Glacial Region's Melt Past 'Point of No Return,' NASA Says
A rapidly melting glacial region of Antarctica has passed “the point of no return,” threatening to increase sea levels, according to the National Aeronautics and Space Administration.
“The collapse of this sector of West Antarctica appears to be unstoppable,” Eric Rignot, a glaciologist at NASA’s Jet Propulsion Laboratory and the University of California, Irvine, said yesterday in a statement.
NASA estimates the glaciers in the Amundsen Sea region contain enough water to raise global sea levels by 4 feet (1.2 meters). United Nations researchers in September said sea levels have risen by 19 centimeters (7.5 inches) since the Industrial Revolution, and may rise an additional 26 centimeters to 98 centimeters by 2100.
“This sector will be a major contributor to sea level rise in the decades and centuries to come,” Rignot said in the statement. “A conservative estimate is it could take several centuries for all of the ice to flow into the sea.”
The findings are backed up by a separate study due to be published in the journal Science on May 16. Researchers at the University of Washington in Seattle determined that the Thwaites Glacier may already be collapsing. They released their independent findings early to coincide with the NASA paper.
Rignot is lead author of a study that has been accepted for publication in the journal Geophysical Research Letters, NASA said. The team used radar observations from the two European Earth Remote Sensing satellites, ERS-1 and ERS-2, to track the movement of the “grounding lines,” the place where the floating portion of glacier meets land.
They determined that the glaciers have become so thin that they are now floating in areas where they used to be grounded. They found the Pine Island Glacier’s grounding line retreated by 31 kilometers (19 miles) in parts between 1992 and 2011. The Thwaites Glacier retreated as much as 14 kilometers and the Smith/Kohler Glaciers lost about 35 kilometers in places.
As the grounding lines retreat inland, there’s more space below the ice for sea water, which accelerates melting. The researchers also found the masses of ice are flowing faster toward the sea, causing further thinning.
The Thwaites Glacier is already in the early stages of collapse, according to the Science paper, whose lead author is Ian Joughin, a glaciologist at the University of Washington. Losses are likely to be “moderate” this century, before accelerating, and opening up other parts of the Antarctic ice sheet to melt, the researcher said.
“Previously, when we saw thinning we didn’t necessarily know whether the glacier could slow down later,” Joughin said in a statement. “In our model simulations it looks like all the feedbacks tend to point toward it actually accelerating over time; there’s no real stabilizing mechanism we can see.”
Scientists have homed in on the West Antarctic Ice Sheet because the level of melting detected there is greater than the far bigger and more stable Eastern portion of the continent.
Ohio State University glaciologist John Mercer said as long ago as 1968 that the region was a “uniquely vulnerable and unstable body of ice,” according to NASA. In 1978, Mercer wrote in a paper in Nature that man-made carbon dioxide emissions threatened to trigger a “rapid deglaciation” of West Antarctica.
“The alarming thing about the glacial evidence is that the rate of change is happening at a human timeframe as opposed to a geological timeframe,” John Skalbeck, a professor of geoscience at the University of Wisconsin-Parkside, said in a telephone interview. “It’s the rate of change that has geoscientists most alarmed. We’ve not seen these types of rates from the geological past.”
Antarctica’s ice sheets hold enough water to raise sea levels by 58.3 meters (191 feet), though that’s not likely for thousands of years, according to the latest estimate from the United Nations Intergovernmental Panel on Climate Change.