Gletsjers zuidoosten Groenland versnellen hun smelt.
Two University of Maine scientists studying the effects of climate change in the Arctic have discovered that two glaciers in Greenland are moving at a not-so-glacial pace. The scientists returned last week from a five-week expedition to the east coast of Greenland, where they studied the movement of five glaciers. They found that two of the glaciers are moving at a far faster rate than just a few years ago, raising the questions about the effects of regional warming.|
One of the glaciers, called Kangerdlugssuaq, was moving at the rate of nearly 9 miles a year, making it one of the world's fastest-moving glaciers, the researchers said. In the late 1990s, it was moving at about 3.5 miles a year. "It's a bit alarming because the ice sheets of Greenland and Antarctica are so larger that it usually takes thousands of years for these types of changes to actually occur, not five or 10 years," said Gordon Hamilton, a professor at the university's Climate Change Institute.
The glaciers' accelerated speeds in Greenland suggest that the climate is warming up, at least in that region, Hamilton said from his office in Orono.
Hamilton used to take measurements of Greenland's glaciers every year in the mid-1990s as part of a NASA endeavor called the Program for Arctic Regional Climate Assessment, or PARCA. More recently, he has been studying Greenland's glaciers at the Climate Change Institute using satellite imagery.
This year, Hamilton and Leigh Stearns, a doctoral student, traveled to Greenland in June aboard Greenpeace's ice cutter, Arctic Sunrise, which was visiting the region on a separate expedition.
For the research, a helicopter flew the pair from the ship to the glaciers, which look like massive snow fields filled with jagged mountains of ice and snow every which way. In all, they studied five glaciers, each of which is about 5 miles wide, 30 miles long and half a mile thick.
To take measurements, they drilled holes into the ice and placed Global Positioning System devices in them to measure precisely the forward motion of the glaciers by satellite. They took readings over the course of several days, calculated the speeds of the glaciers and extrapolated the data into annual measurements.
The three northern glaciers that Hamilton and Stearns visited were moving at about 2.5 miles a year, the same rate they've been moving at since scientists first started measuring them in 1968, Hamilton said.
But that wasn't the case with the two southernmost glaciers, Kangerdlugssuaq and Helheim.
Kangerdlugssuaq was moving at a rate of 8.7 miles a year -nearly half a football field a day -up from 3.5 miles a year in the 1990s. Helheim was moving at about 7.1 miles a year, up from nearly 5 miles a year only four years ago.
"We almost fell off our chairs we were so shocked," Stearns said. "The first thing you do as a scientist when you get a result like that is recheck it and recheck it. I thought I had made a mistake."
The glaciers transport ice from the heart of the Greenland ice sheet to the ocean. When they enter the water, they discharge icebergs that can contribute to sea level rise.
Hamilton said it's thought that the glaciers are moving faster than ever because the ice is melting faster. When the ice melts, the water trickles from the glaciers' surface to the bottom, where it acts as a lubricant on the bedrock on which the glaciers slide.
Sea levels now are rising at a rate of 2 millimeters a year, Hamilton said. At that rate, it would take about 175 years for the oceans to rise one foot.
Having one or two glaciers moving into the oceans at a faster rate wouldn't have a profound effect on sea levels. But there are questions about whether other glaciers worldwide are experiencing the same thing or will in the years ahead.
"That's the major concern. If this starts to happen everywhere, it'll have a big effect," Hamilton said.
Bob Thomas, a former manager for polar sciences at NASA, said he has measured similar accelerated movement of Jakobshavn Isbrae glacier on Greenland's west coast. That glacier, he said, was moving at about 4 miles a year in 1997 but had doubled it's speed by 2003.
"The remarkable thing is that at least three (and almost certainly more) glaciers, widely separated around Greenland, are all accelerating more or less at the same time," Thomas said in an e-mail from Poland. "This suggests a climate trigger, particularly as we know that recent summers have been unusually warm."
Hamilton said he and other scientists are well aware of skeptics who downplay the notion of global warming. But the consensus is not only real it is probably caused by humans.
"Every critic has a different argument on why climate change is a myth or is made up," he said. "But speaking in general terms, the scientific evidence is that climate change has human origins."
Bron oorspronkelijk artikel: Associated Press, 1 augustus 2005
2005 wordt smeltrecord Groenland
Uit de reeks van satellietmetingen van CIRES sinds 1978.