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How much will sea level rise?

Filed under: — group @ 4 September 2008 - (Español) (Italian)

… is the question people have been putting a lot of thought into since the IPCC AR4 report came out. We analysed what was in the report quite carefully at the time and pointed out that the allowance for dynamic ice sheet processes was very uncertain, and actually precluded setting a upper limit on what might be expected. The numbers that appeared in some headlines (up to 59 cm by 2100) did not take that uncertainty into account.

In a more recent paper, our own Stefan Rahmstorf used a simple regression model to suggest that sea level rise (SLR) could reach 0.5 to 1.4 meters above 1990 levels by 2100, but this did not consider individual processes like dynamic ice sheet changes, being only based on how global sea level has been linked to global warming over the past 120 years. As Stefan discussed, any non-linear or threshold behavior of ice sheets could lead to sea level rising faster than this estimate. Thus, otherwise quite conservative voices have been stressing the ‘unknown unknown’ nature of this problem and suggesting that, based on paleo-data (for instance), it was really hard to rule out sea level rises measured in feet, and not in inches. (Note too, the SLR is very much a lagging indicator, and will continue for centuries past the time that atmospheric temperatures have stabilised).

The first paper to really try and assess the future limits on dynamic ice sheet loss appeared in Science this week. Pfeffer et al looked at the exit glaciers for Greenland and West Antarctica and made some back of the envelope calculations of how quickly the ice sheets could dynamically drain.

Good news: they rule out more than 2 meters of sea level coming from Greenland alone in the next century. This is however more than anyone has ever suggested and would be comparable to the amount that disappeared at the Eemian (125,000 years ago) (see this post for more on that).

Bad news: they can’t rule out up to 2 meters in total.

In summary, they estimate that including dynamic ice sheet processes gives projected SLR at 2100 somewhere in the 80 cm to 2 meter range, and suggest that 80 cm should be the ‘default’ value. This is remarkable in a number of ways – first, these are the highest estimates of sea level rise by 2100 that has been published in the literature to date, and secondly, while they don’t take into account the full uncertainty in other aspects of sea level rise considered by IPCC, their numbers are significantly higher in any case. And this week the Dutch ‘Delta Commission‘ published its estimate of sea level rise that the Dutch need to plan for (p111): 55 to 110 cm globally and a bit more for Holland, based on a large number of scientists’ input. [Clarifying update: this is meant to be a “high end estimate”.]

Lest readers think this is no big deal, the estimates for the number of people who would be affected by 1 meter of sea level rise is more than 100 million – mainly in Asia. Of some recent relevance is the fact that the storm surge caused by Gustav in New Orleans was within 1 foot of the top of the levees. Another 3 ft caused by global sea level rise would have put a lot more water into the ‘bowl’.

Thus better estimates of sea level rise from ice sheets remain a high priority for the climate community. More sophisticated models and deeper understanding are coming along and hopefully those results will be out soon.

We were going to leave it at that, but we’ve just seen the initial media coverage where this result is being spun as a downgrading of predictions! (exemplified by this Reuters piece, drawing mainly from the U. Colorado press release). This is completely backwards. We stress that no-one (and we mean no-one) has published an informed estimate of more than 2 meters of sea level rise by 2100. Tellingly, the statement in the paper that suggests otherwise has no reference.

There have certainly been incorrect assertions and headlines implying that 20 ft of sea level by 2100 was expected, but they are mostly based on a confusion of a transient rise with the eventual sea level rise which might take hundreds to thousands of years. And before someone gets up to say Al Gore, we’ll point out preemptively that he made no prediction for 2100 or any other timescale. The nearest thing I can find is Jim Hansen who states that “it [is] almost inconceivable that BAU climate change would not yield a sea level change of the order of meters on the century timescale”. But that is neither a specific prediction for 2100, nor necessarily one that is out of line with the Pfeffer et al’s bounds.

Thus, this media reporting stands as a classic example of how scientists get caught up trying to counter supposed myths but end up perpetuating others, and miss an opportunity to actually educate the public. The problem is not that people think that we will get 6 meters of sea level rise this century, it’s that they don’t think there’ll be anything to speak of. Headlines like that in the Reuters piece (or National Geographic) are therefore doing a fundamental disservice to the public understanding of the problem.

