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Thread: Antarctica Ice Sheet to collapse, but not quickly

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    Antarctica Ice Sheet to collapse, but not quickly

    From R&D magazine

    National Science Foundation- (NSF) funded researchers at the Univ. of Washington have concluded that Antarctica's fast-moving Thwaites Glacier will likely disappear in a matter of centuries, potentially raising sea level by more than a half-a-meter (two feet).

    Data gathered by NSF-funded airborne radar, detailed topography maps and computer modeling were used to make the determination.

    The glacier acts as an ice dam, stabilizing and regulating movement toward the sea of the massive West Antarctic Ice Sheet. The ice sheet contains enough ice to cause another 3 to 4 meters (10 to 13 feet) of global sea level rise.

    "There's been a lot of speculation about the stability of marine ice sheets, and many scientists suspected that this kind of behavior is under way," said Ian Joughin, a glaciologist at the university's Applied Physics Laboratory (APL) and the first author on the paper. " This study provides a more quantitative idea of the rates at which the [ice sheet] collapse could take place."
    But before you start building an ark...

    While the word "collapse" implies a sudden change, the fastest scenario based on the data, the researchers said, is 200 years, and the longest is more than 1,000 years.

    The findings are published in the May 16 edition of the journal Science.
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    the fastest scenario based on the data, the researchers said, is 200 years
    This likely assumes under ice lubrication has a minor effect. We'll get to see how well theory matches with the actual under-ice topography.
    Last edited by Squink; 2014-May-13 at 03:47 PM.

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    Phil Plait (remember him?) has a blog post about it.

    Stupid stuff that annoys me: Despite knowing better, I persist in looking at the comments on Phil's global warming posts. They make my brain hurt.
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    Good of Phil to point out that we're talking about a slow collapse, not an immediate one-- but still very alarming news.

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    Re Trebuchet: Ditto. I'll post this gem I found on Yahoo! comments (if you've ever read those, you know how rare *that* is) that sums it up nicely.

    Sadly, want to lose I.Q. points. Read Yahoo posts, they use 21 century information and apply First century logic to the subject. I hope your proof is braced on science NOT.
    Apologies for the digression.

    More topical: I think Greenland will give us more trouble--and sooner--than Antarctica will, the more so for being in the hemisphere where heating is sure to be greatest. IIRC, it was melting in Greenland that contributed most to the higher sea level in the previous Eemian interglacial.

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    In geologic terms, I wonder if this collapse can be considered sudden. In human terms probably not...but I'm wondering if information is being 'dumbed down' for the benefit of our largely scientifically illiterate population.

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    Quote Originally Posted by redshifter View Post
    In geologic terms, I wonder if this collapse can be considered sudden. In human terms probably not...but I'm wondering if information is being 'dumbed down' for the benefit of our largely scientifically illiterate population.
    I think the answers are yes, yes, and yes
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    Actually, there might also be some tectonic implications to the loss of some of the ice sheets for the whole planet. Antarctica is a volcanically active region, at this point it is a complete unknown how the volcanoes of the regions will react to the loss of a huge amount of mass that's over them. The loss of that ice mass could lead to more frequent volcanic eruptions, and those could potential lead to a cascade failure of an even larger region of ice. A VEI 6 eruption could add enough heat to the ice to melt about 1/4 of the total continents ice total, raising ocean levels but about 8 meters in a years time.
    Last edited by dgavin; 2014-May-14 at 01:52 AM.

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    I remember reading years ago that the average sea level rise during the last deglaciation was only about two feet per century. Slow in human terms, perhaps, but more than enough for huge geographic changes.

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    I have a sinking feeling that this estimate will actually follow a trajectory more extreme than the worst-case scenario. I've been researching this for a story I'm writing, but I'm consistently finding that the authors (researchers) made assumptions extrapolated from models instead of actual measurements and either forgot, ignored or admitted they didn't know how over variables would factor in. For example, I think the IPCC sea level rise estimate used thermal increase only and didn't factor in ice sheet melt at all until the last year or so.

