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How much future sea level rise? More evidence from models and ice sheet observations.

Filed under: — eric @ 26 March 2006

Lots of press has been devoted to four papers in this week’s Science, on the topic of ice sheets and sea level.

We’ve already discussed the new evidence that Greenland’s glaciers are speeding up. What is new this week is an effort to evaluate the impact of future warming on Greenland by looking at what happened to it last time it got very warm — namely during the Last InterGlacial (LIG) period, about 125,000 years ago. The same group of authors looked at this in two ways, using NCAR’s Community Climate System model (CCSM) coupled to a state-of-the-art 3-D ice sheet model.

First, in a paper by Otto-Bliesner et al. they ran simulations for the Last Interglacial, and took a look at what happened to the ice sheets. They find that most of the icefields in Arctic Canada and Iceland disappear, and that the Greenland ice sheet is reduced to a steep ice dome in central and northern Greenland. These results are in very good agreement with the available ice core and other paleoclimate data evidence, which indeed show that the Canadian ice sheets disappeared during the LIG, and strongly suggest that much of southern Greenland was deglaciated.

Second, in a paper by Overpeck et al., they examine the implications for past and future sea level rise. The results show that the Greenland and other Arctic ice sheets probably did not contribute more than 3.4 m to the LIG sea level rise. However, data from coral reefs exposed above sea level today, and other evidence, point to an LIG sea level at least 4 m and possibly as much as 6 m greater than today. This suggests that the balance came from the Antarctic ice sheet. This is turn implies a strong sensitivity of the Antarctic ice sheet to sea level rise and climate warming — an idea that goes back to John Mercer (1976) but that had until recently fallen out of favor in much of the glaciology community.

Projecting forward in time, the implication is that our future will also see 4-6 m of sea level rise, and that — given the recent evidence for accelerated flow of both Greenland and Antarctic glaciers — this may occur much faster than we expect. In the model simulations, Greenland may already be warmer in 2100 than it was at the height of the LIG. The rate of sea level rise associated with the warming into the last interglacial was probably greater than 10 mm/yr* while current sea level rise is roughly 3 mm/yr. To the extent that the LIG is a good analog for our future, sea level rise is therefore rather likely to accelerate.

Also in this week’s Science are two articles that further strengthen the case that ice sheets are quite sensitive to warming climate. A paper by Göran Ekström et al. shows that the increased speed of Greenland glaciers occurs in distinct lurches (observed as micro “ice-quakes”) that are strongly seasonal, with the greatest number occuring in late summer. This provides evidence that meltwater plays an important role in the acceleration of Greenland’s glaciers. Essentially, the idea is that surface melting that occurs in the summer can make its way quickly down to the glacier bed, lubricating the bed and allowing the glaciers to slide more rapidly. The “ice quakes” occur because the rough bedrock surface causes the glaciers to stick; they only accelerate when enough hydraulic pressure has built up to help float the glacier over the bumps. This is strong evidence that climate, not merely “internal ice sheet dynamics”, has contributed to the recent increases in Greenland’s glaciers. Indeed, a doubling of the rate of quakes has occurred over the past five years, just as the aerial extent of surface melting has increased.

Finally, in a very nice bit of work Velicogna and Wahr use data from the “Gravity Recovery and Climate Experiment” (GRACE) satellites to show that the Antarctic ice sheet has been losing mass at a rate of 150 +/- 80 km3 each year since 2002. That’s equivalent to about 0.4 mm of sea level rise each year. This is about twice other recent estimates, while IPCC 2001 actually gives negative 0.1 mm/yr. What is especially nice about Velicogna and Wahr’s study is that by using gravity measurements they have measured mass changes directly, avoiding the problem of virtually all previous measurements of ice sheet mass change, which usually measure either input (snowfall) or loss (calving, melting, or thinning of the ice), but not both at once.

What does all this news mean in practice? Reading the editorials in Science, and quotations from various researchers in newspaper articles, one might be under the impression that we should now expect “catastrophic sea-level rise” (as Science’s Richard Kerr writes). Of course, what is catastrophic to the eye of a geologist may be an event taking thousands of years. In the Otto-Bliesner et al. simulations, it takes 2000-3000 years for Greenland to melt back to its LIG minimum size. And while we don’t advocate sticking with the typical politician’s time frame of 4 or 5 years, the new results do not require us to revise projections of sea level rise over the next century or so. This is because even with Arctic temperature continuing to rise rapidly, there will still be significant delay before the process of ice sheet melting and thinning is complete. There is uncertainty in this delay time, but this is already taken into account in IPCC uncertainty estimates. It is also important to remember that the data showing accelerating mass loss in Antarctica and rapid glacier flow in Greenland only reflect a very few years of measurements — the GRACE satellite has only been in operation since 2002, so it provides only a snapshot of Antarctic mass changes. We don’t really know whether these observations reflect the long term trend.

