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  1. 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.

    Comment by gavin — 18 Sep 2008 @ 5:39 PM

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

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

    Comment by David B. Benson — 18 Sep 2008 @ 5:41 PM

  3. 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.

    Dave

    Comment by Dave Rado — 18 Sep 2008 @ 6:14 PM

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

    Comment by David B. Benson — 18 Sep 2008 @ 6:31 PM

  5. 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.

    Comment by RichardC — 18 Sep 2008 @ 7:43 PM

  6. 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.

    Dave

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

    Comment by Dave Rado — 18 Sep 2008 @ 7:55 PM

  7. Dave Rado,

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

    Comment by Figen Mekik — 18 Sep 2008 @ 8:00 PM

  8. 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.]
    –eric]

    Comment by eric — 18 Sep 2008 @ 8:12 PM

  9. 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!

    Comment by Nigel Williams — 18 Sep 2008 @ 8:18 PM

  10. 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:
    http://www.whoi.edu/page.do?pid=7545&tid=282&cid=40786&ct=162

    and http://uwnews.org/article.asp?articleID=41159

    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.

    http://www.sciencemag.org/cgi/content/abstract/295/5558/1275

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

    Comment by Ike Solem — 18 Sep 2008 @ 8:50 PM

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

    http://www.guardian.co.uk/environment/2008/mar/16/glaciers.climatechange

    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?

    http://www.sciencedaily.com/releases/2008/09/080905164328.htm (pyrenees glaciers melting, gone)

    Picked up here and there, but not blasted out over the wire like the UBoulder press release was.

    http://www.sciencedaily.com/releases/2008/03/080317154235.htm “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.

    http://news.google.com/news?hl=en&um=1&ie=UTF-8&tab=wn&q=pyrenees+glaciers&scoring=d

    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:
    http://www.sciencedaily.com/releases/2008/09/080915121319.htm

    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]

    Comment by Ike Solem — 18 Sep 2008 @ 8:56 PM

  12. 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]

    Comment by John Monro — 18 Sep 2008 @ 9:08 PM

  13. 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]

    Comment by RichardC — 18 Sep 2008 @ 10:02 PM

  14. This article is interesting.
    http://www.jamaica-gleaner.com/gleaner/20080330/focus/focus6.html

    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
    http://www.nature.com/ngeo/journal/v1/n1/full/ngeo.2007.28.html

    This is the scary one from down under….
    Coral reef clue to fast sea rise
    http://www.guardian.co.uk/world/2005/feb/24/australia.environment

    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.

    Comment by paulm — 19 Sep 2008 @ 12:39 AM

  15. 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…

    Comment by John Mashey — 19 Sep 2008 @ 1:26 AM

  16. #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.

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

    Comment by CobblyWorlds — 19 Sep 2008 @ 2:26 AM

  17. 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]

    Comment by Lawrence Coleman — 19 Sep 2008 @ 2:36 AM

  18. 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:
    http://en.wikipedia.org/wiki/Manufacturing_Consent:_The_Political_Economy_of_the_Mass_Media

    And for more info about their so-called Propaganda Model see:
    http://en.wikipedia.org/wiki/Propaganda_Model

    Comment by Lennart — 19 Sep 2008 @ 2:50 AM

  19. 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]

    Comment by GlenFergus — 19 Sep 2008 @ 3:46 AM

  20. 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.

    Comment by Ricki — 19 Sep 2008 @ 4:17 AM

  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.

    Comment by Martin Vermeer — 19 Sep 2008 @ 4:37 AM

  22. 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.

    Comment by dagobert — 19 Sep 2008 @ 5:15 AM

  23. 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 ]

    Comment by pete best — 19 Sep 2008 @ 5:17 AM

  24. 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:
    http://wattsupwiththat.wordpress.com/2008/09/17/new-paper-from-christy-suggests-atmosphere-hit-max-co2-forcing-in-1998-feedback-missing/

    and of interest an article Abrupt Climate Change Focus Of U.S. National Laboratories at
    http://www.sciencedaily.com/releases/2008/09/080918192943.htm

    Comment by Dill Weed — 19 Sep 2008 @ 6:27 AM

  25. 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.

    Comment by Charlie — 19 Sep 2008 @ 8:09 AM

  26. 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]

    Comment by Ray Ladbury — 19 Sep 2008 @ 9:01 AM

  27. 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.

    Comment by stephan harrison — 19 Sep 2008 @ 11:08 AM

  28. 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?

    Comment by Food Tube — 19 Sep 2008 @ 11:19 AM

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

    http://environmentalresearchweb.org/cws/article/opinion/35820

    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….”

    Comment by Timo Hämeranta — 19 Sep 2008 @ 12:13 PM

  30. #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.

    Comment by CobblyWorlds — 19 Sep 2008 @ 12:28 PM

  31. 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.]

    –eric

    Comment by Jerry Steffens — 19 Sep 2008 @ 1:40 PM

  32. 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?

    Dave

    Comment by Dave Rado — 19 Sep 2008 @ 3:07 PM

  33. 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. ( http://www.sourcewatch.org/index.php?title=Edelman )

    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.

    http://www.potomacflacks.com/pf/2006/12/oil_industrys_1.html

    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:

    http://www.sciam.com/article.cfm?id=how-much-will-global-warming-raise-sea-levels&page=2

    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.

    Comment by Ike Solem — 19 Sep 2008 @ 3:27 PM

  34. I’ll chime in with Dill (#24) on getting a response to http://www.sciencedaily.com/releases/2008/09/080918192943.htm – 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]

    Comment by Guy — 19 Sep 2008 @ 3:32 PM

  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.

    Comment by Lynn Vincentnathan — 19 Sep 2008 @ 3:47 PM

  36. 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.

    Comment by Mr Henderson — 19 Sep 2008 @ 4:26 PM

  37. 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.

    Comment by RichardC — 19 Sep 2008 @ 5:55 PM

  38. Difficult to see where 80cm comes from.
    http://www.globalwarmingart.com/images/thumb/0/0f/Recent_Sea_Level_Rise.png/700px-Recent_Sea_Level_Rise.png

    The slope would have to break immediately upwards by at least 3X, reversing recent trends in the opposite direction.
    http://sealevel.colorado.edu/current/sl_noib_global_sm.jpg

    Comment by Patrick Henry — 19 Sep 2008 @ 7:08 PM

  39. Guy (34) — This link

    http://www.coolantarctica.com/Antarctica%20fact%20file/science/global_warming.htm

    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.

    Comment by David B. Benson — 19 Sep 2008 @ 8:59 PM

  40. 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]

    Comment by Thomas — 19 Sep 2008 @ 11:13 PM

  41. 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.”

    Comment by sidd — 19 Sep 2008 @ 11:29 PM

  42. 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]

    Comment by Timo Hämeranta — 20 Sep 2008 @ 3:16 AM

  43. Inline #34 – Gavin, on my previous postings in the http://www.realclimate.org/index.php/archives/2008/09/how-much-will-sea-level-rise/ 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 – http://www.ft.com/cms/s/0/232915f4-7aff-11dd-adbe-000077b07658,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.

    Comment by Guy — 20 Sep 2008 @ 3:48 AM

  44. #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.

    Comment by GlenFergus — 20 Sep 2008 @ 3:50 AM

  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.

    Comment by Barton Paul Levenson — 20 Sep 2008 @ 5:30 AM

  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.

    Comment by Philip Machanick — 20 Sep 2008 @ 6:55 AM

  47. 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?

    Comment by Brian Carter — 20 Sep 2008 @ 8:10 AM

  48. 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]

    Comment by John Wilson — 20 Sep 2008 @ 8:54 AM

  49. 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.

    Comment by Hank Roberts — 20 Sep 2008 @ 10:30 AM

  50. 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.

    http://www.aviso.oceanobs.com/fileadmin/images/news/indic/msl/MSL_Serie_J1_Global_IB_RWT_PGR_Adjust.png

    Comment by John Lang — 20 Sep 2008 @ 11:42 AM

  51. 39 David, one would expect temperatures to only rise at the margins and underside of the shelves, as that’s where warmer sea water exists. Old data (1999) but http://www.geophys.washington.edu/Surface/Glaciology/projects/ross_sea_history/conway+.pdf
    says that the Ross ice shelf’s grounding line is retreating ~120 metres per year. Anyone have current data?

    http://www.earth-prints.org/bitstream/2122/2976/1/ANDRILL_geotimes.pdf
    Dr Naish’s team drilled through the Ross and concluded that it has collapsed quickly in the past.

    As far as “providing” ice, lots of WAIS is on a reverse-slope marine bed. http://upload.wikimedia.org/wikipedia/commons/b/b7/AntarcticBedrock.jpg
    The further it retreats, the deeper the grounding line gets, and the more efficient the thermohaline pump where heavy warmer salt water dives to replace fresh meltwater at the grounding line. It’s a nasty positive feedback that is much enhanced by increases in ocean temperature.

    Eric, I’m guessing few folks here have access to such papers. Short excerpts accompanying each link would be appreciated. Thanks.

    Comment by RichardC — 20 Sep 2008 @ 1:24 PM

  52. Question, (and I am sure there is link someplace here)

    – I realized that I needed a good way to explain average sea level rise. The reason is that when I look at the water here in NYC and I think, “well, here’s high tide. If the water was six feet higher, it doesn’t look so bad.”

    That’s probably really, really wrong, but I wanted to know if anyone has a way to explain what 6 feet (or two meters) of SLR would look like, that would help. I mean, in New York (Manhattan) when I check out the google maps widget it doesn’t look like much would happen. I realize it is very different out by Kennedy Airport in Queens. The thing is, SLR is usually discussed in terms of averages, and sometimes measured in millimeters.

    So when I see a study saying the SLR is in X millimeters, and do an “eyeballing” it seems small, and I guess that’s what I need some help visualizing. Like, when I see an NYT story that says sea level rose 8 mm per year (I am making that up) it seems pretty innocuous, and so I was looking for help in getting my head around what those measurements mean.

    Comment by Jess — 20 Sep 2008 @ 2:30 PM

  53. Speaking of sea level rises I need a little clarification.
    In his testimony to the UK court Hansen said that sea level was now rising at double the rate of the 20thC. But according to CSIRO it is rising at 50% more than the rate in the 20thC.

    Which is correct?

