Study: Coral Reef Islands Grow with Rising Sea Level

Fatato Island
Fatato Island. Source Tuvalu Islands

Guest essay by Eric Worrall

Another study confirming that coral reef islands are dynamic, and adjust rapidly to changes in sea level.


Island ‘drowning’ is not inevitable as sea levels rise


Coral reef islands across the world could naturally adapt to survive the impact of rising sea levels, according to new research.

The increased flooding caused by the changing global climate has been predicted to render such communities – where sandy or gravel islands sit on top of coral reef platforms – uninhabitable within decades.

However, an international study led by the University of Plymouth (UK) suggests that perceived fate is far from a foregone conclusion.

The research, published in Science Advances, for the first time uses numerical modelling of island morphology alongside physical model experiments to simulate how reef islands – which provide the only habitable land in atoll nations – can respond when sea levels rise.

The results show that islands composed of gravel material can evolve in the face of overtopping waves, with sediment from the beach face being transferred to the island’s surface.

This means the island’s crest is being raised as sea level rises, with scientists saying such natural adaptation may provide an alternative future that can potentially support near-term habitability, albeit with additional management challenges, possibly involving sediment nourishment, mobile infrastructure and flood-proof housing.

The research was led by Gerd Masselink, Professor of Coastal Geomorphology in Plymouth, working with colleagues at the University of Auckland (New Zealand) and Simon Fraser University (Canada).

Professor Masselink, who heads Plymouth’s Coastal Processes Research Group, said: “In the face of climate change and sea level rise, coral reef islands are among the most vulnerable coastal environments on the planet. Previous research into the future habitability of these islands typically considers them inert structures unable to adjust to rising sea level. Invariably, these studies predict significantly increased risk of coastal flooding and island inundation, and the concept of ‘island loss’ has become entrenched in discourses regarding the future of coral reef island communities. In turn, this has led to attention being focused on either building structural coastal defences or the exodus of island communities, with limited consideration of alternative adaptation strategies.

“It is important to realise that these coral reef islands have developed over hundreds to thousands of years as a result of energetic wave conditions removing material from the reef structure and depositing the material towards the back of reef platforms, thereby creating islands. The height of their surface is actually determined by the most energetic wave conditions, therefore overtopping, flooding and island inundation are necessary, albeit inconvenient and sometime hazardous, processes required for island maintenance.”

Co-author Professor Paul Kench, currently Dean of Science at Simon Fraser University, Canada, said: “The model provides a step-change in our ability to simulate future island responses to sea level rise and better resolve what the on-ground transformations will look like for island communities. Importantly, our results suggest that island drowning within the next few decades is not universally inevitable. Understanding how islands will physically change due to sea level rise provides alternative options for island communities to deal with the consequences of climate change. It is important to stress there is no one-size-fits-all strategy that will be viable for all island communities – but neither are all islands doomed.”

For the research, scientists created a scale model of Fatato Island, part of the Funafuti Atoll in Tuvalu, and placed it in the Coastal Ocean and Sediment Transport (COAST) Lab at the University of Plymouth.

It was then subjected to a series of experiments designed to simulate predicted sea level rises with the results showing that the island’s crest rose with the rising sea level, while retreating inland, as a result of water overwashing the island and depositing sediment on the island’s surface.

A numerical model was validated using these laboratory experiments, and three numerical modelling scenarios were then used to assess how the island adjusted to a sea level rise of 0.75m, the global average increase predicted for 2100 by the Intergovernmental Panel on Climate Change.

During the numerical simulations, the island crest rose by just under 0.7m, showing that islands can keep up with rising level and confirming the laboratory experiments, although the precise future rate of sea level rise will be critical in determining their future.

