Getting it Wright on sea level rise

Sea level rise of up to 40cm around New Zealand by the middle of this century is already locked in and will cause significant problems for coastal communities and infrastructure, according to a new report just released by Dr Jan Wright, the Parliamentary Commissioner for the Environment. The report — Changing Climate and Rising Seas: Understanding the Science [pdf] — provides an overview of why sea levels are currently rising and why they are expected to continue rising over the rest of this century and beyond. A follow-up report due next year will “show in some detail which areas of the coastline around the country are most vulnerable to sea level rise and assess the risk to infrastructure in those areas”.

Introducing the report, Dr Wright said that the scientific evidence is now irrefutable. “The climate is changing and causing the sea to rise”.

“A rise of 30 cm may not sound much, but its impact will be very costly for many landowners. Damaging coastal floods will become increasingly frequent. The insurance industry is becoming aware of, and responding to, the increased flooding risk. Some councils and communities have already started to face hard questions.”

Commenting on the report for the Science Media Centre, Associate Professor Nancy Bertler of the Joint Antarctic Research Institute, Victoria University of Wellington/GNS Science, said:

The report provides an excellent summary on the current knowledge of past and future sea level rise including the main drivers and the regional patterns. Dr. Wright highlights the concern of the scientific community on the possibility of substantial and abrupt future contributions from the West Antarctic ice sheet.

Additional important considerations are that: worldwide over 200 million people live within one metre of sea level. The last time atmospheric carbon dioxide concentration was at 400 ppm (3-5 million years ago) the associated global temperatures caused the Greenland and West Antarctic ice sheets to catastrophically collapse – raising global sea level by around ten to twenty metres.

The rate at which sea level will rise has important implications on our ability to adapt. New research suggests that sea level could rise as quickly as 4 metres per 100 years (or 1 metre per 25 years). Assuming even a modest global sea level increase of 50 cm by 2100 (IPCC scenario RCP 4.5), the frequency of coastal inundation in New Zealand is predicted to increase by a multiplier of 1000 times.

Under such a scenario, an annual event becomes a daily event, a ‘100 year’ event occurs several times per year. As an approximation: every 0.1m rise triples the frequency of inundation events.

Dr Wright focusses on the near term implications for New Zealand, a sensible choice given the tendency to dismiss sea level rise as a problem for the distant future, but in my view she misses an opportunity to spell out the strong relationship between atmospheric CO2 levels and equilibrium sea level. The last time CO2 stood at 400 ppm, global sea level was about 20m higher than today. That’s where we’re heading, unless we can get greenhouse gas levels down, and it has very important implications for emissions policy. But I’m nit-picking…

Changing Climate and Rising Seas is a very readable introduction to the science of sea level rise, and gives a very clear picture of the state of current knowledge. It’s a welcome addition to what passes for national discourse on the inevitability of climate change and the necessity of adapting to what it brings. Next year’s report on regional impacts will be even more important.

61 thoughts on “Getting it Wright on sea level rise”

  1. Strangely enough, no one in Christchurch seems to be worried about sea level rise, judging by all the new builds that are happening in Brighton right now.

    There are several new houses that have sprung up in the last few months on Marine Parade, and they are selling for quite a good price too

      1. I have already got a full insurance payout from our coastal property and we are rebuilding at 700m above sea level.

        So you could say we have got things covered on that front.

        1. we are rebuilding at 700m above sea level.

          Hmmm…. a climate change denier who is moving away from the coast; I wonder why that might be?

          Perhaps Andy knows something that we do, too?

  2. Gareth

    What is the point in making comments if every discussion is basically taken over by Andy S and responses to him. Its putting me off and I am sure many others off from bothering to engage. Its your blog, and a good one, but ruined by Andy on a daily basis. I am assuming he is genuine, but cant help himself. Can I suggest limiting him to, say, 1-2 comments per post. We pretty much know what he is on about.

