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On straw men and Greenland: Tad Pfeffer Responds

Filed under: — eric @ 18 September 2008

In a recent post about sea level rise, we highlighted a paper by the University of Colorado’s Tad Pfeffer and others in which they show that one can rule out more than 2 meters of sea level rise in the next century. While we liked the paper very much, we also complained that Pfeffer and colleagues had created a bit of a straw man, by implying that it had been seriously proposed that Greenland’s near term contribution to sea level rise could be much larger than that. In fact (we said), none of us in the climate science community ever took such ideas seriously, even if the popular press thought we did. Tad responds by pointing out that in fact there is published work attributing considerable likelihood to such extreme scenarios, and that there are numerous studies that at the very least strong imply it. He also reminded me that their paper actually rules out a contribution of more than about 50 cm from Greenland, significantly below some other recent published estimates. That makes their work even more important, since there are several publications that definitely consider upwards of one meter (from Greenland alone) by 2100 to be plausible. Pfeffer et al. conclude that that is simply not the case (at least in their informed view). Still, we remind readers that our chief complaint was that Pfeffer et al.’s work was taken by many in the media as a downward revision to sea level rise estimates, whereas in fact most informed estimates had put an upper limit well below that. See our earlier post on the IPCC Sea Level numbers.

In any case. Pfeffer et al’.s response to our post follows below. Fair enough.

A response to RealClimate’s post on our paper about sea level rise

W.T. Pfeffer, J.T. Harper, and S. O’Neel
15 September 2008

We have read with interest – and, we admit, surprise – the RealClimate post concerning our 5 September publication in Science entitled “Kinematic Constraints on 21st Century Sea Level Rise.” The source of our surprise, however, is probably not what the RealClimate authors imagine – we had fully expected a vigorous defense of very high rates of sea level rise (greater than 2 m/century), but not a denial that such rates had ever been hypothesized.

We do not state anywhere in our paper that 2m or more of SLR by 2100 has been published as a peer reviewed and “informed estimate”. We do state that this has been ‘inferred’ and ‘argued’ as a “viable 21st century scenario”. We believe there is value in constraining the upper limits to the role of ice dynamics in future SLR. And, from what we know about historical rates of SLR in conjunction with what ‘we know we don’t know’ about ice dynamics, we believe it is reasonable to ponder very high rates of SLR in the next century. However, we also believe that it is problematic to project such a ‘hypothesis’ as a supported theory without proper testing by the scientific method. The question raised by RC is whether or not this hypothesis has circulated within the scientific community.

In his 2007 paper (Environ. Res. Lett. 2(2007)) Hansen proposes a rate of sea level rise of “5 m this century.” This is hypothetical, but he is confident that it is a “far better estimate than a linear response”. This is accompanied by his statement that he finds it “almost inconceivable that BAU climate change would not yield a sea level change of the order of meters on the century timescale.” The provisional nature of his discussion is irrelevant; it is an explicit statement that 5 m of sea level rise in this century is a possibility he regards as viable, published in the scientific literature by the person who is arguably (and deservedly) the most visible and authoritative climate scientist in the world. No reader of this paper would assume that Hansen didn’t actually mean what he said. Hansen reinforced this idea in other publications and statements, including in his briefing to Congress on 23 June 2008 (“sea level rise of at least two meters is likely this century”). Our analysis specifically tested the likelihood of next-century sea level rise of more than 2 m, and Hansen explicitly hypothesized 5 m of sea level rise in this century.

Hansen has gone on record with specific numbers, but other published studies including the 2006 Overpeck and Otto-Bliesner Science papers left the upper limit open ended, and certainly implied it could be quite high. The fact that this idea was present in the scientific community was confirmed for us by 8 scientific presentations we gave on this topic in the past year (5 in the US, including the Fall 2007 AGU and 3 in Europe). At none of those talks did anyone in the audience question what high forecasts we were referring to. The comments we got back on our work were overwhelmingly positive, and were along the lines that what we had presented was a good next step – both to move past the IPCC’s low sea level forecasts, and as a response to the persistent hypotheses of very high rates of sea level rise that were circulating. Criticisms, where they were voiced, were largely that we were underestimating the power of dynamics and that rates of sea level rise well in excess of 2 m/century might occur in spite of our conclusions.

We agree that the media coverage of our paper (as well as others before it) has undesirable side effects. Wherever we had the opportunity we pressed media writers not to use terms like “exaggerated” or “high sea level forecasts debunked,” and we have consistently stressed that our results indicate a very significant sea level rise and are no justification for any kind of complacency. We have stressed that even our low end scenario of 0.8 m of SLR would have tremendous consequences. However, we stand by our statements that sea level rise at rates of substantially more than 2 m this century were in fact put forward as a likely possibility.

Earlier this summer Andy Revkin published a piece in the New York Times about what he has termed the “Whiplash Effect”: confusion created in the public mind by media coverage of rapidly evolving scientific ideas. There has certainly been some whiplash in this case. However it is others who cracked the whip. We have simply refused to let go of the other end.

126 Responses to “On straw men and Greenland: Tad Pfeffer Responds”

  1. 1
    gavin says:

    Tad et al, thanks for commenting. There are a number of issues here, and so I think it’s best to start off with what we can probably all agree on. First, the more informed estimates of sea level rise become, the better off we will be, and so your assessment of some of the kinematic constraints is certainly a welcome addition to the literature. Second, as you clearly state, these numbers are significantly in excess of the ‘headline’ numbers that came out of the IPCC report. As you are also aware, IPCC punted on what the worst case scenario could be given non-linear dynamic ice feedbacks. Thus, it is clear to me that your constraints are a significant up-grading of possibilities in the future (and hence our surprise at the thrust of your press release and some of the coverage).

    However, scientists, like nature, abhor a vacuum. In the absence of any trustworthy glaciological constraints on the rates of future SLR, it is only natural that scientists will turn to the paleo-record and to heuristic attempts to get an idea of what is possible. It is clear that the paleo-record shows greater than meter/century rises during the deglaciation (MWP 1A), or even in the Holocene (Carlson et al, 2008). Therefore these possibilities cannot be neglected a priori. It is also clear that conditions during the last interglacial (LIG, 125 kya BP) that temperature changes were close to what is anticipated by the end of the century. At that time, equilibrium sea level rise was between 4 and 6 meters higher than at present (with maybe 2 or 3 meters coming from Greenland). Thus for climate conditions that are not too far away from the situation now, multi-meter sea level rise is certainly an eventual possibility (the rates of change at the LIG having not been constrained). And indeed, a simple heuristic calculation such as done by Hansen in the ERL paper easily gives numbers in the range of meters.