Media Contact

Alan Williams



The abstract of the study;

Coral reef islands can accrete vertically in response to sea level rise

Gerd Masselink, Eddie Beetham and Paul Kench

Vol. 6, no. 24, eaay3656
DOI: 10.1126/sciadv.aay3656 


Increased flooding due to sea level rise (SLR) is expected to render reef islands, defined as sandy or gravel islands on top of coral reef platforms, uninhabitable within decades. Such projections generally assume that reef islands are geologically inert landforms unable to adjust morphologically. We present numerical modeling results that show reef islands composed of gravel material are morphodynamically resilient landforms that evolve under SLR by accreting to maintain positive freeboard while retreating lagoonward. Such island adjustment is driven by wave overtopping processes transferring sediment from the beachface to the island surface. Our results indicate that such natural adaptation of reef islands may provide an alternative future trajectory that can potentially support near-term habitability on some islands, albeit with additional management challenges. Full characterization of SLR vulnerability at a given reef island should combine morphodynamic models with assessments of climate-related impacts on freshwater supplies, carbonate sediment supply, and future wave regimes.

Read more:

Charles Darwin first proposed coral reefs are dynamic structures in 1842, based on his observations. WUWT has reported on other coral studies over the years which confirm Darwin’s theory.

Good to see climate modellers are finally incorporating this information into their sea level projections.

79 thoughts on “Study: Coral Reef Islands Grow with Rising Sea Level

  1. Oh no, really ?

    The research, published in Science Advances, for the first time uses numerical modelling of island morphology alongside physical model experiments to simulate how reef islands – can respond when sea levels rise

    They only had to ask the readers here at WUWT, they knew that since ever.

  2. I thought this was pretty well-established, given the relatively rapid increase in sea level since the end of the last Ice Age. Why is modeling needed if it’s been demonstrated in practice?

    • Excellent question. I think it is because people trust models more than their own eyes – and have no brains. Unlike Darwin who realised this clearly and wrote a little book about it. He knew nothing about rising sea levels – thought the islands were sinking. But he had brains.

      • Well, in fact the islands are sinking due to the cooling of oceanic lithosphere as the plate moves away from the ridge. Beneath a lot of coral, Bermuda is actually an ancient volcano. So are French Frigate Shoals and Midway. The rise in sea level is a much more recent phenomenon. During the Eemian, sea level was significantly higher than now, so you can see coral reefs well above sea level in the Bahamas. All very dynamic those little critters.

        • The reverse has happened too. Niue is the world largest coral island, 104 sq miles, which is a raised central coral plateau around 200 ft above sea level , and lower level coastal ring of 80 ft.
          Very radioactive soil as well.

    • I’m always reminded of the chapter in Isaac Asimov’s “Foundation” where Mayor Salvor Hardin is explaining to the Foundation’s “Scientists” that their idea of the scientific method is fundamentally wrong. He points out that visiting Imperial envoy Lord Dorwin’s idea of scientific research was to compare the works of “the old masters.” That conducting original research (as indicated when Salvor Hardin asks if he plans to visit any of the possible originating planets) “was a wather wound about a wiggamawolish way to conduct wesearch.” This obscene reliance upon modeling rather than actual experimentation and observation is indicative of the same sort of stagnation.

      • You would be right if we were living in the past, where conducting science meant discovering things that were real. But in the post-modern scientific method, it’s all about proving things which fit the narrative: climate ‘science’, we’re all going to die of Covid, the sky is falling; choose your favourite disaster.

    • I too think that’s a good question, and many scientists are very skeptical, if not critical of these models, like Dr Nils-Axel Morner. I too think that it’s a matter of Geo-ethics. Dr Morner is probably the greatest living expert in Oceanography and has been studying the issues surrounding sea level rises, and indeed refuting bogus claims of alarmist shills for several decades. He has given numerous public lectures, and made dozens of videos and TV/Radio interviews. See this recent lecture, where he explains the reality of the situation as it was just a few months ago.

    • Because it is much easier to sit at a computer in an office than work in the core shack on a drill site? It’s noisy out at the drill, and cold and hot, wet and dry, and you have to handle dirty real rocks covered in drilling mud, yuk–that’s just not ideal working conditions. And drillers can swear a lot.

      (i.e., a lot of that information was gained in the late 40’s by drilling the Leduc reef complex, and understanding the formation of stacked reef complexes since. And I’m sure others earlier in the Permian Basin–there has to be some reason that I learned this in university in the mid 60’s.)

      • Len Werner, I wasn’t sure you knew about drill sites until you added “And drillers can swear a lot.” French-Canadians are really good, but Australian drillers can make you blush.

