Antarctic ice cliffs may not contribute to sea-level rise as much as predicted

From MIT Earth, Atmospheric, and Planetary Sciences

MIT-Ice-Stability_0

Jennifer Chu | MIT News Office

Monday, October 21, 2019

Study finds even the tallest ice cliffs should support their own weight rather than collapsing catastrophically.

Read this at MIT News

Antarctica’s ice sheet spans close to twice the area of the contiguous United States, and its land boundary is buttressed by massive, floating ice shelves extending hundreds of miles out over the frigid waters of the Southern Ocean. When these ice shelves collapse into the ocean, they expose towering cliffs of ice along Antarctica’s edge.

Scientists have assumed that ice cliffs taller than 90 meters (about the height of the Statue of Liberty) would rapidly collapse under their own weight, contributing to more than 6 feet of sea-level rise by the end of the century — enough to completely flood Boston and other coastal cities. But now MIT researchers have found that this particular prediction may be overestimated.

In a paper published today in Geophysical Research Letters, the team reports that in order for a 90-meter ice cliff to collapse entirely, the ice shelves supporting the cliff would have to break apart  extremely quickly, within a matter of hours — a rate of ice loss that has not been observed in the modern record.

“Ice shelves are about a kilometer thick, and some are the size of Texas,” says MIT graduate student Fiona Clerc. “To get into catastrophic failures of really tall ice cliffs, you would have to remove these ice shelves within hours, which seems unlikely no matter what the climate-change scenario.”

If a supporting ice shelf were to melt away over a longer period of days or weeks, rather than hours, the researchers found that the remaining ice cliff wouldn’t suddenly crack and collapse under its own weight, but instead would slowly flow out, like a mountain of cold honey that’s been released from a dam.

“The current worst-case scenario of sea-level rise from Antarctica is based on the idea that cliffs higher than 90 meters would fail catastrophically,” Brent Minchew, assistant professor in MIT’s Department of Earth, Atmospheric and Planetary Sciences. “We’re saying that scenario, based on cliff failure, is probably not going to play out. That’s something of a silver lining. That said, we have to be careful about breathing a sigh of relief. There are plenty of other ways to get rapid sea-level rise.”

Clerc is the lead author of the new paper, along with Minchew, and Mark Behn of Boston College.

Silly putty-like behavior

In a warming climate, as Antarctica’s ice shelves collapse into the ocean, they expose towering cliffs of grounded ice, or ice over land. Without the buttressing support of ice shelves, scientists have assumed that the continent’s very tall ice cliffs would collapse, calving into the ocean, to expose even taller cliffs further inland, which would themselves fail and collapse, initiating a runaway ice-sheet retreat. 

Today, there are no ice cliffs on Earth that are taller than 90 meters, and scientists assumed this is because cliffs any taller than that would be unable to support their own weight.

Clerc, Minchew, and Behn took on this assumption, wondering whether and under what conditions ice cliffs 90 meters and taller would physically collapse. To answer this, they developed a simple simulation of a rectangular block of ice to represent an idealized ice sheet (ice over land) supported initially by an equally tall ice shelf (ice over water). They ran the simulation forward by shrinking the ice shelf at different rates and seeing how the exposed ice cliff responds over time.

In their simulation, they set the mechanical properties, or behavior of ice, according to Maxwell’s model for viscoelasticity, which describes the way a material can transition from an elastic, rubbery response, to a viscous, honey-like behavior depending on whether it is quickly or slowly loaded. A classic example of viscoelasticity is silly putty: If you leave a ball of silly putty on a table, it slowly slumps into a puddle, like a viscous liquid; if you quickly pull it apart, it tears like an elastic solid.

As it turns out, ice is also a viscoelastic material, and the researchers incorporated Maxwell viscoelasticity into their simulation. They varied the rate at which the buttressing ice shelf was removed, and predicted whether the ice cliff would fracture and collapse like an elastic material or flow like a viscous liquid.

