Kiribati, sea level rise, and poverty

According to reports the Pacific island nation of Kiribati is heading for a watery grave, courtesy of rising sea levels caused by man-made climate change:

Guardian:  In March the Intergovernmental Panel on Climate Change published the volume on adaptation of its fifth assessment report, confirming in starker terms forecasts first outlined by scientists in 1990. Within a few decades, small islands in the Pacific and Indian oceans risk being extensively or even completely submerged.

And the burial ceremony is already under way:

Huffington Post:  At the end of February the scenes in the South Pacific atoll island nation of Kiribati were dramatic and frightening. Waves crashed across the lagoon side of South Tarawa, the capital of Kiribati, swamping everything in their path. For the locals, there was nowhere to go as the waves left a trail of destruction, flooding the hospital in Betio, destroying food crops and fouling the already severely limited freshwater lens.

It sounds as if Kiribati is doomed, and a part of it may well be. But if so it will be because of too little water, not too much.

Shown on the map below is the island nation of Kiribati (pronounced Kiribas, by the way), which is made up of 34 islands with a total land area of 800 square kilometers dispersed over 3.5 million square kilometres of ocean. The two islands with tide gauge records, Tarawa and Kiritimati (pronounced Kirisimas and originally known as Christmas Island) are labeled:

Figure 1 shows the short tide gauge record for Betio, the nation’s capital, on the island of Tarawa (data from PSMSL). The trend line shows a sea level rise of a little less than 90mm over the last 22 years, equivalent to a rate of rise of 4mm/year. This is indeed a substantial rate of rise, but it’s questionable whether a trend line drawn through data this erratic that cover a period this short means very much.

Figure 1: Betio tide gauge record, monthly readings plotted relative to local datum

The Kiritimati record shown in Figure 2, however, is twice as long and therefore much more diagnostic. It’s also a good match to Betio even through the records are 3,000km apart, with a trend difference since 1993 of only about 1 mm/year (Tarawa higher). The two records effectively verify each other:

Figure 2: Betio and Kiritimati tide gauge records

And how much sea level rise does Kiritimati show? About 40mm over the last 41 years, or 1 mm/year, according to the Figure 3 trend line. At this rate complete inundation of Kiritimati, which has a maximum elevation of 13m, will take 13,000 years.

Figure 3: Kiritimati tide gauge record, monthly readings plotted relative to local datum

Obviously Kiribati is not in imminent danger of disappearing below the waves. Recent studies in fact show that coral atolls in Kiribati and elsewhere in the Pacific tend to be growing in size rather than shrinking. But what causes the huge periodic variations in sea level at Betio and Kiritimati? As shown in Figure 4 the variations at Kiritimati are closely associated with the El Niño Southern Oscillation (I say “associated with” and not “caused by” because the sea level changes lead the Niño3.4 Index by several months, but a discussion of why this happens is outside the scope of this post):

Figure 4: Kiritimati tide gauge record versus Niño3.4 Index, monthly readings.

But regardless of the exact cause of the variations they have the impact of raising sea  levels at Kiritimati by up to 250mm above normal for weeks on end, the equivalent of 250 years of sea level rise at 1 mm/year. As far as I am aware no adverse impacts from sea level rises of this magnitude have as yet been recorded on Kiribati.

However, Kiribati does get periodically inundated by the “king tides” that occur when a spring tide comes accompanied by a storm surge . The king tide of February 8 and 9, 2005, which struck Kiribati with waves up to 2.8m high and caused widespread flooding (see image below) was one. (Although the residents can’t complain too loudly. Were it not for the sediments these king tides bring in Kiribati would not be there):

These king tides are claimed to be an impact of man-made climate change and they indeed pose a threat to Kiribati, but they are part of the natural cycle in atoll environments and have nothing to do with man-made climate change. But the main threat to Kiribati comes from other issues that also have nothing to do with man-made climate change and which could ultimately force the resettlement of a large number of Kiribatians regardless of what the ocean does.

