May 12, 2014
New Study Declares That The Loss Of West Antarctic Glaciers Is ‘Inevitable’
redOrbit Staff & Wire Reports - Your Universe Online
A rapidly melting region of the West Antarctic Ice Sheet appears to have reached an irreversible state of decline, meaning that nothing can be done to prevent the glaciers from melting into the sea, researchers from NASA and the University of California, Irvine claim in a new study.
The researchers came to that conclusion after analyzing four decades worth of data on glaciers located in the Amundsen Sea sector of West Antarctica. Those glaciers currently contribute significantly to rising sea levels, contributing as much melting ice into the ocean each year as the entire Greenland Ice Sheet.
The glaciers, which contain enough ice to raise global sea levels by four feet, are melting faster than most scientists had expected, lead author, glaciologist and UC Irvine professor Eric Rignot said in a statement Tuesday.
In fact, Rignot said that the Amundsen Sea glaciers have already “passed the point of no return.”
[ Watch the Video: Runaway Glaciers In West Antarctica ]
He added that his team’s findings, which have been accepted for publication by the journal Geophysical Research Letters, will require current predictions of sea level increase to be revised upwardly.
“This sector will be a major contributor to sea level rise in the decades and centuries to come,” Rignot explained. “A conservative estimate is it could take several centuries for all of the ice to flow into the sea.”
According to NASA officials, there are three primary lines of evidence pointing towards the eventual demise of these glaciers: changes to their flow speeds, the percentage of each glacier that floats on seawater, and the slope and depth below sea level of the terrain over which they are flowing.
In a paper published last month, Rignot and his colleagues detailed how the speeds at which the glaciers are traveling have accelerated steadily over the past 40 years, increasing the amount of ice draining from them by more than three-fourths between 1973 and 2013. Their new paper focuses on the other two factors.
The glaciers in the West Antarctic grow out from land over the ocean, with their front edges afloat on the seawater, the researchers said. The point at which they lose contact with land is known as the grounding line, and the overwhelming majority of all glacier melt occurs on the underside of the glacier floating on seawater beyond this line.
“Just as a grounded boat can float again on shallow water if it is made lighter, a glacier can float over an area where it used to be grounded if it becomes lighter, which it does by melting or by the thinning effects of the glacier stretching out,” the US space agency said. The glaciers which Rignot’s team are studying have thinned enough that they can now float above area where they one rested on land, meaning that their grounding lines are moving inland.
“The grounding line is buried under a thousand or more meters of ice, so it is incredibly challenging for a human observer on the ice sheet surface to figure out exactly where the transition is," said Rignot, who is also affiliated with NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. “This analysis is best done using satellite techniques.”
He and his fellow investigators used radar observations captured by the European Earth Remote Sensing (ERS-1 and ERS-2) satellites between 1992 and 2011 to map the inland retreat of those grounding lines. Using a special technique known as radar interferometry, they were able to take precise measurements of how far inland the vertical movements of the glaciers extended in order to locate their grounding lines.
“The accelerating flow speeds and retreating grounding lines reinforce each other. As glaciers flow faster, they stretch out and thin, which reduces their weight and lifts them farther off the bedrock,” NASA said. “As the grounding line retreats and more of the glacier becomes waterborne, there's less resistance underneath, so the flow accelerates.”
“Slowing or stopping these changes requires pinning points -- bumps or hills rising from the glacier bed that snag the ice from underneath,” the agency added. “To locate these points, researchers produced a more accurate map of bed elevation that combines ice velocity data from ERS-1 and -2 and ice thickness data from NASA's Operation IceBridge mission and other airborne campaigns.”
Their analysis confirmed that there were no pinning points located upstream of the current grounding lines in all but one of the six glaciers in the region, with Haynes Glacier serving as the lone exception. The bedrock topography also revealed that the glacier beds slope deeper beyond sea level as they extend further inland, meaning that the warmer ocean water is inescapable and will continue to melt them more quickly.
Considering the accelerating flow rates, the lack of pinning points and sloping bedrock, Rignot said that there is only one possible conclusion: “The collapse of this sector of West Antarctica appears to be unstoppable.”
“The fact that the retreat is happening simultaneously over a large sector suggests it was triggered by a common cause, such as an increase in the amount of ocean heat beneath the floating sections of the glaciers,” he added. “At this point, the end of this sector appears to be inevitable.”