    Thanks

    Comment by Dave Andrews — 20 Sep 2008 @ 2:47 PM

  54. 45 – Barton, I don’t see it working. It takes decades for permafrost to warm up and centuries for the deep ocean. The difference between now and warming up from glacial is that we’re starting from a much higher baseline, giving the system a much bigger and faster kick, and using CO2 instead of orbital cycles. The remaining ice is closer to the poles, so that mitigates it a bit.

    If mankind were to stop spewing CO2 at 385ppm, do you think the ultimate peak would be fairly close to 385ppm?
    http://www.csiro.au/news/PermafrostCarbon.html
    I agree we’d get a quick nudge down, but if we take the permafrost carbon inventory of perhaps double the atmosphere as a simplistic guess for future CH4/CO2 feedback in the pipeline (instead of trying to nitpick marine clathrates, etc etc), we’d peak at 1100ppm or so. Other opinions?

    47 – Brian, only if you live in/close to Greenland. For other areas, apparent local sea level rise will be a tad more since the oceans will increase in mass and drag the coasts down with them.

    49 – Hank, an excellent idea, but what about the Faux Gnus effect? Either you let the whole thing degrade into a “You’re wrong” “No, YOU’RE wrong” shouting match, or you end up with a counter-show. After all, there’s REALLYRealClimate… Have you noticed the tremendous increase in skeptical internet traffic at the grass roots level? Lots of sites to pick from nowadays – WattsUpWithThat? SolarCycle24. Barry Moore at http://jennifermarohasy.com/blog/ just used Spencer Weart’s stuff to “prove” Gavin Schmidt is full of it. “In conclusion, I agree with Weart, there are no easy answers and the IPCC case is far from proven. ”

    I think it’s going to take an ice-free arctic to gain traction. “Fortunately” that’s just around the corner.

    Comment by RichardC — 20 Sep 2008 @ 2:56 PM

  55. Timo Hämeranta @42,

    So why has the sea level consistently fallen during ice ages, and risen during inter-glacials?

    Comment by Nick Gotts — 20 Sep 2008 @ 3:29 PM

  56. Paulm above referred to the 2005 drill cores that found mangroves below the Great Barrier Reef and dated them to a 200-year range, suggesting a very fast sea level rise there; another press release here with a bit more info:
    http://velocity.ansto.gov.au/velocity/ans0005/article_06.asp

    I’m curious whether the scientists contributing to this thread knew about this and know of any followup — any chance that the Australian coastline sank suddenly rather than sea level rising that fast there?

    Comment by Hank Roberts — 20 Sep 2008 @ 3:42 PM

  57. Re #11 reply: Eric, what I wonder in particular about the new Howat et al paper is that they describe thinning extending quickly inland (quoting from the press release):

    ——————–

    Howat and his colleagues concentrated on the southeastern region of Greenland, an area covering about one-fifth of the island’s 656,373 square miles (1.7 million square kilometers). They found that while two of the largest glaciers in that area – Kangerdlugssuaq and Helheim – contribute more to the total ice loss than any other single glaciers, the 30 or so smaller glaciers there contributed 72 percent of the total ice lost.

    “We were able to see for the first time that there is widespread thinning at the margin of the Greenland ice sheet throughout this region.

    “We’re talking about the region that is within 62 miles (100 kilometers) from the ice edge. That whole area is thinning rapidly,” he said.

    Howat says that all of the glaciers are changing within just a few years and that the accelerated loss just spreads up deeper into the ice sheet.

    ——————–

    I find it hard to reconcile these results with the Pfeffer et al conclusion that gateways are constraining the melt (unless it’s the case that the constraining effect is predicted to not become obvious until the rate of melt is much greater than at present).

    Also, I had asked in the other thread about this recent Eos paper finding a large degree of frictional melting in a recent Greenland jokulhlaup. Was the extent of this effect previously understood, and is it consistent with the present understanding of how the melting of the ice sheet will proceed? Excerpting:

    “On the basis of the stage-discharge relationship, the maximum Watson River discharge during the jökulhlaup is calculated to have been approximately 540 cubic meters per second, and the total runoff during the event is estimated to have been 28.8 million cubic meters (Figure 2b). Outflow from the ice-dammed lake is estimated to have been 11.3 million cubic meters; the additional 17.5 million cubic meters is due to frictional melting of ice as the flood traveled in contact with the glacier, together with an input from base flow.”

    Comment by Steve Bloom — 20 Sep 2008 @ 5:29 PM

  58. Guy (43) — Use 350 ppm. These folks

    http://www.350.org/

    did

    Comment by David B. Benson — 20 Sep 2008 @ 6:17 PM

  59. Hank Roberts (56) — I suggest burial by landslide or mud from extreme rainfall event. Here is a link describing this sort of problem near Cairns, Queensland, a typical departure port for visiting part of the Great Barrier Reef:

    http://www.falsecape.org.au/content.php?pageid=45

    However, as a whole, Australia is extremely tectonically stable:

    http://www.daff.gov.au/rfa/publications/whep-meeting/thematic

    Comment by David B. Benson — 20 Sep 2008 @ 7:44 PM

  60. > 30 or so smaller glaciers there contributed 72 percent of the total

    Steve, have you checked the specific sources of the smaller glaciers?
    Why are they “smaller” glaciers?

    I wonder — perhaps they don’t flow through ‘gateways’ and the large ones do? My hunch is the few large glaciers draw from the central ice mass through ‘gateways’ and the many smaller glaciers instead form mostly from snowfall on the outside of the ring of mountains around the icecap. Just speculating on this, I don’t have sources but perhaps someone can say whether there’s a different origin for the “smaller” glaciers.

    Comment by Hank Roberts — 20 Sep 2008 @ 7:53 PM

  61. re: #52 Jess

    flood.firetree.net is a useful tool for getting rough ideas. Zoom in on the map, and set the SLR in meters, and it grays out anything below sea levels (which of course, does *not* mean underwater). Do *not* use for real planning purposes, just to get a feel, since SLR varies, elevations aren’t necessarily great, etc, etc. The specific link is for +2m centered on NYC.

    As an exercise, pick an area you know well, simulate a town planner, and raise the SLR from 0 to +1m to +2m …. and guess at dates, and figure out what strategies you take.

    Specifically:
    a) Do you build dikes?

    b) If so, where? Do you protect everything that’s already there, and keep raising the dikes, or do you draw the line further inland. If so, what do you tell the people outside the line?

    c) In considering the NYC area, the 3 major airports are near sea-level. Do you protect them all?

    d) Resources required for protection vary by the geography. For example, convex land isn’t too bad, because as the water goes up, the perimeter needing to protection shrinks, so you might be tempted to do the first dike further uphill.

    Concave shore is just the reverse, because the perimeter lengthens with SLR. Of course, with a concave shore that has a relatively short mouth, you might just close that off, and then have much less shoreline to protect directly. In some sense, that’s what the Dutch did with the ZuiderZee Works, although of course that wasn’t to protect against rising SLR.

    Of course, cities built around major river mouths have their own extra issues, i.e., that’s a particular kind of concave that has water flowing through it, and hence a long perimeter, and you can’t easily close it off without a lot of pumping. For example, one can imagine closing off the Southern end of the SF Bay, as not much water flows in from the South. It’s hard to imagine closing off the GoldenGate Bridge area.

    One always needs to make sure there will be enough energy to run pumps as needed, since area behind dikes will need pumping some of the time, i.e., see how New Orleans works.

    Comment by John Mashey — 20 Sep 2008 @ 11:20 PM

  62. David, did you find any source for info on that 2005 paper?

    Looking at the topography, the reef’s offshore a ways; the paper would suggest it was a barrier island covered with mangroves that was submerged. No cliffs nearby, no river deltas shown. But that’s only inference from looking on the map. Perhaps someone here’s from Australia or familiar with the research and can give us some facts on it.

    Comment by Hank Roberts — 21 Sep 2008 @ 12:33 AM

  63. Serious question from a skeptic:

    If C02 is such a profound green house gas, and it has risen from 280ppm to 380ppm over the last century or so (?), why is it not blindingly obvious that human-induced climate change is happening, and had a profound effect already? As far as I know, the climate in California is much like it was in the 1850′s, and are things really much different?? Why should I worry about 450-500ppm?

    THIS IS A SERIOUS QUESTION, NOT RHETORICAL. If this is a true problem I want to do something about it. I understand this is probably not the appropriate place to post, but I’ve searched for an answer to this (I think) obvious question without result. I figure many knowledgeable people read this site, and can easily answer. Will check back in a day or so.

    Comment by Mark in SF — 21 Sep 2008 @ 12:49 AM

  64. Re #60: I don’t really know, Hank, other than to point out that Howat stated that the small glaciers are draining the interior.

    Comment by Steve Bloom — 21 Sep 2008 @ 1:33 AM

  65. #58 – 350.org is a good site and one I want to embrace wholeheartedly, but their target seems to be based around Hansen alone. Also I’m surprised that their major NGO supporters seem thin on the ground – I assume because many are stll working to other targets thinking them sound. Are they sound?! These are precisely the reasons I’m desperately trying to get a specific 350ppm CO2 conentration RC response – still not forthcoming (10 attempts in 12 days and counting…) Remember, I’m not asking the impossible for an absolute definitive safe figure, but a reasonable target that stands a good probability of being safe, given all that we currently know, but is open to revision. RC’s Target CO2 posting seems to cautiously welcome the underlying science, but critically falls short of commenting on that vital conclusion.

    I’ve called it the elephant in the room in the entire debate, and that still stands as far as I can tell. With (seemingly) only James Hansen giving a figure for policymakers, there is little chance of real action being taken by the people that matter because they will simply point out his isolation. I’m nervous about the figure as I am antipating flack in the form of contradictiory statements from the scientific community. (as usual, existing links to other recent papers that I have missed or recent public statements by other senior climatologists referencing a target figure will be very welcome!)

    Incidentally, I found another recent story related to this by Tom Flannery – a study by Roger Pielke (doesn’t say which one), Tom Wigley and Christopher Green saying that the action needed to get emssions down will be much greater than forecast by the IPCC (report here – http://www.smh.com.au/news/environment/the-coal-conundrum/2008/09/19/1221331207201.html) – if 350 is an appropriate target, it suggests it will be an even more phenomenally tough one than we already knew. Phew.

