Sea-Level Rise Of 10 Feet May Be Unavoidable Because Of Melting Linchpin Glacier

By Ben Wolford on May 12, 2014 3:24 PM EDT

This satellite image taken April 13 shows a field of icebergs in Antarctica's Pine Island Bay. Thwaites Glacier, on the bottom right, is retreating rapidly. (Photo: European Space Agency)
This satellite image taken April 13 shows a field of icebergs in Antarctica's Pine Island Bay. Thwaites Glacier, on the bottom right, is retreating rapidly. (Photo: European Space Agency)

Key glaciers in West Antarctica are melting so quickly that nothing is likely to stop them from eventually unleashing 10 feet of sea-level rise over the course of many centuries.

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A pair of papers published today in Science and Geophysical Research Letters show for the first time that Thwaites Glacier is the main linchpin in a melting ice cap — a stopper that, when pulled, cannot be replaced. Many scientists compare West Antarctica to a wine bottle on a slope with a few glaciers acting as the cork. "We are at the point where the bottle has been uncorked," said Eric Rignot, a scientist with NASA's Jet Propulsion Laboratory, in a news conference. "We can't tell exactly when this happened and who did it, but this is a good analogy."

Rignot is the lead author of the Geophysical Research Letters paper, which bases its conclusions on 40 years of observations of Antarctica's most unstable region, known as the Amundsen Sea Embayment. Through satellite images, aircraft-mounted radar, and experiments on the ground, he and his colleagues have determined that warm ocean water will only continue to cause Thwaites and other key glaciers to retreat. They have not discovered any topographical features or changes to the ocean's current that could reverse this process. "It has passed the point of no return," Rignot said.

The map shows Thwaites Glacier, the main outflow of ice from West Antarctica. (Photo: University of Texas)
The map shows Thwaites Glacier, the main outflow of ice from West Antarctica. (Photo: University of Texas)

The research published in Science reaches the same conclusion, though through predictive models rather than strictly observation. Led by Ian Joughin, of the University of Washington, the paper suggests that Thwaites Glacier will melt only modestly over the next 100 years but then rapidly "collapse" after that. Collapse is a relative term; Joughin estimates it could take anywhere from 200-900 years.

Total melting of the glaciers alone would contribute around four feet of sea level rise. But scientists believe that these ice formations act as gates that prevent warm ocean water from reaching the interior of West Antarctica. As they retreat, the rest of the ice sheet will flow more quickly out to sea, enough to contribute some 10 feet of sea-level rise.

Since the 1970s, oceanographers believed that this part of Antarctica could be the entry point for major changes in the Earth's southern ice cap. Ever since the oceans began their modern encroachment on the world's coasts in the late 19th century, Antarctic ice melt has contributed trace millimeters to overall sea-level rise. Most of the 1.7 mm per year sea-level increase is caused by ice loss in the Greenland Ice Sheet and by the swelling of the ocean as it warms. This new research suggests West Antarctica will be a main player in the next century.

Though technically solid, ice moves. In Greenland and Antarctica, the miles-thick sheets of ice are so heavy that they tend to force downward and outward under their own weight. Glaciers are like rivers of ice that channel this movement toward the ocean. Once they reach the ocean, they float out over the water in what's known as an ice shelf and eventually break off in chunks called icebergs. In a stable system, snowfall replaces the ice that is lost, keeping things in balance.

Lately, stronger winds likely caused by climate change have been churning the seas in strange ways. Warmer water deep in the ocean has been creeping toward the ice sheets where they touch the ocean floor, melting this ice and causing the sheets to retreat faster and faster. As this "grounding line" retreats, it allows more ice to flow. Snowfall can't keep pace.

Scientists had long observed this cycle of ice loss, grounding line retreat, and the inability of snowfall to replace what was lost. But more research had been necessary to determine whether Thwaites, Pine Island, and the other glaciers could re-stabilize. If there were a hill upstream, for example, it could act like a door stop. However, radar mapping of the sea floor underneath the glaciers suggests that's not the case. "The chain reaction is at a point that is unstoppable," Rignot says.

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