Is sea-level rise a problem?

In my post last week about what if anything had changed since I started taking an interest in Anthropogenic Global Warming I made a brief mention of the threat of sea-level rises that might threaten coastal cities. I thought six years ago, and still think, that the data just don’t have the accuracy that would support almost any statement about sea levels, other than we have a lot still to learn.

The current dispute is about whether or not the sea levels are rising, and if they are, whether or not the rise is accelerating, and if it is, by how much. If the fine details of the dispute are new to you, a quick summary is that a warmer sea will expand in volume, and a warmer land mass and atmosphere will help to melt glaciers and other land-based ice masses, which will also increase the volume of the oceans. How do we know what is happening? There are tide gauges, and some of them have been about for quite a long time. And the orbiting satellites are able to measure the height of the oceans. Do the tide gauges and the satellites agree? No, they don’t. Oh, and to further complicate things, the land masses of the earth are not stable. Some are rising, and some, like the land around Venice, are subsiding. So it is not always clear what is being measured.

And we are talking about tiny differences: about 1.7mm a year, across 70 per cent of the surface of the globe. The IPCC claimed in its Fourth Assessment Report that by 2100 the sea levels could be between 18 and 59 cm higher, which on average means annual increases of between 1.8mm and 5.9mm. Our Climate Commission, an organisation whose scientific acumen as revealed in its published work does not impress me, has been much more gloomy, seeing global warming produce seas that could be a metre higher than they now are by the end of the century.

Well, a very recent paper has been published by Nils-Axel Moerner and Albert Parker that looks closely at the Climate Commission’s estimates, and they weren’t impressed either. Moerner is a controversial figure in sea-level studies, notably for his straightforward rejection of any suggestion that the Maldives are under threat through sea-level rises — he has been studying the Maldives for a long time. Parker, who seems in the past to have been been someone called Boretti, has published on oceans, and is at the University of Ballarat. As always, I look at the data and the argument, not simply at the authors, or the journal in which their paper has been published (in this case an Indian journal).

The paper has a most useful introductory section on the use of tidal gauge records, from which I learned a good deal, including the need to keep cyclic changes in the ocean levels in mind (for example, the Pacific Decadal Oscillation). As we know ENSO pushes water around in the Pacific to a surprising degree, and that needs to be considered too. Their view, which is also mine, is that ‘the situation is far from conclusive and straightforward’ — but then, I think that about most aspects of ‘climate change’!

What conclusion did Moerner and Parker come to? They used all the tidal gauges that have a decently long history, not the small set of gauges referred to by the Climate Commission, which have a short time frame. Some of these go back a long way — Fremantle, for example, has a continuous 113-year history. Sydney’s is comparably long. The 86 tidal gauges used by Moerner and Parker produce ‘no evidence [of] any significant changes in the rate of sea-level change’. Further, ”[t]he average sea-level rise over the period 1990-2010 is a negligible 0.1 mm/year for the 70 stations not used by the Climate Commission’ [my emphasis]. If you put them all together you get a general average of 1.5mm per year. One argument is that things have been like that for centuries.

The authors then compare what they have done with the standard measurements used around the world, including satellite altimetry. Their calculations, they argue, are in broad agreement with the average rates of global tide gauge networks around the world. Their Figure 3 shows that the official Australian claim put forward by the Climate Commission is wildly higher than anything that has been measured elsewhere.

Moerner and Parker may be wrong. But they are using publicly available data, and arguing with caution and commonsense. And if they are wrong, then the opposing arguments too must be put forward with caution and commonsense. It is worth remembering that the IPCC has reduced its estimates of sea-level rise in each of its four assessment reports, beginning in 1990 and concluding in 2007. My expectation is that in its fifth report, due next year, the estimates will be somewhat lower still.

But in the meantime we will hear further scary talk about how rising sea levels will threaten coastal settlements. I can live with environmental lobby groups doing this. I find it quite unacceptable that a government Climate Commission can do so, without setting out the ‘ifs’ and ‘buts’ that any educated Australian would want to see..

