New Research Suggests Sea Level Could Rise Faster, Sooner

January 26, 2015

From the Abstract – “Potential Antarctic Ice Sheet retreat driven by hydrofracturing and ice cliff failure”:

In response to atmospheric and ocean temperatures typical of past warm periods, floating ice shelves may be drastically reduced or removed completely by increased oceanic melting, and by hydrofracturing due to surface melt draining into crevasses. Ice at deep grounding lines may be weakened by hydrofracturing and reduced buttressing, and may fail structurally if stresses exceed the ice yield strength, producing rapid retreat. Incorporating these mechanisms in our ice-sheet model accelerates the expected collapse of the West Antarctic Ice Sheet to decadal time scales,

Ars Technica:

It has been a bit of a head scratcher. Records of sea level during the last few million years tell us that there have been some warm periods where sea level may have been as much as 20 meters higher than it is today. When fed the conditions that prevailed at the time, however, our computer models of ice sheets haven’t been able to reproduce such a swelling of the ocean.

The models can simulate that much sea level rise, but it requires temperatures much higher than were seen during those warm periods. Realistic losses of ice from Greenland and the fragile, western part of Antarctica (the West Antarctic Ice Sheet) could only provide something in the neighborhood of 3 to 10 meters of sea level rise. That leaves 10 to 17 meters for the East Antarctic Ice Sheet—the largest and most stable ice sheet—to chip in. Convincing the miserly East Antarctic Ice Sheet to be that generous with its contents isn’t easy, which is why the models required such high temperatures.

So what are the models missing? Penn State’s David Pollard and Richard Alley, and University of Massachussetts, Amherst’s Robert DeConto had an idea for something to try. Two things to try, really. They added a pair of physical processes to an ice sheet model that weren’t simulated previously. The first was hydrofracturing. When water reaches the ice sheet from rain or ice melt at the surface, it fills crevasses in the ice.

If they’re filled to a great enough depth, the water pressure forces the crevasse to open even deeper—that’s termed hydrofracturing. The other process results from the simple fact that a sheer cliff of ice can only be so tall before it collapses under its own weight—a condition not encountered in too many places today.

One place it does occur is where floating glaciers calve large icebergs. These occur on the coastal outlet glaciers at the edges of ice sheets that are the most vulnerable to warming. The glacier thins towards its outer edge, and at some point it grows thin enough that it begins to float. The point at which it floats off the bottom is called the “grounding line”—from there out to the end of the ice is called an ice shelf. Ice shelves that grind against the shore (think of it floating in a bay or fjord) act to hold back the flow of ice behind them. These shelves gradually melt from below as they float in their seawater bath. But they can also melt from above and shed large bergs of ice at their outer edge.

ant_iceshelves

Map shows where Ice sheets are grounded to bedrock below sea level

 

Both hydrofracturing and cliff failure can increase the shedding of icebergs from shelves, hastening their demise and uncorking the glacier behind them. Once these things happening near the grounding line, though, they can really accelerate its retreat if it’s in an unstable configuration where the ground surface drops as you head inland. (Significant portions of Antarctica match that description.) Once you start retreating in that situation, the glacier may have to retreat a long way to find a stable position again.

Having added representations of these two processes to the model, the researchers simulated a sudden change from modern conditions to warmer conditions like those past periods of very high sea level. Then they watched the virtual Antarctic glaciers respond.

The results were dramatic. The new processes combined to have a huge impact. Instead of about 2 meters of sea level rise, Antarctica lost enough ice to raise global sea level 17 meters over several thousand years. The fragile West Antarctic Ice Sheet collapses in a matter of decades, rather than centuries or millennia. There’s 5 meters of sea level rise in the first two centuries, after which retreat in portions of the East Antarctic Ice Sheet really get going.

antarctic_iceloss2015_alleyetal-4

Ice distribution over time in new simulations of a 400 ppm CO2 world like our own..the model is significant in that it posits a 2° C temperature rise – a level often characterized as “safe” by policymakers.

Much more work will be required to make sure these new processes are being simulated accurately, but the early returns show it could put researchers in the ballpark of solving the puzzle of past high sea levels.

The relevance for our present situation is less direct, as the warming in the simulation was not realistic, but the possibility that West Antarctica could lose ice faster than we thought is a serious one. Richard Alley, whose work on this possibility we’ve covered before, explained to Ars via email, “I believe (and I suspect many people do) that it is important for us as scientists to provide not only the most-likely future outcome, but also the range of possibilities, including some sort of assessment of best-case and worst-case outcomes. Best-case is fairly easy, I believe, but worst-case is not; however, providing both is likely to be useful to many people.”

“The physical knowledge that too-tall cliffs fail is very old and familiar to every miner or quarry-worker. The physical knowledge that ice is not the strongest rock on the planet is also rather old. And, the suggestion that cliff failure could affect West Antarctic stability dates back to 1962,” Alley wrote. “We now have stronger evidence that sufficient West Antarctic retreat could lead to a higher calving front than any on Earth today, and higher than a stability limit suggested by recent papers. Putting that understanding into projections of the future, as in our new paper, has implications for the worst-case scenario. And, testing against the paleoclimatic record provides support for that understanding.”