The first issue is overpopulation. The 103,000 citizens of Kiribati inhabit a land area of 800 sq km, but because of migration from outlying islands half of them now live in an area of 10 sq km in and around the capital of Betio on South Tarawa. And South Tarawa’s population continues to grow.

Second is resource overutilization. Like all coral atolls South Tarawa gets its fresh water from an aquifer underlying the central lagoon where accumulated rainwater has displaced the salt water, and such aquifers will stay fresh as long as extraction isn’t excessive. But even with water available for only two hours a day the demands of 50,000-plus people are already turning the South Tarawa aquifer brackish. As noted in this BBC article a large enough king tide could in fact shut it down altogether:

If the seawater came in over the top, it would have an immediate and catastrophic effect, causing salination for 15 months to two years – this could make the water undrinkable.

Third comes pollution. From the same BBC article:

… we have contamination from housing, agriculture, from people holding pigs, the sanitation practices …. water is very contaminated, especially where people live over the top of their wells. Nearer the islands’ centres of population, the beaches are covered in all manner of waste from litter to excrement. When the tide is up, it does look like a paradise. When the tide goes out, you see the horrible degradation ….

And the underlying cause of all these problems is, of course, poverty. Kiribati is a desperately poor country. Its $1,600 per capita GDP puts it on a par with Sudan.

So are there going to be refugees from Kiribati? Quite possibly, although they won’t be fleeing climate change. They will be fleeing poverty. But we can be sure it won’t be presented this way at the Paris Climate Conference.

A final comment. Last year Kiribati paid $8.77 million to purchase 2,000 hectares of replacement land in Fiji “to escape climate change“. It would have done a lot better to use the money to fix the leaks in South Tarawa’s water system.

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13 Responses to Kiribati, sea level rise, and poverty

  1. “[Kirbati] would have done a lot better to use the money to fix the leaks in South Tarawa’s water system.”

    This is right on the mark.

    GDP of $1600 per capita would equate to a GDP of around $650 per month per family. Median INCOME per family would be about half that. Perhaps 50% of families would have a monthly income under $300 per family, slightly higher in the towns.

    To pay the full capital and operating costs for a piped water supply system takes $750-$1000 per month as the median monthly family income, depending on the source of bulk water.

    Apart from labour costs, most inputs for piped water supply are internationally traded. Economists would therefore have allowed only about 10% reduction in the average cost of production based on savings from low labour costs in Kirbati.

    Many low income countries and regions within countries have inadequate water supply systems even in towns. In some countries capital costs of water supply systems are subsidized by the central government. In such places customers pay only for operations and maintenance.

    However, water rates are often too low to fund maintenance. So central governments, with the assistance of donors, often periodically fund the rehabilitation of poorly-maintained water supply systems. This may have been a more appropriate use for the $8.77 million mentioned in this blog article instead of the bizarre solution actually adopted: purchase of land in Fiji.

    Since Kirbati has a small population, the donor agency responsible may not have sent a full team with sufficient skills and experience to address such a complex technical, social and economic problem.

    Because of this tendency to send junior advisers to smaller countries, you can sometimes anticipate by the requirements set out in the donor’s recruitment notice that a client country is going to get hopelessly inadequate advice.

  2. I cannot see a couple of graphs, issue on my end so maybe this is answered.

    On Figure 3 if we are looking at a possible inundation event, should we not look only at the peak tides? What is the trend of events only over 7100mm?

  3. Euan Mearns says:

    Great post Roger. Can you humour me and run a regression through the Nino 3.4 data please.

    And we have about 120 m sea level rise since the end of the ice age. How do these coral atolls respond to glaciation? Do they become denuded following sea level fall and then build again during the subsequent rise? Or do they simply get a lot bigger during the low stand events?

    • Roger Andrews says:

      Euan: The regression line is effectively flat. Niño3.4 is an index, so it should be flat.

