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  1. I’m a moderately informed layperson, I suppose. I found this to be one of the best IPCC summary pieces I’ve seen.

    (Mind you, I did have an initial misreading of a graph label as “Antarctic ice-sheet rabid dynamics,” and that did seem a bit of an emotional reaction.)


    Comment by Scott Belyea — 15 Oct 2013 @ 9:58 AM

  2. “By 2300, for unmitigated emissions IPCC projects between 1 and more than 3 meters of rise.”

    But what is the worst-case by 2300, based on a worst-case of about 1.5m by 2100, as argued by Levermann and Grinsted? That would imply about 3 cm/yr of SLR by 2100, and probably some further acceleration during the next century, right? So would it be reasonable to say the worst-case for 2100-2300 is about 4 meter/century, so almost 10 meters of total SLR by 2300?

    This would be about the worst-case estimate by Meehl et al (2012), based on semi-empirical models:

    IPCC could not reach consensus on the value of the semi-empirical models. But should policy makers, and citizens, only use science on which a great deal of consensus exist? Or should they use a risk and precautionary approach and conclude that a worst-case of about 10 meters by 2300 cannot confidently by excluded by science at this point? Would 10 meters by 2300 as a worst-case be a scientifically sound conclusion?

    Comment by Lennart van der Linde — 15 Oct 2013 @ 10:08 AM

  3. I’d like to add that there is no consensus on the skill of current generation process based models of sea level rise. I think it is safe to say that there is disagreement over the relative levels of confidence should be assigned to current process based vs semi empirical approaches. Both approaches should IMO have been included in the reported uncertainty ranges. I frankly think that this would also much closer represent the level of uncertainty there is in the sea level community. See e.g. the comparison between AR5, SEMs and “ice sheet experts” here:

    Comment by Aslak Grinsted — 15 Oct 2013 @ 10:12 AM

  4. An important addition by Anders Levermann is his statement that worst-case estimates should get lower as science progresses, not go up:

    “In the case of sea level, society might want to know what is science’s best guess for the future rise, but for any practical purposes of coastal protection it is the worst case that is relevant. What is the upper limit of sea-level rise? An upper limit is different from a best guess and has at least two peculiar properties that are trivial but important. First, for all practical purposes, the upper limit cannot be exceeded. That means that if you build costal protection with respect to this upper limit, then you are safe, independent of scientific uncertainty or socio-economic scenarios. Second, an estimate of an upper limit is getting lower the more information is available — i.e., the more our scientific insight deepens. You start with the highest number available and then seek scientific evidence that allows dismissing this value and pushing the number down until you find no further reason to decrease it. Then you have your upper limit and you are safe.”

    Comment by Lennart van der Linde — 15 Oct 2013 @ 10:19 AM

  5. Very helpful, thanks.

    Comment by Christian — 15 Oct 2013 @ 10:28 AM

  6. this one by Paul Voosen has a high paywall, sorry to say.

    [Response: Sorry – when I saw it it wasn’t behind a paywall. Now it is for me, too. stefan]

    Comment by Hank Roberts — 15 Oct 2013 @ 11:19 AM

  7. Hi Stefan,

    Thanks for this thorough and interesting post. It’s nice to see that the SLR work in AR5 is not as egregiously conservative as in AR4, but it still very much sounds like there is a hyper aversion to Type I errors which leads to these still likely conservative low ranges (in particular, the unwillingness to explore the upper tails of the distribution).

    As the IPCC discussion evolves this fall and winter about the future of the report, some folks have suggested smaller, quicker, more targeted reports (along the lines of the Special Report on Extremes, SREX). I’d be curious to hear your and the RC folks thoughts. First, what’s your sense on this as a viable and useful option? Second, would a Special Report on SLR be a useful targeted report? It seems like the science is evolving fast, the policy relevance is high, and it needs to be explored in more detail and with a more balanced risk-management perspective…

    Best regards,

    Bill Anderegg

    Comment by Bill Anderegg — 15 Oct 2013 @ 11:29 AM

  8. Very useful. I reposted it to Facebook just now, adding the figures in feet; more people (of the type we wish to influence) understand feet much better!

    Comment by John Burgeson — 15 Oct 2013 @ 11:31 AM

  9. This is what I posted to Facebook just a few minutes ago. JB

    Comment by John Burgeson — 15 Oct 2013 @ 11:33 AM

  10. Sorry — The key IPCC findings about past and future sea-level rise: (1) global sea level is rising, (2) this rise has accelerated since pre-industrial times and (3) it will accelerate further in this century. The projections for the future are much higher and more credible than those in the 4th report but possibly still a bit conservative. For high emissions IPCC predicts a global rise by 52-98 cm (that’s 5 to 10 meters; a meter equals 3 + feet) by the year 2100, which will threaten the survival of coastal cities and entire island nations.Even with aggressive emissions reductions, a rise by 28-61 cm 3 to 6 meters; or 5 to 18 feet, is predicted. Goodbye Galveston.

    Comment by John Burgeson — 15 Oct 2013 @ 11:34 AM

  11. I also posted “Also — “aggressive emission reduction is just not going to happen. So plan for 15 to 30 feet. OH BTW, it gets higher after that; I have not yet seen an estimate of where it will level off. Perhaps someone here has such an estimate?”

    Comment by John Burgeson — 15 Oct 2013 @ 11:37 AM

  12. Nice paper. Do we know for which element (steric or water transfer from ice) and in which proportion climate models tend to underestimate the historical SLR , when their results are compared to climatologies? Thanks.

    Comment by questions — 15 Oct 2013 @ 11:58 AM

  13. That means that if you build costal protection with respect to this upper limit, then you are safe

    But the upper limit might be higher than the upper limit estimate? A lot could and will change since the entire planets gravitational field will readjust, which means more seismic activity. And SLR is likely to be exponential, hence why it accelerates. Coastal protection needs to account for higher storm surges, affected by storm strength, storm size and uneven SLR distribution and re-configuring of ocean flow.

    Even if you have coastal protection in place, a tsunami could easily roll over it.

    But the coastal levee, 10 meters tall, 3 meters wide and running for 2.4 kilometers, crumbled in the March 11 tsunami.

    Some survivors said residents may have placed too much faith in the levee, known locally as “the Great Wall,” leading to a higher number of dead and missing people.

    “The tsunami’s height was twice that of the levee,” said Giichi Kobayashi, a 76-year-old fisherman in the district, his face stiffening.


    Each degree of global warming might ultimately raise global sea levels by more than 2 meters

    Comment by prokaryotes — 15 Oct 2013 @ 12:31 PM

  14. > 52-98 cm (that’s 5 to 10 meters; a meter equals 3 + feet)
    > by the year 2100

    NO! WRONG!

    Comment by Hank Roberts — 15 Oct 2013 @ 12:37 PM

  15. For John Burgeson:

    Comment by Hank Roberts — 15 Oct 2013 @ 12:39 PM

  16. RE: John Burgeson – “52-98 cm (that’s 5 to 10 meters; a meter equals 3+ feet)”

    52-98 centimeters = 0.52 – 0.98 meters
    1 meter = 3.28084 feet

    Comment by Benjamin Tennen — 15 Oct 2013 @ 12:49 PM

  17. John Burgeson: 52-98cm is half to one meter. You have misplaced a decimal point.

    Comment by Dave Berry — 15 Oct 2013 @ 1:03 PM

  18. Thanks for writing this.

    I don’t understand how adding [a] the upper limit of the estimate of the MBAIS collapse contribution (several decimeters, so let’s say .5 m), to [b] the upper limit of the “likely” range, provides a “worst case” estimate (if that is what is done in the Levermann/e360 quote/link above).

    Don’t you FIRST have to, somehow, assess [c] the upper limit of the *very* likely, or *extremely* likely, range (w/o collapse contributions) and THEN add [a] the upper limit of the collapse contribution (ie, and THEN add the .5 m) ?

    That is, wouldn’t you need to do something similar to what Aslak Grinsted did (as in the Grinsted/glaciology link above), but with some kind of different (component-based) assessment of [c] (ie, not a sigma-based derivation that starts from the interpreted-as/treated-as “likely” ranges)?

    Finally, either way, an assessment like this would give the worst case based, at least for some components, on RCP8.5, the worst of the scenarios, but not in itself a “worst case,” right?

    Grateful for corrections, clarifications, comments, answers. Thanks.

    Comment by paulina — 15 Oct 2013 @ 1:14 PM

  19. From the linked table by #3 Aslak Grindsted, it seems like the FAR gave the most realistic estimate of the sea level rise, even better than AR5, according to the “ice sheet experts” as well as taking into the account the bias in leaving the semi-empirical models out.

    Could it be the ESLD effect getting stronger due to greater mass media pressure not to be alarmist?

    Comment by John L — 15 Oct 2013 @ 2:07 PM

  20. This all begs the question, what is a reasonable upper-limit for the year 2100? >1m? >2m?

    Comment by Missoula — 15 Oct 2013 @ 4:56 PM

  21. Do the AR5 regional sea level rise estimates take into account gravitational effects of ice cap reductions? As per the discussion in Jerry Mitrovica’s video?

    [Response: Of course, Stefan ]

    Comment by KR — 15 Oct 2013 @ 10:14 PM

  22. 1)The ANDRILL results seem to give a timescale of 1kyr for WAIS collapse. I recall a comment by Bindschadler stating that 1Kyr should be seen as an upper limit. And I recall Mercer’s warnings from many years ago.


    2)Gregoire depiction of saddle collapse (eg 67N Greenland)
    3)albedo forcing as Box has illustrated
    4)EAIS may be less stable than thought

    Every millimeter of SLR from Greenland is accentuated at the other end of the world in Antarctica, as Mitrovica has pointed out, and every millimeter lifts the ice shelves stabilizing the Antarctic glaciers. Last year Greenland melt at 574 Gton (GRACE) was a millimeter and a half averaged globally, more down south. And as the southern ocean warms, the circumpolar winds tighten their girdle, intensifying the Ekman rise of warm circumpolar deep water melting into the vasty deeps beneath Antarctica.

    Do you feel lucky ?


    Comment by sidd — 15 Oct 2013 @ 10:14 PM

  23. Sadly, the average person will believe it when and only when they see it.

    That will be someone living in 2100, most of whom will not remember 2050 let alone 2000. To their eyes the new sea level will be normal. *

    *And no one of consequence will be interested in stories of those over 75 recalling when they were 15.

    [Response: You should be aware, though, that in 2100 there will not just be a “new sea level” but more importantly a rapidly rising sea level – at the highest end of the IPCC scenarios at a rate of 16 cm per decade, which is about equal to what we had in the 20 th Century – not per decade but for the whole century. stefan

    Comment by Non-Scientist — 15 Oct 2013 @ 10:54 PM

  24. I was able to get past the paywall at The Chronicle for Higher Education. Seemed like a good synopsis of the characters. But I wouldn’t know any better, either way.

    Here’s a quote from near the bottom of that article and ascribed to John A. Church, who served as one of the coordinating lead authors, with Peter U. Clark being the other…

    “I daresay we will be attacked by both sides,” he said, “for having too high numbers and having too low numbers.”

    What is left unsaid is that the attacks from one side for having too high numbers will be coming from denialists. The attacks from the other side for having too low numbers will be coming from those far more informed about the topic and disappointed by what didn’t make it into the report.

    The summary there makes it sound as though Dr. Church was suggesting they captured the right middle road of informed knowledge. But from reading this page and many of the various links therein (such as Aslak Grinsted’s), I find Jason Box’s comment (quoted in this page’s article) all the more pointed: “There was controversy after AR4 that sea level rise estimates were too low. Now, we have the same problem for AR5 [that they are still too low].”

    Comment by Jon Kirwan — 16 Oct 2013 @ 5:22 AM

  25. Could someone explain what figure 3’s legend means by the annotation “No Antarctic PGs”?

    [Response: PG=Peripheral Glaciers. These are excluded in those analyses to avoid double counting according to the IPCC figure caption. (And, no I don’t really understand this). The source paper is Marzeion et al. (2012a) (#OA) so you might get a clearer answer there. – gavin]

    [Further Response: See comment below for more details]

    Comment by Douglas McClean — 16 Oct 2013 @ 8:30 AM

  26. Peer review in action, posts 14-17.

    Comment by Brennan — 16 Oct 2013 @ 8:37 AM

  27. Brennan, peer review’s meant to be done _before_ publication (grin).

    Has anyone checked whether John B has fixed that error?

    John Burgeson says:
    15 Oct 2013 at 11:33 AM
    This is what I posted to Facebook

    Good example of why peer review is done — and was needed. It’s a low threshold to catch obvious errors before they go out.

    Comment by Hank Roberts — 16 Oct 2013 @ 11:56 AM

  28. Also see the full paper by Meehl et al (2012):

    About their worst-case estimates for 2100 and 2300 they say:
    “[T]he semi-empirical method… indicates greater increases than the IPCC AR4 example, with sea-level rise of nearly 115 cm and 145 cm by 2100 in RCP4.5 and RCP8.5, respectively, with an eventual increase approaching 440 cm and 960 cm for RCP4.5 and RCP8.5, respectively, by 2300. These values inform the upper range of the shading in Fig. 3 that encompasses the larger estimates. But the limit of the higher end of the shading is depicted as being indistinct to reflect that these are only estimates. There is no real way of knowing if these higher total sea-level rise values are credible, or if higher or lower values are more likely.”

    So even this worst-case may not be a worst-case, but it seems we simply cannot really know at this point.

    Comment by Lennart van der Linde — 16 Oct 2013 @ 12:25 PM

  29. It is amazing to me that there can be so much uncertainty about what would seem to be an extremely simple, well understood type of physical change–the melting of ice.

    But as we have seen with the wildly inaccurate (all on the conservative side) models for Arctic sea ice melt, modeling the seemingly simple process of ice melting in a warming world turns out to be not at all simple or straight forward.

    And if this process of water changing state, which is pretty much just a process of physics and a bit of chemistry, is so very easy to get wrong–specifically, is so easy to model too conservatively so the models predict wrongly that it will be a very slow process when in fact it seems to be a much faster process–how confident can we be that other models and estimates of processes that involve multiple feedbacks that include chemical and biological interactions as well as physical ones aren’t even more wildly inaccurate on the ‘conservative’ side?

    Comment by wili — 16 Oct 2013 @ 8:24 PM

  30. Thanks to Stefan for this summary of what currently seems to be the biggest problem in climate science. John Church, Peter Clark and the other 12 lead authors of Chapter 13 have clearly been struggling to deal with a complex problem. But they are in a situation where for the science it is sometimes better to be a bit conservative, and then proved wrong, rather than exaggerate the problem, and then become totally discredited. That is not risk management in the normal sense, but it has come up in some earlier IPCC assessments.

    However, while semi-empirical models are being recognised in the report, more could be done to merge these in with process based models. For example, some other areas of science are using ways of combining aleatory and epistemic forms of uncertainty to produce fuzzy intervals or developments of the Dempster-Shafer approaches which deal with ranges going from what is ‘belief’ (e.g current process models) to what is ‘plausible’ (e.g semi-empirical).

    Recognition of these different forms of uncertainty is shown a bit subtly by Chapter 13 giving 5-95% ranges from the models and then saying that these are ‘likely’, i.e only believed to be 66% of the total range. The synthesis in section 13.8 also says that neither a ‘very likely’ range nor upper bound can be defined. And while for planning purposes that raises the question as to whether more of the residual 34% of the full range is on the high side or low side of the ‘likely’ range, this section does say that coastal planning needs to be considered in a risk management framework.

    While the IPCC approach to uncertainty could be improved, getting coastal planning to take account of even 0.5 m SLR seems an even bigger challenge. So Figure 13.25 which shows the very large multiplication factors that this causes for coastal flooding could actually be the best wake up call coming out of the chapter.

    [Response: Thanks for your thoughts, Martin. Coastal planning: here in Germany the ongoing process of upgrading our coastal defences is based on the assumption of up to 1.5 meters of sea-level rise. Any volunteer expert willing to write a post on those multiplication factors in Fig. 13.25, showing how even for 0.5 m SLR the frequency of flooding events of a given height increases drastically in many locations? This is am important issue which I did not cover above.

    p.s. A few questions to you as IPCC veteran: why is underestimating a risk not so bad but overestimating it destroys our credibility? What is the cause of this asymmetry? And isn’t that exactly the kind of thinking that leads to “erring on the side of least drama”? And shouldn’t we as scientists in the public interest be more concerned about the risk to coastal cities than about the risk to ourselves and our reputations? – stefan]

    Comment by Martin Manning — 17 Oct 2013 @ 1:12 AM

  31. Hi Stephan

    Would you feel comfortable providing an analysis of the impressive discrepancy between the IPCC estimates and those of Hanson and Sato, who state that more than 5 meters SLR is likely by 2100? Are there mistaken assumptions or missing feedbacks at play? Thanks.

    [Response: I haven’t seen any scientifically credible basis for those 5 meters. -stefan]

    Comment by Roger Lambert — 17 Oct 2013 @ 5:10 AM

  32. What’s the rough breakdown of sea level rise attribution for human GHG emissions and emergence from the little ice age?

    Comment by Alex — 17 Oct 2013 @ 9:38 AM

  33. Alex@32,
    Huh? That doesn’t even make any sense. The LIA ended over a century and a half ago. For warming to occur there has to be an energy source. Mr. Sun ain’t it.

    Comment by Ray Ladbury — 17 Oct 2013 @ 11:17 AM

  34. > 31, Roger Lambert, Stefan
    Hansen answers that question the same as Stefan; Hansen also hasn’t seen any scientifically credible basis for those 5 meters:

    … what are the shapes of the ice sheet mass loss curves for Greenland and West Antarctica? Is there evidence that they may be exponential? It’s too early to tell, as shown by Fig. 1 above. The picture may begin to be clearer within the next several years. The problem is, by the time the data record is long enough to be convincing, it may be exceedingly difficult or impossible to prevent sea level rise of many meters.

    > 32, Alex, Little Ice Age
    The Little Ice Age and the Medieval Warming were named by people experiencing the local climate in parts of Europe. The people experiencing them assumed they were global climate changes.

    You’ll find bloggers passionately arguing that they must have been global, because [Anything But The IPCC], and since no evidence of them appears in global sea level records, that must prove climate change doesn’t affect sea level.

    But absence of evidence is not evidence of absence.

    A great many people have looked at the paleo record at many locations, and more such records — each for a particular site — are being published.

    A global event would have happened everywhere at the same time. So far that pattern hasn’t been found, near as I can tell. Instead local events happened that didn’t coincide.

    Check your source if you read that either warm period or “little ice age” was global — is it a blogger’s claim? Be skeptical. It’s part of a PR story, if so.

    Or was it a science journal? Weigh the evidence. Tell us where you found it.

    Life is full of little surprises.

    Comment by Hank Roberts — 17 Oct 2013 @ 12:01 PM

  35. The Hansen “Fig.1” link I tried to post broke.
    That should point to

    Ten years ago almost believed the Antarctic could be unstable, and few thought that the geology we could see left behind when the continental ice caps melted indicated any kind of rapid event. Some few thought meltwater could go right through glaciers year after year, build up, and burst out. One glaciologist said that glacial ice would close any openings during each winter, not get riddled by holes that would persist.

    You can find some of that accumulated in the comments over several years at

    I was, there, reading and asking questions. You can see I was not as worried then as Hansen (grin) but more concerned than the ice experts quoted there were, then.

    The inline replies at that link are appropriately skeptical, as the scientific evidence began to accumulate. Drumlins, for example — did the ones found all over form slow, or fast? That has long been debated. Then someone watched one form — rapidly. So, if drumlins, found everywhere the ice caps melted, are evidence of fast change then — hmmmmm.

    Scientists don’t yet have evidence to say continental ice could change fast — but have long believed it wasn’t likely.

    Nevertheless, it moves.

    Comment by Hank Roberts — 17 Oct 2013 @ 12:19 PM

  36. Wili,
    It is not quick so simple as the “melting of ice.” Predictions of an ice-free Arctic ranged from 2013 (Maslowski) to 2058 (Liu, et. al.) to 2100 (Jahn and Hlland). Much of this uncertainty is related to the complex interaction between the Arctic air and water leading to the absorption of energy in the summer and radiation in the winter. Predicting the melting of the Greenland and Antarctic glaciers is much more complex.

    Add to the previous factor the IPCC projected 21st century temperature rise of 0.3 – 4.8C (depending on the RCP interval selected), and it becomes surprising that the predicted sea level rise is contained in such a small interval. All this does not even take into account plate tectonics.

    Comment by Dan H. — 17 Oct 2013 @ 12:32 PM

  37. Stefan: “Any volunteer expert willing to write a post on those multiplication factors in Fig. 13.25, showing how even for 0.5 m SLR the frequency of flooding events of a given height increases drastically in many locations?”

    Barging in (sorry!). I’m not an expert in anything but wringing unwanted flood water out of the lower floor of my house; I can offer only anecdotal information.

    A sea level rise of “only” 0.5m can be quite drastic indeed. Why? Because there’s an extraordinary difference between a house with no water on the floor versus one with “just” a centimeter inside where it’s not supposed to be, when one takes into account such things as sharing a house with water or leftover deposits of silt on the floor. Indeed it hardly matters whether there’s half a meter or only a centimeter of wrongly placed water in a home; it turns out that any interior flooding of whatever amount effectively makes a house useless for its intended purpose.

    In our case we don’t have a problem with the ocean but our story may nonetheless be helpful. Our own house was constructed in a context where it coexisted happily with the outdoors– just barely– similarly to many homes in immediate vertical proximity to water. It turns out that only a small statistical difference one way or another in rainfall intensity is what allows our house to be livable or not. We’re lucky that we can engineer our way out of our problem, for the time being.

    There are other ways to make our own luck, including doing what we can to improve our statistics whether they be frequency and size of storm surges or the style of rainfall we receive. Remarkably enough we do seem to have that power but it turns out to be an unfortunate “skill.”

    Comment by Doug Bostrom — 17 Oct 2013 @ 1:11 PM

  38. @Roger Lambert #31,

    Where do Hansen & Sato say 5m of SLR by 2100 is likely?

    As I understand them they think 2-3 meters by 2100 may be possible under BAU. And they point out that with a 10-year doubling time of the ice sheet contribution to SLR you would get about 5m around 2100. It seems Hansen doesn’t rule this out entirely, but I don’t think he has said it’s likely.

    He and Sato do point to a plausible negative iceberg cooling feedback which may limit the worst-case SLR by 2100 to about 2.5m and the rate of rise to about 5-6m per century in the next centuries. This is pretty close to what some semi-empirical models seem to find as a worst-case.

    Comment by Lennart van der Linde — 17 Oct 2013 @ 1:23 PM

  39. > Hansen … where …

    Dang, the blog software here persists in breaking this link:

    Try copying it into another browser window and it’ll work.

    Comment by Hank Roberts — 17 Oct 2013 @ 3:51 PM

  40. 29 wili says, “if this process of water changing state…is so easy to model too conservatively…how confident can we be that other models and estimates of processes that involve multiple feedbacks that include chemical and biological interactions as well as physical ones aren’t even more wildly inaccurate on the ‘conservative’ side?”

    Because the models work better with temperature than melt. Paleodata and modern data support the temperature data but not the melt data. This could result in erroneous temperature data as albedo changes, but I’d amateurishly think that the end result for temperature would be closer to reality than the melt predictions.

    Comment by Jim Larsen — 17 Oct 2013 @ 5:32 PM

  41. sea rising is a natural phenomena – sediments washed from the hills into the -#b] places like lake Chad, Aral sea getting dry = less water on the land = more water into the sea.

    movements of the tectonic plates makes one part of island, or continent to rise other part / parts to sink – that isn’t sea rising:

    Comment by stefanthedenier — 17 Oct 2013 @ 8:09 PM

  42. “You should be aware, though, that in 2100 there will not just be a “new sea level” but more importantly a rapidly rising sea level – at the highest end of the IPCC scenarios at a rate of 16 cm per decade, which is about equal to what we had in the 20 th Century – not per decade but for the whole century. stefan

    1. Tx for the info. If (probably when) SLR=16cm/decade average people near the coast will finally notice.
    2. They can notice, then declare it’s God’s Will and must not be opposed ;-)

    Comment by Non-Scientist — 17 Oct 2013 @ 8:32 PM

  43. @Ray Ladbury

    Huh? That doesn’t even make any sense. The LIA ended over a century and a half ago. For warming to occur there has to be an energy source. Mr. Sun ain’t it.

    The LIA represents a roughly one degree C increase in global temperature that has not fallen since. After reading your comment, I built a 1-D, transient model of the Greenland ice sheet. With a step change in temperature at the surface of the ice sheet, and assuming a constant thickness of 2km, the time required for the mid-point of the ice sheet to reflect only 50% absorption of the energy reflecting the temperature increase is… 159.5 years.

    So, you see, my question makes sense. I’m still waiting for an estimate.

    Comment by Alex — 17 Oct 2013 @ 8:46 PM

  44. Thanks for the commentary.

    A few years ago I attended a great 1-day session on Preparing for Sea Level Rise in the Bay Area – A Local Government Forum.

    It started with talks by scientist on what was known and unknown, then on to strategies for dealing with such, in an area that has a large amount of valuable infrastructure right at sea level, including Silicon Valley and 3 airports.

    But planning for SLR is very different and much uglier than just planning to deal with extreme storms, and they split us into groups, gave us descriptions of imaginary towns on the Bay, and said Plan. Among other awkwardnesses:
    a) Sewage plants like to be near sea-level, but below where people live.
    b) In the long term, it might be most-effective to pick a line to defend a ways up the hills … but oddly, those who own property below tend to think otherwise.
    c) One can build dikes, but when it rains, the water does not flow uphill from areas now below sea level. This is different from a storm that temporarily floods some area and then drains away.
    d) One of the main roads is Rt 101, and it is just barely above high tide.

    The encouraging part of the experience was spending a day with town planners who passionately cared what their towns would look like in 50-100 years, wanted to understand the science and talk about strategies. I would feel better if I though the SF Bay Area was necessarily a representative place.

