“The reefs will maintain equilibrium with sea-level rise,” said Scott Smithers of James Cook University in Townsville, Australia. “Waves are what will allow them to keep their head above water.”
“During big storms, the waves wash over the beaches and deposit sand inland,” explained Paul Kench, head of the University of Auckland’s School of Environment, who like Smithers is a coastal geo-morphologist. “That’s how the islands rose above the reef thousands of years ago and that’s what they’ll keep on doing as long as their reefs produce sand.” Atoll sand is made of broken bits of coral and coralline algae and of the skeletons of mollusks and tiny creatures called foraminifera. Noting that ocean acidification and a warming ocean will be increasing their mortality, he added, “That’s not significant in geological time, because a reef can produce sand for centuries after it dies.”
But no one is saying that the expected growth spurt will be as pleasant for the people living on atolls as life has been for the last 3,000 years, which were marked by sea-level stability. Even if islands aren’t submerged, scientists agree that climate change will create major problems—at the very least the same ones that coastal residents will face everywhere. “The low-lying areas will go under water more frequently as the sea level rises,” said Colin Woodroffe of the University of Wollongong in Australia. “And the narrower parts of the islands will be washed over more often.” What makes the process hard to predict is that there are no topographic maps of most atolls because the higher parts are usually covered in vegetation—trees, bushes or grasses—so satellites can’t measure just how high they are above the water. On most islands, people, like vegetation, stick to the higher, less exposed parts.
Christmas Island, which at 150 square miles is five times the size of Manhattan, is the biggest atoll island in the world by land area. There, the sea-level rise will likely be benign, the scientists agree: The peninsula where London, the capital, is located (which is also where most people live) is 20 feet above sea level. In addition, Christmas, whose Kiribati spelling is Kiritimati but is pronounced Christmas, has enough fresh water for four times its population of 6,000, according to a European Union study.
But 2,000 miles to the west in South Tarawa, Kiribati’s narrow, six-square-mile capital island crowded with 50,000 people, the picture is much darker. Over the past half-century, residents of the 15 other Gilbert Islands have flocked there in search of jobs and better schools for their children. The island, once a Japanese fortress and the site of a World War II battle, was already hardly pristine. Now, many live in flimsy beachside houses that are routinely awash in high tides. To minimize flooding, they built poorly designed seawalls that regularly collapse. Meanwhile, the government increased South Tarawa’s area by 19 percent over 30 years by building causeways between islets and creating new land over the reef with lagoon sand poured behind seawalls. The widespread erosion and flooding that resulted “is primarily due to [local] human activities,” which unless stopped will “increase erosion and susceptibility of the reef islands to anticipated sea-level rise,” one study concluded.