On the other hand, none of the new evidence points in the direction of smaller rates of sea level rise in the future, and probably nudge us closer to the upper end of the IPCC predictions. Those who have already been ignoring or naysaying those predictions now have even less of a leg to stand on. Coastal managers, real estate developers, and insurance companies, at the least, would be wise to continue to take such predictions seriously.** As Don Kennedy and Brooks Hanson write in the lead Editorial, “accelerated glacial melting and larger changes in sea level should be looked at as probable events, not as hypothetical possibilities.”

*Note that we don’t actually have good constrains on the rate of sea level rise from the penultimate glacial period (~140,000 years ago) to the last interglacial (LIG, ~125,000 years ago). However, we have very good data on the more recent glacial-to-interglacial transition, between about 14,000 and 7,000 years ago. During that time, sea levels rose at an average rate of about 11 mm/year, and at rates much higher than that for short intervals.
**Consider for example, that 1 m of sea level rise would change the frequency of what are now 100-year floods in metropolitan New York to once in every four years events. (See here and Rosenzweig, C. and W.D. Solecki (Eds.). 2001. Climate Change and a Global City: The Potential Consequences of Climate Variability and Change – Metro East Coast (MEC). Report for the U.S. Global Change Research Program, National Assessment of the Potential Consequences of Climate Variability and Change for the United States, Columbia Earth Institute, New York. 224 pp)

87 Responses to “How much future sea level rise? More evidence from models and ice sheet observations.”

  1. 1
    pete best says:

    Does the rate of climate warming matter ? I have read recently that the rate of CO2 release by humankind is 30 times faster than natural means alone and that this is unprecedented in the history of climate on the earth.

    [Response: This is old news! You might want to check out some of our earlier posts: here, here, and here for example. -eric]

  2. 2
    Karen Street says:

    I didn’t see a mention of Antarctica’s temperature in 2100, which is also likely to be warmer than during the last interglacial — is this because the Antarctic ice sheets are assumed to be slower to respond, and won’t be as important by 2100?
    What are current estimates on sea level rise this century? Outside of the Pacific Island States, many of which will be lost, where else will there be major impacts?
    Thank you so much for your service!

    [Response: Warming doesn’t have as direct an impact on most of Antarctica, which is so high and so cold that even modest warming won’t cause it to start melting. Still, there is already significant melting and glacier retreat on the Antarctic Peninsula (see here). And since much of the Antarctic ice sheet is grounded below sea level, it may ultimately be more sensitive than Greenland. As for sea level rise details, a good place to start is: the IPCC report section on the subject. -eric]

  3. 3
    llewelly says:

    ‘And since much of the Antarctic ice sheet is below sea level’
    Eric … surely you meant: ‘And since much of the Antarctic ice sheet is grounded below sea level’

    [Response: Yes indeed, thanks! –eric]

  4. 4
    george naytowhowcon says:

    Dear Sirs/Madam’s, In all of the research I can sort through I have found little refference to weather modification and global warming trends. I have reviewed the site:


    Curiously, what I find interesting is the all out assault against high Cirrus clouds (water vapour ice crystals formations)with chemical aerosols. I have made many ground observations of artificial cloud formation of high cirrus clouds being absorbed into chemical trails from jets. I think that untill a full disclosure of these practices and thier ramifications and data associated with such projects is discussed openly, then the truth of artificial cloud cover and infra red heat trapping in the lower level atmosphere can help expose the artificial and perhaps deliberate heating of clouds and atmosphere. This of course impacting the sea ice maximum and minimum extents.
    Also Dr. Dmitriev , a prominant russian scientist reports a new layer of mono atomic water vapour in earths atmosphere. Do you have any confirmation of this new gas layer?
    thanx, george

  5. 5
    Eachran says:

    OK you people. Where do we go from here please?

    Thanks to Father William I have gone down this road to learning about our planet : thanks William.

