The weak underbelly of a giant Antarctic ice sheet just lost a berg more than four times the size of Manhattan

By Tom Yulsman | September 26, 2017 10:00 am
The Sentinel1 satellite captured this image of a 100-square-mile chunk of ice calving from Antarctica's Pine Island Glacier on September 23, 2017. (Source: Stef Lhermitte)

The Sentinel-1 satellite captured this image of a 100-square-mile chunk of ice calving from West Antarctica’s Pine Island Glacier on September 23, 2017. (Source: Stef Lhermitte)

We’ve now got yet another worrying sign that human-caused warming is causing the behemoth West Antarctic Ice Sheet to come unglued, threatening to raise sea level by 10 feet over time.

You can see that sign in the image above from the Sentinel-1 satellite.

The image shows a 103-square-mile tabular iceberg — equal in size to four and a half Manhattan islands — breaking off from the floating edge of the Pine Island Glacier in West Antarctica on September 23rd. It was posted to Twitter by Stef Lhermitte, a remote sensing expert at Delft University of Technology in the Netherlands.

The glacier is like a cork in a bottle, helping to restrain nearly 10 percent of the West Antarctic Ice Sheet from pouring out into the sea.

As the September 23rd calving event shows, the cork is eroding.

That was not the first time a chunk of the cork broke loose. In a very similar event in 2015, an iceberg twice as large calved from the glacial front. You can see that event in this time-lapse of Sentinel-1 images, as well as growth of the rift that led to the Sept 23rd calving:

study published last year provides insight into what’s going on. Essentially, the floating ice shelf portion of the glacier appears to be breaking up from the inside out.

The study showed that the 2015 calving event had its origins when a rift formed at the base of the ice shelf — and in the center, not at its edges as is typically seen. Over two years it grew upward, broke through the surface, and propagated outward toward the margins of the shelf, eventually setting the iceberg loose in late July and early August of 2015.

The same things seems to have happened with this latest event.

“Rifts usually form at the margins of an ice shelf, where the ice is thin and subject to shearing that rips it apart,” explained Ian Howat, a glaciologist at Ohio State and lead author of the study, quoted in a release from the American Geophysical Union. So why is the Pine Island Glacier behaving differently?

Something must have 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,” according to Howat.

In 2014, research showed that the Amundsen Sea Embayment in West Antarctica, into which the Pine Island Glacier flows, is hemorrhaging ice faster than any other part of the continent. The study found that the melt rate of glaciers in this fastest-melting part of Antarctica tripled in just a decade.

And in spring of 2014, two separate studies suggested that a large portion of the West Antarctic Ice Sheet, or WAIS, had passed the point of no return. Thanks to warm water intrusion beneath them, the research showed that the WAIS had begun an irreversible retreat.

If that’s true, over the course of a 100 years or so, the ice draining from the WAIS would raise sea level 10 feet, eventually swamping entire cities.

Here’s how I described it in a story for Discover magazine’s Year-in-Science issue:

Imagine you’re canoeing the Niagara River when you notice mist ahead. You’re still quite a distance from Niagara Falls, but the river’s swift: There’s no turning back.

Two separate studies published last spring suggest that climate change has carried the West Antarctic Ice Sheet, or WAIS, across a similar threshold. The glaciers that flow off WAIS and dump ice into the sea already have contributed nearly 10 percent to the recent increase in global sea levels.

The research suggests that for a large portion of WAIS, this process “has passed the point of no return,” says Eric Rignot of the University of California, Irvine, the lead author of one of the studies. That means the ice sheet is now in irreversible retreat, and steps to slow global warming won’t stop the ice sheet from raising the sea level 10 feet, swamping cities. But there is a silver lining: Full collapse may take centuries, perhaps providing time to move populations at risk out of the way.

The most recent calving event from the Pine Island Glacier is actually the sixth major one since the year 2000, according to Stef Lhermitte. But 2015 and 2017 “are different from previous events as the calving results from internal rifts with calving fronts further inland,” he wrote in a Tweet on September 23rd.

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  • Matthew Slyfield

    And how many Manhattans is the entire Antarctic Ice sheet? 1,000,000? 2,000,000

    How about being more honest and presenting iceberg sizes in percentages of the total Antarctic ice sheet volume. The only reason it isn’t done that way is because doing it that way would make these “giant” icebergs seem as insignificant as they really are.

    • Russ Beauchemin

      Know anyone in the Houston area? They may be able to clarify the meaning of the word “significant” for you.

      • OWilson

        Remember that hoarding is counter-productive! :)

    • Erik Bosma

      Cork, bottle…were you paying attention?

