Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Glaciers not on simple, upward trend of melting

14.02.2007
Two of Greenland's largest glaciers shrank dramatically and dumped twice as much ice into the sea during a period of less than a year between 2004 and 2005. And then, less than two years later, they returned to near their previous rates of discharge.

The variability over such a short time, reported online Feb. 9 on Science magazine's Science Express, underlines the problem in assuming that glacial melting and sea level rise will necessarily occur at a steady upward trajectory, according to lead author Ian Howat, a post-doctoral researcher with the University of Washington's Applied Physics Laboratory and the University of Colorado's National Snow and Ice Data Center. The paper comes a year after a study in the journal Science revealed that discharge from Greenland's glaciers had doubled between 2000 and 2005, leading some scientists to speculate such changes were on a steady, upward climb.

"While the rates of shrinking of these two glaciers have stabilized, we don't know whether they will remain stable, grow or continue to collapse in the near future," Howat says. That's because the glaciers' shape changed greatly, becoming stretched and thinned.

"Our main point is that the behavior of these glaciers can change a lot from year to year, so we can't assume to know the future behavior from short records of recent changes," he says. "Future warming may lead to rapid pulses of retreat and increased discharge rather than a long, steady drawdown."

The findings come on the heels of the widely publicized Intergovernmental Panel of Climate Change's report issued Feb. 2. Some scientists criticized the report for disregarding the surprisingly high discharges of ice from Greenland's glaciers since 2000 when the panel estimated the amount of future sea level rise that will be caused by melting glaciers.

In the summary for policy makers (http://www.ipcc.ch/SPM2feb07.pdf), the Intergovernmental Panel on Climate Change explained its position saying, "Dynamical processes related to ice flow and not included in current models but suggested by recent observations could increase the vulnerability of the ice sheets to warming, increasing sea level rise. Understanding of these processes is limited and there is no consensus on their magnitude."

"I think the IPCC authors made a responsible decision in producing their estimates while noting the recent discharges are a real concern that we do not yet understand well enough to make accurate predictions," says Ian Joughin, a glaciologist with the UW's Applied Physics Laboratory and co-author on the Science Express article.

Getting accurate computer models of Greenland and Antarctic glaciers is important because 99 percent of the Earth's glacial ice is found in those two places. Glacial ice is second only to the oceans as the largest reservoir of water on the planet.

Previous findings published a year ago showed that Greenland's glaciers had doubled their discharge between 2000 and 2005, but these results were based on "snapshots" of discharge taken five years apart, Howat says.

"Did an equal amount of discharge occur every year? Did it happen all in one year? Is there a steady upward trajectory? We didn't know," he says.

Last week's Science Express article adds details from Greenland's second and third largest glaciers, Kangerdlugssuaq and Helheim, in the southwest part of Greenland. The two are known as "outlet" glaciers because their front edges reach all the way to the sea, unlike other glaciers that are landlocked. Together the two glaciers represent 35 percent of East Greenland's total discharge. The scientists examined the glaciers' speed, geometry and discharge between 2000 and 2006.

At Kangerdlugssuaq, roughly 80 percent of the total increase in discharge occurred in less than one year in 2005, followed by a 25 percent drop the following years, the authors say. At Helheim, discharge increased between 2000 and 2003, and then by an even greater amount between 2004 and 2005. It then dropped in 2006 to its near 2000 value.

The scientists say what they've learned is that the shape of these two glaciers changed as they surged toward the sea, changes that put the brakes on. The glaciers lost ice as their front edges began calving, became lighter and floated off the bottom, which led to more ice breaking off as the ice was buoyed up by water. The fronts stablized once the ice had retreated to shallower parts of the fjords and again rested on the bottom.

They also found the pace toward the sea was faster at the front edge of the glaciers than farther up the mountain. For example Kangerdlugssuaq's front edge increased in speed by 80 in 2005 percent while 19 miles inland the speed increased 20 percent. This caused the glaciers to thin, stretch and weigh less overall, which also slowed them down.

"All this in a matter of a few short years for these two glaciers is not the way glaciologists are used to thinking," Howat says. "We're used to thinking of the ice sheets in terms of millennia or centuries."

Sandra Hines | EurekAlert!
Further information:
http://www.washington.edu

More articles from Earth Sciences:

nachricht NASA eyes Pineapple Express soaking California
24.02.2017 | NASA/Goddard Space Flight Center

nachricht 'Quartz' crystals at the Earth's core power its magnetic field
23.02.2017 | Tokyo Institute of Technology

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Stingless bees have their nests protected by soldiers

24.02.2017 | Life Sciences

New risk factors for anxiety disorders

24.02.2017 | Life Sciences

MWC 2017: 5G Capital Berlin

24.02.2017 | Trade Fair News

VideoLinks
B2B-VideoLinks
More VideoLinks >>>