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Thursday, June 3, 2010
Low-lying Pacific islands regarded as "poster child" examples of the threat from rising sea levels are expanding not sinking, a new study has revealed.
By Paul Chapman in Wellington
Published: 7:00AM BST 03 Jun 2010
Scientists have been surprised by the findings, which show that some islands have grown by almost one-third over the past 60 years.
Among the island chains to have increased in land area are Tuvalu and neighbouring Kiribati, both of which attracted attention at last year's Copenhagen climate summit.
In the study, researchers compared aerial photographs and high-resolution satellite images of 27 islands taken since the 1950s.
Only four islands, mostly uninhabited, had decreased in area despite local sea level rises of almost five inches in that time, while 23 stayed the same or grew.
Seven islands in Tuvalu grew, one by 30 per cent, although the study did not include the most populous island.
In Kiribati, the three of the most densely populated islands, Betio, Bairiki and Nanikai, also grew by between 12.5 and 30 per cent.
Professor Paul Kench, of Auckland University, who co-authored the study with Dr Arthur Webb, a Fiji-based expert on coastal processes, said the study challenged the view that the islands were sinking as a result of global warming.
"Eighty per cent of the islands we've looked at have either remained about the same or, in fact, got larger.
"Some have got dramatically larger," he said.
"We've now got evidence the physical foundations of these islands will still be there in 100 years," he told New Scientist magazine.
He said the study suggested the islands had a natural ability to respond to rising seas by accumulating coral debris from the outlying reefs that surround them.
"It has long been thought that as the sea level goes up, islands will sit there and drown. But they won't," Professor Kench said.
The trend is largely explained by the fact that the islands comprise mostly coral debris eroded from encircling reefs, which is pushed up on to the islands by wind and waves.
Because coral is a living organism, it continues to grow and establish itself in its new home, so the process becomes continuous.
Land reclamation and deposition of other sediment also contribute to the process.
"These islands are so low lying that in extreme events waves crash straight over the top of them," Professor Kench said.
"In doing that they transport sediment from the beach or adjacent reef platform and they throw it on to the top of the island."
But the two scientists warn that people living on the islands still face serious challenges from climate change, particularly if the pace of sea level rises were to overtake that of sediment build-up.
The fresh groundwater that sustains villagers and their crops could be destroyed.
"The land may be there but will they still be able to support human habitation?" he said.
Naomi Thirobaux, a student from Kiribati who has studied the islands for a PhD, said no one should be lulled into thinking erosion and inundation were not taking their toll on the islands.
"In a populated place, people can't move back or inland because there's hardly any place to move into, so that's quite dramatic," she said.