    I really dont like what I am reading. I understand almost everything except the truly technical bits but even there I can cope with my knowledge of basic physical principles which serve everyone in good stead : understanding “Albedo” is a piece of cake with the reflectiveness of earth (and yes and by the way, I support more satellites properly positioned to measure that), or, add energy and everything expands and becomes more violent and unpredictable – good for children that, and I hope that Mr Beck has the energy and time to do a “Childs Guide” to add to his site. Mr Beck : I can do a consumer response survey with my grandchildren if you want.

    I dont really care whether the timescale is 50 years or 500 years : it is the outcome that is worrying and requires attention – the lead times for social action are often enormous.

    So what to do?

    A number of my friends have been presented by me with the question : if you were to die today would you be able to say that the world is a better place today than when you were born?

    Not an unfair question but very difficult to answer. My mother, aged 83, when asked this paused for what seemed a long time and then said : “For medicine ; yes”.

    Well, it seems to me that that question, on improving the way we live together, is the real challenge.

  6. 6
    Gar Lipow says:

    Leaving aside the question of sea level rises, what are the implications of increased icemelt for warming rate? Elsewhere on this site you pointed out that icemelt forcing creates greater feedback than CO2 forcing. So assume that the sensitivity total is 2.9 degrees, but icemelt is at a higher rate than projected so we get more feed back. Can you translate that into a sensitivity equivalent so that perhaps 2.9 degree sensity is the equivalent of a 3 degree sensitivity due to the increased feedback or whatever? Or is that asking too much of current modeling?

  7. 7
    Jim Roland says:

    Jim Hansen wrote in the UK daily newspaper The Independent, 2/17/06: “The last time the world was three degrees warmer than today – which is what we expect later this century – sea levels were 25m higher. So that is what we can look forward to if we don’t act soon. None of the current climate and ice models predict this.” When would he have been referring to?

    I’ve read about studies suggesting that sea levels reached over 20m above present around 420,000 – 400,000 years ago. But ice core study says that CO2 and CH4 are at their highest for 650,000 years, so presumably the warmer period described by Hansen was farther back still?

    [Response: He is referring to the mid-Pliocene (around 3 million years ago). The sea level estimates for 400,000 years ago you refer to are probably overestimates, I think there is a paper by McManus and colleagues that discusses that, but I can’t find the reference. – gavin]

  8. 8
    Robert Beck says:

    So, if the evidence indicates that during the last interglacial most Arctic and some Antarctic ice fields melted, and ocean levels rose to 4-6 meters above present levels, does that not at least suggest that human contributions to the present warming act largely to increase the rate (not the extent) of warming? Is it not probable that the ice caps would melt eventually regardless of human intervention?

    [Response: Not all interglacials are created equal. The peak NH summer insolation at the Eemian was signifcantly stronger than it was for the mid-Holocene – and it has been decreasing since. See the figure 1 in the Overpeck et al paper. – gavin]

  9. 9
    David B. Benson says:

    Re #7: Robert Beck, according to orbital forcing the globe should be in a slight cooling trend now. So, on a long-run average, I would expect small increaes in frozen water.

    Have you looked into Coby’s site, listed on the sidebar: A Few Things Ill Considered? This might clarify some matters.

  10. 10

    The nineteen foot line is clearly visible in the Exuma Cays in the Bahamas.

  11. 11
    j Cuddy says:

    Has anyone published data on changes in particulate content and chemical makeup of the paleo ice cores? Seems to me that signifcant changes in these would have a huge impact on ice sheet melt rates but I haven’t seen any published information.
    J. Cuddy

  12. 12
    Coby says:

    Hi Eachran,

    I am thinking about a “dummy’s” guide, a children’s guide demands a bit more graphical artist skills than I have! Have you seen this site?
    Your grandchildren may appreciate that.

  13. 13
    joel Hammer says:

    Lately we have heard over and over again that the computer models have been wrong. Dr. Hansen recently was quoted as calling the computer models of Greenland’s glaciers worthless. That is a strong statement. The modelers say the models have badly underestimated the damage. The skeptics say the models are just wrong. This time, both could be right.

    So, why bother with models? Why not study nature and not computer programs?

    BTW, if the models have badly underestimated the damage, there are two possiblities:
    1. The models are wrong.
    2. Nature is wrong.