    Comment by John Mashey — 17 Oct 2013 @ 8:51 PM

  45. Jim Larsen at #40 said: “Because the models work better with temperature than melt. Paleodata and modern data support the temperature data but not the melt data.”

    Thanks, Jim. I hadn’t thought of that.

    Comment by wili — 17 Oct 2013 @ 10:04 PM

  46. @41 from stefanthedenier is there to provide us with some comedy relief, right?

    Comment by Marco — 18 Oct 2013 @ 12:29 AM

  47. This might belong in the Unforced variations thread, but I was hoping someone reading this thread might recall the reference.

    I am trying to recall a recent paper arguing for fast sea level rise at the end of the Eemian. Unfortunately all i find in my currently available archive with is the 2000 paper in Chemical Geology by McCulloch and Esat, which is, amazingly enough, available freely through a search at

    Chemical Geology 169 (2000) 107–129
    “The coral record of last interglacial sea levels and sea surface temperatures”
    Malcolm T. McCulloch) , Tezer Esat

    From a site in the Huon Peninsula in Western Australia, through clever isotopic dating, they deduced that:

    “During the penultimate deglaciation, there was much more rapid and sustained increase in sea level compared to the last deglaciation. The final 80 m of sea level rise took only ~2 ka during the penultimate deglaciation …”

    I am almost sure that there is fairly recent work documenting rapid transgression at the end of the Eemian, (perhaps from Barbados or NE coast of N. America ?)

    Would be glad for leads.


    Comment by sidd — 18 Oct 2013 @ 1:01 AM

  48. stefanthedenier: Wow! I didn’t realize there was one website with so many scientific inaccuracies in one place! If I were so inclined, I could spend weeks refuting each and every one of the supposed “facts” on this site. But I am not so inclined. I have a life.

    Comment by Jim Eaton — 18 Oct 2013 @ 1:36 AM

  49. stefanthedenier: “Aral sea getting dry” as a natural phenomenon.

    Priceless, truly.

    “Formerly one of the four largest lakes in the world with an area of 68,000 square kilometres (26,300 sq mi), the Aral Sea has been steadily shrinking since the 1960s after the rivers that fed it were diverted by Soviet irrigation projects.”

    STD is getting his anthropocene all jumbled.

    Comment by Doug Bostrom — 18 Oct 2013 @ 1:56 AM

  50. Sidd,

    I suspect this is the paper you are looking for:

    O’Leary, M. J., Hearty, P. J., Thompson, W. G., Raymo, M. E., Mitrovica, J. X., & Webster, J. M. (2013). Ice sheet collapse following a prolonged period of stable sea level during the last interglacial. Nature Geoscience, 6(9), 796–800. doi:10.1038/ngeo1890

    Aslak Grinsted has a nice compilation of some other recent papers on evidence for WAIS collapse during the last interglacial:

    Comment by perwis — 18 Oct 2013 @ 8:11 AM

  51. > Alex … LIA represents a roughly
    > one degree C increase in global temperature

    According to whom, Alex? Why do you believe this? What source are you relying on for the, er, global statement?

    I think I found the one recent paper suggesting that. It’s a claim based on a record from one site. Just one location.

    It’s been made much of at a few blogs arguing that changing temperature doesn’t affect sea level. That’s not what it actually says. But have you looked beyond that one paper? Morano’s really not a good source, if he’s where you’re getting this idea. If not, where?

    Rate of change matters.

    Tell us if this is your own conclusion from logic, or something you read — and if so, where — and we* might be able to help find more useful information.
    *we being frequent amateur readers like me.
    Failing that, if you give some citation to what you’re relying on, the real scientists here will be able to discuss it.

    Comment by Hank Roberts — 18 Oct 2013 @ 9:01 AM

  52. Martin Manning and Stefan Rahmstorf #30:

    Stefan, you say in your post that “The range up to 98 cm is the IPCC’s “likely” range, i.e. the risk of exceeding 98 cm is considered to be 17%, ”

    Martin, you say that “while for planning purposes that raises the question as to whether more of the residual 34% of the full range is on the high side or low side of the ‘likely’ range, this section does say that coastal planning needs to be considered in a risk management framework.”

    We have at least two different interperations here on how to interpret the IPCC “likely” range here? Which is to correct interpretation? Martin’s way or Stefan’s way?

    The IPCC is not very clear on this. All that is stated int the SPM and the IPCC Uncertainty Guidance Note (Mastrandrea et al 2010), is that “Likely” means “66-100% probability”.

    What speaks for Martin’s interpretation is that the lower bound is much more uncertain. The IPCC Sea level chapter authors says that “The time-mean rate of GMSL rise during the 21st century is very likely to exceed the rate of 2.0 [1.7–2.3] mm yr–1 observed during 1971–2010” (p 13-53), which suggests that the lower bound is not so uncertain, while they say that “there is currently insufficient evidence to evaluate the probability of specific levels above the likely range.”

    What speaks for Stefan’s interpretation is that this is that the IPCC authors may already have taken this into consideration when assigning the “likely” interval. I have not yet found any specific mention of this in the report, other than the following from Chapter 1:
    “In the WGI contribution to the AR5, uncertainty is quantified using 90% uncertainty intervals unless otherwise stated. The 90% uncertainty interval, reported in square brackets, is expected to have a 90% likelihood of covering the value that is being estimated. The value that is being estimated has a 5% likelihood of exceeding the upper endpoint of the uncertainty interval, and the value has a 5% likelihood of being less than that the lower endpoint of the uncertainty interval. A best estimate of that value is also given where available. Uncertainty intervals are not necessarily symmetric about the corresponding best estimate.”

    Does anyone know for sure how the uncertainty intervalls should be interpreted? Have I missed something?

    Comment by perwis — 18 Oct 2013 @ 9:04 AM

  53. Also for Alex: if you’re relying on Asafoku at Pielke Sr., cited to Asafoku’s paper “On the recovery from the Little Ice Age” in Natural Science, vol.2, No.11, 1211-1224 (2010): — do read about the publisher.

    So there, just guessing, I’ve found two places Alex might be getting this (not counting Morano’s). Pretty weak notion so far. Of course, they laughed at Galileo ….

    Comment by Hank Roberts — 18 Oct 2013 @ 9:37 AM

  54. Blanchon et al (2009), also referred to by Grinsted, seems to be the most outspoken paper on possibly very fast SLR during the Eemian:

    But it seems unclear how strong their evidence is. They infer a rate of SLR of more than 36 mm/yr for a total jump in SLR of about 3 meters in less than a century. I can’t see if they found direct evidence for that and how certain their evidence is.

    Maybe others here know more?

    Comment by Lennart van der Linde — 18 Oct 2013 @ 9:44 AM

  55. Sorry, I meant ‘about 2-3 meters’ in less than a century, not ‘about 3 meters’.

    Comment by Lennart van der Linde — 18 Oct 2013 @ 9:47 AM

  56. > I can’t see if they found direct evidence
    Are you looking at that PDF, at the supporting material section?
    What’s lacking? Did you look at any of the 75 papers citing that one?

    Comment by Hank Roberts — 18 Oct 2013 @ 11:36 AM

  57. A typo in my comment above: it should say “the UPPER bound is much more uncertain”.

    I would be grateful if someone could point me to a reference that explains in more detail what the IPCC authors intend with the uncertainty intervals. I would guess this is not the first time people have been confused about this.

    Comment by perwis — 18 Oct 2013 @ 11:52 AM

  58. #36 Dan H. All this does not even take into account plate tectonics.

    I’m a geologist. Please explain how plate tectonics are relevant to a discussion of sea level rise in the next 100 years? Are you confusing isostatic rebound here?

    Comment by tokodave — 18 Oct 2013 @ 11:59 AM

  59. Perwis, as a bystander, I found this somewhat helpful; it’s written for the authors:

    Climatic Change
    October 2011, Volume 108, Issue 4, pp 675-691, Open Access
    DOI 10.1007/s10584-011-0178-6

    The IPCC AR5 guidance note on consistent treatment of uncertainties: a common approach across the working groups

    A goal for the Fifth Assessment Report, which is currently under development, is the application of a common framework with associated calibrated uncertainty language that can be used to characterize findings of the assessment process. A guidance note for authors of the Fifth Assessment Report has been developed that describes this common approach and language, building upon the guidance employed in past Assessment Reports. Here, we introduce the main features of this guidance note, with a focus on how it has been designed for use by author teams. We also provide perspectives on considerations and challenges relevant to the application of this guidance in the contribution of each Working Group to the Fifth Assessment Report.

    The “Related Content” link takes you to more recent specific items

    Comment by Hank Roberts — 18 Oct 2013 @ 12:57 PM

  60. Mr. perwis: Thanx for the reference to O’Leary et al., which uses data from Western Australia also. I was actually thinking of Blanchon (2009) referred to by Mr. Linde, although I note that the 36mm/yr in the supplementary discussion refers to the Holocene and not the Eemian. They do have an interesting discussion of SLR at the end of the LIG, arguing for a faster than millenial rise, occurring on an ecological timescale.

    “However a millennial-scale interval is inconsistent with paleoecological data which requires that back-stepping was more rapid and occurred on ecological time-scales, as outlined in the following argument:

    i. The lower-crest shows no evidence of coral-community adjustment prior to its demise. This means that cessation of reef growth was ecologically rapid. Nor was the surface of the lower crest subsequently re-colonized by corals, only by a cap of coralline algae. This not only means thatreef-crest corals likely suffered a mass mortality event43, but that the environmental change was permanent. In other words, reef-crest demise and shift to another marine environment occurred rapidly on an ecological time-scale.

    ii. Coral communities in distal areas of the patch-reef complex also died rapidly with no time for adjustment. They were subsequently eroded and re-colonised by a sediment-tolerant community. The erosional break, however, prevents any assessment of the timing of that community shift.

    iii. But coral communities in proximal areas of the patch-reef complex were not eroded and show a continuous transition into the new environment (lower-tract lagoon to crest of upper tract) that occurred on a cm scale (see sections D4 and E2). This confirms that there was an ecologically rapid shift to a reef-crest environment ie, it occurred over the life-span of one or two generations of coral. (Note that this rapid transition was not caused by progradation of the upper-reef crest ovethe patch-reef complex because facies seaward and landward of the crest are composed of mixed assemblages). In other words, reef demise and back-stepping must have occurred on an ecological time-scale.”

    Comment by sidd — 18 Oct 2013 @ 1:16 PM

  61. @Hank #56,

    As Sidd (#60) notes Blanchon et al 2009 seem to mainly refer to Meltwater Pulse 1A as indirect evidence for a rapid Eemian SLR of more than 36 mm/yr. But since I’m no expert I don’t really understand how strong this evidence is.

    For example: what is the ecological speed limit, so to speak, for coral reefs to be able to keep up with SLR? Is that 36 mm/yr or less? How certain are we of this limit?

    And should these regional rises still be corrected for gravitational effects to determine the globally averaged rise? How large are the uncertainties?

    Blanchon et al also refer to Rohling et al 2008 for other (uncertain) evidence of rapid SLR during the Eemian, but it seems Grant et al 2012 (including Rohling) regard Rohling et al 2008 as an overestimate. So could Blanchon et al 2009 also be an overestimate?

    On the other hand, what if they are right after all?

    Comment by Lennart van der Linde — 18 Oct 2013 @ 3:24 PM

  62. Hank Roberts, the issue of whether the cooling period between 1550 – 1850 was global or limited mainly to the northern hemisphere, as implied by NASA’s definition in the link below, wasn’t really my point, but it may affect the magnitude of the attributions I was interested in. My point was that it takes a long time, even hundreds of years, for energy to diffuse into the largest ice sheets on the planet. This would seem to be relevant to understanding the causes and dynamics of sea level rise.

    Comment by Alex — 18 Oct 2013 @ 5:30 PM

  63. Alex,
    Your way of looking at this doesn’t make sense. If the planet is warming, it must be because there is more energy going in than leaving. The planet doesn’t just have some equilibrium temperature that it always goes back to. So, no, you don’t make sense.

    Comment by Ray Ladbury — 18 Oct 2013 @ 5:41 PM

  64. > it takes … even hundreds of years

    That’s what we used to think.
    But why do you still think so?

    What we all learned years ago is what we think, unless we look into what’s new. Where are you looking for new information?

    What’s interesting is what we can find by looking.
    No one was looking at the underside of the big ice sheets, til recently. There was argument about the possibility there had been rapid change, but there was no evidence (other than argument about, say, the channeled scablands, and observations of jokuhlaupts in some places).

    Now, we have observations starting to come in.
    That’s where the surprises have all come from.

    That’s why people are concerned.

    If we just held with what you believe now — what everyone believed ten years ago — we wouldn’t worry.

    Now, we have some new observations to think about.
    I’m not arguing for the sudden collapse into little ice cubes and rush to the ocean notion.

    But I agree with Hansen — by the time we have evidence, it could well be too late to stop a rapid change, if one’s in the offing at our present rate of change.

    Cautionary principle — what do you think about that?

    Comment by Hank Roberts — 18 Oct 2013 @ 5:54 PM

  65. Grant et al 2012:

    Rohling et al 2008 (2007 online):

    Blanchon et al 2009 refer to Rohling et al 2008 (2007 online), which estimated a maximum rate of SLR during the Eemian of 2.5 meter/century about 123.5 kyr ago. Blanchon et al think their 2-3 meter/century rise was around 121 kyr ago.

    Grant et al (2012) don’t give an estimate for a maximum rate, but give a common rate of up to 0.7 meter/century during the Eemian. They don’t exclude higher rates though.

    IPCC AR5 WG1 chapter 5 says:
    “LIG sea level rise rates of between 1.1 and 2.6 m per century have been estimated based on a foraminiferal 18O record from the Red Sea (Rohling et al., 2008a). However, the original Red-Sea chronology was based on a short LIG duration of 124–119 ka, after Thompson and Goldstein (2005). The longer LIG duration of 130–116 ka indicated by the coral data (Stirling et al., 1998) reduces these rates to 0.4–0.9 m per century, and a revised chronology of the Red Sea sea level record adjusted to ages from Soreq Cave yields estimates of sea level rise rates of up to 0.7 m per century when sea level was above present level during the LIG (Grant et al., 2012).”

    Chapter 13 says:
    “For the time interval during the LIG in which GMSL was above present, there is high confidence that the maximum 1000-year average rate of GMSL rise associated with the sea level fluctuation exceeded 2 m kyr–1 but that it did not exceed 7 m kyr–1 (Chapter 5) (Kopp et al., 2013). Faster rates lasting less than a millennium cannot be ruled out by these data.”

    Kopp et al 2013:

    They note that the Eemian and today are quite different periods with respect to insolation (and GHG-forcing) in particular, so the question is what Eemian SLR can and cannot tell us exactly. Blanchon seems to think 5 meter/century SLR is possible in the coming centuries, maybe already starting in this one.

    Comment by Lennart van der Linde — 18 Oct 2013 @ 6:42 PM

  66. > hundreds of years … diffuse

    Ah, there’s your misunderstanding. You’re thinking about diffusion, and in that you’re right, diffusion of heat through solid ice is slow.

    The surprise in the last few years wasn’t about diffusion.

    DOI: 10.1002/jgrf.20079

    Comment by Hank Roberts — 18 Oct 2013 @ 7:03 PM

  67. Alex,
    If you define LIA as “the cooling period between 1550 – 1850” you’re going to have a problem telling (in your words again) “human GHG emissions and emergence from the little ice age”.
    That’s because anthropogenic GHG emissions were already significant at that point due in large part to deforestation and CH4 emissions (coal use accounts for ~3GtC in the 1851-1875 period and much less before that).

    But if you could for the sake of the argument disentangle “human GHG emissions and emergence from the little ice age”, you would only have to feed whatever warming you attribute to a non-anthropogenic rebound from the LIA into a model such as this one to get its contribution to the sea level:

    You also state: “My point was that it takes a long time, even hundreds of years, for energy to diffuse into the largest ice sheets on the planet. This would seem to be relevant to understanding the causes and dynamics of sea level rise.”
    But it’s not the melting of the core of the largest ice sheets which is currently causing the sea level to rise! It’s melting at the margins, and not necessarily the margins of the largest ones. And ice has a way of flowing downslope to the margins of ice sheets.
    All your point means is that it would take hundreds of years for the sea level to rise tens of meters which is not what people are presently most concerened about (a few meters would be bad enough).
    Energy can be transmitted quite rapidly through ice that’s undergoing a lot of surface melting by the way. Look up “moulin”.

    Comment by Anonymous Coward — 18 Oct 2013 @ 7:18 PM

  68. Alex writes:
    “My point was that it takes a long time, even hundreds of years, for energy to diffuse into the largest ice sheets on the planet …”

    I seem to recall a talk by Alley where he pointed out that (i am paraphrasing from memory) :
    “We used to think that it took thousands of years for the heat to get in the ice sheet. Now we see that it gets there in 5 minutes”

    while speaking of moulin formation in Greenland.

    Latent heat is a a wonderful thing, especially when one phase is mobile. Heat transfer is no longer a diffusive process, it becomes a percolative process , with percolation connectivity exploding as we near the transition temperature from below in the immobile phase. I am not yet aware of anyone reporting a critical exponent or power law for meltwater percolation through a kilometer chunk of ice. In fact I can’t recall if anyone ever did such percolation networks when the percolating fluid is the hi T phase of the substrate and substrate is near the critical point for fusion. Anyone know of something like that ?

    Put in the pressure dependent melting point and the gravity gradient and make it even more fun.

    Comment by sidd — 18 Oct 2013 @ 8:27 PM

  69. @perwis #57 I’m not certain this is your question but it is something not well understood I’ve noticed. There are uncertainties in projections between upper & lower bounds because these are simulation “models” not calculations. A calculation, which produces a single result, is not possible for the climate system, too complex. I’ve written simulation “models” for elevator systems, orders of magnitude simpler. There’s some randomness (the chaos theory) and the “models” must reflect that and run the 100 years simulation (they use 15-minute intervals) numerous times with the same basic known formulae of the climate processes but varying the specifics a tad to match reality, else they model only a reality in which a rain drop hits your roof “just so”. The mean gives the likely projection and the range shows how “flakey” the climate system is or isn’t to small changes in the overall patterns. A calculation, which produces a single result, cannot do this.

    Comment by Barry E Finch — 18 Oct 2013 @ 11:18 PM

  70. > Richard Alley
    Mentioned with a link, in the earlier topic here, with inline comments

    Comment by Hank Roberts — 18 Oct 2013 @ 11:48 PM

  71. @wili #29 Arctic & Antarctic scientist Dr. Dan Lubin discusses observations & models in 2008 at Global Warming and the Polar Regions Signs of Human Impact University of California Television (UCTV). As example, he discusses the net +3.4 wm-2 forcing due to aerosols (pollution, mostly Europe & Asia) constrained above the Arctic throughout winter by the Polar Night Jet. I expect there are many factors affecting heat quantities in this zone, likely not yet all known or quantified.

    Comment by Barry — 19 Oct 2013 @ 2:36 AM

  72. Sidd, is this the Alley talk you were thinking of?

    I think what you were thinking of is what he says shortly after minute 19. The numbers he gives are “about ten thousand years” for regular conduction, “about ten minutes” for heat transfer through drainage of moulins.

    Comment by wili — 19 Oct 2013 @ 6:33 AM

  73. #52 perwis
    IPCC’s handling of uncertainties is at least very poorly communicated. As you point out even great scientists in the area like Manning and Rahmsdorf get confused.

    From the IPCC AR5 uncertainty guidance note:
    “A statement that
    an outcome is “likely” means that the probability of this
    outcome can range from ≥66% (fuzzy boundaries implied)
    to 100% probability.”

    I’m more and more convinced that the use of “likelihood intervals” like 66%-100% is a pure conceptual error. People misinterpret it because they are intuitively correct that it should be a single number. There is no point communicating how uncertain the experts are on their own judgement mixed up with the uncertainty in the determination of parameters. And they already have the concept of “confidence” for that! In addition the fixed set of intervals does not even allow to express this uncertainty in any meaningful way. It is also simply self-contradictory to have intervals like 66-100% overlapping 90-100% etc.

    It may be that they mixed up the intervals with approximations which correctly must be used. Like alternatives 90%, 95%, 99% etc.

    Just to clarify, this doesn’t necessarily mean that there is anything wrong with the assessments per se or the science behind it.

    Comment by John L — 19 Oct 2013 @ 7:00 AM

  74. Ray, you are confused and need to read my posts more carefully. I never said that the earth or an ice sheet will revert to some equilibrium temperature. I asked how much of the currently observed sea level rise is attributed to recent anthropogenically-caused warming and how much to warming over the last several hundred years that is presumably not anthropogenically dominated. The response time of the largest masses to a warming atmosphere is the root of the question.

    Others didn’t seem to have a problem understanding that, and helped by pointing out some of the complexities involved in the melt process and how it might affect the timescale.

    I will add that the transport time from a warmed atmosphere to the ocean is the bigger term, and no less interesting. The mass is huge, depth can be deep, specific heat is large, but circulation will speed the process. These complexities are all likely part of the reason my question remains unanswered. But it is still a relevant one, and it most certainly “makes sense”.

    Comment by Alex — 19 Oct 2013 @ 9:14 AM

  75. > how much to warming over the last several hundred years
    > that is presumably not anthropogenically dominated

    What “warming over the last several hundred years that is presumably not anthropogenically dominated” do you refer to?

    Are you presuming that the underlying trend over several hundred years is an warming trend?

    Is there a journal article to that effect?

    My impression is that we’re in the typical slow cooling phase after the end of an ice age, but for human activity, so the “warming” you’d be assuming would be a negative number: and references there

    Comment by Hank Roberts — 19 Oct 2013 @ 1:53 PM

  76. Alex said: “warming over the last several hundred years that is presumably not anthropogenically dominated”

    Why would you presume that there is any such thing as non-“anthropogenically dominated” net warming over the last several hundred years?

    We are (or would be without AGW), after all, in the late stages of an interglacial, so we should have expected things to be gradually cooling over the last hundred years, if we hadn’t started dumping massive amounts of extra C into that atmosphere.

    IIRC, there was a recent paper on this. I’ll see if I can track it down (unless one of our other intrepid paper-tracker-downers finds it first).

    Comment by wili — 19 Oct 2013 @ 2:23 PM

  77. What “warming over the last several hundred years that is presumably not anthropogenically dominated” do you refer to?

    Why would you presume that there is any such thing as non-”anthropogenically dominated” net warming over the last several hundred years?

    The folks over at suggest that the warming after the 1550-1850 cooling period was a result of increased solar activity and decreased volcanic activity (or conversely, the LIA itself was a result of decreased solar activity and increased volcanic activity). They cite a half dozen or so papers there, if you wish to look them up.

    Comment by Alex — 19 Oct 2013 @ 3:53 PM

  78. So you already knew the answer to the question before you asked it? Hmmm.

    Over the last eight thousand years, global temps have dropped on average about on tenth of a degree C every millennium. So in general, we might expect slight continued cooling over the last few centuries.

    But yes, things like volcanic activity can cause short term wobbles in this longer-term tragectory.

    Comment by wili — 19 Oct 2013 @ 5:45 PM

  79. > 1550 to 1580
    That’s longer ago than the last several hundred years.

    The longer the span of time, more data points — it gets easier to decide if your chaces are good you’re detecting a trend.

    More so when the data points back year after year are all equally reliable, and of course they’re not whichever proxies and temperature series you pick from.

    Did they have papers about the time span you ask about?

    I wish we had a librarian here.

    Comment by Hank Roberts — 19 Oct 2013 @ 6:59 PM

  80. 2 typos, should be: 1550-1850; chances

    Comment by Hank Roberts — 19 Oct 2013 @ 7:00 PM

  81. One of the issues is surely that the artificial cut off point of 2100 confuses some people, and gives deniers opportunities. The further the graph goes on to show the likely equilibrium sea level, the better. That way communication of the dangers might be improved.

    Comment by guthrie — 20 Oct 2013 @ 6:11 AM

  82. Alex, your question presumes a long time constant for equilibration of the climate that is not supported by evidence. Moreover, were the equilibration time constant that large, it would in turn imply a high climate sensitivity. Sure you want to go there?

    Comment by Ray Ladbury — 20 Oct 2013 @ 8:25 AM

  83. Sorry for the delay in responding, but in response to perwis#52 my reading of recent papers suggests that estimates of the contribution to SLR from glaciers and thermal expansion in the AOGCMs seem to have fairly symmetric probability distributions. But estimates of the ice sheet contribution in recent papers on models (such as Bindschadler et al, 2013, J. Glaciology, 53:195) and reviews of expert opinion (such as Bamber & Aspinall, 2013, Nature Climate Change, 3:424) both show probability (or possibility) distributions more definitely skewed towards the upper end of the range.

    If there was a definite probability distribution for SLR coming from all of that then a ‘likely’ range can be defined so that the probabilities of being above or below it are each 17%. But when subjective judgments are being used to come up with fuzzy statistics based on a range of expert opinions and ‘likely’ just means a probability somewhere in the range 66 – 100% then it seems to be much less clear whether that range remains centered around some median value. Neither of the IPCC guidance notes on uncertainties has been very clear about how a ‘likely’ range should be defined when expert opinions on the median can differ. But when you look at the likelihoods given for different parts of the range for equilibrium climate sensitivity it seems that the ‘likely’ range tends to get centered on the mode rather than the median when aiming for some form of consensus. For a positively skewed distribution this brings the ‘likely’ range down.
    On Stefan’s point I agree that scientists should avoid a tendency to ‘err on the side of least drama’. But also social communication is becoming the major challenge. Where I live there is now a major controversy because the local government has reclassified about 1000 coastal properties as subject to erosion and storm surges and that seems headed for the courtroom because their property values have been affected. So there can be a lot of drama even when planning for something like 0.5 m SLR. I’m not worried about scientists risking their reputations so much as society refusing to listen to things they don’t want to hear. Better adaptation strategies start with acceptance of changing risks and development of community response. Part of that is to get recognition of thresholds for sustainability of coastal properties, such as loss of insurance cover, and then proactive discussions about the options for retreat or cost of sea walls etc. Perhaps it’s clearer to say that I still think we need to plan for SLR between 0.5 and 1.5 m over the next 100 years, but when talking to people with houses in the low elevation coastal zone I’d rather discuss what things would look like at 0.5 m and because that is going to happen sooner than we would like, we need to plan for it now.