They model the effects of various starting heights, or thicknesses of ice, from 0 to 1,000 meters, along with various timescales of ice shelf collapse. In the end, they found that when a 90-meter cliff is exposed, it will quickly collapse in brittle chunks only if the supporting ice shelf has been removed quickly, over a period of hours. In fact, they found that this behavior holds true for cliffs as tall as 500 meters. If ice shelves are removed over longer periods of days or weeks, ice cliffs as tall as 500 meters will not collapse under their own weight, but instead will slowly slough away, like cold honey.

Full article here.

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48 thoughts on “Antarctic ice cliffs may not contribute to sea-level rise as much as predicted

  1. Can we collectively get together and sue the u.n. and the ipcc? If xr can get lawyer’s and a full legal team, then why can’t the people’s who know the scientific truth? If there is enough evidence to show that the U.N. is lying, then it would be brilliant to allow people to live peacefully and build better stronger Infrastructure instead of billions wasted on solar panels and wind farms.

    • Yes, and the grounds should be based on RICO applied to the criminal conspiracy between the IPCC and the UNFCCC whose stated and demonstrated purpose is to commit a financial fraud against humanity that makes Bernie Madoff look like a petty thief.

  2. Nice to see something being studied in a rational way. Completely flood Boston? Utilizing GoogleEarth ™ it looks like six (6) feet of sea rise would go into the city between one (1) and four (4) blocks. Miami Beach is a different story, but not the way AlGore tells it.

    • Another natural occurrence that we cannot control. Just who or what does the current population think they are?

  3. The way I see it is that once the edge of an ice sheet reached the grounding line, or some other shallow point, or the shore edge, collapsing ice would buttress the ice cliff from further collapse. It wouldn’t just disappear.

  4. Damn! I want Gore and Obarmy’s sea front mansions flooded. Can we hope for some rapid geothermal melting?

    • The above published study, IMLO, is a prime example of “junk science” agitprop.

      Anyway, ……..

      Water flows, ….. ice melts to become water.

      Ice is a naturally occurring crystalline inorganic solid with an ordered structure.

      Ice (all ice, even glacial ice) melts, …… slides …… and/or fractures …… but it doesn’t bend, warp or twist.

      External applied pressure causes ice to fracture, ……. the primary cause being the force of gravity.

        • commieBob – October 24, 2019 at 5:09 pm

          It deforms as it flows. link

          C-Bob, …. I will admit being 20% wrong but not 100%. The 20% because I was ignorant of said “deformation” as defined as follows, …… to wit:

          In an ice crystal the water molecules are arranged in layers of hexagonal rings. These layers are called the basal planes of the crystal, ………

          The bonds between molecules situated in the same basal plane are much stronger than the bonds between molecules located in different basal planes. This causes the ice crystal to deform by gliding on its basal planes. The planes glide past each other like the cards in a deck that is pushed from the side.
          http://www.iceandclimate.nbi.ku.dk/research/flowofice/ice_crystal_structure/

          And C-Bob, …. the deforming of glacier ice is an extremely slow process which takes years to be noticeable, ……. whereas the fracturing and breaking of glacier ice is an extremely fast process in comparison ….. with both processes being dependent upon their “resistance” to the force of gravity.

          Its always a good day when I learn something new.

  5. Reviewing the UAH data on the South Pole, there appears to be a warming trend of 0.25°C over the last 40 years. Spectacularly uninteresting. How can scientists ignore this incredibly stable temperature data and predict events that seemingly cannot happen.

  6. Because agendas striving to replace free market capitalism require these impossible events to seem probable.

    The problem is not the scientists ignoring this, as many don’t and are quite vocal about it, but is the politicians, MSM and citizens who lack the ability to do any kind of due diligence on their own and believe in a CO2 caused catastrophe because their ideology requires them to. It’s the case of positive reinforcement (feedback) turning otherwise thinking brains into mush.

    • I suspect due to the Politics of climate change even the more honest scientists are mum for fear of extention and career ruin if they spoke up.
      That is a big tool of the left socialist practiced every day all day on every subject.

  7. Forgive me for being a simpleton….

    But if part of the ice is already water, even with the land is supporting some of the mass, the ice would still cantilever some its mass into the oceans.

    I really see this as no different than dropping ice cubes into glass of water but perhaps that is too simple of a model.

    Someone please correct me if my thinking is off.

