in 1995-2000 -- when compared with measurements from 1975 to 2000.
Three top scientists used maps, satellite imagery and digital elevation models to measure the change in velocity of 63 Patagonian glaciers over 25 years.
They found the glaciers are losing the equivalent of 10 cubic miles of ice every year -- enough to raise the world's sea level an estimated four-one-thousandths of an inch.
The shrinking is reflective of rising global temperatures, scientists say, and is happening to glaciers around the world. As the melting causes sea levels to rise and freshwater supplies to disappear, scientists warn of potential worldwide economic and environmental disaster if the process isn't reversed.
The biggest factor driving the thinning of Patagonia's glaciers is higher temperatures, said Eric Rignot of the National Aeronautics and Space Administration and one of the study's authors.
But he said the glaciers themselves play a role as many are prone to "calving" -- the process by which icebergs break off into surrounding oceans and lakes.
"These types of glaciers are unstable, and more sensitive to climate change," Rignot said. "If the climate warms, they can go into a state of retreat. Once they start to advance, they do it quickly."
Rignot was joined in the study by Andres Rivera of the University of Chile and Gino Casassa of that country's Center of Scientific Studies.
They reported that the melting of the Patagonian icefields now accounts for 9 percent of annual global sea-level change from mountain glaciers.
Located near the southernmost tip of South America, the Patagonian glaciers cover a remote region totaling 6,600 square miles. Enormous glaciers, some blinding white and others a deep blue, fill a rugged landscape of rivers, fjords and virgin pine forests.
Some parts receive up to 100 feet of snow a year.
Given the size of the Patagonian icefields, Rignot believes their research will help to understand how other large ice sheets, like those of Greenland and Antarctica, will respond to future climate change.
Global temperatures have been warming steadily since the mid-1970s. Some temperature variation is normal, Rivera said, but the increases over the past thirty years are much higher than the natural variation observed before that time.
Many scientists believe greenhouse gases, created by human activity, are the main cause of rising temperatures. But Rignot said scientists cannot be sure that human activity is causing glacier melt.
"Glaciers are melting because it's warmer...," Rignot said. "Whether the cause of warming is from human activity or natural cycles, we can't say for sure."
Higher temperatures, regardless of their cause, can wreak economic and environmental havoc, scientists say.
"The glaciers are a symptom of a global malaise, rather like a fever might indicate that you have a virus," said Raymond Bradley, director of the Climate System Research Center at the University of Massachusetts.
The Patagonian glaciers were hard to study in the past, Bradley said, but with NASA's new radar imaging technology, the glaciers are yielding information that confirms a worldwide phenomenon.
"It turns out what is happening there is what is happening in other places, like Peru, Bolivia and Colombia -- all of the high mountain glaciers are melting," Bradley added.
In North America, similar changes have been noticed in glaciers in Washington state's Cascade mountains, Glacier National Park in Montana and Canada.
Almost 80 percent of the ice on Mount Kilimanjaro in Kenya is gone, Bradley said. New Guinea's glaciers are vanishing, as is Arctic sea ice.
"It's all part of the same phenomenon, which is global warming," Bradley said.
A glacier is an extended mass of ice that forms from snow accumulation over years and then moves slowly outward. As glaciers melt, they can form mountain lakes that can build up and suddenly burst through dams and flood surrounding areas, Rivera said.
This has happened in Peru, Nepal and Alaska.
Italy had a close call this past summer when a lake suddenly formed from melting ice in the Alps, threatening villages below and forcing the Italian army to pump water away.
Still, many communities depend on glacier runoff for their freshwater supplies. Rignot said as glaciers shrink, those supplies are threatened.
"If it rains, you have water," he said. "If it doesn't rain, you have no water."
Rignot cited the near-total disappearance of the Chacaltaya glacier near La Paz, Bolivia, as an example. The city is scrambling to find new freshwater sources, he said. Peru and Ecuador face similar challenges.
The process could reverse itself, albeit slowly, said Rivera.
With decades of cooler temperatures, he said, the Patagonian glaciers could begin to expand again.
If greenhouse gases are reduced, climate trends could start moving in the other direction. "If climate signals change in the future, glaciers will respond," Rivera said.
The scientists hope their study draws attention to the need to protect the Patagonian icefields. "The region is amazing," Rivera said. "It's one of the most beautiful regions on Earth."