At first glance it may not seem so, but the story of the now-vanished island of Nahlapenlohd, a couple of kilometres off the south coast of high volcanic Pohnpei Island in Micronesia, is full of resonance for understanding the effects of recent climate change in the northwest Pacific Ocean. For Nahlapenlohd Island was so large in the year 1850 that not only did it support a sizeable coconut forest but it was able to accommodate a memorable battle between the rival kingdoms of Kitti and Madolenihmw. Memorable because it was the first in Pohnpeian history to have involved beachcombers and imported weapons like cannons and muskets. And relevant to climate change because this once sizeable island is today no more, the oral histories telling that so much blood was spilled in this fierce battle that it stripped the island of all its vegetation causing it to shrink in size … and eventually to disappear. You can see the location of ancient Nahlapenlohd Island on the map below.
Like many oral tales, this one tries to explain island disappearance post-1850 by reference to a historical event. In the light of what we know today, the more plausible cause of island disappearance is the net sea-level rise that has affected the entire western Pacific since the early nineteenth century, accelerating significantly within the past few decades.
Islands have recently been noted as having disappeared in parts of Solomon Islands, southwest Pacific, as a result of recent sea-level rise. The same is true of the reef islands off Pohnpei in the northwest Pacific. Surveys of twelve of these islands have shown that not only have some – like Nahlapenlohd – completely disappeared but that most others have become smaller within the last decade. Some of these islands – like Laiap and Ros – have lost 60-70% of their land area within this time (see next picture) and are likely to be completely erased from Pohnpeian geography within the decade or so.
The reason why islands in the northwest Pacific (Micronesia) and southwest Pacific (Solomon Islands) have become the earliest casualties of sea-level rise in this vast ocean is that these regions are those where sea level has been rising fastest within the past few decades, typically two to three times the global average. In parts of Micronesia, sea level between 1993 and 2012 rose at 10-12 millimetres each year, compared to the global average of 3.1. While this fast rate of sea-level rise is unlikely to be sustained indefinitely, it does provide us with a window through time showing what the geography of island worlds might look like by the middle of the 21st century when sea level in the Pacific could be 30-40 centimetres higher than it is today. For reef islands, by virtue of being composed almost wholly of unconsolidated sand and gravel, are those types most vulnerable to wave erosion. Whole islands, even some island nations, with which we are familiar today are likely to be rendered uninhabitable and even to ‘disappear’ within the next thirty years.
Yet ranged against that pessimistic prognosis, we should note that not all of Pohnpei’s reef islands are disappearing, at least not at the same rate, and some have fortuitously evolved protection that may allow them to long outlive their neighbours. The coasts of some islands – like Kehpara and Nahlap – have become ‘armoured’ by huge boulder beaches emplaced during large storms, often along their most exposed coasts, as shown below.
Other reef islands – like Dawahk – off the leeward coast of Pohnpei are becoming skeletonized; waves wash across the island removing the sand and leaving only rocks, held in place by a maze of giant mangrove roots. This is how it looks.
What such studies show is sea-level rise is a clear threat to the habitability and the existence of low reef islands in the world’s oceans. Short-term interventions by Nature – such as boulder-beach formation – or by people – such as seawalls – are unlikely to change the long-term outcome. Such islands are transients in the oceans, most in the Pacific having formed only after sea level began falling about 4000 years ago exposing reef platforms on which sediment began to be piled. Today, sea-level rise will eventually remove these islands, as it has certainly done countless times before. The harbingers of this are clear to see today.
There is of course a human dimension to this that cannot be ignored. While few people today call the reef islands of Pohnpei home, they are similar to many larger reef islands within Micronesia from which people may well be involuntarily displaced within the next few decades. Where these people might go, where they might be accommodated in ways that preserve their dignity as well as their unique cultures are questions that island decision-makers could be asking now – as indeed many are.
People reached the islands of Micronesia (from the Philippines) about 3500 years ago, following an unbroken ocean crossing of 2300 kilometres – an extraordinary achievement when you consider that people in most other parts of the world at that time rarely sailed out of sight of land. So to have survived on islands in the middle of the ocean for more than three millennia, it is certain that Micronesian societies – like those in many other Pacific Island groups – must have developed considerable resilience to environmental shocks. On high islands in Micronesia, the evidence for this is manifest. Ancient stonework constructions line many parts of the coastline, testimony to a long history of resisting shoreline change, sometimes of manipulating it for human advantage.
Perhaps nowhere is more evocative of this today than Nan Madol, shown above, a megalithic complex built a thousand years ago on ninety-three artificially-constructed islands off southeast Pohnpei. There are many explanations about why Nan Madol was created. Perhaps the truth is that it is an expression of dogged human resilience – one of hundreds along Micronesian coasts – in the face of an unruly Nature.
Much of this research was formally published in 2017 under the title “Identifying and assessing evidence for recent shoreline change attributable to uncommonly rapid sea-level rise in Pohnpei, Federated States of Micronesia, northwest Pacific Ocean” in the Journal of Coastal Conservation with Augustine Kohler and my long-term collaborator Roselyn Kumar. Parts of this page were extracted from my article, Islands lost to the waves: how rising seas washed away part of Micronesia’s 19th-century history, published in The Conversation in November 2017 and freely available to read here.