    • Not an expert or eskimo, but you mention ice cubes in a glass of water – please notice that the water level in the glass will rise as yoy drop some ice cubes in the glass. After a while, when all the ice has melted, you will notice that the water level will sink a bit.

      With regard to inland (permanent) ice in Antarctica: If you over time get more precipitation, snow, the ice sheet will increase in height, increasing the horizontal pressure and cause increased calving and gletcher advance. Within a reasonable temperature and precipitation range, the opposite will happen if the precipitation decreases, then you will have less calving and less gletcher advance.
      I got the above explanation from the late Svend-Erik Hendriksen, Greenland/Denmark in 2009.

      • Yes ice or snow has a bit of gas entrapment either in the volume of frozen of water or in the void spaces of the ice crystals structure is not the same volume as the melted liquid.

        I do not think this is about the inland ice. Yes, the ice moves but, it only flows in the direction that gravity allows.

        I was making a supposition, perhaps a poor supposition, about the ice and at the water’s edge per the article or partially in the water. Where the water, in this case the oceans, were already supporting some of the ice’s mass.

        A curious thought just occurred to me. What is the total displaced volume/mass of water for all the ships we, the human species, currently have in our inventory? I am going to see if I can find this number or “reasonable” estimate to it.

  8. A 2nd thought occurs to me.

    Are they suggesting that a cantilevered mass’ structure should not or cannot fail?

    Again forgive the simple model…

    Take a ream of paper and slowly slide it off a workbench top, eventually it will buckle and fail.

    • The Wilkins ice shelf broke up in 2008, due not to warming but to the sea level mechanically flexing it. Here is the sea level at Rothera, 200 miles up the peninsula, but opening to the same section of the ocean.

      http://www.rockyhigh66.org/stuff/rothera_antarctica_tide_series.png

      After some modest flexing, sea level began serious oscillation in mid-April, 2008. This continued into June, when the shelf gave up. The temperature was such that the new open water was freezing around the icebergs.

      • Yes the sheet extends to open water and is at the mercy of other non-static vectors. Similar to the original Tacoma Narrows Bridge but with water as the resonance oscillator instead of the wind.

        Got it. Thanks!

      • Mike
        Thanks for the chart, the vacillation in sea level is not unique to 2008, the breakup occurred that year, that’s the only difference.

        Note that the increase in vacillation starts in very late April and continued throughout the winter. Not because it was winter, but because of equatorial convection volume increases and changes in NH polar atmospheric dynamics. The relationship between the poles tightens causing increased wind speeds and disturbance in the southern ocean and the atmosphere above.

        These actions ultimately play a significant role in the SH temperature, as reported by NCEP CFSR / CFSv2
        Regards

  9. “… scientists have assumed that the continent’s very tall ice cliffs would collapse …”

    “To get into catastrophic failures of really tall ice cliffs, you would have to remove these ice shelves within hours, which seems unlikely no matter what the climate-change scenario …”

    Ms Clerc brings some uncertainty into the discussion. And a simple model of ice has demonstrated that the “scientists'” consensus assumption may just be rubbish. If the MIT results are shown to be valid, this is yet another Climate Science (TM) fail.

  10. I’m puzzled.
    Sea ice has no effect on MSL, Archimedes figured that out a while back. Land ice a mile or so thick creeping into the ocean will sit on the sea bed until 95% submerged. Unless it reaches a precipitous submarine drop off it is hard to see how enough ice could splash down to effect sea level. To raise sea level by 1 mm requires 360 billion tons of land ice or 360 cubic Kilometers a far cry from the building size chunks that tourist boats hope to see.
    What am I missing?
    Cheers
    Mike

    • My reading of their explanation is that if the floating ice shelf were to crack off and float away (or melt into the sea), the remain ice sheet that is resting upon the land would then have a shear vertical cliff face. Previously, it had been presumed that if that cliff face was taller than 90 meters the face would sheer off and topple into the sea like a giant domino separating from a block of giant dominoes. Then the next slab would shear off and topple like another giant domino. They assumed this shearing off and toppling would proceed up the valley that contained the glacial ice sheet. All these ice slabs would slide into the sea in rapid succession, raising sea level rapidly by displacing sea water as they sank into the sea up to their floating point.
      They now think the face would more likely deform rather than shearing off. The deforming front face would then become a buttress holding back the glacier.