Update: Marc Roberts sends along this cartoon illustrating the problem… (click for full size).

386 Responses to “How much will sea level rise?”

  1. 251

    re #247–

    Agreed. He offers whiny demand, shrill accusation and lots of confusion–and I mean *lots*. I’m not learning anything from him, and he is clearly not here to learn himself.

  2. 252
    Mauri Pelto says:

    The comments section do not do justice to some of the excellent research coming out of Greenland. I cannot believe I am reading about rain weakening a glacier. How many days have I spent in the rain on a glacier, including three inches in one day this summer. how many glaciers exist in a temperate climate where rain is the dominant weather pattern for 200-300 days a year from Patagonia to Alaska. Obviously rain does lead to surface melt and but it does not weaken a glacier. We had the opportunity this August, not the first time, to hideout in a glacier cave, stream carved channel at base of glacier, during a rainstorm. Even with all of that rain, and the air temp of 10 C, outside the cave, it is interesting to see the new ice on the floor of the cave and at the glacier-becrock interface. Most of the good research is focussed on the acceleration of marine terminating glaciers, a detailed analysis of these is needed here soon, but not today. In terms of melting a recent paper examines the heat balance terms leading to melting of the Greenland Ice Sheet. They identify that depending on your elevation the terms vary in importance. However, short wave radiation is the domninant term, with sensible heat flux becoming important at the lower elevations and latent heat flux being minor. Note Figure 7 in the paper.

  3. 253
    Marcos Mattis says:

    Having done a bit more study on holocene sea levels it appears that there are now a number of studies showing GLOBAL sea levels up to 6m higher than present as recently as 8000-3500BC. For example: amongst other studies, with variations of between +0.5m and +6m above present sea level – often in areas which have had little/no geological uplift in the last 10000yrs.

    Does this not prove that recent mid-holocene temperatures may have been higher globally than present?
    It is often cited that equatorial regions may have been cooler during the mid-holocene warm period and therefore overall global average temps were NOT above present – so what climate mechanism would allow this and could [said mechanism] repeat itself?


    [Response: Global sea level was not 6m higher 8000 years ago. Perhaps you would like to point out where the Greenland sized ice sheet that must have grown since then could be found? The best global estimates instead indicate a gentle rise throughout this whole period. As for these two shells from India, it’s most likely that either local uplift has been underestimated, or that assessments of the local interpretation might be incomplete. This is a difficult thing to do accurately, but the weight of evidence is clearly against a Holocene sea level stand higher than today. – gavin]

  4. 254
    xxx says:

    Re 249. He is not alone.

  5. 255
    Marcos Mattis says:

    RE: Gavin,

    agreed that there is uncertainty on uplift but I would not be so quick to dimiss ALL studies on mid-holocene sea levels because they may ALL have uplift wrong – and there are quite a few which I will try and find again. I only saved the one I posted above! As I said they vary between 0.5m and 6m so big difference of opinion on all.

    Your earlier story on the mid-holocene:

    makes strong case that mid-holocene warming was northern hemisphere only, but I haven’t seen evidence there was so much orbital variation 3500 years ago (I pick this date as it is within the range as a date having possibly higher sea level than now). Fair enough to say milti-millennial variations, Milankovich, precession etc, but if you could point me to a study that cites orbital differences 3500 years ago I would rest easier on this matter!


    [Response: Orbital variations peaked in the early Holocene, so I’m not sure what you are looking for. Look at Chapter 6 (fig 6.9) for an assessment of Holocene changes by latitude. – gavin]

  6. 256

    It seems that we may be having some anomalies in post numbers. I was agreeing with Ron Taylor, #248, not #247. (If the confusion is mine, then I apologize for an unnecessary post.) But it does seem that several other posts are off by a number or two, and it does make the discussion noticeably harder to follow. For my part, I will try to be really scrupulous in getting the right number up there.

    [Response: It’s related to the moderation of comments – not your fault. But feel free to use the permalink for each comment as a link to a reference. That doesn’t change. – gavin]

  7. 257

    Richard Wakefield posts:

    So in other words no meaurable effect at all. Problem is, we cannot rewind the clock and take our CO2 out and see what happens can we.

