Runaway Glacier melt in West Antarctica Ice

The leading edge of the floating ice tongue of the Pine Island Glacier, Antarctica. 

Credit: M. Wolovick

Reports that a portion of the West Antarctic Ice Sheet (WAIS) has begun to irretrievably collapse, threatening a 4-foot rise in sea levels over the next couple of centuries, surged through the news media last week.

But many are asking if even this dramatic news will alter the policy conversation over what to do about climate change.

West Antarctic Ice Sheet (WAIS)

Glaciers like the ones that were the focus of two new studies move at, well, a glacial pace. Researchers are used to contemplating changes that happen over many thousands of years.

This time, however, we're talking hundreds of years, perhaps—something that can be understood in comparison to recent history, a timescale of several human generations.

In that time, the papers' authors suggest, melting ice could raise sea levels enough to inundate or at least threaten the shorelines where tens of millions of people live.

"The high-resolution records that we're getting and the high-resolution models we're able to make now are sort of moving the questions a little bit closer into human, understandable time frames," said Kirsty Tinto, a researcher from Lamont-Doherty Earth Observatory who has spent a decade studying the Antarctic.

"We're still not saying things are going to happen this year or next year. But it's easier to grasp [a couple of hundred years] than the time scales we're used to looking at."

The authors of two papers published last week looked at a set of glaciers that slide down into the Amundsen Sea from a huge ice sheet in West Antarctica, which researchers for years have suspected may be nearing an "unstable" state that would lead to its collapse.

The West Antarctic Ice Sheet (WAIS) is mostly grounded on land that is below sea level (the much larger ice sheet covering East Antarctica sits mostly on land above sea level).

Advances in radar and other scanning technologies have allowed researchers to build a detailed picture of the topography underlying these glaciers, and to better understand the dynamics of how the ice behaves.

Where the forward, bottom edge of the ice meets the land is called the grounding line. Friction between the ice and the land holds back the glacier, slowing its progress to the ocean.

Beyond that line, however, the ice floats on the sea surface, where it is exposed to warmer ocean water that melts and thins these shelves of ice.

As the ice shelves thin and lose mass, they have less ability to hold back the glacier.

What researchers are finding now is that some of these enormous glaciers have become unhinged from the land – ice has melted back from earlier grounding lines and into deeper basins, losing its anchor on the bottom, exposing more ice to the warmer ocean water and accelerating the melting.

The glaciers studied by Eric Rignot’s research team. 

Red indicates areas where flow speeds have increased over the past 40 years. 

The darker the colour, the greater the increase. 

The increases in flow speeds extend hundreds of miles inland. 

Credit: Eric Rignot.

In their paper published in Geophysical Research Letters, Eric Rignot and colleagues from the University of California, Irvine, and NASA's Jet Propulsion Laboratory in Pasadena, Calif., described the "rapid retreat" of several major glaciers over the past two decades, including the Pine Island, Thwaites, Haynes, Smith and Kohler glaciers.

"We find no major bed obstacle upstream of the 2011 grounding lines that would prevent further retreat of the grounding lines farther south," they write.

"We conclude that this sector of West Antarctica is undergoing a marine ice sheet instability that will significantly contribute to sea level rise in decades to come."

More information: Widespread, rapid grounding line retreat of Pine Island, Thwaites, Smith and Kohler glaciers, West Antarctica from 1992 to 2011, E. Rignot, J. Mouginot, M. Morlighem, H. Seroussi, B. Scheuchl, Geophysical Research Letters (2014)

Marine Ice Sheet Collapse Potentially Underway for the Thwaites Glacier Basin, West Antarctica, Ian Joughin, Benjamin E. Smith, Brooke Medley, Science (2014)