[Readers who followed the discussion in the Comments here will see that I have taken seriously John Hunter’s criticisms of the Moerner/Parker paper. I accepted that paper at face value, because it seemed to me based on good data. Plainly I need to do more work on it, and will do so, returning in due course with a supplementary post. ]

12 Comments

  • Henry2 says:

    Don I’m going to quote you in comments on Skepticlawyer … I hope you don’t mind

    • giordano bruno says:

      Hi all. As the naive average rate of rise at the worldwide tide gauges of enough length (170 locations > 60 years) has been 0.24 mm/year with zero acceleration … There are still 996.5 mm missed of the 1000 mm by a century in the now 85 years left. One more prediction of the climate scarers seems wrong.

  • John Hunter says:

    There is some interesting background at:

    http://www.desmogblog.com/2013/04/28/ufos-sea-level-rise-and-magnetism -climate-science-denial

    and

    http://theconversation.com/peer-review-isnt-perfect-and-the-media-does nt-always-help-11318

    The latest Morner and Parker paper is just more of the drivel promulgated by Parker/Boretti, Morner and an interesting fellow called Thomas Watson …..

    • Don Aitkin says:

      John,

      I went to your links, and found that the desmogblog one was basically a denunciation of the author(s), and had little analysis of the data or anything else. The Conversation I have written about, and despair of, since the editorial control there means that only the orthodox position ever gets published as an article (a matter referred to several times in the discussion of the essay you linked to).

      Again, it is really pointless denouncing a scientist as writing drivel, unless you are able to say where the drivel is. I said that Moerner was controversial, and that he had studied the Maldives for a long time. Do you have objections to what he has written there? Or what he has written in the article I referred to? If so, what are your objections? As I said, I am unworried about who authors are, or where they publish. I am most interested in what they say, and the data and other support for what they say. If it’s crap, then I tend to pass them by next time. But I read the argument first.

      • John Hunter says:

        Don,

        As I and others pointed out in the Coastal Engineering Discussion of Boretti’s paper and in our Ocean Engineering response to Watson’s and Parkers “comment” on our earlier paper (references are in the The Conversation and desmogblog articles), the stuff that Boretti/Parker repeats endlessly is scientific drivel (actually some of it is plain lies). And even to a non-scientist, the stuff that Thomas Watson writes (as referenced in the desmogblog) is clearly drivel, is it not? Morner is another of Boretti/Parker’s collaborators who has also been known to write drivel (just Google “Morner” “IPCC” “stole” “tree” for a start).

        Or if you want a bit of a laugh (although it’s really pretty serious), see:

        http://www.members.iinet.net.au/~johnroberthunter/www-swg/morner_email s.txt

        When you’ve done this, let me know what you think (if you can’t get hold of the scientific papers to which I refer, I’ll gladly email them to you – you have my email address, so just ask).

        John

        • Don Aitkin says:

          I’ll go to your discussions later today, but you are still drifting off the topic. Tidal gauges papers, and there are many of them, are an attempt to deal with the questions of sea-level rise and speed. I know of the Moerner ‘tree’ episode, but that does not call into question his work on sea-levels in the Maldives over a very long time. Nor does it call into question his current paper.

          Surely the right approach is to show where he is wrong, not that he is not someone you respect. But I’ll suspend further comment until I’ve read the discussion you refer to.

          • John Hunter says:

            Hi Don,

            I’m sure you know of people who have been writing stuff over a number of years, whose writings you looked at in depth some time ago and whose writings you decided were utter crap. Do you continue to critically read their writings or have you decided that there are better things to do with your time? Boretti/Parker, Morner and Watson all fall into this camp for me – I don’t waste my time checking everything they write in order to see if there is a grain of truth in it.