    What I want us to calculate is how melt in WAIS and GIS at the same time may increase MSL enough to further buoy and lubricate the ice sheets, including EAIS. I also wonder what effect post-glacial rebound will have on the Trans-Antarctic Mountains, which are volcanic. Moreover, I wonder what, if any, these events might have on the ring of fire volcanoes due to changes in shore crust loading from rising seas. Also, rising seas will necessarily raise the atmosphere, including the snow line, although much of this will be dependent on local effects. Also, warming seas in the arctic may release methane clathrates, and I'm not sure if this is accounted for in models, and from what I've read when methane is used in models, it's ignored after 20 years, but it breaks down into CO2 which is resident for a century on average.

    I also want to know what effect extreme temperatures might have on the ice sheets. Some people, I'm not sure if it was a denialist or an alarmist or a ignoramus, but I recall reading someone saying that a +4 change in average temp will result in a max summer temp of +4 added to the current average temp. *headdesk* What I want to know is how probability of weather effects will add together to create larger (higher) temperature excursions (heat waves) that can have a rapid effect on segments of a glacier, collapsing large sections in short order.

    BTW, in case anyone's interested, check out the article for Meltwater Pulse 1A if you haven't already. Evidence suggests that sea level rose 20 m in 500 years. Someone suggests that it was as quick as 200 years, though I'm not sure I follow their line of thinking. (Not that I necessarily think it can or will happen here, the dynamics are too different to copy-paste assumptions.)

    Oh, and as for Mean Sea Level rising, the mean average isn't. The geoid is affected by mascons. However, some of these mascons are made of ice and are melting. This will alter the geoid and calculations suggest that when the Greenland Ice Sheet melts, the water will stop hanging around Greenland and will end up along the Atlantic seaboard, which will rise more than the average sea level rise.
    Last edited by Ara Pacis; 2014-May-23 at 08:25 AM.
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    There is nothing we can do about it according to Nasa.

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    Quote Originally Posted by Theory of Everything View Post
    There is nothing we can do about it according to Nasa.
    That and the minimum 200 years, plus my own life expectancy = who me worry?
    Depending on whom you ask, everything is relative.

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    Quote Originally Posted by mkline55 View Post
    That and the minimum 200 years, plus my own life expectancy = who me worry?
    Well, known maximum human lifespan is 122 years...

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    Quote Originally Posted by mkline55 View Post
    That and the minimum 200 years, plus my own life expectancy = who me worry?
    With a margin of error of +/- 200 years.
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    Quote Originally Posted by mkline55 View Post
    That and the minimum 200 years, plus my own life expectancy = who me worry?
    So you have no children, relatives with children, friends with children, don't care about humanity in general, etc, etc, etc?
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    Quote Originally Posted by Trebuchet View Post
    So you have no children, relatives with children, friends with children, don't care about humanity in general, etc, etc, etc?
    None who will be able to stop the Antarctic ice changes. And none living who will be incapable of climbing 20 or even 100 meters sometime in the next 200 years. Humanity in general should adapt by moving a few feet away from the current shores. They managed it at the end of the last ice age. I'm sure they can manage it in the future.
    Depending on whom you ask, everything is relative.

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    And society is exactly the same as it was ten thousand years ago, and there are no complications to be considered.
    _____________________________________________
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    Quote Originally Posted by Gillianren View Post
    And society is exactly the same as it was ten thousand years ago, and there are no complications to be considered.
    Nor has the human population increased from what it was 10,000 years ago.

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    Quote Originally Posted by Romanus View Post
    I remember reading years ago that the average sea level rise during the last deglaciation was only about two feet per century.
    Zero sea level rise for 999 years, followed by a 20 foot change over the course of 1 year, gives an average sea level rise of only two feet per century. From what I've seen, the density of reliable data points is a little for thin for confidently drawing smooth curves using a least squares best fit.

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    There were definite MSL jumps; but that average is what we have to work with outside of focusing on specific meltwater pulses.

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    Sure, but those jumps could be real attention getters when they occur.
    Magnitude and timing of the sea-level jumps preluding the 8.2 ka climate event (two sea level events, one being 3 meters over about 200 years).
    Best not to smooth over the possibility completely.

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    Well, lets assume the melting of WAIS takes 200 years at an even rate and that the nominal rise in MSL is 5 m (I've seen values from 3 to 7). That's still one foot of MSL rise in ~12 years, or 1" per annum. If you consider the topology of major cities, you could have major cities becoming uninhabitable in half a century or less. This is ignoring sea level rise from GIS melting, EAIS melting, other glaciers melting and thermal expansion or variations in the geoid.