    PS – I appreciate that strictly speaking this off topic, but since it is a) essentially it is pertient to the outcomes of pretty much ever single thread on here and b) so important, I feel I must keep trying… thanks for everyone’s patience!

    Comment by Guy — 21 Sep 2008 @ 2:17 AM

  66. Re 42 Gavin, it seem we have to wait a bit more to see polar ice sheets growing for more heat when yr models have continuously overestimated polar amplification, please see:

    “Contrary to recent assessments based on theoretical models [IPCC, 2007] the anthropogenic warming estimated directly from the historical observations is more pronounced between 45 S and 50 N than at higher latitudes…. Climate models may therefore lack – or incorrectly parameterize – fundamental processes by which surface temperatures respond to radiative forcings…In contrast with climate model simulations, the zonal surface temperature changes…do not increase rapidly from mid to high latitudes.”

    Ref: Lean, Judith L., and David H. Rind, 2008. How natural and anthropogenic influences alter global and regional surface temperatures: 1889 to 2006. Geophys. Res. Lett., 35, L18701, doi:10.1029/2008GL034864, September 16, 2008, online http://pubs.giss.nasa.gov/docs/2008/2008_Lean_Rind.pdf

    Well, I can’t surprise you when we both know nobody knows how climate will evolve in near or far future.

    Comment by Timo Hämeranta — 21 Sep 2008 @ 2:56 AM

  67. John Mashey at #61:

    Specifically:
    a) Do you build dikes?

    If the stuff is valuable, too right; ample precidents.

    b) If so, where? Do you protect everything that’s already there, and keep raising the dikes, or do you draw the line further inland.

    This is not a new question. It applies to every city or town building or raising its flood levee. Politics aside (OK, I know…), you build it in the location which maximises the benifit : cost ratio (or some similar metric).

    If so, what do you tell the people outside the line?

    As per the town leeve, one says “Bad luck – move, or take ya chances.”

    c) In considering the NYC area, the 3 major airports are near sea-level. Do you protect them all?

    Yep. For expensive infrastructure like this it is definitely going to be worth building the levee for 2m SLR. 10m SLR, maybe not…

    d) Resources required for protection vary by the geography. For example, convex land isn’t too bad, because as the water goes up, the perimeter needing to protection shrinks…

    Huh? The 2-D slope shape does not affect the wetted perimeter. Guess you mean bowl-shaped vs mound-shaped. I.e. valley vs hill (peninsular)?

    For example, one can imagine closing off the Southern end of the SF Bay, as not much water flows in from the South. It’s hard to imagine closing off the Golden Gate Bridge area.

    The value of the infrastructure potentially protected by a Golden Gate barrage is gigantic. So the very large cost of a closure may well be justifiable – and it is certainly do-able. Yes, the pumping issue is huge, but while the SLR remains of the same order as the tide range (as here, at 2m SLR?) a tidal closure (a la Thames) will be feasible, and will reduce (not eliminate) pumping.

    Comment by GlenFergus — 21 Sep 2008 @ 3:31 AM

  68. Dykes! Around the coast OF THE ENTIRE CIVILISED WORLD!!! You must be kidding! Will you have helicopters to drop sand bags for you? Nope. Will you have fuel for the scrapers and diggers to shift the dirt? Nope. Will you have spare energy to run the pumps? Nope. Will you have surplus cement or steel for the gates and weirs? Nope.

    Once our governments publicly acknowledge that we have to recognise sea level rise, then we will see decisions being made around where we can afford to spend remaining resources. Society will rapidly be driven to the logical conclusion that we cannot afford to rebuild our social infrastructure again and again for every increment in sea level rise. We can only rebuild once, and that has to be at or above the 100 metre line to be clear of the eventual 80 metreS sea level rise.

    Comment by Nigel Williams — 21 Sep 2008 @ 3:55 AM

  69. According to Aviso, current sea level rise rates are 24cm/century, and the second derivative of the six year trend is negative – suggesting that 24cm number will get smaller in the near future.
    http://www.aviso.oceanobs.com/fileadmin/images/news/indic/msl/MSL_Serie_J1_Global_IB_RWT_PGR_Adjust.png

    Comment by Patrick Henry — 21 Sep 2008 @ 8:26 AM

  70. Having read both the article and press release, the press release for the Pfeffer article was irresponsible (http://www.colorado.edu/news/r/c3cb8187d1bf611c77bbf951ffc3e96a.html). This press release was under his control, so it is not a journalism error. It seems clear that he was upset by estimates of an extremely large Greenland contribution to sea level rise. However, it should also have been clear that the AR4 IPCC may have strongly underestimated the Greenland contribution (in Ch 10, the maximum Greenland contribution estimate by 2100 was 12 cm). A responsible press release would have discussed both–that the Pfeffer et al. minimum estimate for a Greenland sea level contribution was 25% above the IPCC maximum estimate. The paper discussed this–why didn’t the press release???

    Comment by Mitch Lyle — 21 Sep 2008 @ 8:36 AM

  71. Mark (#63),
    It is blindingly obvious. What more do you need?

    Comment by Figen Mekik — 21 Sep 2008 @ 9:59 AM

  72. Mark in SF, Good Lord man, where are you getting your info that climate hasn’t changed? Talk to a vintner and see where they are opening new vineyards. Read some actual data. The Start Here section on the front page has some good pointers. Second, since when is California the whole world? Have you looked at the melting glaciers and polar ice in the Northern hemisphere–and at the edges of Antarctica? You can look this stuff up as my good buddy Hank is fond of saying.

    Comment by Ray Ladbury — 21 Sep 2008 @ 10:20 AM

  73. Can we find adequate enough ways to escape “whiplash effects” and warn each other in the human community of impending danger before we “reap the whirlwind”?

    We in the family of humanity are going to be forced to do better in our efforts to communicate in a more reality-oriented way about ominously looming threats of an human-driven, global calamity of some kind. If we keep doing precisely what our leaders are saying and doing now, the future for our children looks bleak. We can surely do more and do it better. After all, human beings are remarkably intelligent, ingenious and adaptive.

    Before we can determine what new and different to do, perhaps a brief analysis of our current, distinctly human-induced, global predicament is in order. Consider for a moment some of the ways in which my generation of leaders has gone so terribly wrong.

    First, the leaders in my generation of elders wish to live without having to accept limits to growth of seemingly endless economic globalization, of increasing per capita consumption and skyrocketing human population numbers; our desires are evidently insatiable. We choose to believe anything that is politically convenient, economically expedient and socially agreeable; our way of life is not negotiable. We dare anyone to question our values or behaviors.

    We religiously promote our widely shared and consensually-validated fantasies of `real’ endless economic growth and soon to become unsustainable overconsumption, overproduction and overpopulation activities, and in so doing deny that Earth has limited resources and frangible ecosystems upon which the survival of life as we know it depends.

    Second, my not-so-great generation appears to be doing a disservice to everything and everyone but ourselves. We are the “what’s in it for me generation.” We demonstrate precious little regard for the maintenance of the integrity of Earth; shallow willingness to actually protect the environment from crippling degradation; lack of serious consideration for the preservation of biodiversity, wilderness, and a good enough future for our children and coming generations; and no appreciation of the vital understanding that humans are no more or less than magnificent living beings with “feet of clay.”

    Perhaps we live in unsustainable ways in our planetary home; but we are proud of it nonetheless. Certainly, we will “have our cake and eat it, too.” We will own fleets of cars, fly around in thousands of private jets, live in McMansions, exchange secret handshakes, frequent exclusive clubs and distant hideouts, and risk nothing of value to us. We will live long, large and free. Please do not bother us with the problems of the world. We choose not to hear, see or speak of them. We are the economic powerbrokers, their bought-and-paid-for politicians and the many minions in the mass media. We hold the much of the world’s wealth and the extraordinary power great wealth purchases. If left to our own devices, we will continue in the exercise of our `inalienable rights’ to outrageously consume Earth’s limited resources; to recklessly expand economic globalization unto every corner of our natural world and, guess what, beyond; and to carelessly consent to the unbridled global growth of human numbers so that where there are now 6+ billion people, by 2050 we will have 9+ billion members of the human community and, guess what, even more people, perhaps billions more in the distant future, if that is what we desire.

    We are the reigning, self-proclaimed masters of the universe….. the thousands of greedy little kings of capital concentration, big business potentates and governmental sinecurists. We enjoy freedom and living without limits. Of course, we adamantly eschew any talk of the personal responsibilities that come with the exercise of personal freedoms or discussions of the existence of biophysical limitations of any kind.

    We deny the existence of human limits and Earth’s limitations.

    Please understand that we do not want anyone presenting us with scientific evidence that we could be living unsustainably in an artificially designed, temporary world of our own making….a manmade world filling up with gigantic enterprises, virtual mountains of material possessions, and boundless amounts of filthy lucre.

    Third, most of our top rank experts appear not to have found adequate ways of communicating to the family of humanity what people somehow need to hear, see and understand: the rapacious dissipation of Earth’s limited resources, the relentless degradation of the planet’s environment, and the approaching destruction of the Earth as a fit place for human habitation by the human species, when taken together, appear to be proceeding at breakneck speed toward the precipitation of a catastrophic ecological wreckage of some sort unless, of course, the world’s colossal, ever expanding, artificially designed, manmade global political economy continues to speed headlong toward the monolithic `wall’ called “unsustainability” at which point the runaway economy crashes before Earth’s ecology is collapsed.

    Who knows, perhaps we can realistically and hopefully hold onto the expectation that behavioral changes in the direction of sustainable production, per human consumption, and propagation are in the offing…..changes that save both the economy and the Creation.

    Steven Earl Salmony
    AWAREness Campaign on The Human Population, established 2001

    Comment by Steve Salmony — 21 Sep 2008 @ 10:25 AM

  74. If C02 is such a profound green house gas, and it has risen from 280ppm to 380ppm over the last century or so (?), why is it not blindingly obvious that human-induced climate change is happening, and had a profound effect already? As far as I know, the climate in California is much like it was in the 1850’s, and are things really much different?? Why should I worry about 450-500ppm?

    Thanks for a good question. What is tripping you up are the delay loops in the system. Currently, global temperature is 0.7C warmer due to the net effect of various greenhouse gases and aerosols. That may not sound like much. In continental locations, and at high latitudes, it will be more. But sure, in a single location it will be swamped by natural variability, or “weather”.