    1. Oh I’m sorry if I am “ruining” your blogging experience

      [Childish invective snipped. Either engage politely with the subject of the post and the conversation that develops, or you’ll be back on moderation. GR]

      1. Oh sorry Rupert, I will desist from commenting here in future

        Remind me again what you have contributed to this blog?
        All I hear is an endless stream of sneering
        I will refrain from any further comments in the near future

        The semi-literate pensioners from the Coromanel can prattle on about “wicket and wired problems” and fantasise about killing all Americans

        Have a nice day Rupert

      1. The relentless Graphs and links to data whilst your chums prattle on about AGW slowing down the earths rotation and causing earthquakes

        At least this “narcissist” is vaguely connected to planet Earth unlike the acid casualties posting here.

  3. “Oh sorry Rupert, I will desist from commenting here in future” – we should be so lucky!

    Complaining about sneering – that’s pretty rich, coming from you.

    I must direct a confused friend here – not to read the junk contributions, but the content of the report.

  4. The person calling themselves AndyS must surely be a Heartland mercenary, although he or she denies this without a shred of evidence. It is the only explanation I can think of as a normal person would not spend so much of their time here, life is short enough as it is.

  5. Interesting chat with Jan Wright here. She makes a good point about NZ needing to do both adaptation and mitigation. The message being delivered to the government is pretty clear – we need to start doing stuff now, all this crap about being a fast follower has to stop.

  6. Global sea level rise from about 1900 – 1970 was 1.8mm per year. From roughly 1970 – 2014 it has been about 3.5mm per year (according to the jason topex information) so there has been an acceleration over the last 100 years. Even the most conservative view on global warming suggests to me a further acceleration to about 7.0 mm per year is plausible over coming decades. At least 400mm should be counted on by mid century.

    It is just stupidity not to consider this when planning building or infrastructure development. The government need to get their head out of the sand and show some leadership.

        1. Actually I can’t read that paper thingy on my computer, it doesn’t render in a form that I can read. The Skeptical Science link doesn’t seem to support the notion that SLR is accelerating either. Some of the commentators on SkS seemed to have a problem with the methodology too, last time I looked. Splicing together data from different acquisition methods across temporal boundaries seems popular in climate science but is not widely used in other areas of science and engineering to my knowledge

          There has been no SLR in most of NZ for the last 10 years or so, yet the Wright paper is suggesting that we should expect a SLR rate that is > 3 times the 20th C average rate before 2050, and yet there is no empirical evidence from what I can see to support this

          Anyway, not my problem anymore. It’s the problem of ChCh and “visible G String Fridays” CERA

          1. Hmmmm sorry to hear that you have difficulty in reading andy. perhaps you missed this bit in Skeptical Science

            In a process that is accelerating, all three ice caps are losing mass. While nobody is suggesting any of the ice caps will melt away to nothing, only a small amount of melting would cause great problems.

            A 1% loss of ice from these three sources would produce a likely increase in sea levels of around 76cm. With the thermal expansion implied by such melting, and contributions from melting glaciers, the oceans would actually rise far more.

            1. I am having problems reading the ebook link you sent. It is not a generic reading problem

              Your quotes from SKS provide various hypothetical future scenarios

              What I am really looking for is empirical evidence that SLR is accelerating and will reach the levels suggested in the report

              This seems to be eluding me

            2. Are you suggesting that melting ice caps and glaciers is “hypothetical”?

              Greenland and Antarctica are currently loosing around 500 cubic kilometres of ice annually! The Canadian Ice cap is only a quarter of what it was 100 years ago and Glaciers world wide are steadily diminishing – and you call that hypothetical?

            3. I am referring to the hypothetical levels of sea levels we would see in NZ and elsewhere, not the melting of icecaps

              My decisions on whether to build a house in NZ next to the sea should be based on decisions around what is happening in the area, not on what is happening in Greenland

            4. You want empirical evidence of what will happen in the future? Interesting. How exactly will we gather this empirical evidence of future SLR rates?

            5. I would like to see some empirical evidence that supports the theory that sea level rise will accelerate to three times the 20th century average over the next 35 years.

              No where in this report does it explain how these figures are calculated

            6. You clearly haven’t read the report. Its numbers are taken from IPCC AR5, so you should direct your attention to the relevant section of the WG1 report for the detail. But it does provide a good overview of all the factors that go into SLR.

