Ice sheet retreat

It is quite regularly pointed out – by Steve Bloom and others – that the Pliocene (5 – 3 million years ago) is quite interesting since the temperatures were 2 – 3oC higher than today, sea levels were 20 – 25m higher than today, yet CO2 levels were about the same as today (400ppm). As I understand it, however, it’s never been clear why sea levels could be so much higher than today, since it would require a significant retreat of the East Antarctic Ice Sheet (EAIS) and this is something that models have not been able to simulate.

A recent paper by Pollard, DeConto and Alley (Potential Antarctic Ice Sheet retreat driven by hydrofracturing and ice cliff failure, however, has tried to address this issue. What this study suggests is that floating ice shelves may be drastically reduced or removed completely by increased oceanic melting, and by hydrofracturing due to surface melt draining into crevasses. As I understand it, increased oceanic melting causes cliff failure.

The maps showing the retreat of the EASI are shown below. As one might expect, even though this process could explain the sea level rise during the Pliocene, it still took 1000s of years.

Figure 3 from Pollard, DeConto & Alley (2015).

Figure 3 from Pollard, DeConto & Alley (2015).


Figure 4 from Pollard, DeConto & Alley (2015)

Figure 4 from Pollard, DeConto & Alley (2015)

Maybe the more interesting figure is the one on the right which shows how sea level rises if cliff failure and hydrofracture are included or not. As illustrated in the maps above, the overall sea level rise takes 1000s of years. However, as the paper says, ice-sheet model accelerates the expected collapse of the West Antarctic Ice Sheet to decadal time scales. So, not only can the sea level rise during the Pliocene be explained by cliff failure and hydrofracture, these processes could also result in a rapid initial rise in sea levels due to the collapse of the West Antarctic Ice Sheet (WAIS).

Anyway, that’s all I was going to say. This is not really my area of expertise, so I’m mainly posting this because it seems interesting and in the hope that I might learn more from those who choose to comment.

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71 Responses to Ice sheet retreat

  1. afeman says:

    Something that dawned on me this weekend – do any of the ice models take into account the ice sheets getting bouyed up by SLR, thereby effectively pushing back the grounding line? I would imagine that would add to the instability of any sheet with a grounding line below sea level.

  2. Andrew Dodds says:

    It’s interesting that Mountain Ranges can undergo ‘Orogenic Collapse’ with what I would assume to be similar drivers – when buttressing fails, mountain ranges spread out laterally with extensional faults – the Tibetan Plateau is starting this right now. Makes mountains go down much faster than you might expect.

    I suspect that once the buttresses of ice sheets – Ice shelves, grounding lines, whatever – fail we’ll see something similar.

  3. afeman,
    Good question. I’m not sure. This paper says

    The model predicts ice thickness and temperature distributions over the Antarctic con- tinent, evolving due to slow deformation under its own weight, and to mass addition and removal (precipitation, basal melt and runoff, oceanic melt, calving of floating ice, and cliff failure described below). Floating ice shelves and grounding-line migration are included. It uses hybrid ice dynamics and an internal condition on ice velocity at the grounding line (Schoof, 2007). Bedrock deformation is modeled as an elastic lithospheric plate above local isostatic relaxation.

    There’s more information in the Supplementary information, but I haven’t had much of a chance to look at that.

  4. John Hartz says:

    Not directly related to the OP, but very interesting nontheless is the following article posted on the BBC today.

    Earth was a frozen Snowball when animals first evolved

  5. This seems odd to me. Ice shelf fracturing etc etc is a way to get quasi-rapid ice sheet collapse – something exciting within 1,000, say. But when you have 100 kyr you don’t need anything so sudden, no?

  6. William,

    But when you have 100 kyr you don’t need anything so sudden, no?

    If you mean, the Pliocene lasted for millions of years and so the melt rate could have been much slower, then that seems a fair point. However, the abstract of the paper does say

    However, most climate and ice sheet models have not been able to simulate significant EAIS retreat from continental size, given that atmospheric CO2 levels were relatively low throughout this period.

    which I took to mean that they hadn’t been able to reproduce the melt even over those timescales. You’ll know better than me if they can actually run these models for 100 kyr or longer, though.

  7. Windchasers says:

    There is another possibility here, I think. Say that changes in some other physical determiner of climate, like the height of a mountain range, or the location of continents and currents could have changed the effective climatic state in the Pliocene relative to now, creating a warmer Earth.

