Paradise submerged
A sea levels rise, what will happen to island nations such as the Maldives?
I can’t understand a word they’re saying, but the energy in the room tells me that my students are engaged. There are four groups, each with a worksheet. While the worksheet is in English, the students are speaking Dhivehi, the official Maldivian language. The conversation goes back and forth within each group – even the students who didn’t seem to be paying attention when I was speaking look interested now. Occasionally someone writes something down, but most of the work is in the discussion. The point of the exercise is for them to bring their own knowledge, experience and enthusiasm – I’m just providing tools to help with planning and decision-making.
I’m in Male – the capital of the Maldives – teaching invasive plant species management to a diverse group from different government agencies as well as the university. They are primarily young, mostly in their twenties with a few in their thirties. Many have studied overseas. One did her PhD in Australia, her husband and young son tagging along with her. One even studied in New Zealand, acquiring a taste for Whittaker’s chocolate while she was here.
I’ve been thinking of that group a lot lately. The loss of international tourism has been hard on New Zealand, but we have other industries which have been largely unaffected, like the export of food. Tourism, directly or indirectly, makes up about 20% of our employment, and overseas visitor spending contributes about 20% of our foreign exchange earnings. It’s a big loss, but it’s not catastrophic. For the Maldives, those figures are 60% of total employment and nearly 80% of foreign exchange. There are few countries in the world so dependent on tourists for their income – not even places like Mauritius and Fiji have figures this high.
Without tourism, the Maldives has a subsistence economy. Fish, coconut and locally-grown vegetables make up a big part of the diet, and it’s likely that people have fallen back on these as their incomes have disappeared. But, without tourism, they are going to have a hard time buying fuel or funding services such as health and invasive species management. It’s a grim picture for that lovely group I met back in 2014.
But that’s not the only reason I’m worried for their future. There’s a much more serious threat in the longer term – climate change. The Republic of Maldives is made up of a string of atolls containing more a thousand islands - all incredibly low-lying. The maximum elevation is 2.4 metres, and that’s only on a few dunes. More than 80% of the land area is less than a metre above sea level. Lately, I’ve been wondering what will happen to the Maldives when the sea level rises. Is the beautiful archipelago doomed? Does it have a future at all?
When we look at maps of the world, the boundary between land and sea is always a definite line. Sea borders are uncomplicated borders. Two countries may occasionally fight over a specific island or a patch of sea, but, most of the time, it is land borders which are the problem. Sea borders are much harder to dispute. Land borders are artificial lines drawn by humans, sea borders feel natural and real.
Stand directly on the coast, though, and the boundary isn’t quite so solid. The tide rises and falls every day, a reminder that the line between land and sea is, literally, fluid. Water moves up and down, eating away at sand, soil and stone, and the coastline constantly changes. Even then, we know approximately where the sea is, and where the sea is not. The line shifts, but it doesn’t seem to shift far.
Our perception, though, is far from accurate. If I look at Wellington, my home, both human action and geological forces have changed the coast beyond recognition in the space of two centuries. The most dramatic change came in 1855, when a large earthquake raised areas of land by 1.5 metres, creating, among other things, the strip of land which now contains the motorway and railway line from Wellington City to the Hutt Valley. The Basin Lake disappeared, becoming land which was turned into the Basin Reserve.
Slower, but affecting a much larger area, was the reclamation. This started around the same time as the earthquake, and by the 1870s, around 70 acres of land had been reclaimed between the bottom of Willis Street to the Railways Station. Reclamation continued for another century, eventually turning 155 hectares of sea into inner city land.
When I walk along the street in one of the reclaimed areas, it seems to be as solid as any other land, but that’s an illusion. The land which we claim from the sea is not the same as land which was there all along. We can see that in the hazard maps, which show that the reclaimed areas are among the highest risk in an earthquake. We can’t simply turn the sea into land without consequence.
The changes to Wellington’s coastline haven’t been all one way, though. Coastal erosion is a constant threat wherever we have buildings and infrastructure close to the coast, and Wellington is no exception. Earlier this year, the south coast was battered by huge waves, and not for the first time. It’s no longer possible to pretend that these are freak events, and the Greater Wellington Council is now talking about the concept of ‘managed retreat’ from some coastal areas.
It’s frightening to imagine that areas which we currently think of as “land” may not remain so. Humanity has been lucky for the last 2000 years, as global sea levels have been relatively stable until quite recently, and we’ve got used to the idea that the land is the land and the sea is the sea. We’ve built our cities, towns and infrastructure as if sea levels are constant, because they mostly have been during the time we’ve been building them. However that has already started to change. New Zealand has seen a 20 cm rise in sea level since 1900, resulting in increased coastal flooding during storms. And it’s only going to get worse.
There are two different reasons why climate change causes sea levels to rise. The first is the obvious one – ice caps and glaciers increase their rate of melting, putting more water into the sea. But there’s another cause as well – as the ocean’s water warms, it expands slightly. This heat-induced expansion has contributed about 40% of the sea level rise we have seen so far.
There’s another factor to take into account though – what the land is doing. As well as large changes, such as the land which rose out of the sea during the 1855 earthquake, there are small but steady changes in land levels from tectonic movement. The lower North Island is sinking by 1-3 millimetres per year. It sounds tiny, but if it is added to the sea level rise in Wellington – about 2.7 millimetres per year – it’s far from insignificant.