    I prefer to think the models are wrong. In that case, there are several possiblities:
    1. The modelers have just made small errors in their parameters.
    2. There are factors the modelers simply don’t know about or haven’t included in their models.
    3. Some, or many, factors interact one with the other, making any attempt at modeling the weather a joke.

    You would think the modelers would be embarrassed by the failure of their models to “predict” the future. I haven’t noticed a lot of introspection from the modelers. Now, they will just tweak them a bit to make them comform to current measurements.

    [Response: You’ve made several disconnected statements and perhaps one of us will provide a more lengthy response as time permits. I’ll just note that confusion of weather and climate doesn’t help whatever case you are trying to make. If you really mean that you disbelieve that weather forecasting is possible, then you are in the good company of some well known political figures, who have disbelieved, say, model-based forecasts of hurricanes off the coast of Lousiana… Now, if you are talking about modeling climate, that’s a somewhat different topic… -eric]

  14. 14
    frankhillis says:

    “*Note that we don’t actually have good constrains on the rate of sea level rise from the penultimate glacial period (~140,000 years ago) to the last interglacial (LIG, ~125,000 years ago). However, we have very good data on the more recent glacial-to-interglacial transition, between about 14,000 and 7,000 years ago. During that time, sea levels rose at an average rate of about 11 mm/year, and at rates much higher than that for short intervals.”

    Aren’t CO2 levels now much higher than they were in either of those periods? And only going to get higher? Why should the rates from either of those events be applied to the current situation?

    Come to think of it, wasn’t there also a period called the “topsy turvy century,” where truly fantastic sea level fluctuations occurred? Is that at all relevent to the situation we face now?

    Exactly how useful are either of the two periods mentioned to understanding the situation we have now?

    I’ve read this blog entry a couple of times. The title is “How much future sea level rise? More evidence from models and ice sheet observations.” You mention some papers and articles that have come out recently. Then you address the title of your entry with the following (a few things picked out):

    “What does all this news mean in practice? Reading the editorials in Science, and quotations from various researchers in newspaper articles, one might be under the impression that we should now expect “catastrophic sea-level rise” (as Science’s Richard Kerr writes). Of course, what is catastrophic to the eye of a geologist may be an event taking thousands of years. …

    Coastal managers, real estate developers, and insurance companies, at the least, would be wise to continue to take such predictions seriously.** As Don Kennedy and Brooks Hanson write in the lead Editorial, “accelerated glacial melting and larger changes in sea level should be looked at as probable events, not as hypothetical possibilities.””

    What exactly are your predictions for sea level rise over the next 100 years. Spell it out explicitly. 3mm a year is nothing. One century takes it .3 meters or 12 something inches. Over a century. No real estate developer has such a long term view of real estate unless it can be gotten for essentially nothing. If you can’t flip it relatively quickly it is meaningless. Insurance companies take a longer view, but it is more like decades, not centuries. And what the hell is a coastal manager? I’ve never heard of this office in my life.

    You certainly have some idea in your head of what you expect to see. Yet you managed to say very little in your article. Bland, inoffensive, nothing to inspire any controversy.

    But what exactly do you REALLY think will happen? Are you steering clear of coastal real estate? Looking for a position away from the coast? What? Threat of sea level rise overblown? Expect it to stay 3mm a year for the next thousand years? Rise to 5mm? What are you expecting?

    [Response: Bland, eh. If you are bored, you might try this: Day After Tomorrow. As for me, I wasn’t planning to inspire controversy actually, since as far as I’m aware this isn’t controversial. Sea level is going to rise somewhere between 1/2 and three feet in the next century or so. It could be much much more (say, two times as much). If you live 1/2 foot above high tide level (as many many many people do), either way it is a big deal. Am I personally steering clear of coastal real estate? Yes. –eric]

  15. 15
    David Howell says:

    Seems like a pretty intelligent site. I have two questions. 1. Is there anything to the idea that an ice age could be created by scuttling a handful of ships loaded with iron filings in the Pacific Ocean? And 2. Regarding the calculations of how much we can expect sea levels to rise…do the calculations count only on the amount of water that derives from melting ice, or do the calculations also include the increased volume of seawater that comes from expansion due simply to heating of the oceans?
    And I guess a third incidental question: what are the relative contributions of melt water and heating expansion?

    [The answers are NO, YES, and Thermal expansion is estimated to account for about 1/2 of the total. Recent work has updated this number I believe but I’ll have to look it up. The 2001 IPCC estimtes for the various contributions of various sources is shown in the graph, here –eric]

    Thank you.