    I’ve been curious about this lately, whether there actually are separate climatic states that can exist at a given insolation, GHG concentration, etc.. with switching between the states being either chaotic or hysteretic. SoD has been talking about it.

    Let’s say it turns out that multiple climate states are possible with the current set of forcings. And let’s say that the CO2 sensitivites of these different states vary. Well, then, the geography and ecoology between these states would vary far less different than would the current geography and ecology be, as compared with the Pliocene. Meaning, if there are some factors that could vary to set up multiple climate states and sensitivities today, there are even more factors that could explain any differences between the Pliocene and today. Maybe it’s another climatic state, with a higher sensitivity.

    Does this make sense?

    I’ve seen data for both sides. On the one hand, there are proxies, which constrain the global temperatures in the Holocene to be relatively flat. On the other hand, other proxies suggest vastly different regional climates at different times through recorded history, which could basically indicate another climate state with a similar (average) temperature.

  8. Michael 2 says:

    John Hartz, thanks for the interesting story on Snowball Earth and evolution; wondering whether the first animal cells caused the snowball or the snowball compelled evolution of animal cells (more likely both at the same time).

    I haven’t previously heard of “snowball Earth” so I appreciate learning something right here today.

    I notice the BBC’s obligatory nod to CAGW: “Right now our appetite for fossil fuels is hotting things up dangerously fast.”

    I suppose that is British for “heating things up”.
    http://www.express.co.uk/news/nature/528643/Winter-2014-weather-warning-snow-arctic-freezing-temperatures-forecast

  9. Steve Bloom says:

    “it still took 1000s of years.”

    We don’t know that.

  10. Michael 2 says:

    I have a doubt about the veracity of “express.co.uk” it looks a bit like a tabloid. Maybe the BBC has something to say. A bit less dramatic and not a single mention of global warming or “hotting”:

    http://www.bbc.com/news/uk-30602834

  11. Steve Bloom says:

    Windchaser, I think it’s pretty clear that the background conditions determine the climate state. Note that while relatively minor step changes do seem possible as background conditions shift, e.g. the Mid-Pleistocene Transition, the fact that the massive glacial climate swings (themselves a consequence of known changes in background conditions) haven’t popped the climate into one of those postulated other states stands as really strong evidence that that sort of thing doesn’t happen, and indeed can’t. Change the background conditions quickly and massively as we’re doing now and all bets are off, except for the one that it’s going to be getting a lot hotter, of course.

    I think I mentioned before that I have it from Harry Dowsett last month that fresh Pliocene SL results are headed toward maxima of over 50 meters, presumably as they become fine-grained enough to catch short-term EAIS fluctuations. I will, eventually, follow up on this and do a post.

    One caveat to the use of “decadal” is that conditions in Antarctica haven’t quite reached the necessary initial state for the process to begin. So, you know, party on.

  12. Windchasers says:

    the fact that the massive glacial climate swings (themselves a consequence of known changes in background conditions) haven’t popped the climate into one of those postulated other states stands as really strong evidence that that sort of thing doesn’t happen, and indeed can’t.

    Who’s to say they haven’t? Would it necessarily be evident in the historical proxies? (On the contrary, I keep seeing evidence in the proxies that suggest this is happening).

    Heck, IIUC, it looks like the PDO controls the frequency of La Nina vs El Nino on a ~60 year cycle. That’s basically two climate microstates right there, with a naturally occurring oscillation between them. It’s a substantial change in precipitation in many places, if the dominance of El Ninos vs La Ninas changes.

    It seems to me that the presence of extreme regional climatic events may be the result of different global climate states. But here, in case this helps clarify the kind of thing I’m thinking about:
    http://scienceofdoom.com/2015/01/04/natural-variability-and-chaos-eight-abrupt-change/

    Really, this just means that the real-world statistics may be “lumpy”, with variation in various regional climatic attributes clumping together into groups instead of distributing normally. And it may or may not have much to do with the sensitivity to CO2.

  13. John says:

    Reblogged this on jpratt27.

  14. Peter Jacobs says:

    William Connolley writes: “This seems odd to me. Ice shelf fracturing etc etc is a way to get quasi-rapid ice sheet collapse – something exciting within 1,000, say. But when you have 100 kyr you don’t need anything so sudden, no?”