    Still, if you went to the countryside you’d likely find folk testifying that growth conditions have significantly changed. (Still I’m surprised at Californian longevity. Eye witnesses from 1850?)

    About those delay loops: firstly, we live on an ocean planet. Without the oceans we would already have 1.5C warming. It will catch up with us in a few decades, no matter what we do.

    And there are things we just cannot do, like turning the switch on all our coal fired power plants. Those are huge investments and written off over 30-50 years. Same for real estate with their space heating systems, and urban sprawl with its assumption of cheap personal transport.

    If we decide now to start replacing them by C-neutral plants, the process will end by mid-century. And then, the warming “committed to” (but not realized until again decades later) will be as much as 3C. Double that in continental or high latitude locations.

    I won’t mention China or India. I will mention Iceland. Was there last month, they told me that all of their glaciers will be gone in 150 years. Their landscape, the backdrop of their sagas… Serious? Debatable. Blindngly obvious? You bet.

    You see, climate degrees are a lot bigger than weather degrees. The last Ice Age was just -5C. We’re getting there.

    Comment by Martin Vermeer — 21 Sep 2008 @ 10:45 AM

  75. 61 – John, say that as a prudent capitalist, you purchase land x metres above sea level, and after all the data is in, you are projected to soon own stable oceanfront property. Then the folks lower than you decide to reach in your pocket and build a dike which will prevent you from enjoying the fruits of your good choices. Doesn’t that smack of double theft?

    23 – Pete, no way. Take Hansen’s doubling exercise. He used 10 years. Say he’s off a bit and it’s 7 years or 15 years. For a 100 year period, aprox last year response (close enough): 7 –> 17,000 10 –> 1,000 15 –> 100. And then there’s the other logarithmic unknown of carbon feedbacks. Some say BAU is ~500. A small change in assumptions and it’s 5000 (CO2 equivalent – CH4 is multiplied by 23). How deep will water percolation get and so thaw permafrost? http://www.canada.com/topics/technology/science/story.html?id=f1b50558-c079-4afb-936a-c7625f420d08 says that as long as the current spike isn’t worse than 120kya, deep permafrost should be OK. I think 120kya was mild compared to where we’re going. Will the thermohaline system change location/strength? Current marine hydrate deposits depend on the current configuration. Add it all up and the answer you seek will have error bars far larger than the data itself.

    35 Lynn, given that we won’t turn off the CO2 spout instantly, the answer is likely 80 metres. (others will disagree) We can inject sulphur and try to stop the meltdown, but GHGs affect polar areas the most and dimming work best in the tropics. Polar stratospheric injection of sulphur is probably the technique we’ll end up trying, but keeping your feet warm (tropics) and head cool (poles) while adding thick blankets (GHGs) over your whole body is a difficult task when the pesky atmosphere keeps scattering your AC units (sulphur)

    And like the dike issue above, if this all comes to pass, what happens when Russia (and maybe Canada) start defending themselves from the sulphur attack by destroying launch sites? After all, Russia and Canada would become massively dominant world powers as owners of most of the viable property left on the planet. What right do other countries have to take that away?

    Comment by RichardC — 21 Sep 2008 @ 11:11 AM

  76. > Greenland, small/large glaciers, drainage

    Looks like most of my questions will be answered to the extent there are answers by
    Eric Rignot’s Chapter 5, in this book:

    Sudden and Disruptive Climate Change
    Earthscan, 2008
    ISBN 1844074773, 9781844074778

    He there has an illustration showing the drainage basins for many of the glaciers. (Google books doesn’t show the color illo, unfortunately).

    I haven’t found a map yet showing which glaciers cross the mountains above vs. below sea level. Glenn above writes that Pfeffer says melt will be limited because

    > ice must discharge to the ocean through bedrock gateways

    I’d think a “bedrock gateway” could go both ways — if the bedrock is below sea level, sea water can enter; if above sea level, as Mauri has pointed out clearly and repeatedly, the ice will fill melt voids in the winter.

    This search gets a good bit of info. I’m done til I read more on this

    http://scholar.google.com/scholar?num=50&hl=en&lr=&newwindow=1&safe=off&scoring=r&q=Greenland+glacier+topography+%22sea+level%22&as_ylo=2008

    Comment by Hank Roberts — 21 Sep 2008 @ 11:12 AM

  77. Re #63

    I live across the bay from you and I’ve seen climate change. The easterly winds used to come in September or early October, and now come in November. Last year’s winds were weak, I never saw that before. Sunrise didn’t used to be an exceptional event, but it was more normal for the summer sun to emerge from the fog sometime between 2 and 4, well some days and some years it didn’t emerge. Now many think that sunrise is normal. I used to teach seniors, so pay attention to warm days after spring break, as they were considered official cut days (by the students). In 6 years, I saw 5 such days. As of 1997, I never see fewer than 5 warm days between spring break and semester end, and might see 20 or more. (Warm by Berkeley standards)

    You can also check IPCC Working Group 2, chapter 1. You may not have been paying attention to dramatic increases in forest fires, or what the spittle bug and kelp have been up to, but others have.

    Elsewhere people have been noticing critter and flora movement at Yosemite and elsewhere, regional extinction of butterflies. The Chronicle covers this–here’s one such article in the The Difference a Degree Make series.

    Comment by Karen Street — 21 Sep 2008 @ 11:41 AM

  78. re: #67 Glen
    You seem to have the opinion that this is no problem.

    Can you explain your relevant experience in dealing with such issues? Can you point at coastal planning sessions you’ve been involved with (websites?), so the rest of us can discover the cheap and easy solutions that the professionals around here don’t know and worry about?

    Comment by John Mashey — 21 Sep 2008 @ 12:06 PM

  79. > As far as I know, the climate in California is much
    > like it was in the 1850’s, and are things really much
    > different?? Why should I worry …

    You should worry because what you don’t know can hurt you.
    You should worry about learning how to look these things up.

    Just one example below — not the answer, just an example.
    You can find answers for yourself.

    For more, talk to your school’s librarian, or if you’re out of school go to the reference desk at your public library. Tell the librarian you want to become able to learn for yourself. They will help.

    http://ams.allenpress.com/perlserv/?request=forward-links&doi=10.1175%2F1520-0442(1995)008%3C0606%3ALSAFOR%3E2.0.CO%3B2

    Comment by Hank Roberts — 21 Sep 2008 @ 12:27 PM

  80. For that link above to work, you’ll have to copy it and paste it into your web browser’s navigation window — the parentheses break it as it appears here.

    Comment by Hank Roberts — 21 Sep 2008 @ 12:28 PM

  81. I can’t surprise you when we both know nobody knows how climate will evolve in near or far future.

    Actually we can, and we have. It will get warmer.

    No surprises there.

    Comment by Thomas Lee Elifritz — 21 Sep 2008 @ 12:39 PM

  82. Patrick Henry says: “According to Aviso, current sea level rise rates are 24cm/century, and the second derivative of the six year trend is negative – suggesting that 24cm number will get smaller in the near future.”

    Six-year “trend”. Thanks Patrick. That’s funny.

    Comment by Ray Ladbury — 21 Sep 2008 @ 1:39 PM

  83. 65 Guy, CO2 was 280ppm, and has never been over 300ppm in an era where our climate has existed. So pick 280 or 300. Anything higher is risky. Hansen said 350 only with the mitigating statement that it was an initial maximum target that could be moved downwards. Since we are at 385, the answer from a policy standpoint is, “As low as we can get it as fast as we can get there,” so 350 is the number you’re looking for today.

    Comment by RichardC — 21 Sep 2008 @ 2:16 PM

  84. Its good to see RealClimate providing the story behind confusing news coverage. Thanks to Tad Pfeffer, J. Harper, and S. O’Neel for adding to the discussion and clarifying their position.

    Jess (#52) 6ft of sea rise in Manhattan is a big deal. I used to work in a building on the waterfront in the Wall Street area. Considering that the first floor is at maybe 8 feet above sea level any buffer in case of even a minor storm is gone. This is very expensive real estate in a very crowded area too.

    I also walk and jog on the path that runs along the shore of the southern half of Manhattan, and six feet of sea level rise would flood many areas, including the entire subway system.

    Comment by Joseph O'Sullivan — 21 Sep 2008 @ 2:46 PM

  85. Even if one wants to look at just California, plenty of climate change has been observed. Fortunately the state government is not in denial about the problem, so it’s easy to access the information. The main portal is here.

    Comment by Steve Bloom — 21 Sep 2008 @ 3:29 PM

  86. I haven’t had time to read all of these postings – let alone Jim Hansens DIRE piece (though I DID just download it and I will do so; and Thank You, by the way, for telling the WHOLE SCARY Truth Dr. Hansen); but, out of what I did scan, I didn’t seem to notice any references having been made in regards to the possibility that the Fresh Meltwater comming off of the Greenland Ice Sheets – and them plunging striaght to the bottom of the North Atlantic Ocean – could shut down the so-called ‘Atlantic Conveyor’.
    As I understand it, this would not only plunge Europe into a New Ice Age – by shutting down the Gulf Streams Warm ‘Return Flow’ – it would also lead to a dramatic warming of the Southern Oceans Surface Waters, and a subsequently – and equally dramatic – increase in the rate at which the Antarctic Ice Sheets are themselves Melting.
    It seems to me that the ‘One-Two Punch’ of a New Northern Hemisphere Ice Age, combined with the kinds of unprecedented (read: MUCH more than 5m) SLR that would accompany it, would constitute the ‘worst of all possible cases scenario’.
    In fact; I seem to remember reading, in the article that dealt with this issue (in SciAm or NewSci, most likely), that the author(s) were hypothosizing that this very effect may have been responsible for the LIG!!!
    Any thoughts or new Info on this subject for me (US! The “Carbon Free”), Gang? Please send me a fresh E-mail alert if you have any thoughts to share – whether you start a new post or not; as I’m out to Terrify those ‘Drill, Drill, Drill’ Idiots (say it like ‘The Brain’ would to Pinky!) into sensible submission, one Blog Entry at a Time!!!
    ‘Build’ Me The Truth, and They Will Come (Around)!