  16. 16

    Are ice dynamics models able to recreate the rate of sea level rise during meltwater pulse 1A yet? If the answer is still no, then I suggest that we have no idea how fast sea level rise might go in the next century…

    [Response: This is a fair point. There is no question that ice dynamics models are still in their infancy. However, it is not entirely relevant whether we understand happened in 1A because we are severely data limited. In contrast, we are quickly gathering a lot of data on the present state of glaciers and ice sheets. eric]

  17. 17
    Alan says:

    I have watched the climate debate for more than 25yrs and I think the science has at last asserted itself over the politics ( even GWB agrees with the basic facts ). One of the side-effects of this “battle” is that the accepted science (IPCC) (looks like) it has underestimated the speed of the change. Maybe this a result of being extra conservative in order to fend off financially motivated and politically powerfull critics. Regardless of accuracy, I would like to congratulate all the scientists involved for defending and promoting the “republic of science” against the worst odds.

    A lot of attention has been given to sea level rises because of the direct and somewhat predictable affect on major cities. Theoretically if we can predict the extent of sea level change then we can plan our way around it without getting our feet wet.

    What bothers me is that a rapidly rising ocean is only the most visable symptom of a planet with a fever. The “birds and bees” are out of sync with each other already. If “the climate” was shifting ( say ) twice as rapidly as predicted by the IPCC, what is the likelthood of “symptoms” such as wide spread crop failures, disrupted fisheries, pasture into dust?

  18. 18
    pete best says:

    Re #17. Once again people want to know the effects that climate change will have on their the environment in real terms but this is not necessarily the job of climate science to do that as making such predictions can be scientifically damaging to ones career as it does not have a scientific basis.

    Generally Science leaves the fortune telling to environmental groups and the like and it is this naming of scientific literature by environmentalists that seem to land science in hot water although I believe that Jim Hansen of NASA has stated that human kind could have as little as 10 years to avert serious climate change.

  19. 19
    C. W. Magee says:

    How do you get paleoclimate data for an area that has been under ice for most of the past 100,000 years?

    [Response:Drill! See The Greenland Ice Cores –eric]

  20. 20
    James Doggart says:

    Would you comment on the Davis et al study published in Science since i gives a little perspective to the Velicogna and Wahl article.

    [Response: To which article are you referring? -eric]

  21. 21
    Stephen Balbach says:

    “Flood Maps” mashes up NASA elevation data and Google Maps, and offers a zoomable localized visualization of the effects.

  22. 22
    Tom says:

    Re No. 14 and Eric’s response to that post.

    Thanks to you for raising the chief question that I had which was “OK, Greenland and Antarctic ice are apparently declining more quickly that we once thought, but what does that translate into in terms of projected sea-level rise by 2100, provided the trends continue. I took a quick peek back at figure 11.12 referenced in Post No. 2 (the IPCC 2001 multi-scenario by AOGCM projections). Eric, these projections suggest a range of up to about 0.7 meters (2 feet) of SLR by 2100 for the A1Fi which is a rapid growth and fossil fuel intensive emission scenario. Even the most extreme combination does not yield 3 feet.

    I have three follow up questions (1) Eric, where does your estimate of 0.5 to 3 ft come from? (2) Can anyone comment on the current IPCC Fourth Assessment Report SLR projections and (3) Can the recent findings reported in Science be translated into a specific amount of increase in SLR projected for 2001? I note that Overpeck did not try to answer question 3 . . . I have not yet seen Kerr’s article.

  23. 23
    Seppo Syrjälä says:


    In the fijian news is a mention that sea level there has risen 8 cm in 13 years. That makes it 6 mm / year. Article indicates that also normal variability has some effect on this but web story is rather short on that and there is no link to in the news piece for the actual study as far as I can see.

  24. 24
    Tony Noerpel says:

    re #17 and #18. Alan has a valid point. There is lots of science regards species extinction and this may be the most salient aspect of environmental degradation, including AGW. There was a fine paper by Thomas et al. in Nature in the fall of 2004 suggesting that species extinction could be between 17 and 35% by 2050 based on mid range AGW models from the third IPCC report. Maybe Realclimate could host a guest post from a biologist on this impact. Humans need the services of coral reefs, fungus, ground hogs, pollinators, ocean fisheries, forests, and plankton to survive. Maybe we don’t need polar bears and seals, but what kills them can’t be too good for us. I think this is science.

