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Wilkins ice shelf collapse

Filed under: — gavin @ 6 April 2009

Since people are wanting to talk about the latest events on the Antarctic Peninsula, this is a post for that discussion.

The imagery from ESA (animation here) tells the recent story quite clearly – the last sliver of ice between the main Wilkins ice shelf and Charcot Island is currently collapsing in a very interesting way (from a materials science point of view). For some of the history of the collapse, see our previous post. This is the tenth major ice shelf to collapse in recent times.

Maybe we can get some updates and discussion of potential implications from the people working on this in the comments….?


613 Responses to “Wilkins ice shelf collapse”

  1. 101
    Jaydee says:

    82 Timothy Chase

    I studied Materials Science and Engineering about 25 years ago, we didn’t study ice and I haven’t really touched the subject since so take this with several pinches of salt.

    First, I suppose you could say breaks occur when energy is transmitted to a place where the energy holding things together is less.

    Second the direction of the force on the bridge is unclear to me but from the position of the islands, I would guess it was along the length of the bridge in tension or compression.

    Third the ice in the sheet seems (to my eye) to have a “grain” (possibly more than one), it is not homogeneous so the morphology of the break will be complicated.

    To extend your window analogy, imagine a stack of long microscope slides on edge and then start stressing them. Where will the breaks occur? Hard to say…

    All guess work really.

  2. 102

    Comment #62

    RT,

    I can’t believe you asked that question — this was beautifully mapped by NASA-GISS and all over the news.

    See Figure 2 in this article by Andrew Glikson:

    http://webdiary.com.au/cms/?q=node/2725

    And while I’m here — Gavin, please define the terms SAM and NAM, I am more clueless than usual.

    [Response: Sorry. Northern Annular Mode (aka Arctic Oscillation ~ NAO == North Atlantic Oscillation); SAM= Southern Annular Mode (aka. Antarctic Annular Oscillation) - basically the first mode of variability in the sea level pressure or geopotential height fields. Positive phases are associated with an increased strength of the mid-latitude jets (i.e. increased westerlies). - gavin]

  3. 103
    Thomas Hariman says:

    OK , im an A level student of history , i barely scrapped a C in GCSE Science , Two questions what does this breaking up of the Wilkins Ice shelf mean in the grand scheme of things and now for quite a broad question on the business of climate change in general , when is it generally scienfically accepted that we the general population will start to see stark effects of climate change on humanity , so if this seems like an idiot question .

  4. 104
    Nick says:

    Nylo @#93, the Wilkins hasn’t detached from the mainland; that’s no way to describe what can easily observed in the satellite record. It has experienced episodes of retreat during the last decade at least, while the shrinking remainder remains attached to land. It is not behaving like a water droplet breaking off under its own weight,on reaching some critical mass. If the shelf was in a stable state,it would show calving and advancing at ideal locations between pinning points and the open sea.

  5. 105
    Rod B says:

    ccpo (73), me thinks you are confusing unbiased inquiry with bending over…

  6. 106
    SecularAnimist says:

    Lawrence Brown wrote: “These collapses are like canary’s in coal mines.”

    Now, now. While a buildup of toxic fumes in the coal mine may increase the likelihood of canary deaths, it is wrong to attribute the death of any one canary to the buildup of toxic fumes.

  7. 107
    Mark says:

    re #106, yeah, canaries died from natural causes thousands, even millions of years before we humans brought them down into mines.

    Pfft.

  8. 108
    Mark says:

    “when is it generally scienfically accepted that we the general population will start to see stark effects of climate change on humanity”

    Well, now.

    If you’re in certain areas, you are seeing it now.

    Being an affluent country, we in the UK haven’t seen much effect since we can just spend our way out of the problem or wait until it bites someone else HARDER because we ought to have done something but didn’t.

    California has seen a lot of problems in rainfall pattern changes, mind, as has Australia. Changes that affect some humans (a long way away) and are a result of climate change. Innuit are seeing massive changes, but they don’t have the money to be “important”. And so on.

    Now.

  9. 109
    P. Lewis says:

    Thomas Hariman says

    when is it generally scienfically accepted that we the general population will start to see stark effects of climate change on humanity

    See, for example, “Changes in Precipitation and Drought Patterns” and “Melting Glacial Ice” here and judge for yourself when that might be.