    Comment by James Staples — 21 Sep 2008 @ 4:47 PM

  87. Mark (63),

    James Hansen does a good job explaining Global Warming. Reading his PDFs will give you a comprehensive understanding of the argument for GW, explanation of forcings (particularly CO2, which you asked about) and of the difference between historical evidence vs computer models. Go to: http://www.columbia.edu/~jeh1/
    select Files/Links and download all pdfs starting with 2004. After your done with that…

    Roll up your sleaves, enlarge the print on your monitor and read everything here. This is by far the best site to gain a comprehensive understanding of the science and its complexities. (They are not paying me to say this!) I’ve been lurking in the weeds for several years. I recommend starting with Hansen’s material first.

    Here the evidence get laid out and explained, areas of weakness are identified and explored, assumptions get identified, tested and challenged – civilly, too!

    This site is the place to go when your not satified with someone making unsupported claims or just attacking and denying. GRRR!!!

    Kudos, Gavin et al.

    Dill Weed

    Comment by Dill Weed — 21 Sep 2008 @ 5:05 PM

  88. Also re California info, see this publications page.

    Comment by Steve Bloom — 21 Sep 2008 @ 5:11 PM

  89. Re #80: Or do it as an embedded link, Hank. Then there’s no problem with a line break no matter how long the url gets.

    Comment by Steve Bloom — 21 Sep 2008 @ 5:16 PM

  90. Guy (65) — I think RichardC in comment #83 makaes the point quite well; we don’t know enough to be much more precise about an eventual target; we do know enough to know that we have now committed the earth to sea level rise (at some rate) for centuries to come.

    Hank Roberts (62) — If a barrier island the result could be obtained by a large sea surge overtopping the island and burying the mangroves, possibly moving those to the lnadward side of the island. In any case, a sudden local sea level rise via rapid subsidence is most unlikely and such a rapid change due to proglacial lake release (or whatnot) even less so.

    Comment by David B. Benson — 21 Sep 2008 @ 5:44 PM

  91. Re. #86, James Staples, that’s highly unlikely – and some highly respected oceanographers would go further and say it’s impossible. There are enough high or medium likelihood scenarios to worry about, there’s really no need to exaggerate the threat, which is very serious without exaggerating anything.

    The IPCC rates the possibility of Atlantic conveyor shut-down as extremely unlikely. Regarding the hypothesis that it has happened in the distant past, the oceanographer Carl Wunsch has emailed me in the past to say:

    That’s a very controversial, if widely popular, interpretation of very fragmentary data. There is almost no information at all on the *rates* at which the ocean circulation moved in the past. Much of the paleoclimate community has confused the correct inference that water properties changed (got fresher or warmer for example) with the conclusion that means that the flow rate had to change. Of course, it could have changed, and almost surely did under different climate conditions, but the story of “shutdown” is part of the over-dramatization that led Gore astray. It would be a breakthrough in paleoceanography to find a measure of water movement rates. It *is* true too, that one can make numerical models, that when overlain with a large layer of fresh water that they reduce the so-called meridional overturning circulation. Those models have been used to buttress the shutdown story. But they raise a long series of problems including the fact that major ice melt events do not seem to have occurred at the “right” times, that fresh water comes in at the edges mainly, not in the middle of the ocean, and that the models do not properly represent the physics of the upper ocean.

    Dave

    Comment by Dave Rado — 21 Sep 2008 @ 6:32 PM

  92. Earlier (on the orginal thread on this topic), concern was raised (by at least me) regareding WAIS stability. The Wikipedia page has a moderate, even calming, stance (except at the very end):

    This paper, “Ice Sheet Stability and Sea-Level Rise”

    http://www.sciencemag.org/cgi/content/full/315/5820/1803

    states, in part, “Thus, in the foreseeable future, sea-level rise should not threaten the ice sheet’s stability [for Whillans Ice Stream out to the Ross ice shelf].”

    Here is a 1998 review paper which states, in part, “Almost all sea-level rise would occur beyond the twenty-first century. However, these outcomes are predicated on changes in basal melt rates that could accompany global warming of only a few degrees, warming that could be determined by emissions that occur during the twenty-first century. Given the long residence time of atmospheric carbon dioxide, and thermal inertia in the oceans, decisions being considered now could irreversibly affect WAIS in the distant future.”

    http://www.geo.utexas.edu/courses/387h/PAPERS/Oppenheimer%201998%20Nature.pdf

    [Since there is going to be a computer-based study of this question of WAIS stability, Captcha wisely states "it investment".]

    Comment by David B. Benson — 21 Sep 2008 @ 7:22 PM

  93. Re: #63
    “why is it not blindingly obvious that human-induced climate change is happening, and had a profound effect already?”

    All of the effects of the increase in greenhouse gas emissions have not taken effect yet. Further warming from the present increases are still “in the pipeline” as they say. One of the reasons for the lag is the delayed reaction of the surface waters of the oceans to the absorption of heat and it’s ultimate contribution by releasing this heat back to the atmosphere.

    Comment by Lawrence Brown — 21 Sep 2008 @ 8:16 PM

  94. 84 Joseph, you’re right. I’d add in that the geographic range of tropical storms will probably increase, so NYC, which currently has one Cat1 Hurricane every 15 years, might get more frequent visits and from stronger storms. There’s no need for increased numbers of hurricanes for that to happen, only that they survive the trip north as they are fed by warmer waters.

    85, speaking of Blooms, Steve, gardeners everywhere have noticed that they can get away with planting too soon according to the old charts, and their tomatoes last a couple weeks longer in fall. There’s a big debate in the green thumb world about whether to republish the old climate zone charts. Bird watchers are noticing the changes too as species dwindle and show up in the wrong place at the wrong time. Nature is getting confuzzled.

    86, James, Dr Hansen’s work is tame. It assumes sanity and incredible luck. Folks get more insane as the luck runs out. Wars between nations, classes, religions, and social groups get ugly if, as Dr Lovelock predicts, 6.1 out of 6.6 billion people must die. Dr. Lovelock is the original Earth Systems (Gaia) scientist. It’s possible he’s wrong, but he’s no crackpot. As to your ice age prediction, I seriously doubt it. Killing the conveyor would only mitigate northern warming, not reverse it. The Arctic Ocean losing its ice is almost certainly involved in the initiation of northern thermohaline demise, so albedo change will compensate. Besides, the Gulf stream is only 1/2 driven by thermohaline. The 1/2 that is driven by coriolis can never die until the continents move or the Earth stops spinning. And IF a “northern ice age” tried to start up, it would IMMEDIATELY kickstart the northern thermohaline, and prevent the ice age! (Note: the real thermohaline is driven by Antarctica. The stuff in the North Atlantic doesn’t even make it to the ocean floor. We just focus on it because we’ve got a Eurocentric bias.)

    Comment by RichardC — 21 Sep 2008 @ 9:12 PM

  95. Somehow the link to the Wikipedia page didn’t make it into my previous post. Here it is:

    http://en.wikipedia.org/wiki/West_Antarctic_Ice_Sheet

    This 2002 abstract, “Risk Estimation of Collapse of the West Antarctic Ice Sheet”

    http://www.springerlink.com/content/u428134536q00138/

    states in part “However, a refusal by scientists to estimate the risk leaves policy-makers with no sound scientific basis on which to respond to legitimate public concerns. Here we present a discussion of the likelihood of WAIS-collapse, drawing input from an interdisciplinary panel of experts. The results help to summarise the state of scientific knowledge and uncertainty. While the overall opinion of the panel was that WAIS most likely will not collapse in the next few centuries, their uncertainty retains a 5% probability of WAIS causing sea level rise at least 10 mm/year within 200 years.” That’s 1 meter/century.

    Comment by David B. Benson — 21 Sep 2008 @ 9:13 PM

  96. Yet more California::

    Sacramento Bee “Sierra Warming” page (inc. a linked blog)

    A Change in the Wind” blog by SoCal journalist Kit Stolz (not all climate change)

    Between the two of them they don’t miss much of interest re CA climate.

    There’s also a new paper out in GRL that commenter Lazar quoted at length over at the Open Mind blog.

    California can afford a lot of infrastructure, but between sea level rise and the need for a year-round water supply it’ll be interesting to see if we can manage it.

    Comment by Steve Bloom — 21 Sep 2008 @ 9:48 PM

  97. Re Mark in SF @63: “If C02 is such a profound green house gas, and it has risen from 280ppm to 380ppm over the last century or so (?), why is it not blindingly obvious that human-induced climate change is happening, and had a profound effect already?”

    Well, we are seeing profound effects already in the Arctic and in the Antarctic Peninsula and in mountain glaciers all around the world, but to answer your question, it is not blindingly obvious in more temperate climates because we have not yet seen all of the warming that an increase of 100ppm will produce. This is because so far much of the added warmth has been absorbed by the ocean, which warms very slowly due to its enormous mass. But even if CO2 were to stop increasing tomorrow, that extra 100ppm will remain there for many, perhaps hundreds of years, continuing to add warmth, and as the ocean slowly warms to equilibrium then more of the warming will be felt at the surface. This is what climate scientists mean when they say that there is warming “still in the pipeline.” But, of course, CO2 is not about to stop rising tomorrow or any time soon, so it’s not just the warming “in the pipeline” that we have to worry about.

    “Why should I worry about 450-500ppm?”

    Because the last time there was that much CO2 in the atmosphere Earth, including California, was a much warmer and very different place from what it is now, yet all of our infrastructure has been built to cope with the climate we have now.

    “As far as I know, the climate in California is much like it was in the 1850’s, and are things really much different?”

    Are you sure? You might want to check agricultural records showing a steady long-term trend in lengthening growing season for some crops in California, and northward creep of climate zones suitable for some crops. You might also want to check hydrological records showing decreasing trends in snowpack depth in the Sierra.

    Comment by Jim Eager — 21 Sep 2008 @ 10:31 PM

  98. Re #93: This is somewhat a matter of perspective. Arguably for the more informed among us the time to have gone into a blind panic was twenty years ago when Jim Hansen announced the apparent detection of an anthropogenic signal in global climate. Of course that’s not how scientists prefer to go about things, but after twenty years some of them are beginning to show public signs of impatience. Hansen was first, but encouragingly others seem to be following.

