>>“If you were faced with the threat of the disappearance of your nation, what would you do?”
That’s the question Enele Sopoaga, the prime minister of the tiny Pacific Island nation of Tuvalu, asked fellow world leaders at the United Nations climate summit in Lima, Peru, in December.
It’s a question that leaders of Pacific Island states have been asking for decades. As a warming climate drives sea levels upward, low-lying island nations face an uncertain future—or no future at all, say these leaders, who warn of their nations’ imminent disappearance.<<
>>These are desperate questions. But how real is the threat? Are island nations like Tuvalu, where most of the land is barely above sea level, destined to sink beneath the waves, like modern-day Atlantises?
Not necessarily, according to a growing body of evidence amassed by New Zealand coastal geomorphologist Paul Kench, of the University of Auckland’s School of Environment, and colleagues in Australia and Fiji, who have been studying how reef islands in the Pacific and Indian Oceans respond to rising sea levels.
They found that reef islands change shape and move around in response to shifting sediments, and that many of them are growing in size, not shrinking, as sea level inches upward. The implication is that many islands—especially less developed ones with few permanent structures—may cope with rising seas well into the next century.
But for the areas that have been transformed by human development, such as the capitals of Kiribati, Tuvalu, and Maldives, the future is considerably gloomier. That’s largely because their many structures—seawalls, roads, and water and electricity systems—are locked in place.<<
>>Some islands grew by as much as 14 acres (5.6 hectares) in a single decade, and Tuvalu’s main atoll, Funafuti—33 islands distributed around the rim of a large lagoon—has gained 75 acres (32 hectares) of land during the past 115 years.
Two-thirds of the reef islands in the study migrated lagoon-ward as their ocean-side coastlines eroded and sediment built up on the side facing the lagoon. One of Funafuti’s islands shifted more than 350 feet (106 meters) over 40 years.
Reef islands, Kench says, are among the most dynamic landforms on Earth. And Tuvalu’s are some of the most dynamic on record.<<
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Geomorphologists, who study landforms, speak of an island’s “carbonate budget“—its sedimentary profit-and-loss account. On the income side of the ledger is the rubble, gravel, and sand produced by the reef ecosystem or imported into it, by storms, for instance. On the expenditure side is sediment lost by being abraded to microscopic fineness, dissolved in seawater, or exported by waves or currents into the deep ocean.
The budget can stay more or less balanced for decades, centuries, even millennia, and then experience a sudden blowout, as when Cyclone Bebe hit Funafuti in 1972. Overnight the storm deposited a 12-mile (19-kilometer) ridge of coral rubble up to 13 feet (4 meters) high.<<
More:
https://www.nationalgeographic.com/news/2015/02/150213-tuvalu-sopoaga-kench-kiribati-maldives-cyclone-marshall-islands/