  25. 25
    Almuth Ernsting says:

    Re 18:

    I would disagree with you about scientists being generally cautious and environmentalists getting them into trouble by doing their own ‘fortune-telling’. The most detailed climate impact forecasts I have ever heard come from the Hadley Centre – those are the only forecasts that could conceivably remind you of ‘fortune-telling’ (particularly the way they are consistently reported by the media with absolute certainty!) They put information to the public about likely rainfall changes (with exact percentage changes) between now and 2050 or 2080 in different regions within the UK. I presume that they really want to bring home the reality of what the most likely result of climate modelling will mean for people – they want people to understand that climate change is and will be real. I sometimes worry whether such precise forecasts could be dangerous – I have seen one Guardian science editor claiming that the current drought cannot be linked to climate change because climate change will make the UK’s winters wetter (I understand that is only the most likely scenario, and if we cannot say for certain that a record-breaking drought is linked to GW then at least we know that those droughts are becoming more common globally because of GW and we cannot rule out a link with the one in the south of England just now – at least that’s my understanding).

    In the UK many of the main environmental NGOs tend to be far more cautious than, say, the Avoiding Dangerous Climate Change conference last year! There is widespread fear that we should not make it look too scary but should promote positive messages (not my own way of thinking – I think everybody just needs to be honest about what is known and what is not known for certain but is not ruled out, rather than worrying about how other people might react).

    Personally, I do think that it is important for scientists to explain their own understanding in simple enough terms for ordinary people to understand (this weblog of course does a great job at explaining complicated science to lay people!). And if James Hansen is extremely worried that sea level rises may become far more dramatic than models suggest that I am glad to know. It’s a matter of saying ‘I am worried, this could happen, and this is why I cannot rule it that it will happen’ – and those messages really can only come from experts, not (credibly) from environmentalists (other than by quoting experts).

  26. 26
    Hank Roberts says:

    This may be a reference to the same Hansen interview several recent posters have mentioned, saying they think Hansen said that modeling isn’t working – I haven’t found any original transcript or source, so I’m trying to figure out what he actually did say.

    Found at this advocacy page:

    Attributed to:
    Warm, Warmer, Warmest
    by Nicholas D. Kristof The New York Times 5 March 2006

    Part of the challenge in modeling climate is that we’re already off the charts with greenhouse gases like nitrous oxide, carbon dioxide and methane. “We’ve driven them out of the range that has existed for the last one million years,” noted James Hansen, NASA’s top climate expert. “And the climate has not fully responded to the changes that have already occurred.”
    End quote.

    Anyone got a first-hand source?

    [Response: His article in the Independent (reprinted here)
    He is specifically referring to ice sheet models, not GCMs. – gavin]

  27. 27
    Yann says:

    Hey folks – I thought you ought to know that Eric is the proud new father of a son. In 15 years from now, we’ll hear them arguing about whether 3-pin, randonnee or snowboarding is the best way to go ;-)

    [Response: No kid of mine will snowboard! -eric]

    [Response: You say that now… – gavin]

  28. 28
    Lynn Vincentnathan says:

    RE #25, it may get to the point once people are convinced that GW is real and dangerous, that people may overattribute all sorts of harms to GW, with the idea of letting science prove otherwise. (I’m a bit at that stage myself.)

    I was surprised to learn that sudden glacier movements in Greenland were causing local earthquakes. What next, GW causes or contributes to volcanos?? I’ll believe it, if scientists find it’s so.

    [Response: These “earthquakes” are just detectable seismic noise (detectable with sensitive instruments that is). Bedrock in Greenland is very old and stable, and nothing like what we normally mean by “earthquake” is likely to happen there. –eric]

    At long last yesterday ABC News started covering GW without using much of a pro-con format, though they did have George Will on This Week trot out “Scientists in the 70s were warning of an ice age,” and “it’ll cost trillions to combat GW.”

    Before yesterday major media nearly never covered GW, & when they did it was almost always in pro-con format (heavy on the skeptics for “balance”). Jim Leherer last year when speaking of GW (which is also rare on his Newhour), mentioned “GW, which SOME scientists say is happening…”

    Now ABC is wondering out loud why a huge portion the public think scientists are in big disagreement about whether or not GW is happening.