    Dr. Connolley, if you look at the second image in this post (Fig 4 in the actual paper), I think that you’ll see that the combination of the mechanisms are relevant to both rapid, large decay in the short term (particularly for the WAIS) as well as the overall magnitude of the ice loss and SLR (due to the EAIS) on much longer timescales. Although they don’t show a 100kyr simulation in this figure, there is one in the SI. After several thousand years GIA allows grounding lines to reestablish and so the SLR slows and eventually RSL drops a little (peak SLR reached after ~3-4kyr at ~17-18m, and then slowing dropping to ~16m by 100kyr).

    Essentially, without these processes, a lot of “realistic” ice sheet models had a hard time getting the EAIS to melt, even under conditions in which we’re confident it did must have like the mPWP (due both to RSL reconstructions of the period e.g. Miller et al., 2012 as well as physical evidence from the region itself e.g. marine seds as in Cook et al., 2013).

  15. Peter Jacobs says:

    Steve Bloom writes: “I think I mentioned before that I have it from Harry Dowsett last month that fresh Pliocene SL results are headed toward maxima of over 50 meters, presumably as they become fine-grained enough to catch short-term EAIS fluctuations.”

    I am very skeptical of this. For the mPWP? From proxy data? +20m, sure. +30m, plausible. Higher than that? I would like to see some very, very convincing evidence. 50m? That sounds unbelievable.

  16. Steve Bloom says:

    It sounded high to me, too, Peter, even bearing in mind that the associated means would be quite a bit lower. Anyway, that’s what he said. I’ll try to prioritize following up with him soon.

    For context, this remark occurred in a conversation about the unfortunate manner in which IPCC higher-ups chopped the top 12 meters off the Miller et al. (2012) Pliocene SL range (which topped out at 32 meters). Iironically given the results of the paper discussed in the OP, this seems to have been done so as to make DeConto and Pollard’s 2009 results not look too ridiculously out of step.

    But what’s 12 meters among friends? :/

    AIUI the early Pliocene would also be a candidate for high SL, although given the focus of recent research I would suspect the PRISM “time slice.”

    This would have to be based on proxy data from the recent Antarctic shelf cores, only partially analyzed as yet. I suspect Harry was talking about work yet to be published, although there was a 2013 paper (Cook et al. IIRC) that hinted pretty broadly at much faster ice sheet response and thus much higher SL numbers to come.

  17. Steve Bloom says:

    Aha, you mentioned those papers in your prior comment.

  18. Steve Bloom says:

    You seem to have shifted from a large global claim to a much smaller regional one, Windchaser. As to the latter, sure, very plausibly.

  19. Steve Bloom says:

    TBC on one point, Peter: If it turned out the actual Pliocene highstand was ~ 35 meters, it would be unsurprising to see the error bars run up to 50 meters or even little higher. So this is maybe ~ 10 meters above what the paleo community was thinking a few years ago, which given substantially higher-resolution data doesn’t seem so amazing on the face of it. But it is an amazing volume of melt relative to the understanding of even 10 years ago (and who now recalls the halcyon days of Pfeffer et al. 2008?), and I would note that we are pushing the ice sheets rather harder than they were being pushed back in the Pliocene.

  20. jyyh says:

    Some hopefully helpful notes…. Systemwise there’s of course the minor issue of connecting the Americas with a land bridge… but does it eventually matter whether the warmed up waters of the Pacific come about to mess with the AMOC straight in the middle or taking a round in the SH first? This especially since most rivers discharge to Atlantic making it almost as large a water circulation feature than the Pacific itself? Of course the Bering strait would been deeper then, too, easing the access of the not-cold waters of North Pacific to the Arctic Ocean,

  21. jyyh says:

    That is to say in the future world containing more moisture some of the rivers could increase their discharge to Atlantic as has been already happening (so I’ve gathered) in Siberia warming up the ocean surfaces in Atlantic. Sure the entry points of these warmer-than-previously waters aren’t the same as in Pliocene but does it eventually matter. This though might take a pretty long time to be realised, f.e. the increased action of Hadley cells would need to wet some of the larger deserts first. Are we due a Green Sahara phase before the Ice Sheet decompose to the +25m ASL? What would be needed is a simulation that would forcibly introduce a large influx of river waters to all the oceans since what goes up must come down (the increased air-moisture from the ocean gets to the tropopause (that’s getting higher up) and falls anyway, the extra moisture does not stay in the air anylonger than currently (I would say)). Map or two would be in order to the OP..

  22. Dave Werth says:

    afeman,

    That’s something I’ve thought about before too. One thing to keep in mind is that sea levels around Antarctica are considerable higher than they otherwise would be because of the gravitational attraction of all that ice. As the ice melts the gravitational attraction drops which might be a counter to sea level rise locally. How it all balances out I have no idea.