Over the next hundred years, the Ministry for the Environment is suggesting that New Zealand should expect sea level rises ranging from 55 centimetres to 136 centimetres. If land subsidence continues at the present rate, it will add about 20 centimetres to those totals. For a hilly city like Wellington, that doesn’t sound like a lot, and it’s true that the number of homes and other buildings at risk is relatively small. But a lot of our important roads are coastal and low-lying, and even if they aren’t going to be submerged, they will be much more vulnerable in storms. The sea level rise may not be catastrophic just yet, but it will be inconvenient, and expensive.
The picture for countries like the Maldives, though, is very different. With 80% of the land area less than a metre in elevation, it’s more than just coastal roads at risk. On the other hand, the picture of what, exactly, will happen to all of those low-lying islands is far from clear. Having predictions for Wellington doesn’t tell us much about what will happen in the Maldives.
Around the world, the sea level is not the same, for a range of different reasons, including the force generated by the earth spinning, and variations in gravity in different parts of the world. Sea level rise will not be the same either – in fact, there are a few areas where the sea level has dropped since 1993. In 2004, an article in a well-respected journal made the claim that the Maldives was one of those areas, and that the sea level around the Maldives had fallen 20-30 cm since the 1970s. The article also documented evidence for other significant fluctuations over the last 1000 years, including a period where the sea level was up to 60 cm higher than today.
These figures have been rebutted, in that same journal, but they do highlight just how difficult it is to measure historical sea levels. What isn’t disputed is that, although the last 2000 years have been relatively stable, sea levels have been higher than they are now within the last 10,000 years. There was a peak in sea levels, known as the mid-Holocene high stand, which occurred 3000-7000 years ago. How high this peak was, and exactly when it was, isn’t clear – what is clear is that it occurred at different times and at different levels in different locations. In many locations, peak sea levels were more than a metre higher than they are today. And this has important implications for the Maldives and other coral atolls.
There is currently some dispute about the way that coral atolls, such as the islands of the Maldives, or those in the Pacific, are formed. The traditional thinking is that the coral which formed atolls once fringed volcanic islands (there’s a video explaining the process here). The volcanoes erode and sink away, but the coral remains. Eventually, the coral builds up and breaks the surface of the water, forming an island.
There are islands, such as Rodrigues in the Indian Ocean, where that process does seem to be occurring. There’s an old, eroded volcano in the middle, a barrier reef and small coral islands in places on the edge of the reef. But for the atolls of the Maldives, there’s no sign of any old volcano breaking the surface. It’s now thought that they developed by a rather more complex process – one which depends upon fluctuating sea levels. Although there were ancient, sunken volcanoes, these were a long, long time ago, more than 50 million years ago. Large flat-topped banks of corals formed where those volcanoes once were, during a warming period in the earth’s climate, when sea levels were rising, around 5-2.5 million years ago. Coral growth kept pace with a slow, steady sea level rise, then, when the warming period ended and sea levels dropped, the coral was exposed. As the sea retreated, falling to levels more than 100 metres lower than today, it left behind massive mesas, table-like mountains, which were eroded by the rain. The shape of the coral mountains means that they eroded more in the centre, eventually creating a ring rock which became the ring of the atoll.
But that’s still only part of the story. What’s remarkable about atolls, whichever theory you follow, is that the islands are still growing – literally. The reef coral is alive, adding in volume both horizontally and vertically. In the case of the Maldives, the steady, consistent monsoon winds contributed to steady and consistent reef growth and island building since the end of the last ice age 12,000 years ago. This understanding – that atoll reefs and islands grew during a period of rising sea levels – has changed the previously pessimistic thinking.
The conventional thinking on atoll islands was that they had formed rather more recently, just a couple of thousand years ago. Since this was a period of stable sea level, this led to the thinking that atolls would be swiftly inundated when sea levels rose. Now, researchers are rather more hopeful that islands like those of the Maldives will survive – that island formation will be able to keep pace with the rising seas, as long as this doesn’t happen too fast.
But that doesn’t mean the future for the Maldives is secure. After all, most of the problems we face from rising seas aren’t so much a problem of the land disappearing, but rather of losing the infrastructure we have built on that land. Then there’s the issue of sand mining – digging up sand from the bottom of lagoons to use in construction – which is contributing to coastal erosion. As sand is removed from the sea, it destabilises the surrounding coast, and the beaches begin to erode away.
Finally there’s the issue of whether the coral will survive at all. Rising sea surface temperatures are leading to episodes of coral bleaching, where corals in shallow water can die. The Maldives have had numerous bleaching episodes over the last 50 years, including a couple of massive ones, the first in 1998 and then another in 2016, when the coral had only just recovered from the previous episode. So far, the reefs are proving resilient – recovering strongly from mass die-off's, especially from areas called “hope spots” where the corals survived. Maldivians are keeping a close watch on their reefs, as well as experimenting with techniques to encourage faster recovery, such as coral transplants.
So, the future picture for my Maldivian students is not as grim as I first feared. Those stunning islands aren’t necessarily going to just disappear beneath the waves. But nor is their future guaranteed. At some point, if nothing else, dealing with climate change is going to get very expensive for both Wellington and the Maldives.
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