    These pieces of evidence show that discussion and further investigation of the possibilities of multi-meter sea level rise should be continued and cannot be ruled out a priori. However, stating that something is conceivable is not the same as making a prediction. The Overpeck and Otto-Bliesner papers made no prediction (or even projection) for SLR by 2100, and your implication that they were somehow negligent in not doing so is a little strange. Their study of equilibrium change cannot provide such a constraint and so you seem to be taking them to task for simply not assuming that SLR can be rapid. I would point out as well that their study’s conclusions that maybe 2 to 3 meters of sea level rise at LIG equilibrium came from Greenland (maybe even a little less taking the Wilerslev et al results into account) rather undermine the claim in your paper that people (unnamed) have predicted 2 and 5 meter rises from Greenland alone in the next century. I can find no evidence of this anywhere in the literature. I note you confuse global and Greenland-alone in your text above.

    Your main criticism seems to be reserved for Jim Hansen. Despite the fact he is my boss, he is certainly not immune from criticism on that score. However, you are, I think, wrong in this case and have misread him. The ERL paper that you provide as the only example of a specific 5m/century prediction, is curiously enough a discussion about how difficult it is for some in the glaciological community to publicly express their concerns about the state of the ice sheets and the implications (something I have also noticed). The ‘prediction’ you refer to is a simple doubling calculation to demonstrate that non-linear responses could produce multi-meter/century SLR in theory. And since we know that has happened in the past, that can’t actually be wrong. It was a calculation that had no information from the ice sheets, or the climate forcing or anything, therefore I think I am quite right in not describing it as an “informed estimate”. Jim has made his actually worst case scenarios abundantly clear in many interviews, in the Washington Post for instance: “sea level rise that can be measured by feet more than inches”, and in the ERL papers itself “measured in meters”, and in the quote you picked up on. It is not picking nits to point out that all of these statements are basically consistent with the 2m upper bound you came up with.

    Eric has made the point that perhaps you were reacting not to actually predictions, but to perceptions among the public, maybe engendered by misleading headlines. That there have been misleading headlines is clear, but I cannot find any related to Hansen’s ERL paper. Media misconceptions should of course be countered and true explanations given, but I see no evidence that the media on the whole has got this story wrong. If anything, the bulk of the coverage (which followed the IPCC report) was way too conservative, and commentators like Bjorn Lomborg get much more press with claims that sea level rise will be less than 10 inches by 2100, than anyone with claims that it will be 20 ft.

    To conclude, my main emotion here is disappointment. The issue of sea level rise, and the impact that may have in future seem to me to be one the key implications of climate change for which there are no winners and for which the costs may be enormous. It therefore deserves to be discussed and investigated much more widely than it has been (and as I said, your paper is a useful addition, though I doubt it will be the last word). That educational process is surely larger and more important than crticising a single paragraph in a relatively obscure publication that got no media attention. Had your press release been more accurately titled as “Global Sea-Rise Levels By 2100 May Be Lower Than One Person Hypothesised But Much Larger Than What Was Reported Following The Publication Of The IPCC Report And If This Happens It Will Be Really Bad News” you would have done the community a much better service.

  2. 2
    David B. Benson says:

    Tad & Eric — Thank you for tkaing the time to write this.

    I, too, find 80 cm this century quite, quite alarming.

  3. 3
    Dave Rado says:

    Eric’s intro is very hard to read – could it be made larger? I realise the aim was to differentiate it from what follows, but maybe italics or blue text or some such method would work better.


  4. 4
    David B. Benson says:

    Dave Rado (2) — Your browser should have a ‘Text Size’ option.

  5. 5
    RichardC says:

    James Hansen’s 5 metres is a good quote, but what about the other James?

    I think the trajectory of estimated future change is more crucial than the estimate itself. We’ve gone from estimates of “negligible” to “metres” from ice melt in only a few years, and I’m not convinced that Lovelock is wrong when he says, “Modelers don’t have the foggiest idea about the dynamics of melting ice sheets,”

    Tell me what’s wrong with this logic: The only thing keeping Greenland frozen is the ring of mountains surrounding the ice sheet, which keeps lower, warmer air from reaching the ice except at small breaks in the mountains. Looking at the glacier retreats posted on this site, the ice has already retreated as far as it can without tremendous increases in area exposed to warm sea level air, and there is no second line of defence. The mountains also provide structural support. The ice at and below sea level will be weak, and the slope of the ice wall will be nearly vertical, a perfect recipe for the repeated shearing of ice off the face of the sheet.

    IIRC, the limit on mass loss was attributed to the narrowness of passes in the mountains, but if the ice loss is behind the mountains as the ocean reaches beyond them, and mixes salt into the system with tides, then only the flushing of salt and icebergs via meltwater would limit the rate of melt in the (brand new) Greenland Sea. Did you assume the Arctic Ocean would be ice-free in summer beginning in 2020? 2040? Has the 2008 melt season changed your analysis? (sorta directing this query at both RealClimate and Pfeffer et al) Once an ocean current develops which links any two of the current glacial outlets in southern Greenland, wouldn’t catastrophic collapse be imminent? I find it difficult to imagine the GIS surviving 92 more years.

  6. 6
    Dave Rado says:

    Hi David – I know, but it’s inconvenient to have to enlarge the text size just in order to read the intro and then reduce it again in order to read the rest. Just my opinion.


    [Response: We've made it a bit more readable now. --eric]

  7. 7
    Figen Mekik says:

    Dave Rado,

    Scroll up while holding the control key down. It makes the text bigger.

  8. 8
    eric says:

    For the record, I don’t entirely agree with Gavin on this. Pfeffer et al. were not merely responding to public opinion, but also the way that the fate of Greenland was being discussed seriously among the glaciology community. I was delighted to see Tad’s paper come out because there has been a lot of irresponsible buzz in the scientific community about this, and nipping it in the bud is helpful. If we make predictions — or statements that are viewed as predictions by the public — and it then becomes obvious that they won’t be borne out, then science loses credibility and we all lose. It is all about improving the science, and it really doesn’t matter where the inspiration for making improvements comes from.
    [As readers will note, we are not always in 100% agreement at RealClimate. That's fine. Self criticism is usually productive.]