    Comment by Martin Manning — 20 Oct 2013 @ 8:29 AM

  84. So you already knew the answer to the question before you asked it? Hmmm.
    This is beginning to venture into the absurd. No, I still do not know the answer to my question: How much of the currently observed (~0.2m) sea level rise is attributable to warming during the naturally-dominated recovery from the Little Ice Age? Answering that question requires understanding the timescales of heat transfer from the atmosphere to the ocean and ice sheets. And yes, Hank, 1850 is within several hundred years, and also well within the time frame of simple heat conduction to the center of a thick ice sheet.

    The answer to my question may not be an easy one to come up with, but it is directly relevant to any projection of future sea level rise, such as the ones discussed in the body of this post. Therefore, the authors of that report section should presumably have an answer, or at least an estimate.

    Comment by Alex — 20 Oct 2013 @ 9:13 AM

  85. There’s a bug in the html transition from preview to post. Only the first line above should be italicized as a quote from wili.

    Comment by Alex — 20 Oct 2013 @ 9:14 AM

  86. Alex, are you assuming intact ice? Diffusion isn’t constraining temperature change because the ice isn’t simple.

    Are you assuming a change in sea level during the 1550-1850 cold spell? Do you assume a recovery must have happened?

    Point to something we can read, rather than just telling us your assumptions, logic, and reasoning, if you have sources.

    Seriously, move the conversation along, eh?

    Comment by Hank Roberts — 20 Oct 2013 @ 12:18 PM

  87. PS for Alec, have you read ?

    Comment by Hank Roberts — 20 Oct 2013 @ 12:24 PM

  88. Re: Bindschadler et al., J. Glaciology 2013.

    I take it that this is the SeaRISE project paper ? This examines 10 ice sheet models, discovers that:

    “In most cases, the ice volume above floatation lost is linearly dependent on the strength of the forcing. Combinations of forcings can be closely approximated by linearly summing the contributions from single forcing experiments suggesting that non-linear feedbacks are modest.”

    Stipulated that the projections from the models can be linearized as described. But I fear that the models diverge from reality, especially for ice sheets on submarine beds. Has anyone actually come up with a model that matches the pacing and magnitude of previous WAIS collapse as shown in, say, ANDRILL data ? Or, closer to the present, a model that reconstructs putative ice sheet retreat resulting in MWP1A transgression ?


    Comment by sidd — 20 Oct 2013 @ 1:42 PM

  89. PS for Alec– here, a brief excerpt from the 2011 RC topic suggests to me that there’s not yet enough information to decide whether either temperature or sea level changed at the time — the uncertainty, for that time span, is greater than the small changes that would matter.

    I’m not trying to tell you you’re wrong; I’m trying to find out what you’re assuming, what you know, and why you know it.

    Mike and Martin were clear about what they did and didn’t know back in 2011, and what assumptions were made. That helps:

    What is the basis that makes the suggestion that the temperatures were not as warm as indicated during AD500-1000 more valid than perhaps the M08 reconstruction suggesting that the SLR estimate instead is incorrect?

    [Response: That’s a very fair point. Both alternatives, in my view, are equally viable. Future work will hopefully better pin this down. -Mike]
    Comment by Davos — 24 Jun 2011 @ 1:38 PM


    M #58:

    would a plausible physical explanation be that the deep ocean and ice sheets are still responding somewhat to the post-glacial temperature increase (eg, T-T0,0>0), but that the faster components of SLR like the surface oceans and glaciers were actually responding to the decrease in temperature since the early Holocene?

    Very perceptive, M. That is pretty much what I believe is happening.
    Comment by Martin Vermeer — 29 Jun 2011 @ 1:37 PM

    Just to say, I think Alec’s way oversimplifying the question and making assumptions for which I haven’t found support yet. Hoping Alec will look further at the 5th IPCC Report (the actual topic here) and see whether his question could be answered within the limits of the uncertainties. I think not.

    Comment by Hank Roberts — 20 Oct 2013 @ 1:56 PM

  90. The response time of the largest masses to a warming atmosphere is the root of the question.

    Alex, are you presuming that any warmth transmitted to ice must come from the atmosphere?

    I would have thought everyone was on board with the idea that the big effects on the margins of the icesheets (and on Arctic sea ice which doesn’t affect this SLR discussion) were from warmed water. Which undermines the undersides and the edges … which allows the ice to flow more quickly … which means more ice gets into contact with warmer water more quickly … which melts more ice.

    Comment by adelady — 21 Oct 2013 @ 9:32 AM

  91. Stefan and Hank, re:

    “> 31, Roger Lambert, Stefan

    Hansen answers that question the same as Stefan; Hansen also hasn’t seen any scientifically credible basis for those 5 meters:

    … what are the shapes of the ice sheet mass loss curves for Greenland and West Antarctica? Is there evidence that they may be exponential? It’s too early to tell, as shown by Fig. 1 above. The picture may begin to be clearer within the next several years. The problem is, by the time the data record is long enough to be convincing, it may be exceedingly difficult or impossible to prevent sea level rise of many meters.”

    Yet, Hanson and Sato in “Paleoclimate Implications for Human-Made Climate Change” say:

    “BAU scenarios result in global warming of the order of 3-6°C. It is this scenario for which we assert that multi-meter sea level rise on the century time scale are not only possible, but almost dead certain”


    “What about the intermediate scenario, EU2C? We have presented evidence in this paper that prior interglacial periods were less than 1°C warmer than the Holocene maximum. If we are correct in that conclusion, the EU2C scenario implies a sea level rise of many meters.”

    They seem to be arguing, from my layman’s perspective, that there is historical evidence to argue that ice sheet loss will be exponential. And that while our observations are, as yet, too premature to verify this exponential loss, they do seems to be arguing that it seems likely?

    Comment by Roger Lambert — 21 Oct 2013 @ 9:54 AM

  92. Roger, do you have the original text on that? Searching the quotes I found secondary sources/reviews with that quote taken from a book chapter:

    There’s a link to that page, but not the actual text, at

    Comment by Hank Roberts — 21 Oct 2013 @ 11:39 AM

  93. Alex, et. al.,
    You may to examine a brief synopsis of the research done on sea level rise over the past three centuries:

    The uncertanty in global measurements increases substantially prior to 1850. This may not answer your initial question, as it does not differentiate between natural and manmade.

    Comment by Dan H. — 21 Oct 2013 @ 12:12 PM

  94. @Roger #91,

    I think ‘on the century time scale’ means one to several centuries and ‘multi-meter’ means two or more meters, not necessarily five meters in this century.

    The EU2C scenario means many meters after several (or many) centuries (or millennia), as I understand it.

    Comment by Lennart van der Linde — 21 Oct 2013 @ 12:42 PM

  95. #83 Martin Manning
    From your comment I do the interpretation that the likelihood interval is intended to capture the range of expert opinions. OK, then it makes relatively more sense. After all, in the end there is a group of experts that must agree about the formulation. But still, the use of “fuzzy statistics” in communication is very questionable (IMHO) and only risks leading to confusion and artificial levels of uncertainty. The “level of consensus” might better be separated as its own variable.

    For example, in the case of sea level rise an (arguably) equivalent clearer statement:

    “For the scenario RCP8.5 there is a 75% chance of a sea level rise of 52-98 cm to 2100 over 1986-2005. This assessment has medium confidence and low consensus”.

    The 75% is the average (or better, median?) expert judgement. Confidence is the belief in the model used to derive the numbers and corresponds to how much this judgement is predicted to change with further research. The level of consensus corresponds to the spread of expert opinions.

    [Response: I don’t think the likelihood statement in this case reflects a “range of expert opinions”. The way I understand it, a few of the IPCC sea level authors made a calculation of a model-based 90-percent uncertainty range. Then the authors said: because the range of model results included in this calculation probably does not reflect the full uncertainty of the problem, we call this 90% model range the assessed “likely” range. If it was constructed in this way, I would have to agree with Martin that this “likely” range can be asymmetric, i.e. with more uncertainty at the top end than the bottom end. So the probability of exceeding 98 cm is not 17% as I initially assumed but could be greater than that. -stefan]

    Comment by John L — 21 Oct 2013 @ 5:37 PM

  96. > ‘on the century time scale’
    Good point by Lennart.
    It’s a poor scale that has only one tick on it.
    It has to mean it shows up on a scale of plenty of centuries.

    Comment by Hank Roberts — 21 Oct 2013 @ 6:39 PM

  97. Lennart@93, I would have to disagree. I don’t think anyone would class 2 as multi and I don’t think that was the intent of the writer. And the century time scale to me means a century.

    Comment by Keith Woollard — 21 Oct 2013 @ 7:20 PM

  98. > I would have to disagree

    Have you found a copy of the whole paper? What do the authors say?

    Comment by Hank Roberts — 21 Oct 2013 @ 9:26 PM

  99. After having recently ranted here about the lack of models describing MWP1A, I recall that I have previously ranted here about precisely such a model

    Gregoire(2012) doi:10.1038/nature11257

    describing saddle collapse of the N American sheets in last deglaciation.

    I shall watch 67N in Greenland carefully. And keep better track of my rants.


    Comment by sidd — 21 Oct 2013 @ 10:00 PM

  100. So let me see Hank, you and Lennart are allowed to guess at what the author means and I am not? I am reading the paragraph as a normal, sensible, educated English speaker

    Comment by Keith Woollard — 22 Oct 2013 @ 12:25 AM

  101. Hansen & Sato 2011 say:

    “We suggest that ice sheet mass loss, if warming continues unabated, will be characterized better by a doubling time for mass loss rate than by a linear trend. Satellite gravity data, though too brief to be conclusive, are consistent with a doubling time of 10 years or less, implying the possibility of multi-meter sea level rise this century.” (p.1)

    “Hansen (2007)suggested that a 10-year doubling time was plausible, and pointed out that such a doubling time, from a 1 mm per year ice sheet contribution to sea level in the decade 2005-2015, would lead to a cumulative 5 m sea level rise by 2095.” (p.22)

    “The eventual sea level rise due to expected global warming under BAU GHG scenarios is several tens of meters, as discussed at the beginning of this section. From the present discussion it seems that there is sufficient readily available ice to cause multi-meter sea level rise this century, if dynamic discharge of ice increases exponentially.” (p.23)

    “Exponential change cannot continue indefinitely. The negative feedback terminating exponential growth of ice loss is probably regional cooling due to the thermal and fresh-water effects of melting icebergs. Temporary cooling occurs as icebergs and cold fresh glacial melt-water are added to the Southern Ocean and the North Atlantic Ocean.” (p.24)

    “By 2065, when the sea level rise (from ice melt) is 60 cm relative to 2010, the cold freshwater reduces global mean warming (relative to 1880) from 1.86°C to 1.47°C. By 2080, when sea level rise is 1.4 m, global warming is reduced from 2.19°C to 0.89°C.” (p.25)

    “[B]urning all or most fossil fuels guarantees tens of meters of sea level rise, as we have shown that the eventual sea level response is about 20 meters of sea level for each degree Celsius of global warming. We suggest that ice sheet disintegration will be a nonlinear process, spurred by an increasing forcing and by amplifying feedbacks, which is better characterized by a doubling time for the rate of mass disintegration, rather than a linear rate of mass change. If the doubling time is as short as a decade, multi-meter sea level rise could occur this century.” (p.27)

    The negative iceberg cooling feedback ends the exponential growth of SLR, according to H&S. In their model example the rise from 2080-2100 would still be about a meter, if I understand correctly. So that would make SLR by 2100 about 2.5 meters in total.

    So what does multi-meter mean? Somewhere between 2-5 meters for this century, and many more for the next centuries, if H&S are correct.

    Comment by Lennart van der Linde — 22 Oct 2013 @ 1:19 AM

  102. #95 John L
    Yes, your version of how to state the SLR projection for RCP8.5 would definitely be clearer. But would the lead authors agree? I don’t know.

    This is a long standing problem in climate science. Morgan & Keith (1995, Subjective judgements by climate experts. Environmental Science & Technology 29, 468-476) showed that for some basic questions a very careful way of determining the views of experts can lead to a bimodal distribution rather than just a broad range of views around a single mode value. This then raises questions about the usefulness of a median.

    Also I’m not just using the terms ‘fuzzy’ or ‘possibility’ in a loose sense as these are both being used quite extensively in other fields of science. There is a journal called ‘Fuzzy Sets and Systems’ and several journals cover ‘possibility theory’ – e.g. a good paper is: Dubois, 2006, Possibility theory and statistical reasoning. Computational Statistics & Data Analysis 51, 47-69.

    Uncertainties are here to stay, and the new estimates for SLR coming from models show that they are also increasing, so we need to get better at living with them.

    Comment by Martin Manning — 22 Oct 2013 @ 6:40 AM

  103. Here’s a scenario. Note that a lot of the Antarctic ice sheet is grounded well below sea level (over 2km down in parts) and that a lot of that below sea level ground extends right to the ocean. If a warming ocean starts to melt ice from underneath and it comes away in increasingly large chunks, all it takes is significant isostatic rebound to create a domino effect, and a very large chunk comes away. That means even more rebound, deep under water. That sort of thing tends to cause tsunamis.

    No one AFAIK has a model that can predict how this sequence of events could unfold. But perhaps we will see the experiment performed?

    Comment by Philip Machanick — 22 Oct 2013 @ 7:34 AM

  104. #97, 98, 100–“So let me see Hank, you and Lennart are allowed to guess at what the author means and I am not? ”

    Keith, they didn’t say that; they presented their own interpretations for your consideration. You *could* choose to actually consider them.

    Comment by Kevin McKinney — 22 Oct 2013 @ 9:49 AM

  105. So how plausible is exponential growth of ice mass loss from GIS and AIS? Why would CO2-emissions grow exponentially, but not ice mass loss? Hansen & Sato give the example of a 10-yr doubling time, but how about a 20- or 15-yr doubling time?

    Ice mass loss from the ice sheets over 2005-2010 was about 1 mm/yr of SLR (Shepherd et al 2012). So let’s say this will be the average over 2000-2020. A 20-yr doubling time implies about 64 cm of SLR-contribution by 2100, so about 1.2 m of total SLR (assuming about 20 cm from glaciers and about 35 cm from thermal expansion). The rate of SLR would by about 16 mm/yr from 2080-2100.

    A 15-yr doubling time, starting with about 1 mm/yr from 2005-2020, implies about 115 cm of SLR-contribution from the ice sheets by 2100, so about 1.7 m total SLR by 2100, and assuming about 4 cm/yr rise from 2095-2100. By 2200 and 2300 this could imply about 5.7 m and 9.7 m, assuming a constant rate of SLR of 4 cm/yr during this period and no strong kinematic constraints.

    A 14-yr doubling time, starting with circa 1 mm/yr from 2002-2016, implies about 178 cm of SLR-contribution from the ice sheets by 2100, so about 2.3 m total SLR by 2100, assuming about 5 cm/yr rise from 2086-2100. By 2200 and 2300 this could imply about 7.3 m and 12.3 m, assuming a constant rate of SLR of 5 cm/yr during this period and no strong kinematic constraints.

    A 14-yr doubling time implies about a 5%/yr acceleration in ice mass loss. How plausible is that, assuming CO2-emissions rise about 2-3%/yr? Maybe the acceleration in the rise of CO2-concentrations would be a better metric? An acceleration of 5%/yr would imply either strong continued use of fossil fuels and/or a strong positive feedback in lower carbon uptake by carbon sinks and/or higher release by sources. Or would rise in temperature/forcing/ocean heat uptake be the better metric, since also albedo changes in the Arctic, for example, could accelerate the warming and melting/disintegration of the ice sheets?

    Anyhow, to me this seems a worst-case scenario that we cannot rule out at this moment, so continued emissions pose a great risk to our common future (not to speak of possibly even more abrupt ice-mass changes and other risks of further warming).

    Comment by Lennart van der Linde — 22 Oct 2013 @ 9:57 AM

  106. > I am reading the paragraph as a
    > normal, sensible, educated English speaker

    How does that work for you when reading science papers?
    I don’t trust myself to know what an excerpt means, without the context — science papers usually define their terms.

    Let’s find out. It will be fun.

    Comment by Hank Roberts — 22 Oct 2013 @ 10:03 AM

  107. 103 Philip M said, ” That sort of thing tends to cause tsunamis.”

    The ice shelves are already floating.

    “significant isostatic rebound”

    Ice deforms and adjusts far faster than isostatic rebound. We’re still experiencing rebound from the last ice age.

    Comment by Jim Larsen — 22 Oct 2013 @ 12:31 PM

  108. Back in 2001, we got our first, surprising look at the base of the icecap:

    Equipped with two cameras and lights, JPL’s ice probe revealed what appears to be a basal water system, or series of water channels at the base of the ice stream. In places, this water-filled cavity measured approximately 1.4 meters deep (4.6 feet). Based on previous calculations, researchers expected the depth of a water basal cavity to be only in the millimeter range.

    To the researchers’ surprise, they also found rock and other debris embedded in the ice much higher than expected. It was believed that frozen debris would be found no higher than two meters (almost seven feet) off the base of the ice stream. In contrast, the visual data shows frozen debris some 26 meters (85 feet) off the base, which has yet to be explained.

    A layering effect in the ice was also uncovered by the probe. Though not yet fully understood, it is thought that, upstream, ice and gravel have frozen onto the base of the ice sheet. With the ice streams constantly moving, water may slide under debris-laden layers, lifting them up, allowing the process to repeat.

    “The layered information will turn out to be very interesting,” said Carsey. “These layers tell us about processes upstream.” By analyzing these ice layers, researchers may learn how ice streams flow and stop flowing.

    Comment by Hank Roberts — 22 Oct 2013 @ 2:20 PM

  109. There’s newer information on deep ice probe work, e.g.
    lists for example
    Christoffersen P., Tulaczyk S., Carsey F., and Behar A., “A quantitative framework for interpretation of basal ice facies formed by ice accretion over subglacial sediment”, Journal of Geophysical Research, (in Press)

    and much else out there, e.g.
    Nature Geoscience 2, 585 – 588 (2009)
    Published online: 20 July 2009 | doi:10.1038/ngeo581
    Formation of mega-scale glacial lineations observed beneath a West Antarctic ice stream

    … a dynamic sedimentary system that undergoes significant change by erosion and deposition on decadal timescales.

    The assumption that Antarctica won’t change for thousands of years is as outdated as thinking continents don’t drift.

    Comment by Hank Roberts — 22 Oct 2013 @ 2:29 PM

  110. Here’s a nice article which discusses tides and ice streams/shelves. They found one ice stream (the Rurford) varies its speed by up to 20% every two weeks to coincide with spring and neap tides. Tidal forces far outweigh sea level rise and isostatic rebound.

    Comment by Jim Larsen — 22 Oct 2013 @ 2:43 PM

  111. *Rutford

    Comment by Jim Larsen — 22 Oct 2013 @ 2:45 PM

  112. One more point about Hansen & Sato: 2100 is of course an arbitrary year; the eventual rise and magnitude of the rise in sea level are the most relevant variables for adaptation and mitigation considerations.

    With a 20-yr doubling time the rate of rise could be about 32 mm/yr from 2100-2120 and the total rise almost 2 m by 2120.

    It seems H&S think about 5-6 meter/century is the maximum rate of rise under BAU and that about 10 meter of long-term SLR is almost inevitable by now, even if we would somehow manage to return to 350 ppm CO2 within a few centuries.

    How long would it take to reach this maximum rate of rise and how long could that rate be sustained under different forcing scenarios? How could we adapt to such rates and magnitudes of SLR? How can we avoid the worst scenarios? How will IPCC AR5 answer these (and other) questions? How will humanity as a whole answer them?

    Comment by Lennart van der Linde — 22 Oct 2013 @ 5:03 PM

  113. Martin Manning #83:

    From a practical climate adaptation perspective it would be useful to have something like
    p(x>0.98 m)=y%, where x=GMSLR in year 2100 given RCP8.5

    But interpreting the IPCC definition of “likely”, then all we can say on the subjective judgments of the authors in the SLR chapter of the IPCC is:
    p(x>0.98 m)=anywhere between 0% to 34%

    Then, if we are risk-aversive we could choose to base our adaptation plans on p(x>0.98)=34% and if we are risk-takers we could choose p(x>98)=0%.

    Is this how those of us working with climate change adaptation should interpret the IPCC numbers? If not, why not?

    Finally, it is worth noting that the recent NOAA expert assessment provides a much more unequivocal statement:
    “We have very high confidence (>9 in 10 chance) that global mean sea level will rise at least 0.2 meters (8 inches) and no more than 2.0 meters (6.6 feet) by 2100.” (Parris et al 2012).

    Parris, A., P. Bromirski, V. Burkett, D. Cayan, M. Culver, J. Hall, R. Horton, K. Knuuti, R. Moss, J. Obeysekera, A. Sallenger, and J. Weiss. 2012. Global Sea Level Rise Scenarios for the US National Climate Assessment. NOAA Tech Memo OAR CPO-1. 37 pp.

    Comment by perwis — 22 Oct 2013 @ 9:04 PM

  114. Perwis #113,

    That NOAA Assessment is indeed very interesting compared to IPCC AR5. Would it be fair to say thay NOAA estimates the likelihood of more than 1 m of SLR by 2100 as about 50% under RCP8.5? And the chance of more than 2 m as about 5%?

    If so, it seems they give Hansen & Sato a 5% chance of being right. To ignore this chance, would be a significant risk for society to take, in my book, in view of the potential effects of such a large and fast SLR.

    Comment by Lennart van der Linde — 23 Oct 2013 @ 1:10 AM

  115. From one of the chapter authors, referring to comment #25:

    There are two elements to PGs in this caption. In the case of the “No Antarctic PGs,” this refers specifically to the glacier model results from Marzeion et al., where they used CRU data (“observed climate” in caption for Fig. 13.7), for which there are none for Antarctica, thus their modeled glacier contribution does not include Antarctic PGs.

    The “No Antarctic PGs” in the figure legend on panel (a) for the “Individual CMIP5 AOGCMs” and the “CMIP5 AOGCM mean” should not be there, and will be removed in published draft. It does belong with “Adjusted CMIP5 AOGCM mean” because the “adjustment” is the addition of the other terms (land water and glaciers except Antarctic PGs – see above) to the AOGCMs.

    Then the figure caption refers to the ice-sheet contributions since 1993, which are from Chapter 4’s (cryosphere) assessment of all methods of measuring changes in the mass of the ice sheets. Since some of these methods (i.e., GRACE) cannot resolve the PGs around the ice sheets, Chapter 4 included the PGs with the ice sheets in reporting the ice-sheet mass change. The dotted line on the figure is the “adjusted model mean” beginning in 1993 which is the OAGCM (thermal expansion) PLUS land water, glaciers, and the ice-sheet contributions.

    But since the PGs around Greenland and Antarctica are included in these ice-sheet contributions, the glacier contribution to the “adjusted model mean” since 1993 excludes the PGs.

    The figure caption was not very clear and will undergo some clarification for the published version.

    Comment by gavin — 23 Oct 2013 @ 1:37 AM

  116. The IPCC AR 5 paper Summary for Policy Makers under Section 3 Observed Changes/B3 Cryosphere states;

    The average rate of ice loss from the Greenland ice sheet has very likely substantially increased from 34 [–6 to 74] Gt yr–1 over the period 1992–2001 to 215 [157 to 274] Gt yr–1 over the period 2002–2011.
    The average rate of ice loss from the Antarctic ice sheet has likely increased from 30 [–37 to 97] Gt yr–1 over the period 1992–2001 to 147 [72 to 221] Gt yr–1 over the period 2002–2011.

    In round terms this is an increase of polar ice melt mass loss from 60 Gt per year to 360Gt per year or a six-fold increase.

    With GHG emissions increasing exponentially why wouldn’t this ice melt rate continue to also rise exponentially?

    Coastal planning policy makers globally would be wise to monitor this ice melt closely as it will be a useful tool in determining the projected maximum credible sea level rise estimation for different time frames.

    Comment by Tom Bond — 23 Oct 2013 @ 1:39 AM

  117. “With GHG emissions increasing exponentially why wouldn’t this ice melt rate continue to also rise exponentially?”

    Good question. Even more so when you factor in feedbacks.

    So can some of our math wizzes calculate where a sextupling of ice cap melt every ten years would put us in 2100 wrt SLR?

    Comment by wili — 23 Oct 2013 @ 6:31 AM

  118. Regarding polar melting:

    Remember that as you move toward the poles, the ice will become more stable. At some point, you will have run up against ice that only sees a few months of sun per year. Runaway melt isn’t something that will keep me awake at nights.

    Comment by Ray Ladbury — 23 Oct 2013 @ 9:27 AM

  119. New ocean observing system to be deployed in North Atlantic subpolar region to comprehensively measure overturning circulation.

    This ocean observing system (an impressive ocean engineering achievement, once the team gets it to work as intended) may provide data to compel future changes to SLR projections for US/Canada seaboard. A slowing of northward Atlantic surface currents will lead to increased SLR along western Atlantic coast.

    Comment by Sloop — 23 Oct 2013 @ 11:45 AM

  120. Good point, Ray. I would be more comforted by it if sun were the only factor in the melt. Certainly the scarcity of sun at the north pole hasn’t seemed to keep things from what sure looks to me like a “runaway” (here meaning rapidly accelerating) melt of Arctic sea ice, especially when one looks at the volume numbers/graphs.

    Comment by wili — 23 Oct 2013 @ 12:03 PM

  121. Ray, at what elevation do you live?

    Comment by Lennart van der Linde — 23 Oct 2013 @ 12:19 PM

  122. This is a long standing problem in climate science. Morgan & Keith (1995, Subjective judgements by climate experts. Environmental Science & Technology 29, 468-476) showed that for some basic questions a very careful way of determining the views of experts can lead to a bimodal distribution rather than just a broad range of views around a single mode value. This then raises questions about the usefulness of a median.