  10. 110
    sidd says:

    Re: Greenland ice shelves/Ellesmere island.

    Recent breakups, in no particular order: Ward Hunt. Ayles. Markham. Serson.

  11. 111
    Craig Allen says:

    Mark: we’re seeing it alright.

    Australia’s greatest river continues to die in the ass (literally, but the rot is now creeping through its guts as well).

    >> Murray flows lowest in a century.

    >> Murray River ecosystem on the brink of collapse

    We are now at the point with this and many other south-eastern river systems where fish and crustaceans are being collected from the last few pools where they are found, and transferred to aquaculture in order to stave off extinction.

    Talk of ecosytem triage is starting to seem optimistic.

    Meanwhile coastal New South Whales and Queensland have just coped a 1 in 100year flood several months after a previous devastating flood – go figure!

  12. 112
    Hank Roberts says:

    Thomas, I could help you up to the point that you use the word “stark” –at that point it becomes a matter of opinion. What do you care about?
    If it’s your grandchildren, then “stark” is something that will affect them when it happens.

  13. 113
    Xavier says:

    Thanks all for your interesting responses! I didn’t expect to receive such a flood of replies. By the way I’m not a denialist – just curious. I can see from the NSIDC site that ice concentration is both growing and decreasing depending on where you look around the Antarctic. Is this likely to be to do with how the ocean currents circulate around the continent?

  14. 114
    Nick O. says:

    #31 – Mauri, regarding the potential rift nr the word ‘Wilkins’, heading roughly at 2 o’clock from Latady Island, I was wondering about this myself (#17); indeed the whole of that stretch must be a bit suspect now. With Winter approaching fast, we may not see further changes this season, though.

    #82 – Timothy, would the wave effect also explain the way we see development of a saw-toothed appearance on the lower fragmenting edge? I’m just trying to work out whether this results from internal pressures from the bridge, or external ones being applied to it, or maybe some awkward combination of the two. Could also be related to spatial variations in the bed form.

  15. 115
    Jack Roesler says:

    This article really got me going.

    http://www.winnipegfreepress.com/opinion/westview/obamas-emission-cuts-pragmatic-suicide-42572987.html

    A 90% loss of population? Is that possible?

    [Response: A bit excessive, I'd say.... -gavin]

  16. 116
    Ray Ladbury says:

    Walt Bennett,
    Dawn has yet to pass the Turing test, let alone show promis of having a positively sloped learning curve.

  17. 117
    MarkB says:

    Re: #58

    Hank Roberts,

    I’m looking at the study posted in #45. Figure 1 on page 17:

    ftp://ftp.nodc.noaa.gov/pub/data.nodc/woa/PUBLICATIONS/grlheat08.pdf

  18. 118
    Hank Roberts says:

    More for Thomas Hariman — as an A student in history, do you study how people perceive change over time? I recall reading years ago that changes on the order of three percent per human generation have simply been imperceptible, as long as people relied on what their grandparents remembered. Do you know of anything currently being studied by historians about rates of change?

  19. 119

    Jaydee wrote in 101:

    Second the direction of the force on the bridge is unclear to me but from the position of the islands, I would guess it was along the length of the bridge in tension or compression.

    Third the ice in the sheet seems (to my eye) to have a “grain” (possibly more than one), it is not homogeneous so the morphology of the break will be complicated

    A grain? Like wood does.

    Of course with water there will be no preferred direction, but with ice, once it starts to form, some directions will be preferred over others — like a snowflake. But in this case it is probably more the result of a limination of layers, one year after the next.

    Given the preferred directions, the substance will be more vulnerable to forces in some directions relative to others. Case in point, graphite has a book-like structure where sheets lie on top of one-another. Push down on the front of the book and it is quite sturdy. But push at a right angle to this and sheet after sheet (or perhaps bunches of sheets — never tried such a ghastly experiment) will peel away. As such in one direction graphite is stronger than diamond.

    Then there is steel. The strongest steel is typically very finely-grained. Like the high carbon Damascus steel made by the Arabs in the Middle Ages (relative to Europe — as the Moslem world was going through a renaissance at the time). But high-carbon steel normally forms very large grains. This was one of the major problems with the hull of the Titanic. It was high carbon, and large crystals lent a grain to the hull such that once a crack began it tended to continue along the length of the hull, leading to flooding in four of five compartments — if I remember correctly.