      Second question – I really don’t know. I guess erosion will tend to make an atoll follow sea level down. A lot of work has been done on what happens to atolls when sea level rises but not much on what happens when it falls.

    • Seth Roentgen says:

      Euan. When sea level falls, the atolls remain intact because they are reefs: that is cemented carbonate. They aren’t simply piles of carbonate sand. Carbonate systems are very active in geological terms.

      When sea level falls, the corals migrate down the flanks, leaving a barren pinnacle. Fresh water percolating down through the system will dissolve (karstify) and saturate with carbonate, and precipitate wherever it evaporates. Certainly at the water table. The corals then migrate back up the flanks of the structure as sea level rises.

      There are loads of examples in the geological record where carbonate pinnacle reefs retain close to their original physical structure due to them being cemented as they formed, whereas surrounding clastic (siliceous/clay) sediments have undergone significant compaction. Pinnacle reefs are major plays in the Alberta oilfields. (From memory, the great divide in sedimentology is between carbonate and clastic. I’m the latter).

      • Seth: Do you know of any existing “barren pinnacle” islands? Or have they all been overtaken by post-glacial sea level rise?

        • Seth Roentgen says:

          Roger. Yes I do. A place to go is southern Thailand (a terrible hardship, I try to visit at least once a year). Most of us have seen images of the spectacular limestone structures around Phuket, for example. Many of these are karst remnants of a carbonate shelf which has been uplifted an eroded/dissolved.

          Some are remnants of the original primary reef/atoll structures. In 1980 I visited one about 3 hours by boat off Koh Samui. It comprised a cylinder about 50m high and maybe 200-300m diameter. We landed on a tiny beach and made our way through a fissure in the wall to swim in a lake in the centre of the atoll. It was a surreal experience. You could clearly see the fossil corals in the wall. These things are porous, so the water in the atoll was seawater, and the level at sea level.

          This from memory, and when I was an amateur geologist. Don’t quote me on the numbers. By “barren”, I mean barren of corals. Exposed reefs are very quickly colonised by land plants.

          • Thanks Seth. very interesting. I guess we are going to have to wait for the next Ice Age before we can swim between vertical coral walls in the Tarawa lagoon. 😉

      • Euan Mearns says:

        Fascinating Seth. So the theory is that 10,000 yrs ago Kiritimati was a 120 m tall carbonate pinnacle sticking out of the ocean? And sea level has risen almost exactly back to the summit?

        • Seth Roentgen says:

          Euan & Roger. Sea level is a very slippery beast. Ignoring tides, it changes at rates varying from decades, through the familiar glacial cycles, to 10’s of millions of years. Yes, your “120m carbonate pinnacle” is correct. Glacial/interglacial episodes are quasi-stable in ice-age timescales. At maximum glaciation, sea level falls approx 140m, and during interglacials with ice sheets on Antactica and Greenland sea level rises to approx where it is now.

          Over geological time scales the volume of the ocean basins changes with the rate of sea floor spreading. At mid ocean ridges, new, hot crust is formed. As the new crust moves away from the MOR, it cools and contracts. When sea floor spreading rates are high (e.g. the opening of the Atlantic) the proportion of hot/expanded crust relative to cool/contracted crust is high, and that displaces sea water on to the continental margins. Cretaceous marine deposits are found globally on what is now tectonically stable dry land. The
          is worth reading to get an idea of the effect of tectonics on sea level and continents.

          • Seth Roentgen says:

            A correction to “120m carbonate pinnacle”. The Pacific island/atolls are carbonate structures sitting on/clinging to seamounts. Essentially extinct volcanos truncated at or about sea level. Where the basalt finishes and the carbonate begins, I don’t know. A better picture would be of a volcanic cone encrusted by and capped with coral.

  4. johndroz says:


    As usual, in insightful, interesting post.

    Re your early comments about the shortness of one of the tide gauges, independent studies by SLR experts have concluded that a 50 year period of SLR measurements are necessary before any meaningful conclusions can be deduced (e.g. <>).

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