    Comment by Morgan Wright — 24 Oct 2013 @ 8:16 AM

  123. re 103 Philip Machanick, 107 Jim Larsen

    regarding isostatic rebound – there is a plastic part and an elastic part. The elastic part is fast – presumably on the time scale that it would take seismic waves to travel relevant distances. The elastic part is about 30 % of the total (William F. Ruddiman, “Earth’s Climate: Past and Future”, W.H. Freeman and Company, New York, 2001, p218) …

    (PS some of the elastic part is relieved as the plastic part takes over, because plastic deformation would be responding to the force that supports elastic deformation; however the elastic component that matches compression at increased pressure must remain (isostatic adjustment reduces the pressure anomaly at depth – at a given location, and also following the material when there is sideways flow above)… and also, see next sentence).

    … However, the crust – or at least the upper part of it (?) – has some rigidity and can support (some) shear stresses indefinitely …

    (the lithosphere as a whole is harder to deform, but does; the asthenosphere is more plastic – due to greater dissolved H2O due to the history of relative lack of partial melting, rather than the greater partial melting (which would deplete the rock of H2O as melt escapes upward, leaving behind lithospheric rock, from what I’ve read (Karato, Shun-ichiro, “The Dynamic Structure of the Deep Earth”, Princeton University Press, Princeton, 2003))

    …- ie a load on the surface, or removal or addition thereof, won’t need or change the underlying crust with the same distribution – it will be spread laterally.

    (Though it is interesting to consider an ice sheet grounded below sea level, with the top of the ice removed – what if some ice was temporally stuck against the bottom, before it broke free… That’s the one thing missing from the movie “2012” – why didn’t they show those ~1 mi high tsunamis rolling over Antarctica – seriously, a missed opportunity for some adrenaline (and norepinephrine?)-charged CGI magic… but anyway…)

    I actually have wondered about what that means for sea level rise. If the oceans sank 30 % of their equilibrium response to the increased mass … well, okay, water is a little less than 1/3 density of (uppermost) mantle -uppermost mantle is about 3.3 kg/L ( Dott, Robert H. Jr., and Donald R. Prothero, “Evolution of the Earth” 5th ed., McGraw-Hill, Inc, St. Louis, 1994, p119), so the equilibrium response would be 2.3/3.3 ~= 70 % of the rise from volume increase without any isostatic adjustment (depressing the mantle by 1 m creates a negative mass anomaly equal to 3.3 m of H2O – this ignores elastic compression, which must remain), so the short term response would be ~ 91% of what it would be without adjustment) … but the water is being added all the way to the shifting coastline itself, so the edge of the continent is being weighed down too … but crustal rigidity would result in an increased downward slope to the sea, so maybe the net isostatic change at the coast tends to be zero, thus allowing the 91% rise in sea level to be realized there…????? (PS I only understand this stuff on an introductory level)…

    …well, the maps above show much greater regional variation than that in some places.

    (If the graph Fig. 10-10 B in Ruddiman p.217 is taken literally – which I’m not sure it’s meant to (it has a schematic feel to it, although there are tick marks and labels on one axis), it looks like isostatic response reaches 1/2 equilibrium value ~ 1500 years (eyeballing), ~4/5 @~5000 yrs (eyeballing), and nearly complete by 18000 – 19000 years.)

    Comment by Patrick 027 — 24 Oct 2013 @ 7:03 PM

  124. … oh, I think some of that stuff may vary with the spatial scale of the load/changes and presumably the oceanic crust will flex more easily than the continental crust just because it’s thinner (and often warmer) (and I think the oceanic lithosphere may be thinner too but I just put my books away so that’s it for now).

    Comment by Patrick 027 — 24 Oct 2013 @ 7:11 PM

  125. (PS some of the elastic part is relieved as the plastic part takes over, because plastic deformation would be responding to the force that supports elastic deformation; however the elastic component that matches compression at increased pressure must remain (isostatic adjustment reduces the pressure anomaly at depth – at a given location, and also following the material when there is sideways flow above)… and also, see next sentence).

    I forgot about the temporary shear strains that would also reduce (but spread) the pressure anomaly at depth initially, so I’m not sure exactly how the pressure anomaly varies over time, but that’s way off on a tangent.

    Comment by Patrick 027 — 24 Oct 2013 @ 8:01 PM

  126. A complication is that (if I remember correctly) isostatic rebound has zero total volume change, so the area that has lost its load rises and the surrounding area sinks to compensate. If for example the Greenland ice melts and the area that was under it rises, the coastal area and the shelf will sink to compensate. Irrespective of what happens adjacent to Greenland, the global sea level rise will be reduced. No doubt this has been allowed for in the SLR calculations.

    Comment by Brian Carter — 25 Oct 2013 @ 12:01 PM

  127. If you go to the following website:

    and then click on the button in the upper right-hand corner labeled: “Arctic Sea Ice Forum” and then click on the button labeled: “Antarctica” you will find almost a thousand posts referencing peer reviewed evidence that supports the position that the AR5 SLR projections do not adequately capture the risk of the Antarctic contribution to SLR both this century and into the future. While individually each one of the referred lines of evidence can be discounted, and/or ignored, cummulatively these lines of evidence clear indicate that the IPCC AR5 SLR projections will very likely be revised upward (probably several times) as more data is collected and trends for accelerating ice mass loss from the Antarctic Ice Sheet, AIS, and particularly from the West Antarctic Ice Sheet, WAIS, become better documented.

    Comment by AbruptSLR — 26 Oct 2013 @ 11:46 AM

  128. Thanks to several who pointed out my terrible error in this thread earlier. I apologise with a very red face. Schoolboy error!

    Comment by John Burgeson — 26 Oct 2013 @ 4:24 PM

  129. “it will accelerate further in this century”

    It may accelerate, but it has certainly not accelerated during the past 2 decades. Before a brave may => will transformation is attempted, we need an explanation for the observed slight deceleration during the satellite era.

    CU Sea Level Research Group
    Deceleration is about 0.2 m/cy² on both datasets.

    Comment by Berényi Péter — 27 Oct 2013 @ 8:15 AM

  130. > observed slight deceleration
    You linked to the AVISO page; seems to me that it explains the wiggles you “observe” in the text rigt on the page. There’s nothing there about detecting a change in rate in that data.

    sea level trends patterns observed by satellite altimetry are transient features.

    Comment by Hank Roberts — 27 Oct 2013 @ 10:54 AM

  131. @129

    Is the “deceleration” in sea level based on fitting a quadratic? What’s the justification for that model? If we don’t assume a model and just use lowess regression, the pattern of sea level change does not look anything like a quadratic, nor is there deceleration.

    Comment by L Hamilton — 27 Oct 2013 @ 11:23 AM

  132. Regardless of your view on whether human activity is contributing to climate change, I hope we can agree that the flaring of waste natural gas from North Dakota oil and gas fields is a terrible waste that should be quickly addressed. See nyt article at. see photo USA at night at

    Comment by Murphy mahoney — 27 Oct 2013 @ 12:00 PM

  133. The following reference makes it very clear that over the last two decades, the measureable SLR has been accelerating:

    Calafat and Chambers; GRL, July 2013; doi: 10.1002/grl.50731

    Calafat, F. M., and D. P. Chambers (2013), Quantifying recent acceleration in sea level unrelated to internal climate variability, Geophys. Res. Lett., 40, 3661–3666, doi:10.1002/grl.50731.

    “Sea level observations suggest that the rate of sea level rise has accelerated during the last 20 years. However, the presence of considerable decadal-scale variability, especially on a regional scale, makes it difficult to assess whether the observed changes are due to natural or anthropogenic causes. Here we use a regression model with atmospheric pressure, wind, and climate indices as independent variables to quantify the contribution of internal climate variability to the sea level at nine tide gauges from around the world for the period 1920–2011. Removing this contribution reveals a statistically significant acceleration (0.022 ± 0.015 mm/yr2) between 1952 and 2011, which is unique over the whole period. Furthermore, we have found that the acceleration is increasing over time. This acceleration appears to be the result of increasing greenhouse gas concentrations, along with changes in volcanic forcing and tropospheric aerosol loading.”

    Comment by AbruptSLR — 27 Oct 2013 @ 12:14 PM

  134. “0.022 ± 0.015 mm/yr2”

    ASLR, I’m guessing you have done the calculations on what such a rate of acceleration, if it persists, would mean for total SLR (even without sudden rises) for 2050, 2100…?

    Comment by wili — 28 Oct 2013 @ 11:26 AM

  135. Wili #134,

    Calafat & Chambers 2013 say:
    “[S]ince 1973, SL accelerations have been increasing at a significant rate of 0.002mm/yr3 until reaching its present value of 0.022 ± 0.015mm/yr2 for the 60 year record centered around 1982… [T]he detected SL acceleration is likely not part of a natural cycle.”

    So let’s assume, conservatively (?), that average SLR is about 3 mm/yr in 2000 and that the average acceleration will be about 0.05 mm/yr2 for the period 2000-2020. Let’s further assume this acceleration doubles every 20 years (so the acceleration increases by about 3.5 %/yr2). Then average SLR would be about 4 mm/yr in 2020 and about 3.5 mm/yr in the period 2000-2020. So SLR over that period would be about 7 cm.

    The average acceleration would be about 0.1 mm/yr2 from 2020-2040, so by 2040 the average SLR would be about 6 mm/yr and the average SLR over this periode would be about 5 mm/yr. So total SLR over this period would be about 10 cm.

    Continuing this excercise would imply an average acceleration from 2040-2060 of about 0.2 mm/yr2, so average SLR would be about 10 mm/yr by 2060 and average SLR over this period would about 8 mm/yr, with a total SLR of about 16 cm.

    For 2060-2080 the average acceleration would be about 0.4 mm/yr2, so average SLR would be about 18 mm/yr by 2080 and average SLR over this period would be about 14 mm/yr. Total SLR from 2060-2080 would then be about 28 cm.

    The average acceleration would be about 0.8 mm/yr2 from 2080-2100, with average SLR about 34 mm/yr by 2100 and about 26 mm/yr for this whole period. Total SLR for this period would then be about 52 cm.

    Adding all this up would give about (7 + 10 + 16 + 28 + 52 cm =) 113 cm of SLR over this century, and a rise of 3-4 cm/decade by 2100, so maybe 3-4 meter/century, so total SLR could then be about 4-5 meters by 2200 and 7-9 meters by 2300, assuming no significant further acceleration (or deceleration).

    Comment by Lennart van der Linde — 29 Oct 2013 @ 7:03 AM

  136. Thanks, LvdL, and sorry for my mathematical laziness. That fits my general impression that the current rates of acceleration will not yield more than a few inches/dozen centimeters within the next few decades, but then things start getting much worse quite quickly. Of course, this is all just curve fitting. I expect there could be some major discontinuities, possibly on both sides (as you say, acceleration or deceleration): Richard Alley, among others, has pointed out the possibility, at least, of much more abrupt SLR; Hansen has pointed out that at some point all that ice being dumped in the Ocean is likely to cool down the planet for a while, though he was mostly thinking about GIS loss to the Atlantic and subsequent cooling (or slowing down of warming?) of the Northern Hemisphere, iirc.

    If we are to go beyond mere mathematical projections–what (other) major feedbacks are likely to kick in that might affect this trajectory either way?

    (And thanks again for doing my maths for me.)

    Comment by wili — 29 Oct 2013 @ 1:37 PM

  137. Wili,
    You cite Hansen’s most famous negative feedback factor of large amounts of ice cooling the local oceans (and then the associated atmosphere, another negative feedback would be that as the Hadley Cells continue to expand (north and south)the associated larger desert regions send dust into the Southern Ocean to promote plankton growth and associate sequestration of Carbon Dioxide.

    The number of possible positive feedback factors are much more numerous including: (a) an albedo flip as the polar sea ice and marine ice sheet (the WAIS) retreat faster than modelled; (b) a projected change of the Filchner-Ronne Ice Shelf, FRIS, from a cold ice shelf to a warm ice shelf due to projected changes in wind driven local ocean currents could promote a collapse of the FRIS; and some people believe that the Ross Ice Shelf, RIS, could follow soon thereafter; (c) increases in eustatic SLR from ice mass loss from the GIS could destabilize many of the coastal glaciers in both the WAIS and the EAIS; (d) degradation/loss of the permafrost could pump much more methane into the atmosphere than previously projected; (e) increases in the intensity and/or frequency of EL Nino events would clearly accelerate the rate of SLR; (f) once sufficient ice mass loss occurs from an ice sheet the local seismic activity would increase which would promote more ice mass loss; (g) a possible flip in the atmospheric circulation cells to a pattern associated with an equable climate; and probably most certainly (h) the warming of the Southern Ocean’s Circumpolar Deep Water, CDW, (associated with the current El Nino hiatus period) will certainly promote future acceleration of ice mass loss from both the WAIS and the EAIS due to the advection of warm water against the groundlines for key glaciers/ice sheets/ice shelves.


    Comment by AbruptSLR — 29 Oct 2013 @ 6:20 PM

  138. Wili,

    Not to sound like an alarmist but some other random negative feedback factors that I did not list previously include:
    (a) increase in wildfires due to climate change; (b) increase in the warming potential of methane due to changes in atmospheric chemistry as the methane concentration increases; (c) increasing polar storm activity increases ice mass loss, increases polar amplification and increases upwelling of warm CDW in the Southern Ocean; (d) the basal geothermal heating increases (particularly in the WAIS) as ice mass loss increases the upwell of magma behind the thin lithosphere; (e) increase in the rate of ice calving as glaciers (particularly in the WAIS) retreat down a negative slope on the seafloor; (f) increase in methane hydrate decomposition with global warming; (g) increased release of soil organic carbon (SOC) from terrestial sources (particularly forests) with global warming; (h)the cleaning up of air pollution (aerosols) particularly in China will increase radiative forcing; (i)global warming will likely decrease the absorption of carbon dioxide in both the ocean and terrestial sinks; (j) the albedo flip associate with vegetation growth in the Arctic (in addition of surface ice loss and carbon black deposits (particularly in Greenland)); (k) displacement of polar regional plankton with nano-plankton (that does not sink as well) due to regional ocean warming; (l) change in dimethylsulphite (DMS) due to ocean acidification; (m) increased surface ice melt in Antarctica leading to more ice mass loss (and more SLR); (n) albedo flip due to increased area of permanent land inundation (eg Florida, Louisiana, river deltas around the world); (o) increases in the global hydrolocial cycles; and (p) non-linear interactions between all of these negative feedback factors.

    Comment by AbruptSLR — 30 Oct 2013 @ 10:04 AM

  139. ASLR wrote: “The number of possible positive feedback factors are much more numerous”

    That is my impression, too. May I add to your excellent list:

    –As the GIS melts, the elevation of its highest areas (and really all areas) drops down to levels that are warmer on average, thus melting them faster, lowering them faster…

    –melt pools on the surface of the ice sheet encourage biological activity that changes the albedo of that part of the ice sheet, thus forming more and bigger pools, more biological activity…

    –As ice melts, it can reveal the dust in older ice and concentrate it on the surface, thus changing albedo…

    –more of a forcing than a feedback, but there was an article a year or two ago iirc that claimed that higher CO2 levels actually directly weakened ice structures.

    Do we have any idea how much carbon is under these ice sheets that will be released as they melt back?

    I would love to hear that there are other powerful negative feedbacks to offset some of these.

    Comment by wili — 30 Oct 2013 @ 10:31 AM

  140. The article at the following link indicates how chaos theory can be used to estimate the probabilities of dragon king events (such as ASLR):

    Comment by AbruptSLR — 30 Oct 2013 @ 10:44 AM

  141. > ASLR
    Nice list. Got citations for those items? It’d be most helpful to have pointers to your sources for each of them.

    Comment by Hank Roberts — 30 Oct 2013 @ 10:45 AM

  142. Lennart,
    Extrapolating a 50-year acceleration trend over three centuries may not prove fruitful. Continuing your acceleration would yield 20-25 m by 2500, more than the entrire Greenland and West Antarctic ice sheets combined. C & C also noted that the acceleration existed only since 1952, and “is due to external forcing (anthropogenic and/or natural).” I think the critical wording in your post is “assuming no significant further acceleration or deceleration.”

    Comment by Dan H. — 30 Oct 2013 @ 10:55 AM

  143. Earth is nearly as warm now as it was during the last interglacial period, about 125,000 years ago. At that time, sea level was 4 to 6 meters (13-20 feet) higher. It seems that this higher sea level was due to the melting Greenland and West Antarctic ice caps.

    Comment by Hank Roberts — 30 Oct 2013 @ 11:30 AM

  144. Dan #142,

    You’re right that extrapolating several centuries on may be not prove fruitful, but then again it my prove more fruitful then assuming the process-based ice sheet models are mature enough to fully trust them.

    It does seem likely, not to say inevitable, that any acceleration will stop sooner or later. The question is when and why?

    Many experts seem to think we don’t understand the ice sheets well enough at this point to exclude such an extrapolated scenario, so from a risk- and rights-based perspective it seems unwise and wrong to simply follow the process-based models.

    Comment by Lennart van der Linde — 30 Oct 2013 @ 12:27 PM

  145. Lennart,
    The lack of understanding is a huge stmbling block, and another reason not to extrapolate too far. The other issus is that C & C used nine tidal gauges from the U.S., Europe, and Australia for their analysis. Their acceleration and uncertainty calculations are for these sites, which varied substantially (one actually showed a sea level decline). Expanding their results to the entire ocean basin adds greater uncertainty to their calclations.

    Of course acceleration must stop – the icecaps have a limited supply of frozen water. As mentioned in C & C, the acceleration is dependent on the external forcings. Changes there will lead to further acceleration or deceleration.

    Comment by Dan H. — 31 Oct 2013 @ 6:52 AM

  146. Hank,

    Here is a reference on the increasing intensity of El Nino, with global warming:

    Other references can be found here:,13.0.html

    and here:,41.0.html

    and here:,70.0.html

    Comment by AbruptSLR — 31 Oct 2013 @ 9:33 AM

  147. Dan H – “Continuing your acceleration would yield 20-25 m by 2500, more than the entrire Greenland and West Antarctic ice sheets combined.”

    EAIS not get a look in then?

    Comment by Hasis — 31 Oct 2013 @ 10:26 AM

  148. > Abrupt
    Sorry, I wasn’t clear.

    Could you cite to primary sources — papers published in science journals?

    Often, newspaper and blog sources do mention where they found what they’re telling you. Sometimes it’s just another blog, copypasting. It’s always worth checking.

    If you take the time, and look up the original paper — you may get better information. Otherwise you end up repeating what someone on the Internet somewhere says it says.

    Gavin asks us readers to use DOI when citing sources. You’ll generally be able to provide that if you look for it.

    Not doubting your opinion — just wanted to ask if you’d looked into the claims yourself. It’s generally a good idea.

    Comment by Hank Roberts — 31 Oct 2013 @ 11:22 AM

  149. Dan,

    Paleo data suggest that the current CO2 level could already lead to 10-20 meters of SLR in the long term (e.g. Foster & Rohling 2013), not to speak of the effects of much higher CO2 levels. The question is how fast this could happen. It seems 3-5 meters per century cannot be excluded at this point, even if process based models don’t show such fast rises (yet?).

    The current and potential future forcing (globally) seems so much stronger than those in the past, that it would seems very risky to put too much trust in the current process based models. We don’t know enough, but what we do know, suggests to me that semi-empirical and expert extrapolations are very useful and needed complements to the process based models for informing mitigation and adaptation decisions.

    Comment by Lennart van der Linde — 31 Oct 2013 @ 12:48 PM

  150. Hank,

    For your information: ASLR posts all the original sources on the forum-pages he linked to. If your read them you find many papers supporting his statement here.

    Comment by Lennart van der Linde — 31 Oct 2013 @ 12:52 PM

  151. AbruptSLR (146: 31 Oct 2013 at 9:33 AM -8:00 GMT), you write:

    Here is a reference on the increasing intensity of El Nino, with global warming: [bbc news article] Other references can be found here…

    Looking at the links that you provided to a board forum, all I see are posts referencing Antarctica, the West Antarctic Ice Sheet and sea level rise. While I find links to official websites, I am not immediately seeing any references to any peer reviewed literature, e.g. the Proceedings of the National Academy of Sciences, which incidentally becomes open access after six months. Moreover, judging at least from the titles of the posts themselves, I am not seeing anything referencing El Nino or its increased intensity.

    Perhaps you could provide a link or two to a peer reviewed paper on that topic here? Preferably something open access, if possible. Requiring Hank and others (including myself) to sift through posts at a message board to find your references to on topic peer reviewed papers when nearly all the posts are about something else seems a bit unfair. Thank you!

    Comment by Timothy Chase — 31 Oct 2013 @ 1:30 PM

  152. > on the forum-pages he linked to….
    > you find many papers supporting his statement

    It’s good to cite primary sources (with DOI) for claims.
    Science isn’t any one single paper — it’s a process over time.
    The DOI takes you to where you can see that. Blog posts don’t.

    Comment by Hank Roberts — 31 Oct 2013 @ 2:26 PM

  153. From ASLR’s links, I find this paper on El Nino:

    And for example these papers on many of the possible ice loss mechanisms, forcings and feedbacks:,70.msg934.html#msg934


    It’s a lot of work to cite all or some of these separately linked, but feel free to look them up. I’m sure ASLR would be more specific if he has time.

    Comment by Lennart van der Linde — 1 Nov 2013 @ 3:16 AM

  154. Hasis,
    You are correct. If anything, accumulation will continue there. As Lennart mentioned earlier, we simply do not understand the ice sheets well enough to propose an accurate picture. The Rosenthal paper

    showed much warmer waters around 10,000 years ago without substantial melting, although that was when Conway (1999) determined that melting first started occurring on the WAIS.

    Comment by Dan H. — 1 Nov 2013 @ 8:31 AM

  155. All,

    It is true that I do not have time to customize my posts to each new topic, but I will try posting some of my references about the risks of ASLR:

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    Comment by AbruptSLR — 1 Nov 2013 @ 9:21 AM

  156. Here are some more references:
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    Comment by AbruptSLR — 1 Nov 2013 @ 9:23 AM

  157. Here are some more:
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    Comment by AbruptSLR — 1 Nov 2013 @ 9:24 AM

  158. These are all that I have time for now:

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    [158] Velicogna, I. and Wahr, J., (2013), “Time-variable gravity observations of ice sheet mass balance: Precision and limitations of the GRACE satellite data”; Geophysical Research Letters, DOI: 10.1002/grl.50527.
    [159] Vermeer, M., and S. Rahmstorf. (2009a), “Global sea level linked to global temperature.” Proceedings of the National Academy of Sciences 106 (51) (December): 21527-21532. doi:10.1073/pnas.0907765106.
    [160] Vermeer, M. and Rahnstorf, S., (2009b) “Global Sea Level Linked to Global Temperature”
    [161] Washington W., M. Knutti, Mechl G.A., Teng H., Tebaldi C., Lawrence D. Buja L. and Strand W.G., (2009), “How much climate change can be avoided by mitigation?” Geophys. Res. Lett. 36 L08703.
    [162] Waugh, D.W., Primeau, F., DeVries, T., Mark Holzer, M., (2013); “Recent Changes in the Ventilation of the Southern Oceans”; Science: Vol. 339 no. 6119 pp. 568-570; DOI: 10.1126/science.1225411
    [163] Weitzman, M., (2007), “The Stern Review of the economics of climate change”, Journal of Economic Literature, 45, pp. 703-724.
    [164] Weitzman, M., (2009a), “On Modeling and Interpreting the Economics of Catastrophic Climate Change,” Review of Economics and Statistics, 91, pp. 1-19.
    [165] Weitzman, M., (2009b), “Additive damages, fat-tailed climate dynamics, and uncertain discounting”; Economics – The Open-Access, Open-Assessment E-Journal, 3, pp. 1-29.
    [166] Weitzman, M., (2010), “Risk-Adjusted Gamma Discounting”; Journal of Environmental Economics and Management, 60, pp. 1-13.
    [167] Willis, J.K. and Church, J.A., (2012), “Regional Sea-Level Projection”, Science, Vol. 336, pp 550-551.
    [168] Winkelmann, R., Levermann, A., Krieler, K., and Martin, M.A., (2012), “Uncertainty in future solid ice discharge from Antarctica”, The Cryosphere Discuss., 6, 673-714, doi:10.5194/tcd-6-673-2012.

    Comment by AbruptSLR — 1 Nov 2013 @ 9:25 AM

  159. ASLR, if you want to do science, or even science writing, dumping your entire list is no more helpful than handwaving at your prior blog posts.

    Most of that list is familiar to those who’ve read here a while. No surprises, no news. Quite a few of the authors are participants in the conversation here. Do you know which of them are here?

    Either you do the work of citing sources for your claims, or you don’t.

    Either way, it’s your task. You don’t acquire a reputation by using a pseudonym, having no publications, and assuming others will do the work.

    Your heart is no doubt in the right place. That’s not the problem.

    Comment by Hank Roberts — 1 Nov 2013 @ 10:15 AM

  160. Ok, so that’s all reposted from

    Critique of Most Common SLR Guidance Criteria w.r.t Abrupt SLR
    “… On the off chance that some of the authors of the IPCC AR5 WG1 on SLR (and/or other Forum readers) might have missed (or missed the significance of) some of the following references …”

    You can use HTML to point to the blog rather than copypaste it.

    Comment by Hank Roberts — 1 Nov 2013 @ 10:42 AM

  161. Thanks aSLR. That’s enough I think, for the time being: a valuable ready reference.

    Question: how abrupt? In geological time, I think it’s arguable that we have it now. Certainly the overflow in big tides where I live (near Boston harbor) is noticeably more regular and encroaching more since the 1980s, but I’m expecting an acceleration.

    A lot of people tend to think you might mean overnight. Or months. Or just 2 or 3 years. But in geological time a hundred years would be a wink.

    Comment by Susan Anderson — 1 Nov 2013 @ 10:43 AM

  162. On Holocene sea level:

    On Holocene surface temperature:

    On the new paper by Rosenthal et al, see Mike Mann’s take here:

    This new paper says ocean heat content is rising 15 times faster than at any other time during the Holocene, so pretty soon SLR may be many times faster than earlier in the Holocene as well, would be my first conclusion.

