Sea level rise?

Posted by William M. Connolley on March 12, 2009
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Time to break my lengthy science drought by trying to get back up to speed on what sea level is supposed to do. Sea levels rising faster than expected: scientists says Reuters, and they lead with Stefan Rahmstorf predicting more than a meter in 100 years. Reuters make the common mistake by saying The U.N.’s Intergovernmental Panel on Climate Change in 2007 predicted global warming would cause sea levels to rise by between 18 cm and 59 cm (7 inches and 23 inches) this century. To be fair to them, IPCC practically begged people to get this wrong; that is the value excluding weird things happening to ice sheets (Lomborg makes the same mistake, but he knows this stuff too well to do it accidentally: from him, it is deliberate misinformation; SR calls Lomborg on this, but more politely than me). Unfortunately, the chances of weird things happening is still unknown.

One thing that is worth pointing out (an observation not new with me; I think SR may be the first to say it) is that the IPCC low-end 18 cm is utterly implausible. SLR is already 1.8 mm/yr, and it isn’t going to slow down. Quite what the current value is I’m not sure… lets look at IPCC: From 1961 to 2003, the average rate of sea level rise was 1.8 ± 0.5 mm yr-1. For the 20th century, the average rate was 1.7 ± 0.5 mm yr-1, consistent with the TAR estimate of 1 to 2 mm yr- 1. and For the period 1993 to 2003, the rate of sea level rise is estimated from observations with satellite altimetry as 3.1 ± 0.7 mm yr-1, signifi cantly higher than the average rate. The tide gauge record indicates that similar large rates have occurred in previous 10-year periods since 1950. It is unknown whether the higher rate in 1993 to 2003 is due to decadal variability or an increase in the longer-term trend.

Reuters are quoting folk from the recent International Scientific Congress Climate Change in Copenhagen (note that this *wasn’t* an IPCC conference; if you believe the about stuff it was just a U Copenhagen event). So while the conference “key message” is suitably apocalyptic, it isn’t really clear who is signed up to the message; if you believe the disclaimer, no one is. Ho ho, via BL I find that This is not a regular scientific conference. This is a deliberate attempt to influence policy. Ah well.

So what do people actually say in their abstracts? Church, Gregory et al. are sensible people. But saly they followed the traditional pattern of writing their abstract before finishing their talk, so there isn’t much of use there. Sea level has been rising at close to the upper end of the IPCC Third Assessment Report (and AR4) projections. Despite the importance of sea-level rise, the last two IPCC reports have not been able to satisfactorily close the se-level budget [sic]. Here, we present updated estimates of the observed rate of rise from both satellite altimeter and in situ observations. We will build on recent progress in closing the sea-level budget… Two useful things there: first, the boring one: the sea level budget still isn’t closed: or in everyday speech, you can’t get the observed sea level rise out of the known contributions, without some violence to error margins. Second, SLR is *close to* the IPCC upper end: *not* above it.

Grinsted et al. say what they said before. And they are part of a strand of thought which has given up on getting future SLR out of the GCMs, and will get it from historical analogues instead. Bamber et al. reassess the likely SLR from a collapse of W Ant.; this comes into the “scientifically interesting but practically useless” category, because the question at issue is not whether it will be 5m or 3.5m or something else, but how fast it will occur. And the answer to that is still “probably nothing much will happen this century or the next, but who knows”.

Dahl-Jensen says the Greenland was 5K warmer in the Eemian and SL was 5m higher but Greenland didn’t melt (take *that*, Hansen) completely, only contributing 1-2m of SLR.

So, not a lot going on really. Wot about the blogosphere? IoD says “Sea level rise a red herring?. I think his point is that whilst SLR is easy to understand as being bad, there are lots of other things that could be bad too. Which is true. Nurture doesn’t have much to say, though they pick up on Bamber. Errm, did anyone else comment? Sorry if I missed you – please comment.