    As it is, I predict Miami will be abandoned by mid-century, definitely by the end of the century. Other cities may be able to get by with sea dikes, but from what I've read the porous rock in southern Florida might make that solution impossible. I could be wrong, but erosion from normal processes and hurricanes will exacerbate the problem. I recently heard that Washington DC is at sea level, despite its distance from the ocean. Maybe once the sea starts flooding up the Potomac, we'll see action on the issue - too late of course.
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    The collapse of a major ice shelf is one scenario I could see as causing a sudden upsurge in sea level.
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    There is a huge amount of latent heat trapped in that ice which must have a cooling and negative feedback effect. I once calculated the latent heat as compared to the net solar radiation of the antarctic and it would take hundreds of years to melt the ice once the temperature rose to the melting point. I did that in a conversation with an alarmed colleague who was worried about melting within a decade. I only mention this because my observation is that the latent heat implications are rarely if ever commented in public fora.
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    Quote Originally Posted by profloater View Post
    There is a huge amount of latent heat trapped in that ice which must have a cooling and negative feedback effect. I once calculated the latent heat as compared to the net solar radiation of the antarctic and it would take hundreds of years to melt the ice once the temperature rose to the melting point. I did that in a conversation with an alarmed colleague who was worried about melting within a decade. I only mention this because my observation is that the latent heat implications are rarely if ever commented in public fora.
    I've mentioned it, in not so few words, in my thread, "What if all the ice melted". However, it should also be noted that ice doesn't need to melt in order to raise sea level.

    It should also be noted that the poles are warming through mechanisms other than "net solar radiation" on their surface area.
    Last edited by Ara Pacis; 2014-May-27 at 07:52 PM.
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    Antarctic Ice Sheet unstable at end of last ice age, new study finds
    A new study has found that the Antarctic Ice Sheet began melting about 5,000 years earlier than previously thought coming out of the last ice age – and that shrinkage of the vast ice sheet accelerated during eight distinct episodes, causing rapid sea level rise.
    ...
    The largest of the eight episodic pulses outlined in the new Nature study coincides with meltwater pulse 1A.
    "During that time, the sea level on a global basis rose about 50 feet in just 350 years – or about 20 times faster than sea level rise over the last century,"
    noted Clark, a professor in Oregon State's College of Earth, Ocean, and Atmospheric Sciences. "We don't yet know what triggered these eight episodes or pulses, but it appears that once the melting of the ice sheet began it was amplified by physical processes."
    Our coastal cities would not like a sea level rise on the order of 1.4 feet (0.43 meters) per decade.

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    Quote Originally Posted by Ara Pacis View Post
    I've mentioned it, in not so few words, in my thread, "What if all the ice melted". However, it should also be noted that ice doesn't need to melt in order to raise sea level.

    It should also be noted that the poles are warming through mechanisms other than "net solar radiation" on their surface area.
    Yes I agree with all that. The ice near the edges is of course warmed from the sea underneath. My point is that vast amounts of ice will reduce the sea temperature close to 0 which is a negative feedback effect.
    sicut vis videre esto
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    Quote Originally Posted by profloater View Post
    My point is that vast amounts of ice will reduce the sea temperature close to 0 which is a negative feedback effect.
    However, if sea level rises under a nonmelting iceshelf, you'll get stress on the shelf, and perhaps increased fracturing, a positive feedback effect as those bergs float into warmer waters. Plus, once you eliminate iceshelves, the damns holding back the landward glaciers are gone and you're open to surges.
    Heat of fusion is a big factor here, but it's far from the only one in play.

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    In 1978, concluding a discussion in Nature about the threat of West Antarctic Ice Sheet collapse, glaciologist John Mercer wrote:

    "One of the signs that a dangerous warming trend is under way in Antarctica will be the breakup of ice shelves on both coasts of the Antarctic Peninsula, starting with the northernmost and extending gradually southward."

    I wonder if he imagined the speed at which Larsen A and Larsen B subsequently disintegrated (1995 and 2002).

    I found the paper itself a fascinating and relatively easy read, with discussion of the various climate model results and the unknowns about feedbacks, here. (639 kB)

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    Quote Originally Posted by Squink View Post
    Plus, once you eliminate iceshelves, the damns holding back the landward glaciers are gone and you're open to surges.
    Heh, a solution occurs; set sailors at each glacial foot and let them swear the ice back into place.
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