    Comment by Lennart van der Linde — 1 Nov 2013 @ 12:18 PM

  163. Sea level rise could be as much as “6 feet in 100 years” — NPR’s Science Friday today, that’s the worst case from a Corps of Engineers guy interviewed about protecting New York/New Jersey (a retrospective on Hurricane Sandy)

    Comment by Hank Roberts — 1 Nov 2013 @ 1:36 PM

  164. 1)AbruptSLR was requested to post citations for his claims. He did so, pointing to the original web site where he had posted them, together with discussion. Some readers were not satisfied, so he posted a citation list here. He was again attacked, and advised to post a reference to the original site (which he had already done …) If there are some shortcomings in the format of the reference list posted here, that matter might be best discussed on the “Unforced Variations” thread.

    2)More fruitfully, let us discuss if the citations do indeed support his claims. Apparently the citations posted were not novel to some readers. Therefore those readers might be best situated to respond as to whether the papers do support the claims put forward by AbruptSLR ?

    3)I take my own advice in 2). Work cited by AbruptSLR by Ding and Steig (among others), who point out that it is not just a stronger Southern Annular Mode forced by ozone depletion over Antarctica that enhances the influx of Circumpolar Deep Water (CDW) under ice shelves. They argue that a large part of the enhancement comes from tropical influences, particularly in austral fall, and that modelling indicates that these influences are likely to increase, so that ozone recovery may not stem hot CDW influx melting southern ice shelves. This is unfortunate, I had hoped for reduced influx as ozone recovered. Perhaps Prof. Steig might comment further as to how robust the projections are ?

    4)The paper by Pfeffer et al. on kinematic constraints on glaciers reports upper bound of 2m SLR from icesheets by 2100. But the more I think on this, the weaker the analysis seems, especially in West Antarctica. Glaciers are not melting by rushing to the sea and melting at calving front in West Antarctica. Rather, the sea is tunnelling under them and subtracting volume above flotation from below.

    5)In a larger sense: every new feedback we find seems to act for the worse and not for the better. Our hopes grow frailer with every discovery. At this point, I see no way to rule out events on the scale of Melt Water Pulse 1A, but perhaps those among us who are already so familiar with the literature might ?


    Comment by sidd — 1 Nov 2013 @ 2:32 PM

  165. Hank, come on,

    First you ask references for the almost 20 feedbacks that ASLR listed. He points to a list and to posts where these have been discussed before, but then you say that’s not good enough, and that the list doesn’t contain any news. If you’re asking someone to put more effort into this dialogue, it’s only fair to put some more effort in it yourself, in my opinion. It almost sounds like you think you’re the schoolmaster who’s testing his students. Or am I missing something?

    Comment by Lennart van der Linde — 1 Nov 2013 @ 3:40 PM

  166. And the good news is [Not]: … Parts of Oceans warming 15 times faster now than in the previous 10,000 years.

    Comment by SekeRob — 1 Nov 2013 @ 3:45 PM

  167. LOL. Having seen ASLR’s posting on other sites, I knew we were in for a treat when hank asked him for references.

    Perhaps it would be more productive to the conversation if ASLR would pick out one or two papers that he thinks are most convincing wrt his point of view, then we could discuss those in more details, and other articles specifically relevant to whatever issues come up could then be introduced at the right time?

    Good catches, LvdL.

    Comment by wili — 1 Nov 2013 @ 3:53 PM

  168. > pick out one or two papers that
    > he thinks are most convincing
    > wrt his point of view

    (1) Mr. ASLR’s list is the papers he in March wrote that the forthcoming IPCC report, when available, “might have missed (or missed the significance of)” and

    (2) that 5th IPCC Report on sea level is available now, and

    (3) this topic is about that 5th IPCC report on sea level,

    Mr. ASLR can find out if the IPCC 5th “missed (or missed the significance of)” any paper on his list by looking at their sources.

    Chapter 13 IPCC WGI Fifth Assessment on sea level are at (PDF) cites the sources used at pp. 13-71 through 13-88 of the Final Draft (7 June 2013) as of today. Go to for the current links, as they do change.

    The list (today) starts with

    Ablain, M., A. Cazenave, G. Valladeau, and S. Guinehut, 2009: A new assessment of the error budget of global mean sea level rate estimated by satellite altimetry over 1993–2008. Ocean Science, 5, 193-201, cited by 59 later papers

    and ends with

    Zwally, H. J., and M. B. Giovinetto, 2011: Overview and assessment of Antarctic Ice-Sheet mass balance estimates: 1992-2009. Surveys in Geophysics, 32, 351-376, cited by 28 later papers.

    You go to the IPCC chapter; download the PDF (get the actual current work, not someone’s old copy on some blog somewhere).

    Copy the cite; paste it into Scholar.

    Lo — current information, as best we amateur readers can do.
    Science works, not by picking papers that support what you believe, but by reading _all_ the work. Ideas that can’t survive being tested aren’t useful.

    It’s not an “attack” to expect references for claims.
    Anyone who’s ever defended a science thesis can tell you.

    Science isn’t a popularity contest. This is how it works.

    Comment by Hank Roberts — 2 Nov 2013 @ 9:12 AM

  169. AbruptSLR had stated in 146:

    Here is a reference on the increasing intensity of El Nino, with global warming: [BBC news article] Other references can be found here…

    In this context, I had specifically asked for peer reviewed references regarding the increasing intensity of El Nino under global warming.

    In response to my request, Lennart van der Linde stated in 153:

    From ASLR’s links, I find this paper on El Nino:

    From the abstract, I find:

    Although this issue has been investigated many times during the past 20 years, there is very little consensus on future changes in ENSO, apart from an expectation that ENSO will continue to be a dominant source of year-to-year variability.

    Power, Scott, et al. “Robust twenty-first-century projections of El [thinsp] Nino and related precipitation variability.” Nature 502.7472 (2013): 541-545.

    As such there would seem to have been very little support for the view that El Niño will become more intense as the result of global warming.

    However, they continue:

    Here we show that there are in fact robust projected changes in the spatial patterns of year-to-year ENSO-driven variability in both surface temperature and precipitation. These changes are evident in the two most recent generations of climate models, using four different scenarios for CO2 and other radiatively active gases. By the mid- to late twenty-first century, the projections include an intensification of both El-Niño-driven drying in the western Pacific Ocean and rainfall increases in the central and eastern equatorial Pacific.


    As such, this would appear to be a new result, first published 2013-10-24, a little over a week ago. I wouldn’t be surprised if this result stands, but there may very well be direct responses to this study, and it will likely be tested at least in part by other studies in the same area over the next few years. Personally, while I suspect there will be an intensification of El Niño, I do not believe that one can claim that there is as of yet much justification for this in the peer reviewed literature, that is, unless there are papers that the authors of the above study missed.

    Comment by Timothy Chase — 2 Nov 2013 @ 11:01 AM

  170. Zwally(2011) doi:10.1007/s10712-011-9123-5
    available freely at

    seems to have been overtaken. That paper argues for a very small Antarctic contribution to SLR, but this causes problems with overall SLR budget as shown in Chen(2013) doi: 10.1038/NGEO1829 and conflicts with newer estimates as in Shepherd(2012) doi: 10.1126/science.1228102 and Velicogna(2013) doi:10.1002/grl.50527

    The latter papers use improved ice models and GIA estimates and find an accelerating component to mass waste from both Greenland and Antarctica.

    I see that Chen(2013) alludes to the new ICE6G model

    ” The improvement in the upcoming ICE6G model is expected to significantly reduce the discrepancy among PGR models, … ”

    PGR is post glacial rebound, which leads to a large part of the uncertainty for Antarctica. Has anyone seen any work based on ICE6G lately relating to current mass waste loss rates ? I see some paleo work, but nothing on GRACE corrections. I will look harder.

    In this regard, i recall that at this time last year Fettweis or Tedesco or somebody posted the then latest GRACE data for Greenland. Seems like this years results should be available about now, has anyone spotted it ?


    Comment by sidd — 2 Nov 2013 @ 12:15 PM

  171. Good points, hank. Except that we should not fool ourselves into thinking we are doing science here, we are having a conversation. Science may require a fool appraisal of all available evidence, but it is very hard to have a conversation about hundreds of articles at once, imho.

    Comment by wili — 2 Nov 2013 @ 2:00 PM

  172. Unfortunately, my last post appears to have been caught in the spam filter, but essentially it said that:

    In order to focus discussion (per Wili’s suggestion), I propose that the Pine Island Glacier (PIG) – Thwaites Glacier system is the best case to consider to begin the discussion of the risk of abrupt sea level rise, ASLR, (including being influenced by all of the multiple feedback factors that I previously posted), as by themselves this drainage basins could contribute over 2-feet of SLR.

    In this regard I cite the following two references focused on the Thwaites Glacier

    First: “Dynamic (in)stability of Thwaites Glacier, West Antarctica”, B. R. Parizek, K. Christianson, S. Anandakrishnan, R. B. Alley, R. T. Walker, R. A. Edwards, D. S. Wolfe, G. T. Bertini, S. K. Rinehart, R. A. Bindschadler, S. M. J. Nowicki, Article first published online: 16 MAY 2013, DOI: 10.1002/jgrf.20044; Journal of Geophysical Research

    Second: “Weak bed control of the eastern shear margin of Thwaites Glacier, West Antarctica”; Joseph A. MacGREGOR, Ginny A. CATANIA, Howard CONWAY, Dustin M. SCHROEDER, Ian JOUGHIN, Duncan A. YOUNG, Scott D. KEMPF, & Donald D. BLANKENSHIP; Journal of Glaciology, Vol. 59, No. 217, 2013 doi: 10.3189/2013JoG13J050

    Per the following abstract, the first reference includes the following quote citing the “ephemeral” nature of the stability of the Thwaites Glacier if circulating waters substantially reduce the basal resistance in the gateway area:

    Parizek et al 2013 Abstract:
    “In addition to the SeaRISE data sets, we use detailed aerogeophysical and satellite data from Thwaites Glacier as input to a coupled ice stream/ice-shelf/ocean-plume model that includes oceanic influences across a several kilometers wide grounding zone suggested by new, high-resolution data. Our results indicate that the ice tongue provides limited stability, and that while future atmospheric warming will likely add mass to the surface of the glacier, strong ice stream stabilization on bedrock highs narrower than the length of the grounding zone may be ephemeral if circulating waters substantially reduce basal resistance and enhance melting beneath grounded ice within this zone.”

    MacGregor et al 2013 clearly cite: (a) the possibility that the Thwaites Glacier may have retreated back at least to the eastern shear margin during the Eemian, as the radar signal might indicate the occurrence of marine sediment beneath the glacier; and (b) the SW tributary glacier could be activated by one more major calving event for the Pine Island Ice Shelf (PIIS); which in turn could active the eastern shear margin for the Thwaites Glacier, that should accelerate ice velocities out of the Thwaites Gateway, with associated ice thinning and grounding line retreat.

    – The continued retreat of PIG combined with the recurring major El Nino events (though 2060) could synergistically increase what I call “horizontal advection” of warm CDW from the trough leading to the PIG to the trough in the Thwaites Gateway leading to the Byrd Subglacial Basin (BSB); where the ice is current thinner and has more crevasses since the local ice tongue surge event during the late austral winter and spring of 2012; and thus the ice is this trough area is much more susceptible to calving acceleration from the warm Circumpolar Deep Water (CDW).
    – The possibility that Glacial Isotatic Adjustment (GIA) corrections will increase estimate ice mass loss estimate from PIG/Thwaites by up to 40%, raises the possibility that the basal meltwater subglacial hydrological system is more active under both the PIG and especially under the Thwaites Glacier than previously expected; and if so this active subglacial drainage system would promote ice mass loss.
    – The austral winter of 2013 was the warmest on record, thus raising the probability that in the near future there will be more days of surface melt during the austral summer, which would likely flow into the increasing number of surface crevasses in the ice in the Thwaites Gateway (especially as it thins); which should promote accelerated calving of the ice in this area (which is not constrained laterally as is the PIIS).
    – The observed trend of increasing concentration of methane in the atmosphere over Antarctica will likely lead to increased coastal wind velocities which will likely increase the flow of warm CDW into the Amundsen Sea Embayment (ASE); which will promote ice mass loss for both the PIG and the Thwaites Glacier.
    – Based on the observed snowfall trend it is unlikely that snowfall will increase before the grounding line for the Thwaites Glacier retreats to upstream of the gateway; at which point an increase in snowfall will actually accelerate the local calving by providing more driving force to promote rapid calving and groundling line retreat after the 2040 to 2060 timeframe.
    – It should be remembered that any significant acceleration of ice mass loss from the Greenland Ice Sheet (GIS) in the 2013 to 2060 timeframe will help to de-stabilize the PIG/Thwaites system by raising sea level in the ASE due to the fingerprint effect.

    While there are many other feedback factors, it is impossible at this time to predict the rate and amount of their synergistic interaction; and thus we will need to keep a close watch on this critical area in the coming years in order better assess the timing of any possible tipping point in the PIG/Thwaites system.

    Comment by AbruptSLR — 2 Nov 2013 @ 2:15 PM

  173. First a quibble about the Parizek paper: they seem to be using the words “lee” and “leeward” as a synonym for “landward.” This is not my understanding, “leeward” or “alee” is an antonym for windward” as far as I know. Am i correct in my interpretation of their usage or have i got it wrong ?

    Now to more substantial matters. Three points struck me as important.

    1) the use of a grounding zone instead of a grounding line, whose importance is illustrated by the comment:

    “Removing the ice shelf, equivalent to greatly increased melting beneath floating ice but no change in melting beneath grounded ice across a discrete grounding line, has little influence on TG. However, the entire domain deglaciates in only 40 years if a smaller but still substantial increase in melting is applied not only to the floating ice but also to the node at the grounding line. Numerically, this is equivalent to a grounding zone of the same length as the last grounded finite element (typically 1 km), with the melt rate increasing from near zero at the upglacier end to the ice-shelf value (200 m/yr) at the downglacier end.”

    2)The importance of coupling the ocean to ice as is done in run M4:

    A weakness in some of the runs is the imposed basal melt rate in M1,M2, and M3 runs. The coupled ocean ice model in M4 i think is more reliable, and shows features absent in M1, M2 and M3, and breaks the linearity of response:

    “Short of the M3-magnitude forcing, VAF changes increase linearly with spatially constant prescribed melt rates (Figure 7c). However, with the coupled ice-ocean simulation (M4), this linearity breaks down … As peak melt rates ( 40 m/yr, lower right vertices) are concentrated near the grounding line, spatially variable melt leads to efficient removal of the ice shelf (cf. Figure 6d and 6e) [Little et al., 2009; Walker and Holland, 2007; Parizek and Walker, 2010] and a nonlinear response to the average melt magnitude (roughly 50–70% more volume loss than a linear trend would predict for a spatially constant 15 m/yr melt rate; see arrows in Figure 7c).”

    3)the presence and influence of subglacial water several kilometers upstream of the grounding “line.” This relates to 1) above. They see evolution of subglacial hydrology in their models, and this evolution coupling with the width of the grounding zone greatly influences retreat (or growth.) In this context, another weakness of their model is the reduced dimensionality, as they admit:

    “As discussed above, the strong variations in basal topography transverse to flow suggest that seawater may penetrate inland in some regions and then spread laterally. Melting of ice above such a layer would be less than in the ice-shelf cavity, where ocean circulation is vigorous. However, under some conditions, it is likely to be notably larger than beneath fully grounded ice where the enhanced melting from transport of warmed ocean waters exceeds the reduced melting from lubrication suppressing basal friction.”

    They go on to find:

    “Thus, if the grounding zone is narrower than the distance between the peak of the bedrock ridge and the downstream edge of the subglacial lake, then grounding line stabilization occurs; otherwise, catastrophic retreat begins (136 km in 55 years), with no other points of stabilization in our model domain.”

    They repeat the caveat about reduced dimensionality:

    “Because of our reduced dimensional modeling, we note that these cavities are potentially interconnected with the ocean in the transverse dimension.”

    In the Appendix they point out the importance of tidal pumping (which is not explicitly included in the model):

    ” Model estimates for likely subglacial materials yield a low-tide pressure drop beneath this flexural uplift that is larger in magnitude than the oceanic pressure drop from the tide. This may cause tidal pumping of seawater upglacier. This ocean water then may be spread farther inland by strong water pressure variations associated with ice flexure [Murray and Clarke, 1995; Walker et al., 2013]. Such pumping may explain why radar data collected across grounding lines typically show a bright reflection typical of ice over seawater extending inland and only gradually fading to a weaker reflector more consistent with a thin layer of freshwater [Walker et al., 2013].”

    They warn:

    ” … our results do not yet provide reliable projections of best estimate or upper limit sea level rise from TG. While our assumptions of a linear decrease in basal melt and weakening of the basal drag coefficient in the grounding zone are aggressive, they are not worst case scenarios.”

    I think this is an important advance in modelling, highlighting the importance of accurate basal topo measurement. I eagerly await the next iteration of such models, especially to remove the limitation of reduced dimensionality, and utilizing detailed topo.

    I shall try to put some of the grafs on the web with comments in my copious(not!) spare time …


    Comment by sidd — 2 Nov 2013 @ 6:07 PM

  174. I should add one important point to my comment above

    4)the importance of bed rheology: an effectively plastic bed can _stabilize_ against retreat. This might be a ray of hope. I do no clearly see if such a “plastic” bed is realistic, but the possibility that the glacier can sculpt its own bed to stabilize itself is a tantalizing, if far-fetched glimmer of good news.

    “However, with a nearly plastic basal rheology and xgz = 7 km, the GZ3P simulation forms two subglacial lakes in the grounding zone but ultimately stabilizes (Figures 10e, 12c, and 12d) as basal stresses are spread across a larger length scale. Furthermore, thinning waves propagate rapidly across the entire glacier (cf., m = 1 bed), and only minor geometric adjustments are required to deliver the ice flux necessary to maintain grounding on the bedrock ridge. Because little change in driving stress is required to compensate large marginal forcings arising from the 7 km grounding zone, only the last ~45 km of grounded ice has a significantly different profile
    (|s| > 20 m) when compared to the end of the T1 standard simulation. Therefore, given the high-resolution basal topography in the grounding zone, higher bed exponents tend to stabilize the TG system. This novel result further highlights the need for additional data and analyses to determine bed type [Anandakrishnan et al., 2003; Joughin et al.,2004, 2009; Walker et al., 2012].”

    They go on to warn however:

    ” This significant stability can be overcome, however, if we reduce the upstream flux by 11%. Even though episodic advances persist late into the deglaciation, this additional forcing leads to rapid retreat (Figures 10f, 12e, and 12f)”


    Comment by sidd — 2 Nov 2013 @ 6:43 PM

  175. As a follow-on to my previous post, the following abstract come from the linked sources and are relevant to the question of potential abrupt SLR contribution from the Thwaites/PIG drainage basins:
    Contact: Secretary General, International Glaciological Society

    Ice sheets and sea level – data, models and ways forward
    Corresponding author: Richard B. Alley
    Corresponding author e-mail:

    “The ‘unknown unknowns’ of ice-sheet behavior have been shrinking rapidly under the coordinated efforts of surface observations, airborne and satellite remote sensing, and modeling, together with atmospheric, oceanic and geologic investigations around the ice sheets, including paleoclimatic studies. For most ice-sheet regions, it is now possible to place useful limits on likely rates of change, quantify uncertainties and define research plans for reducing those uncertainties. Unfortunately, this optimistic outlook does not apply universally. Sufficient retreat of the Thwaites Glacier grounding zone, for example, could shift a calving front into a region of combined width and water depth larger than any outlet on Earth today, raising physical questions that are not as yet close to being answered and that may prove very difficult to constrain tightly. The community faces the challenge of continuing the highly successful work of reducing uncertainties in well-characterized flow regimes, while identifying and characterizing those physical processes that are not yet well represented in key places. Furthermore, policy-makers would like guidance from plausible scenarios until those physical processes are better represented. The need for coordinated observations and modeling is thus growing, not shrinking.”

    I strongly agree with Alley et al 2013’s statements cited above about the Thwaites Glacier, and I note that our current lack of certainty on the topic of the (in)stability of the Thwaites/PIG system poses a hazard that merits considerable focus on coordinated observations and advanced modeling (beyond what is practicable today).

    Comment by AbruptSLR — 2 Nov 2013 @ 7:00 PM

  176. wili wrote in 171:

    Good points, hank. Except that we should not fool ourselves into thinking we are doing science here, we are having a conversation. Science may require a fool appraisal of all available evidence, but it is very hard to have a conversation about hundreds of articles at once, imho.

    Well, if someone wishes to suggest that their position is well-supported by the literature then I would recommend citing a review or two. Absent that, it might help to do a little of their own objective survey. A cherry pick need not apply. If they wish instead to discuss the latest finding, I certainly don’t have a problem with that, either, so long as they make it clear that this is what they are discussing rather than something that has wider support.

    We may not be doing science, but we should try to insure that, when we appeal to science we are actually appealing to the science, representing it accurately, not our own personal hunches. This does not however mean that we must always hold with the most conservative estimate, either. If we represent the uncertainties accurately, we can point out that uncertainty oftentimes implies risk.

    Comment by Timothy Chase — 2 Nov 2013 @ 8:21 PM

  177. That should have been ‘full appraisal’ instead of ‘fool appraisal,’ though perhaps I should just let the Freudian slip stand?

    Comment by wili — 2 Nov 2013 @ 9:51 PM

  178. Sidd,

    Thanks for the great input about the Parizek et al 2013 paper.

    For those interested in the details of the MacGregor et al 2013 paper, I provide the following link to a pdf and I post the abstract to this paper:

    “ABSTRACT. Recent acceleration and thinning of Thwaites Glacier, West Antarctica, motivates investigation of the controls upon, and stability of, its present ice-flow pattern. Its eastern shear margin separates Thwaites Glacier from slower-flowing ice and the southern tributaries of Pine Island Glacier. Troughs in Thwaites Glacier’s bed topography bound nearly all of its tributaries, except along this eastern shear margin, which has no clear relationship with regional bed topography along most of its length. Here we use airborne ice-penetrating radar data from the Airborne Geophysical Survey of the Amundsen Sea Embayment, Antarctica (AGASEA) to investigate the nature of the bed across this margin. Radar data reveal slightly higher and rougher bed topography on the slower-flowing side of the margin, along with lower bed reflectivity. However, the change in bed reflectivity across the margin is partially explained by a change in bed roughness. From these observations, we infer that the position of the eastern shear margin is not strongly controlled by local bed topography or other bed properties. Given the potential for future increases in ice flux farther downstream, the eastern shear margin may be vulnerable to migration. However, there is no evidence that this margin is migrating presently, despite ongoing changes farther downstream.”

    Comment by AbruptSLR — 2 Nov 2013 @ 10:45 PM

  179. The following linked reference and associated abstract presents relatively recent numerical findings that certain GIS and WAIS glaciers (including the Thwaites Glacier) may be at risk of ” catastrophic disintegration”:

    Bassis, J.N., and Jacobs,S., (2013), “Diverse calving patterns linked to glacier geometry”, Nature Geoscience, 6, 833–836, doi:10.1038/ngeo1887

    “Iceberg calving has been implicated in the retreat and acceleration of glaciers and ice shelves along the margins of the Greenland and Antarctic ice sheets. Accurate projections of sea-level rise therefore require an understanding of how and why calving occurs. Unfortunately, calving is a complex process and previous models of the phenomenon have not reproduced the diverse patterns of iceberg calving observed in nature. Here we present a numerical model that simulates the disparate calving regimes observed, including the detachment of large tabular bergs from floating ice tongues, the disintegration of ice shelves and the capsizing of smaller bergs from grounded glaciers that terminate in deep water. Our model treats glacier ice as a granular material made of interacting boulders of ice that are bonded together. Simulations suggest that different calving regimes are controlled by glacier geometry, which controls the stress state within the glacier. We also find that calving is a two-stage process that requires both ice fracture and transport of detached icebergs away from the calving front. We suggest that, as a result, rapid iceberg discharge is possible in regions where highly crevassed glaciers are grounded deep beneath sea level, indicating portions of Greenland and Antarctica that may be vulnerable to rapid ice loss through catastrophic disintegration.”

    Comment by AbruptSLR — 2 Nov 2013 @ 11:39 PM

  180. While the following linked, referenced (with abstract), paper is not specifically directed towards SLR contribution from the West Antarctic Ice Sheet, WAIS; nevertheless, if correct, it does indicate the potential for ice sheet collapse under conditions comparable to modern conditions:

    O’Leary, M.J., Hearty, P.J., Thompson, W.G., Raymo, M.E., Mitrovica, J.X., and Webster, J.M., (2013), “Ice sheet collapse following a prolonged period of stable sea level during the last interglacial”, Nature Geoscience; doi:10.1038/ngeo1890.

    “During the last interglacial period, 127–116 kyr ago, global mean sea level reached a peak of 5–9  m above present-day sea level. However, the exact timing and magnitude of ice sheet collapse that contributed to the sea-level highstand is unclear. Here we explore this timing using stratigraphic and geomorphic mapping and uranium-series geochronology of fossil coral reefs and geophysical modelling of sea-level records from Western Australia. We show that between 127 and 119 kyr ago, eustatic sea level remained relatively stable at about 3–4 m above present sea level. However, stratigraphically younger fossil corals with U-series ages of 118.1±1.4 kyr are observed at elevations of up to 9.5 m above present mean sea level. Accounting for glacial isostatic adjustment and localized tectonics, we conclude that eustatic sea level rose to about 9 m above present at the end of the last interglacial. We suggest that in the last few thousand years of the interglacial, a critical ice sheet stability threshold was crossed, resulting in the catastrophic collapse of polar ice sheets and substantial sea-level rise.”

    Comment by AbruptSLR — 3 Nov 2013 @ 6:14 AM

  181. op. cit.

