Where sea-level rise isn’t what it seems

Whilst working for the Maldives government I was always aware of the need to resist the temptation of making sweeping statements about the impacts of climate change and sea-level rise in the service of wider political ends. I saw part of my role as advisor to push back against the simplistic view that given that we know that the planet is warming, and the seas are rising, surely the impacts  – in terms of erosion, flooding events and disasters – should increasingly be visible now, right?

A new paper published in the AGU’s house journal Eos Transactions shows why caution is often justified. Here (via a screengrab, as the entire thing is behind a password) is the 1993-2011 sea level trend data from Tarawa atoll, part of Kiribati in the central Pacific:

Whoa! No sea-level rise there, then. And yet of course climate campaigners – and even the Kiribati government – understandably anxious to highlight the future existential threat to the islands, have used storm surges, flooding events and suchlike as evidence of current sea-level rise impacts. Which they are almost certainly not, at least not in Tarawa atoll anyway.

To me the graph is interesting for two reasons. The first is the absence of any trend over the last 20 years towards increased sea levels in that part of the Pacific. This should be expected, because sea level rise as a computed average means that the oceans are rising in more places than they are falling, but they are falling in some places nonetheless. (Just as a few areas of the globe have got colder over recent years.) The second is the sheer up-and-down massive variability in actual sea levels, which is linked to the El Niño cycle. The author (Simon Donner, a geographer from the University of British Columbia, Canada) points out in the Eos paper that the monthly mean sea level dropped by nearly half a metre (45cm) between March 1997 and February 1998 because of switch from El Niño to La Niña conditions, and peaks of 15cm were seen in each of the recent El Niño events – which as the author points out is “equivalent to 50 years of global sea level rise at the rate observed since 2000 of 3 mm per year”.

So the problem with attributing sea-level rise impacts is the same as with attributing heat-waves, droughts, floods or other extreme events to climate change – you have to try to figure out what would have happened absent the global warming trend (in order to distinguish genuine impacts from noise), and also distinguish background changes from more direct anthropogenic interference which might confuse the picture. In a heatwave, for instance, were the extreme temperatures caused by the urban heat island effect in a more built-up area?

In Tarawa atoll, direct human interference probably explains the majority of what is often pointed to as evidence of sea-level rise impact, according to Donner. Because few readers will be able to access the paper online, I will take a leaf out of Judith Curry’s book and quote extensively from it here:

The combination of natural weather – and climate – driven variability in sea level and the astronomical tidal cycle can lead to flooding and erosion events, particularly in sand-dominated systems like atolls and barrier islands. For example, the 2004–2005 ENSO event contributed to two major flooding events in Tarawa. During a ‘king’ tide on 10 February 2005, water flooded several causeways between the islets in South Tarawa and damaged the hospital in the town of Betio. A second flooding event occurred 2 weeks later, despite the lower daily tidal range, because of record high winds (47 knots at Betio) and record-low surface level pressure (999.2 hectopascals). Even though the maximum gauge height was 25 centimeters below that reached 2 weeks earlier, the northwest winds generated lagoon waves that again breached sea walls, flooded causeways, and damaged homes and public infrastructure.

These flooding events, though statistically more likely to happen as global average sea level rises, are themselves no more evidence of rising sea level than an individual heat wave is evidence of rising global temperatures. Despite a continued global average sea level rise, the gauge height reached on 10 February 2005 in Tarawa has not been surpassed since.

The paper then goes on to discuss some direct human impacts which can impact shoreline dynamics with or without a sea-level trend:

Three types of shoreline modification that are typical in low-lying island nations have altered sediment supply and island shape in South Tarawa [Webb, 2005]. First, land reclamation, accomplished by infilling behind a constructed sea wall, has increased land area in some locations but exacerbated erosion and inundation in others. The shoreline of islets like Bairiki has been extended lagoonward through the construction of government facilities, landfills, maneabas (community meeting houses), and individual homes [Webb and Kench, 2010]. At the same time, poor engineering of sea walls has led to erosion at the airport and the hospital [Webb, 2005] on the islet of Bikenibeu and also led to inundation of reclaimed lands along the lagoon shoreline in Abarao and other islets.

Second, the practice of mining of beaches and barrier reefs for construction materials, common in Kiribati, Tuvalu, and other atoll nations, can make the shoreline more vulnerable to tidal extremes and storms [Webb, 2005]. Almost three quarters of the households in South Tarawa mine sand, gravel, and reef rock from the lagoon or the ocean reef, with one third doing so more than once a week [Greer Consulting Services, 2007]. Although the effect of beach mining on the shoreline is difficult to distinguish from that of other coastal processes, concern is sufficient to warrant European Union investment in a midlagoon dredging project to provide an alternative source of fill.