    This is at a right angle from what I had initially thought, but I think you might be on to something here — and it would be exactly the sort of thing that Gavin might find “interesting.” Basically this reminds me of a piece of wood which is compressed at a right angle to the grain. It would tend to splinter — along long longitudinal lines.

    But why would it be compressed? Because the ice is expanding — due to higher temperatures. Of course one could also argue that there are torosional forces where the ice is being twisted by incoming waves — which would also cause it to splinter along the grain But my “bet” (for whatever it is worth) is on compression due to expansion.

  20. 120
    Tim Bagnell says:

    How much of an effect are rising sea levels having on the loosening and breaking up of sea-borne ice shelves that are attached to land? Or has anyone looked into this factor?

    To me it seems that if we are loosing an island nation in the pacific, upward presure, from rising oceans, on ice that is locked to static land positions would have as big an impact on the ice shelves’ integrity as the water’s temperature.

  21. 121
    Phillip Shaw says:

    Re: #85
    Mark,

    It is a small point but Antarctica is not a dessert. Baked Alaska is a dessert. Antarctica is a desert.

  22. 122
    steve says:

    ref #52 “The End-Permian was caused by CO2 from a super-volcano”

    I am a bit perplexed how this hypothesis has gained so much traction that people speak of it as fact instead of one of several hypothesis. This is especially perplexing when it is taken into account that it relies on a huge amount of volcanism such has never been seen since. We do know that an incredible amout of acid rain must have occurred. We do know that light was blocked and the earth would have suffered from sudden cooling. We have observational information of a much, much smaller but similar in composition eruption from Laki that showed the dramatic effects on life this eruption caused. Certainly there is evidence of dead zones which could be caused by warming oceans, but as we know from the dead zones in the Gulf of Mexico these can also occur as a result of nutrients being added to the waters and volcanoes release a considerable amount of nutrients. We have evidence that methane was released but disrupting the earths crust to this extent could certainly cause release of methane and could cause water level changes which also can release methane. We have isotope evidence but first it is from creatures that were alive at the time and biological processes do not always use isotopes in the same ratio they are available and we have little if any real knowledge of the processes by life forms from hundreds of millions of years ago. Then of course the isotope composition can be affected by the environment after the life form itself dies. I would say yes, co2 is one of many hypothesis that are waiting to be disproved and, considering the age of the evidence, will remain that way until the end of our days.

  23. 123
    Mark says:

    Potato, tomato.

    :-P

  24. 124
    SecularAnimist says:

    Jack Roesler wrote: “A 90% loss of population? Is that possible?”

    Of course it is possible. For example, the Himalayan glaciers that provide much of the fresh water supply for southern and eastern Asia are melting away. When they are gone, a billion or more people will be without fresh water. Without fresh water, they will die.

    At current levels of warming — even without any further warming — the melting away of those glaciers appears unstoppable and irreversible. With the additional warming that is almost certainly locked in given current accelerating rates of CO2 emissions, they are only going to melt away sooner.

    And that’s just one of many problems. There will be similar huge losses of glacier-fed fresh water elsewhere, such as in South America or California. And the widespread, intense droughts that we are already seeing will only spread and intensify, with consequent large scale failures of agriculture all over the world. And oceanic fisheries on which billions of people depend for protein will disappear.

    It is hard for me to envision any plausible scenario in which there will not be a very substantial die-off of the human species by the end of this century.

  25. 125
    Hank Roberts says:

    MarkB, the FTP site you’re pointing to is a copy of the Levitus paper, much discussed. Look it up.

    If you search for that FTP link you’ll see the question you’re asking has been passed around from one blogger to another, with none of them finding the prior discussions. See those for the context.

    http://www.google.com/search?q=Levitus+realclimate

  26. 126

    Comment #110

    Dear sidd,

    Thanks, but I am not talking about anything near northwest Greenland or Ellesmere Island — those little breakups were widely publicized.

    Please look at the coordinates — they are for north-northeast Greenland, not northwest.

  27. 127
    Hank Roberts says:

    Tim Bagnell, 120, asking about whether rising sea level makes ice shelf separation more likely — I asked about it earlier, here’s a bit from that. You can probably bring this up to date by searching on some of the key terms and following up cites:

    ——-
    — Sea level rise can exert huge leverage, bending ice sheets along the grounding line where they fracture.