    Well, yes, actually, we can. Just run a GCM simulation of the period with and without rising CO2. dT = B – A. Discuss.

    Thus I maintain, 1850-1945 CO2 emissions had virtually NO effect on the temperature. It would have risen anyway.

    Due to what? The sun accounts for some of it, but not all of it. Volcanoes and industrial aerosols are negative forcings. Where is the energy coming from in your model?

  8. 258
    sidd says:

    Mauri Pelto wrote on 11 September 2008 at 6:52 am:

    thank you very much for the reference, this is precisely the kind of data i was asking about.

    on another note: are their any new (this month) data on the Wilkins ice shelf in WAIS ? the last i saw, there was only a small neck of ice sheet unbroken.

  9. 259
    Jim Eager says:

    Re Barton @257, Richard has no model, only rhetoric.

  10. 260
    tamino says:

    Volcanoes and industrial aerosols are negative forcings.

    But the absence of volcanic eruptions can behave as a positive forcing when the system has a component with a long time constant. The early 20th-century lull in volcanic activity is at least partially responsible for early 20th century warming.

    Just for laughs, I ran the volcanic forcing estimates from GISS through a zero-dimensional TWO-component model, with a short time constant for one component (a la atmosphere) and a long time constant (30 yr) for the other (a al oceans). I was surprised at the size of the warming caused by the lull in volcanic forcing for the early 20th century.

    However, I very much doubt that the anthropogenic impact during the early 20th century was nothing at all. CO2 levels were notably higher than pre-industrial, and the radiative forcing of that CO2 is not zero.

  11. 261

    Re #252 where Mauri wrote: “I cannot believe I am reading about rain weakening a glacier.”

    I presume that you are referring to my post #242, where I wrote “Ben Nevis in Scotland, roughly the same height as the Greenland ice sheet receives 4 m (12 feet) of precipitation per year.”

    Obviously, I did not explain what I was tying to say very well. I was not arguing that the rain will melt the ice. I was arguing that water vapour would melt the ice by losing its latent heat of condensation. The problem is to estimate how much water vapour there would be available to do that. Since the rain falling on Ben Nevis originated as water vapour that had been carried there by winds, then that gives a (very) rough estimate of the amount of water vapour that would be available to melt the ice, provided that it did not condense and fall as rain first.

    Once the water vapour does condense, then the rain will only be able to transfer sensible heat to the ice. Even if the rain is 10 degs. C warmer than the ice it will still only melt 10/333 grams of ice for every gram of water. Water vapour melts 2500/333 grams of ice for every gram of water vapour.

    FWIIW, I have just checked in Sharp, Robert P. (1960) “Glaciers” , Condon Lectures, Oregon State System of Higher Education, Eugene, Oregon and on page 22 he shows the same calculations as mine for the relative effects of rain and water vapour.

    I’ve read Pfeffer et al. and they assume that surface melt will remain constant, hence it is not surprising we disagree. They certainly do not consider the effects of the Arctic sea ice disappearing, which now seems inevitable.

    I admit I am surprised by figure 7 from Van dem Broke et al. where sensible heat far exceeds latent heat gain from the air. I can only assume that the air is extemely dry, since it is originating in the polar vortex and passing mainly over land and cold sea ice on its route to west Greenland. Without the Arctic sea ice, the air will pass over a wet Arctic ocean and so will be more humid than it is at present.

    One problem with science these days is that it is extremely compartmentalised. Those who know about glaciers work separately from those who work on sea ice. The consequences to the general circulation from loss of sea ice is yet another discipline. As an amateur I feel it is my duty to wave a red flag when I see an obstruction on the railway track of which the engine driver and the signal box are unaware.

    Cheers, Alastair.

  12. 262

    Thanks, Gavin. I hate to display the full extent of my naivete here, but–so I can click on the date/time line to pull up a index number for the comment, such as this one for my #256: index.php?p=598#comment-98264

    Should I just paste it in as I did above, or is there a slicker/clearer way to do this?