            7. You are still asking for empirical evidence of future events. How can we give you empirical evidence of what the SLR rate will be in 35 years time?

            8. On “retirement” I worked for a time, part-time in surveying. Now you might think that that has nothing much to do with sea level rise – but as it happens the Otago University school of Surveying has been monitoring sea level around NZ for some time. Surveyors determine all heights as heights above sea level – so just what the sea level is, is a pretty important thing to know – particularly in setting out storm water drains in places like Twin Lakes in Ruakaka where the main storm water drain has a gradient of about 1%.
              Also you will be pleased to know that actually there is data available on Sea – Level Rise going back to around 1900 and it indicates that, yes there is Sea level rise (taking into account movements of the crust) of about +1.6 ± 0.15 mm/yr.
              So please no more BS andy. And as has been previously explained – sea level rise varies around the globe. So while it may not be happening fast here and now – that is no guarantee that it won’t in the future.

            9. thanks, your figures corroborate with my understanding that an average of around 1.7 mm a year occurred across the last 100 years or so. tonkin and Taylor for their christchurch SLR survey acknowledges zero over the last 10 years, but that is just a “hiatus” I guess.

              The issue still remains, however, how we are going to achieve three times the 20th C rate in the next 35 years, which seems to be a “certainty” according to some.

            10. There has been no SLR in most of NZ for the last 10 years or so, yet the Wright paper is suggesting that we should expect a SLR rate that is > 3 times the 20th C average rate before 2050, and yet there is no empirical evidence from what I can see to support this” my bold

              but there has been – the fact that The long-term Relative Sea Level change (RSL) stopped at 2007 doesn’t mean that sea level stopped rising. Indeed the most recent study in Auckland incorporating data from this century indicates a slight (but as yet not statistically significant) increase in yearly increases. The Wright paper is using the empirical evidence that satellite altimetry shows average Global SLR to be increasing annually at >3.1 mm/yr. That NZ has not experienced this rate to date is really no cause for complacency. There are a number of factors that affect local rates of SLR all of which seem to be acting in our favour at this time (apart from subduction).

              For instance: Sea temperatures around southern NZ are maintained at a relatively constant level by the cooling waters of the southern oceans. The southern oceans are beginning to warm, but they are still cold enough to cool our waters. When the northern currents wash down the NI east coast during summer SL particularly in the Hauraki gulf rises.

            11. Andy, sorry, you are distorting the SLR debate with nonsense.
              Your comments of Zero SLR over 10 years at AKL harbor are totally ignorant of the bigger picture.
              Have a look again at the “bigger picture” from the ChCh Tonkin Taylor report here:

              This picture has a “Line of Public Perception” drawn in, the one that “Pausists” like Andy S are falling pray to or, in case of Andy S, try to wiggle into some argument to fight their silly blog battles.

              Andy: That greenish line is the SL at the AKL port. The SL in NZ (as in most other particular locations) is affected by oscillations of the ocean system on a decadal and multi-decadal scale as you can see. The global average SLR and its trend is what you need to focus on.

              As you can also see, we are sort of “due” for the next excursion upwards from the global trend around NZ from these oscillations.

              People wanting to behave like a stubborn kindergarten kid can find lots of decades and multi-decadal periods where the sea level has been “falling” at the Port of Auckland on that graph.

              So carry on and pull the proverbial sheep skin over your eyes if you can’t comprehend any of this. However in your case I believe you actually understand all this rather well but chose to turn this into a silly fight on purpose with the intent to confuse the minds of others.

              Either you are incompetent or you are a belligerent troll that purposefully distorts evidence. There is little middle ground really. Take your pick.

            12. I take this line from the T&T report, Thomas

              Note, there is variance within the long term trend of sea level rise and the latest data from New Zealand port tide gauges shows the mean sea level has remained relatively constant for the last decade (Hannah & Bell, 2012).


              (Page 9)

              That is what the report says, and that is what I am stating

              Is that OK?

            13. Sure Andy, it has, but as you know, this is completely meaningless in the debate of where we are heading. Staring at the “noise” in the signal will not eliminate the long term trend. But ignoramuses will try to justify their denial. Same story with the air temps. The “Pausists” have no case. Same story, same ignorance (real or played), to derail the real discussion.