    Consider the leverage the whole floating area of an ice sheet exerts along the fulcrum line when the floating part is lifted a quarter inch above the prior average.
    http://www.igpp.ucsd.edu/PDF/research/2006/IGPP_Annual_Report_2006_lo.pdf.

    “Ice shelf rifting: In 2005-06 … study rifts at the front of the ice shelves. … little is known about the processes involved in rift propagation, and we do not know how these processes will respond to climate change. …. [rift] propagation is faster in the summer than in winter (Fricker et al., 2005a). …. rift propagation is episodic and occurs in discrete events separated by approximately 2 weeks. [highest lunar tides? -hr]

    “… ICESat data to study the vertical structure of rifts and the mélange which fills them, revealing that mélange accounts for about 30% of the entire ice shelf thickness (Fricker et al., 2005c; Figure 1). …

    “… In 2005-06, … CESat data to map the grounding zones of the ice shelves – the dynamically-active transition zones between grounded and floating ice. ICESat can “see” the tide-forced flexure zone between fully grounded continental ice and fully floating ice shelf ice, identifying the landward and seaward limits of ice flexure …..”

    http://scrippsnews.ucsd.edu/article_detail.cfm?article_num=685

    “… glaciologists believe areas called ice “shelves,” floating slabs of ice that extend from the coasts of the Antarctic Ice Sheet out to sea, may be the first indicators of how climate change is affecting the Antarctic continent because of their direct contact with the ocean and their sensitivity to air temperature warming. Some ice shelves are located in conditions that are close to the melting point of ice, and are therefore more sensitive to changes in atmospheric temperature.

    “… ice shelf “rifting”-ice fracturing that cuts through the entire thickness of an ice shelf and represents the first stage of the process in which icebergs eventually break away from the main ice mass-on East Antarctica’s Amery Ice Shelf.

    “… One paper describes the behavior of the ice shelf rift over a nine-year period, while another paper describes changes over time periods as little as seconds.”

    ——-
    From comments and questions in the thread at:

    http://sciencepolicy.colorado.edu/prometheus/archives/climate_change/001004less_than_a_quarter_.html

  28. 128
    Mark says:

    “I am a bit perplexed how this hypothesis has gained so much traction that people speak of it as fact instead of one of several hypothesis.”

    What are these other hypotheses, and how does the data support them steve. It’s just as easier (even easier, if anything) to say “there are several other possibilitis” especially when you don’t mention them.

    “This is especially perplexing when it is taken into account that it relies on a huge amount of volcanism such has never been seen since.”

    Well yes, animals who lived during a mass extinction level event like that tend not to tell people what they saw. Being dead and all.

    Look at the Deccan traps.

    Look at Yellowstone.

    Do you think these volcanoes dozens of miles across never blew up???

  29. 129
    ccpo says:

    Re: #105

    “ccpo (73), me thinks you are confusing unbiased inquiry with bending over…

    Comment by Rod B — 7 April 2009 @ 9:05 AM”

    I teach English for a living. You can’t get what you claim from what I wrote unless either joking or a denier.

    Which is it?

    Cheers

  30. 130
    RichardC says:

    115 Jack asked, “A 90% loss of population? Is that possible?”

    It is extremely unlikely. When it’s geoengineer or die, well, the choice is blatantly obvious. Anyone who thinks that we won’t brimstone the atmosphere is as clueless as the skeptics. Carrying on the discussion as if it won’t happen is dishonest. Ocean acidification and climate selection are the real issues. The time when AGW could be solved “naturally” is past.

  31. 131
    walter crain says:

    yikes! no glaciers in the himalayas… secularanimist’s glacier/freshwater thing sounds like crazy talk, but that’s only because we have been distracted from thinking about (and planning for) the effects because we’re still arguing over whether it’s happening.

  32. 132

    re 101
    Jaydee, when I studied materials science ice was included , indeed, when I studied mineralogy , it was included too. So both you and hank Roberts should be aware that since its modulus is a couple of orders of magnitude lower than that of an average silicate rock, a landward ice sheet flowing at tens of meters per year under its own weight will respond to local isostasy raising the land at a rate of millimeters per year by bending easily under the strain , not cracking off like a cleaved diamond.