  9. 9
    Nigel Williams says:

    As a lay observer of this discussion I find comfort in the fact that Tad, Eric, Gavin and James will all be found to be correct at some moment in the not too far distant future. So lets not stress too much about divergence of perception of perceptions and instead lets keep the political will rolling to get the science done ASAP.

    Behind peak oil and impacts of climate change on habitation and food supply, sea level rise will be the final wet blanket that will sweep inexorably over the inhabitants of the old Holocene. We need the best information of when and where so we can make the best plans we can for the expenditure of remaining resources.

    So lets stop squabbling in the back there – and get on with your homework!

  10. 10
    Ike Solem says:

    I suppose it all boils down to how long it takes to reach equilibrium? So this argument about sea level rise is an argument about the transient response.

    Climate models have underestimated rates of Arctic response to warming, which is worth thinking about, and the current rate of increase of atmospheric CO2 is some 30X that seen in the ice core record, which means that historical comparisons might not be too useful.

    Given that uncertainty, I’d far rather see scientists produce 50-year limits, 100-yr limits, 150-yr limits, 250-yr limits – those are the kinds of predictions that would be interesting, as they would give you an idea of how fast the approach to equilibrium might be.

    However, I just looked at the press release for the paper, and it is surprising that it doesn’t reference IPCC predictions at all, but rather refers to “some scientists.” Straw man seems about right.

    For a useful example of what a well-balanced press release on a glacial melt topic looks like (hydrofracturing and meltwater lubrication), see Woods Hole:


    The most intriguing result is that meltwater is not the reason for the acceleration of the outlet glaciers (it appears to play a main role in the broader flatter regions).

    No big dramatic attention-grabbing headline, though, meaning not a whole lot of press coverage – a few one-paragraph blurbs on FOX and NPR, is all I could find (People’s Daily China was interested, though) – so WHOI and UW need a better PR team, I guess? Ouch.

    However, before we cast too many aspersions, take a look at some more balanced coverage by Scientific American:

    … Nor is it clear whether something might suddenly occur to change that upper estimate. “If those two big ice shelves [in Antarctica] go out, then it’s an entirely different situation,” Pfeffer says. “But there’s no good evidence that that’s going to happen over the next century.”

    Hmmmm… what kind of evidence would be needed to address that question? Ocean temperatures around Antarctica – and that’s unknown. Ice depth trends around Antarctica? Also unknown.

    Doesn’t really look like too much has been ruled out, after all.

  11. 11
    Ike Solem says:

    As long as were talking about the cryosphere, many (if not most) of the world’s mountain glaciers will be gone in 100 years:

    From 1850 to 1970, the team estimates net losses averaged about 30cm a year; between 1970 to 2000 they rose to 60-90cm a year; and since 2000 the average has been more than one metre a year. Last year the total net loss was the biggest ever, 1.3m, and only one glacier became larger. Worldwide, the vast majority of the planet’s 160,000 glaciers are receding, ‘at least’ as much as this, says Haeberli, probably more – a claim supported by evidence from around the world…

    …Based on the forecast increase in global temperatures this century, the UNEP report warned of ‘deglaciation of large parts of many mountain regions in the coming decades’. Perhaps most shockingly, it predicted two-thirds of China’s glaciers would disappear by 2050, and ‘almost all would be gone by 2100.

    I generally get science press releases from sciencedaily… did these recent ones get much press coverage? (pyrenees glaciers melting, gone)

    Picked up here and there, but not blasted out over the wire like the UBoulder press release was. “Glaciers melting faster than expected”

    Now, the press coverage there was really interesting. A complete blackout in the U.S. with the notable exception of Andy Revkin at the NYT, and lots of coverage in the international press.

    Andy Revkin just won one of journalism’s more prestigious awards – I recommend sending him a congratulations/thank you note.

    I do find that a little revealing, though – why does one story get prominent wire coverage, and another gets ignored? Well, that’s easy – media bias in favor of fossil fuel interests, due to the fact that the same major shareholders in fossil fuels are also the major shareholders in media corporations?

    Must be a conspiracy theory. Never mind.

    P.S., journalists:
    Here’s a fresh one on Greenland’s glaciers, 9-18-2008:

    How does that relate to Pfeffer et. al?

    [Response: We'll take a look at that paper. I see one of the co-authors every week, but wasn't aware of this paper. That tells you have busy we all are. And busy-ness (information overload) probably explains a lot of the variance in science journalism too. It is more lack of time and resources than conspiracy, I think.--eric]

  12. 12
    John Monro says:

    Interesting, to this layperson, there seems to be a bit of scientific rivalry here.

    I think the IPCC should revisit its estimates of possible sea level rise now, not waiting for a future report, and instead of backing away from making at least a good estimate of possible sea level rises due to glacial or ice sheet melt. No-one’s going to be shot if they get it wrong, but by completly ignoring such ice melting, they are leaving a huge vacuum of understanding in the public at large, and and room it would seem for contention in the scientific community. It is not an adequate response for the IPCC to say the matter is too hard, that’s their job, they just need to do the best they can. After all, of all the likely effects of climate change, sea level rise could well be the most serious, we need more guidance. All information, from Hansen to Pfeffer, needs to be considered.

    [Response: A fair point. IPCC AR5 will certainly consider all the latest stuff. But meanwhile it's up to individuals and groups to publish there results, so IPCC has something to work with. As to scientific rivalry, I would say that we're all in agreement on the science. The rivalry here is more about how one presents the science on does. It's more philosophical and there is no way to prove who is right. Gavin's basic point is "let's stick with the science itself", and I by no means disagree. I'm sure Tad doesn't either. The problem is, not everyone is playing by that rule, so it is easier said that done. -eric]

  13. 13
    RichardC says:

    If a duplicate, please remove… captcha issues.

    Eric says: If we make predictions — or statements that are viewed as predictions by the public — and it then becomes obvious that they won’t be borne out, then science loses credibility and we all lose.

    I say the timidity which results from such a stance is a disservice to the public. So what if you are wrong? As my ancestor in the Revolutionary War said, “Give them Watts, boys,” when as a preacher he tore up Watts hymnals to use as rags for musket loading. Say what you feel and proudly evolve your opinion as you learn. “I was wrong” is the statement that gathers the most respect and science can’t lose credibility unless it is unwilling to tear up hymnals. Science lost credibility with the craven exclusion of ice melt from sea level rise estimates. “It” gave in to pressure from Bush’s administration when it should have held firm. Twas an obvious failure known ahead of the fact and wrong cuts both ways as the evolution of knowledge and data in the climate field is astoundingly fast and transparent. So much so that science has no precedent to work with. The traditional conservative scientific hymnal of “wait until the data is irrefutable” is wrong in this case. You’re on the front lines and billions of lives are at stake. Seize the day.