Last, the construction of causeways between islets has altered islet evolution. Unlike a bridge, a solid, hard-topped causeway limits or blocks the natural flow of sediment between the ocean and the lagoon. Causeway construction allowed nearshore currents to deposit sediment along the lagoon beaches of South Tarawa islets like Bairiki and Nanikai [Solomon and Forbes, 1999]. These densely populated islets have actually grown in area over the past few decades [Webb and Kench, 2010] because of the unintentional impacts of local development on sediment supply, land reclamation, and natural processes. This accretion, however, came at the cost of other islets. The lagoon islet of Bikeman, which was dotted with coconut trees during the Battle of Tarawa, is now a sandbar that disappears from view at high tide. Despite some claims to the contrary by climate activists, the loss of this once popular resting spot for fishermen is primarily due to the construction of the Betio-Bairiki causeway, which redirects sediment flow.

This leads to important communications issues, of course.  So whilst I have no truck with sceptics like Nils-Axel Mörner, who use highly-questionable anecdotes in one small area to ‘prove’ that the entire global rise in sea levels isn’t happening, I do feel that any degree of exaggeration simply leaves an open goal for sceptics to belittle the real challenges these island countries face. It is therefore counter-productive as well as dishonest (intentionally or unintentionally). Ergo:

The failure to consider the contribution of natural variability and direct human modifications can lead to misattribution of flooding events or shoreline changes to sea level rise. Tarawa, the most easily accessible atoll in Kiribati, is a popular destination for journalists and activists interested in observing and communicating the impacts of sea level rise on a low-lying nation. For example, a Greenpeace slide show within an explanation of what sea level rise means that depicts the 2005 flooding remains among the top responses to an Internet query of “Kiribati” and “sea level rise.” These common images of flooded homes and waves crashing across the causeways—collected during an anomalous event on islets susceptible to flooding due in part to local modifications to the environment—can provide the false impression that Tarawa is subject to constant flooding because of sea level rise.

The attribution problem is further magnified by the political situation. The Kiribati government faces the difficult challenge of raising international awareness about the local impacts of climate change to support adaptation and mitigation efforts. Interpreting the causes of shoreline changes or flood events, as well as predicting the local impacts of sea level rise, is challenging for a developing country with limited resources for scientific investigations. Many individual observations of erosion, flooding, or groundwater salinization, recorded in community consultations for internationally funded climate change adaptation programs, are thus attributed to climate change without scientific analysis [e.g., Mackenzie, 2004]. These events are presented as examples of climate change impacts in promotional materials and at international events (e.g., “Our Road to Copenhagen,” a Kiribati side event at COP15 in Copenhagen), without any mention of ENSO-driven natural variability or local shoreline modification.

Such unverified attribution can inflame or invite skepticism of the scientific evidence for a human-caused increase in the global sea level. After Webb and Kench [2010] reported that the area of 23 atoll islets in Kiribati and neighboring countries had remained stable or increased over the past 20–60 years, some of the international news media reported that the effects of sea level rise on atoll nations were exaggerated and that Kiribati is not threatened by future sea level rise (e.g., R. Callick, Coral islands left high and dry, The Australian, 2010). Though the study did show evidence that atoll islets were dynamic and do not necessarily decrease in area in response to sea level rise, the islets in question remain vulnerable to inundation from global mean sea level rise in the future, as the authors stressed in a subsequent briefing note.

The challenge of differentiating between observed changes in the coastal environmental and the projected impact of sea level rise is not unique to Kiribati. For example, the Carteret Islanders of Papua New Guinea have been migrating from their home atoll for decades because overpopulation, human development, and natural disasters, in addition to sea level rise, have caused coastal erosion and reduced water availability [Connell, 1990]. Nevertheless, the Carteret Islanders are commonly called the world’s first climate change “refugees” in outreach and documentary films (e.g., The Rising Tide).

The upshot?

Instead of incorrectly attributing individual flood events or shoreline changes to global sea level rise, scientists and climate communicators can use such occurrences to educate the public about the various natural and human processes that affect sea level, the shoreline, and the shape of islands. This would better prepare the public and policy makers for the changes that societies are likely to experience as global sea level rises in the coming decades.