  29. 29
    pete best says:

    Re 25

    Science is nearly always cautious and never uses language such as the press would use to justify something. Scientific personnel may offer predictions of future conditions here on Earth based on models but this is the press labelling it as truth to the wider public rather than the scientists themselves prophesizing for they cannot do that and peer review finds people out.

  30. 30
    Eachran says:

    Post 12. Coby how could you do that to me? The site is a disaster area.

    My offer still stands and if one sticks to basic and verifiable scientific principles one can go a long way with children/grandchildren – whom I may say are a very demanding audience.

    I see this site is now subject to AW too – not bad under the circumstances. Perhaps realclimate could set up a counselling service for all my aged and guilty friends and relatives.

  31. 31
    David B. Benson says:

    Another 40 cm? I recall that the ice in Patagonia and other locations different from Greenland and Antartica, if it were all to melt, would contribute 40 cm to the sea stand. So should we add another 30 cm or so to the guestimates given in earlier posts?

  32. 32
    llewelly says:

    I’m not sure where you got 40 cm from. If you got it by multiplying 0.4 mm/year by 100 years to get 40 cm, be aware that the 0.4 mm/year mentioned in the article is from Antarctia alone; it doesn’t include Greenland, or Patagonia, etc. Also, the melting of Antarctia’s ice sheets is unlikely to be linear. I believe it is expected to accelerate. If you got the 40 cm from elsewhere, I’m afraid I’m not much help …

  33. 33
    Paul says:

    In post #14, in the response section, eric states:

    “”Sea level is going to rise somewhere between 1/2 and three feet in the next century or so. It could be much much more (say, two times as much).””

    So….it could be 6 inches, it could be 3 feet, or heck, even 6 feet. Is this not a case of “covering one’s bases” no matter what the outcome is?
    Such wildly divergent predictions seem to highlight the huge uncertainties in the science of AGW, not strengthen it.

    [Response:Gee, you’re right. I guess all this science is just hogwash, eh? Next time my doctor tells me, “well, you have a malignant tumor, but it may or may not become more serious,” I’ll decide that all doctors are charlatans and stop using their services. –eric]

  34. 34
    David B. Benson says:

    Re #31, #32: I recall the figure of 40 cm from T.M. Cronin’s “Principles of Paleoclimatology”. To repeat, this was his figure for the sea stand rise due to complete melting of all ice other than Greenland and Antarctica.

  35. 35
    llewelly says:

    Re 32 (me) oops, sorry, Please ignore my post. It contains bad, bad math; 0.4 mm/year by 100 years would be 40 mm, not 40 cm.

  36. 36
    C. W. Magee says:

    Does increased melting mean an increased chance of slowing the Thermohaline circulation? Wouldn’t that have the effect of cooling the SE Greenland/Iceland area of the N. Atlantic? Is it possible to model the fastest allowable rate of melting that can happen before this negative feedback occurs?

  37. 37

    Re #27 “Hey folks – I thought you ought to know that Eric is the proud new father of a son.”

    Congratulations to Eric.


  38. 38
    Lynn Vincentnathan says:

    Yes, congrats, Eric!

  39. 39
    llewelly says:

    C. W. Magee, you might find this RC article helpful, particularly Stefan’s response to comment 4.

  40. 40
    Robert Beck says:

    Re: #8 & #9: Thank you, Gavin Schmidt and David Benson — points taken. So, additional facts point to a scenario something like that posited by W. F. Ruddiman of U VA, wherein orbital obliquity-driven cooling caused by declining insolation and augmented by decreasing CH4 is reversed by agriculturally induced CO2 and CH4 emissions, beginning as much as 8000 years ago. We apparently over-shot the mark in this industrial age, and now the Earth is over-heating. The situation is delicate — Too little GHG and we slip down that long, cold slope into glaciation; too much, and we lose the Everglades, Bangladesh, etc. Can we engineer our way out of this box? (Ref: “The Anthropogenic Greenhouse Era Began Thousands of Years Ago”; W.F. Ruddiman, Climatic Change 61: 261-293, 2003)

  41. 41
    Anonymous says:

    This really is fantastic news! All that land currently buried beneath ice will become usable again. A vastly greater area than will be covered up by the rising sea-levels. So much more of the planet will have a comfortable climate.

    I guess the only risk to this wonderful scenario is that the fossil fuels run out sooner than anticipated and the greenhouse gases fall back into line. I am keeping my fingers crossed that that won’t happen.