    [Response: Use html tags: <a href=”#comment-98264″ > </a> like so. – gavin]

  13. 263
    Aaron Lewis says:

    Hank ,

    Personal communication from an engineering manager at a large government agency. He writes and reviews Requests For Proposals for both state and federal projects in the south-western US. RFPs are confidential documents. I do not know which project he was working on at that time.

    Normally, an engineer could base his design on historical climate data. However, if he had reasonable cause to believe that such a design basis would not protect the public safety, then it is not an acceptable basis of design. There is a reasonable expectation of SLR, thus historical data is not a defendable basis of design.

    It was late at night, and he was stressed enough that he had switched from merlot to brandy.

    The IPCC SLR estimates do not contain dynamic ice movements. Dynamic ice sheet movements are a reasonably foreseeable factor, and therefore must be considered in the development of the design basis of critical public safety infrastructure. I think everyone is in agreement on that. I think everyone is in agreement that not much ice can melt in place. The question is whether there are any mechanisms that would allow substantial volumes of ice to fall (WAIS) or be flushed into the sea (GIS).

    We have never seen the breakup an ice sheet first hand. Thus, we cannot rely on what is familiar. We have to look at physics and material science. We need to do this in a hurry, because the engineering managers are drinking up all of our brandy

  14. 264
    Hank Roberts says:

    > “99.9999 percent”

    I can’t find it with the online search tools I know how to use. I’d guess that is a wish in an RFP — some drafter is trying to get some contractor to promise them an impossible result. If it’s specified as being assurance about the _future_ two centuries rather than the historical experience, it’s even more wishful.

    Any legal requirement would be public information and ought to show up in the indexes. That’s all I can say.

    As always, trust only after you can verify what people claim.

  15. 265

    Re #256 Kevin,

    I was confused by the number you used since you seemed to be agreeing with Richard Wakefield response to me :-(

    But I thought I would mention that if you use the name the person as well as the post number then that avoids most confusions. I think most regulars do that anyway, having been caught out by the renumbering ourselves.


    Cheers, Alastair.

  16. 266
    Hank Roberts says:

    > 99.9999

    And I do empathize with your engineer friend. If he’s seriously trying to design for the worst case possible in the next 200 years, I guess the question is whether his customers’ grandchildren are going to experience anything as extreme as a methane clathrate blowout and rapid change like the PETM may have had.

    The first two here are cautionary. I can’t imagine designing infrastructure for this:

    If you think this is at all likely, you’ll want to go shopping for something well away from most of the troubles — say a large family-owned ranch in Paraguay atop the Acuifero Guarani with a nice big landing strip on it. But who’d think that far ahead, eh?

  17. 267
    Lennart says:

    According to the recent report by the Dutch Delta Commission SLR in a worst-case scenario could be 1.3 meters in year 2100 and 4 meters in 2200, based on the latest scientific insights. But what does this mean for the period after 2200? Could SLR stabilize at around 6 meters, for example, by year 2300 or 2500? Or could it continue, or even accelerate, to 8 meters by year 2300 and 12 meters by 2400? Now Pfeffer e.a. say it could be 2 meters by year 2100, so maybe it could be 6 meters by 2200 and 12 meters by 2300?

    I’m also wondering how to interpret Table 1 in Lenton e.a. (2008), “Tipping elements”:

    Looking at the GIS and WAIS figures, do they mean that in a worst-case SLR could be a maximum of 12 meters by year 2300? Or is this too pessimistic an interpretation? What would be a more appropriate one?

  18. 268
    Ron Taylor says:

    Aaron Lewis makes a valuable point, which brings up once again the difference between scientific conservatism and engineering conservatism. The scientist does not want to say more than he can credibly demonstrate to be true. The engineer has to consider the risk associated with any outcome that is “reasonably” probable. And I assume that the greater the risk, then the lower the probabilities that have to be taken into account. How would you determine the hundred year flood line in coastal areas today? My training is in aerospace engineering, so I probably have not expressed this correctly. But it would seem that the large uncertainties in SLR will pose some real challenges in the civil engineering world. And I imagine a lot of people, like insurance companies, bond investors, etc. will have in interest in how they handle them.