  23. Windchasers says:

    Well, steve, how different do the climatic states have to be, to be called separate states? Assuming the same average temperature. How much would regional climates have to vary from what they have now? (Normally, you’d look at how smoothly varying the statistics were, across all the states, vs how much they clump).

    I guess I don’t see why there’s only one possible state of the global climate, even at a given temperature and forcings. Do the climate models resolve the oceans, clouds, etc., and the feedbacks well enough that we can really rule these out as a possibility? I don’t think so. IIUC, we lack the computational power to really explore the long-term climate statistics with eddy-resolving models.

  24. Windchaser,

    I’ve been curious about this lately, whether there actually are separate climatic states that can exist at a given insolation, GHG concentration, etc.. with switching between the states being either chaotic or hysteretic. SoD has been talking about it.

    That’s certainly possible. My understanding is that we’d expect this to be a hysteresis effect and would depend on whether the forcings were increasing or decreasing. There’s quite a nice illustration here. Could chaotic internal processes also play a role? Possibly, I’m not really sure. In a sense Dansgaard-Oeschger events may be an example of this, but they seem to be more short and rapid changes that recover, than genuinely different climate states for the same level of external forcing.

  25. Steve Bloom says:

    “That’s certainly possible.” I’m not sure how useful that linked example is. Can you suggest something from the Phanerozoic?

  26. Steve,

    I’m not sure how useful that linked example is. Can you suggest something from the Phanerozoic?

    Well, sure, if you mean that it’s unlikely that there could be two possible climate states when the ice sheets are already small, then I would probably agree. I was simply agreeing that, in general, our climate state is not simply defined by the level of external forcing.

  27. Steve Bloom says:

    Windchaser, you’re begging the question about global climate. Some regional variation is to be expected, I think, although that may be largely just a function of climate never really being static. Indeed, IIRC on close examination most such variations have been found to be forced. You need to do more than handwaving here.

  28. Steve Bloom says:

    Anders, do you mean to say that at the scale of global climate there are persistent non-forced effects? I’m just not seeing it.

  29. Steve,
    Today, no. I was simply making a general point that hysteresis means that you can have two states for the same level of external forcing. I’m unaware of any evidence for persistent non-forced effects in today’s type of climate state. Whether they exist in other states, probably depends on whether you think something like a D-O event is persistent or not.

  30. Steve Bloom says:

    Also, I’m not sure even —

    My understanding is that we’d expect this to be a hysteresis effect and would depend on whether the forcings were increasing or decreasing.

    — is the sort of thing Windchaser was arguing for. I think you need an example with two different states that can persist given the same conditions.

  31. Steve Bloom says:

    Crossed replies. Yes, agreed. FWIW, I would class D-O events together with ENSO.

  32. Steve,

    I think you need an example with two different states that can persist given the same conditions.

    I know that the example I gave was simply a model, but is that not true in the hysteresis scenario, or are you suggesting that if you stopped changing the external forcing, it would switch to a single state? I don’t know the answer.

    I understand that at each end of the hysteresis loop, there isn’t any evidence for two states. Either we’re in a snowball Earth, or we’re relatively ice free, so it’s certainly not true that there can always be two possible states. I was simply acknowledging that it does seem possible under some scenarios. Given that that seems a reasonable statement, I’m not sure why I should avoid saying it.

  33. Steve Bloom says:

    Anders, I do think it would, eventually. And also, are those really two states being described? Or rather, if they are two states, wouldn’t you get something similar plotting the ice-over and ice-out behavior of a pond?

  34. Andrew Dodds says:

    Steve Bloom, aTTP:

    Given the current continental configuration, you could hypothesize several distinct ‘states’…

    a) Full glacial conditions (Eurasian and North American Ice sheets)
    b) Current Interglacial – Full GIS, Full Antarctic ice sheet.
    c) Warmer Interglacial – North GIS only, EAIS only.
    d) Pliocene state – Reduced EAIS only.

    The state you get being determined by things like CO2 levels and Milancovitch parameters.

    And the experiment is, if you use one of these states as a starting configuration for a GCM with current CO2/insolation levels, does it stay there.. i.e. if you restore the full ice sheets to the world of 1850, are they stable?

    The problem is complicated by the fact that orbital parameters change on the kind of timescales that you’d expect the system to come to rest, and state changes themselves change CO2 levels. Even so, it is fairly easy to show that the big ice sheets don’t have a continuous range of stable volumes, and that pretty much implies that there is not a continuous range of stable temperatures and sea levels.