      SR

      • if the floating ice shelf were to crack off and float away (or melt into the sea), the remain ice sheet that is resting upon the land would then have a shear vertical cliff face.

        Nothing new there above, happens all the time.

        it had been presumed that if that cliff face was taller than 90 meters the face would sheer off and topple into the sea like a giant domino separating from a block of giant dominoes. Then the next slab would shear off and topple like another giant domino.

        They assumed this shearing off and toppling would proceed up the valley that contained the glacial ice sheet.

        WHOA, ….. WAIT A MINUTE, ……. iffen it was gonna do that, ….. why didn’t it “sheer off” way up the valley to begin with and the whole damn glacier slide into the ocean in one fell swoop?

        “DUH”, ….it didn’t do it because it won’t sheer off until the glacier’s leading edges slides past the “grounded” shoreline into open water where “gravity” can stress the ell out of it and it fractures.

    • “What am I missing?”

      The tourists don’t understand any of that when they see all that ice falling, which is obviously raising the sea level in Miami.

      This is a very interesting piece of research.

      • Yes that is correct, the floating sea ice caving into the water does not increase sea level, but the ice that is so deep and is supported by the sea bed caving into the sea does increase sea level.

  11. My understanding is that this ice is already floating on the sea, so any rise has already occurred. Also any build up of ice comes from the sea as evaporation, then and that then falls as snow, so its all balancing out.

    A lot of the problem comes from what the models say is correctly said to be projections, i.e. guesses , but the Media then pick this up and says that its proper data, Then they the Media writes up their scare stories, it sells papers or TV time. and that is what its all about.

    Now of course the IPCC should step in and correct this, but it suits their long term agenda to say nothing.

    MJE VK5ELL

  12. Where’s the evidence that the ice shelves are going to collapse into the ocean, even if it does rise by the insane amounts predicted?
    The most that would happen is that once the oceans have risen enough to eliminate the grounding, the flow of ice will speed up.

  13. Not as bad as we thought? How dare they? Better make sure these folks don’t get any more grant money! Can’t have facts getting in the way of the narrative, can we?

    Seriously – glaciology is not exactly a new branch of science. The fact that no one else has dared to point out the flaws in “catastrophic ice cliff collapse” before shows just how much influence the climate cabal has over the practice of scientific research in the 21st century.

    It wouldn’t surprise me if Ms Clerc’s career in academe doesn’t advance as fast as she would like.

  14. If the local climate seriously warmed then maybe the ice cliffs would be only 89 meters tall.
    Christ on a bike in the afternoon, what does it take to hammer only a little bit of common sense into these people?

  15. For Antarctic ice shelf shearing it’s not height per se that matters so much as the ice weight and specifically weight distribution.

    In short – the key player is Cliff Mass.

    • Height is important. Vertical glacier fronts are usually about 50 meters high and very rarely more than double that. And the vertical weight distribution is essentially the same everywhere – it is determined by the compaction of the snow into ice.

  16. Under certain very specific circumstances an ice-sheet can calve out completely relatively quickly (say in a couple of centuries or so). It requires:

    1. The rock under the ice must be below sea-level
    2. The depth below sea-level must be >90% of the ice thickness
    3. The rock under the ice must slope inwards from the ice-front (i e the opposite of the normal slope)
    4. The downward slope of the rock bottom must be steeper than the upward slope of the ice surface
    5. There must be no thresholds or other pinning points
    6. The hydrostatic pressure below the ice must be lower than the pressure of sea-water at the same depth

    As you might imagine this is not very likely to happen.

    By the way I had always thought that this ice cliff collapse was a scenario that only applies to an exposed, grounded ice-front standing in deep water (typically >500 meters water depth is required). That it cannot under any circumstances happen when there is ice shelf in front of the grounded ice is so obvious that it never occurred to me that anyone would even consider it, simply for the reason given here. Ice flows. As a matter of fact that is the definition of a glacier: a mass of ice that is large enough that it will flow under gravity. Climate scientists are quite remarkably ignorant of basic earth science.

