Melting of West Antarctic's glaciers pass 'point of no return'

The Amundsen Sea region represents only a small part of the whole West Antarctic Ice Sheet, but contains enough ice to raise global ocean levels by 3-4 meters. (Credit: NASA/GSFC/SVS)

Tuesday, May 13, 2014, 10:56 PM - The glaciers of West Antarctica have been melting away at a rather alarming rate in recent years, to the point where over 100 billion tons of ice is being lost each year, and according to two new studies, these glaciers have reached the point of no return, meaning that their collapse is now inevitable.

As West Antarctic loses ice, either as meltwater straight into the ocean or as icebergs calving off to float free from the continent, the majority of that loss is happening along the Armundsen Sea coast. This region, with no fewer than six major glaciers flowing through it, has been experiencing a dramatic increase in ice mass loss since the late 1990s. Along with the losses from the Greenland ice sheet, this has contributed about one-third of the sea level rise that's been measured in recent years. 

Studies by NASA and the University of California, Irvine, and from NASA and the University of Washington, examined satellite data on how fast the glaciers are flowing, how much of each glacier is floating on top of the sea surface, the slope of the terrain under the glaciers and how deep the terrain has been pushed below sea level by the weight of the ice, as well as computer models projecting future scenarios of ice flow. The conclusion that these studies are pointing to is that the loss of ice now appears to have reached a 'point of no return' which will lead to the slow collapse of the entire ice sheet. 

"The collapse of this sector of West Antarctica appears to be unstoppable," said Eric Rignot, a glaciologist with UC Irvine and NASA's Jet Propulsion Laboratory who lead one of the studies. "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. At this point, the end of this sector appears to be inevitable." 

Rignot discusses the findings of his research in this video:

According to Ian Joughin, a glaciologist at the University of Washington’s Applied Physics Laboratory, their research points to a similar conclusion.

"Previously, when we saw thinning we didn't necessarily know whether the glacier could slow down later, spontaneously or through some feedback," he said in a UW press release. "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."

The UW study goes on to say that the Thwaites Glacier - one of the fastest moving ones in the region - acts like a linchpin for the other glaciers. Once it goes, sliding right into the ocean to break up and melt, the others will quickly follow. The West Antarctic ice sheet is estimated to have enough ice in it to raise global sea levels by around 3-4 meters. 

The only good news about all this is that, as pointed out above, this is a slow collapse - at least from our perspective. The estimates from these studies give us somewhere between 200-900 years before this collapse is going to happen, which is nearly instantaneous compared to the tens of millions of years it took for this ice to accumulate on Antarctica. Faster and higher temperature rises, coupled with less snowfall put the collapse closer to the 200 year mark. Slower and lower temperature rises and more snowfall delay the complete collapse the longest.

Read more about the instability of the West Antarctic ice sheet in JPL's primer sheet. The UC Irvine study will appear in an upcoming issue of Geophysical Research Letters, and the UW research will be printed in the May 16 issue of Science.

Sea ice vs land ice

It's inevitable that when loses of ice from Antarctica come up, the subject of record levels of sea ice surrounding the continent come into play - typically in an effort to counter the facts and show there is nothing to worry about. On the contrary, though, the record gains in sea ice around Antarctica are tiny compared to the losses elsewhere (especially in the Arctic), and the gains are a direct result of the ice losses from the glaciers on the Antarctic continent. As water melts and flows off of these glaciers or icebergs calve off and melt, the fresh water from the ice floats atop the denser salt water. Since changes in ocean currents and mixing due to climate change have shifted wind patterns around the south pole, causing that region to warm much slower than the rest of the world, this has caused the south polar vortex to increase in intensity, increasing wind speeds around Antarctica. If it was all salt water around the continent, this wouldn't cause much of a difference in sea ice amounts, but since the fresh water is floating on top and it freezes at a higher temperature than the salt water, it quickly freezes into ice. However, this gain in sea ice is no boon to the region and no counter to ice loses in the Arctic. Unlike the Arctic which (at least currently) retains some sea ice extend in the northern summer, the ice almost completely disappears from around Antarctica in the southern summer. So, the combined loss of land ice and the melting away of sea ice there represents an overall net loss of ice from Antarctica. 

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