  35. Steve,
    I don’t actually know. You may be right that there is only one persistent state for any set of external conditions.

  36. John Hartz says:

    Michael 2: Re your response to my link to the BBC’s Snowball Earth article, you’re welcome.

    I think you are a bit more open-minded than I intitially pereceived you to be.

  37. Andrew Dodds says:

    M2 –

    The Express is more cartoon than newspaper.. they have a long tradition of publishing apocalyptic weather forecasts from fringe sites as front page news,

    So far, this winter in the UK has been warmer than usual – in the South West we’ve had 3-4 frosts, none sharp, and one very light dusting of snow so far. Last Friday it was up to 14 degrees C in my garden. There is snow forecast overnight, although it probably won’t be there in the morning.

    A cynic would suggest that global warming has, by warming winter faster than summer, made us go from ‘mild and damp 9 months of the year (3 cold)’ to ‘mild and damp 12 months of the year’. Yay.

  38. Steve Bloom says:

    Linking to that Express article seemed more reflexive than open-minded, John.

    But what I’m struck by is m2’s admission of ignorance about Snowball Earth. I spent an awful lot of time learning about the climate system in part because I like to understand things but also so I could make at least semi-informed comments in venues such as this. It’s a little depressing to see proof that m2 has not, even while enthusiastically holding forth on a wide variety of climate-related topics.

  39. Steve Bloom says:

    Andrew, those comparisons are interesting. If we were around 30,000 years ago we’d probably have thought of the continental NH ice sheets as stable, but as it turns out they’re caught in a cycle of growing until they collapse.

    Perhaps we could consider an Earth without Milankovitch cycles and with stable CO2, in which case there probably could be multiple stable states featuring continental NH ice sheets. But that’s not the planet we live on. Ice sheets are highly dynamic and only appear to be otherwise because of short human lifetimes.

    (For m2: Ice sheets have been uncommon on this planet ever since the end of the last snowball state ~ 600 mya, and large Pleistocene-like ice sheets have been out-and-out rarities. You live on a planet that doesn’t want to have the glacial conditions under which our species has evolved and thrived. Maybe that’s a hint to not push your luck.)

  40. toby52 says:

    I had scanned in this page from David Archer’s The Long Thaw for a post elsewhere, but it seems relevant here:

  41. BBD says:

    M2

    I haven’t previously heard of “snowball Earth” so I appreciate learning something right here today.

    I notice the BBC’s obligatory nod to CAGW: “Right now our appetite for fossil fuels is hotting things up dangerously fast.”

    How did the climate system get out of the albedo-locked icehouse state?

  42. John Hartz says:

    Seve Bloom, Re M2, “The journey of one-thousand miles begins with the first step.”

  43. John Hartz says:

    Speaking of what’s going on in the cryosphere…

    Approximately 85% of the glacial ice on Mount Kilimanjaro disappeared between 1912 and 2011, and the remainder could disappear before 2020, according to a 2012 report by Nasa. These are the same glaciers that survived three periods of abrupt climate change thousands of years ago, the most recent of which brought with it a 300 year drought starting in 2200 BC.

    Will Gadd: “We were climbing ice that isn’t going to be there next week” by Jared Lindzon, The Guardian, Jan 13, 2015

  44. BBD says:

    John

    So long as that step is in the right direction

    🙂

  45. Peter Jacobs says:

    toby52

    It’s been a long time since I’ve read that book, I might want to revisit it. And your graphic is topical. Work published since that book came out has suggested that the Eemian/MIS5e was both a little cooler marked by somewhat higher peak RSL (Dutton et al., 2015 in QSR). That would put its dot a little more in line with the other paleoclimatic reference points.

  46. Steve Bloom says:

    Right, John, but sometimes that first step turns out to be the start of a demonstration of Zeno’s Paradox. 🙂

  47. Steve Bloom says:

    Sorry, should add: So it’s a journey that never ends, but also never gets beyond about 2 meters.

