Sinking South Pacific Islands: Climate Change or Tectonic Shifts?

Graphic: Tectonic shifts in the South Pacific.

Environmentalist organizations have used images from South Pacific islands to illustrate the disastrous effects of rising sea levels. But a group of French researchers has found that the problem is much more complicated: The islands are also being pulled under by shifting tectonic plates.

When Ballu and her team set out to find the location where they measured the island’s elevation seven years ago, they discover that their most important survey marker, originally placed a safe distance from the beach, is now underwater, with the sea eroding the metal piece and its concrete base. “That’s probably caused it to slide down,” remarks geologist Stephane Calmant, 52, who fears this renders the marker “useless.”

Still, this development offers proof of at least one thing: that the coast here is in motion. But the question remains: Is the sea level rising, or is the island sinking? “The questions we’re trying to answer here on Vanikoro have global significance,” Ballu says.

Indeed, since water levels are rising faster around the islands of the South Pacific than anywhere else on Earth, the region has become an important object of study for oceanographers, climate researchers and geologists. At the same time, it draws the attention of politicians and ecologists to these remote islands.

Not far south of Vanikoro, the island of Tegua is home to the people the United Nations declared the world’s “first climate change refugees” in 2005. On Tegua, part of the island nation of Vanuatu, an entire village had to relocate due to rising water levels, and global media publicized photographs of a coconut plantation submerged in water, reclaimed by the sea.

That village relocation on Tegua “underlines the increasingly drastic measures now underway to conserve low-lying communities as a result of the rise in human-made emissions to the atmosphere,” the United Nations Environment Programme (UNEP) warned at the time. Klaus Töpfer, a German politician with Chancellor Angela Merkel’s center-right Christian Democratic Party (CDU) and the UNEP’s executive director at the time, bleakly noted: “The melting and receding of sea ice and the rising of sea levels, storms surges and the like are the first manifestations of big changes underway which eventually will touch everyone on the planet.”

Battle for Every Millimeter

But does the fate of the village on Tegua really lend itself to being held up as a symptom of global warming? The researchers from France have their doubts, and they’re here on Vanikoro to look for evidence.

Their first tool is a machete. Valérie Ballu is now looking for the second survey marker. Her colleague Alain Le Breüs pulls out hand-drawn sketches resembling a treasure map. But without even needing to look at the map, Alek Silo, a local, points a bony hand toward a young mango tree.

And, indeed, the researchers find their survey marker there under the bushes. They quickly unfold a yellow-and-red tripod of the kind land surveyors use. “Now the battle for every millimeter begins,” Ballu says.

She checks the position of the GPS antenna, then asks Alek to cut down a couple of young trees that are interfering with reception. “We need signals from as many GPS satellites as possible for our measurements,” Ballu explains. “That increases our accuracy.” The display on her GPS device ultimately indicates contact with 16 satellites.

These devices will store position data from satellites every 30 seconds for 48 hours. “The longer we measure, the more precise the results,” Ballu says.

Determining the minute motions of the Earth’s crust down to the millimeter is no easy task. The planet is not a rigid sphere. Instead, it is constantly reshaped by the force of gravity exerted by the moon and sun as well as by other planets, such as Mars and Jupiter.

Those bodies tug not only at the Earth’s surface, but also on the GPS satellites, creating discrepancies in their orbits. “All these things cause a loss of precision,” Ballu explains.

Ballu is in a hurry. Her team has less than 48 hours to determine whether other parts of the island’s coastline are disappearing as well, and they have plans to visit the village of Temuo on the eastern side of the island. After lunch on their research ship Alis, operated by France’s IRD institute for development research, they once again lower their motorboat into the water.

On their way, the research team is caught in a tropical rain shower. Then they come upon a beach where they can see coconut palms with their roots exposed by the water through a steaming veil of rain. Are these the initial signs that the island is sinking, or that the sea level is rising?

Right under their feet, she explains beneath the palm frond roof of Temuo’s village school, one plate is slipping under another. Ballu splays her hand to represent the Australian Plate disappearing under the Pacific. “No soap soap,” Ballu adds, jerking her left hand — the plates snag against one another and the built-up pressure is released.

Earthquakes and tsunamis strike Vanikoro regularly, but people here are at the mercy of the forces of nature in a longer-term way, as well: On its slowly sinking course, the Australian Plate is dragging Vanikoro along into the depths.

Ballu was able to document that this is the case for the nearby island of Tegua in a well-received publication last year. That island sank nearly 12 centimeters (five inches) between 1997 and 2009, to the point that the coconut plantation now famous at global climate conferences was underwater. “The sea level rose, but three quarters of that was caused by the land’s subsiding,” she explains.


Spiegel has the full article

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