  19. 269
    walter pearce says:

    Re: 266

    Hank, I’ll wager it wasn’t #43. Maybe Poppy.

  20. 270
    Aaron Lewis says:

    Re # 252
    I have hid from the rain in ice caves that are now gone. (We did not climb on rainy days because the ice was too soft. It may not have been the rain, it may have been the water vapor in the air :)

    Did you acutally measure and track the strength of the ice?

    While ice axes and crampons do not go very deep into the ice, still they offer a sample of ice strength every foot or so up an ice face. Ice screws offer a sample of ice strength 2 ft below the ice surface. How long until the ice deforms under the climbers body weight is a good realtive measure of ice strength. For an ice climber, if the ice deforms too fast, it is unclimbable. We paid attention to ice strength.

    My experience is that (surface) ice is stronger on bright, cold, sunny days than on rainy days. Granted, we mostly climbed on smaller bits of ice with much less thermal inertia, but the concept should be similar. I would also note that the differece between strong ice and weak ice may be only a couple of hundred vertical meters.

  21. 271
    Steve Bloom says:

    Mauri, as you may have seen there is an article in the 8/26 Eos about measured runoff from a jokulhaupt that occurred in Greenland about a year ago. What I found most interesting about it was that the amount of direct runoff from the lake was only about 40% of the total, the larger amount being nearly all from frictional melting of the ice by the draining water. Does this throw the Pfeffer et al results into question?

  22. 272
    Richard Wakefield says:


    [Response: This isn’t a soapbox for you to repeat the same old thing over and again, when you have been given plenty of correct advice (and links to the forcings, and links to the model responses). If you are interested in the real answers to your questions, they lie there. If not, go play somewhere else. – gavin]

  23. 273
    Mauri Pelto says:

    Alistair, no it was not your comment on heat transfer via melt that was totally offbase. It was A. Lewis conjecturing on the instant collapse due to rainwater weakening. Reminds me of the reporter I had on a glacier two years ago who thought it could just swallow him up even standing on the solid part. It was a long day for him. Steve, as I recall the hydrologic balance included the jokulhaup, but that did not include all the meltwater in the watershed, thus basal melt would only be a portion of the remainder. But, drat I Recycled that EOS.

  24. 274
    David B. Benson says:

    Lennart (267) — I’m an amateur at this, but I’ll opine that 12 meters of sea level rise is most likely to take at least six centuries and probabnly more like twelve.

  25. 275
    Hank Roberts says:

    Mauri, I have that Eos still. Is this what you needed? Else tell me what to look for and I’ll type it in.

    “… discharge during the jokulhlaup 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. 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….”

    Earlier: “… an accuraccy of 5-10% during low flows; peak flow estimates were less accurate …”

    EOS v 89 no. 35 26 August 2008

  26. 276
    sidd says:

    In regard to the reference posted by Mr. Pelto:

    the stations S5,S6 and S9 are at (6Km from ice edge,490m elevation), (38Km, 1020m) and (88Km, 1520m) respectively from table 2. In Figure 3, i read decreases is surface elevation of 17m, 7m and 0m respectively, over 4 yr.

    comparing stations S5 and S9, the average slope at the beginning is (1520-490)/((88-6)*1000)=0.0126 . similarly comparing S5 and S6 i obtain 0.0166

    at the end of the 4 yr period, the slope between S5 and S9 increase to 0.0128 (1.5%) and the slope between S5 and S6 increases to 0.0172 (increase of 3.5%)
    the numbers for the slopes between S6 and S9 are 0.01 increasing to 0.0986
    (increase of 0.9%)

    my question is: as this slope increases toward the edge of the ice sheet, will it not get oversteepened beyond the angle of repose and thus increase the velocity of the ice sheet toward the margin. i see no measurements of ice velocity at these stations in this paper, i assume because the velocity was too small to measure ?

  27. 277
    Guy says:

    #254 – I’d love to know which other climate scientists are alongside Hansen (genuine comment). I see plenty of support from afar, but I’m unaware of other prominent scientists following him to international governments – and into courtrooms.