I couldn’t agree more. If island nations are making themselves more vulnerable to the slow process of sea-level rise by mining sand, destroying reefs and so on, they need to know about it – and not be encouraged to blame it all on outsiders causing climate change. In the case of the impacts currently affecting Kiribati, ‘mitigation’ means changing local practices as much as changing global ones. And therein lies a lesson for us all.


  1. Barry Woods

    Nils is more of an expert that you ate Mark.. little unfair to label him as a sceptic

    He is just a little cross to be labelled a denier, (by others) just to merely point out many of the issues that you just have.

    Ie lots of what you have just written, would get you called a sea level rise denier, in many quarter’s, just for talking,about all the issues.

    Nils is angry with the IPCC, which is not to be angry with science, or to be a sceptic or a denier. It us to be angry with the politicisation of science.

    I have met him once.. nice chap, but perhaps come across badly compared to the PowerPoint generation of science.

    There is an Ippc report that if you dig deep enough, does give his criticisms, some

  2. Barry Woods

    Oops Android cut me off

    .. support.

    At planet under pressure. One speaker spoke about trying to persuade construction companies not to do this..

    Similarly, islands like Tuvalu are at the edge of human habitabilty. Ie dependeent on rainwater, isolated. Not where you would choose to live. Add to that population pressures, on scare resources anyway. Make any real or imagined projected sea level rise the least if people problems, along with local marine polution, etc

    Yet all to often this is all forgotten, as far easier for local peoples, politicians to blame their environmental failings on someone/somethingelse

    Hopefully, all these issues can be discussed, with out dome enviros, going into knee jerk climate change denier mode.

    Do check out how exactly the ipcc come up with sea level figures, as their is some justification of the criticisms of the methodology

  3. martyn

    Barry – you entire post above is based on dividing people into tribes, not on what is written by Mark.

    There are many scientists and “warmists” to guess at a label you might apply who constantly question details of the science, and debate how best to communicate our understanding in ways that deal with the general global problem and the local impacts, and the variations in confidence that scientists have in different areas of climate science.

    Indeed – many of the issues that have been used by those arguing against IPCC view – like so-called Himalya-gate – were uncovered not by “sceptics” but by scientists who accept the general IPCC thrust but question everything.

    I don’t agree with Mark on everything but am glad he challenges and probes. But what is important is he does this using all evidence and rigorous standards of checking – not by cherry-picking.

    1. Barry Woods

      Mark divide people into tribes – ref his Nils comment – I’m suggesting not to.

  4. martyn

    Barry – much more in agreement with end of second post which wasn’t there when I responded. Perhaps if “deniers” would be more responsible there would be more chance of what you call for – you can’t just blame the other side.

    1. Mark Lynas (Post author)

      Thanks to both for your comments. Barry, I do feel that Nils Axel-Morner’s work has been shown to be sub-standard – in my (albeit rather polemical) post with George on this, we linked to many scientific rebuttals, and also to the tide gauge data from Maldivian sites showing clear long-term rises. I have also had emails forwarded which show that Axel-Morner came up with all sorts of excuses for refusing even to look at and analyse that data. As Martyn says, the challenge for us all as sceptics (with a small ‘S’!) and truth-seekers is to ask for evidence always. We must also challenge ourselves of course – one of the strongest human impulses is to always seek self-affirmation (termed ‘confirmation bias’), and even scientists succumb to that on a regular basis. In my view it is an entirely honourable thing to want to raise awareness of the plight of Pacific islanders – but the impacts that we cite need to be clearly attributable to climate change if we want to help rather than hinder in the long run.

    2. Barry Woods

      if people get called ‘deniers’ for merely pointing out all these issue, they would not get so cross at people that called them ‘deniers’

      I’m trying to persuade people to end the vicious circle of name calling- it is v hard.

      To be clear, there is a problem within the environmental sphere.
      To point out in the past that Kiribati is not (at the moment sinking)
      is to have been called all sorts of names, by some, and accusations made about anybody suggesting these very real issues, especially construction/erosion (ie must be a sceptic/denier, part of fossil fuel denial industry)

      As is clear, from the above, and anybody that knows these islands, there are large man-made impact in the environments of these island, population pressure making things much worse. and that sea -level rise is a distraction from all these local issues.

    3. Barry Woods

      Martyn – what do you mean if the deniers were more responsible.. People have only been repeatably called deniers by the likes of greenpeace, etc. for pointing out all the stuff Mark has just written about and complaining about the hyperbole

      There come a point, when people get irritated and angry about this and they say sod ‘responsibility’, because they see lobbyists & politicians are not being responsible by hyping sea level. And they decide it is a political fight against the rhetoric, of some large and overly powerful green NGO’s and politics, and they react. (mostly badly and counterproductively)

      Which of course, just makes the polarisation worse..