    [Response: I don't disagree with you here, actually. The difference is between saying "this could happen" and "this will happen". It may appear that Pfeffer and co. were responding to a "this could happen" from Jim Hansen. But I think they were responding to a strong "this will happen" sentiment that they heard among scientists. The real question is whether it is appropriate to have squabbles among scientists in the pages of Science. This is certainly part of Gavin's concern. The problem is that scientists are humans just like everyone else, and we tend to listen more when we the paper is in Science then when it is in the Journal of Glaciology. We all complain about people who think this way, but we all think this way.--eric]

  14. 14
    paulm says:

    This article is interesting.

    evidenced in Jamaica and elsewhere by physical coastal features stranded inland, such as wave-cut notches and elevated coral reefs. Interestingly, there are similar features at about the two-metre mark above present-daysea level.

    We are definitely going to get around a 2m rise at some point in the near future! (May be it might come 101 years time)

    Does it give us a good indication of where levels will stabilize as different ice sheet melt. This is probably due to the climate settling in a particular state with respect to temperature.

    There is lots of evidence out there which suggests that rapid mluti-meter SLR does occur:
    High rates of sea-level rise during the last interglacial period

    This is the scary one from down under….
    Coral reef clue to fast sea rise

    Remember many individuals were saying that the arctic sea ice was suppose to be melting in 80+yrs time. Now it looks like its going to melt in the next 5yrs! Seems to me we should include past information more in the models that we do.

    I think Hansen is probably more on track the these guys.

  15. 15
    John Mashey says:

    Actually, this seems like business-as-usual for science at the edge of what we know.

    But, in communicating to the public, I’d claim that:

    1) First, one has to start getting gvoernments to start baking *any* amount of sea-level rise into their planning processes, i.e., start recognizing that there’s an issue.

    2) Then, we can argue whether it’s 1m, 2m, 5m in 2100. I suspect science will have a lot better idea *way* earlier than most coastal governments will have even started to think about the issues seriously. [For example, I'm curious to see what Galveston does.]

    A few months ago, I attended a San Francisco Bay Area local government meeting onpreparing for Sea-Level Rise. (Web page moved since last time I posted).This was a competent and professional meeting, with a lot of people actually starting to think about what might need to be done for 50-100 years off. It is *not* easy for local governments to think that way.; Experiencing planning scenarios at that meeting hints there will be some very tense politics over things like locations of dikes… and of course, neighboring towns need to cooperate.

    I’d be interested in comparing. Can people point at other local planning efforts, especially on Gulf Coast/East Coast?

    I ask because I’m not sure the SF Bay Area is necessarily a representative l sample…

  16. 16
    CobblyWorlds says:

    #12 John Monro. Re the IPCC:

    As far as I’m aware IPCC AR5 is due around 2013. In terms of the Arctic situation I don’t think reporting much earlier than that may be worthwhile. Even by 2010 we’ll only have 2 years on top of 2007/2008 and with the time needed for an organisation as big as IPCC to produce a report would push things on to 2011/2012. So it may not be much earlier than 2013 anyway. In terms of the future evolution of climate change: So much now depends on the what happens in the Arctic and whilst there remains uncertainty as to what is next in terms of the sea ice there is a consequent uncertainty in it’s secondary impacts.

    Thank you for taking the time to respond, and do keep hold of your end of the whip. Bounding possible outcomes is vital work.

  17. 17
    Lawrence Coleman says:

    Very interesting discussion! The fact also that CO2 is now more than double what it was in the holocene and you can safely state that all bets are off.

    [Response: No it isn't. Current CO2 levels are around 36% higher than the Holocene. They are however twice what they were in the last ice age. - gavin]

    It is definately a non linear scenario as we are talking about mulitple +ve feedbacks in play so a compounding graph will fit the model better. It’s not just ice albedo and a warming ocean , it’s methane hydrates beginning to come on board as we speak, melting tundra, increasing forest depletion, coal power stations in china..etc..etc. all busy amplifying the situation. You couldn’t predict the speed of the current rapid ice melt of the arctic latitudes by going through paeliological records of the past 650k years – we are in uncharted waters!!
    Can anyone please clarify this or give me better understanding.. Solar maximums are regular, I believe they could be initiated by gravitational pull of the massive planets on the sun’s outer membrane – (we are currently nearing the end of one of those). This heightened solar radiation somehow for reasons I’m not sure increases the amount of Co2 in the atmosphere and this in turn forces temp. Unfortunately for us the solar max coincided with our growing obsession with fossil fuels and burgeoning population explosion. So the current level of CO2 is natural but with anthroponenic amplification. Could someone please explain why more solar radiation would cause a rise in CO2?? I’m not clear on this.

    [Response: You are indeed very confused. No, the current CO2 level is not "natural". Read this please. --eric]

  18. 18
    Lennart says:

    A very good and relevant discussion so far, for me as a layman. I’m wondering what James Hansen thinks of the Pfeffer-paper (aren’t we all?). My basic question remains: have Pfeffer e.a. taken all possible ice loss and climate feedback mechanisms into account? If not, what would or could be the most important ones they’ve neglected so far? Maybe Pfeffer or others could expand some more on that?

    As for the media coverage, there’s no need for conspiracy theories, since the explanation by Herman and Chomsky of the political economy of the mass media (‘Manufacturing Consent’) seems to me very relevant in media coverage of climate change, peakoil and SLR. Being naive about that does climate scientists no good, I think. For info about Herman’s and Chomsky’s work see for example:

    And for more info about their so-called Propaganda Model see:

  19. 19
    GlenFergus says:

    Pfeffer et al implicitly assume that for Greenland to contribute to SLR, ice must discharge to the ocean through bedrock gateways, which necessarily constrain the rate. I wonder why the alternative – in situ melt – is excluded?

    My model is the collapse of the piedmont lobe of the San Quintín Glacier in Patagonia. This is the largest piedmont lobe in the southern hemisphere (view from sea level), and it has all but vanished in the last two decades. No ice discharged to anywhere. The thing basically just stewed in its own juices, in one very wet process. Ok, it’s nothing at all like the GIS, but is this kind of process completely excludable?