    If you want stiffer ice, try dispersion hardening it with particles ( colloidal silica, sawdust, penguin feathers, whatever,) that will interfere with grain boundary and dislocation motion – even at arctic temperatures ice is within 100K of its melting point and so prone to several different creep mechanisms- try googling ‘creep maps ‘ for a diagram of their time-temperature curves.

  33. 133
    J.S. McIntyre says:

    re 124: “There will be similar huge losses of glacier-fed fresh water elsewhere, such as in South America or California.”

    Actually, in the case of California, it’s water is provided primaarily by the yearly replenishment of its snowpack, and not from glaciers. The problems we’re experiencing now – a 30% drop in snowpack content from the norm, a trend that has continued over three years now – is part of the ongoing decline of precipitation in the Western States.

    But even that 30% decline is deceptive – where the snow fell is of equal importance. As I understand it through folks I know in the Forest Service, the northeastern part of the state is much worse off than the mountians to the south. As one person who works that area described it, NE California really never had a winter this year. Word has it that they’ve been calling in teams a month early to prepare for what is expected to be a rough fire season…the third in a row.

    Another poster mentioned California as an example of a place where the effects of AGW are apparent. If you want to meet a group of people that are pretty much sold on this idea, you should talk to the people who fight the fires. I think you’ll find a lot of believers.

    My apologies for wandering a tad off-topic…

  34. 134
    steve says:

    ref #128 Mark, the Siberian Flats covered an area the size of Australia.

    volcanism, impact and tectonic plate shifts are all competitive hypotheses, I seem to remember reading
    others before but they seemed a bit far fetched and I don’t recall what they were called. I seem to remember one that said it was soil erosion as a base cause.

    I think I covered volcanism well enough. The other two have similar arguments. Some combine two or more such as impact causing volcanism.

  35. 135
    SecularAnimist says:

    RichardC wrote: “When it’s geoengineer or die, well, the choice is blatantly obvious. Anyone who thinks that we won’t brimstone the atmosphere is as clueless as the skeptics.”

    And anyone who thinks that the human species has the ability to geo-engineer its way out of global warming needs to present some evidence of such capabilities.

    So far — based on thousands of years of history and tens of thousands of years of prehistory — the only demonstrated ability for large-scale modification of ecosystems that human beings have shown is the ability to wreck them. Which we have done over and over again.

    The idea that we will learn, within years or decades, how to “manage” the entire planet’s climate and biosphere — including ongoing, perpetual “fine-tuning” of the chemical content of the atmosphere — seems extremely implausible to say the least. Nor have any large-scale geo-engineering schemes been presented so far that give any confidence that they would work, or that they would not have hideous unintended consequences.

  36. 136
    Hank Roberts says:

    Russell, did you read the Scripps papers?

    I realize that theory and observation often differ. That seems the case here. The people who went to the ice describe behavior that you say is impossible.

    What does one do in such circumstances? Arguing with me won’t help, because I’m simply quoting published work.

  37. 137
    Hank Roberts says:

    PS, Russell, this may be helpful. All I have is the abstract, but you may have access to the full text if you’re at an academic institution. Let us know?:

    Earth and Planetary Science Letters
    Volume 280, Issues 1-4, 15 April 2009, Pages 51-60
    doi:10.1016/j.epsl.2008.12.027

    Ice shelf disintegration by plate bending and hydro-fracture: Satellite observations and model results of the 2008 Wilkins ice shelf break-ups

    Abstract

    Satellite remote sensing observations of three break-up events in 2008 for the Wilkins Ice Shelf (28 February to 6 March, 27 May to 31 May, and 28 June to mid-July) provide unprecedented detail of ice shelf calving during rapid break-up. The observations reveal that the Wilkins break-ups occur through a distinctive type of shelf calving, which we term ‘disintegration’, as well as more typical rifting and calving. Here we focus on the disintegration process, which is characterized by repeated rapid fracturing that creates narrow ice-edge-parallel blocks, with subsequent block toppling and fragmentation forming an expanding iceberg and ice rubble mass. We use these data to develop and test a model of floating ice plate disintegration in which ice plate bending stresses at the ice front arising from buoyancy forces can lead to runaway calving when free (mobile) water is available. High-resolution satellite images and laser altimetry of the first break-up event provide details of fracture spacings, ice thicknesses, and plate bending profiles that agree well with our model predictions. We suggest that surface or near-surface meltwater is the main pre-condition for disintegration, and that hydro-fracture is the main mechanism. Brine layers from near-waterline brine infiltration can support a similar process, but this is less effective unless regional ice stress patterns contribute to the net stress available at the crack tip for fracturing. A combination of brine-enhanced fracturing and changing internal net extensional stresses was the likely mechanism behind the latter two Wilkins events.
    _______
    “operation hurting” says ReCaptcha

