The tiny Pacific island nation of Tuvalu, thought to be under threat from sea level rise, has actually expanded in land area over the past 40 years and is likely to continue to be habitable a century from now, scientists say.
Research by the University of Auckland mapped shoreline change of each of Tuvalu's 101 islands across its nine atolls over a 40-year period.
Mapping of island size and position shows that Tuvalu has experienced a net increase in land area of 2.9 per cent or 73.5ha. Overall 74 per cent of islands in the group - a total of 73 - are larger now than forty years ago.
Yet sea level rise in the region has been happening at twice the global average over the past 40 years.
"We tend to think of Pacific atolls as static landforms that will simply be inundated as sea levels rise but there is growing evidence these islands are geologically dynamic and are constantly changing," said researcher Professor Paul Kench.
"The study findings may seem counterintuitive given that sea level has been rising in the region over the past half century, but the dominant mode of change over that time on Tuvalu has been expansion, not erosion," he said.
Graphic showing changes at (a) Nanumaga reef platform island, (b) Fangaia island, (c) Fenualango island (d) Reef islands Nukulaelae reef rim, (e) Teafuone island.
Source: University of Auckland
Professor Kench says sea level is just one factor that can influence island change and a range of environmental processes have contributed to that pattern including sediment supply and wave patterns.
Those processes, particularly during extreme events such as Cyclone Bebe in 1972, could account for the expansion of larger mixed sand-gravel islands and gravel islands, while smaller islands which are predominantly sand are more likely to have been destabilised, he said.
"On the basis of this research we project a markedly different trajectory for Tuvalu's islands over the next century and while we recognise that habitability rests on a number of factors, loss of land is unlikely to be a factor in forcing depopulation of Tuvalu."
Rather than simple re-location or migration, the researchers say new adaptations could be considered that involve the community in decision-making on issues of planning, development goals and land tenure systems that take into account the dynamic nature of islands.
The research team used aerial photos going as far back as 1943, and photo collections from 1971 and 1984 with updated satellite imagery from 2004-2014, to compare how the shoreline of each atoll changed between 1971 and 2014.
The research has just been published in Nature Communications.