Some Scientists Predict These Islands Are Doomed

October 26, 2018

Low-lying, white-sand islands, lined with palm trees and perched on tropical coral atolls, are a vacation dream. It has long been claimed that they will eventually disappear as sea levels rise due to global warnings, but when that will happen has been unclear.

A study published Wednesday (April 25) in the journal Science Advances suggests that the islands could become uninhabitable in just 40 years. However, other scientists have strongly questioned the study’s conclusions.

The study is based on an analysis of waves rolling onto a highly militarized island – which doesn’t look at all like a vacation fantasy – on Kwajalein Atoll in the Marshall Islands in the Central Pacific. The study was funded primarily by the U.S. Department of Defense.

The atoll is made up of tropical and subtropical corals that grow around the volcanic rim as it sinks into the sea. The corals and marine animals with calcareous skeletons were ground up by the waves, which eventually formed enough sand that the waves pushed it onto the reefs to form islands. The islands began to appear about 5,000 years ago, and many were eventually colonized by Polynesians, Micronesians, and Melanesians.

Curt Storlazzi, lead author of the paper, told Live Science that the largest of these waves, which are thought to have reached a height high enough to wash away the atolls every 20 to 30 years in the past, would flood at least half of each island each year when sea levels rose about 3 feet (1 meter). This could happen as soon as 2105, according to some of the ice melt scenarios the scientists have simulated, or as soon as 2055 under more pessimistic models involving the collapse of ice shelves.

The calculations would apply to atolls around the globe, or about 25,000 islands, Storaci said.

“There’s nothing wrong with waves washing over islands per se,” said Storaci, a geologist with the U.S. Geological Survey at the University of California, Santa Cruz, who studies waves.” When it happens once every 20 years, communities have time to recover from the effects of flooding.” Afterward, he said, rain washes away salt that has seeped into the porous, sandy ground and refreshes the freshwater lens located a foot or two below the island’s surface, which floats above the water. In other words, plants and people can survive.

But at the rate of once a year, plants would die, freshwater wouldn’t have time to return, and people wouldn’t be able to repair flood damage to roads and homes – so they’d just leave, Stolazzi said.

Research critics say most atolls will be fine.
Paul Kenzie, head of the University of Auckland’s School of the Environment and author of the prolific atoll study, said the new study’s analysis of Roy Namur’s wave dynamics may only apply to six or seven islands around the world – not all of them.

“It was the waves that washed over the islands that brought them to their current configuration,” said Kench, who was not involved in the Storazzi study, in a telephone interview from New Zealand.” As sea levels continue to rise, so do islands, and they can impede flooding events. So these are unlikely to become as frequent as the paper predicts.”

He added that the study also ignores the response of atoll residents, who could build new structures on stilts and use foreign aid to get solar-powered desalinators.

In February, Kench, along with Murray Ford and Susan Owen, published a paper in the journal Nature Communications showing that the islands that make up Tuvalu and their inhabitants are doing well as sea levels in the Central Pacific have risen by nearly 6 inches (15 centimeters) over the past half-century, and that this resilience is expected to continue. Another study by Kench and the same co-author, this one published in the 2014 issue of the journal Geophysical Research Express, found that the Marshall Islands’ Jabat Island emerged when sea levels rose at roughly the same rate as they do today. Overall, he said, he studied the evolution of at least 600 atolls and found that the vast majority stayed the same or naturally increased in size, and he expects most atolls to remain about the same size for the rest of the century.

Unlike almost all other atolls, Kenzie said, Roy Namur was completely bulldozed for military purposes during and after World War II.” The island has been reconfigured to the point where it has lost its ability to receive sand and grow,” he added. Similar damage has also damaged Kiribati’s capital, South Tarawa, where 60,000 people are crammed into six square miles (16 square kilometers) of land that is highly vulnerable to flooding.

The limitations of the “doomed atoll” discovery
Storlazzi insists that his findings apply to atolls around the world, and he doesn’t deny that waves washing over a typical sand island will cause it to rise. But he explains that in this study of Roy Namur, the team assumed that the island would not rise at all.

Storlazzi explained that the model did not account for the island’s rise because the margin of error in such predictions is too wide. In addition, the growth “is only one-tenth of the thickness of the overtopping, so there will always be more overtopping during large wave events than the island can grow vertically to offset them,” he said. It is these events that will make life on these atolls impossible, he adds.

Instead, Kench and other geomorphologists say, the record shows that as the sea rises, waves push up sand ridges on the beach, preventing the rest of the island from being submerged. In addition, the new study does not take into account the vertical growth of coral in reef beaches created by waves. This means that if the sea level rises by 3 feet, these flats will have much more water and much larger waves. However, as sea level rises, corals do grow vertically on these flats. How fast it will continue to do so remains unclear as hot weather events kill off more and more coral.

Kench added that the study highlights the problem of islands, where man-made modifications such as seawalls, causeways and land reclamation disrupt the natural mechanisms that allow sparsely populated or pristine islands to naturally adapt to sea level rise.

Virgini Douat, a professor of coastal geography at the University of La Rochelle-CNRS in France, specializes in atolls. She agrees with Kench that all but the most miserable atolls seem to have adapted well to sea level rise so far.

But that doesn’t mean that the inhabitants of these islands are guaranteed a bright future.” If we hint at a world that is becoming very warm, I think there will be a combination of phenomena that will interact in ways we can’t begin to predict,” Duvat told Live Science.

“For example, if corals start to die off en masse and can’t recover, they may continue to produce sand to feed the beaches for a century, but the number of accessible fish on the reefs will collapse and people won’t have enough food,” she said.” Or soil salinization could kill coconut trees, the only source of cash for most people.

“You can’t take the current processes and expect to see them continue for a century,” she adds.” That’s why I’m cautious.”