            But in this case, I’ll humour you and start going through the Morner and Parker paper showing you a few of the problems – after a few of these, I’ll stop as I have better things to do. So here goes:

            1. The title: “Present-to-future sea level changes: The Australian case” – this is based on the claim that Boretti/Parker has made in numerous papers, which is that the absence of a significant observable acceleration in sea-level rise casts doubt on the generally-accepted projections of future sea-level. We thought we had put this to bed in our Discussion on an earlier paper by Boretti in Coastal Engineering (see Hunter and Brown, 2013. Discussion of Boretti, A., “Is there any support in the long term tide gauge data to the claims that parts of Sydney will be swamped by rising sea levels?”, Coastal Engineering, 64, 161-167, June 2012) where we said: “observational evidence of present sea-level acceleration provides no evidence which would, at present, cast doubt on the 1990-2100 projections of the IPCC AR4, or the common and well-founded expectation that sea level could rise by at least 500 mm during the 21st century”. Boretti was invited to respond to the discussion and he did (see http://arxiv.org/abs/1303.5519) – and if you read this “response”, you’ll realise that it isn’t a “response” at all – it doesn’t address our arguments and is, instead, just a parroting of his general (and strange) beliefs about sea-level – which is presumably the reason why the editors rejected it and it survives only on the arxiv website (where he posted it). Much the same thing happened when Watson and Boretti/Parker commented on our Ocean Engineering paper – they didn’t address the issues of the paper, but instead used it as an excuse for more advertising of their strange views – which is why we responded as we did (as described in the desmogblog article by Graham Readfearn). Boretti/Parker seems just as incapable of answering simple questions in a direct way (see the email trail provided with the desmogblog article).

            2. Abstract (“we are able to demonstrate that ….. there is an absence of acceleration over the last decade”): As we pointed out in our Discussion of Boretti’s Coastal Engineering paper (Hunter and Brown, 2013; see above), Boretti (and I assume this holds for Morner too) seems incapable of estimating the uncertainty in a calculation of observed acceleration. When you do estimate the uncertainty, you realise that accelerations observed over the past two decades have a relatively large uncertainty (as one would expect), such that the observations are quite consistent with current sea-level projections for this century. In other words, with only a 20-year record, the “noise” in the acceleration is too great to indicate whether or not the observed “signal” is “the same as” the projected signal. So this doesn’t “prove” that the model projections don’t fit the observations – it just shows that we don’t have enough information to say one way or the other.

            3. Abstract (“the National Tidal Centre claims that sea level is rising at a rate of 5.4 mm/year”)”: this is where it gets time-consuming – if you search through the paper you’ll find “5.4 mm/year” in a number of places:

            (a) In the Introduction where it says “They conclude the sea level has changed by ….. about 5.4 mm/year over the period 1990-2010” – it isn’t clear to whom “they” refers – it could be the Climate Commission report (reference 3), the “projection” paper of Rahmstorf (reference 34) or Church and White (reference 11). However, I can find no reference to a “5.4 mm/year” in any of these papers.

            (b) In “The Use of Tide Gauge Records” (“There are many different values proposed ranging from the very high values of 5.4 mm/year”) which cites reference 2, which links to an NTC website and two reports from the NTC. One of these reports does contain a reference to “5.4 mm/year” but this is to an estimate of sea-level rise for the gauge at Esperance for 1992 to 2008 – it certainly doesn’t refer to any general estimate of Australian sea-level rise.

            (c) In “The Australian tide gauge records” (“The ABSLMP[2] and AFGCC[3] statement of sharply rising sea levels with an average sea level rise of 5.4 mm/year for the period 1990-2010 is, of course, based on far too short period of recording.”): again, this refers to references 2 and 3 which, as noted above, don’t seem to contain a reference to “an average sea level rise of 5.4 mm/year”. They also don’t contain the word “sharply” in any reference to sea-level.

            (d) In “The Australian tide gauge records” (“….. the official statement of the NTC (AFGCC) that Australia is experiencing strong sea level acceleration with a present sea level rise of 5.4 mm/year cannot be validated …..”): again, I can find no “5.4 mm/year” in these references.