      Just try repeating anything Mark has just written, including local responsibility, to those groups shouting ‘climate justice’, you will be swiftly labelled as a ‘denier’

      The science says most of the environmetal issues currently around these islands are NOT to do with sea-level rise (at this time) but to say so, is to be insulted and ridiculed. At least that is my experience.

      What happens in the future is of course a different issue and very much open to debate. The point is, politically, claims are made they are drowning now, because of ‘climate change’

      So I really welcome Mark’s highlighting of the fact that the issues of small islands are not just down to one parameter, and acknowledging the politicisation of the issue, as a factor.


    4. martyn

      It gets awkward because I wasn’t keen to use “deniers” as a catch all term, but for the sake of brevity ended up doing so.

      I disagree with your fundamental point that environmentalists, or warmists, or whatever object to pieces that challenge aspects of our understanding of climate impacts. If the science is robust, and the conclusions not extrapolated beyond all reason then most welcome it as advancing knowledge, and try and locate it within our overall knowledge.

      It is the frequent cherrypicking and misuse of such material by some “deniers” that gets backs up and makes dialogue harder. That is what I think is irresponsible.

    5. Barry Woods

      And greenpeace doesn’t cherry pick!

      ie they claim 300k people are dying of climate change every year, which is not supported by any rigorous science, they use rhetoric about ‘climate denial’ about anyone that challenges them

      The ‘deniers’ do not have the media at their disposal, nor multi million budgets, like Greenpeace, FOE, wwf, etc.. nor the resources of the departments of state.

      everyone should be responsible. but it is very asymetric discussion, unfunded bloggers, vs multinationals ngo’s and governments..

    6. Toby

      No, they just have paupers like the Koch Brothers and the Scaife Foundation.

    7. benpal

      Toby says: 24 August 2012 at 7:35 pm
      “No, they just have paupers like the Koch Brothers and the Scaife Foundation.”

      Now, THIS is a highly intelligent contribution to the debate. This kind of argument is typically used when you are out of factual arguments. Just for the record: The Koch Brothers are sponsors to a large number of universities and institutes, irrelevant what they think of climate change.

      This is the most stupid comment in an otherwise interesting and balanced discussion.

  5. martyn

    Also not at all sure you are right that green groups would object to Mark raising local decisions and their impacts on flood risk – have read much on mangrove swamps, reef protection etc.

  6. Barry Woods

    try it for yourself.

  7. WB

    Mark, aren’t you the guy who arranged the photo of the Maldives govt folks all in their scuba gear, sitting at their desks under water? To ‘highlight the problem of sea level rise’. If not, apologies, for mistaking you. If you were, however, how do you reconcile your own false propaganda with that pic with this post now that’s all about accuracy?

    1. Mark Lynas (Post author)

      No, I didn’t arrange the underwater cabinet meeting. I would defend it though – obviously it was a press stunt (and a very successful one), but also the issue of sea level rise is entirely real, as the EOS paper I refer to in the blog is at pains to point out. This is about getting the best information on the relative contributions of SLR and direct human impacts in a particular location… it will be different elsewhere.

    2. chris y

      For me, the underwater cabinet meeting was a tipping point.
      It was a canonical ‘jump the shark’ moment.
      That was when I realized that climate change driven SLR had nothing to do with careful science, and everything to do with sucking money out of developed countries.

      NOAA Tides and Currents lists Kiribati SLR as 0.58 mm/yr, +/- 0.87 mm/yr, from 1949 to 2007.

  8. richard

    also good to point out that in the maldives and other islands they have been using the coral for building for decades and the coral has still not recovered from the heavy usage in the 1970’s which leads to sea erosion.

    though they are building airports and hotel resorts at sea level so seems no worries about sea level rise.

    Moreover having gone through: The South Pacific Sea Level and Climate Monitoring Project (SPSLCMP0. This has placed the most sophisticated equipment ever developed (SEAFRAME) on 12 Pacific Islands

    i do not see any sea level rise of any note.

