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Researcher shows Pacific Islands may be threatened by rising sea levels

A geology professor is examining the shorelines of island nations once thought to be on the brink of disappearance. His research shows that while the islands may continue to exist, their inhabitants face a dangerous future.

Island nations such as Tuvalu and Kiribati have long been described as potential victims of climate change because they were expected to disappear underwater. But last year, researchers from the University of Auckland in New Zealand and the South Pacific Applied Geoscience Commission in Fiji presented evidence that these low-lying Pacific islands were maintaining their size under rising sea levels.

In a new paper published online in the journal Sedimentology, KU associate professor of geology Gene Rankey provides evidence that even if the islands are not shrinking, their future still may be perilous because their shorelines are undergoing major transformations. The rate of change also appears to be increasing.

“Even if an island does not change size, but the shoreline moves, it can be devastating,” Rankey said. “The distinction is important for islanders who literally build their houses right to the shoreline. If the shoreline shifts, and you live in the place where it shifted, you are in trouble.”

Titled “Nature and stability of atoll island shorelines: Gilbert Island chain, Kiribati, equatorial Pacific,” the 29-page paper provides the first detailed study of shoreline change on 17 islands from the Maiana and Aranuka atolls in the Republic of Kiribati. The nation is located in the equatorial Pacific, about 2,500 miles southwest of Hawaii.

In the study, Rankey analyzed satellite remote sensing data, employed differential global positioning system measures of shoreline position and elevation, and analyzed sediment samples from the atolls. The results were compared to aerial photographs taken in the past and other historical measurements.

Rankey found that between 2005 and 2009, about 50 percent of the atolls’ shoreline displayed discernable shifts in position. In some locations, the shoreline expanded toward the ocean at net rates of up to about 8 meters per year (1 meter is the same as about 3.28 feet). In other places, the shoreline eroded at net rates of up to 18 meters per year.

Observations over four years suggest that this variability was probably not directly influenced by “marked sea-level change,” Rankey said, but climate change may still be playing a role. Theories about the cause include the cumulative effect of the increasing speed at which the sea level is rising and the impact of the climate cycle known as the El Niño/Southern Oscillation.

Rankey compared his work in Kiribati to that of a doctor monitoring a critically ill patient. His job is to understand what is occurring and make a prognosis — a prediction that is still impossible to complete. Further study is required, Rankey said.

The 2010 study on low-lying islands was written by Paul Kench of the University of Auckland in New Zealand and Arthur Webb of the South Pacific Applied Geoscience Commission in Fiji and published in the journal Global and Planetary Change.

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