            (e) In “The Australian tide gauge records” (“….. in line with the 20-years SEAFRAME mean record of 5.4 mm/year (op. cit.)”: again, I can find no “5.4 mm/year” in these references.

            (f) In “Discussion” (“….. we compare the different data sets and confront the Australian governmental offices claim of a present mean rise in sea level of 5.4 mm/year obtained from the 16 SEAFARE (sic) stations …..”): again, I can find no “5.4 mm/year” in the references.

            (g) In “Discussion” (“From this comparison it seems obvious to us that the Australian governmental value of 5.4 mm/year must be significantly exaggerated”) and repeated in the “Conclusions”: again, I can find no “5.4 mm/year” in the references.

            If you do a Google on “5.4 mm/year Australian sea level rise” (without the quotes), you (not surprisingly!) mainly find references to the Morner and Parker paper. However, if you go to http://www.skepticalscience.com/news.php?n=1153&p=2 you’ll find a comment (number 51) which sheds some light on this (I’m obviously not the only one to have a problem with the “5.4 mm/year”) – it says “I have tracked down the source of Morner’s claim that the ABSLMP shows a 5.4 mm per year sea level rise. If you take the average of the raw trends of all 16 AMSLMP (sic) stations from their time of construction to June 2011, it is 5.37 mm/year. These are the trends before any adjustment for local changes in height of the equipment relative to surveyor’s datum points, and before reverse barometric adjustments.”. So – the “5.4 mm/year” apparently comes from Morner averaging the raw (not corrected) trends. It is not an “Australian governmental offices claim of a present mean rise in sea level” – it is simply an average of raw observations – which, incidentally, Morner and Parker don’t disagree with because this is what they say:

            “Confining the rate analysis to the last 10-20 years, as the Australian governmental offices have done[2-4], would have given meaningless rates in the order of 6.0-6.5 mm/year (Figure 2a) in line with the 20-years SEAFRAME mean record of 5.4 mm/year (op.cit.). Such values cannot be used for longer-term predictions[30,31].”

            So this is a strawman argument par excellence. The authors just averaged the publicly-available raw observations from the NTC SEAFRAME gauges (which started during the years 1990 to 1993). The authors don’t seem to disagree with the actual observations, but they then attribute this average to the “Australian governmental offices claim of a present mean rise in sea level” (suggesting that the Australian Government are presenting this as an estimate of the present long-term trend). However, nowhere can I find the “Australian Government” suggesting that these 1990-2010 (roughly) observations are indicative of a long-term trend – in fact one of the NTC reports cited specifically say “the presence of low frequency variations can mask the underlying long-term trend in sea level records that are shorter than several decades” and the other says “the presence of these low frequency variations can mask the underlying long-term trend in sea level records that are less than three decades in length”. In fact, it has been well-known among sea-level scientists for a long time that you can’t estimate long-term trends from relatively short sea-level records – 12 years ago, Douglas (one of the sea-level experts at that time) argued that records of at least 50 to 80 years duration may be required to yield robust estimates of sea level rise at a given site – so this is not news to those in the game!

            So, to summarise this point, the authors base most of their paper on the strawman argument of an “Australian governmental offices claim of a present mean rise in sea level”, which is, in fact, simply an average of publicly-available raw observations.

            Incidentally, there is more discussion of Morner and Parker at the above SkepticalScience site (http://www.skepticalscience.com/news.php?p=2&t=55&&n=1153).

            4. Introduction (“In their report published in 2007, the Intergovernmental Panel on Climate Change[1] concluded that sea level (SL) is likely to rise between 18 and 59 cm or 38.5±20.5 cm by year 2100. Though this is a significant lowering from previous estimates by IPCC, viz. 62.5±47.5 cm in 1990, 53.5±40.5 cm in 1995, 48.5±39.5 cm in 2001 and 38.5 cm±20.5 cm in 2007”:

            (a) The quoted projection from the 2007 report is incorrect – it omits an important term called the “scaled-up ice sheet discharge”, which is around 20 cm for the highest emission scenario. For the period 1990-2100, the actual range of the projections is 18 to 81 cm or 49.5±31.5 (see http://www.cmar.csiro.au/sealevel/sl_proj_21st.html).