    [Response: They include an estimate of Greenland surface mass loss (a max of 7 cm by 2100). But they don't explore that uncertainty for their headline numbers. SMB is quite uncertain, and earlier in their paper they hypothesise a 10x increase in SMB by 2100 (which I assume implies a ~5 times increase in accumulated SLR from this over the century assuming linear growth), which might be an extra uncertainty of another 35 cm maybe. However I might have got this wrong since I don't understand why in their first calculation the 10x SMB test only appears to add a factor of 2.7 to the accumulated SLR - their Table 1. If that is due to the time-change in SMB (ie the growth is very slow and only increases towards the end), then it might be a another 12 cm. - gavin]

  20. 20
    Ricki says:

    I must support John Monro in calling for more frequent IPCC reports. However, due to the process they have to go through it would be better to set up a formal up-dating process where modifications could be made to predictions on a monthly basis.

    This would have to be based on a lesser degree of certainty as there would be less signoff by the participants. We need something like this from the scientific community URGENTLY as we are rapidly running out of time. This would be a critical loot to galvanise governments and communities to change what they are doing.

  21. 21

    RichardC #5:

    The only thing keeping Greenland frozen is the ring of mountains surrounding the ice sheet, which keeps lower, warmer air from reaching the ice except at small breaks in the mountains.

    Actually no. What keeps Greenland frozen is its low temperature :-) and huge heat capacity… it’s a huge mass of stuff. Consider how a continental ice sheet it built up and maintained: snow falls on top — i.e., a couple km above sea level, where it is pretty cold — and is slowly compressed to ice. It keeps its low temperature, at which ice is pretty tough. Then it slowly “creeps” downward and outward.

    It’s only around the edges and at the face of the bedrock due to geothermal heat, that the ice is warmer and softer, and may melt easily.

  22. 22
    dagobert says:

    Don’t we all tend to believe in and quote science with at least some influence by our greater believes? So Tad Pfeffer et al put kind of an upper limit to Greenland’s SLR contribution for this century and apparently nobody can see anything wrong with the sience as such. There may have been some problems with who they seem or claim to respond to in the first place and of course there’s the usual “told you so” from people who claimed they knew all along – but apart from that, this is just science at work and the results are no reason for anybody to feel relieved. But there are still those, who all of a sudden claim, that Pfeffer is wrong because his findings don’t fit their believes. I don’t think the claim, that there have been stronger SLR in the paleo-record prove Pfeffer any more wrong than claims of vineyards in northern England around 1000ad put Mann wrong. All it proves is that denialism (of science) aparently works both ways. For my personal use, limited as it is, I’ll stick to Pfeffer’s numbers until somebody comes along and finds a serious flaw in his work or discovers something truely new.

  23. 23
    pete best says:

    Surely the issue relates to the science of “non linear response”. After all if the ice was being lost in a linear fashion to a known temperature rise then it would have been in the IPCC AR4 report but it would have been deemed scientific (?) rather than currently unknown with any known certainty.

    Modern mathematical science is 300 years old (Principia Mathematica in 1672)and it is mainly linear in nature. the non linear has only recently with the advent of powerful computers started recieving proper scientific scrutiny but it is unclear to me that the science of the past 300 years is as useful because the non linear response to forcings etc is messy and not as predcitable it would be fair to say and therefore not scienttifically rigourus enough and hence we end up with known unknowns of being unable to predict future behaviour of such things as ice sheets.

    Surely the IPCC and others at GISS can come up with based on the based available observational evidence and paretial difference equations and paleo climatic data a bloody good guess as to what response ice sheets will have to a known temperature rise come BAU to overall CO2 levels of 450 to 550 ppmv come the centurys end.

    Otherwise the speculation will continue.

    [Response: Well, of course this is what Pfeffer et al have done, essentially. That's why it is the last word on this subject, at least for the moment. --eric ]

  24. 24
    Dill Weed says:

    This is my favorite site for level-headed, informed discussion of climate change. It seems you have slipped into intramural, academic squabbling over something that is not really substantial (outside of ego). I like it better when you are debunking deniers and thumping obfuscators while at the same time explaining the science! So it’s with fondness and appreciation that I say, “Get back to work!” (Whip crack).

    Allow me to suggest some new fodder:

    and of interest an article Abrupt Climate Change Focus Of U.S. National Laboratories at

  25. 25
    Charlie says:

    Sea level rise has already taken its toll on many people, especially those that live on small islands where drinking water and crops are being poisened by salt. These people have nowhere to go.
    As such a number of small islands have got together to petition the UN Security Council to take climate change as seriously as it does wars. Please help them. The earlier we start tackling this, the more that can be saved later.

  26. 26
    Ray Ladbury says:

    Here I think it is useful to look at the difference between scientific and engineering “predictions”. Science looks to predict SLR with as much accuracy as possible subject to the constraints of evidence. Here as with CO2 sensitivity, most of the uncertainty is on the high-side of the best guess, but we are mainly concerned with the best estimate.
    Engineering has to take into account the uncertainty–they need to know for “design” or mitigation purposes how bad things could get. Hansen’s guestimate is more along these lines. When the engineering estimate is not acceptable, we need to sharpen our pencils and see if we can come up with a better estimate that still bounds reality. Tad’s paper straddles the line between a sharpened engineering estimate and a scientific estimate. Things could still be worse, but it’s a better “best guess”.

    [Response: Precisely. That's my take on it as well.--eric]

  27. 27
    stephan harrison says:

    Re GlenFergus (19). I worked on the San Quintin glacier in 1992 and 1993 and published on it in 1996 and 2000. In 1993 the terminus was advancing (I walked from grass-covered moraines onto the ice surface) but all the water from the snout was flowing back up-glacier. The reason why the snout broke up is probably because the terminus is surrounded by high LIA moraines and has probably produced a fore-bulge. This meant that the water ponded under the terminus, initiating calving. It will probably now calve continuously until the terminusr recedes a couple of km. The glacier to the north (San Rafael) also has well-developed morianes systems and it, too, was once a piedmont lobe but now has a calving front.

    I’m not sure you can use the San Quintin as an analogy for the Greenland Ice Sheet.

  28. 28
    Food Tube says:

    Why is so little attention is being paid to the effects c02 on the oceans in terms ph? Is this problem real and proven? Could lower ph really cause a collapse of the marine ecosystem? If so I’m confused as to why SLR, warming on land, etc. are stealing the show. Could RC post some info on this issue?