        • Ron Long
          June 11, 2020 at 12:29 pm

          Kiwi geologists are pretty good at that too when a radioactive neutron source gets stuck 300m down a drillhole.

          • Awright, that’s a CHALLENGE–I once watched a Longyear French-Canadian driller fight for an hour with stuck rods some 800 feet down in serpentine, then finally give up and swear at the drill for a solid 5 minutes, and stomp out of the shack….only to turn around, go back in, and SPIT on the drill.

            (Whew, glad I added that comment then, lest you guys thought I was just some kind of ‘internet poseur’.)

        • Len Werner
          June 11, 2020 at 3:30 pm

          Well, the source is still up there on Cape York in Queensland…it’s yours if you want it! Let me know and I’ll give you directions…think Permian coal.

          It’s been sitting there since 1979 so probably a bit less radioactive than it was so somewhat safer to take home as a souvenir.

          • I’ll bet that required the submission of at least 50 reports.

            In the spat-on-drill case above, the drill foreman appeared on the site a few minutes later, took hold of the drill, and within about 20 minutes had managed to free the rods! They sent the wireline down and we got the core and left, so I have no story to report on how the French-Canadian driller accepted that. But I gathered from the whole episode that spitting on a drill is the ultimate insult after one’s entire swearing lexicon has been exhausted–twice–and failed, you just can go no further.

            Either that, or by that stage of rage a French-Canadian driller loses all sense of rationality. It may be a good thing, our gun laws up here; in other jurisdictions that poor drill might have never run again.

      • Latest Google Earth image (Jun2017) of Fatato (8°32’51.14″S 179° 9’44.36″E) shows the lagoon side drying out. June2003 shows it blue-green wet. Sept2005 shows the connector sand bars underwater. Nov2005 shows the sea level all the way up to the trees. Nov2013 shows the connecting sand bars back up. Dec2014 has the sand bars awash again. June2017, the bars are dry.
        Not flat.

    • Thank you! I was asking myself that very question about a second after I read the words “using numerical modeling.”

      For crying out loud, what happened to the actual scientific method? You know, the one that relies on testable hypotheses and data?

      Anyone? Bueller?

      • Hey don’t laugh about numerical modeling. You’ll offend some people who come on here who have yet to figure out how a pencil and the back of an envelope can be utilized together.

    • Why do they use models?

      Because good models allow one to look systematically at a wide variety of situations. In areas of science/engineering where models are sufficiently accurate, models work just fine.

      IMHO, the problem is the “good” part not the “model” part.

        • Thanks for that link, good article. For me the best statement is:

          “The salient point then is that in our march to simplify reality with useful models, of which Farnam Street is an advocate, we confuse the models with reality. For many people, the model creates its own reality. It is as if the spreadsheet comes to life. We forget that reality is a lot messier. The map isn’t the territory. The theory isn’t what it describes, it’s simply a way we choose to interpret a certain set of information. Maps can also be wrong, but even if they are essentially correct, they are an abstraction, and abstraction means that information is lost to save space. (Recall the mile-to-mile scale map.)”

      • And note that they validated their computer model with tests on a physical model. Shows some smarts.

        Regardless of the critiques here in the comments, these folks are to be commended for subverting the paradigm dominant in climate “science”. They have now probably been consigned to eternal perdition.

  3. “Coral reef islands can accrete vertically in response to sea level rise”
    Old hat:
    The Structure and Distribution of Coral Reefs, 1842, Charles Darwin

  4. Even without this evidence, a simple piece of deductive reason would suffice; given that the global sea level has risen hundreds of feet since the end of the last ice age, ask yourself, what would be the probability that at this particular moment in time, the sea would have reached exactly the level of the islands, and no more? The probability would be extremely small, maybe one in a few thousand. But here we are. Something must be happening that keeps the two levels together for any sea level.

    • Vincent,

      Coral atoll reefs form on and around extinct volcanic sea mounts that sink slowly over time due to the thin oceanic crust that supports them. Sea-level rise is just one part of the story. If the sea level were to rise more rapidly than the rate of sinking, the reefs would migrate down the slopes of the sea mount, forming a fringing reef.

      • Jan E Christoffersen
        June 11, 2020 at 2:09 pm

        Yes, Jan, as has been pointed out earlier Darwin had it all sorted out over 150 years ago. Why do we endlessly have to reinvent the wheel. I blame the school system in part…not enough hard science.