  38. 138
    Hank Roberts says:

    P.S., perhaps the theory and observations do agree. Russell Seitz wrote:

    “… a landward ice sheet flowing at tens of meters per year under its own weight will respond to local isostasy raising the land at a rate of millimeters per year by bending easily under the strain , not cracking off like a cleaved diamond.”

    That would describe the tide coming _in_, bending the ice up.

    Perhaps something different happens when the tide goes _out_?

    “… , the ocean tides that flow underneath ice shelves can push them up and down by several feet over the course of a day”
    http://scrippsnews.ucsd.edu/pressreleases/fricker_iceshelves.cfm

    from the Scripps link above:
    http://scrippsnews.ucsd.edu/pressreleases/images/fricker.heli_over_loose_too.jpg
    “… helicopter is shown flying low over a rift area”

    “ice shelf “rifting”-ice fracturing that cuts through the entire thickness of an ice shelf and represents the first stage of the process in which icebergs eventually break away from the main ice mass-on East Antarctica’s Amery Ice Shelf.”

    As a doctor I knew long ago used to say, “In theory, theory and practice are the same, but in practice, they differ.”

  39. 139
    Sabahan says:

    Any bets on which ice shelf will go next?

  40. 140
    David B. Benson says:

    Just to posit some different ideas: the Circumpolar Vortex is more intense in recent decades; it draws up deep water at a greater rate; it pushes surface water more intently as a fairly permanent “storm surge”; being more intense, wind induced ocean currents are stronger.

    The photos of Wilkins breaking up reminds me of fault block landforms; Wilkins going downslope on the changed currents.

    Just suggestions; feel free to blast way.

  41. 141
    Marcus says:

    Mark (#55/#117): I don’t have any privileged information about ocean heat content, but my guess would be that given an underlying trend plus random fluctuations that the upward fluctuations will often look quite dramatic. In addition to 2001 to 2004, there are ’93 to ’97 and ’72 to ’75 which also have somewhat large increases. The other issue is that you don’t always expect ocean heat content changes to mirror surface temperature changes: in fact, in years when ocean heat content increases dramatically, that might be due to larger than usual oceanic heat sink effects, such that ocean heat content increases will sometimes be coupled with slower surface temperature increases.

    It could be interesting to look at coupled ocean-atmosphere models and see if that hypothesis holds: eg, where there are long periods without temperature rise in a high forcing scenario, are there larger increases in ocean heat? Mind you, there are other reasons for changes in heat accumulation: changes in cloudiness (which will force both oceans + surface temperatures), changes in mixing from deeper than 700m, volcanic eruptions, etc.

  42. 142
    Hank Roberts says:

    David, that fits the abstract, I think:
    “… bending stresses at the ice front arising from buoyancy forces …” in the presence of “surface or near surface meltwater” to make the fractures persist.

  43. 143
    Hank Roberts says:

    SciAm:
    “We expect in the next few days and weeks, that the northern ice front will lose between 800 and 3700 square kilometres of ice,” says Angelika Humbert of Münster University, Germany, who has been using ESA’s Envisat probe to monitor the events.”
    http://www.newscientist.com/article/dn16918-giant-mass-of-antarctic-ice-set-for-collapse.html

    More detail here for anyone who reads German:
    http://www.uni-muenster.de/Physik.GP/Polargeophysik/Wilkins-Schelfeis.html

    This image in particular may be more detail on the cracks that Mauri mentioned earlier in this thread
    http://www.uni-muenster.de/imperia/md/content/geophysik/polargeophysik2/bilderfotos/28nov2008_large.pdf

  44. 144
    David B. Benson says:

    Hank Roberts (142) — Sort of, but that requires ice melt. Which brings up the other major change caused by the intensification of the Circumpolar Vortex; it tightens poleward, exposing the Antarcttic Pennisula to more of the weather northwards, significantly warming Wilkins et al.