He continued, “It is still too early to say that this is an accurate worst-case scenario. Step-application of the [warming] is too extreme, clearly… but, it is within the realm of possibility that for the time-scale of collapse, the true worst worst-case scenario could be even a bit faster than modeled here; the renewed interest in this topic is recent, and the number of scientific papers exploring the physics remains low.”

 

11 Responses to “New Research Suggests Sea Level Could Rise Faster, Sooner”


  1. Don’t you get embarrassed with such articles?

    We could also be eaten by a black hole that spontaneous materialises in CERN.
    We could also be invaded by aliens.
    We could all wake up and find this life was just a dream and we are actually just a robot.

    We could one day read some real science on this blog

    But some things are just very unlikely.

    • redskylite Says:

      “Don’t you get embarrassed with such articles?”

      Of course not – if you read the article it is talking about the worst case scenario. When planning any major project you need to consider a range of scenarios.

      The melt is actually happening and is measurable as is the temperature rise, which scenario we follow largely depends on our own actions. The scientists quoted in the article are very real experienced and educated, so how can you compare it to a ridiculous dream, or something that has been dismissed by the CERN scientists.

    • ubrew12 Says:

      The context for this article is an ‘alarmist’ IPCC that, every few years or so, has to revise its year 2100 sea level rise estimate upward rather than downward. This pattern of behavior is now 20 years old and, at some point, one would imagine that people like you would become embarrassed instead. ‘Could’ is ubiquitous in Science. If you’re looking for certainty, try Religion.


    • Dear Scottish Sceptic {Nullius addictus iurare in verba magistri (be sceptical of the experts)}

      —–
      On Jan 17 you posted “A problem with CO2”

      “My grand theory of the causation and progress of ice-ages was making steady progress before Xmas until I hit a small snag: CO2 levels do not work as a greenhouse gas! But neither do they just respond to temperature! I’ve been thinking about it for a while without making progress, so I’m hoping that writing this article will stimulate some ideas to get around the log jam.

      [Description of log jam is in the post]
      http://scottishsceptic.co.uk/2015/01/17/a-problem-with-co2/

      Any ideas?
      —–

      Here’s an idea. Be skeptical of, but don’t ignore the experts.
      Cheers…

    • dumboldguy Says:

      To add to Charles Zeller’s response to “any ideas?”, you might want to look at this link (view it at the “intermediate” level). It’s no wonder you’re not having luck on your “grand theory”, since you don’t understand the science (and don’t seem to really want to). Do as Charles says and pay attention to some experts.

      http://www.skepticalscience.com/co2-lags-temperature-intermediate.htm

      I’m sorry to see that you are such an ignorant fool that you have embarrassed yourself with this series of inane “we coulds” and have the balls to so smugly say we “could some day see some real science” on Crock. You’re lucky Peter is tolerant of fools—-that comment on top of your earlier idiocies on other threads would result in banishment if it were my choice. You bring NOTHING of value to the discussion.

      I’d say “go away” to you so that we can get on with dealing with the REAL science that is behind ALL Crock articles without being distracted by your foolishness, but it’s “very unlikely” that you would comply.

    • greenman3610 Says:

      This is a study of reality. We already know that ice sheets are losing mass much faster than projections of just a few years ago. Three key data sets, two from satellites, GRACE and ICESAT, as well as NASA IceBridge flyovers, are all in agreement that Antarctica and Greenland losses together have doubled in the last 5 years.
      http://www.bbc.com/news/science-environment-28852980
      That is reality. Not a model. Not a projection.

      That rate of acceleration brings the loss very much in line with the scenarios depicted in the study mentioned above, in fact, showing that the new models are more in line with what is actually being observed than previous work.

      This is a blog about real, measurable things. Clearly that is why you find it so disconcerting.
      Perhaps you’d find the kind of science you like over at Fox News – where I see they have a really cool section on dinosaurs.

  2. lesliegraham1 Says:

    But it is certain that the Earth’s ice is melting, that the process is rapidly speeding up and as recently as 14,300 years ago – during Meltwater Pulse 1A – the oceans rose at least 15 feet in a single century and possibly as much as 70 feet in two centures.
    Which, after all, is what this latest piece of research is about – trying to figure out WHY the ocean can rise as much as 70 feet in 200 years.

    Of course there is no way to be certain that this will happen again but, by the same token. there is no way to be certain that this will NOT happen again.

    It’s those pesky ‘uncertainties’ again you see. They cut both ways.

    If you have any evidence that this is not the case we would all be very interested to see it.

    More of your infantile nonsense? Not so much.

    • Andy Lee Robinson Says:

      Well said Leslie.
      Remember that good old phrase that most if not all people aspire to in adversity:

      “Plan for the worst, hope for the best”

      If the media won’t let the people know what the worst might be, then how can they plan for it? 🙂

    • Gingerbaker Says:

      The uncertainties do NOT cut both ways.

      We have historical evidence that 400 ppm [CO2] causes X amount of SLR. We have evidence that [CO2] drives temperatures. We have evidence that CO2 is a greenhouse gas.

      On the other side of the ledger is one amateur’s stubborn and petulant doubt about scientific facts.


  3. Sorry, first-time commenter, hadn’t realized that the system threw out web addresses. For the desired sites, please google the titles. David Noel.


  4. […] From the Abstract – "Potential Antarctic Ice Sheet retreat driven by hydrofracturing and ice cliff failure": In response to atmospheric and ocean temperatures typical of past warm periods, floating…  […]


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