        • Alastair,

          Good to hear from you again in “COVID-free” N.Z. Yes, Darwin was a purdy darn smart geologist.

          I blame politicians for everything – they are at the top of the food (fool) chain.

          • Jan E Christoffersen
            June 12, 2020 at 1:41 pm

            Good to make contact again. Did you see my comments upthread about neutron sources down a hole? Might bring back similar memories…I’m sure all geologists have such stories.

            Maybe flick us a private email…I seem to have lost yours. abrickellatxtradotcodotnz.

        • Big boo boo above – should have read “If the sea level were to fall more rapidly than the rate of sinking, the reefs would migrate down the slopes of of the sea mount, forming a fringing reef.

    • There are lots of submerged or partially submerged islands whose above-water areas used to be much larger than they now are. There’s a whole chain extending west and northwest from the Hawai’an islands out past the French Frigate Shoals to Midway Island and beyond, some of which are above water, but all of which are almost certainly much smaller above-water than they once were. Beyond Midway and Kure Atoll, the Emperor Seamount chain extends up to nearly the Aleutians, and is all now underwater.

      There are various reason for this submergence. Many of the islands, shoals and submerged reefs in the Hawaii-Emperor chain do not support large coral reefs today, and maybe never did–they’re too far north of the equator. In that way, they differ from islands in the more tropical South Pacific and elsewhere, where the reefs (and detritus derived from the reefs) keeps pace with subsidence.

  5. Just look at the rock record. Sometimes they keep up, sometimes they drown. With stable relative rise in sea level reef can keep their heads up for millions of years and accumulate hundreds of feet of reefal limestone.

    No need to give models credit for something nature has shown us clearly.

      • There’s one small atoll to the east of the Cook islands , which is now just a sort of enclosed reef with no sand cays. There’s an entrance to the lagoon which those who have sailed there say is quite unique sitting in quite calm waters sourrounded by the open ocean rolling swells.
        The loss of the sand cays may have occured 70-80 yrs ago , largely because it’s in the Pacific cyclone belt and probably a sequence of cyclone hits washed away the sand. Well before the global warming hit the news.

  6. They only had to ask David Middleton. Or any one of tens of thousands of geologists on this Blue Marble.

  7. “Previous research into the future habitability of these islands typically considers them inert structures unable to adjust to rising sea level.” Question who were these idiots. Nothing on earth remains the same everything changes. Geologically things can change in a blink of an eye.

  8. Hmmm, model outputs or Charles Darwin’s observations? Give me a nanosecond to decide which has more weight.

  9. I sure would love to know where this sea level is rising because it is not rising where I was born and raised and it sure isn’t rising where I stay in Florida in the winter. Do we have bulkheads that keep it from rising only where the intelligent people live?

  10. The first para of their abstract ==
    “Increased flooding due to sea level rise (SLR) is expected to render reef islands, defined as sandy or gravel islands on top of coral reef platforms, uninhabitable within decades. Such projections generally assume that reef islands are geologically inert landforms unable to adjust morphologically.”
    Shows breathtaking ignorance on the part of the authors. And these are professors not clueless schoolkids . I despair and Darwin must bein seventh heaven that such luminaries give hie theory their approval see the linc foranice piece of sarc.

  11. The real threat facing inhabited coral atolls is excessive freshwater extraction. Pump it out faster than the recharge rate and your drinking supply becomes salty. Not a problem with subsistence-level populations, but it becomes one quickly for a tourist destination with hotels and lots of people taking showers and flushing toilets.

    Good thing you can always build modern desalination plants running on, well, fossil fuel …
    (Irony so strong you can pick it up with a magnet)

    • ‘Allan Watt, level 7 ‘irony so strong you can pick it up with a magnet’.

      Ah ha. Baldrick was right, irony is like goldy or silvery but just made from iron.

