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Look Out Below: Antarctic Melting From Underneath

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Ice experts have long known that Antarctica is losing ice at the margins of its vast ice sheets, where the frozen continent meets the sea — presumably, they thought, from icebergs breaking off and floating away.

According to a report published in Science, however, more than half the ice loss is coming from warming ocean waters, which are melting the ice from underneath.

"This has profound implications for our understanding of interactions between Antarctica and climate change,” said lead author Eric Rignot, of the University of California, Irvine, in a press release.

More than half of Antarctic's ice loss is coming from warming ocean waters, which are melting the ice from underneath.
Credit: NASA

Those interactions are crucial because Antarctica holds enough ice to raise sea level by a catastrophic 180 feet if it all melted or slid into the sea. That won’t happen anytime soon. But even without significant Antarctic melting, climate scientists project that the oceans, which have already risen by an average of 8 inches since 1900 as a result of heat-trapping greenhouse gases, could go up by another 2 feet or more by the end of this century. Combined with the storm surges that accompany hurricanes and other major coastal storms, the risks to lives and property will continue to grow.

Exactly how fast and how high the sea will rise, however, depends on how the ice sheets on Greenland and Antarctica react to the warming, along with the ice locked in mountain glaciers.

That’s something scientists are still puzzling out. In Antarctica, scientists have become increasingly aware that ice shelves — huge sheets of ice that are partly afloat on the sea — can melt from the bottom up. Since they’re already floating, this doesn’t contribute directly to sea level rise. But glaciologists believe that their mass acts as a brake on the seaward flow of land-based glaciers. If the ice shelves vanish, those glaciers could begin dumping their ice into the sea at a faster rate, which would add to sea level.

Depending on the slope of the sea floor, moreover, the melt rate of some ice shelves could suddenly accelerate. “We don’t necessarily have any evidence for a dramatic change right now,” said Martin Seagirt of the University of Edinburgh, in a 2012 interview with Climate Central, “but it’s on the threshold.”

Still, it wasn’t clear how much of a factor this could be overall. The new study, based on measurements of the ice shelves themselves by NASA aircraft combined with improved maps of the bedrock at Antarctica’s margins and models of regional snowfall, shows that about 1.3 trillion metric tons per year of ice sheet shrinkage between 2003 and 2008 -- or 55 percent of the total -- came from underwater melting, compared with about a trillon tons from iceberg calving. That’s significantly more than anyone had thought.

The study also shows that the melting is uneven, with 85 percent of the ice loss coming from small ice shelves, while the mammoth Filchner, Ross and Ronne shelves contribute just 15 percent.

Overall, the message is that warming water may already be a more important factor in ice loss than warming air, and that the imbalance may continue to grow. The study, Rignot said, “basically puts the Southern Ocean up front as the most significant control on the evolution of the polar ice sheet." 

Related Content 
Sandy's Storm Surge Explained and Why It Matters 
Risks of Hurricane Sandy-like Surge Events Rising 
Around the World, Small Mountain Glaciers Add to Sea Level Rise 
Antarctic Ice Shelves Melting from Below, Study Finds 
The Bad News Continues to Flow About Antarctica's Ice 
Soaring Temps in West Antarctica May Fuel Sea Level Rise

Comments

By Patty Melt (Juno, Alaskya 99850)
on June 18th, 2013

We’ve experienced massive ice melts & no appreciable harm to our planet.

Praise the lord!  The truth has been revealed.

Whatever will be, will be.  Que Sera Sera.

Reply to this comment

By Berynn Schwerdt
on June 20th, 2013

Termites have been eating away the timber holding up my house, but it’s still standing. Que sera sera.

Reply to this comment

By Jim Franklin (Swindon UK.)
on June 20th, 2013

Ice is melting from below…now there is a surprise, has anyone bothered investigating whether the cause of this could in fact be the massive super-volcanic dome that sits below east Antarctica and is responsible for Ross Island which boasts the most southerly identified active volcano (Mt Erebus).

Has anyone considered that the breaking up of the ice on this part of the continent, which is not seen in the West where the ice pack has grown in recent years could be the result of natural tectonic activity below the surface?

Considering the trans-antarctic current assists in protecting the continent from out site ocean influences I think we need to look at all possible causes and either rule them in or out based on credible science not assumptions.

Reply to this comment

By Dave (Basking Ridge, NJ 07920)
on June 20th, 2013

Good point Jim. For instance also:

“The recent discovery of a volcano beneath the West Antarctic Ice Sheet by scientists from the USGS and cooperating institutions is of considerable interest because it indicates a broad regional heating, allowing ice to move more easily.”
http://pubs.usgs.gov/fs/antarctica/

Of course it’s still a warmer ocean whether the source in this case is geothermal, global warming or a combination. If the melting really is accelerating, as it appears to be, then one also wonders what the change in salinity etc may be doing to that circulating current. A trillion tonnes a year plus of basal melting…

Reply to this comment

By Hollington (Minneapolis)
on June 20th, 2013

interesting.
55% of ice melting from 2003-2008 was due to underwater melting.
any idea about how much melting was due to underwater melting in other decades?
say 1973-1978?
that would serve as a control so we could better understand what these new findings mean.

I think calling it “global warming” is a small-minded generalization, unless you can see
and understand what the data is telling you.

unmentioned in this article is the fact that the antarctic ice sheet is at its historical maximum. 
that’s a little piece of data that underscores how difficult it is to understand the world’s climate
from reading just one study.

Reply to this comment

By Neil W. Dorian (Hastings, Fl. 32145)
on May 16th, 2014

Whether one calls for cake or pie at the end of a meal still doesn’t change the actuality of its function as a desert. Calling Climate fluctuations by any other name, ie global warming, global cooling, climate change etc. doesn’t change the fundamental truths that there are significant changes in the enviroment in which we are living and that the preponderance of evidence is that, despite the exact causes, our lives and those of our offspring will be affected in ways we cannot entirely grasp at this time.
Unless we overcome the wall of denial, about whether there is something happening or not, and all pull together to prepare humanity to adapt to these coming changes, we will come to understand the deeper meanings of the end time story in the book that has already been revealed.
  Imagine the sudden consequence of the effects of a caldera eruption underneath the Antarctic Ice Cap. Any disagreement as to whether melting is faster underneath or in the middle or on the top, and how long it will take to raise sea levels to affect our Super Bowl Sundays, all becomes a moot point as we scramble about looking for a Noah like character to let us aboard HIS Ark.As we tread water amid a sea of bobbing heads, maybe then we could put our differences aside to agree that maybe an “Inconvient Truth” was basically correct and the “drill, baby, drill” profit minded folks were incorrect.

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