    • I always figured that ice shelves were in essence extensions of glaciers. They are far too thick to be “sea-ice”. Even in extreme cold sea-ice in the arctic seldom gets more than 5 m thick, and the antarctic ice shelves can be 1000 m thick. To be that thick they must be constantly fed by glaciers flowing off continental Antarctica.

      Once this ice sits in water 9/10th is under water, so you have 900 m under water and 100 m sticking up. The “cliffs” mentioned in this story are only 90 m tall. Hmm. Does one actually have to “step up” from the top of a cliff to the top of the ice shelf? If so, I can see why some would picture the looming ice shelf as propping up the cowering cliff.

      To me it seems there must be an amazing outflow of glaciers to build and maintain an ice-shelf 1000 m thick over areas which can be as large as the state of Texas. This outflow would not decrease in a case of Global Warming; it might even increase, due to greater snowfall over Antarctica due to greater humidity. To me it seems unlikely the ice shelf would cease being replenished by glaciers, and therefore would only erode away at its most outer edge, in cases of extreme warming.

      If an entire ice shelf did somehow manage to break away in its entirety, it would result in no immediate sea-level rise, but in the most massive iceberg yet seen, perhaps even as large as Texas. This indeed might have an effect, but it would likely involve chilled SST rather than sea-level rise, and a weather change in places like South Africa or New Zealand.

      If, and only if, an ice-shelf fractured right along the coast and moved swiftly away in its entirety could the coastal “ice cliffs” crumble in any manner that might rise the levels of the sea. Anything slower and less drastic seems likely to have the cliffs flow like glaciers, replenishing the Ice-shelf even as it departed.

      I recall hearing scary stories in college dorms back around 1972, involving some huge part of Antarctica falling into the sea and causing world-wide floods. Such things were discussed while smoking weed, and I think we hoped they would happen so we’d never face graduation and getting a Real Job. (We also discussed the likelihood of an asteroid striking Wall Street, and California falling into the sea.)

    • “tty:

      4. The downward slope of the rock bottom must be steeper than the upward slope of the ice surface”

      v’ ;!

  17. ICE SHELVES, HURRICANES, TEMPERATURE RISE- WHO CARES!!
    FOCUS HARD ON ARTICLE ABOUT SEA LEVEL AND PHOTOS TAKEN OVER 150 YEARS AGO AT LA JOLLA COVE IN SAN DIEGO CA.!!!
    WE NEED A HUNDRED SCIENTISTS TO go THERE AND FIGURE OUT WHAT IT MEANS FIRST!! PUT ALL THE OTHER STUDIES ON HOLD!!! THE COVE MUST STUDIED TO THE POINT OF ABSOLUTE EXHAUSTION!!! THE ONLY CONCLUSION MUST ASK WHY NO RISE (OR FALLING) OF OCEAN IN 150 YEARS AND PROVE SCIENTIFLY THE FINAL CONCLUSION.
    THIS STUDY IS NOT WHAT AND WHEN IN CLIMATE CHANGE IS. ITS WHAT HAS HAPPENED AND IS HAPPENING NOW, THAT IS THE ONLY REALLY IMPORTANT TIME FRAMES. IM SICK OF SOME SCIENTISTS JUST STATED “TODAY MIAMI WILL DISSAPEAR IN 50 YEARS! THAT DOES MEAN JACK SHIT!! BUT THE PHOTOS- WOW!!
    NOTE: I LIVE IN SAN DIEGO AND SAW IT with MY OWN EYES!! I SIGHED IN RELIEF “THIS BEAUTIFUL PLANET IS GONNA BE JUST FINE” EVEN FELT A FEW GOOSE BUMPS!
    I’D LOVE TO SEE A PERMANENT 24 hour camera set at the COVE FOR REAL TIME WATCHING OF THE OCEAN RISING SO OMINOUSLY!!!

    [Next time, try not “shouting” in all caps. It’s difficult to read and your comment probably won’t get approved. -mod]

  18. I’m not a scientist, nor do I pretend to fully understand the complexities of such a situation. But would the water beneath the ice shelves not support it?

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