  45. 145
    mauri pelto says:

    In examining the extent of rifting on Wilkins ice shelf, and noting that the rifts are signs of pre-conditioned weakness. it is important to note that the rifts extend south from the bridge. But that there is no sign of rifting south of the rifts that extend toward the northeast corner of Latady Island. On the face of it this may suggest that the remaining Wilkins Ice Shelf at that point is not pre-conditioned yet for rapid collapse. I would suggest the collapse will unfold more like the Wordie Ice Shelf than the Larsen Ice Shelf B. Take a look at its disintegration from 1974-1992. Note it had some key pinning points as well. http://pubs.usgs.gov/fs/fs17-02/fs017-02.html

  46. 146
    Mark says:

    steve, #134.

    What?

    You didn’t seem to say anything there.

    You say that the theories are (apart from supervolcano eruption)

    Siberian traps (assume Deccan traps in siberia) (Supervolcano)
    Volcanism (assume vulcanism) (Supervolcano)
    Impact (subduction, I assume, to get eruptuins) (volcanoes and a lot of them)
    tectonic plate movement (same as impact)
    Soil erosion ???? Maybe as a sequestering of CO2 in weathering, not a source

    But nothing about how they fit the data nor how they differ from Supervolcanoes which you said you found strange was taken as right.

    Please try again.

    What could be an alternative explanation for the PETM that isn’t a supervolcano and how does it fit the data better?

  47. 147
    Mark says:

    Russel, #132.

    You seem to have missed out that no matter how slowly it moves, or how bendy it is, there’s a maximum curvature it can manage to hold before either departing from the contour or breaking.

    So if it drops off a 1ft ledge, it either breaks within the bulk or leaves an air gap. With a million tons of ice over it? That last option doesn’t seem really to be an option.

    Similarly if it goes off out to sea.

    I’m not sure how well that maximum curvature can be applied to a glacier, since it’s definitely not homogeneous. But I do know it exists. Each time I break my plastic card to destroy an old one, I use that fact to rip it.

  48. 148
    Lawrence Brown says:

    Secular Animist wrote in relation to coal mines- ” it is wrong to attribute the death of any one canary to the buildup of toxic fumes.”

    Okay, maybe I should use another analogy. It’s like the ground shaking and cracking before an earthquake,or like seeing an approaching shark’s fin,while swimming. It’s time or even past time to take some action in these cases to haul your (self edit)out of the path of danger, no matter how you slice it.

    The breaking off of ice shelves that hold land ice,falls into this category.The shelves keep the land ice from flowing into the sea could well bring a non-linear response leading to dramatic changes. It’s time to do something. Don’t forget that even if we stopped all anthropogenic forcings right now, we are still committed to a number of decades of warming as the planet comes to equilibrium with present forcing. These forcings are still “in the pipeline”.

  49. 149
    cougar_w says:

    In the interest of conserving energy (human, electrical, and otherwise) I suggest we save this post and associated comments to recycle in 7 months (with minor edits) when we’ll be talking about near-record minimal Arctic ice extent and Arctic Circle ice sheet failures. Those too will be due to volcanos, natural variation, UHI effect, cosmic rays and wacky models, and the deny-o-sphere will again blame the problem on climate scientists who have a s3kret agenda, fail to understand basic math, measure the wrong things, don’t understand the difference between weather and climate, and talk funny or act superior.

    Just trying to help.

    [ and the oracle says: "declared spiciest"! I wins! ]

    cougar

  50. 150
    Hank Roberts says:

    Ah, here are the high resolution images:
    http://www.esa.int/esaEO/SEMYBBSTGOF_index_0.html

    Most recent, April 4, where you can see “the disintegration process, which is characterized by repeated rapid fracturing that creates narrow ice-edge-parallel blocks”

    http://esamultimedia.esa.int/images/wilkinsarctic/pub/images/ASA_IMM_1PNPDE20090405_115601_000002422077_00481_37108_311_100m_img.jpg

    Including many more cracks back into the body of the remaining ice shelf.

    Well, I guess this is going to increase the total area of sea ice reported for the coming Austral winter season!


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