    Comment by Hank Roberts — 3 Nov 2013 @ 9:42 AM

  182. ASLR, you can search the site, e.g. for that paper:“doi%3A10.1038%2Fngeo1887”

    Comment by Hank Roberts — 3 Nov 2013 @ 9:45 AM

  183. Stefan, I keep re-reading your opening post on this and getting more out of it each time. I’d encourage others to do the same, treat this as studying the science, not as a chatroom conversation. Most of us are the audience here.

    I particularly appreciated Stefan’s pointer to

    Every link in the opening post leads to more reading worth serious attention on this subject. The scientists have, I think, made very clear how we’ve changed the future of the planet already.

    Comment by Hank Roberts — 3 Nov 2013 @ 9:51 AM

  184. The following linked reference (and abstract) indicates that due to modeling issues associated with the Glacial Isostatic Adjustment, GIA, it is possible that the ice mass loss from the Amundsen Sea sector glaciers (including PIG and Thwaites) may be under estimated by about 40%. Currently, British researchers are installing more GPS sites in this area in order to try to resolve this issue (which may take many years-worth of data). However, in the meantime this uncertainty implies greater public risk not greater public safety.

    Groh, A., Ewert, H., Scheinert, M., Fritsche, M., Rulke, A., Richter, A., Rosenau, R., and Dietrich, R., (2012), “An investigation of Glacial Isostatic Adjustment over the Amundsen Sea sector, West Antarctica”, Global and Planetary Change, December, Vols. 98-99, pp 45-53

    The present study focuses on the Amundsen Sea sector which is the most dynamical region of the Antarctic Ice Sheet (AIS). Based on basin estimates of mass changes observed by the Gravity Recovery and Climate Experiment (GRACE) and volume changes observed by the Ice, Cloud and Land Elevation Satellite (ICESat), the mean mass change induced by Glacial Isostatic Adjustment (GIA) is derived. This mean GIA-induced mass change is found to be 34.1 ± 11.9 Gt/yr, which is significantly larger than the predictions of current GIA models. We show that the corresponding mean elevation change of 23.3 ± 7.7 mm/yr in the Amundsen Sea sector is in good agreement with the uplift rates obtained from observations at three GPS sites. Utilising ICESat observations, the observed uplift rates were corrected for elastic deformations due to present-day ice-mass changes. Based on the GRACE-derived mass change estimate and the inferred GIA correction, we inferred a present-day ice-mass loss of − 98.9 ± 13.7 Gt/yr for the Amundsen Sea sector. This is equivalent to a global eustatic sea-level rise of 0.27 ± 0.04 mm/yr. Compared to the results relying on GIA model predictions, this corresponds to an increase of the ice-mass loss or sea-level rise, respectively, of about 40%.”

    Comment by AbruptSLR — 3 Nov 2013 @ 10:54 AM

  185. Researcher such as Stefan Rahmstorf and Aslak Grinsted, certainly do not deny that the risk of the collapse of portions of the West Antarctic Ice Sheet, WAIS, may not be adequately included within the AR5 SLR projections, as indicated in the information in the following website links (maintained by Aslak Grinsted):

    Therefore, readers should not think that I am criticizing any such researchers. However, I will state that picking a date for non-linear SLR projections like 2100 is deceptive because a few years thereafter (say one hundred years from now 2014) the SLR could be very much higher; and also non-linear interactions not fully captured by current “ice experts” [such as those assessed by Bamber & Aspinall (2013), see reference below)] projections, may cause the “ice experts” to change (possibly increase) their projections of ice mass loss from the WAIS in the future, when their models become more powerful/calibrated (possibly to incorporate data from some of the recent scientific findings that I am referencing).

    Bamber, J.L. and Aspinall, W.P. (2013), “An expert judgment assessment of future sea level rise from the ice sheets”, Nature Climate Change; Volume:3, Pages: 424–427; doi:10.1038/nclimate1778.

    Comment by AbruptSLR — 3 Nov 2013 @ 11:27 AM

  186. ASLR, so far you’re mostly restating points made by Stefan in the original post that opens this thread.
    Yes, Aslak Grinsted’s pages are very helpful, as are the other links Stefan provides. You should read them.

    You use the word “deceptive” to describe the use of 2100 as a marker. I’d say you’re deceiving yourself if you think that’s the end of what’s discussed. Look at the very last lines of the AGU chapter, in the PDF.

    Your claim the scientists are being “deceptive” would mislead anyone who hasn’t read the AGU chapter.

    Note more than 200 people have recommended reading this (bottom of the main post, click the button).

    Please be aware you’re writing for an audience.
    Check the assumptions you’re making before posting what you believe.

    If you’re just posting without reading, then, well, bless your heart.
    Whoever you are.

    Comment by Hank Roberts — 3 Nov 2013 @ 1:59 PM

  187. The following linked reference, and associated abstract, indicates that the CDW entering the troughs leading to the PIG (which contributes to the CDW leading to the Thwaites Glacier) have increased in volume between 2000 and 2010. I note that the year from 2000 to 2010 were all El Nino hiatus years, and that it is likely that when the current El Nino hiatus period ends, that the volume of CDW passing through the troughs leading to the PIG and the Thwaites Glacier, may accelerate during El Nino periods:

    From circumpolar deep water to the glacial meltwater plume on the eastern Amundsen Shelf
    Y. Nakayama | M. Schröder | H.H. Hellmer
    Deep Sea Research Part I: Oceanographic Research Papers; Volume 77, July 2013, Pages 50–62

    “Abstract: The melting of Pine Island Ice Shelf (PIIS) has increased since the 1990s, which may have a large impact on ice sheet dynamics, sea-level rise, and changes in water mass properties of surrounding oceans. The reason for the PIIS melting is the relatively warm (∼1.2°C) Circumpolar Deep Water (CDW) that penetrates into the PIIS cavity through two submarine glacial troughs located on the Amundsen Sea continental shelf. In this study, we mainly analyze the hydrographic data obtained during ANTXXVI/3 in 2010 with the focus on pathways of the intruding CDW, PIIS melt rates, and the fate of glacial meltwater. We analyze the data by dividing CTD profiles into 6 groups according to intruding CDW properties and meltwater content. From this analysis, it is seen that CDW warmer than 1.23°C (colder than 1.23°C) intrudes via the eastern (central) trough. The temperature is controlled by the thickness of the intruding CDW layer. The eastern trough supports a denser CDW layer than the water mass in Pine Island Trough (PIT). The eastern intrusion is modified on the way into PIT through mixing with the lighter and colder CDW from the central trough. Using ocean transport and tracer transport calculations from the ice shelf front CTD section, the estimated melt rate in 2010 is ∼30myr−1, which is comparable to published values. From spatial distributions of meltwater content, meltwater flows along the bathymetry towards the west. When compared with earlier (2000) observations, a warmer and thicker CDW layer is observed in Pine Island Trough for the period 2007–2010, indicating a recent thickening of the CDW intrusion.”

    Comment by AbruptSLR — 3 Nov 2013 @ 2:12 PM

  188. For those not familiar with the Antarctic, Bertler et al (2006, see reference below) explains the reason that more warm CDW flows into the ASE during El Nino periods [due to shifts in the Amundsen Sea Low, ASL (or the Amundsen-Bellingshausen Seas Low, ABSL)], see my associated statement to this affect in my preceding post.

    Bertler, N.A., Naish, T.T., Mayewski, P.A. and Barrett, P.J., (2006), “Opposing oceanic and atmospheric ENSO influences on the Ross Sea Region, Antarctica”, Advances in Geosciences, 6, pp 83-88, SRef-ID: 1680-7359/adgeo/2006-6-83.

    Furthermore, the following reference (and abstract) not only indicates how important/unique the Bellingshausen – Amundsen Seas Sector is but also just how poorly the current GCMs, and RCMs, model this critical area (and as cited above the ABSL together with El Nino events can accelerate ice mass loss from the Amundsen-Bellingshausen Seas Sector Ice Sheets, as the warm CDW promotes grounding line retreat for the affected glaciers):

    The influence of the Amundsen-Bellingshausen Seas Low on the climate of West Antarctica and its representation in coupled climate model simulations. J. Scott Hosking, Andrew Orr, Gareth J. Marshall, John Turner, and Tony Phillips, Journal of Climate 2013; doi:

    “In contrast to earlier studies, we describe the climatological deep low-pressure system that exists over the South Pacific sector of the Southern Ocean, referred to as the Amundsen-Bellingshausen Seas Low (ABSL), in terms of its relative (rather than actual) central pressure by removing the background area-averaged mean sea level pressure (MSLP). In doing so, we remove much of the influence of large-scale variability across the ABSL sector region (e.g., due to the Southern Annular Mode), allowing a clearer understanding of ABSL variability and its effect on the regional climate of West Antarctica. Using ERA-Interim reanalysis fields the annual cycle of the relative central pressure of the ABSL for the period 1979 to 2011 shows a minimum (maximum) during winter (summer), differing considerably from the earlier studies based on actual central pressure which suggests a semi-annual oscillation. The annual cycle of the longitudinal position of the ABSL is insensitive to the background pressure, and shows it shifting westwards from ~250° E to ~220° E between summer and winter, in agreement with earlier studies. We demonstrate that ABSL variability, and in particular its longitudinal position, plays an important role in controlling the surface climate of West Antarctica and the surrounding ocean by quantifying its influence on key meteorological parameters. Examination of the ABSL annual cycle in seventeen CMIP5 climate models run with historical forcing showed that the majority of them have definite biases, especially in terms of longitudinal position, and a correspondingly poor representation of West Antarctic climate.”

    Again the poor CMIP5 model projections of the ABSL annual cycle raises more uncertainties about the AR5 SLR projections; which does not reflect well on the use of the AR5 projections for protecting the public.

    Comment by AbruptSLR — 3 Nov 2013 @ 5:29 PM

  189. Also, the following reference (as abstract) explains the fingerprint effect of rapid ice melt on SLR, which indicates that ice mass loss from the WAIS has a much larger effect on Northern Hemisphere, NH, areas that such an ice mas loss has on eustatic sea level. As most of the world’s affected populated centers occur in the NH the consequence of AR5 underestimating SLR contribution from the WAIS would be more serious that from non-Antarctic sources:

    Hay, C.C., Morrow, E., Kopp, R.E., and Mitrovica, J.X., 2012, “Estimating the sources of global sea level rise with data assimilation techniques”, Proceedings of the National Academy of Sciences, doi: 10.1073/pnas.1117683109.

    “A rapidly melting ice sheet produces a distinctive geometry, or fingerprint, of sea level (SL) change. Thus, a network of SL observations may, in principle, be used to infer sources of meltwater flux. We outline aformalism, based on a modified Kalman smoother, for using tide gauge observations to estimate the individual sources of global SL change. We also report on a series of detection experiments based on synthetic SL data that explore the feasibility of extracting source information from SL records. The Kalman smoother technique iteratively calculates the maximum-likelihood estimate of Greenland ice sheet (GIS) and West Antarctic ice sheet (WAIS) melt at each time step, and it accommodates data gaps while also permitting the estimation of nonlinear trends. Our synthetic tests indicate that when all tide gauge records are used in the analysis, it should be possible to estimate GIS and WAIS melt rates greater than ∼0.3 and ∼0.4 mm of equivalent eustatic sea level rise per year, respectively. We have also implemented a multimodel Kalman filter that allows us to account rigorously for additional contributions to SL changes and their associated uncertainty. The multimodel filter uses 72 glacial isostatic adjustment models and 3 ocean dynamic models to estimate the most likely models for these processes given the synthetic observations. We conclude that our modified Kalman smoother procedure provides a powerful method for inferring melt rates in a warming world.”

    Comment by AbruptSLR — 3 Nov 2013 @ 5:44 PM

  190. I return to Parizek, and my misgivings increase.

    Consider: ” … spatially variable melt leads to efficient removal of the iceshelf …” in relation to Fig. 7 where they show that spatially variable melt patters remove much more ice than imposing an average melt rate would suggest.

    I think the reason is the following. Melt depends linearly on heat delivered, so we can say
    dM/dt=dQ/Ldt, where dM/dt is mass melted per unit time, L is latent heat, dQ/dt is heat delivered per unit time. But dQ/dt is driven by CDW influx, which increases as meltwater efflux sucks warm CDW in below the freshwater going seaward. dQ/dt can be written as


    Tcdw and tmelt are self explanatory, C is of course specific heat, and v is velocity of CDW influx (equal to melt efflux modulo density differences) and v increases as melt rate increases, v=kdM/dt. So the faster the melt, the more heat is delivered.

    dM/dt = C(Tcdw-Tmelt)k(dM/dt)/L, implying exponential increase in melt rate in local hotspots, the efficiency of spatially variable melt is much larger than a linear average indicates.

    Now, this leads to another remark in Parizek, and the Bertler and Nakayama papers referred to by AbruptSLR. Parizek states

    “We note that recent observations by Jacobs et al. [2011] indicate that in some regions near Pine Island Glacier, the CDW layer has since warmed … ”

    So the heat flux is temporally variable as well as spatially variable. Precisely the same argument I have made above leads to the conclusion that temporally variable melt will be much more efficient at removing ice than once would imagine from a linear temporal average.


    Comment by sidd — 3 Nov 2013 @ 8:28 PM

  191. More support evidence for the point the Sidd makes in post 190 can be found in the following two articles about the PIG:

    T. P. Stanton, W. J. Shaw, M. Truffer, H. F. J. Corr, L. E. Peters, K. L. Riverman, R. Bindschadler, D. M. Holland, S. Anandakrishnan (2013), “Channelized Ice Melting in the Ocean Boundary Layer Beneath Pine Island Glacier, Antarctica”, Science,13 September 2013: Vol. 341 no. 6151 pp. 1236-1239 , DOI: 10.1126/science.1239373.

    Anne M. Le Brocq, Neil Ross, Jennifer A. Griggs, Robert G. Bingham, Hugh F. J. Corr, Fausto Ferraccioli, Adrian Jenkins, Tom A. Jordan, Antony J. Payne, David M. Rippin & Martin J. Siegert, (2013), “Evidence from ice shelves for channelized meltwater flow beneath the Antarctic Ice Sheet”, Nature Geoscience; doi:10.1038/ngeo1977.

    and more generalized information on this matter (with regard to marine terminating glaciers) can be found in the following two references:

    Enderlin, E. M., Howat, I. M., and Vieli, A.: The sensitivity of flowline models of tidewater glaciers to parameter uncertainty, The Cryosphere, 7, 1579-1590, doi:10.5194/tc-7-1579-2013, 2013.

    Callens, D., Matsuoka, K., Steinhage, D., Smith, B., and Pattyn, F.: Transition of flow regime along a marine-terminating outlet glacier in East Antarctica, The Cryosphere Discuss., 7, 4913-4936, doi:10.5194/tcd-7-4913-2013, 2013.

    Comment by AbruptSLR — 4 Nov 2013 @ 7:02 AM

  192. Some readers may not be aware that the West Antarctic Ice Sheet, WAIS, is the last remaining marine ice sheet in the world and thus is particularly sensitive to both volume increases and temperature increases of warm CDW advecting to both the grounding lines and beneath associated ice shelves in this area (particularly for the Thwaites Glacier and associated Amundsen Sea Embayment, ASE, marine terminating glaciers). Indeed, the following reference makes it clear that the flow of warm CDW through the troughs leading into the ASE, continues year round, whether, or not, sea ice, or El Nino events, are extant:

    L. Arneborg, A. K. Wåhlin, G. Björk, B. Liljebladh & A. H. Orsi, (2012), “Persistent inflow of warm water onto the central Amundsen shelf”, Nature Geoscience, Volume: 5, pp 876–880, doi:10.1038/ngeo1644.

    Furthermore, my posts 187 and 188 show this flow of warm CDW increases in El Nino periods, yet most CMIP5 hind-castes of the ABSL (ASL) do not adequately correlate to the ENSO historical record, and thus are likely to under predict ice mass loss from the ASE glaciers during El Nino periods (which may not have been noticed given the present El Nino hiatus, but which by definition also implies that when the current El Nino hiatus period end that the frequency of El Nino events will be more likely on average to the end of the century). Furthermore, my first post referenced the Power et al 2013 (see reference repeated below) that indicates that El Nino events are likely to become more intense with increasing global warming, which was not previously understood in the AR5 process. Thus the AR5 projections of SLR contributions from the marine glaciers in the ASE in particular (and marine terminating glaciers in general) are likely to be too low with regard to the influence of El Nino events.

    Power, S., Delage, F., Chung, C., Kociuba, G. and Keay, K., (2013), “Robust twenty-first-century projections of El Nino and related precipitation variability”, Nature, 502, 541-545, doi:10.1038/nature12580.

    Comment by AbruptSLR — 4 Nov 2013 @ 7:42 AM

  193. Sidd mentioned that CDW advection can increase due to increased saline pump interaction with the ice shelf/glacier, and I have mentioned that: (a) the volume of CDW has been measured to be increasing in the troughs leading to the ASE (possibly due to the measured increase of volume in the Southern Ocean); (b) the CDW flow will increase due to the increase frequency of El Nino events (due to the end of the hiatus period) and in intensity as global warming increases. Furthermore, global warming will (among numerous other things) : (a) increase the temperature of the CDW; (b) increase local storm action (which increases ice mass loss, see Fogt et al 2011); and (c) will increase surface ice melting (and associated water drainage to the basal water). However: (a) the Central West Antarctica is among the most rapidly warming regions on Earth [see: Bromwich, D.H., et al., (2013), “Central West Antarctica among the most rapidly warming regions on Earth”. Nature Geoscience; Vol. 6, p. 139; doi:10.1038/ngeo1671]; and (b) I believe that there is considerable evidence that the RCP radiative forcing scenarios used in the AR5 SLR projections are insufficient to fully characterize the risk of higher global temperatures (than that characterized by the RCP scenarios), for reasons such as the following:

    Schuur and Abbott (see Schuur, E.A.G. and Abbott, B., (2011), “High risk of permafrost thaw”, Nature, 480, 32-33, Dec. 2011.) were the first to identify that the RCP radiative forcing scenarios do not include methane emissions from the expected permafrost degradation (this has been confirmed by the IPCC), which is particularly disturbing for RCP 8.5 scenario (which is projected to induce considerable permafrost degradation this century), and even more so if the Arctic Sea Ice grades sooner than AR5 projects, because methane has a Global Warming Potential (GWP) that is currently at least 25, and more likely 35 (see Shindell et al 2009 and Shindell et al 2013, cited below), times greater than that for carbon dioxide (which is a significant error as for RCP 8.5 methane emissions from permafrost degradation is estimated by Schuur and Abbott (2011) to be approximately 2% of all GHG emitted by the degraded permafrost. Thus both due to ignoring methane emissions from permafrost degradation and due to being calibrated to match lower a GWP for methane than is likely due to methane chemistry in the atmosphere, the IPCC global warming projections and associated SLR projections are mostly likely lower than what will be experienced in the future.

    Shindell, D.T., Faluvegi, G., Koch, D.M., Schmidt, G.A., Unger, N., and Bauer S.E. (2009), “Improved Attribution of Climate Forcing to Emissions”, Science, Vol. 326 no. 5953 pp. 716-718, DOI: 10.1126/science.1174760.

    Shindell, D.T., O. Pechony, A. Voulgarakis, G. Faluvegi, L. Nazarenko, J.-F. Lamarque, K. Bowman, G. Milly, B. Kovari, R. Ruedy, and G. Schmidt, (2013), “Interactive ozone and methane chemistry in GISS-E2 historical and future climate simulations”, Atmos. Chem. Phys., 13, 2653-2689, doi:10.5194/acp-13-2653-2013.

    Comment by AbruptSLR — 4 Nov 2013 @ 10:37 AM

  194. ASLR, there’s a difference between an ore and a metal.
    The difference is called refinement.

    Stefan started this thread with a careful discussion of what’s in the IPCC report, what’s not in it, and what he considers the facts to be and where he and others differ from what’s in the IPCC report.

    You’re just duplicating at great and wordy length some of what’s in other people’s writing, without sorting it out at all.

    Refinement is helpful.
    You could be.
    Please. Make the effort.

    If you’re reading anything anyone here says at all.

    If you aren’t reading the comments, others won’t either.

    I’m done with ya. Carry on.

    Comment by Hank Roberts — 4 Nov 2013 @ 10:38 AM

  195. For those not familar with Fogt’s work (related to ASE weather and the ENSO teleconnection), please review the following references:

    2012 Fogt, R. L., A. J. Wovrosh, R. A. Langen, and I. Simmonds. The Characteristic Variability and Connection to the Underlying Synoptic Activity of the Amundsen-Bellingshausen Seas Low. J. Geophys. Res., 117, doi:10.1029/2011JD017337.

    2011Fogt, R. L., D. H. Bromwich, and K. M. Hines. Erratum to: Understanding the SAM influence on the South Pacific ENSO teleconnection. Climate Dynamics, 37, 2127-2128.

    2011Bromwich, D. H., D. F. Steinhoff, I. Simmonds, K. Keay, and R. L. Fogt. Climatological aspects of cyclogenesis near Adèlie Land Antarctica. Tellus A, 63, 921-938.

    2011Fogt, R.L., (associate editor and author). Antarctica [In “State of the Climate in 2010”]. Bulletin of the American Meteorological Society, 92, S161-S171.

    2011Fogt, R. L., D. H. Bromwich, and K. M. Hines. Understanding the SAM influence on the South Pacific ENSO teleconnection. Climate Dynamics, 36, 1555-1576.

    Comment by AbruptSLR — 4 Nov 2013 @ 10:45 AM

  196. ASLR

    I for one am enjoying your posts, very interesting, take Hanks advice and ‘carry on’

    Comment by Tom Bond — 4 Nov 2013 @ 6:11 PM

  197. ASLR

    I for one, am enjoying your posts, very interesting. As Hank advises ‘carry on’.

    Comment by Tom Bond — 4 Nov 2013 @ 6:15 PM

  198. Just to be a little bit clearer about my meaning, I believe that the references that I have posted provide support to Hansen’s position that a SLR of 2-3 meters by 2100 may be possible under our current BAU scenario.

    Furthermore, I would like to point out that I do not believe that RCP 2.6 is a plausible scenario anymore; yet the IPCC includes this scenario in all of its risk probability distributions; while if it were to be eliminated, the probabilities of greater forcing scenarios occurring would increase proportionally. Also, I believe that the GCMs used in the AR5 findings do not do a good job of projecting the extent of Arctic Sea ice in the future, and I believe that the Arctic Sea extent retreat sufficiently to have a significantly greater positive feedback effect (than considered by the IPCC) due to changes in both albedo and atmospheric humidity (due to reduced sea coverage and increased water temperatures).

    Comment by AbruptSLR — 4 Nov 2013 @ 6:41 PM

  199. I believe that Lempert et al 2012 (see linked reference below) do a relatively good job of quantifying the risk of abrupt sea level rise, ASLR, by statistically expanding previously existing Probability Distribution Functions, PDF, from both extended scenarios of Pfeffer et al 2008 and from CO-CAT 2010 (see figures 7 and 8 of the linked pdf)to include ASLR considerations ignored by the IPCC WG1. The probabilities of SLR this century shown in Figure 8, fully support my (and Hansen’s) position that from 2 to 3 m of SLR is feasible by the end of this century. If nothing else, Pfeffer et al 2008 is a widely cited reference, and statistically extending this work to include the risk of ASLR is a practical approach/methodology that the IPCC could consider adopting in order to provide policy makers with a better idea of how much risk that the public actually faces from SLR:

    Lempert, Robert, Ryan L. Sriver, and Klaus Keller (RAND). 2012. Characterizing Uncertain Sea Level Rise Projections to Support Investment Decisions. California Energy Commission. Publication Number: CEC-500-2012-056.

    Comment by AbruptSLR — 4 Nov 2013 @ 10:53 PM

  200. ASLR: …I do not believe that RCP 2.6 is a plausible scenario anymore…

    You’re not alone. For all the criticism of the IPCC, RCP 2.6 is the actual nugget of science fiction with which critics could take legitimate issue.

    RCP 2.6 is how the emissions path would appear in the years just after the final scenes of “12 Monkeys,” or in the Koch brother’s most fevered nightmares. Not going to happen, the horse is out of the barn, etc.

    I’ll hazard a guess that RCP 2.6 was included only for purposes of illustration of some kind, what might have been if only Al Gore had not been fat.

    Comment by Doug Bostrom — 5 Nov 2013 @ 1:37 AM

  201. ASLR #199,

    I’m trying to understand what Lempert et al 2012 do and do not say. On pp.18-19 I read:
    “Pfeffer et al. (2008) analyze kinematic constraints on the sea level rise contributions from landbased ice and derive lower and upper bounds of 785 and 2008 mm for sea level rise in the year 2100 and a “more plausible” estimate of about 800 mm. We introduce two adjustments to the Pfeffer et al. (2008) results because these previous results neglect uncertainties due to thermosteric sea level rise and the divergence between global mean and local sea level change. The lack of uncertainty assessment of about the thermosteric sea level rise component is addressed by adding an additional rise of -230 to + 200 mm. This uncertainty range is derived from a comparison of observed sea levels and an ensemble of runs from an Earth System Model of Intermediate Complexity, that includes a three-dimensional dynamic ocean general circulation model and samples key parametric uncertainties (Sriver et al. 2012). The local circulation effects are approximated with an additional rise of +/- 300 mm. This range is approximately the range of projected local sea level rise anomalies with respect to the global mean at the end of this century (Meehl et al. 2007). This range is also roughly consistent with the divergence of the simple parabolic fit to the local (PoLA) and global (Jevrejeva et al. 2006) observations extrapolated to the year 2100 (results not shown). These two adjustments yield a modified lower and upper bounds for the annual mean local sea level in 2100 of 255 mm to 2508 mm with a more plausible value of 950 mm (Figure 7).”

    So for global mean SLR by 2100 they take into account a small chance of a maximum of 2208 mm and for local mean SLR they think this maximum is 2508 mm, if I understand their figure 7a correctly. It seems they don’t think 3000 mm of global (or local) mean SLR by 2100 is possible. Or do I miss something?

