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Pacific Islands Defying Sea-Level Rise--For Now

One of the (many) worries about global warming is that low-lying island nations in the Pacific Ocean will get swallowed up by rising sea levels. Last fall, government officials from Maldives put on scuba gear and staged an underwater cabinet meeting as a sort of awareness-raising publicity stunt. And from everything we know, these island nations are going to have a rough time in a warmer world. But two researchers just published a study showing that the picture's a fair bit more complicated than scientists have long thought.

The authors, Paul Kench of Auckland University and Arthur Webb of the South Pacific Applied Geoscience Commission in Fiji, studied some 27 coral atolls in the central Pacific and found that, over the past few decades, most of the islands have actually been growing in size. Only four have shrunk. In Tuvalu, one of the more populous island nations at risk of going under, seven of nine islands have increased in area.

Now, this isn't happening because sea-level rise is all a big hoax—in fact, the seas have risen 4.8 inches over that period. What's happening is that the islands have been shifting in shape: Some parts are getting swallowed up by the seas, while other parts are expanding because the higher waves are knocking debris from the coral reefs that circle the islands onto the beaches. Here's how two islands in the Funafuti atoll of Tuvalu have been transformed over the past twenty years (dotted line is the coast as of 1984, solid line is circa 2004):

Some climate skeptics have been touting these findings as yet more proof that global warming isn't so bad. But that's a pretty simplistic reading of the study. Via e-mail, Webb was blunt about this point to me, writing, "It is VERY important to understand that our study does not in any way suggest these islands do not remain extremely vulnerable to sea level rise—they do." For one, if an island's shifting around, that still poses a problem, since it's not always easy to just pick up homes and move to a different location. (That seems to be the situation facing the Cateret Islands in Papua New Guinea.) What's more, the islands are only gaining area around their edges, they're not actually lifting up. Most of the land on the atolls still sits just one meter above sea level. So they still face the risk of drowning, especially if sea-level rise keeps accelerating.

The other wild card here are the coral reefs. Because they're living organisms, the coral can constantly supply fresh material to help build these islands. But as sea temperatures heat up and the oceans absorb more CO2 and become more acidic, those reefs will likely start dying. Via e-mail, Kench says it's still unclear what this will mean for countries like Tuvalu and the Maldives. One possibility is that acidification could weaken coral skeletons and produce even more sand and gravel for the island beaches. Or maybe not. The whole process, he notes, is still poorly understood. Even if the islands are, in some ways, more resilient than we thought, the warnings are still apt.