Glaciers in Greenland are dissipating at more than twice the rate they did a decade ago, researchers from the University of Kansas and NASAs Jet Propulsion Laboratory report.
Researchers Pannir Kanagaratnam, at KUs NSF Center for Remote Sensing of Ice Sheets, and Eric Rignot of NASAs Jet Propulsion Laboratory in Pasadena, Calif., write in the Feb. 17 issue of Science magazine that the mass loss of ice through enhanced glacier flow and enhanced runoff is increasing with time, particularly on the periphery of the glaciers. The deterioration is concentrated along channels occupied by outlet glaciers that discharge into the sea.
Even within this short time frame, large-scale changes are being observed, Kanagaratnam said.
The researchers used data from Canadian and European satellites and advanced synthetic aperture radar capable of measuring ice thickness developed by professors and graduate students at KU. With these tools they were able to conduct the first known comprehensive survey of glacial ice discharge rates in Greenland over the past decade.
Previous estimates of mass loss from non-surveyed glaciers relied upon models of ice melt that assumed their ice flow rates did not change over time. A 2004 report authored by Rignot and involving researchers at KU, showed that almost immediately after the 2002 Larsen B ice shelf collapse in Antarctica, glaciers flowed up to eight times faster than they did prior to the break-up. The speed-up also caused glacier elevations to drop, lowering them by up to 125 feet in six months.
Rignot and Kanagaratnam theorized that if glacier acceleration is, in fact, an important factor in the evolution of Greenlands ice sheet, the contribution to sea level rise from Greenland was being underestimated. They decided to measure Greenlands glacial melt rates, determine their variances over time and how those variances affect the discharge of ice from Greenlands ice sheet into the ocean.
Their data, collected through the satellites and airborne radar supported by NASA, indicate the 21 largest glaciers accelerated 28.5 percent between 1996 and 2000 and 57 percent between 1996 and 2005. The flow acceleration varies substantially from glacier to glacier, they report, but is nonetheless widespread and systematic. The researchers found the ice sheet mass balance declined by roughly 220 cubic kilometers about 52.7 cubic miles, or one-tenth the size of Mount Everest in 2005. Its contribution to sea level rise is approximately a half millimeter a year. In 1996, the increase in sea level from Greenlands ice sheets was roughly .2 millimeters.
We do not know how much of it is due to natural climate change and how much of it is due to human influence Kanagaratnam said. But the fact is that temperature is definitely rising, and there is a strong correlation between the temperature rise and sea level rise.
The Science article notes that over the past 12 years parts of Greenland have experienced an increase of average annual temperature of about 5 degrees Fahrenheit. We cannot infer too much from a local temperature change of that magnitude. However, if the temperature of that magnitude extends worldwide, then the glaciers will probably have an irreversible retreat he said.
Engineers and researchers at the Center for Remote Sensing of Ice Sheets (CReSIS) are developing new tools, technology and computer models to better understand what is happening to the earths polar ice sheets.
We are continuing to develop our instruments and signal processing techniques to help get thickness over areas that were difficult to measure before, Kanagaratnam said. The outlet glaciers are especially challenging since the surface (of the bedrock) is very rough and the ice is generally warmer. The radar does not like these situations, but we are developing more sensitive systems and signal processing techniques to measure the thickness in these areas.
In future studies, researchers will more closely examine the conditions of the bedrock hoping to determine whether it is rough, smooth, wet, or dry and pinpoint the role it plays in the mass loss of ice. New radar and computer modeling tools developed at KU will help the team secure this information.
I think it is disconcerting to see the ice melting at such a rapid rate, Kanagaratnam said. There is a large population living in the coastal areas and rising sea levels will affect them. I hope that the research that is being done at CReSIS and other institutions will help nations deal with the impact of climate change.
Kanagaratnam is a research assistant professor at the NSF Center for Remote Sensing of Ice Sheets, based at the University of Kansas. The Center for Remote Sensing of Ice Sheets, which is led by Distinguished Professor Prasad Gogineni, was established in June 2005 with a $19-million grant from the National Science Foundation. Kanagaratnam earned his bachelors, masters and doctoral degrees in electrical engineering from KU. In 1998, he was selected to receive a prestigious NASA graduate fellowship, and in 2003 he won KUs Dorothy Haglund Prize for Outstanding Doctoral Dissertation.
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The NSF Center for Remote Sensing of Ice Sheets headquartered at the University of Kansas