Meanwhile, I don’t seem to have got very far in discovering what SLR is likely in the future, mostly because I think no-one knows or even has a very good idea. With all the uncertainties in the models, I’m leaning towards the historical analogue approach, which probably points to something in the 0.5m-1.5m range for the next 100 years. But don’t quote me.

Some of my past art: 2008/09/sea_level_rise_pfeffer_et_al.

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  1. #1 Steve Bloom
    2009/03/12

    Did Hansen ever say Greenland had melted even close to completely during the Eemian? I don’t think so. I do recall him saying something like that regarding MIS-11 (whence came the biological material the D-J abstract mentions).

    Something I’ve wondered about is the extent to which the Milankovitch cycle-related forcing during the past interglacials differs from the emissions-related (GHGs and black carbon) forcing of the present. In particular the short-term threat (not yet quantified AFAIK) to the GIS seems to be from warming currents melting the glaciers that occupy below-sea-level channels leading into the interior. Would those currents have existed in the past?

  2. #2 David B. Benson
    2009/03/12

    Greeeland during interglacial 2 (the Eemian) is shown in a nice graphic in IPCC AR4. It looks about 1/2–2/3 melted. In any case, the NGISP ice core proves that it didn’t all melt during interglacial 2.

    The SLR (by century’s end) estimates vary from a low of 0.8 m to an (very unlikely) high of 2 m. The various coastal engineers who have to plan for such things are using numbers in the 1.3–1.5 m range, I believe.

    [No! This is not true. 0.8m is *not* a low end estimate. You're referring to Pfeffer et al. I think. That paper is full of assumptions that can be trivially challenged - they do so themselves. Their estimates are more like upper bounds that lower bounds. I'm rather concerned about the noise pollution around on this subject -W]

  3. #3 Nicolas Nierenberg
    2009/03/13

    WC,

    I believe you already know that the 18-59cm figure is taking the bottom and tops of the error bars on the various scenarios. This seems like one way of describing the consensus view from AR4. These are called the 5-95% ranges on page 70 of WG1.

    They do include the quote “These ranges do not include uncertainties in carbon-cycle feedbacks or ice flow processes because a basis in published literature is lacking.” While this is an important caveat I don’t think it says that the estimate is wrong.

    Of course there are some scientists who believe it is understated.

    [Yes, I'm aware of that. You're making the misreading I was talking about -W]

  4. #4 humorix
    2009/03/13

    To me, the volume of an icicle is superior has his volume in water. When the ice melts the level of the sea go down. (and not the opposite).

  5. #5 Dunc
    2009/03/13

    And the answer to that is still “probably nothing much will happen this century or the next, but who knows”.

    [...]

    With all the uncertainties in the models, I’m leaning towards the historical analogue approach, which probably points to something in the 0.5m-1.5m range for the next 100 years.

    Whether you regard 0.5m – 1.5m of SLR as “nothing much” rather depends on where you live, and whether you’re looking at average SL, or maximum SL in, say, a once-in-a-century storm surge. 1m is probably (I think…) enough to turn a once-in-a-century disastrous overtopping of sea defences (think 1953) into a once-in-a-decade event. Say goodbye to East Anglia and Norfolk. (Not to mention Bangladesh)

    [You misunderstand. "nothing much" refers to the W Ant contribution. 1m SLR is generally regarded as significant, though I don't have a strong personal opinion on that. Some bits of East Anglia would be improved by being under water :-) -W]

  6. #6 Eachran
    2009/03/13

    So you are a 1m man, are you? That’s the number?

    For my own purposes in trying to understand the implications of global warming I put you in the positive skeptics group. So adjusting for that, unscientifically speaking, I make it 1m minimum.

    Interesting comments over on RC from the engineers sometime ago on margins for error, I think that it was in the posts attached to Mr Schmidt’s piece on the Thames Barrier. And interesting comments from one of the UK Institutes recently on what the plan is for the next 250 years for London in particular. I think that they were working on a basis of 7m, which also seems reasonable if the experts are correct.

