There is a widespread belief that rising sea levels will inundate several Pacific island communities, and in some cases entire countries, by the end of the century (see here, here and here for example). Several recent studies that examine the geomorphology of Pacific islands, however, suggest that the situation is more complex than is often presented. They suggest that while sea-level rise (SLR) could pose a threat to some parts of the Pacific, it is unlikely to do so on its own. John Connell, an Australian geographer, suggests that:
… atolls face multiple problems, only one of which is climate change. Yet it remains impossible to attribute specific environmental changes to climate change, however much of an “aggravating factor” it appears. SLR is greater in the western Pacific than elsewhere in the region but is yet to have a significant influence on environmental change, and is not the main control on shoreline variability, erosion or island size. Flooding and coastal erosion have been the outcome of tectonic changes, El Niño Southern Oscillation-related tidal and storm surges, cyclones, wind waves and human modifications.
A greater understanding of the role that wave activity, tides, plate tectonics, trade winds, seawalls, corals, mangroves and coastal development play in changes to island morphology could help to shape the development of adaptation strategies.
The leaders of countries such as Kiribati and Tuvalu, which are less than five metres above sea level at their highest point, fear that rising seas will make their countries uninhabitable by the end of the century. For most of the South Pacific region, however, sea-level rise is unlikely to pose a significant threat on its own. The most dramatic changes to coastlines have so far occurred as a result of extreme events (such as earthquakes, cyclones or large tidal surges), seawalls and inappropriate planning and development.
In the Solomon Islands (where sea-level rise has been double the global average for the past 20 years), ‘rates of shoreline recession are substantially higher in areas exposed to high wave energy, indicating a synergistic interaction between sea-level rise and waves.’ A total of 11 out of 20 islands on the exposed northern coast of Isabel Province lost more than 20 per cent of their area between 1947 and 2014. Of those islands, five have been completely submerged. Meanwhile, in the more protected region around Roviana Island, the area of six islands increased slightly while that of six others decreased slightly. Understanding the role that waves and other factors play in the process could help to determine the best place to relocate people if that need should arise.
Research conducted by geomorphologists from the University of Auckland suggests that fears about sea-level rise inundating entire countries ‘are based on flawed assumptions that islands are static landforms, which will simply drown as the sea level rises. There is growing evidence that islands are geologically dynamic features that will adjust to changing sea level and climatic conditions.’ Over the past 40 years the sea level, as measured by tidal gauges in Tuvalu, rose by about twice the global average. Satellite imagery, however, indicates that the land area of Tuvalu increased by almost three per cent (73.5 hectares) since the early 1970s. There is, however, some debate as to whether that new land is habitable (the Tuvaluan Prime Minister claims that it is not). It is possible that an unusual amount of sediment, coral and other marine debris washed ashore in Tuvalu over the last four decades, thereby increasing the land area at a greater rate than normal. It is also possible that those conditions might not exist in the future and, if so, sea-level rise might pose a threat to the country.
People living on the Carteret Islands, a low-lying atoll (that was predicted to be completely submerged by 2015) to the north of the Papua New Guinean island of Bougainville, recognise ‘…that erosion is part of a “normal process” and that human agency has played some role in erosion and have long taken steps to modify and defend eroded areas and secure land elsewhere.’ Sea-level rise might be the main threat to the Carteret Islands, but there is little scientific proof that climate change is the main cause and there could be other factors involved. Connell notes that ‘Science, invariably cautious and invisible, is quite absent in the Carteret Islands; hence, sea-level rise has become the sole source of environmental change: a “garbage can anarchy” where once separate and complex phenomena have become systematically interrelated.’
Conditions in the Solomon Islands, Tuvalu and the Carteret Islands cannot simply be extrapolated to other countries or areas of the South Pacific, however, as each group of islands faces different weather, tidal and climatic conditions. A review of atoll island land areas, which analysed a dataset of 666 Pacific atoll islands spread across the region, also suggests that there is no widespread sign of physical destabilisation in the region as a result of rising sea levels. It appears that sea-level rise is yet to significantly affect the South Pacific.
That is not to say, however, that there will not be destabilisation in the future. There are suggestions that if sea levels rise more rapidly, there will be a greater chance of inundation. For most of the last 40 years, global sea levels have risen by 3-5mm per year. If that increases to around seven millimetres per year (as seen in the Solomon Islands over the last two decades) then it is possible that sea-level rise alone could threaten a greater number of Pacific islands.
If the region is to adapt to that change, however, a greater understanding of all of the factors involved in island formation and erosion will be necessary. That way people can be relocated to areas that are best able to withstand environmental change.