      • I have a geological map from the 1870s where they have the notation “IRONY” in a couple of spots that we would now call “rusty” or “gossanous”

        The only coral islands that won’t grow with rising sea level (if it actually was going to rise at an increased rate) are the ones that are paved over with concrete

    • Some of these islands are not large enough to have any significant fresh water to extract. Midway Island, for example, does not–which is why Joseph Rochefort and his band of crypt analysts were able to determine that the Japanese target in June 1942 was Midway, not the Aleutians or somewhere else (as the analysts in DC had thought).

      • The Aleutians were also targeted in a hare-brained diversionary scheme, as so often in IJN planning, over-complicated.

  12. …. and there I was reading from a BERKELEY SENIOR FELLOW essay that the real nexus of climate change was colonial racism and poverty……. and that climate change and sea level rise cannot be read outside a history of colonialism and neocolonialism, capitalism and imperialism….Additionally, the combination of higher sea levels and increased storm seasons, in unpredictability and intensity, leads to storm surges….

    Link here, but be warned keep a bucket handy…
    Sea Level Rise, Marshall Islands and Environmental Justice :

  13. The current relative sea level rise rate at Tuvalu is about 1.5 mm/yr. This would lead to about 120 mm by 2100, not 750 mm. Also Tuvalu is sinking at a rate of about 1.9 mm/yr accounting for all or a bit more than all the observed relative sea level rise. As Alan Watt says, perhaps they are pumping a bit to much fresh water from their aquifer?

    There are thousands of coastal tide gauges throughout the world, none of which (except perhaps for Manila beginning in 1960 probably because of magma movements) show such large increases as the report authors assume. The information above is readily available from and it took me a few minutes to find it. The only good thing I can say about this report is that it was done by a UK university so I, an American, probably didn’t pay for it.

  14. Why don’t the look at not so old studies ?
    Small atoll islands may grow, not sink, as sea levels rise

    But Paul Kench of the University of Auckland, New Zealand, and colleagues found no evidence of heightened erosion. After poring over more than a century’s worth of data, including old maps and aerial and satellite imagery, they conclude that 18 out of 29 islands have actually grown.
    As a whole, the group grew by more than 18 hectares, while many islands changed shape or shifted sideways.

    Much better than models ! 😀 And facts. 😀

    • As I said previously, ask any of tens of thousands of geologists and they will happily give you a discourse on the formation of atolls which encompasses most of the islands in contention. They start as a volcanic pimple which may or not breach the ocean surface and as they subsequently subside into the ocean due to the weight of their volcanic effluent and the physics of isostatic equilibrium, reefs grow at the margins of the islands and eventually become the only remaining edifice. They grew faster than the post-glacial rise and will continue to, absent human interference which is the main issue.

  15. As you say, WUWT readers have known this stuff for ages. But isn’t there a problem in islands which are highly developed, where roads and buildings cover much of the surface? The Maldives, for instance? This must surely interfere with the natural process.

    • There are suggestions sea walls can interfere with the natural reef accumulation process. Willis thinks eating all the local parrot fish interferes with production of coral sand. And of course dynamiting local reefs can have an impact on coral growth.

      But there are also ways human interference can likely help reef growth, for example use of sea groynes can slow the movement of water and encourage the water to drop sand where you want it.

    • There is your answer:
      Maldives: climate change could actually help coral islands rise again

      However, such scenarios of inundation and drowning assume that the land surface remains static and unchanged. But, what if the land could build vertically as sea level rises?

      This is what colleagues and I have been examining in our research, now published in Geophysical Research Letters. We studied five reef islands in the southern Maldives and found that they were actually built when sea levels were higher than they are today.

      The respective study from 2018

  16. When as a twelve year old school boy I, in 1946, learned of the extent of sea level rise since the end of the ice age I quickly deduced that low level coral atolls must have a mechanism for growing with sea level rise. Many times since then I have been bemused by the number of scholars who seem not to have made this elementary deduction and bewail the immenent fate of the islands. If there is any doubt about an islands future, all that is necessary is to go and look at it. That it should be necessary to carry out experiments to determine their future behaviour seems astonishing. In the end this is not a study of the behaviour of coral atolls: it is a study of the behaviour of models of coral atolls.

  17. Well knock me down with a feather!

    Of course if anyone had actually looked at a map of, say, French Polynesia, they might’ve noticed these vast ancient atolls where the central volcano had eroded and shrunk millions of years ago.