      1. Andy S you said: “Oh sorry Rupert, I will desist from commenting here in future”
        Obviously the urge to tell us once again how utterly ignorant you are took over again.

        1. Where we have different ways of measuring over time it is nice to be able to overlap them which is the case with sea level rise. However it is very easy to infer that SLR will accelerate because (a) 90% of trapped heat goes into the oceans to expand them and (b) we are adding more greenhouse gasses that trap this heat every year and even increasing the rate of that too. Thus the heat control is being turned up continuously as well.

          1. the lower Albedo due to melting north polar ice exposing dark absorbent ocean, plus acceleration of melting arctic and antarctic glaciers and subtropical glaciers.

            1. Thomas, I have been asked to remain polite and engage with the discussion in a constructive way, so I would like to take the time to thank you for the content-free and unsolicited abusive response to my simple question.

              It is really appreciated, and thanks again!

  7. An interesting persecutive into the mind set of the “skeptic” was given to us unintentionally this week by one Joe Fone who linked to a red neck site with an asinine article by a retired space engineer “climatologist” who has written a bit of dreck about it getting colder. Actually the thing that caught my eye wasn’t the “It’s going to get bloody cold!” nonsense but another article on “Robot Submarine Finds Antarctic Ice Thicker Than Believed” – the opening sentence of which started

    Global warming theories just took a major hit with a surprising discovery by British, U.S. and Australian researchers who found that Antarctic underwater ice is much thicker than scientists had believed it to be.

    Hmmmmm I thought is that the same research reported on Skeptical Science by John Abraham “Warm waters melting Antartica..”

    It seemed to be. In one its described as a “robot submarine” and in another its a sea glider. No matter, what actually was the report. John Abrahams review naturally linked directly back to the published research on Nature geoscience “Thick and deformed Antarctic sea ice mapped with autonomous underwater vehicles”
    whereas the Newsmax article lined to another right wing sight opposed to “BIG GOVERNMENT” and an article headed “ROBOT PROVES ANTARCTIC ICE THICKER THAN THOUGHT”
    Each article skewed the findings to their view (much like the children’s party game “pass it on”) the actual findings getting more and more obscure:
    The next link was to another news report – this time more accurate and with far less spin
    “Australian underwater robot reveals more Antarctic sea ice than previously thought”

    the pertinent piece being:

    Launched off a British and an Australian ship at three sites around the Antarctic Peninsula, the robot — known as SeaBED — has returned data that suggested ice thickness might have been underestimated in previous research, and that the sea ice was considerably deeper than previously thought.

    The measurements covered 50 hectares and found that ice in some areas was up to 17 meters thick.

    It then linked to the Nature article linked to above.

    Notice how an article reporting some research where scientists investigating and validating some previous work on sea ice and finding that the previous estimates by satellite and drilling were inaccurate is then reported as falsifying Global warming! Nothing could be further from the truth. If the full volume of Antarctic sea ice was unknown before the study, then determining the volume more accurately hardly diminishes the science.

    Indeed the really interesting aspect of the research is given by John Abraham in his article linked to above – whereby the warming southern Oceans are melting the sea ice from beneath. If you haven’t read I suggest you have a read now.

    Of course none of this is acknowledged in the right wing news blogs because
    a. they haven’t read the original and
    b. that scenario doesn’t fit with their world view.

  8. On page 41-42 it states that the IPCC “only uses peer reviewed papers” and that

    Under its 2013 ‘Business-as-Usual’ scenario for greenhouse gas emissions, the IPCC estimated that sea level would rise by between 52 and 98 centimetres by 2100

    but then

    A survey of 90 experts on sea level rise found that most estimated a larger sea level rise by 2100 than the projections in the 2013 IPCC report. Under the same ‘Business-as-Usual’ scenario, they predict a rise of between 70 and 120 centimetres.

    I’m not sure whether they are following the IPCC or the “90 experts” in this report’s findings.

    EDIT: However, if you take a third of 120 you get 40cm, which would imply that they are taking the worst case scenario from the “90 experts” findings.

