Bloomberg.com
Alex Morales
January 12, 2009 01:15 EST
Jan. 12 (Bloomberg) -- The rapid shrinking of glaciers in Greenland during recent years may stall, diminishing the Arctic island’s potential contribution to rising sea levels blamed on global warming, a U.K.-led research team found.
The study in the journal Nature Geoscience indicates the faster-than-normal ice loss observed in many of Greenland’s glaciers in the early 2000s won’t be sustained, said Andreas Vieli, a glaciologist at Durham University in northern England.
“Our modeling suggests that these very high rates of glacier retreat can’t be maintained for very long,” Vieli, a co-author of the paper, said in a telephone interview.
Scientists are improving their knowledge of glaciers so the data can be used to predict their longevity. Greenland contains enough ice to raise sea levels by about 7 meters (23 feet), threatening coastal villages around the world, if it melted.
A United Nations global warming panel said in 2007 that melting ice may contribute to rising oceans this century while acknowledging that uncertainty surrounds how much ice Greenland will lose. The latest findings may help calibrate UN models.
The Durham University-led scientists used a computer model to analyze changes in Helheim Glacier, in southeast Greenland. They concluded the driver of the melting was a break at its snout in the sea that had a domino effect inland. They also found glaciers stabilize after an initial rapid retreat.
While the researchers studied one glacier, they said their findings apply to glaciers in similar terrain that are grounded at their snout in a trough reaching below sea-level. The scientists didn’t use their model to predict future melting of Greenland’s glaciers caused by global warming.
Discarded Theory
Helheim retreated by 7 kilometers (4 miles) over three years ending in 2005, losing 15 million tons more of ice than in 2000 at its peak, according to a February 2007 study in the journal Science. It’s since advanced about 4 kilometers, Vieli said.
Vieli and his colleagues used a computer model to test two hypotheses as to the cause of Helheim’s retreat. One is that increased melt-water was lubricating the base of the glacier and accelerating its passage to the sea. The other is that a break-off of the ice mass’s snout triggered a domino effect back along the glacier. Using the lubrication theory, they couldn’t replicate the glacier’s observed sudden retreat. The second hypothesis proved a close match and is the likely cause, Vieli said.
“We found was that these outlet glaciers are extremely sensitive to fluctuations in climate and ocean temperature at the terminus,” Vieli said. “When temperatures go up a bit, there’s a strong reaction in terms of mass loss: They start to flow fast and thin rapidly. But also, they adjust very quickly to the new temperature or climate setting.”
Predicting Future
Researchers at the University of Texas at Austin in 2006 said in Science that melting of Greenland’s ice sheet had “increased dramatically,” prompting a debate among a panel of scientists and policy makers that produced the UN’s most detailed study of global warming, in 2007. The group is known as the Intergovernmental Panel on Climate Change, or IPCC.
The IPCC forecast seas will rise by 18 to 59 centimeters (7 to 23 inches) by 2100, while acknowledging “limited” understanding of the dynamics of Greenland’s ice sheet. Observations made since 2003 weren’t included in the UN analysis.
The latest study will help scientists to tune existing computer models for ice sheets to predict future melting, Vieli said.
“The big ice sheet models which have been used for the IPCC 2007 report to figure out how much ice-loss and sea-level rise there will be in the future can’t reproduce these dynamic changes of outlet glaciers,” Vieli said. “We showed that we’re not far away from modeling this. We need a bit more time and development.”
http://www.bloomberg.com/apps/news?pid=20601100&sid=aXm16yRTS344&refer=germany
Alex Morales
January 12, 2009 01:15 EST
Jan. 12 (Bloomberg) -- The rapid shrinking of glaciers in Greenland during recent years may stall, diminishing the Arctic island’s potential contribution to rising sea levels blamed on global warming, a U.K.-led research team found.
The study in the journal Nature Geoscience indicates the faster-than-normal ice loss observed in many of Greenland’s glaciers in the early 2000s won’t be sustained, said Andreas Vieli, a glaciologist at Durham University in northern England.
“Our modeling suggests that these very high rates of glacier retreat can’t be maintained for very long,” Vieli, a co-author of the paper, said in a telephone interview.
Scientists are improving their knowledge of glaciers so the data can be used to predict their longevity. Greenland contains enough ice to raise sea levels by about 7 meters (23 feet), threatening coastal villages around the world, if it melted.
A United Nations global warming panel said in 2007 that melting ice may contribute to rising oceans this century while acknowledging that uncertainty surrounds how much ice Greenland will lose. The latest findings may help calibrate UN models.
The Durham University-led scientists used a computer model to analyze changes in Helheim Glacier, in southeast Greenland. They concluded the driver of the melting was a break at its snout in the sea that had a domino effect inland. They also found glaciers stabilize after an initial rapid retreat.
While the researchers studied one glacier, they said their findings apply to glaciers in similar terrain that are grounded at their snout in a trough reaching below sea-level. The scientists didn’t use their model to predict future melting of Greenland’s glaciers caused by global warming.
Discarded Theory
Helheim retreated by 7 kilometers (4 miles) over three years ending in 2005, losing 15 million tons more of ice than in 2000 at its peak, according to a February 2007 study in the journal Science. It’s since advanced about 4 kilometers, Vieli said.
Vieli and his colleagues used a computer model to test two hypotheses as to the cause of Helheim’s retreat. One is that increased melt-water was lubricating the base of the glacier and accelerating its passage to the sea. The other is that a break-off of the ice mass’s snout triggered a domino effect back along the glacier. Using the lubrication theory, they couldn’t replicate the glacier’s observed sudden retreat. The second hypothesis proved a close match and is the likely cause, Vieli said.
“We found was that these outlet glaciers are extremely sensitive to fluctuations in climate and ocean temperature at the terminus,” Vieli said. “When temperatures go up a bit, there’s a strong reaction in terms of mass loss: They start to flow fast and thin rapidly. But also, they adjust very quickly to the new temperature or climate setting.”
Predicting Future
Researchers at the University of Texas at Austin in 2006 said in Science that melting of Greenland’s ice sheet had “increased dramatically,” prompting a debate among a panel of scientists and policy makers that produced the UN’s most detailed study of global warming, in 2007. The group is known as the Intergovernmental Panel on Climate Change, or IPCC.
The IPCC forecast seas will rise by 18 to 59 centimeters (7 to 23 inches) by 2100, while acknowledging “limited” understanding of the dynamics of Greenland’s ice sheet. Observations made since 2003 weren’t included in the UN analysis.
The latest study will help scientists to tune existing computer models for ice sheets to predict future melting, Vieli said.
“The big ice sheet models which have been used for the IPCC 2007 report to figure out how much ice-loss and sea-level rise there will be in the future can’t reproduce these dynamic changes of outlet glaciers,” Vieli said. “We showed that we’re not far away from modeling this. We need a bit more time and development.”
http://www.bloomberg.com/apps/news?pid=20601100&sid=aXm16yRTS344&refer=germany