    The fun thought is when the ice age was in full swing they must’ve looked like giant 100m high limestone castles because of the lower sea level.

  18. Well no gawddamned sh*t!!!!!! That is what the f**k coral does! Gawddamned moronic f**ks.

  19. There are around 10,000 coral islands and associated reefs, mostly in the Pacific, and most are only around three meters or so above sea level. Are we to assume that before the post glacial sea level of about 130 meters they were all 133 metres above sea level? Of course not, they grew along with sea level rise with only about 5% failing to keep pace and becoming drowned. They will continue to grow as long as humans don’t interfere with the natural processes of island growth, such as by construction and otherwise preventing the natural buildup of coral sand with each storm, killing coral by pollution and dynamiting, overfishing of parrot fish and others that are critical to reef health. As others have said, Charles Darwin figured out how coral reefs work almost two hundred years ago.

  20. Old timers here will remember that Willis Eschenbach has filtered much of this knowledge about coral islands into these pages, for years. He’s taught us about island- building Parrot fish, fresh water lenses and all sorts of reality- based information which runs counter to the half- truths and outright lies of the climate fear merchants.
    Thanks, Willis.
    (Almost called him “Uncle” Willis)

  21. “During the numerical simulations, the island crest rose by just under 0.7m, showing that islands can keep up with rising level and confirming the laboratory experiments”

    Perhaps try empirical research, otherwise called getting out and having a look at a few islands…
    Or even stay in and do a bit of research… comparing an old map of Wake Island [1943] and a Google Earth Image [2020] shows almost no difference.

    In 2015 even National Geographic wasn’t convinced that islands were disappearing

    • The author of the above Nat Geo article, Kennedy Warne, is a card-carrying climate hysteric, renowned for his doom-laden writing and UN-speak radio interviews, ie. we’re all gonna die unless…!

      Admittedly he quotes Prof Paul Kench, who travels to various islands and atolls and gets sand and seaweed under his fingernails (and researches tidal graphs & satellite pics), yet Kench’s observations are drowned – swamped, if you will – by such tired cliches as ‘warming seas’ and ‘ocean acidification’ and ‘UN recommendations’ and we’re all gonna drown unless…

      Having grown up with my dad’s Nat Geo magazines as a kid (oh the places you shall go!) I gave up on them long ago when the carbophobes took over. Great photos still; shame about the preaching.

  22. All I could think about, as I ran down this rabbit-hole, was Paul Eschenbach and his parrotfish, which were producing enough clean coral sand to overcome the “Gaia-centric” models!

  23. It’s good to see a study re-affirming what has been known for some time about coral atoll islands getting attention in the media that usually favors climate alarmism. Unfortunately the authors uncritically regurgitate this nonsense:

    three numerical modelling scenarios were then used to assess how the island adjusted to a sea level rise of 0.75m, the global average increase predicted for 2100 by the Intergovernmental Panel on Climate Change

    The measured average rate of sea level rise over the last 27 years, 3.1 mm per year, implies sea level rise of 0.31m by 2100.

    The crazy 0.75m number is from the RCP8.5 über apocalypse scenario which predicts a range of 0.45 to 0.82 meters and temperate rise of 2.6 to 4.8 C. Measured temperature rise over the last 40 years suggests about 1.4 C by 2100, putting sea level and temperature rise squarely in the mild RCP2.6 range.

    With each passing year the disparity increases between observations and the RCP8.5 predictions. At this point, it would probably take a catastrophic ten-fold increase in Antarctic and Greenland glacier melt to catch up. Makes you wonder why scientists keep using the increasingly implausible RCP8 scenario. Ignert? Or fearmongering?

  24. I actually recreated this in one of my coral propagation tanks … I had a big swimming pool pump that ran for 6 hours of the day to create a strong tidal current … the effect was to raised the water level by 2cm due to the drainage system design. My sps coral branches grew to the higher level of the water and flattened out into rounded knobs, and during the low tide were exposed.

    • Streetcred
      June 12, 2020 at 1:13 am

      That sounds interesting. How long did you run it for and how quickly did the coral grow upwards? Can you translate this into mm/year upwards growth?

      How big was the tank…was the 2cm higher level just due to the pump piling water up at one end of the tank?

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