            (b) The quoted projection from the 2001 report is not quite right – it should be 9.2 to 85.9 cm or 47.6±38.4 for the period 1990-2100.

            So the projection from the 2007 report does not represent a “significant lowering” from the 2001 report – in fact the two projections are in pretty good agreement (given that the definitions of the uncertainties were slightly different) – the central values are only 2 cm different.

            5. Introduction (“In this paper, we will try to demonstrate that neither the mean rates given nor the proposed sea level acceleration can be substantiated by observational facts”): Firstly, the “mean rates” ARE “observational facts” – the “5.4 mm/year” is an average observed rate, albeit one that is from raw data and taken over a relatively short period so that it isn’t indicative of a long-term mean. Secondly, there is no “proposed sea level acceleration” – there are just curves which represent projections over this century (e.g. those produced by the IPCC). If Boretti/Parker had bothered to read our Discussion to his Coastal Engineering paper, he’d have learned that, in fact, the IPCC (2007) projections have a very small acceleration from 1990 to 2010 – an acceleration that is so small as to be undetectable by sea-level observations. So Morner and Parker are pissing in the proverbial wind, by continuing with this argument which Boretti/Parker has already done to death.

            It was at this point that I gave up. If you want to continue checking on the accuracy of the authors’ claims (e.g. comparing what they say about a given reference and what the reference actually says) then go ahead – but I’ve spent far too much time on this already.

            Both Morner and Boretti/Parker (and many other contrarians) have a deep suspicion of climate models without, presumably, understanding what a “model” really is. Boretti/Parker has indicated, in a number of other papers, that he would rather just linearly extrapolate the last century’s sea-level trend out to 2100 to provide a “projection” – without realising that linear extrapolation is “model”, albeit a rather uninformed one. Contrary to what you will hear from the contrarians, the models used by the IPCC for providing projections of sea-level rise, now do a pretty good job of hindcasting the sea-level rise over the past century (see Church, Monselesan, Gregory and Marzeion, 2013. “Evaluating the ability of process based models to project sea-level change, Environmental Research Letters, 8, 014051) – they also now do a very good job of showing that, and explaining why, there has been virtually no acceleration of sea level over the past 20 years.

            If you send me your email address, Don, I can send you copies of the papers I’ve referenced above.

            Cheers,

            John

          • John Hunter says:

            Hi Don,

            I took quite a bit of trouble writing my last post to you, indicating why Morner and Parker (2013) is drivel. I did it because I think that you are a person who can be convinced by solid evidence and not be confused (at least for long) by much of the rubbish that appears on the blogosphere (and also in some of the rather obscure online journals that have not been around long enough to have earned much credibility). So – I’d be glad to hear if your views have changed at all.

            Also, I spend some of my time advising policymakers and planners on the vertical height that they should allow for future sea-level rise. From now until 2100, I’d allow around 0.8 metre, based on projections which are generally accepted by climate scientists, and on information about local tides and storm surges (I say “around” and there is a regional component to this, so please don’t quote me as saying that “the height allowance should be 0.8 metres”).

            Now, from you reading of Morner and Parker (2013), and everything else that you have read on the subject, what would you suggest as a height allowance for sea-level rise from now until 2100?

            Finally, you say “It is worth remembering that the IPCC has reduced its estimates of sea-level rise in each of its four assessment reports, beginning in 1990 and concluding in 2007.” This is, as I noted in my previous posting incorrect (I’m surprised that you have just accepted what Morner and Parker claimed, without actually checking it) – the TAR and AR4 projections were very similar. You also say “My expectation is that in its fifth report, due next year, the estimates will be somewhat lower still.” – I wonder why you say this, given that the AR5 drafts have already been leaked on the web and you that you could actually check whether there is any support for your claim. Incidentally, the AR5 WGI report comes out in September 2013, and not “next year”.