    • Tom Yulsman

      Please read my story in full with an open mind. Then if you still have criticisms, we can talk about it.

  • CaptainA

    The Antarctic ice sheet is about 7,000,000 square miles. The 103 sq mile section is therefore approx. 0.0014714 % of the ice sheet. C’mon guys, this is nothing unusual.

    • Erik Bosma

      A cork is also much smaller than a bottle.

    • Tom Yulsman

      Perhaps you should read the entire story and click on the links to check out the scientific papers before you render judgment.

    • HoiPolloiBoy

      The global warming alarmists always compare everything to the size of Manhattan to get the attention of the educated ignoramuses that drive the media.

      • Tom Yulsman

        Mr. HoiPolloiBoy: You are free to disagree with me. That’s fine. But if you want to keep commenting here, try to be serious and avoid ad hominem attacks. Also, for the record, I am not an ignoramus, I do not live in New York City, and I don’t “drive the media.” I have covered science as a journalist since 1980. But I do everything related to this blog in my spare time and by myself.

        • HoiPolloiBoy

          I did not call you an ignoramus. I called the people who drive the MSM media based in New York City ignoramuses, like the Sulzbergers or David Rhodes. My point is, people tend to compare things to the size of Manhattan to get the attention of the New York/Manhattan based media which the rest of the nation’s media follows.

          I apologize if my comment was not clear and insulted you. It was meant to insult the people running the biased MSM.

          • Tom Yulsman

            Thank you for clarifying that, and please accept my apologies for over-reacting. And just so you know, I chose the Manhattan analogy because, well, I grew up in Brooklyn (a long time ago, before it was cool) and that’s what I know!

            Have a great weekend.

          • HoiPolloiBoy

            We’re cool. Good luck with your endeavor.

  • Kurt S

    Awesome then Tom Yulsman. Can you tell us what percentage the Pine Island Glacier is to the rest of the Antarctic glaciers? And then maybe an explanation
    that this one glacial area is only one of many glaciers that are threatened with retreat or all out collapse. And how combined that 10 feet in a hundred years will be dwarfed in comparison.
    Thank you.

  • OWilson

    “IF” ice shelves didn’t break off and melt naturally they would eventually reach the equator, and pose a threat to Caribbean Cruise ships!

    Last I heard, ice shelves breaking off do not raise sea level!

    The airplane is barely a hundred years old, the North and South Poles were only discovered recently, and satellite images have been available for only the blink of an eye.

    Record this, and unprecedented that, together with speculative Hollywood type disaster scenarios, are based on very little “settled science”, and consequently, have lost their impact on a population tired of the hype.

    One should be careful not to extrapolate too much of the Earth’s 4,500,000,000 year history into a the brief lifetime of an AGW advocate.

    Getting from “research suggests” to “that means that the process is irreversible” is a long, long, journey in science, as anyone even remotely familiar with the IPCC FAR 1990 Report! knows! :)

    Every day a “new worrying sign” of doomsday is upon us, but the Earth’s actual average temperature does not follow suit.

    It is still the scientifically statistically insignificant, as measured by NOAA’s satellites, 0.3 degrees over the last 30 years, which, given the huge margin of error of the past failed predictions and the constant “adjustments: being made continually, is really insignificant to the human population.

    More serious threats are from floods, earthquakes, hurricanes, tornadoes, tsunamis, volcanic eruptions, infectious diseases, wars, terrorism, Nuclear Proliferation government corruption, the occasional asteroid extinction event, which Mother Nature herself continues to throw at us, with a shout out to the 250,000,000 or so across the Earth, who have been killed by a progressive agenda against DDT, and the 60,000,000 U.S. children who have been “terminated” by this same progressive agenda, since Roe vs Wade.

    More perspective is needed in the popular press!

    • Citizen Five

      Haha. Denial at its finest and most fact-free!

      • OWilson

        So’s yer old man! :)

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ImaGeo

ImaGeo is a visual blog focusing on the intersection of imagery, imagination and Earth. It focuses on spectacular visuals related to the science of our planet, with an emphasis (although not an exclusive one) on the unfolding Anthropocene Epoch.

About Tom Yulsman

Tom Yulsman is Director of the Center for Environmental Journalism and a Professor of Journalism at the University of Colorado, Boulder. He also continues to work as a science and environmental journalist with more than 30 years of experience producing content for major publications. His work has appeared in the New York Times, Washington Post, Audubon, Climate Central, Columbia Journalism Review, Discover, Nieman Reports, and many other publications. He has held a variety of editorial positions over the years, including a stint as editor-in-chief of Earth magazine. Yulsman has written one book: Origins: the Quest for Our Cosmic Roots, published by the Institute of Physics in 2003.

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