  29. 29
    Timo Hämeranta says:

    It’s interesting and educational to see what the IPCC AR4 lead authors really think:

    Environmental Research Web September 17, 2008

    “The IPCC report: what the lead authors really think

    …Serious inadequacies in climate change prediction that are of real concern:

    …Energy budget is really worrisome; we should have had 20 years of ERBE [Earth Radiation Budget Experiment] type data by now- this would have told us about cloud feedback and climate sensitivity. I’m worried that we’ll never have a reliable long-term measurement. This combined with accurate ocean heat uptake data would really help constrain the big-picture climate change outcome, and then we can work on the details…

    Climate change research topics identified for immediate action:

    • Thorough understanding of the physics and dynamics of the Greenland and Antarctic ice sheets, with a view to predicting sea level rise within 20% for a specified change in climate over the ice sheets….”

  30. 30
    CobblyWorlds says:

    #28 Food Tube,

    From RC:
    Ocean Acidification. From Science Daily as linked to in this previous RC article: Acidifying Oceans Add Urgency To Carbon Dioxide Cuts. When there are new developments you can be sure RC will report, but there’s little point going over the same ground. David Archer’s field is the carbon cycle.

  31. 31
    Jerry Steffens says:

    Rather than simply focusing on how much sea level rise will occur by the year 2100, we should be concerned with how much sea level rise will be INEVITABLE by the end of the century if current emission trends continue. Is it really that much better that our great-great grandchildren will be submerged rather than our grandchildren?

    [Response: Of course, this is the crux isn't it? We'll do a post in the near future that emphasizes this point.]


  32. 32
    Dave Rado says:

    Hi Food Tube

    I believe the problem is that the RC contributors are environmental physicists, whereas the post you are looking for would have to be written by an ocean biologist – although maybe someone like Jim McCarthy could be persuaded to do a guest post?


  33. 33
    Ike Solem says:

    It seems that the scientists are doing their best to get accurate papers published, but are not paying too much attention to how the press is handling those papers. This is normal; scientists mostly want their working peers to read and review their work (peer review), both for practical reasons (funding decisions are also made via peer review) and as a means of communication.

    It would be nice if there were a lot more science journalists at major newspapers who covered the material, but due to cutbacks and lack of time they can’t cover everything, as noted.

    However, there is a means by which some press releases are promoted by industry groups. As an example, the American Petroleum Institute began a $100 million promotional campaign over a year ago. They hired Edelman PR services to design and manage the campaign. ( )

    Part of any such campaign is an effort by public relations (propaganda, it used to be called) firms to promote press releases that serve their agenda and to suppress press releases that damage their agenda. That’s just how PR works. If it is a “well-managed” propaganda campaign, the sponsoring firm will also employ media watchers to see what kind of press coverage they are getting.

    Similarly, Chevron ran a huge “Power of Human Energy” campaign, as well as a “Will You Join Us” campaign that won a PR award for number of positive press mentions – that’s how success is measured in the PR world.

    How does a global PR firm get positive stories into the press? Well, they have their own people scanning any press releases that might come out, and ones they like get sent out directly to reporters. The PR firm tries to generate “buzz” about some press releases, get them out to the wire services, and from there onto the front pages of newspapers and magazines.

    I suppose that many people don’t know how the industry (PR) operates, but that really is the basic program. These tactics are widely used in the pharmaceutical industry as well. It’s not conspiracy, as it is not at all illegal – it is just marketing.

    That’s what a $100 million PR campaign buys – favorable press coverage for your agenda.

    With congressional Dems looking to take on the oil industry next year, the industry’s lead trade group, the American Petroleum Institute, is planning a $100 million PR “image and education effort,” National Journal reports.

    The campaign, “much of which will be coordinated by the PR firm Edelman, will include expensive television, radio, and print ads, tours of oil patch facilities for lawmakers and opinion elites, and financial contributions to sympathetic think tanks and industry-friendly organizations.” The API is asking other like-minded groups to ante up for the multiyear effort.

    Whether or not the press release put out by the University of Boulder was slanted for similar reasons? I have no idea, but it was certainly slanted.

    However, Scientific American (David Biello) had a very balanced article on the paper in question:

    The bottom line: sea levels will rise much more than predicted by the IPCC, based on both present understanding of current glacial melt as well as evidence from the geologic record. “The IPCC noted that their estimates should be seen as minimum estimates,” Carlson notes, “and they are right.”

    What people don’t like is how the science can be spun in one direction or another to serve the interests of various different parties. It’s like politicians who make a big fuss about climate change and renewable energy around election time, and then do nothing about it – until the next election cycle, when they make more speeches.

    What would be truly worrisome is if scientists started behaving like that – twisting and spinning their research to meet the approval of whatever Trofim Lysenko-like figure is holding the purse strings, as was the case in Stalin-era Soviet universities. It’s a very slipperly slope, and we might be closer to that than we’d like to think, in my opinion.

  34. 34
    Guy says:

    I’ll chime in with Dill (#24) on getting a response to – and how it equates to the current discussion. I guess I’m still struggling to understand why MWP 1A-type speed can be safely discounted in the next 100 years, especially since (as many posters have pointed out) a sea-ice free summer is now forecast between 5-30 years, not 80+ as only a few years ago.

    And again, I’ll make this my 8th attempt in 10 days (and counting) to get an RC response to James Hansen’s maximum safe level of 350ppm CO2 to avoid a runaway SLR scenario… at whatever the rate of rise! I do appreciate the workload of you contributors, but this seems such a critical issue that is met with silence.

    [Response: We discussed it a while back. - gavin]

  35. 35

    I’m not as concerned with WHEN the sea will rise up really high, as with the idea that I’m perhaps contributing to that eventual rise.

    As for upper constraints, I figured out when I saw WATERWORLD back in 1995 that there wasn’t enough ice in the cryosphere to raise the seas THAT much (I had no idea what the max could be, but figured that even yo-yos who fell asleep during 8th grade science would know it couldn’t be that much).

    So I figure the upper limit if all ice on earth melts has got to be something much less than that. But as to when, that’s not as important as “I’ve got to do all I can today to help ensure it doesn’t rise very much” or cause drought and death, or the many many other harms.

    In fact, I had not considered sea rise as threatening as many other harms, but on an earlier post, someone made me aware that even a 1 or 2 foot sea rise could do a great deal of harm.

  36. 36
    Mr Henderson says:

    Proofreading: there seems to be an error in the first sentence of RC’s introduction here. ’2 meters of sea level rise in the next century’ should be ’2 meters of sea level rise by the next century’, shouldn’t it? It’s the period up to 2100 that’s the main focus.