    Comment by Steve Bloom — 22 Sep 2008 @ 1:52 AM

  99. Re 93. Lawrence, yes, the accumulation of heat in the oceans is the primary metric of global warming, but it’s distributed unevenly, and we don’t know how much of it will be diluted in cold waters and how much, when and where it will be released to the atmosphere.

    For the moment, both NAO and PDO will cool the atmosphere for the next 20 years or so.

    We have to wait to see the effects you, Jim Hansen et al are waiting.

    [Response: You are better when you simply misquote papers. The heat going into the ocean is not going to be 'released to the atmosphere' any time soon - it is instead part of what will be the higher OHC in a warmer world. NAO and PDO have little or no correlation to the global mean temperature, and your implication that you have 20 year predictability in either is laughable. And as for Hansen, he predicted decades ago that the OHC data would be rising - many years before the analysis was done. Your predictions don't seem to have been quite as prescient. - gavin]

    Comment by Timo Hämeranta — 22 Sep 2008 @ 2:24 AM

  100. #78 John Mashey:

    [edit] Perhaps you can quote where I said – or even implied – that “this is no problem”. Or that there are “cheap and easy solutions”; indeed I said the opposite (“the very large cost of a closure”). FWIW, I’m a professional engineer with 30 years experience in the design of major civil works, including levees and coastal protection. So I guess, on this subject, I’d be one of those “professionals around here”, no?

    Comment by GlenFergus — 22 Sep 2008 @ 3:24 AM

  101. Mark in SF writes:

    If C02 is such a profound green house gas, and it has risen from 280ppm to 380ppm over the last century or so (?), why is it not blindingly obvious that human-induced climate change is happening, and had a profound effect already?

    It is blindingly obvious.

    Comment by Barton Paul Levenson — 22 Sep 2008 @ 3:51 AM

  102. #83 and #90 – Richard and Dave, thanks for that. I get the logic and agree with it. It would so help if RC would just come out and say it though!

    Come on, tell me – does the article Target CO2 at http://www.realclimate.org/index.php/archives/2008/04/target-co2/ say this or not (also look at #18 there)? Am I being pedantic here? I think it stops short, and a target – however qualified – needs to be made much more explicit from RC’s contributors. At the moment, even many NGOs aren’t heading for

    Comment by Guy — 22 Sep 2008 @ 5:45 AM

  103. Steve you have referred to the Howat paper a number of times noting that the smaller glaciers are providing more output than the largest glaciers. First of all the study is focussed mainly on southeast Greenland glaciers. Secondly our attention has been focussed first on the largest glaciers which makes sense. This paper follows on the heels of another paper I have noted on thinning of marine terminating outlet glaciers. What both papers show is that the thinning and acceleration and consequent ice loss is widespread, and not just associated with a few glaciers. Given this it should not be surprising that the smaller marine terminating outlet glaciers that all do drain the ice sheet, can provide an important volume of ice. It should be noted that this is the point of Howat et al., they are not trying to make the point that the smaller glaciers are more important, as they were not comprehensive in examining all glaciers. But it is key to show that it is marine terminating glaciers that have accelerated and small ones too. With respect to the Jokulhlaup you cite, this paper does not cause an issue with our understanding of the ice sheet. They did not identify a specific frictional melting component. They state the remainder is from frictional melting of the actual subglacier drainage and base flow, without tyring to break that down, which would be impossible in their case. The point is base flow could have and probably was the bigger source. The main weakness I see in the Pfeffer et al, paper is that they do not take advantage of the very latest work to articulate that it is accleration of marine terminating outlet glaciers due to force inbalance that is causing the primay sea level change for the GIS, and not the meltwater lubricating effect that many have confused as a prime contributor. In fact immediately after the release of the paper one of the authors was quoting invoking the now dead notion of the Zwally effect, that is enhanced meltwater lubrication being the key to ice accleration, as the main reason for acceleration.

    Comment by mauri pelto — 22 Sep 2008 @ 7:36 AM

  104. Hey everybody,

    Check out this excellent interview about the arctic with Dr. Walt Meier of NSIDC.

    http://wattsupwiththat.com/2008/09/21/nsidc-s-dr-walt-meier-answers-10-questions/#more-3188

    Dill Weed

    Comment by Dill Weed — 22 Sep 2008 @ 9:11 AM

  105. #98
    Steve,
    Thank you for the link.

    Comment by Aaron Lewis — 22 Sep 2008 @ 11:33 AM

  106. > wattsup

    Take your game card: http://timlambert.org/2005/04/gwsbingo/

    > invoking the now dead notion of the Zwally effect,
    > that is enhanced meltwater lubrication being the
    > key to ice accleration

    Mauri, is this notion dead globally, or for specific conditions? I keep seeing mention of flow under ice in Antarctica, and am wondering if you refer to Greenland conditions or to a more basic understanding of ice flow globally. Pointer welcome, glad to read more. I’m assuming getting these issues solved is going to be major decision for the next IPCC report.

    I’m also curious if there is any anticipated tally of research that will be coming with the conclusion of the International Polar Year and the ANDRILL and other large projects. I realize the huge amount of data constrains what can be written up and how quickly.
    __________________
    ReCaptcha: support advised
    !!

    Comment by Hank Roberts — 22 Sep 2008 @ 12:40 PM

  107. More opportunities for data collection (where glaciers are cold at the base, at least):

    Multiple generations of interglacial lake sediment preserved beneath the Laurentide Ice Sheet

    Author(s): Briner JP, Axford Y, Forman SL, Miller GH , Wolfe AP
    GEOLOGY Volume: 35 Issue: 10 Pages: 887-890 OCT 2007
    DOI: 10.1130/G23812A.1

    Abstract: … beneath portions of the northeastern Laurentide Ice Sheet, characterized by cold-based glaciation, sediment sequences representing multiple interglaciations have been preserved within extant lake basins. Radiocarbon and optically stimulated luminescence dating confirm the antiquity of the sediments, thereby extending the terrestrial paleoenvironmental record of the Canadian Arctic by hundreds of thousands of years. The lake sediment record presented here corroborates numerous recent cosmogenic exposure dating studies indicating complex patterns of erosion beneath polar ice sheets. It also demonstrates that the presence of intact interglacial sediments does not demand unglaciated refugia. Similarly ancient sediments may be preserved in many regions formerly covered by Pleistocene ice sheets.

    Comment by Hank Roberts — 22 Sep 2008 @ 12:54 PM

  108. Guy on “Target CO2″ paper (multiple),

    I’ve been lurking for several months.

    In June I took the current draft of that paper as my starting point to get into current climate science: Start with Hansen, start with the most credible worst-case scenario or lowest-CO2 target proposed, work backwards to see how well supported. Could consequences of 21st century warming really be a lot more dire than in IPCC AR4? I obtained and read 34 of the 89 papers referenced in “Target”, plus another twenty or so further papers referenced in those 34, with a slight emphasis on the Last Interglacial (LIG) as a model for what’s certainly in store under BAU, though it’s very uncertain how long that will take. Plus other papers on Hansen’s website.

    I sympathize with your frustration: “Target” makes a compelling case that we really have to get CO2 down to 350 or below, but most of the IPCC and policy discussion hovers around 450-500 – so who is “right”? While non-SLR consequences like drought, flooding, crops, ecosystem migration and species loss look bad enough, 2m or more sea level rise should be the most dramatic, a good place to focus attention. Ice flow dynamics have to matter a lot, and the IPCC’s 80cm doesn’t include them. However long it took, sea level was 4-6m higher during the LIG, with global mean temperature only 1C or so warmer, and CO2 100 ppm or so less than today’s.

    The Pfeffer paper is helpful, putting plausible constraints on the speed of ice discharge. It’s not the last word, as Gavin notes, but further refinements (which could be higher or lower than 2m by 2100) await more science at both GIS and WAIS, glacier physics, and more comprehensive glacier modeling, which simply requires more time. RC and the other climate scientists cannot say definitively whether Hansen is “right” about 350; rather, I imagine, they’re working as hard as they can to refine the science and the models, and they will be for years.

    I’m concerned there is too much focus on 2100, or only looking at the “next 100-150 years”, presumably because most people just can’t handle worrying about farther ahead. With all the latencies in ocean heat content and other parts of that “pipeline”, 450 ppm or higher is guaranteed to put us back in the Last Interglacial, at 4-6m higher sea level within centuries to a few millennia. The only protection against that would be – at some point – getting CO2 levels back down around 280-300 ppm. So at some point in time Hansen’s 350 almost has to be an upper limit, as he says.

    Even if SLR is “only” +1-2m by 2100, if we get to that point with 400 ppm or more CO2, we’re probably also locked in to +2-4m by 2200. Most people are aware of places and events 2000 years ago, and a lot of history in between. Maybe they would respond to arguments about a business-as-usual world of 2200, 2500, 4000 AD.

    Comment by srooke — 22 Sep 2008 @ 1:51 PM

  109. Re 99. Gavin, you do now I don’t make predictions. You do know I always stress the uncertain future. You do know I (almost) always refer to peer-reviewed studies.

    You do know the oceans release heat daily, weekly, seasonally, and in various oscillations and cycles, etc. You do know, too:

    “…Observational and computational progress in physical oceanography, however, over the last 30 years has rendered obsolete the old idea that the fluid ocean is a slowly changing, passive, almost geological system. Instead, it is a dynamically active, essentially turbulent fluid, in which large-scale tracer patterns arise from active turbulence and do not necessarily imply domination of the physics and climate system by large-scale flow fields….”

    Ref: Wunsch, Carl, 2007. The Past and Future Ocean Circulation From a Contemporary Perspective. Chapter in Schmittner, Andreas, John Chiang, Sidney Hemmings, Editors, 2007. Ocean Circulation: Mechanisms and Impacts. AGU Geophysical Monograph Series Vol. 173, 2007, online http://ocean.mit.edu/~cwunsch/papersonline/present_pastocean_rev_2april.pdf

    Well, I see misprint ‘2’ instead of ‘1’ in my quick writing, please see:

    “North Atlantic SST and European and North American surface temperatures will cool slightly, whereas tropical Pacific SST will remain almost unchanged. Our results suggest that global surface temperature may not increase over the next decade, as natural climate variations in the North Atlantic and tropical Pacific temporarily offset the projected anthropogenic warming.”