    James Hansen managed (in part) to get a truly astonishing court decision in the UK yesterday which found Greenpeace protesters who did £35,000 of damage to a coal power station chimney not guilty. This has been a largely over-looked an extremely important story (though the Independent did put it on the front page – Partly because of Hansen’s expert witness testimony, it was agreed that the damage done by coal power exceeded the damage done to the property of e.on, the energy company, so the chimney damage was legitimate and not illegal.

    So… is Hansen’s sense of dramatic urgency which can excuse £35,000 of criminal damage correct? Are we, with reasonable probability, near a tipping point on SLR and other effects of climate change? And who else is directly supporting him?

    [Response: Hansen’s testimony is downloadable here. – gavin]

  28. 278
    Aaron Lewis says:

    Apparently DOI lawyers looked at the language in the CAL- FED Delta ROD, the CAL-FED authorizing legislation (Calfed Bay-Delta Authorization Act) and 50CFR17 in view of DOI engineering policy to come up with required confidence levels for various project’s engineering.

    I read the plain language of those documents/ESA to require 100% performance for some of these projects. Am I missing something? Are there weasel words that I am just not seeing?

  29. 279
    Richard Wakefield says:

    Lennart Says:
    11 September 2008 at 1:21 PM
    According to the recent report by the Dutch Delta Commission SLR in a worst-case scenario could be 1.3 meters in year 2100 and 4 meters in 2200, based on the latest scientific insights. But what does this mean for the period after 2200? Could SLR stabilize at around 6 meters, for example, by year 2300 or 2500? Or could it continue, or even accelerate, to 8 meters by year 2300 and 12 meters by 2400? Now Pfeffer e.a. say it could be 2 meters by year 2100, so maybe it could be 6 meters by 2200 and 12 meters by 2300?

    That is way way too far into the future to speculate. If the scenarios at and (excellent series) are correct, within 200 years the planet’s population could be 10% of today’s.

  30. 280
    Ron Taylor says:

    I want to weigh in with Guy in support of Hansen. It seems to me that he is about the only climate scientist to put his career on the line and he has continued to weigh in at the government policy level more or less on his own. I have been concerned that he may eventually be ground down, and, frankly, I see him as the only one standing between civilization and disaster, as he formally challenges unwise policy decisions. Gavin and others here are providing a wonderful service, but I am wondering how Hansen can get more support from his peers.

  31. 281
    Ron Taylor says:

    Richard, my God, do your realize what you are saying? Population to decline to 10% of todays in 200 years! Do you understand why that speculation is out there? It is primarily because of climate change impacts brought about by the positions of people like yourself. How does it feel to support a position that could lead to 5 billion or so deaths in the next 200 years?

  32. 282
    Hank Roberts says:

    Aaron, I’m not a lawyer, but I think — I’m fairly sure — that any contract spec to survive a “200 year” weather event — flood, tide, whatever — is referring to the past 200 years’ historical experience.

    If there’s a law that’s foreseeing additional anticipated climate change in design specs, I’d like to see it. It would be a good idea.

  33. 283
    Steve Bloom says:

    Re #275: That’s the key phrase, Hank. I’m assumimg from the context that the basal melt component would be negligible. Mauri, to make clear what my question is, if this event can be taken as a guide there seems to be a basis for thinking that the rate of Greenland melt could become decidly non-linear as the volume of meltwater increases. Re Pfeffer et al, did their results take into account this possibility?

  34. 284
    Steve Bloom says:

    Adding to my prior: It looked as if it required some pretty unusual circumstances for these measurements to be taken. Is this the first time this scale of frictional melting has been observed?

  35. 285

    re: Alastair’s #265–


    First, perish the thought! Second, thanks for the suggestion, which you see I have adopted here. But I want to try the html thing–just not tonight; way too tired!

  36. 286
    Chris Dudley says:

    Guy (#277),

    That is an interesting article. It recalls the defense of another activist attempting to shut down a different power plant in New Hampshire. It rested on the Right of Revolution in the State Constitution. In that case, the damage was sawing down a pole. A portion of the law goes like this: “The doctrine of nonresistance against arbitrary power, and oppression, is absurd, slavish, and destructive of the good and happiness of mankind.”