    Currently in the UK the only water authorities which have published work on SLR are Thames and Norfolk (there may be others but I dont know). I sent an e-mail to someone at the appropriate Gov department who hangs out in your neck of the woods in Peterborough asking not unnaturally if the authorities looking after the Wash were in the process of preparing a similar study to Norfolk’s : no reply.

    Norfolk was working on the IPCC numbers, not on 1m.

    France in the meantime has published a paper on regionalization identifying metropolitan centres to be developed, one being Nantes and others being Marseilles and Bordeaux.

    Looks like a lot of dyke building over the next few decades just about everywhere.

    [Not sure what I'd do on planning for the next 100 years. Planning for 250 sounds like a waste of time; probably someone's boondoggle. A nice cosy job with no consequences -W]

  7. #7 Alexander Ač
    2009/03/13

    One of the SLR side-effects is contamanation of underground drinking water – and this can go tens of kms into the inland…. do not forget about that when dicussing “significancy” of SLR,

    best,
    Alexnder

  8. #8 Dunc
    2009/03/13

    You misunderstand. “nothing much” refers to the W Ant contribution.

    Ah, I see. My mistake.

  9. #9 Alexander Ač
    2009/03/13

    Off-topic,

    William, considering recent discussion about temperature increase on crop yield, this *is* interesting:

    “We find that, in general, uncertainties in average growing
    season temperature changes and the crop responses to these
    changes represent a greater source of uncertainty for future
    impacts than do associated changes in precipitation. This
    finding stems from the fact that future temperature changes
    will be far greater relative to year-to-year variability than changes in precipitation, even when considering the most extreme precipitation scenarios.”

    From: “Why are agricultural impacts of climate change so uncertain? The importance of temperature relative to precipitation” – Lobell and Burke, 2008, ERL

  10. #10 Nicolas Nierenberg
    2009/03/13

    WC,

    I guess I didn’t ask directly enough. What is the misreading I am making of the IPCC sea level estimates? I know you said they “begged” me to make the mistake, but I guess I’m missing what it is.

    [That 18 cm to 59 cm is their best estimate of SLR for the century -W]

  11. #11 Nicolas Nierenberg
    2009/03/13

    WC,

    But that is the best estimate in the report from section 10.6. There are a number of caveats of course. I don’t think a correct summary of the chapter is that these are starting points which you have to add uncertain additional amounts to. The paragraph at the bottom of 821 points out one scenario where it might be too high by .02M or too low by .1 to .2M, but this is just discussion.

  12. #12 Magnus W
    2009/03/13

    NN

    It depends of what you know of the caveats… if they will add they will add.

  13. #13 Gareth
    2009/03/13

    Central government guidance to regional/local councils in NZ, published last year, advises them to plan for “up to” 0.8m over the next 100 years. This was based on AR4 plus a fudge factor. I thought it was a low figure when published. If you’re planning to build/maintain significant coastal infrastructure (some of which can be expected to last for hundreds of years), then at the moment you’re stuffed, because “good” figures don’t (yet) exist.

    I think William’s right to lean towards the paleo examples. I’m thinking MWP 1A (and I know that the ice sheet that likely caused that doesn’t exist today, but I’m factoring in WA instability and bad news from PIG).

  14. #14 Nicolas Nierenberg
    2009/03/13

    Magnus,Gareth

    Look its fine to have your own estimate of sea level rise. And for planning purposes people can do whatever they want. But AR4 seems clear to me and the midpoint A1B or A2 figure of .35M is probably what one would call the IPCC best estimate based on a direct reading of the chapter.

  15. #15 Steve Bloom
    2009/03/13

    That figure is now history, Nicolas. The relevant LAs have abandoned it.

  16. #16 Eachran
    2009/03/13

    Mr Connolley, please.

    [Dr? -W]

    You have children, and if you care for and educate them as you seem to do then you are already planning for 100 years.

