#Antarctic ice shelf collapse could raise sea level by 10 feet in your lifetime


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This rift, photographed during NASA’s Operation IceBridge on Nov. 4, 2016, is the second to form in the center of the ice shelf in the past three years. The first resulted in an iceberg that broke off in 2015.

What is going on under Pine Island Glacier’s ice shelf is something that appears to be remote, distant, and even potentially irrelevant to most of us. Unfortunately, what actually happens there has the potential to greatly impact not just millions, but tens of millions of human lives over the next 100 years or so.

OK, so let’s cut to the chase and spell it out – if the ice shelf collapses, then there is enough water locked up there to raise global sea level by about 10-13 feet.

Evidence?

This is a shocking extraordinary claim, so stepping back and asking what the evidence for this scenario is should be your immediate first reaction.

Well, I have an article in The Daily Express that I can link you to and … nah, just kidding.

There is a new peer-reviewed paper that has just been published within Geophysical Research Letters, a well-respected science journal that has an impact factor of 4.4. The paper is entitled …

Accelerated ice shelf rifting and retreat at Pine Island Glacier, West Antarctic

That link above takes you to the full paper (no paywall). Side note, it will only be open access for 30 days. You can grab a PDF of the paper here.

The abstract explains it as follows …

Pine Island Glacier has undergone several major iceberg calving events over the past decades. These typically occurred when a rift at the heavily fractured shear margin propagated across the width of the ice shelf. This type of calving is common on polar ice shelves, with no clear connection to ocean-ice dynamic forcing. In contrast, we report on the recent development of multiple rifts initiating from basal crevasses in the center of the ice shelf, resulted in calving further upglacier than previously observed. Coincident with rift formation was the sudden disintegration of the ice mélange that filled the northern shear margin, resulting in ice sheet detachment from this margin. Examination of ice velocity suggests that this internal rifting resulted from the combination of a change in ice shelf stress regime caused by disintegration of the mélange and intensified melting within basal crevasses, both of which may be linked to ocean forcing.

OK, yes the paper is a tad technical. The American Geophysical Union do also recognise that this is an important issue, so they also have a far more digestible press release that helps the non-subject matter expert get to grips with it.

You will find that Press Release here.

The story here is that this is about a few researchers noticing something rather odd and that led to an insight. Often science works like this, and so the term “That’s odd” leads to a discovery.

In this case some researchers were testing some new image-processing software and noticed something strange within some satellite images. The software revealed that the images taken in 2013 contained evidence that a rift had formed at the very base of the ice shelf nearly 20 miles inland. What they also knew is that in 2015 a nearly 225-square-mile iceberg broke off from the glacier in 2015 and so this early evidence revealed that the rift they had detected within those 2013 images had propagated from the bottom upward over two years, until it broke through the ice surface and set the iceberg adrift over 12 days in late July and early August 2015.

Clearly something odd was going on.

It was evidence of something that scientists had long suspected …

Rifts usually form at the margins of an ice shelf, where the ice is thin and subject to shearing that rips it apart, However, this latest event in the Pine Island Glacier was due to a rift that originated from the center of the ice shelf and propagated out to the margins. This implies that something weakened the center of the ice shelf, with the most likely explanation being a crevasse melted out at the bedrock level by a warming ocean.

– Ian Howat, associate professor of Earth sciences at Ohio State and lead author of the study

The rift within that 2013 image opened in the bottom of a “valley” in the ice shelf where the ice had thinned compared to the surrounding ice shelf.

The valley is likely a sign of something researchers have long suspected: Because the bottom of the West Antarctic Ice Sheet lies below sea level, warmer ocean water can intrude far inland and remain unseen.

They use the term Ocean Forcing to describe this.

We do also know from a 2014 study in the journal Science that the sea in the area of Pine Island Glacier had warmed by about 0.4°-1°F since the 1990s. It might be small, but that matters. The ice shelf touches ground, but the warmer water eats away at the underneath and so eventually a large section of the ice shelf collapses and breaks away.

Here is a small NASA clip that illustrates ocean forcing causing the grounding line to retreat…

So now we know that new valleys forming on the surface would be one outward sign that ice was melting away far below.

“This kind of rifting behavior provides another mechanism for rapid retreat of these glaciers, adding to the probability that we may see significant collapse of West Antarctica in our lifetimes.”

The really troubling thing is that there are many of these valleys further up-glacier, If they are actually sites of weakness that are prone to rifting, we could potentially see more accelerated ice loss in Antarctica.

Indeed yes, if a warmer ocean continues to push the grounding line further back, then we do have right here a mechanism for rapid ice shelf disintegration.

Implications

That press release spells out the implications of all this as follows ….

More than half of the world’s fresh water is frozen in Antarctica. The Pine Island Glacier and its nearby twin, the Thwaites Glacier, sit at the outer edge of one of the most active ice streams on the continent. Like corks in a bottle, they block the ice flow and keep nearly 10 percent of the West Antarctic Ice Sheet from draining into the sea.

Studies have suggested that the West Antarctic Ice Sheet is particularly unstable, and could collapse within the next 100 years. The collapse would lead to a sea-level rise of nearly 10 feet, which would engulf major U.S. cities such as New York and Miami and displace 150 million people living on coasts worldwide.

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