    Comment by Lennart van der Linde — 5 Nov 2013 @ 4:31 AM

  202. Understandably, some individuals would like to have clear well defined probability density functions, PDFs, for SLR. However, I have previously stated that the current generation of models (Global/Regional/Local Circulation Models, GCMs, RCMs and LCMs) cannot yet adequately characterize the risk of the collapse of marine ice sheets and marine glacier (such as the Thwaites, other ASE glaciers, and indeed all WAIS marine glaciers), sufficiently to discount the risk of the partial collapse of significant portions of the West Antarctic Ice Sheet, with in one hundred years.

    If this were to happen, sea level could rise 2 to 3 meters by 2100; however, I cannot provide definitive proof, only increasing amounts of evidence that points in this direction. In this regard I will continue to provide evidence such as the following links related to the recent identification of an elaborate subglacial hydrologic system beneath the Thwaites Glacier:

    Comment by AbruptSLR — 5 Nov 2013 @ 9:30 AM

  203. Lennart,

    Your are missing that in the first part of Figure 7, Lempert et al 2012 first extend Pfeffer et al 2008’s work (which does not include abrupt ice sheet collapse) to the situation; then in Figure 8 Lempert et al 2012 use statistics to include the risk of abrupt ice sheet collapse.


    Comment by AbruptSLR — 5 Nov 2013 @ 1:29 PM

  204. First, In my response to Lennart, after the word “situation” I had meant to insert the words “for the Port of Los Angeles”.

    Second, I provide the following references of climate sensitivity factors related to: (a) the possible future emissions of Soil Organic Carbon (SOC) into the atmosphere; and (b)reduced sulpher emissions into the atmosphere due to the acidification of the ocean. If both of these feedback factors occur with greater activity than assumed in AR5, then global warming should occur faster than projected:

    Nishina, K., Ito, A., Beerling, D. J., Cadule, P., Ciais, P., Clark, D. B., Falloon, P., Friend, A. D., Kahana, R., Kato, E., Keribin, R., Lucht, W., Lomas, M., Rademacher, T. T., Pavlick, R., Schaphoff, S., Vuichard, N., Warszawaski, L., and Yokohata, T.: Global soil organic carbon stock projection uncertainties relevant to sensitivity of global mean temperature and precipitation changes, Earth Syst. Dynam. Discuss., 4, 1035-1064, doi:10.5194/esdd-4-1035-2013, 2013.

    First signs of carbon sink saturation in European forest biomass; Gert-Jan Nabuurs, Marcus Lindner, Pieter J. Verkerk, Katja Gunia, Paola Deda, Roman Michalak & Giacomo Grassi; Nature Climate Change; Volume: 3, Pp:792–796; (2013); doi:10.1038/nclimate1853.

    Global warming amplified by reduced sulphur fluxes as a result of ocean acidification; Katharina D. Six, Silvia Kloster, Tatiana Ilyina, Stephen D. Archer, Kai Zhang & Ernst Maier-Reimer; Nature Climate Change; (2013); doi:10.1038/nclimate1981.

    Comment by AbruptSLR — 5 Nov 2013 @ 4:52 PM

  205. ASLR,

    Could you clarify for me how to read figure 8 in Lempert et ak 2012? It’s about the probability of a certain rate of ASLR starting in a certain year, but how can we deduce a total global mean SLR by 2100 from that figure, if at all?

    I do see in their table 1 that they seem to assume a (deeply uncertain) possibility of ASLR of 30 mm/yr starting somewhere between 2010 and 2100. So can we infer from this that they assume a possibility of 2700 mm of SLR between 2010 and 2100?

    Or put differently: how do you conclude from their figure 8, or otherwise, that they assume a possibility of 3 m of SLR by 2100?

    Comment by Lennart van der Linde — 5 Nov 2013 @ 6:03 PM

  206. I imagine that only a few readers will be interested in the details of the mechanics of glaciers degrading; however, for those who are, the following references provide new insights into the stability of marine glaciers (as opposed to glaciers on land) and why they may be less stable than previously expected (which increases the risk of ASLR):

    Ice-shelf buttressing and the stability of marine ice sheets G. H. Gudmundsson; The Cryosphere, 7, 647–655, 2013;; doi:10.5194/tc-7-647-2013.

    Pattyn, F., and G. Durand (2013), Why marine ice sheet model predictions may diverge in estimating future sea level rise, Geophys. Res. Lett., 40, doi:10.1002/grl.50824.

    Lampkin, D. J., N. Amador, B. R. Parizek, K. Farness, and K. Jezek (2013), Drainage from water-filled crevasses along the margins of Jakobshavn Isbræ: A potential catalyst for catchment expansion, J. Geophys. Res. Earth Surf., 118, 795–813, doi:10.1002/jgrf.20039.

    Comment by AbruptSLR — 5 Nov 2013 @ 7:02 PM

  207. Lennart,

    The text says the annual mean sea level for time index “t” is zt = a +bt + ct2 +c*I (t-t*) (eq. 4)

    Where the first three terms are the well understood SLR (let’s say here AR5 RCP 8.5 SLR projection at the 83% Confidence Level, CL, ie from ocean water thermal expansion and ice mass loss from small glaciers = 980mm), and the fourth term is the uncertain abrupt SLR (from ice mass loss from ice sheets); where the terms are defined in Table 1 (e.g. the rate of abrupt sea level rise is c*, the year the abrupt rise begin is t*).

    Per Section 3.3: “Note that the condition c* > 14mm/yr + 0.3mm/yr(t*-2010) implies a sea level rise contribution from poorly understood processes of about 1400mm in 2100.” Furthermore, the text says that Figure 8 implies that there is a 14% to 16% probability of this being the case (ie say about a 84% to a 86% Confidence Level, CL).

    Thus combing the AR5 “Well-Characterized Uncertainty” upper end of the “likely” range (ie 83% CL) of 980mm plus the Lempert et al 2012 “Deep Uncertainties” “likely” value of 1400mm gives a “likely mean ASLR value” of 2380mm (2.38m) by 2100. However, many SLR experts believe that the AR5 SLR projects are too scientifically conservative (including NOAA), therefore, I believe that a mean ASLR range of 2 to 3m is reasonable (83% CL) for a BAU case.


    Comment by AbruptSLR — 6 Nov 2013 @ 3:29 AM

  208. ASLR,
    Thanks for the clarification, although I still find Lempert et al pretty hard to follow (probably due to my lack of scientific training).

    I think the AR5 SLR-value of 98 cm does contain some contribution (also dynamical?) from GIS and AIS, judging from figures 13.10 and 13.11 on pp.104-105 of chapter 13:

    Other than that, i agree with your risk assessment approach and think we cannot exclude a risk of 2-3m of SLR by 2100, based on what several experts have said on this.

    Comment by Lennart van der Linde — 6 Nov 2013 @ 7:04 AM

  209. Lennart,

    Your comment about the fact that the AR5 SLR projections already include some SLR contributions from both the GIS and the AIS is very true, and raises the question as to what does “Well-Characterized Uncertainty” mean with regard to SLR contributions. Certainly the base PDFs for “Well-Characterized Uncertainty” SLR that Lampert et all 2012 used (by Pfeffer et al 2008 extended and by CO-CAT 2010) to determine the “Deep Uncertainty” SLR contribution, also included larger contributions from the GIS and the AIS than AR5 assumes. Thus by logical extension you are pointing out that my estimate of ASLR of between 2 to 3m by 2100 might be too low. Furthermore if you believe that the RCP 8.5 scenario is too low (because it does not include all of the methane emission sources, albedo flip, and other positive feedback factors that I mentioned), then it is not difficult to believe that this radiative forcing scenario could be increased by about 33%, which could increase the 95% CL mean global temperature increase from 6oC to 8oC by 2100.
    Thus if you both believe that the RCP forcing scenarios are 33% too low and that it is better to use Rahmstorf, Perrett and Vermeer (2011, see reference below)’s semi-empirical method for determining “Well-Characterized Uncertainty” SLR contributions (which also include contributions from the GIS and the AIS), then by 2100 one gets a 95% CL “Well-Characterized Uncertainty” SLR contribution of about 2.11m, to which the “Deep Uncertainty” contribution would need to be added.

    Rahmstorf, S., Perrett, M., and Vermeer, M. (2011), “Testing the robustness of semi-empirical sea level projections”, Clim Dyn, Springer-Verlag, doi: 10.1007/s00382-011-1226-7.

    Furthermore, if all of the “Deep Uncertainty” SLR contribution comes from the AIS then for example for POLA that contribution would need to by multiplied by about 1.4 to account for the regional fingerprint effect; which would give an abrupt mean RSLR by 2100 for POLA of about 4.2m for a roughly 85% to 95% CL as indicated in my reply #1 at the following link, where I provide a full PDF for RSLR for California for RCP 8.5 (with a modified temperature history), which I developed using a methodology roughly similar to that used for Lempert et al 2012, assuming that most of the “Deep Uncertainty” contribution to ASLR comes from the WAIS with a fingerprint factor of approximately 1.4 (for that portion of the contribution), and that the “Well-Characterized Uncertainty” contributions to SLR by 2100 come from Rahmstorf, Perrett and Vermeer, RRV (with a 33% modified RCP 8.5 scenario):,60.0.html

    Comment by AbruptSLR — 6 Nov 2013 @ 12:28 PM

  210. Obviously, when one discusses SLR values with “Deep Uncertainty” at the 95% Confidence Levels, combined together with an aggressive interpretation of “Well Characterized Uncertainty” SLR contributions (note that the CO-CAT PDF used by Lempert et al 2012, is based on Vermeer & Rahmstorf 2009’s semi-empirical SLR values), then the values become uncomfortably high. Furthermore, such high ASLR (which include “Deep Uncertainty” considerations for all ice sheets, not just the WAIS) values can also significantly increase short-term water levels such as those due to such design factors (see Tebaldi et al 2012, cited below) as: (a) tides; (b) storm surge, (c) storm tide, and (d) regional SLR considerations (such as prevailing winds and other regional affects). Also, in areas of high subsidence (such as many river delta areas), these values also need to be included in infrastructure design values. Thus if such values actually occur (were in my last post were based on statistical, as well as semi-empirical SLR, methodologies, which may not be correct) under a BAU scenario, greater than RCP 8.5; then it is clear that society will need to be exposed to risks at higher levels (lower confidence levels), than society is currently use to operating under. Alternately, ice sheet researchers should be given more research funds in order to dispel concerns that such high ASLR values might actually occur:

    Tebaldi, C., Strauss, B.H., and Zervas, C.E. (2012), “Modelling sea level rise impacts on storm surges along US coasts”, Environ. Res. Lett. 7 (2012) 014032 (11pp), doi:10.1088/1748-9326/7/1/014032.

    Comment by AbruptSLR — 6 Nov 2013 @ 6:22 PM

  211. ASLR,
    Now I see where are getting your numbers. Assuming a temperature rise of 6-8°C would generate higher values. Since these numbers are well above the highest estimates for the next century, it follows that 2-3 m would not be seen for centuries also.

    Comment by Dan H. — 6 Nov 2013 @ 9:01 PM

  212. The following linked reference discusses the nature of Dragon-King events comparable to the high-end projections for ASLR:
    and pdf version with supplemental material:

    Predictability and Suppression of Extreme Events in a Chaotic System
    Hugo L. D. de S. Cavalcante, Marcos Oriá, Didier Sornette, Edward Ott, and Daniel J. Gauthier, Phys. Rev. Lett. 111, 198701 (2013), DOI: 10.1103/Physics.6.120

    Comment by AbruptSLR — 7 Nov 2013 @ 7:57 AM

  213. Dan,
    It is true that unless you look at the high end cases, then the risk of ASLR is negligible. That said society is currently exceeding the RCP 8.5 90% CL scenario, and whether we stay on that path or not is anybody’s guess. Nevertheless, according to the following linked reference following the RCP 8.5 66% CL and 90% CL pathways will result in mean global temperatures of about 6oC and 7.5oC by 2100, respectively. So my assumptions are not terribly unreasonable if society stays on its current BAU pathway:

    Rogelj, J., Meinshausen, M. and Knutti, R., (2012), “Global warming under old and new scenarios using IPCC climate sensitivity range estimates”, Nature Climate Change – Letters, doi: 10.1038/NCLIMATE1385

    Comment by AbruptSLR — 7 Nov 2013 @ 7:13 PM

  214. ASLR #203 (and Lennart #201)

    ASLR, you say that Lempert et al (2012) “first extend Pfeffer et al 2008′s work (which does not include abrupt ice sheet collapse) to the situation; then in Figure 8 Lempert et al 2012 use statistics to include the risk of abrupt ice sheet collapse.”

    However, Lempert et al (2012) do not add any additional component for the risk of abrupt ice sheet collapse, they only add more thermal expansion, based on results from Sriver et al (2012), thus adding ca 20 cm to the upper limit in Pfeffer et al (2008). In addition they also add local effects (ca 30 cm), resulting in the graph in Figure 7.

    Regarding, Pfeffer et al (2008) it can be argued that they include some form of abrupt ice sheet collapse in Antarctica, as they assume accelerated discharges from WAIS.

    It is interesting to note that Pfeffer et al (2008) is often used as some kind of “upper bound” for SLR planning, but strangely enough they only include 30 cm for the thermometric component, while there are much higher figures abound. For example, IPCC (2007) go up to ca 45 cm and Katsman et al (2008) has 48 cm and Sriver et al (2012) 55 cm.

    I have yet to see a real “worst case” scenario for SLR…

    Katsman, C. a., Hazeleger, W., Drijfhout, S. S., Oldenborgh, G. J., & Burgers, G. (2008). Climate scenarios of sea level rise for the northeast Atlantic Ocean: a study including the effects of ocean dynamics and gravity changes induced by ice melt. Climatic Change, 91(3-4), 351–374. doi:10.1007/s10584-008-9442-9
    Sriver, R. L., Urban, N. M., Olson, R., & Keller, K. (2012). Toward a physically plausible upper bound of sea-level rise projections. Climatic Change, 115(3-4), 893–902. doi:10.1007/s10584-012-0610-6

    Comment by perwis — 7 Nov 2013 @ 10:10 PM

  215. “I have yet to see a real “worst case” scenario for SLR”

    1)Eemian (Last InterGlacial) 6-20 m above present
    2)MWP1A, need I say more ?5m/century for a few centuries

    Comment by sidd — 7 Nov 2013 @ 11:38 PM

  216. In my post #213, I mistakenly state that Rogelj et al (2012) give values of 6oC and 7.5oC for the RCP 8.5 66%CL and 90%CL mean global temperature projections by 2100, respectively; when I should have said that Rogelj et al (2012) give values of 6oC and 7.5oC for the RCP 8.5 83%CL and 95%CL mean global temperature projections by 2100, respectively. However, if one were to assume that RCP 2.6 is no longer a valid scenario, then my original post is probably much closer to the truth than Rogelj et al (2012)’s values.

    Perwis (post #214),
    I agree that in their Figure 7, Lempert et al (2012)do not add any additional component for the risk of abrupt ice sheet collapse to Pfeffer et al (2008) values. What I was trying to say is that in Figure 8, Lempert et al (2012) present probabilities for the risk of 1.4m of sea level rise contribution by 2100 due to abrupt ice sheet collapse. Also, while many people would agree with you that Pfeffer et al (2008) “.. include some form of abrupt ice sheet collapse in Antarctica, as they assume accelerated discharge from WAIS”, I would call that accelerated discharge from the WAIS “rapid ice mass loss” and not abrupt ice mass loss associated with “Deep Uncertainty”.

    Comment by AbruptSLR — 8 Nov 2013 @ 3:07 AM

  217. Perwis #14,

    Good points. As I said in reply to ASLR earlier, I don’t really understand figure 8 of Lempert et al 2012, but based on the opinion of several experts I think we cannot exclude a risk of 2-3 meters of SLR by 2100.

    Can we exclude more than 3m by 2100? I don’t know, but even 1.5m by 2100 would imply the risk of about 3-5m of SLR from 2100-2200, and maybe even faster SLR after 2200. So even then 3m of SLR could by passed (well) before 2150.

    Could the rate of SLR become as fast, or faster, as during Meltwater Pulse 1A, when it was probably as high as 4-5 meter/century? And how long could such a speed be sustained?

    John Englander has posed this question to Jim Hansen in his book ‘High Tide on Main Street: Rising Sea Level and the Coming Coastal Crisis’:

    His question to Hansen was (p.100, second edition): ‘Could all the ice melt in a thousand years, or even hundreds, causing 212 feet [65m] or more of sea level rise?’

    Hansen replied: ‘The rapidity of the business as usual human-made climate forcing, burning all the fossil fuels in the next century or two, has no paleoclimate analog. With such a forcing, I would expect the time scale for demise of the great ice sheets would be measured in centuries, not millennia.’

    So in principle, according to Hansen, an average rate of SLR of (at least) 6-8 meter/century could be sustained for centuries to a millennium. For shorter periods up to 1 meter/decade would then seem a possibility.

    Can we exclude such a risk? If not, it seems we should take such a risk into account in discussing options for mitigation and adaptation.

    Comment by Lennart van der Linde — 8 Nov 2013 @ 5:33 AM

  218. Lennart,

    I appreciate that the statistical methodology used by Lempert et al (2012) to estimate the “Deep Uncertainty” risk of equaling, or exceeding, 1.4m of SLR contribution to ASLR by 2100 can be difficult to understand, even though the authors are indeed experts in their fields. Furthermore, I appreciate both that: (a) extending the projection period to 2150 (from 2100) can result in higher confidence levels that the 1.4m of SLR contribution from the ice sheets will be equaled or exceeded; and (b) that looking to paleo-evidence (such as the Meltwater Pulse 1A SLR rise event) is a good alternate to using statistical methodology in order to try to bound the risk of ASLR. Following your lead, I would like to make the following selected points regarding use of the paleo-record to try to bound the risk of ASLR:

    (1) With regard to Hansen’s response that: ‘The rapidity of the business as usual human-made climate forcing, burning all the fossil fuels in the next century or two, has no paleoclimate analog. With such a forcing, I would expect the time scale for demise of the great ice sheets would be measured in centuries, not millennia.’: I would like to point out that:
    (a) our current BAU rate of increase in radiative forcing is about 100 times faster than any time in the past several hundred million years, including the rate during the PETM; and
    (b) during the Eemain peak, and/or the Holsteinian peak, the WAIS likely collapsed abruptly, and that current collapse forcing conditions, equal or exceed those extant during the Holsteinian peak, and/or the Eemain peak.

    (2) The NEEM community members (2013) confirmed that the WAIS contributed close to 3.8m of SLR during the Eemian; which is much more than the 1.4m of ASLR contribution that Lempert et al (2012) address, see: NEEM community members, (2013), Eemian interglacial reconstructed from a Greenland folded ice core, Nature, Volume: 493, Pages: 489–494, doi:10.1038/nature11789.

    (3) In regards to paleo-evidence of stronger positive feedback factors than those currently considered by “Well-Characterized Uncertainty” SLR projections:
    (a)Regarding evidence of strong polar amplification, Brigham-Grette et al 2013 state: “Consequently, the distinctly higher observed [temperature and precipitation] at MIS 11c cannot readily be explained by the local summer orbital forcing or GHG concentrations alone, and suggest that other processes and feedbacks contributed to the extraordinary warmth at this interglacial, and the relatively muted response to the strongest forcing at MIS 5e.” Note that MIS 5e roughly matches the Eemian period. See: Brigham-Grette, J., Melles, M., Minyuk, P., Andreev, A., Tarasov, P., DeConto, R., Koenig, S, Nowaczyk, N., Wennrich, V., Rosen, P., Haltia-Hovi, E., Cook, T., Gebhardt, T., Meyer-Jacob, C., Snyder, J., Herzschuh, U. Pliocene Warmth, Polar Amplification, and Stepped Pleistocene Cooling Recorded in NE Arctic Russia. Science. Online. DOI: 10.1126/science.1233137; and
    (b) I note that today on of the best examples of a strange attractor phenomenon (per Chaos Theory) that is not fully represented in current GCMs is the ENSO; while the following reference by White et al (2002) indicates that there is a positive feedback between the Antarctic Circumpolar Wave and the global El Nino-Southern Oscillation Wave; which provide historical evidence that non-linear atmospheric/oceanic interactions can further amplify the rate of future SLR: White, W. B., S.-C. Chen, R. J. Allan, and R. C. Stone, “Positive feedbacks between the Antarctic Circumpolar Wave and the global El Niño–Southern Oscillation Wave”, J. Geophys. Res., 107(C10), 3165, doi:10.1029/2000JC000581, 2002.

    (4) The WAIS Project Members (2013, see following reference) find that data from the “WAIS Divide Core” hole showed abrupt climate change that occurred in the past on timescales of decades (circa 20,000 years ago), and that these abrupt climate changes accelerated the de-glaciation of the WAIS likely due to interactions between the Southern Ocean and the ice sheet: WAIS Project Members, (2013), Onset of deglacial warming in West Antarctica driven by local orbital forcing, Nature; doi:10.1038/nature12376.

    Comment by AbruptSLR — 8 Nov 2013 @ 12:06 PM

  219. sidd #215

    Sure, but I was thinking of published scenarios that can be taken seriously by planners. Published scenarios are very important, as the examples of Pfeffer et al (2008) or Vermeer and Rahmstorf (2009) shows, being used all over the world. But neither of these really try to assess worst-case scenarios.

    Your examples are also out there, but are less used as pure paleo-analogs are not really true analogs, because of the current forcing is different from previous forcings (Eeemian) or because the ice sheets are different (MWP1A). (A striking difference is the UK:s H++ scenario of 2.5 m SLR by 2100 (see Lowe et al 2009), which is based on Rohling et al (2008) assessment of rapid SLR during the Eeemian high stand from proxies from the Red sea )

    Comment by perwis — 8 Nov 2013 @ 6:21 PM

  220. Lennart #217,

    It is harder to exclude impossible scenarios than to say what is possible.

    The philosopher Gregor Betz has a nice discussion of this, where he says that:

    “Another illustrative case are the sea level rise scenarios as reported in the well known figure of the TAR. These scenarios did not contain the possible contribution from the melting Greenland and Antarctic ice sheets (though the IPCC text mentioned these separately). Is this reconcilable with the scenario approach? Admittedly, the dynamics of the ice caps were – and still are – little understood. Yet taking the above implementation serious, lack of knowledge is not a reason to consider some scenario as impossible. In contrast, independent scientific arguments are needed to do so. Therefore, worst case scenarios of Greenland and Antarctic ice melt should be integrated into the sea level rise scenarios because of our lack of understanding.” (Betz 2007, p 7)

    There is a strong bias in the literature against worst-case scenarios, and this is a very unfortunate situation, which I think will lead to many, many decisions all over the world, based on this biased information.

    Betz, G. (2007). Probabilities in climate policy advice: a critical comment. Climatic Change, 85(1-2), 1–9. doi:10.1007/s10584-007-9313-9

    Comment by perwis — 8 Nov 2013 @ 6:34 PM

  221. Perwis #220:
    Further to your statement: ” There is a strong bias in the literature against worst-case scenarios, and this is a very unfortunate situation, which I think will lead to many, many decisions all over the world, based on this biased information.”, I provide the following additional supporting considerations:
    First, I reference Stein & Geller (2012, see link, citation and abstract below) about the challenges of communicating uncertainties in natural hazard forecasts (including ASLR):

    Stein, S. and R. J.Geller, (2012), “Communicating uncertainties in natural hazard forecasts”, Eos Trans. AGU, 93(38), 361.

    “Natural hazards research seeks to help society develop strategies that appropriately balance risks and mitigation costs in addressing potential imminent threats and possible longer-term hazards. However, because scientists have only limited knowledge of the future, they must also communicate the uncertainties in what they know about the hazards. How to do so has been the subject of extensive recent discussion [Sarewitz et al., 2000; Oreskes, 2000; Pilkey and Pilkey-Jarvis, 2006]. One approach is General Colin Powell’s charge to intelligence officers [Powell, 2012]: “Tell me what you know. Tell me what you don’t know. Then tell me what you think. Always distinguish which is which.” In dealing with natural hazards, the last point can be modified to “which is which and why.” To illustrate this approach, it is helpful to consider some successful and unsuccessful examples [Stein, 2010; Stein et al., 2012].”

    From Stein & Geller (2012), I extract the following key passages:

    “One major challenge is that real uncertainties often turn out to have been underestimated. In many applications, 20%-45% of results are surprises, falling outside the previously assumed 98% confidence limits [Hammitt and Shyakhter, 1999]. …. This effect arise in predicting river floods [Merz, 2012] and earthquake ground motions and may arise for the IPCC uncertainty estimates [Curry, 2011].”
    “The Intergovernmental Panel on Climate Change (IPCC) [2007] report compares the predictions of 18 models for the expected rise in global temperature. … The report further notes that the models “cannot sample the full range of possible warming, in particular, because they do not include uncertainties in the carbon cycle.”

    Finally, I present one simple example of how poor communications can mask some of the actual risk of ASLR:

    The drainage basins determined by researchers around Antarctica are based on the areas that would drain out of a given gateway given the current ice surface gradients. One misconception worth discussing is that most researchers report the potential maximum SLR contribution from each of these basins as if the current ice surface gradients will be maintained into the future; which is not the case. For example it is frequently reported that the maximum SLR contribution from PIG and Thwaites Glacier are approximately: 9″ and 18″, respectively, and also many researchers project that ice mass loss from PIG may slow sufficiently in the next 5 to 10 years to limit the SLR contribution from PIG this century to an inch or two; however, as the Thwaites basin adjoins the PIG basin, should the Thwaites Glacier collapse as I have indicated may be possible; then it is possible that several inches of SLR of ice in the PIG basin could drain through the Thwaites Gateway. Such interactive logistics increase the likelihood that higher levels of SLR will occur by the end of this century; above that commonly thought likely.

    Comment by AbruptSLR — 9 Nov 2013 @ 10:06 AM

  222. perwis #219

    You state:
    “sidd #215
    Sure, but I was thinking of published scenarios that can be taken seriously by planners.”