            I’d be really glad of a response to this and my previous post.

          • Don Aitkin says:

            John,

            This has been a very busy three days (my weekends are busier than my weeks, because of the voluntary work I do). I started on a response after reading your paper, couldn’t get the Comment because it was behind a paywall, and then had to do other things. I’ll do my best to reply to both posts tomorrow.

  • Don Aitkin says:

    for John Hunter,

    I am embarrassed and grateful in equal measure that you wrote such a long post. I have not gone into the field in anything like such detail, and I will now have to do so! Parker/Boretti and Watson are not authors whose work interests me, but I came across Moerner years ago, and assumed that his field work was sound. Now I’ll have to go back to it.

    Your Coastal Engineering paper I did read, though it doesn’t mention any of the authors whose work you critics. It seems to me to be a modelling exercise based on 30-year runs. In your Conversation joint piece you say ‘sea levels are rising in response to climate change’, and ‘global sea levels are rising at 3 mm a year but this will increase in the coming decades’ — I felt in each case that there are no grounds for such certainty.

    But I will put a note at the end of my own essay, to the effect that I need to do more on this, will consult with some people whom I know who have some expertise in the field, and return in due course.

    Thank you for the work you put into your posts.

    • John Hunter says:

      Don, you say:

      “Your Coastal Engineering paper I did read, though it doesn’t mention any
      of the authors whose work you critics. It seems to me to be a modelling
      exercise based on 30-year runs.”

      The only “30 years” I can think of is the length of the tidal records that we analysed in our first Ocean Engineering paper (Hunter, Church, White and Zhang, 2013, DOI: 10.1016/j.oceaneng.2012.12.041). This used the IPCC projections for the 21st century and the statistics of tides and storm surges to generate vertical “allowances” for sea-level rise. It was nothing to do with anything that Boretti/Parker had done, but Watson and Parker chose to use it as a vehicle to promote yet more of their normal drivel – a “comment” – which was so bad that it received the short and curt response (Hunter, Church, White and Zhang, 2013, DOI: 10.1016/j.oceaneng.2013.03.013) referred to in the desmogblog article.

      I think you are mixing up the papers – our one in Coastal Engineering (Hunter and Brown, 2012, DOI: 10.1016/j.coastaleng.2012.12.003
      which was a response to a paper by Boretti) and our ones in Ocean Engineering (see above).

      Both our Coastal Engineering paper and our second Ocean Engineering paper were highly critical of Boretti/Parker.

      You also say “In your Conversation joint piece you say ‘sea levels are rising in response to climate change’, and ‘global sea levels are rising at 3 mm a year but this will increase in the coming decades’ — I felt in each
      case that there are no grounds for such certainty.”

      Well, the only number cited is “3 mm a year” and this is just the rounded value of global-average sea-level rise observed since 1995 by satellite altimeters. Most people (including most contrarians, who just say it is correct but “small”) agree with this (Morner doesn’t, but he doesn’t agree with an awful lot). The other things we said are unquantified statements which, if they were quantified would clearly carry an uncertainty estimate. For example, I’d replace “but this will increase in the coming decades” by an estimate of the rate of rise based on future projections – which do involve significant uncertainty. However, I know of no projection that suggest that sea-level will fall this century (I’d say that the minimum rise is around 0.3 metres) and the highest IPCC projections suggest a rise of around 0.8 metres (although some suggest it could be significantly higher). So – I’m sure you know what needs to be done when you have a range of future possibilities, all of which have some policy implications – you do a risk assessment, based on what you know. This is exactly what we did in our first Ocean Engineering paper. What you most certainly shouldn’t do when faced with prospects of an uncertain future is to suggest (as do Morner, Boretti/Parker etc) that not much will happen and that we don’t need to worry about it – these are the guys who have “no grounds for such certainty”.

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