  9. AndyS. Sea level rise does seem to show an acceleration over the last 120 years. Stitching together data from tide gauges and satellite doesn’t really explain the acceleration. For example plenty of the acceleration seems to have happened earlier last century within the period of tide gauge data until about 1990 ( see link below which has a curve imposed on the long term data).

    However obviously you cant just extrapolate a curve either. Future sea level rise predictions reflect increasing warming rates and positive feedbacks.

  10. There has been a request by andyS for empirical evidence that the rate of sea level rise will accelerate in future years. I will ignore the impossibility of providing empirical evidence of what will happen on the future, and instead ask if there are any constraints on the future rate of sea level rise. The only empirical evidence is what has already been observed, but the nature of those observations still mean that we can make some deductions about the possible future behaviour. There is a lot of information about this in AR5, so I won’t go into actual numbers. There is a lot of uncertainty about what the precise values will be, but I am interested from the logical point of view if it can be demonstrated that sea level rise must accelerate. We can make some logical statements about the various values, and compare those values over the past 30 years and over the next 30 years. This will be a bit lengthy, so I will spread it over a few comments if you will bear with me.

    Proposition: that the rate of sea level rise will accelerate over the next 30 years.

    First some definitions:
    All values x refer to values over the past 30 years, and x’ to the values over the next 30 years (e.g. SLR is the mean rate of sea level rise over the past 30 years, SLR’ is the mean rate over the next 30 years etc)

    ECS = Equilibrium Climate Sensitivity to a doubling of CO2
    t(ECS) = time taken to reach new stable temperature required by ECS
    Tm = mean global temperature
    SLR = rate of sea level rise
    SLR(TE) = contribution to rate of SLR from thermal expansion
    SLR(IL) = contribution to rate of SLR from ice loss
    V = volume of ice lost from glaciers and Greenland and Antarctic ice sheets
    m = rate of ice melting

  11. Temperature evolution
    Over the next 30 years, it is extremely likely that global mean temperatures will increase. There is a very high probability, close to certainty, that ECS is greater than 1°C. It has also been demonstrated that t(ECS) is of the order of 30 years. So for any emissions scenario possible, even ceasing all CO2 emissions overnight (something that andyS has assured us would mean the instant end of human civilisation), the lag in the climate system means that global temperatures will continue to rise over the next 30 years (Gareth has blogged on this many times). Even if temperatures were somehow to remain “flat” over the next 30 years, the value of Tm’ will still necessarily be larger than Tm, as there was a demonstrable warming trend over the last 30 years, and therefore the mean over that period is lower than the current global mean temperature. Barring some mysterious force X that will cause global cooling in the next 30 years, we can state as fact that:

    [1] Tm’ > Tm

    Contributions to SLR
    It is known from empirical observations that the two principal factors contributing to the rate of SLR over the last 30 years are thermal expansion and ice loss from the ice sheets of Greenland and Antarctica. We can therefore state that:

    [2] SLR = SLR(TE) + SLR(IL) + SLR(other)

    We can be pretty confident that SLR(other) is a small part of the total rate, and we know from satellite and ground observations that SLR(IL) is significant, because V, the volume of ice loss is a significantly non-zero value (the precise value is irrelevant to this calculation, just that it is non-zero). We can therefore say that:

    [3] (SLR(TE) + SLR(IL)) > SLR(other)

  12. Future contributions to SLR
    We can also make some statements about what the future contributions to SLR will be. The contribution from thermal expansion must necessarily increase, given that Tm’ > Tm – the relationship between water volume and temperature is fairly fundamental physics that is not likely to change any time soon. Therfore:

    [4] SLR(TE)’ > SLR(TE)

    We can also be confident that the volume of ice loss will be larger in the future. Again, it is fairly basic physics that not only does ice melt as ambient temperature increases, but the rate at which ice melts also increases as ambient temperature increases. This holds true pretty much up until the ambient temperature gets to the point where ice sublimates to water vapour (by which time human civilisation is long gone, so we will disregard that). Therfore, given that Tm’ > Tm, we can also say that

    [5] m’ > m

    and by extension also that

    [6] V’ > V

    which then leads to the conclusion, given that SLR(IL) is dependent on V, that:

    [7] SLR(IL)’ > SLR(IL)

    From inequalities [4] and [7], and referring back to [2] and [3], we can then make a definitive statement that:

    [8] SLR’ > SLR

    which means acceleration in the rate of sea level rise.