    First, I would like to say that it appears to me that you (and probably a lot of other readers) are confused by Lempert et al (2012)’s analysis, as first Lempert works for the RAND Corp. and RAND is a very serious consultant to planners such as the Port of Los Angeles, POLA. Therefore, let me try to clarify, how this report does represent an example of what you are asking for, and I will do so using only the Extended Scenarion Pfeffer et al (2008) Beta PDF (which means the “Well-Characterized” SLR contribution corrected for POLA’s conditions) shown in Figure 7 and the probability of equaling or exceeding 1.4m (this value is selected as lower values do not cause POLA to make an investment) of abrupt sea level rise contribution shown in Figure 8 (of that reference for POLA), for a 86% confidence level, CL, case:

    (1) Graphically, the Beta PDF from Figure 7 gives a 86% CL “Well-Characterized” SLR contribution of about 1.8m by 2100.
    (2) Figure 8 gives a 14% probability (or 86% CL) that the “Deep Uncertainty” SLR contribution by 2100 will equal or exceed 1.4m.
    (3) Combining these two 86% CL SLR contribution values (using only extended Pfeffer et al 2008 SLR assumptions, which you note is widely cited by planners), one gets a value of about 3.2m of SLR by 2100, which planners could take seriously if they so decided, if they chose to take responsibility for accepting the methodology used by Lempert et al 2012 to extend Pfeffer et al 2008’s SLR projections.

    Typically, planners only choose to take seriously GCM SLR projections (such as by CMIP5), without making any additional corrections for “Deep Uncertainty” SLR contributions. Also, typically planners choose to ignore high-end SLR estimates using Bayesian approaches such as that given by Hoffman et al (1983, see reference below), which give an estimate of the High-End SLR estimate of 3.68m by 2100:

    Hoffman, J. S., D. Keyes, and J. G. Titus. 1983. Projecting Future Sea Level Rise; Methodology, Estimates to the Year 2100, and Research Needs. Washington D.C.: U.S. Environmental Protection Agency. 121 pp.

    Furthermore, Hoffman et al (1983)’s estimates are included and compared with other early estimates (before planners choose to become limited by GCM SLR projections) in NRC 1987 (see following reference):

    Committee on Engineering Implications of Changes in Relative Mean Sea Level, Marine Board, National Research Council, (1987), Responding to Changes in Sea Level: Engineering Implications, ISBN: 0-309-59575-4, 160 pages, 6 x 9

    The NRC 1987 PDF is available from the National Academies Press at:

    Finally, to put this in prospective I provide the following table of potential maximum SLR contributions from ice melting (to which you would need to add steric SLR contributions):

    Location Potential SLR (m)
    EAIS: 64.80
    WAIS: 8.06
    Ant. Pen.: 0.46
    Greenland: 6.55
    All other ice: 0.45
    Total: 80.32m (263.5ft)

    Comment by AbruptSLR — 9 Nov 2013 @ 2:40 PM

  223. Perwis, ASLR,

    During the last deglaciation increasing insolation in the Northern Hemisphere from about 20.000 years ago caused ice to melt, which lowered albedo and increased temperatures, which released GHG’s and melted more ice, which caused even higher temperatures, and so on, until insolation decreased again at the beginning of the Holocene about 10.000 years ago, which caused warming to stop and cooling to start.

    Roughly we can say that in about 10.000 years the planet warmed about 5 degrees C, CO2-levels rose about 100 ppm and sea level rose about 100 meters. On average temperature rose about 0.05 degrees/century, CO2-levels rose about 1 ppm/century, and sea level rose about 1 meter/century. Over this period lower albedo probably caused about the same radiative forcing as higher CO2/GHG levels.

    Today CO2-levels are almost 100 ppm higher than a century ago, rising at roughly 2 ppm/year, temperature is about 0.7 degrees higher than a century ago, rising at about than 0.15 degrees/decade, and sea level is about 20 cm higher than a century ago, rising at about 3-4 mm/yr. Albedo is decreasing.

    At this moment CO2 seems to be rising about 200 times faster than 10.000-20.000 years ago, temperature seems to be rising about 30 times faster, and sea level seems to be rising three times slower, so far. Albedo is decreasing, but it’s not clear to me how fast compared to this earlier period.

    CO2 rise, temperature rise, sea level rise and albedo decrease are probably all accelerating. The question is: will they accelerate in even proportion to each other, and what are the limits of this acceleration?

    Let’s assume that the current or near future climate forcing is indeed about 100 times as strong as during the last deglaciation. Will temperature and sea level rise then be about 100 times as fast as back then?

    If temperature rises about 5 degrees this century that would indeed be a 100 times faster rise than the 5 degrees rise from roughly 20.000-10.000 years ago. Could sea level then also rise 100 times faster than during this earlier period?

    I’ve not heard anyone suggest 100 meter of SLR would be possible in one century (apart from the fact there’s not enough ice for such a rise). But as quoted in my earlier comment: Jim Hansen thinks that 60-70 meters of SLR is possible, or even likely, in less than a millennium, under BAU forcing.

    That implies he thinks the average rate of SLR over the coming centuries could be up to about 10 times faster than during the last deglaciation, and about double the speed of Meltwater Pulse 1A.

    Does anyone here have reason to believe that Hansen’s estimate is too high, or too low, and if so, why?

    Comment by Lennart van der Linde — 9 Nov 2013 @ 3:15 PM

  224. Lennart,
    To be honest, I have never thought about SLR beyond 2200 before; however, the following linked reference gives an Extended RCP 8.5 95% CL SLR value of about 11m by 2500 using relatively “Well-Characterized Uncertainty” (ie semi-empirical) methodology:

    Sea level projections to AD2500 with a new generation of climate change scenarios
    S. Jevrejeva, J.C. Moore, and A. Grinsted, Global and Planetary Change 80–81 (2012) 14–20.

    Regarding the “Deep Uncertainty” contribution to SLR, I imagine (based on such information as provided in the following links) that if we stay on a BAU pathway that sometime between 2100 and 2300 the Earth’s atmospheric circulation patterns would change to that of an equable climate, where heat from the equatorial regions are transported directly through the atmosphere to the polar regions (which then need not freeze even in winter), and if so then Hansen’s estimated SLR by/before the year 3000 seems reasonable to me:

    Department of Mathematics and Statistics; University of Guelph, Canada; Presented to the BioM&S Symposium on Climate Change and Ecology; University of Guelph; April 28, 2011

    Can Planetary Wave Dynamics Explain Equable Climates?By: Sukyoung Lee, Steven Feldstein, David Pollard, and Tim White; May 3, 2010.

    Persistent near-tropical warmth on the Antarctic continent during the early Eocene epoch, by: Jörg Pross, Lineth Contreras, Peter K. Bijl, David R. Greenwood, Steven M. Bohaty, Stefan Schouten, James A. Bendle, Ursula Röhl, Lisa Tauxe, J. Ian Raine, Claire E. Huck, Tina van de Flierdt, Stewart S. R. Jamieson, Catherine E. Stickley, Bas van de Schootbrugge, Carlota Escutia, Henk Brinkhuis; Nature; 488,73–77 (02 August 2012); doi:10.1038/nature11300.

    The Early Eocene equable climate problem: Can perturbations of climate model parameters identify possible solutions?, by: by Navjit Sagoo, Paul Valdes, Rachel Flecker, and Lauren Gregoire; Royal Society Philosophical Transactions A; 2013.

    Comment by AbruptSLR — 9 Nov 2013 @ 10:27 PM

  225. As far as I understand: Hansen argues that previous transgressions have been paced by the timescale of Milankovitch forcing and not by internal timescale of icesheet response, which could be smaller. As we see today under, geologically speaking, instantaneous, compared to Milankovitch, forcing, the internal icesheet timescale is indeed smaller.

    What it the upper bound on the internal icesheet timescale, how long does it stay around? ANDRILL indicates a millenium or so. That in itself, as Mr. van der Linde points out, is bad enuf.

    What is the lower bound, how fast can it go away ? That answer is worth a great deal of money …
    Hansen says a few hundred years. I tend to believe him, since we see already how fast the icesheets are responding.

    The recent results on sediment cores putatively dated to the PETM, indicating eyeblink fast geological change, is the only paleo example i am aware of that compares to the speed of human forcings. No large icesheet then, of course, too warm already. But there was a great dying then, too.


    Comment by sidd — 10 Nov 2013 @ 12:09 AM

  226. In addition to our “Deep Uncertainties” about ice sheet instability and climate sensitivity, most current SLR projections with “Well-Characterized Uncertainties” rely on the radiative forcing scenarios prescribed by the Recommended Concentration Pathway, RCP, scenarios. Unfortunately,there is considerable “Deep Uncertainty” about the probable future radiative forcing pathway, which are thus not captured by these “Well-Characterized Uncertainty” SLR projections, as partially indicated by the findings of the following two recent reports:

    A bi-annual report by the French Institute of Demographic Studies (INED, released in October 2013) projected that the world’s population will rise to 9.7 billion in 2050 from the current level of 7.1 billion and that India will overtake China as the world’s most populous nation. According to the report, the projected population of other countries in the world by 2050 (in millions) will be: Nigeria (444), US (400), Indonesia (366), Pakistan (363), Brazil (227), Bangladesh (202), Congo (182), Ethiopia (178), Philippines (152), Mexico (150), Russia (132), Tanzania (129), Egypt (126), Uganda (114), Vietnam (109), Iran (99), Japan (97), Kenya (97), Turkey (93), Iraq (83), UK (79), Germany (76), France (72), Sudan(69), Niger(66), South Africa (64), Mozambique (63) and Colombia (63). Due to the lag-time in the trend line for SLR, if all of these 9.7 billion people are not on their personal best behavior in 2050, then it is very likely that the 2100 SLR will exceed that projected for the RCP 8.5 95% CL radiative forcing scenario.

    Unfortunately, the RCP 8.5 scenario does not correctly account for GHG emissions (and thus does not exhibit sufficient radiative forcing) from the likely degradation of the polar permafrost, while the rate and mix of carbon dioxide and methane will be controlled by the moisture content of the thawed soil, according to the following reference (see following link, citation and abstract):

    Long-term CO2 production following permafrost thaw, Bo Elberling, Anders Michelsen, Christina Schädel, Edward A. G. Schuur, Hanne H. Christiansen, Louise Berg, Mikkel P. Tamstorf & Charlotte Sigsgaard, (2013) Nature Climate Change, 3,890–894doi:10.1038/nclimate1955.

    “Thawing permafrost represents a poorly understood feedback mechanism of climate change in the Arctic, but with a potential impact owing to stored carbon being mobilized. We have quantified the long-term loss of carbon ( C ) from thawing permafrost in Northeast Greenland from 1996 to 2008 by combining repeated sediment sampling to assess changes in C stock and >12 years of CO2 production in incubated permafrost samples. Field observations show that the active-layer thickness has increased by >1 cm yr−1 but thawing has not resulted in a detectable decline in C stocks. Laboratory mineralization rates at 5 °C resulted in a C loss between 9 and 75%, depending on drainage, highlighting the potential of fast mobilization of permafrost C under aerobic conditions, but also that C at near-saturated conditions may remain largely immobilized over decades. This is confirmed by a three-pool C dynamics model that projects a potential C loss between 13 and 77% for 50 years of incubation at 5 °C.”

    Comment by AbruptSLR — 10 Nov 2013 @ 5:41 AM

  227. To follow-up on Sidd’s point that we now know (and we continue to learn) a lot more about how fast marine glacier can loss ice mass that contributes to SLR, I provide a few specific examples of recent research that illustrates just how fast that ice mass loss can occur:

    The first reference by Fudge et al 2013 (see abstract below) indicates that the measured basal ice melt rate beneath the Thwaites drainage basin is at least three times faster than researchers had previously imagined (which both results in direct ice mass loss by drainage and also faster ice calving due to a reduction in basal friction due to the lubricating effect of basal water):

    “High Basal Melt at the WAIS-Divide ice-core site, by T.J. Fudge, Gary Clow, Howard Conway, Kurt Cuffey, Michelle Koutnik, Tom Neumann, Kendrick Taylor, and Ed Waddington, 2013:

    We use the depth-age relationship and borehole temperature profile from the WAIS-Divide ice core site to determine the basal melt rate and corresponding geothermal flux. The drilling of the WAIS-Divide ice core has been completed to 3400 m depth, about 60 m above the bed. The age of the deepest ice is 62 ka, younger than anticipated, with relatively thick annual layers of ~1 cm. The borehole temperature profile shows a large temperature gradient in the deep ice. We infer a basal melt rate of 1.5 (±0.5) cm yr-1 using a 1-D ice flow model constrained by these data sets.
    The melt rate implies a geothermal flux of ~230 mW m-2, three times the measured value of 70mW m-2 at Siple Dome. We compile radio-echo sounding data sets to assess the spatial extent of high melt. Deep internal layers are the most useful for inferring spatial patterns of basal melt. Unfortunately, the IceBridge WAIS-core flight and two site-selection surveys did not image consistent reflectors deeper than Old Faithful (2420 m and 17.8 ka). A ground-based survey by CReSIS (Laird et al., 2010) was able to image consistent layers as deep as 3000 m, but the survey is not oriented along the ice-flow direction making interpretation more difficult. There is no obvious draw down of deep internal layers that would indicate an area of localized melt. While this suggests a uniform melt rate within the survey, it might also indicate that other factors (e.g. accumulation gradients, rough bed topography) obscure the influence of basal melt on the internal layer depths.”

    For other publications related to the WAIS-Divide ice core project, see the following links:

    The following article indicates how surface water drainage from water-filled crevasses along the margin of the Jakobshaven glacier could result in the dynamic acceleration of ice mass loss from this marine glacier, and which indicates that the Thwaites glacier (and all other marine glaciers) will likely be subject to the same ice mass loss mechanism in the future:

    Lampkin, D. J., N. Amador, B. R. Parizek, K. Farness, and K. Jezek (2013), Drainage from water-filled crevasses along the margins of Jakobshavn Isbræ: A potential catalyst for catchment expansion, J. Geophys. Res. Earth Surf., 118, 795–813, doi:10.1002/jgrf.20039.

    “Saturated crevasses occur in local depressions within the shear margins of Jakobshavn Isbræ at inflections in the ice stream’s flow direction. Spatio-temporal variability of seven distinctive saturated crevasse groups was examined during the 2007 melt season. The area of saturated crevasses reached its maximum extent, ~1.8 km2, in early July, and remained largely constant until early August. Filling rates are correlated with regional melt production, while drainage rates are highly correlated with areal extent. Estimates on potential drainage volume from the largest crevasse system are ~9.23 × 10−3 km3 ± 2.15 × 10−8 km3 and ~ 4.92 × 10−2 km3 ± 3.58 × 10−8 km3, respectively, over a 16 day interval and are more than required for a distributed basal hydrologic system across this area to temporarily flood bedrock obstacles believed to control basal sliding. Future drainage events, likely extending farther inland with warming, could result in enhanced lateral mass discharge into the ice stream, with implications for the dynamic evolution of the entire basin.”

    Lastly for this post, the linked reference has a free pdf, and I agree with Drouet et al that:

    “Despite the recent important improvements of marine ice-sheet models in their ability to compute steady state configurations, our results question the capacity of these models to compute short-term reliable sea-level rise projections.”

    Drouet, A. S., Docquier, D., Durand, G., Hindmarsh, R., Pattyn, F., Gagliardini, O., and Zwinger, T.: Grounding line transient response in marine ice sheet models, The Cryosphere, 7, 395-406, doi:10.5194/tc-7-395-2013, 2013.

    “Abstract. Marine ice-sheet stability is mostly controlled by the dynamics of the grounding line, i.e. the junction between the grounded ice sheet and the floating ice shelf. Grounding line migration has been investigated within the framework of MISMIP (Marine Ice Sheet Model Intercomparison Project), which mainly aimed at investigating steady state solutions. Here we focus on transient behaviour, executing short-term simulations (200 yr) of a steady ice sheet perturbed by the release of the buttressing restraint exerted by the ice shelf on the grounded ice upstream. The transient grounding line behaviour of four different flowline ice-sheet models has been compared. The models differ in the physics implemented (full Stokes and shallow shelf approximation), the numerical approach, as well as the grounding line treatment. Their overall response to the loss of buttressing is found to be broadly consistent in terms of grounding line position, rate of surface elevation change and surface velocity. However, still small differences appear for these latter variables, and they can lead to large discrepancies (> 100%) observed in terms of ice sheet contribution to sea level when cumulated over time. Despite the recent important improvements of marine ice-sheet models in their ability to compute steady state configurations, our results question the capacity of these models to compute short-term reliable sea-level rise projections.”

    Comment by AbruptSLR — 10 Nov 2013 @ 12:32 PM

  228. I recall posting a question on this board a few years ago asking whether the collapse of the Larsen B ice shelf came as a surprise to the experts. The responses indicated that the Larsen B event took the experts by surprise.

    Little hope perhaps that the concept of abrupt SLR may be viewed with the importance it deserves, because a consensus-driven agreement process would never admit to such processes.

    The concept is, in my view, very important because we have created nuclear infrastructure and systems at current sea level at coastlines whose life times are comparable to the timescales of SLR-induced impact. We have already witnessed ocean-mediated impact on one installation (Fukishima) and that is already stretching industrial capability to maintain semblances of safety in the Asia-Pacific and other regions.

    The topic of abrupt SLR goes to the heart of energy policy for a safe planet.

    Comment by Michael — 10 Nov 2013 @ 2:16 PM

  229. As a follow-up to my post about Drouet et al 2013’s Marine Ice Sheet Model Intercomparison Project’s finding that even for a relatively simple perturbation as the removal of buttressing support of an ice shelf on an adjoining marine glacier (for example consider the case of the SW Tributary marine glacier discussed by MacGregor et al 2013, cited in my post #172, where the next major calving of the PIIS could accelerate the ice flow velocities of the SE Tributary glacier to the point of destabilizing the eastern shear margin of the Thwaites Glacier), currently cannot be modeled, over the short-term, to within a discrepancy of 100% between different current marine glacier models. To this simple example presented by Drouet et al (2013), I would like to note that there are very many other ways to destabilize ASE sector marine glaciers (including the Thwaites, and Pine Island, Glaciers), including (but not limited to):

    (1) Increased advection of increasingly warmer CDW (causing accelerated grounding line retreat) due to such factors as: (i) increased El Nino frequency and intensity both with increasing global warming and the coming end of the current El Nino hiatus period; (ii) increased local upwelling and increased volume of CDW (circumpolar deep water) both due to increasing global warming; and (iii) increased saline pumping action due to increasing volume of ice mass loss.

    (2) Increasing formation of shear zone crevasses near the calving front of the marine glaciers [see Lampkin et al (2013) in my previous post], which may, or may not, fill with surface melt water depending on weather conditions (note that surface ice melt does current occur in the coastal region of the ASE during the peak of some austral summers, and that as the WAIS has one of the fastest rates of surface warming on Earth, it is safe to assume that the frequency of surface melting in this area will increase at a non-linear rate through the end of this century); which will clearly accelerate the rate of calving in these marine glaciers.

    (3) The basal friction in the Thwaites Glacier gateway region is believed to be one of the key factors currently limiting the further acceleration of ice mass loss from Thwaites Glacier; however, as: (i) the distribution of basal friction in the Thwaites Glacier gateway is not well known, this factor believed to limit ice flow acceleration may not be as effective in the future as is currently believed to be the case; (ii) as the ice in the gateway progressively thins it will eventually float over the top of the regions of relatively high basal friction, so eventually this limitation will be removed; and (iii) as the ice flow velocity increases the associated increase in basal melt water (due to increased melting of the glacial ice by internal and basal friction) will serve to lubricate and warm the basal ice thus reducing the ability of the basal friction to restrain further ice acceleration.

    (4) There is a prominent trough located on the western side of the Thwaites gateway (adjoining the Thwaites Ice Tongue, see following Tinto & Bell 2011 reference) that can serve to guide warm CDW directly into the heart of the gateway, once the ice in the trough has thinned sufficiently to maintain a subglacial cavity/void in the trough, which could then accelerate grounding line retreat in this area in a 2D (as opposed to the current 1D) manner. Tinto, K. J. and R. E. Bell (2011), “Progressive unpinning of Thwaites Glacier from newly identified offshore ridge – constraints from aerogravity”, Geophys. Res. Lett., doi:10.1029/2011GL049026.

    (5) Future changes in local coastal wind and associated local ocean current patterns due to global warming, could acceleration the advection of warm CDW into the ASE, thus inducing accelerated groundling line retreat for the affected marine glaciers.

    (6) Increases in tides/storm surge/storm tide and in local/regional SLR in the ASE due to accelerated ice mass loss from Greenland; should accelerate calving of the fronts of the ASE marine glaciers.

    (7) Parallel effect to Thwaites to the Jakobshavn Effect (see Habermann et al 2013, Walter et al 2012, and Van De Veen et al 2011) as soon as the Thwaites groundling line retreats to the lip of the Byrd Subglacial Basin, BSB. (i) Changing basal conditions during the speed-up of Jakobshavn Isbræ, Greenland, M. Habermann, M. Truffer, and D. Maxwell, The Cryosphere Discuss., 7, 2153–2190, 2013,, doi:10.5194/tcd-7-2153-2013; (ii) Oceanic mechanical forcing of a marine-terminating Greenland glacier, Jacob I. WALTER, Jason E. BOX, Slawek TULACZYK, Emily E. BRODSKY, Ian M. HOWAT, Yushin AHN, and Abel BROWN; Annals of Glaciology 53(60) 2012 doi: 10.3189/2012AoG60A083; (iii) Van Der Veen, C. J., Plummer, J., and Stearns, L.: Controls on the recent speed-up of Jakobshavn Isbræ, West Greenland, J. Glaciol., 57, 770–782, 2011. 2155, d o i : 10.3189/002214311797409776.

    Comment by AbruptSLR — 10 Nov 2013 @ 5:37 PM

  230. Would another factor in the acceleration in the break down of the West Antarctic Ice Sheet be simply the ongoing rise in sea level from other sources. Then the rise in sea level from the West Antarctic ice shelf itself will accelerate its own break down.

    Comment by William Hughes-Games — 10 Nov 2013 @ 6:26 PM

  231. You mention that the rise in sea level could threaten island nations. This presumably is referring to coral atoll islands. While sea warming and acidification could certainly destroy atolls by killing corals, is it not true that sea level rise by itself is unlikely to do so and in this respect, the health of the coral atolls, short of warming or acidification, is in the hands of the local inhabitants.

    Comment by William Hughes-Games — 10 Nov 2013 @ 6:34 PM

  232. AbruptSLR #222:

    I am sorry, but I think it is you that are confused by the Lempert et al (2012) study.

    This is how I understand their methodology:

    1. They create a model (p 7) of future annual mean sea level z(t)=a+bt+ct^2+c*(t-t*), where the term a is the sea level anomaly at time zero (2011), b is a constant rate (mm/year), and c is an acceleration term (mm/year2), c* is the rate of abrupt sea level rise and t* is the year abrupt rise begins.

    The first three terms represent “the effects of relatively well-understood processes, such as thermal expansion of the oceans due to rising temperatures and the melting of small glaciers” (p 7), while the fourth term “represents currently poorly understood and poorly constrained processes; for example, potentially abrupt changes in the dynamics of ice flow (e.g., Alley et al. 2007), which is approximate with a step- function increase in the rate of sea level rise c* (mm/year) that occurs after some time t*.” (p 7)

    2. They construct two “extended scenarios” of local SLR in year 2100 (one is based on Pfeffer et al 2008 and one is based on CO-CAT 2010). These are represented as probability density functions in Figure 7. (The reason the extended scenario that is based on Pfeffer et al 2008 is ca 500 mm higher than Pfeffer et al 2008 is that they introduce uncertainty in the thermosteric component of -230 to +200 mm (Pfeffer has no uncertainty in that) and uncertainty from local circulations effects of -300 to +300 mm. They say that the resulting scenarios “range is also roughly consistent with the divergence of the simple parabolic fit to the local (PoLA) and global (Jevrejeva et al. 2006) observations extrapolated to the year 2100 (results not shown).” (p 19).

    3. They make a “rejection sampling approach to approximate or emulate the resulting expert assessment for the projected sea level rise in the year 2100” (p 19). I am not sure how they do this exactly (elsewhere they talk about a “quasi-random Latin Hypercube sample” p 23).

    Anyhow, the end result is a ” joint distributions for c* and t*” (Figure 7 right pane) as well as a “a joint distribution for the parameters a, b, and c, which is largely uncorrelated with that for c* and t*, and thus consistent with that used in Section 3.1.1.” (note on page 19).

    4. We get an indication of what the results of c* and t* are by looking at Figure 8, which I take show all the different variations of the c* and t* parameters that are consistent with the two extended scenarios. The colored lines show the decision-relevant conditions they are interested in.

    We don’t know what the other parameters (a,b,c) are, only that combinations of the parameters c* and t* on the red line means that the (a,b,c,) parameters are consistent with Section 3.1.1 and that this means “roughly 500 mm contribution from well-understood processes” (p 17) and ca 1400 mm of abrupt SLR by 2100 (coming from combinations of c* and t* at the red line).

    To conclude: if I am correct in my interpretation of their paper, they do not derive a scenario of 3.2 m GMSLR by 2100, as AbruptSLR says above. Instead they assume the two “extended scenarios” for local SLR shown in Figure 7 (suggesting a global mean SLR of 2.2 m and 1.7 m respectively), which they then use to deduce the policy-relevant parameters for abrupt sea level change (c* and t*).

    Comment by perwis — 10 Nov 2013 @ 11:35 PM

  233. #231–A more sensible link than I expected, but I don’t think that we can assume the conclusion is correct. There is a severe potential issue with rate of change.

    It’s also a good example of the probable synergy between climate change impacts and other anthropogenic ones.

    Comment by Kevin McKinney — 11 Nov 2013 @ 9:08 AM

  234. William #230,

    Due to the gravitational “fingerprint” effect, when the WAIS loses ice mass, the local sea level drops; however, currently the GIS is losing ice mass faster than the AIS so the sea level around Antartica is currently neither going up or down (but this will likely change in the future).

    perwis #232,

    I have e-mailed one of the co-authors of the POLA SLR study, to see whether he is willing to resolve the correct intrepretation of their study.

    Comment by AbruptSLR — 11 Nov 2013 @ 8:52 PM

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