  9. Paul

    Guys, guys, listen I’m a marine biologist currently working in Chick’n you like between jobs so I know what I’m talking about. I’ve been to the Maldives. I’ve snorkelled in the waters around that atoll and what I saw worries the hell out of me.
    Crabs with 14 claws and three eyes. Lobsters with tails. Swimming puffins with no wings, instead, three elongated fins just behind their tail feathers.
    I’ve witnessed fish that fart. Yes they fart and every time they do you can see tears in their eyes as the pain is so intense.
    People it’s that serious! I’ve counselled fallen lapwings who fall from the sky exhausted by the release of carbon dioxide from a warming sea and the fact that sea level rise makes the distance between migrating flocks and sea surface smaller is increasing this terrible massacre. To date four more lapwings have died since January.
    Now that it seems that rising temperatures are attracting wolves to the islands the danger to the inhabitants from voracious packs of these wolves can only lead to more death.
    I urge you to do something and now. Occupy something. Do it in your town or city today. Even if it’s only a phone booth it doesn’t matter. Just do it.
    Visit my website which, hopefully, should be up and running by late next year. Type “wolves on Tuvalu” into google for more info.

    1. Barry Woods

      Is this comment a parody of an activist…

      It sounds too hysterical to be true…
      If true, whatever is happening to the creatures in you claims. It is ceratainly not due to current to date co2 level rise in the atmosphere or the ocean, or due to a rise in sea level

      Three legged creatures, arc sounds very much more likely due to local marine pollution…

      Just a thought are all those airports being built in dtilts for the future… How high?

  10. Jeremy Poynton

    “highly-questionable anecdotes”

    Excellent description of CAGW. Many thanks. I’ll hang onto that. Good Ad Hom on Mr. Morner as well. Par for the course.

  11. Gary G

    I am puzzled by something you are doing here. I see you refer to ‘skeptics’ and ‘deniers’ as being two different groups…. could you please qualify these terms?

    1. Les Brown

      It’s the same difference as that between an Agnostic and an Atheist. The Climate Change Agnostic is skeptical that it is man caused – maybe yes, maybe no, whilst the Climate Change Atheist denies that it man has anything to do with it.

  12. Gary G

    Apologies, I came back to this thread believing it was the one I had been reading last night. Too many pages to go thru… There it is! I guess my question is to Barry Woods, then.

  13. Henk Lankamp

    The figure doesn’t show trend data, only monthly fluctuations. Data can be found here.
    It doesn’t matter if you choose ‘Monthly sea level data’ or ‘metric sea level data’; both give a positive linear trend of 2.8 mm/yr and the trend is significant (p < 0.01).

    1. Mark Lynas (Post author)

      I can’t see this on the page you link to… did you download the monthly data and calculate the trend yourself?

    2. Henk Lankamp

      That’s right.

    3. Mark Lynas (Post author)

      It’s just that it has a health warning on the raw data of “use with extreme caution” – are you sure you used it correctly? I just think, if you’re right, this is an important fact which should have been in the Eos paper.

  14. Henk Lankamp

    Yes, normally one should use the RLR data, but in this case I used the raw metric data to get the same y-scale as in the graph. It doesn’t matter for the linear trend, because for all data points RLR = raw + 5267 mm for this station.
    When data are cut off at the end of 2010 as in the EOS graph, the trend is a fraction lower (2.7 mm/yr) then the 2.8 mentioned in my first comment (latest data available is August 2011).

    As I don’t have access to the full paper, I can’t tell what is exactly stated there. Does it mention a ‘no sea level rise’?

    1. Mark Lynas (Post author)

      Well, it’s a 4MB file – shall I email it to you? I can see your email from the moderator’s page, assuming you entered the correct one!

      I think you should certainly:

      a) check the data procedure with the author
      b) complain to the author if SLR is 2.7mm/yr and it was not stated in the paper

    2. Henk Lankamp

      Please do, and thanks.
      I will leave a note on the blog of Simon Donner. It looks like he is in Kiribati at the moment.

    3. Mark Lynas (Post author)

      Done. Let me know how you get on!

  15. Craig Hillman

    Mark, I live at Gosford NSW Australia, our Government and local Council have adopted IPCC global average sea level rise projections and added to them resulting in projections of 90cm by 2100, further the local Council has added a sea level rise warning to property titles resulting in distress to local residents and increased insurance costs.
    All this despite MHL ( a NSW gov department ) responsible for sea level rise monitoring advising the average local (Sydney NSW) rise over 100 years is 0.9mm a year and this has dropped to 0.4mm a year for the last 20 years the reverse of IPCC global average projections. I have perused many Government “sea level rise” policy statements and alarmingly none seem to include or reference local data, all rely on IPCC global average projections. Surely the various scientific advisors to the Australian governments are not that stupid?, is this lax science or calculated deceit ?


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