  13. In watching this discussion it grew on me that references made to sea-level rise in various places do not explicitly relate the context in which they may be true, or false.

    I am refering to tecktonic changes, to gravitational changes as ice sheets and glaciers melt and even to changes that occur because of groundwater pumping..

    With respect to tektonic changes I understand that much of the eastern part of the South Island, on the Pacific Plate butts up against the western part of the Australian Plate to form the southern alps. I once read that they were rising at about 7 mm/year but erosion was reducing that to 3.5 mm/yr. The North Island is on the Australian plate, being lifted by the subducting Pacific Plate. In between and moving very slowly south is a region where a kind of battle between these collision modes is taking place.

    So relative sea level is fundamental to understanding what may happen at any particular place on the planet. Something that is supposed to be addressed in the followup report delivered in 2015.

    Meanwhile it will be of benefit to everyone to view Jerry Mitrovica’s 2011 video presentation on fingerprints of global sea level rise, if you have not seen it, or even if you have seen it – all except Andy who would feel over encouraged 🙂

      1. One cause of dropping SL around the Northern regions is rebound of the crust due to reduction of glacial ice cover.
        Some scientists believe that the AGW induced rapid (in geological time scales) redistribution of mass on the Earth surface may induce a spike in earthquake activity.
        and the paper here:

      2. Thanks andy. I’m normally a fan of the way NOAA does things but when I clicked on the NZ sites for more detail I thought it pointless and misleading to convert current SLR linearly to a rise over a 100 years.

        The four gold plate NZ sites may be the same ones referred to in Mitrovica’s dissertation.

  14. My comment is anecdotal. I have been taking my kids to Dunedin’s Edgar center since 2004. It is built on reclaimed land on the edge of Dunedin harbour. In the last 2-3 years the incidence of sea water coming up through the drains and flooding the entranceways to the carpark appears to me, to have significantly increased. I don’t recall many/any incidences of flooding back in 2004/5, this year it seemed that any big high tide, when combined with a low pressure system, would see the sea water coming up.

    We hear on the radio traffic reports of flooding in Auckland on king tides, again, my perception is that this is more common than 10 years ago.

    I have no data to back up my perceptions on this and don’t know if there has been land subsidence in the area. I expect to be slammed by the trolls for commenting about it, but its things like how much more often you have to drive through salt water to take your kids to netball that the ‘average citizen’ starts to notice after a while.

      1. Missing my point andy, I notice how much more often the sea floods the carpark, the data I’d like is a record of how many times the carpark (or other similar low lying areas) floods these days compared to 10 years ago. Same with the road reports of flooding in Auckland. That information may not have been collected, but that is what people notice.

  15. Test Questions on Mitrovca SLR fingerprints: 🙂

    As the WAIS and Greenland each melt will the effects be felt more on the coast off Washington DC or more off Dunedin?

    How far will the South Pole have been displaced once the WAIS has melted?

    How do sea winds effect a slowing of the earth’s rotation?

    1. Q: “How do sea winds effect a slowing of the Earth’s rotation?”

      A: Not at all. Momentum is a conserved quantity, so is rotational momentum. The only way Earth’s rotational momentum can be changed is through the interaction with another body such as the Moon, Sun etc. Processes internal to Earth (such as winds, ocean currents etc.) can not change its overall rotational momentum. In case of the Moon, the rotational momentum of the Earth/Moon system is conserved, however Earth can exchange some of its momentum with the Moon, leaving the momentum of the Earth/Moon system conserved. This is indeed happening as the Moon slowly gains distance from Earth and assumes a growing momentum at the the expense of Earth’s own rotational momentum going down.

      1. Qs 1 and 2 employ mind tricks which do not invalidate the questions but the tricks are obvious to anyone who watched the video I referenced.

        sea winds make sea waves, which crash on beaches etc – that is the clue re Q2

        Physicists working on gravity and sea levels, it appears, do get down to earth! 🙂

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