  37. 37
    RichardC says:

    21 Martin: thanks for the comment. I’ll rephrase. The mountains surrounding the GIS provide a tremendous amount of insulation and they also prevent moving water (think Gulf Stream) from transporting the GIS to warmer locales. Without the mountains, the ice would crack and be transported by water to the tropics, where it would surely melt. The mountains can only perform these two functions if the ice sheet does not retreat and no two gaps in the mountains link up. Once the first linkage if formed, currents will flush through, instead of the current system of flowing outward only. That first linkage will be the start of a quickly expanding Greenland Sea, where the ice dynamics will closely resemble those of the current Arctic Ocean — except that it will be at a lower latitude and higher temperatures. GIS will die quickly. It’s too far below sea level and too far south to survive unless it is large enough to hug its ring of mountains. The current glaciers are becoming tooth-decay which will expand exponentially until two areas of decay link and a Route Canal forms. Then the ice-enamel will be drilled off by saltwater currents almost as quickly as a trip to the dentist.

    23 – Pete, the problem is the confusion between “forcing” and “feedback.” Since we’re in the fossil fuel era, we think of CO2 as a forcing, but CO2 is primarily a feedback. We short-circuited the ‘normal’ system, which is increase in temp (caused by whatever) melts permafrost/clathrates, releasing CH4 which becomes CO2.. etc..) So here, and everywhere else, a totally false picture is drawn, that if mankind stopped spewing CO2, CO2 levels would stabilize. That’s garbage. CO2 feedbacks guarantee that CO2 will rise for centuries after mankind stops spewing. (assuming mankind doesn’t actively take CO2 out of the atmosphere or take other mitigating steps) The skeptic sites say CO2 peaks 800 years after a temperature increase. Even if they are off by a factor of two, that’s 400 years of increased CO2. Currently the permafrosts in Alaska are a degree or two away from melting. In winter, permafrost is insulated by snow – cooling the permafrost is a dry system. In summer, water percolates down, a wet system. Thus, summertime temperatures are the primary driver for permafrost thaw. Combine the two – a significant summertime increase in temps guaranteed by loss of Arctic Ocean ice, and the current closeness to thawing of permafrost, and large-scale methane release is almost guaranteed. It’s not just non-linear, it’s durn near one-off. We need to stop pretending that CO2 is primarily a climate forcing. What happens if you double CO2? Well, you triple or quadruple CO2 (or more), and the skeptics will crow that they were right all along. See? Mankind’s paltry CO2 addition was insignificant compared to the natural increase!

    Eric, you said it well. Point is, when “this could happen” is so friggin scary, people freak. Scientists have traditionally held themselves to a Mr Spock stand-offishness. One never admits that anything in science is of any personal interest. My kids could all die. “Interesting.” Most species could be wiped out. “Fascinating.” It’s ironic that Al Gore got the robot label. In a way, skeptics’ stereotypical Gore insult is the model/goal of scientists. But Gore and scientists are human after all. (And Mr Spock was more than half human – Vulcans were more human than humans – they deliberately subdued their far more emotional nature as a matter of survival!)

    Take heart in this: no matter what, those who desire to impede the progress of knowledge because they already know the answer will be able to dredge up plenty of quotes and repeat them with far more money than you will ever see. There is no risk, because the worst case political result is already guaranteed. Ask Mugwumps. Hmm, if those who take out garbage can be sanitation engineers, then those who spew garbage can be humour scientists. Of course, “One of the best” would know the difference between “funny” and “laughable”– oops, did I say that…Damn the torpedoes and all that.

  38. 38
    Patrick Henry says:

    Difficult to see where 80cm comes from.

    The slope would have to break immediately upwards by at least 3X, reversing recent trends in the opposite direction.

  39. 39
    David B. Benson says:

    Guy (34) — This link

    provides a graphic of recent Antarctica temperature changes per decade. Note that both the Ross and the Ronnie ice shelves have not changed temperature, except right at the margin. So WAIS is well-buttressed and IMO nothing much is going to change for at least 50 years. Even when it does, it doesn’t seem possible, to me, to be able to provide enough ice fast enough to raise sea levels by 5 meters in 400 years. (But the new research program you linked is supposed to end up by saying something from definite.)

    Patrick Henry (38) — From the complete melting of all continental glaciers, leaving only the Antarctic and Greenland icee sheets, the Patagonian ice fields, and maybe some of the ice caps in Nunavut, Canada. That’s in addition to the continuing Greenland ice sheet and Antarctic Penninsula melting.

  40. 40
    Thomas says:

    I have a question about the potential albedo feedback effect on a ablating ice sheet surface. I suspect the albedo change due to dry snow becoming wet, and the difference between wet snow, and wet clean ice is probably fairly well known. My concern is how clean an ablating ice sheet surface will remain after it has been ablating for several decades. How much dark colored material, derived either snow the ablated ice, or directly deposited by the wind may further degrade the albedo. If this turns out to be a large effect, and it is ignored, could it cause a significant underestimate of the surface melt contribution to SLR?

    [Response: This is of course an important thing to take into account, and this is done in the calculations people make. It is not entirely trivial of course, and the answer is quite sensitive to how the calculation is done. There is a nice paper on this here --eric]

  41. 41
    sidd says:

    Re: antarctic/ Ross shelf stability

    paper about the Whillans Ice stream into the Ross ice shelf.
    Wiens et al., Nature Letters, v435, p770 (2008)

    i quote:
    “During each slip event, the ice plain of the WIS [Whillans Ice Stream] (which is greater than 200Km x 100 Km in area and approximately 600m thick) moves by up to 70 cm in approximately 25 min.”

  42. 42
    Timo Hämeranta says:

    When you discuss possible sea level rise, it’s only fair to refer to the prevailing uncertainties e.g. in water cycle, whether sea levels will rise or FALL.

    The general view about WAIS and Greenland ice sheet is that melting will cancel snow accumulation.

    But, perhaps the Max Plank Institute ECHAM4 model turns out to have been the correct one:

    “More heat – more snow accumulation – sea level falls”.

    Ref: Wild, Martin, and Atsumu and Ohmura, 2000. Change in mass balance of polar ice sheets and sea level from high-resolution GCM simulations of greenhouse warming. Annals of Glaciology 30: 197-203.

    Please see also:

    Kukla, George and Joyce Gavin, 2005. Did Glacials Start with Global Warming? Quaternary Science Reviews Vol. 24, No 14-15, pp. 1547-1557, August 2005

    Perhaps we simply have not seen warming enough for sea level fall.