  42. 42
    Stephen Berg says:

    Re: #41, “This really is fantastic news! All that land currently buried beneath ice will become usable again. A vastly greater area than will be covered up by the rising sea-levels. So much more of the planet will have a comfortable climate.

    I guess the only risk to this wonderful scenario is that the fossil fuels run out sooner than anticipated and the greenhouse gases fall back into line. I am keeping my fingers crossed that that won’t happen.”


  43. 43
    Hank Roberts says:

    Look for comments by Matt; if he gets his web page together, you’ll want to visit.

  44. 44
    Anonymous says:

    It is a shame the ice on Antarctica is so thick and at such high altitude, so that even with warming we won’t see the land mass of Antarctica for an awful long time, if ever. Is there anything that can be done about that? Drill lots of holes?

  45. 45
    llewelly says:

    Re #42: Start buying real estate in Greenland now! Let us know how your investment goes!
    Plan carefully though. Past deglaciations have involved a bit of flooding here and there.

  46. 46
    Dano says:

    RE 41, 44:

    See, sarcasm might not always work here, ’cause when glaciers retreat, there is not much organic matter or critters an’ stuff in the soil, hence it’s not arable.

    So, some folks take it literally and might not take the statements for what they are: just short of comedy. You are trying a comedy routine, right?



  47. 47
    A.P. Storm says:


    My speciality is information science, but I wanted to air an idea (or theory) in this arena. I have theorized that the Earth is akin to a giant capacitor in a closed circuit whose past climatic conditions were the result of the amount of oil underground. Simular to an oil filled capacitor in a closed circuit. Thank heaven for the dinosuars and species extinction! If my theories are at all correct, things will continue to worsten.

    Today, we are having a major impact on lowering those natural oil levels. It’s causing the Earth to loose its natural capacitance. Some have theorized a natural shift of magnetic poles may occur. But what if this purposed failure, or weakening, of the magnetized poles isn’t natural? What if the event is a natural response to the Earth’s loss of capacitance? What happens to a closed circuit when it’s oil-filled capacitor fails? My theory has many societal ramifications.

    I’m working on a basic Earth model incorporating my theories, but this will take time since there is a lot of data to simulate. I welcome input from you all.


  48. 48
    John Monro says:

    Goodness, some rather bizarre comments here. It’s not easy being a scientist. What many non-scientists don’t seem to quite understand is that uncertainty is, and always has been, a huge part of science. So much of what we take for granted in scientific knowledge and advancement only arose out of an ocean of uncertainty just as large as the uncertainty with which we are trying to struggle with global warming. A good (ethical) scientist will admit this and, as far as he or she is able, explain the limits of his or her knowledge, only a charlatan will seek to create certainty out of incomplete knowledge or data, and only a charlatan will seek to exploit this uncertaintly for their own ends. We see to 2100 with no more clarity than H G Wells for instance could see the year 2000.

    But that does not excuse us from ignoring what we can clearly see now. For humanity, I think it is now pretty easy. Anthropogenic global warming is a proven fact beyond any kind of reasonable doubt. The quality and quantity of change is under some debate, but as every year passes the warnings from the scientists are becoming more dire. As the whole 6 billions of humanity arose and throve in the climate we now have, which has remained pretty constant for the last 8 thousand years, no-one can then greet some new climate as anything other than the most dire threat to everyone’s existence. There is now a moral or ethical obligation to accept this on behalf of our future generations, every single other consideration is now of secondary importance – politics, economics, cost, comfort, convenience, social inertia, what you will. It will require an effort on behalf of mankind equivalent to fighting the Second World War, except this time no one has to die, be maimed or psychologically scarred for their whole life, nor do cities have to be destroyed or civilisations wrecked. We cannot leave this to people who seek to weigh the health of the world against these other considerations, there is no set of scales that can accomplish this measurement. But until we fully understand this moral imperative, the necessary action to deal with this issue will never, ever come. Sermon over.

  49. 49
    KC Jones says:

    Sorry for a frivolous question, but very recently I was reading a post on some now-forgotten science blog about the accelerating melting of the Greenland ice sheet — and they either linked to or published a beautiful picture of a waterfall of runnoff falling from an ice shelf on Greenland with some people standing along the banks of the rivulet at the top of the fall.

    Does anyone remember this and have a link for me? Thanks!

  50. 50
    M. Chandler says:

    I think the photo you’re referring to is courtesy of Roger Braithwaite and was a cover of Science magazine 12, July 2002. See