    [No, I'm not. My children can plan for themselves when the time comes. I might be planning for my retirement a bit, which is 20 years off, but even that is vague -W]

    For the 250 years, you could look at it in reverse (?).

    So, if three of my mothers were put end to end it would make 250 years. Not long is it?

    In the 1750s Canaletto was knocking about in London painting Thames bridges and Mozart was just about to get going.

    [Yep, and we certainly wouldn't have wanted them to use their powers of prediction to shape the future -W]

    In your own area of Cambridgeshire you have evidence of settlements in the same place for thousands of years : try Flag Fen followed by the Romans (please dont link Biggus Diccus).

    So you could work backwards. What not to do rather than what to do, and then it becomes more obvious. Indeed with a bit of imagination you get to define an envelope within which action might work. We need action because without it we make no progress.

    The big issues include, what’s worth saving and do we lead centralised lives commanded by centralised networks or do we become more independent and self-contained in many ways.

    Cities are interesting places. Where would we build them and how would they run?

    How would we make social and health services responsive to independence?

  17. #17 Magnus W
    2009/03/13

    NN,

    That is with out their caveats…

  18. #18 JCH
    2009/03/14

    Just curious, what was the estimated elevation of Greenland going into the Eemian?

    [Dunno. Not that Greenland has one elevation anyway. From the cores it should be possible to estimate the local temperature, which would be higher if lower down -W]

  19. #19 Eachran
    2009/03/14

    No intention to offend you by calling you Mr Connelly, quite the contrary, it is safely neutral and respectful : with all the cash for ermine stuff in the UK one needs to watch out.
    If you allow me to post on your site in the future I shall take note.
    Your children don’t start with a blank sheet when you set them off in the world, do they? Much of the equipment they need to make independent judgments comes from you, therefore you do plan for 100 years.

    [I disagree. I shall set my children off with a certain measure of resources, but more importantly will have educated them, or arrange for them to be educated, so as to be flexible and resourceful in themselves. But I'm not making plans for them -W]

    As for Mozart, he was one in a long line of composers drawing from his predecessors as well as handing on to his successors. Andrew Lloyd Weber for example uses stuff from classical composers for his musicals.

    [Certainly. But he didn't plan for me, nor would I want him to -W]

    On climate science you personally want to get it right so that the science can develop without time limit. I know this because I’ve read your stuff, and because you are good at your job I rely on your judgment. You are one in a long line of scientists and I suspect you would be a bit miffed if that line was broken.
    But I suspect you know all this and are just pulling my leg.
    There is that trite phrase : failure to plan is a plan to fail. I don’t much like the implications for a 1m SLR for our grandchildren (I have 5 of my own) and I don’t want us to fail future generations.

    [Agreed, we should not fail future generations. I strongly suspect we will be looked back on as enormously greedy -W]

    Anyway, good luck, don’t weaken and have a good weekend. Off to the market now and to buy The Economist and have a few beers.

  20. #20 Taat Laet
    2009/03/14

    WAIS contains 2.2 million km3. Its heat of fusion is 730 10^21 J. If total net antrophogenic forcing reaches ~5 W/m2 (2.5 10^15 W globally) and if all heat is used on the WAIS it will take 9.3 years to melt it. So, it could be done before end of this century, but hardly.

  21. #21 Nicolas Nierenberg
    2009/03/14

    Steve,

    The lead authors of chapter 10 from page 747 were; William Collins, Pierre Friedlingstein, Amadou Gaye, Jonathan Gregory, Akio Kitoh, Reto Knutti, James Murphy, Akira Noda, Sarah Raper, Ian Watterson, Andrew Weaver, and Zong-Ci Zhao.

    The coordinating lead authors were Gerald Meehl, Thomas Stocker.

    Could you direct me to a link where any or all of these scientists have abandoned the conclusions of 10.6?

  22. #22 Nicolas Nierenberg
    2009/03/15

    SB,

    I assume you are now abandoning your earlier comment? :-)