  48. Vinny Burgoo says:

    John Hartz, if photographs of someone climbing the shrinking ice on top of Mt Kilimanjaro can ‘raise awareness of the effects of global warming’ (the Graun article you linked to) it’ll be raising the same sort of awareness that blames, say, all sea-level rise in Jakarta or every last downturn in butterfly populations on global warming – a global warming alarmist’s awareness. Even Skeptical Science ackowledges that other factors are mostly to blame for the loss of Kili’s ice (then says [warning: the following is a paraphrase], ‘Yeah, but so what, this myth might not be a myth but it’s still a myth because global warming is real, people, and don’t you ever forget it’ – which logic deserves some sort of prize.)

    https://www.skepticalscience.com/mount-kilimanjaro-snow.htm

    Also, the Graun gives a NASA source for its prediction that the ice might be gone by 2020, but that linked NASA page actually says 2060, not 2020. The 2020 prediction was probably one of Lonnie Thompson’s. On another computer, I have the complete list of his predictions of when the ice will vanish. Much like Wadhams’ predictions of an Arctic Ocean free of sea-ice in summer, Thompson’ Kili predictions move with the times and, IIRC, generally stay about ten years ahead of the present, so if that 2020 is one of his it’s probably a few years old.

    You could do with being bit more suspicious of the Guardian, you know.

  49. entropicman says:

    BBD
    “How did the climate system get out of the albedo-locked icehouse state?”

    Once the icehouse formed, the rapid erosion stopped and so did removal of CO2 from the atmosphere. Vulcanism gradually replenished the CO2 and raised the temperature.

    Once the temperature was high enough to start increasing the area of open water , the reduction in albedo acted as a positive feedback.

    More discussion here .

  50. BBD says:

    Vinny’s shtick is getting more and more irritating by the iteration.

  51. BBD says:

    entropicman

    I was asking M2, who seems to think that there is no connection between SE states and the topic of GHG forcing. You’ve spoiled it all now. I shall never post here again. 😦

  52. Vinny Burgoo says:

    What does that mean, BBD? That you don’t mind everything being blamed on global warming? That it’s OK for John Hartz to puff an inaccurate/knowingly incomplete Graun article because his heart’s in the right place? Or perhaps that his link to the article didn’t imply approval of it?

  53. Windchasers says:

    — is the sort of thing Windchaser was arguing for. I think you need an example with two different states that can persist given the same conditions.

    That’s literally part of the definition of hysteresis. For hysteresis, there needs to be at least two states that a system can get stuck in, and which state it’s in depends on the history.

    Generally, to get from one hysteretic state to another, we have to apply some kind of forcing (not to be equated with temperature forcing, though that could be an example). Whereas, we may switch between chaotic states even without forcing; it can happen randomly.

    I’m talking about either kind of state, so long as the state can exist and persist for climatic time periods.

    It’s probably helpful to define what I mean by different climatic states. If climate science is anything like materials science, that means we’re talking about statistics. The distribution of various climate variables would be “lumpy” – you’d see a bunch of correlated variables that are all *this* way when the climate is in one state, but they’re all *that* way when it’s in another state, and with little time spent in between the two.

    And average global temperature may or may not be one of those variables. Instead, for instance, we might have something like the temperature variation between coastal Greenland and England. Say in one state we get loose blocking, and the temperature difference between Greenland and England is highly variable, and in another state we get heavy, fixed blocking between the two locations, which fixes the temperature difference quite strongly.

    That’s one example. If the statistics were sufficiently separable for the two states, we’d call them different climates, even if the average global temperature was the same.

    I’m supposing, of course, based on my experience in math and other physical science fields. So if anyone has more information about how separate climates are defined, I’d love to hear it.

  54. Rachel M says:

    Vinny,

    If you look at one of the papers linked to from the NASA site, it says:

    Linear extrapolation of the retreat in each of the three identified glacier assemblages imply the ice cover on the western slopes of Kilimanjaro will be gone before 2020, while the remaining ice bodies on the plateau and southern slopes will most likely disappear by 2040. It is highly unlikely that any body of ice will be present on Kilimanjaro after 2060 if present-day climatological conditions are maintained.

    http://www.the-cryosphere-discuss.net/6/4233/2012/tcd-6-4233-2012.html

  55. Windchaser,
    If you’re going from an almost ice-free state to one with large ice sheets (or towards a full snowball earth) then the path could (probably is) different to what would be followed if we were moving from a snowball earth phase towards an almost ice-free phase. I don’t think, however, that there is any evidence to suggest that there can be more than one persistent climate state when we’re almost ice free (as we are now) or when we’re in a full snowball Earth phase.

  56. BBD says:

    Vinny

    Your obsessive nitpicking and concomitant claims of “alarmism” is beyond tedious. It is also grotesquely unbalanced. When are you going to start to critique the geyser of mendacity and distortion erupting from the fundament of the denialosphere? You need a defence against accusations of gross hypocrisy and crypto-denialism.

