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Seas are rising. Patrick Nunn, University of the Sunshine Coast
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Sea levels are currently climbing by an average of 3 millimetres per year around the world due to climate change. But they are creeping up even faster in the western Pacific, where a natural trade wind cycle has caused an extra build-up of water over the last half-century.
In Micronesia and the Solomon Islands, which lie in the western Pacific, sea levels have risen by up to 12 millimetres per year since the early 1990s.
In 2016, a study led by Simon Albert at the University of Queensland in Australia found that five of the Solomon Islands had been lost since the mid-20th century.
Now, Patrick Nunn at the University of the Sunshine Coast in Australia has observed a similar phenomenon in Micronesia.
Miniature Atlantises
His team conducted coastal surveys, spoke to local people and reviewed satellite images for the island of Pohnpei and several low-lying islands scattered throughout the surrounding reef.
Pohnpei shows surprisingly little coastal erosion, probably because it is relatively high above sea level and ringed by mangrove forest, says Nunn. “Mangroves provide a buffer by absorbing wave energy and trapping sediment,” he says.
Three small islands on the west side are also well-preserved, possibly because they are sheltered from strong winds and waves by the main island, says Nunn. A nearby coral atoll – Ant Atoll – also has very little erosion, which is probably because an adjacent lagoon acts like a sediment trap.
However, several of the other low-lying reef islands – mostly to the south of the main island – have shrunk considerably or disappeared entirely.
Lost to the waves
And some islands have disappeared entirely. Local people told the researchers about two former islands called Kepidau en Pehleng and Nahlapenlohd – the latter of which was famous for hosting a great battle between warring chiefdoms in 1850. Both appear to have vanished within the last century.
Aerial images revealed that another six low-lying islands – in the unpopulated Laiap, Nahtik and Ros island chains – became submerged between 2007 and 2014. Each was about 100 square metres.
These changes in Micronesia are a preview for other low-lying nations around the world, says Nunn. As sea levels continue to rise, many inhabitants will be forced to move to higher ground, he says. This is already happening in the low-lying Carteret Islands of Papua New Guinea, where a resettlement scheme is underway to move the population to Bougainville – a higher island 90 kilometres away.
However, one positive finding from the Micronesia study and others is that not all low-lying islands are destroyed by rising seas, says Albert. Islands that are sheltered, or have mangrove forests or lagoons for trapping sediment, appear to have good resilience, he says.
“These are the first places on Earth to experience really high rates of sea level rise, so they give great insights into what can happen,” says Albert. “But we’re finding there’s a large diversity of responses – not every island will erode.”
Understanding why will help us plan our response as seas rise around the world.
Links
- Five Pacific islands vanish from sight as sea levels rise
- Last days in the Carteret Islands? Climate change, livelihoods and migration on coral atolls
- Migration from atolls as climate change adaptation: Current practices, barriers and options in Solomon Islands
- The legacy of migration in response to climate stress: learning from the Gilbertese resettlement in the Solomon Islands
- Losing ground? Tuvalu, the greenhouse effect and the garbage can
- Escaping a Rising Tide: Sea Level Rise and Migration in Kiribati
- Contrasted Views on Environmental Change and Migration: the Case of Tuvaluan Migration to New Zealand
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