    Ref: Keenlyside, N.S., M. Latif, J. Jungclaus, L. Kornblueh, and E. Roeckner, 2008. Advancing decadal-scale climate prediction in the North Atlantic sector. Nature Vol. 453, No 7191, pp. 84-88, May 1, 2008

    You do know I always say, it remains to be seen…

    [Response: Picture Timo talking to Galileo as he is walking up the Tower of Pisa with his wooden and lead balls:
    Galileo: I predict that when dropped at the same time, the balls will hit the ground after an equal amount of time.
    Timo: But have you seen this paper on the wind?
    Galileo: I'm assuming that the winds are a negligible effect.
    Timo: But what about the uncertainties in time-keeping apparatus - Here's a paper about clocks drifting.
    Galileo: Obviously I am only talking about time differences that detectable with current technology.
    Timo: here's another paper about variations in the gravity field across the planet, and here's one about the impact of operator error in ball dropping stations, and here's another on cosmic ray impacts on small round objects in the air.
    Galilieo: None of those things are relevant.
    Timo: Well, all I'm saying is that we'll have to wait and see.
    Galileo: Hmmm.... (drops balls and they both land at the same time)... See, I was right.
    Timo: Here's a paper on the non-reproducibility of ball dropping experiments.
    Galileo: Sigh.....
    - gavin]

    Comment by Timo Hämeranta — 22 Sep 2008 @ 3:11 PM

  110. Re #104: That’s a nice try by Walt, meaning that his information is, um, sea ice off a polar bear’s back as far as the regular commenters there are concerned. I assume the hope is that many of those who read but do not comment are less set in their ways.

    This is a good place to mention some recent results (WaPo story here, paper here) finding that conservatives (however defined) have an internal dialog such that when they hear information refuting one of their beliefs they tend to become *more* confirmed in it. This effect is not apparent among other segments of society. I notice that one of the authors has a quite active blog.

    While I’m at it, and also relevant to some of the other discussion above, this paper (“Are debatable scientific questions debatable?“) is good advice (abstract):

    “Scientists often find difficulty in engaging in formal public debate about transcientific social issues. Although science is a highly disputatious institution, public argumentation amongst scientists follows very different conventional practices from those that rule in political and legal arenas. Amongst other differentiating features, scientific disputes are typically conducted in writing rather than orally, they are not sharply polarised or formally adversarial, they are seldom addressed to a specific proposition, and they do not reach decisive closure. As a result, the rhetorical style that scientists learn from participation in such practises is not well adapted to the established format of socio-political ‘debate’. For scientists to contribute effectively to such debates, they must learn new ways of making their particular type of knowledge convincing in unfamiliar intellectual and social contexts.”

    Finally, since I feel compelled to complete the trifecta, there’s this paper (“Understanding Public Complacency About Climate Change: Adults’ mental models of climate change violate conservation of matter“) finding that a substantial majority of intelligent humans (the group studied was MIT grad students) have no grasp of stock and flow.

    Comment by Steve Bloom — 22 Sep 2008 @ 3:19 PM

  111. to John Mashey #61 and Joseph O’Sullivan #84

    I know that 6ft would probably be a big deaL, I as trying to visualize how big given that I live in the city as well. The map application Mashey referenced is the google widget I was thinking of, but I was wondering if anyone had links to more accurate readings than that.

    Joseph, I was thinking at what point does the Financial District become like Venice? Pumping out the subway is bad enough as it is. I was wondering at what point do we have to retrofit some tunnels or maybe restore the old tracks on the Brooklyn Bridge, and maybe add them to the Queensboro (which strike me as more feasible projects). I like underground as much as the next guy, but going back to El trains may be necessary in many areas.

    Comment by Jess — 22 Sep 2008 @ 6:18 PM

  112. #111
    Jess,
    OK, you have upgraded NYC, including all the underground electrical and communications utilities.
    What are you going to eat?

    A SLR of six feet is enough to take out much of the fuel, fertilizer and pesticide production facilities used by modern agriculture. Thus, you not only have to find the capital to upgrade NYC but also much of the petrochemical industry on the Gulf Coast.

    What are you going to wear? Most modern fiber is made near current sea level.

    These days everything has a computer chip in it. Where is the plastic used to make the carrier for that computer chip made? Near sea level. Where is your shampoo made? And, the bottle it is shipped in?

    And, out here in California where we grow some of the food of the food that NYC eats, it would not take much of a SLR to knock out the water supplies for irrigation and our drinking water.

    It will be expensive for NYC to maintain its lifestyle. Of course, you are lucky, your airport is a couple of feet higher than SFO or OAK.

    Any of these is fixable. However, if they come faster than we expect or they come all at the same time, then we are going to be in over load mode.

    Comment by Aaron Lewis — 22 Sep 2008 @ 8:37 PM

  113. Steve (110), the 3rd referenced study concluded that highly educated (including in the sciences) people have some mental abnormality that does not permit them to understand that a net positive inflow increases stuff at hand. This being the only way the researchers could explain the subjects’ seeming dichotomy in their comprehension of AGW in its entirety. I find that incredibly pedantic, short-sighted, and ludicrous prima facie.

    Your 2nd referenced study presents some cogent and significant observations that affect the scientist operating in the non-scientific world.

    But I find the contention in 1st reference that only “conservatives” dig in when challenged equally silly prima facie.

    Comment by Rod B — 22 Sep 2008 @ 8:49 PM

  114. More melt-down problems for Wall Street? I just happened across this (still in press, I believe):

    Yin, J., M. E. Schlesinger, and R. J. Stouffer, 2008:

    Rapid sea level rise threatens the Northeast Coast of the United States. Nature. 8/08.

    Abstract: “Human-induced climate change could cause sea level rise (SLR) and slow down the Atlantic meridional overturning circulation (MOC). Low-lying Florida and western Europe are often evoked as the vulnerable regions to these changes. Here based on a state-of-the-art climate model, we report a rapid SLR on the northeast coast of the U.S. during the 21st century. The rapid SLR is projected under various IPCC greenhouse-gas (GHG) emission scenarios including low, medium and high rates. A dynamic (relative to the geoid) SLR induced by the weakening of the MOC is imposed on the global steric (density-dependent) and eustatic (mass-dependent) SLRs, thereby greatly enhancing the SLR rate on the northeast coast of the U.S. The future changes of sea level and ocean circulation therefore pose a great and imminent threat to this heavily populated area.”

    It doesn’t say how much, unfortunately.

    Comment by Steve Bloom — 22 Sep 2008 @ 8:50 PM

  115. Re #113: Rod, I would expect that a conservative denialist would find both of those results objectionable in the extreme. Do keep digging, though.

    Comment by Steve Bloom — 22 Sep 2008 @ 10:21 PM

  116. There was a question asked up-thread about ocean acidification, and serendipitously a new paper has just appeared (press release pasted below). Pertinent to another topic these results seem quite consistent with Hansen’s call for 350 ppm, noting the finding that “even if atmospheric CO2 stabilizes at the current level of 380 ppm, fewer than half of existing coral reef will remain in such an environment.” Putting things in a context of “avoidig dangerous climate change” (referring to the UNFCCC) is also consistent with Hansen’s approach.

    ————————–

    Modest CO2 cutbacks may be too little, too late for coral reefs

    Stanford, CA—How much carbon dioxide is too much? According to United Nations Framework Convention on Climate Change (UNFCCC) greenhouse gases in the atmosphere need to be stabilized at levels low enough to “prevent dangerous anthropogenic interference with the climate system.” But scientists have come to realize that an even more acute danger than climate change is lurking in the world’s oceans—one that is likely to be triggered by CO2 levels that are modest by climate standards.

    Ocean acidification could devastate coral reefs and other marine ecosystems even if atmospheric carbon dioxide stabilizes at 450 ppm, a level well below that of many climate change forecasts, report chemical oceanographers Long Cao and Ken Caldeira of the Carnegie Institution’s Department of Global Ecology in the journal Geophysical Research Letters.

    The researchers’ conclusions are based on computer simulations of ocean chemistry stabilized at atmospheric CO2 levels ranging from 280 parts per million (pre-industrial levels) to 2000 ppm. Present levels are 380 ppm and rapidly rising due to accelerating emissions from human activities, primarily the burning of fossil fuels.

    This study was initiated as a result of Caldeira’s testimony before a Congressional subcommittee on Fisheries, Wildlife and Oceans in April of 2007. At that time he was asked what stabilization level would be needed to preserve the marine environment, but had to answer that no such study had yet addressed that question. Cao and Caldeira’s study helps fill the gap.

    Atmospheric CO2 absorbed by the oceans’ surface water produces carbonic acid, the same acid that gives soft drinks their fizz, making certain carbonate minerals dissolve more readily in seawater. This is especially true for aragonite, the mineral used by corals and many other marine organisms to grow their skeletons. For corals to be able to build reefs, which requires rapid growth and strong skeletons, the surrounding water needs to be highly supersaturated with aragonite.

    “Before the industrial revolution, over 98% of warm water coral reefs were surrounded by open ocean waters at least 3.5 times supersaturated with aragonite” says Cao. “But even if atmospheric CO2 stabilizes at the current level of 380 ppm, fewer than half of existing coral reef will remain in such an environment. If the levels stabilize at 450 ppm, fewer than 10% of reefs would be in waters with the kind of chemistry that has sustained coral reefs in the past.”

    For the ecologically productive cold waters near the poles, the prospects are equally grim, says Cao. “At atmospheric CO2 levels as low as 450 ppm, large parts of the Southern Ocean, the Arctic Ocean, and the North Pacific would experience a rise in acidity that would violate US Environmental Protection Agency water quality standards.” Under those conditions the shells of many marine organisms would dissolve, including those at the base of the food chain.

    “If current trends in CO2 emissions continue unabated,” says Caldeira, “in the next few decades, we will produce chemical conditions in the oceans that have not been seen for tens of millions of years. We are doing something very profound to our oceans. Ecosystems like coral reefs that have been around for many millions of years just won’t be able to cope with the change.”

    “When you go to the seashore, the oceans seem huge,” he adds. “It’s hard to imagine we could wreck it all. But if we want our children to enjoy a healthy ocean, we need to start cutting carbon emissions now.”