    You can read more here:


  37. 287
    sidd says:

    re: frictional melting due to water flow

    surely this is easy to calculate ? let us say that 1g of water falls 1Km. assume for convenience that g is 10m/s^2. the energy released is then 1*10E3*1E6=1E9erg=1E2joule. latent heat of fusion is 80cal/g*4.2J/cal=330J

    so 1g of water falling for a kilometer can at best melt 1/3g ice if everything is at the melting point ?Dixo

  38. 288
    Richard Wakefield says:

    Ron Taylor Says:
    11 September 2008 at 7:23 PM
    Richard, my God, do your realize what you are saying? Population to decline to 10% of todays in 200 years! Do you understand why that speculation is out there? It is primarily because of climate change impacts brought about by the positions of people like yourself. How does it feel to support a position that could lead to 5 billion or so deaths in the next 200 years?

    Not at all. I was refering to those that are predicting this due to peak oil, not AGW. such as The Long Emergency, and I’m not agreeing or disagreeing with them. They are just another extreme view. I’m just saying 200 years is along time in the future. The planet could be in a full blown cooling spell by then, in spite of the models for warming. None of us here will be around to find out and say “told yea!”

  39. 289
    Hank Roberts says:

    Steve, the river coming down from the glacial lake was being studied; a pressure transducer was in place (measuring depth) positioned above bridges at a location with a “well-defined, stable cross sections on bedrock” (that means the flow of water only increased the depth, measured by the pressure transducer). They had already done the work to determine “stage-discharge relationship (R-squared = 0.91) and to convert the stage measurements into a river discharge time series” — and so were instrumented and able to get a detailed record of the event.
    The flood traveled about 35 kilometers down the river before it reached the measuring station.

  40. 290
    Aaron Lewis says:

    As I read the Cal-Fed Delta authorization, it does not specify years. The law says, such and such agencies (including DOI) *shall* build structures that protect the habitat of various critters. It looks like a requirement for 100% performance, forever.

    Talk about long tailed statistics!

    It was agency lawyers that interprted that as a 1/10^6 failure rate within 200 years. Since DOI is the enforcing agency for the ESA, that intrepretation would be given deference in court.

    I note that the Compehensive Everglades Restoration Plan
    was developed by USACE and says,”design for a possible sea level rise of 8 inches in the period 2000->2050″. USACE makes a point of saying they are using numbers from the 1995 US EPA report. However, one sentence jumps out of that report,

    “The reader should have no illusions about the
    adequacy of the models used in this or any report
    projecting future sea level rise.”

    That USACE should reference such a report shows the sad state of estimates of sea level rise.

  41. 291
    Richard C says:

    I’m assuming the glaciers are still retreating. How long will it take for the glaciers to retreat to the point where there is open water inland of Greenland’s mountain ranges?

  42. 292
    Richard C says:

    A worrying verdict regarding criminal damage, but how does a layer of paint cost £35,000?

  43. 293
    Brian Dodge says:

    “…how does a layer of paint cost £35,000?” Easy – lawyers got involved &;>)

    I did some simple (way too simple, but still…) calculations, based on an approximation of 1e7 km2 of ice melt 2m thick each year. When this energy gets hungry after the Arctic ocean loses its cover and starts devouring Greenland, it will take ~300 years for all of the ice to melt.

    Alternately, Howat et. al.
    measured 108 km3 of yearly ice loss, and this is doubling every 2-3 years. If this continues, the ice will be gone in ~30-50 years.

    (someone may want to check my math – I’ve been known to misplace a decimal point)

    No one yet has conceived physical mechanisms which would sustain these rates, but no one understood the mechanisms or predicted the rapid collapse of Larsen B years in advance either.

    (ReCaptcha predicts “427 always”; like all good oracles, whether that is months, years, or decades is left for us supplicants to discover.)

  44. 294
    Lennart says:

    Richard, suppose 2 meters of SLR by year 2100 is possible in a worst case, and 6 meters by 2200, what would that mean for densely populated coastal areas? Are we going to move those cities inland? What would that mean for global economic and political stability? An American think-tank, the Center for Strategic and International Studies, took the possibility of 2 meters SLR by 2100 seriously, based on expert opinion, in this report of November 2007:

    I think it’s important to think such scenario’s through, since the consequences could be enormous if we don’t.