  57. entropicman says:

    BBD

    Sorry.

  58. Vinny Burgoo says:

    Thanks, Rachel, but what’s in that link-from-a-link is not what the linker said. The Graun said [warning: not a paraphrase]: ‘…the remainder [of all Kili ice] could disappear before 2020’.

    I’m 97% certain you won’t be able to find any meaningful support for the Graun’s position. I’ve been following this story on and off for years. Unless the Kili consensus has changed radically in the last two or three, the Graun’s article was either ignorant or knowingly incomplete. With some Graun writers I’d put money on the latter, but I haven’t read anything by Jared Lindzon before.

  59. BBD says:

    entropicman

    No worries 🙂 And you did link to the best synoptic SE site around, which I hope M2 will take time to review.

  60. BBD says:

    That’s right, Vinny. Keep pushing your peanut and ignoring the fact that the real bias issue is yours, not the Graun’s.

  61. Vinny Burgoo says:

    BBD, the day you offer any sort of critique of ‘the geyser of mendacity and distortion erupting from the fundament of the’ NGO-o-sphere (incl. its paid outlets like the Graun) I might start stopping nitpicking alarmist parrotings here at ATTP.

    Unlikely, though. I enjoy nitpicking. Especially a nitpicking of the righteous.

  62. BBD says:

    Except it’s *not* a geyser Vinny. It’s odd, trivial things, here and there. There is in fact no comparison whatsoever with the outpouring of deliberate, calculated mendacity from the denialosphere. You just dug your hole deeper.

  63. John Hartz says:

    Vinny Burgoo: Your concerns about the Guardian article re Mt Kilimamjaro are duely noted and thanks for referencing and linking to John Cook’s rebuttal article, Mt. Kilimanjaro’s ice loss is due to land use posted on SkS.

    Cook’s article is very brief and somewhat dated. Thank you for reminding me that it needs a dust-up. If you have any suggestions about new studies that should be referenced in it, please pass them on.

    It is also important to highlight the footnote to Cook’s article which reads as follows:

    Raymond Pierrehumbert has written a lengthy and informative article Tropical Glacier Retreat that explains the physics of tropical glaciers and the complexities of Mt Kilimanjaro.

  64. John Hartz says:

    Another article on happenings in the cryosphere…

    Over a few summer days in 2012, nearly all of the Greenland ice sheet surface thawed right under the feet of a UCLA-led team of scientists.

    What was not absorbed into snow quickly gathered and flowed across the 20,000-square-mile sheet, coalescing into roaring turquoise rivers. And then most of it disappeared.

    Where all that water went may seem an easy guess. But that’s just the problem with Greenland ice science — some of the guesses have been wrong, according to a study published online Monday in the journal Proceedings of the National Academy of Sciences.

    Ice researchers capture catastrophic Greenland melt by Geoffry Mohan, Los Angeles Times, Jan 12, 2105

  65. Windchaser says:

    ATTP,

    I don’t think, however, that there is any evidence to suggest that there can be more than one persistent climate state when we’re almost ice free (as we are now) or when we’re in a full snowball Earth phase.

    If I recall correctly (and I can’t guarantee that), there’s paleoclimate data that suggests different regional climates from today, and as actual, ongoing states, not just as normally-distributed variation on the current regional climates. E.g., the mega-drought in the Southwest US that may have taken down the Anasazi, and the “MWP” in the north Atlantic. Plus, there’s model data that suggests the possibility of such states, as in SoD’s latest post.

    If the regional proxy data holds, and if it is separable (i.e., if it’s not normally-distributed variation, but “lumpy” variation), then to me this implies separate climatic states. Maybe with chaotic transitions, maybe hysteretic, maybe neither. We’d need to work out the mechanisms behind the states and behind their transitions.

    Obviously, the question is then whether these different states are the result of forcings or not.

    But overall, my point is that even if there’s scant evidence for different climatic states, it also appears there’s also scant evidence against them. I.e., we can’t yet rule them out. We don’t know much about the historical forcings, so we’re reliant on the models to probe this kind of question, and the global models don’t do regional climates very well yet, so I wouldn’t expect them to even resolve these kinds of questions yet.

  66. Everett F Sargent says:

    So, I’m thinking that I would need to see a time series of observational SL data, say on a millennial timescale.