    Comment by Steve Bloom — 22 Sep 2008 @ 10:39 PM

  117. On the topic of a “shutdown” of the “thermohaline circulation,” I’d be interested in seeing a post that summarizes the current thinking. The Lenton et al “Tipping Elements” paper from earlier this year puts more emphasis on it than AR4.
    http://www.pnas.org/content/105/6/1786.full.pdf

    Just wondering what Realclimate’s thoughts are on this topic.

    Comment by cce — 23 Sep 2008 @ 1:32 AM

  118. #108 – Srooke, thanks so much for your contribution – and sympathies! And I totally agree with timescales – most climate science projections stop at 2100, leading to this bizarre logical fallacy among the media at least that EVERYTHING stops there! If SLR and temperature are both still rising by then, the game is surely up. And what ethical gounds are there for caring less about the world after 2100? I understand a reduced emotional response, but that has no moral or intellectual authority. If our actions today only cataclysmically affect people in 400 years time, that’s a real problem in terms of galvanising a response.

    I understand the ever increasing problem of probabilities beyond 2100, but if we are at that point in a world beyond the possibility of any human intervention, this point does need re-inforcing.

    And I also sympathise with the problem of not knowing enough re the 350ppm target. And yet Hansen has weighed in, and policies have to be forged by December 2009, so waiting for more data before saying anything at all isn’t really an option. A simple “that seems a reasonable conclusion on the basis of available evidence” (or not!) from colleagues would massively help.

    12 attempts at a Real Climate specific response to 350ppm in 14 days! I promise I won’t throw my toys out of the pram or be rude, but I must keep asking…

    Comment by Guy — 23 Sep 2008 @ 3:32 AM

  119. The Independent in the UK is leading with this – http://www.independent.co.uk/environment/climate-change/exclusive-the-methane-time-bomb-938932.html

    Highlights:

    Exclusive: The methane time bomb

    The first evidence that millions of tons of a greenhouse gas 20 times more potent than carbon dioxide is being released into the atmosphere from beneath the Arctic seabed has been discovered by scientists.

    The Independent has been passed details of preliminary findings suggesting that massive deposits of sub-sea methane are bubbling to the surface as the Arctic region becomes warmer and its ice retreats.

    In the past few days, the researchers have seen areas of sea foaming with gas bubbling up through “methane chimneys” rising from the sea floor. They believe that the sub-sea layer of permafrost, which has acted like a “lid” to prevent the gas from escaping, has melted away to allow methane to rise from underground deposits formed before the last ice age.

    They have warned that this is likely to be linked with the rapid warming that the region has experienced in recent years.

    Orjan Gustafsson of Stockholm University in Sweden, one of the leaders of the expedition, described the scale of the methane emissions in an email exchange sent from the Russian research ship Jacob Smirnitskyi.

    “We had a hectic finishing of the sampling programme yesterday and this past night,” said Dr Gustafsson. “An extensive area of intense methane release was found. At earlier sites we had found elevated levels of dissolved methane. Yesterday, for the first time, we documented a field where the release was so intense that the methane did not have time to dissolve into the seawater but was rising as methane bubbles to the sea surface. These ‘methane chimneys’ were documented on echo sounder and with seismic [instruments].”

    At some locations, methane concentrations reached 100 times background levels. These anomalies have been seen in the East Siberian Sea and the Laptev Sea, covering several tens of thousands of square kilometres, amounting to millions of tons of methane, said Dr Gustafsson. “This may be of the same magnitude as presently estimated from the global ocean,” he said. “Nobody knows how many more such areas exist on the extensive East Siberian continental shelves.

    The preliminary findings of the International Siberian Shelf Study 2008, being prepared for publication by the American Geophysical Union, are being overseen by Igor Semiletov of the Far-Eastern branch of the Russian Academy of Sciences. Since 1994, he has led about 10 expeditions in the Laptev Sea but during the 1990s he did not detect any elevated levels of methane. However, since 2003 he reported a rising number of methane “hotspots”, which have now been confirmed using more sensitive instruments on board the Jacob Smirnitskyi.

    Comment by Guy — 23 Sep 2008 @ 3:47 AM

  120. Apparently ocean acidification will affect more than just shells (excerpt from a post on the blog of EPOCA — the European Project on Ocean Acifification):

    “Rising acidification of the ocean could reduce fertilisation of marine invertebrates and might eventually wipe out colonies of sea urchins, lobsters, mussels and oysters, according to a study.

    “Scientists knew that ocean acidification was eating away at the shells of marine animals, but the new study has found that rising acidity hindered marine sperm from swimming to and fertilising eggs in the ocean.”

    Comment by Steve Bloom — 23 Sep 2008 @ 4:40 AM

  121. 119 Guy, the quote of methane strength is wrongish. Methane degrades at a fairly constant total amount, not a constant percent. Thus, double methane concentrations, and the half-life of methane doubles. Since methane is so powerful (I’ve searched but never found an instantaneous strength of CH4 VS CO2), this could change the 100 year multiplier from 23 (as it is currently) to 100 PDQ. Yet another non-linear response of a non-linear response of a linear input.

    [Response: The effect is real, but it isn't as strong as you suggest. Calculations in Table 1 in Schmidt and Shindell (2003) suggest you need to multiply concentrations by a factor of 10 to get a doubling of the lifetime. - gavin]

    Comment by RichardC — 23 Sep 2008 @ 8:11 AM

  122. 118 A new paper from the Tyndall Centre suggests that we are heading for 650 ppm.

    http://www.tyndall.ac.uk/media/news/latest_news.shtml

    Add in the methane belching (post 119) from the East Siberian and Laptev Seas and 650 ppm may be on the low side.

    Comment by 4 Degrees plus — 23 Sep 2008 @ 8:15 AM

  123. Re 117 ccc, please see

    Zickfeld, Kirsten, Anders Levermann, M. Granger Morgan, Till Kuhlbrodt, Stefan Rahmstorf, and David W. Keith, 2007. Expert judgements on the response of the Atlantic meridional overturning circulation to climate change. Climatic Change Vol. 82, No 3-4, pp. 235-265, June 2007

    Abstract

    We present results from detailed interviews with 12 leading climate scientists about the possible effects of global climate change on the Atlantic Meridional Overturning Circulation (AMOC). The elicitation sought to examine the range of opinions within the climatic research community about the physical processes that determine the current strength of the AMOC, its future evolution in a changing climate and the consequences of potential AMOC changes. Experts assign different relative importance to physical processes which determine the present-day strength of the AMOC as well as to forcing factors which determine its future evolution under climate change. Many processes and factors deemed important are assessed as poorly known and insufficiently represented in state-of-the-art climate models. All experts anticipate a weakening of the AMOC under scenarios of increase of greenhouse gas concentrations. Two experts expect a permanent collapse of the AMOC as the most likely response under a 4×CO2 scenario. Assuming a global mean temperature increase in the year 2100 of 4 K, eight experts assess the probability of triggering an AMOC collapse as significantly different from zero, three of them as larger than 40%. Elicited consequences of AMOC reduction include strong changes in temperature, precipitation distribution and sea level in the North Atlantic area. It is expected that an appropriately designed research program, with emphasis on long-term observations and coupled climate modeling, would contribute to substantially reduce uncertainty about the future evolution of the AMOC.

    Further:

    Drijfhout, Sybren S., W. Hazeleger, F. Selten and R. Haarsma, 2008. Future changes in internal Atlantic Meridional Overturning Circulation variability. Climate Dynamics Vol. 30, No 4, pp. 407-419, March 2008, online http://www.knmi.nl/publications/fulltexts/climdyn08.pdf

    Abstract

    The response of the internal variability of the Atlantic Meridional Overturning Circulation (MOC) to enhanced atmospheric greenhouse gas concentrations has been estimated from an ensemble of climate change scenario runs. In the model, enhanced greenhouse forcing results in a weaker and shallower MOC with reduced internal variability. At the same time at 55°N between 0 and 1,000 m the overturning increases as a result of a change in the area of convection. In a warmer world, new regions of deepwater formation form further north due to the poleward retreat of the sea-ice boundary. The dominant pattern of internal MOC-variability consists of a monopole centered around 35°N. Due to anthropogenic warming this monopole shifts poleward. The shift is associated with a stronger relation between MOC-variations and heat flux variations over the subpolar gyre. In old convective sites (Labrador Sea) convection becomes more irregular which leads to enhanced heat flux variability. In new convective sites heat flux variations initially are related to sea-ice variations. When the sea-ice coverage further decreases they become associated with (irregular) deepwater formation. Both processes act to tighten the relation between subpolar surface heat flux variability and MOC-variability, resulting in a poleward shift of the latter.

    Comment by Timo Hämeranta — 23 Sep 2008 @ 8:35 AM

  124. Re: 121: Methane lifetime is a function of the oxidative capacity of the atmosphere (namely, hydroxyl radical abundance).

    Indeed, increased methane emissions lead to decreased hydroxyl concentrations, but it isn’t a straightforward calculation to determine exactly how much hydroxyl disappears, or how much methane lifetime increases due to that. Also, other factors effect hydroxyl concentrations: NOx emissions, for example.

    Note that increased methane also leads to increased ozone concentrations, for added radiative forcing bang for your methane buck.

    The last time I looked up comparative methane and CO2 forcings, I found a ratio of 21 (methane:CO2) by molecule or a ratio of 60 (methane:CO2) by mass.

    Comment by Marcus — 23 Sep 2008 @ 9:00 AM

  125. 12 attempts at a Real Climate specific response to 350ppm in 14 days! I promise I won’t throw my toys out of the pram or be rude, but I must keep asking…

    And I shall keep asking, has it ever occured to you to do your own research, instead of demanding that others do it for you? Science is about discovery, previously unknown phenomenon become revealed, previously unanswered questions become reasonable, revealing more questions.

    After a while, the constant nagging gets tiresome. Clearly we want to reduce atmospheric carbon dioxide concentration, once we have that ability, the final equilibrium number is pretty much meaningless, call it anything around 300 ppm or so. 350 is probably a little on the high side. Captcha : track esperanto

    Comment by Thomas Lee Elifritz — 23 Sep 2008 @ 9:38 AM

  126. #122 – that Tyndall paper is terrifying. I guess that’s why Hansen says coal phase-out is the only possible way…

    [All: I've closed comments for now, as I can't keep up with responses. More discussion can continue in response to the next post on sea level rise. --eric]

    Comment by Guy — 23 Sep 2008 @ 9:40 AM

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