Coral islands fight off sea-level rise
Source: Agencies |
June 4, 2010, Friday
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SOME South Pacific coral atolls have held their own or even grown in size over the past 60 years despite rising sea levels, newly published research showed yesterday.
Some scientists have worried for years that many of the tiny, low-lying islands throughout the South Pacific will eventually disappear under rising sea levels.
But two researchers who measured 27 islands where local sea levels have risen 120 millimeters - an average of 2 millimeters a year - over the past 60 years, found just four had diminished in size.
Coral islands respond to changes in weather patterns and climate, with coral debris eroded from encircling reefs pushed up onto the islands' coasts by winds and waves.
Professor Paul Kench of Auckland University's environment school and coastal process expert Arthur Webb of the Fiji-based South Pacific Applied Geoscience Commission, used historical aerial photographs and high-resolution satellite images to study changes in the land area of the islands.
Four had gotten smaller, but 23 had either stayed the same or grown bigger, according to the research published in the scientific journal Global and Planetary Change.
The shape-shifting islands changed their sizes through what the pair describe as ocean shoreline displacement toward their lagoons - lagoon shoreline growth or extensions to the ends of elongated islands.
Kench said it had been assumed that islands would "sit there and drown" as sea levels rise, but the islands start responding.
"They're not all growing, they're changing. They've always changed ... but the consistency (with which) some of them have grown is a little surprising," he said yesterday.
Tuvalu, a coral island group that climate campaigners have repeatedly predicted will be drowned by rising seas, has its highest point just 4.5 meters above sea level. The researchers found seven of its nine islands had grown by more than 3 percent on average over the past 60 years.
In 1972, Cyclone Bebe dumped 140 hectares of sediment on the eastern reef of Tuvalu, increasing the area of Funafuti, the main island, by 10 percent. Funamanu island gained 0.44 hectares or nearly 30 percent of its previous area.
A similar trend was found in Kiribati, where three main islands also "grew." Betio expanded by 30 percent (36 hectares), Bairiki by 16.3 percent (5.8 hectares), and Nanikai by 12.5 percent (0.8 hectares).
But Kench warned an accelerated rate of sea-level rise could be "the critical environmental threat to the small island nations," with "a very rapid rate of island destruction" possible from a water depth beyond a certain threshold.
Some scientists have worried for years that many of the tiny, low-lying islands throughout the South Pacific will eventually disappear under rising sea levels.
But two researchers who measured 27 islands where local sea levels have risen 120 millimeters - an average of 2 millimeters a year - over the past 60 years, found just four had diminished in size.
Coral islands respond to changes in weather patterns and climate, with coral debris eroded from encircling reefs pushed up onto the islands' coasts by winds and waves.
Professor Paul Kench of Auckland University's environment school and coastal process expert Arthur Webb of the Fiji-based South Pacific Applied Geoscience Commission, used historical aerial photographs and high-resolution satellite images to study changes in the land area of the islands.
Four had gotten smaller, but 23 had either stayed the same or grown bigger, according to the research published in the scientific journal Global and Planetary Change.
The shape-shifting islands changed their sizes through what the pair describe as ocean shoreline displacement toward their lagoons - lagoon shoreline growth or extensions to the ends of elongated islands.
Kench said it had been assumed that islands would "sit there and drown" as sea levels rise, but the islands start responding.
"They're not all growing, they're changing. They've always changed ... but the consistency (with which) some of them have grown is a little surprising," he said yesterday.
Tuvalu, a coral island group that climate campaigners have repeatedly predicted will be drowned by rising seas, has its highest point just 4.5 meters above sea level. The researchers found seven of its nine islands had grown by more than 3 percent on average over the past 60 years.
In 1972, Cyclone Bebe dumped 140 hectares of sediment on the eastern reef of Tuvalu, increasing the area of Funafuti, the main island, by 10 percent. Funamanu island gained 0.44 hectares or nearly 30 percent of its previous area.
A similar trend was found in Kiribati, where three main islands also "grew." Betio expanded by 30 percent (36 hectares), Bairiki by 16.3 percent (5.8 hectares), and Nanikai by 12.5 percent (0.8 hectares).
But Kench warned an accelerated rate of sea-level rise could be "the critical environmental threat to the small island nations," with "a very rapid rate of island destruction" possible from a water depth beyond a certain threshold.
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