    “The Mid-Pliocene sea-level conundrum: Glacial isostasy, eustasy and dynamic topography”

    (I’ve emailed for the SOM)

    http://www.sciencedirect.com/science/article/pii/S0012821X13006006

    Note that Mitrovica (the dynamic geoid guy) is in that list of authors, and that SL might actually drop ~100 meters in the immediate vicinity of WAIS/GIS (and that this would at least suggest a global geoid model to account for local SL).

    Saying past sea level was 20, 30 or 50 meters higher in the past (mid pliocene sea level) doesn’t actually tell me a whole heck of a lot.

    Now, if someone can point to time periods prior to the mid pliocene sea level ‘highstand’ that were say -30, -50, -80 meters below the mid pliocene sea level ‘highstand’ that also have consummate proxy temperature and CO2 (or GHGe) time series, that might be useful information. And that those time series are anything close to current dynamic conditions would be mighty useful information.

    Meanwhile, IMHO we all are eternally stuck with human timescales. D’oh!

  67. Steve Bloom says:

    Now, if someone can point to time periods prior to the mid pliocene sea level ‘highstand’ that were say -30, -50, -80 meters below the mid pliocene sea level ‘highstand’ that also have consummate proxy temperature and CO2 (or GHGe) time series, that might be useful information. And that those time series are anything close to current dynamic conditions would be mighty useful information.

    Pre-Pliocene times with more ice than now? We’re talking back around the Paleozoic/Mesozoic boundary. Data is thin, although for sure the dynamic conditions were quite different.

    And, er, “consummate”?

    Oh wait, sorry:

    So, I’m thinking that I would need to see a time series of observational SL data, say on a millennial timescale.

    Hilarious. You should go into the comedy business.

  68. Steve Bloom says:

    Volcanoes, Windchaser. And ‘ware the Stadium Wave.

  69. Peter Jacobs says:

    Everett,

    The Mitrovica et al. stuff about GIA uncertainty in some areas of RSL markers casting doubt on 15+ SLR during the mPWP kind of all falls apart when you look at d18O records, coral high stands in tectonically stable areas, basic energy balance-RSL relationships, etc.

    The “maybe we know less than we do” line, especially from someone with big swing-big hit bona rides as Mitrovica does make for at least a few high profile publications, though.

  70. Steve Bloom says:

    Not the Pliocene, but estimated SLR for the Eemian seems to have crept up significantly (press release):

    On a tropical island, fossils reveal past — and possible future — of polar ice

    The balmy islands of Seychelles couldn’t feel farther from Antarctica, but their fossil corals could reveal much about the fate of polar ice sheets.

    About 125,000 years ago, the average global temperature was only slightly warmer, but sea levels rose high enough to submerge the locations of many of today’s coastal cities. Understanding what caused seas to rise then could shed light on how to protect those cities today.

    By examining fossil corals found on the Indian Ocean islands, University of Florida geochemist Andrea Dutton found evidence that global mean sea level during that period peaked at 20 to 30 feet above current levels. Dutton’s team of international researchers concluded that rapid retreat of an unstable part of the Antarctic ice sheet was a major contributor to that sea-level rise.

    “This occurred during a time when the average global temperature was only slightly warmer than at present,” Dutton said.

    Dutton evaluated fossil corals in Seychelles because sea level in that region closely matches that of global mean sea level. Local patterns of sea-level change can differ from global trends because of variations in Earth’s surface and gravity fields that occur when ice sheets grow and shrink.

    In an article published in the January 2015 issue of Quaternary Science Reviews, the researchers concluded that while sea-level rise in the Last Interglacial period was driven by the same processes active today — thermal expansion of seawater, melting mountain glaciers and melting polar ice sheets in Greenland and Antarctica — most was driven by polar ice sheet melt. Their study, partially funded by the National Science Foundation, also suggests the Antarctic ice sheet partially collapsed early in that period.

    “Following a rapid transition to high sea levels when the last interglacial period began, sea level continued rising steadily,” Dutton said. “The collapse of Antarctic ice occurred when the polar regions were a few degrees warmer than they are now — temperatures that we are likely to reach within a matter of decades.”

    Several recent studies by other researchers suggest that process may have already started.
    “We could be poised for another partial collapse of the Antarctic ice sheet,” Dutton said.

  71. John Hartz says:

    What’s happening to the Antarctic ice sheet now is the subject of John Abraham’s article, The Antarctic ice sheet is a sleeping giant, beginning to stir, posted today on the Guardian as part of the Climate Consensus – The 97% blog series.

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