    Everything is possible, but what is probable?

    Nobody knows for sure.

    [Response: If everything is possible, why do you always get to exactly the same conclusion? Try surprising us sometime. - gavin]

    [Response: And take a look at this post on snowfall and temperature --eric]

  43. 43
    Guy says:

    Inline #34 – Gavin, on my previous postings in the thread (which you may have missed) I explained how I saw your referenced article as not dealing with the most critical question raised by the Hansen paper as I see it – I actually asked the same question then in #18. What is the RC contributor’s response to the specific 350ppm target? I found your response then very helpful, right up to the conclusion… whereupon I will admit I was bewelidered to read that you “don’t tend to get hung up on a precise target”. Surely a maximum safe level with a reasonable probability of safety in avoiding critical tipping points is not unreasonable, and indeed vital for policymakers?

    This was the focus of Hansen’s paper – his calculated figure is a maximum of 350ppm. However, in your Target CO2 article, the figure (and focus of that paper) was never even discussed. I do find this odd, and seems to be crucial gap needing to be filled. While Hansen tours the world, talking to governments and appearing in courts all based around this target figure, I have no sense from RC what the wider view of this figure is from climate scientists.

    I’m trying to get an initiative together in the UK, and plainly we need a target! Asking politicians to just get emissions down is practically meaningless. I have lost confidence in 450ppm, and this is largely based on Hansen (and others work). If I need a target, I’m pretty sure that the wider world does too as negotiations continue before Copenhagen (this UK Financial Times report on the current negotiation progress is typically sobering –,dwp_uuid=0701221a-83f9-11dd-bf00-000077b07658.html).

    I would be so so grateful if you could post at some length about the 350ppm target. I appreciate a target is always subject to revision, but at the moment much of the negotiations are based on 450ppm – and from my reading, that might well be completely useless. I can’t think of a more pressing issue that the world faces, to be honest, if Copenhagen is working towards a target that is incompatible with the conclusions of the climate science commmunity.

  44. 44
    GlenFergus says:

    #27 San Quintín:

    Thanks Stephan, interesting. So the terminal lake growing behind the moraine was a key factor in the retreat/collapse. I know the scale and conditions are completely different, but I wonder what would happen if a large terminal (or, rather, marginal) lake were to develop somewhere beside the GIS. Surface melt on the ice sheet is constrained by the albedo, but a lake is dark and could absorb much more solar radiation. Maybe it could attact the ice margin from below, a bit like you describe.

    Pfeffer et al is really a negative study. It says, “This is the worst we can get, maximising all the mechanisms we can think of.” It only works if they’ve thought of all the possibilities.

  45. 45

    RichardC posts:

    The skeptic sites say CO2 peaks 800 years after a temperature increase. Even if they are off by a factor of two, that’s 400 years of increased CO2.

    That’s for a natural deglaciation when the carbon dioxide is coming primarily out of the ocean. That’s not what’s happening now. Stopping human fossil fuel burning is the quickest way to stabilize carbon dioxide.

  46. 46

    David (39): the site you link to doesn’t date its information but the NASA picture used appears to be for 1982-2004.

    The most recent NASA data I could find on the Antarctic 1981-2007 in an article on the Wilkins Ice Shelf disintegration looks much worse: it shows most of the continent as warming.

    I tried to find matching data at the British Antarctic Survey (BAS) but ran out of time. I don’t recall BAS as reporting a major increase as yet outside the Antarctic Peninsula. In any case the Antarctic is a special case because of the ozone hole.

  47. 47
    Brian Carter says:

    As the Greenland ice melts, the reduction of overburden will allow the bedrock to rise in compensation, along with the surrounding mountains, and further out the continental shelf will sink, if my memories of being taught about isostasy are correct! It seems to me that this will reduce the sea level rise somewhat?

  48. 48
    John Wilson says:

    I would like to encourage (beg) Stefan Rahmstorf to weigh in with a summary post pulling all this together. There is a lot of good discussion in the past few sea level rise articles and the comments, and it could benefit from a careful summary and review.

    My contribution to this is that I think that Pfeffer et al. could have benefited from a non-climatologist’s peer review of their article. Someone to help them sharpen the point as to exactly what misconception they were responding to.

    I am research director for an organization that works to stop global warming. I can say that many of the people I work with are confused by the statements that come out, and can easily misinterpret hypotheticals (those referred to by Pfeffer in this post) as scientific findings.

    I agree that the Pfeffer paper is justified in presenting a clear disagreement with the hypotheticals that are widely circulated. Many people have assumed that these hypothetical large sea level rise rates are based on some science (that doesn’t actually exist).

    However, Eric is also correct that the Pfeffer paper clouded the water by failing to engage the IPCC sea level rise numbers directly. While there is popular traction for the ultra-high SLR numbers, the IPCC sea level rise numbers have stronger traction in the planning and policy community as “definitive.”

    As Eric points out, the Pfeffer paper joins other work (e.g., Rahmstorf and posts on this blog) in suggesting that relying on the IPCC sea level rise numbers could be a grave mistake.

    [Response: A good suggestion and one we plan on doing. Stefan has already pulled together a nice up to date graphic that will illustrate this.--eric]

  49. 49
    Hank Roberts says:

    What puzzles me is why we don’t see these researchers and Hansen doing a press interview _together_ to emphasize the importance of this issue.

    It’s as though it’s more important to have — or create — a controversy than to report an explicit and educated cautionary public statement.

    I’d really welcome comments from all those doing this research about whether they are simply contributing their individual papers and waiting for the IPCC to do a summary next time — or whether they are in agreement and could make a statement.

    I do think it wholly regrettable that the original paper and press release spun this as “less than” rather than “more than” — it’s a simple sign error, and we know how long that kind of confusion persists.

    It’s the spin, rather than the holding on, that causes “crack the whip” to happen in the first place.

  50. 50
    John Lang says:

    Just noting that the Jason 1 sea level data has been reprocessed after an error was discovered earlier this year. (Jason-2 is still being calibrated.)

    Jason-1 new sea level increase numbers are 2.4 mm / year (or 1 inch per decade – less than 1 foot per hundred years.)

    In addition, over the past two years, the average increase has slowed to 1.0 mm / year (or 10 cm per hundred years or 4 inches per hundred years) so there will have to be a considerable acceleration of sea level increase to even come close to the lowest predictions presented in these threads.

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