    David, if 4 meters of SLR would be possible by 2200, then how much could it keep accelerating during the following centuries? Jim Hansen says that 20 meters of SLR in 400 years was possible about 14.000 years ago:

    That’s 5 meters per 100 years on average. In what kind of world was this possible? Of course there was much more ice to melt back then, but then the forcings were smaller than now, as Hansen stresses. So do and can we really know how fast the ice could melt in the coming centuries? Let’s say 10 meters by 2300 is possible in a worst-case scenario? How should we deal with that? How should we respond? I suppose we should try to prevent this from happening, if we still can. How fast should we reduce global carbon emissions to stay on the safe side? Hansen thinks we should go back to at least 350 ppm CO2-concentration asap, so we even need to sequester carbon from the atmosphere. IPCC thinks we should reduce carbon emissions by 50-85% below 2000-levels by 2050, just to have a fair chance of staying below 2-2.4 degrees higher temperature, which Hansen thinks is already way too dangerous. And he also mentions peakoil: since we have to find alternatives for oil anyway, why not sooner rather than later? The world is quite rich and can afford it. If we take the risk to postpone this transition, and if SLR and other consequences are more serious than we anticipated, this may seriously reduce our wealth later. How much risk are we willing to take with the lives of our children and their children? I’m 37 now. My sister is 27 and had her first child last week. My niece will hopefully be 70 in 2078. Her children could be 70 by 2105. What kind of world will we leave for them? We all have to adapt to changing circumstances, but we make adaptation much more difficult for our grandchildren if we make their circumstances change too fast, and with no possibility to stop them from continuing to change rapidly. Isn’t that what this whole debate is about in the end?

  45. 295
    Richard Wakefield says:

    Brian Dodge Says:
    12 September 2008 at 9:34 AM
    “…how does a layer of paint cost £35,000?” Easy – lawyers got involved &;>)

    I did some simple (way too simple, but still…) calculations, based on an approximation of 1e7 km2 of ice melt 2m thick each year. When this energy gets hungry after the Arctic ocean loses its cover and starts devouring Greenland, it will take ~300 years for all of the ice to melt.

    Alternately, Howat et. al.
    measured 108 km3 of yearly ice loss, and this is doubling every 2-3 years. If this continues, the ice will be gone in ~30-50 years.

    (someone may want to check my math – I’ve been known to misplace a decimal point)

    No one yet has conceived physical mechanisms which would sustain these rates, but no one understood the mechanisms or predicted the rapid collapse of Larsen B years in advance either.

    Does this take in account additions each winter?

  46. 296
    Lennart says:

    Also interesting:

    According to this research SLR this century would be about 1 meter from faster glaciers. So the question is if there’re other mechanisms that could cause additionial SLR?

  47. 297
    Hank Roberts says:

    Aaron, there’s something of a summary on Cal-Fed and the Delta here:

    I can’t figure out from the clues your engineer friend has given what problem is driving him to drink, but there are plenty of them.

    Building to avoid impact on habitat, or to protect habitat, or to restore habitat — these are very different, and differ for each species and habitat. And the Sacramento has, or had, many such.

  48. 298
    Richard Wakefield says:

    This is an interesting side experiment to see how much ice added to Greenland, at least this part of Greenland, each year.

    The aircraft were found under 268 feet of ice. That’s over 50 years. Thus the accumulation of ice is about 5 ft per year. In 300 years, that’s 1500 ft of new accumulation. How does this affect the rates of melting?

  49. 299
    Nick Gotts says:

    Re #292 [Richard C]
    I disagree completely: a splendid verdict for non-violent direct action: voting and more conventional campaigning are essential, but NVDA can indicate a seriousness of commitment which elicits respect (it can also be self-indulgent, of course). No-one except possibly the participants were put at risk by the protest, while we are all being put at risk by the UK government and energy companies like E.on, which are pushing for a new programme of building coal-fired stations with only the paper-thin excuse they will be “CCS ready”.

  50. 300
    Lennart says:

    Ahum, sorry, didn’t check that Harper is the colleague of Pfeffer…