A chain of tiny, remote Hawaiian islands could become the largest marine sanctuary in the U.S. as soon as next year.
But the rare wildlife living there could disappear beneath the waves by the end of this century because of global warming, a new study warns.
A team of Hawaii-based scientists calculates that two-thirds of some islands in the Northwestern Hawaiian Islands (NWHI) could be submerged by 2100.
A scattered archipelago stretching some 1,200 miles (1,930 kilometers) across the Pacific Ocean, NWHI is home to colonies of unique animals that may be swamped as their low-lying islands succumb to rising sea levels, researchers say.
Animals at risk include rare seals, sea turtles, and bird species found only on NWHI.
The NWHI consist of islands, atolls, and pristine coral reefs and are slated to form part of the largest national marine sanctuary in the United States, if approved by the Bush Administration.
Threats to the islands from future sea level rise were assessed for the first time by a team led by Jason Baker of the Pacific Islands Fisheries Science Center, part of the U.S. National Oceanic and Atmospheric Administration (NOAA).
Studies suggest that sea levels rose almost 6 inches (15 centimeters) during the 20th century.
Levels are expected to rise farther and faster this century, as global warming accelerates the melting of glaciers and polar ice caps, and as higher water temperatures expand the volume of the world's oceans.
The team created 3-D computer models of NWHI to gauge the possible impact of future sea level rises using scenarios forecast by the Intergovernmental Panel on Climate Change (IPCC) based in Gland, Switzerland.
Their findings suggest that by 2100 up to 65 percent of some islands would be lost if the sea level rose 18.9 inches (48 centimeters), which is the average IPCC projection.
The team also found that a 34.6-inch (88-centimeter) rise—the maximum sea level rise forecast by 2100—could result in up to 75 percent of NWHI wildlife habitat disappearing.
The researchers report their findings in in the latest issue of the journal Endangered Species Research.
Hawaii's Vulnerable Species
Vulnerable species include the critically endangered Hawaiian monk seal, one of the world's rarest marine mammals; the Hawaiian green sea turtle; and the Laysan finch, one of four endemic birds.
Other species found only on the NWHI include 3 land snails, 12 plants, and more than 60 invertebrates.
"Oceanic islands in general tend to have high levels of [unique species], due largely to their isolated nature, and the Hawaiian archipelago is the most isolated in the world," NOAA's Baker said.
"These little islands are important nurseries for monk seals, sea turtles, and millions of seabirds," he added.
"Yet much of this lively activity occurs just a few meters above sea level."
In the worst-case scenario, Baker says, some islands would come close to disappearing entirely.
For example, up to 99 percent of Trig Island could be submerged.
Trig Island has become the main birthing site for Hawaiian monk seals after the loss of other sites to the sea.
Researchers suggest this has led to overcrowding on the island, resulting in increased predation of seal pups by sharks.
Writing in Endangered Species Research, the team says further loss of the seal's habitat "can only be expected to exacerbate an already lamentable situation."
The Hawaiian green sea turtle is similarly at risk, the team says, with more than 90 percent of females laying their eggs on one NWHI atoll.
The study suggests the main island haven for the Laysan finch isn't in danger, but smaller colonies would be wiped out under the average scenario for sea level rise, increasing the overall risk of extinction.
Nor is sea level rise the only threat to NWHI wildlife from global warming, the team says.
Surveys led by Greta Aeby of the Hawaii Institute of Marine Biology in Kaneohe have revealed damage to reef systems in the region in recent years caused by coral bleaching.
Bleaching is a phenomenon linked to higher water temperatures that can cause corals to die.
Scientists fear coral bleaching events may become more frequent as ocean temperatures rise.
The study team, however, suggests there may be a way to help counter the effects of sea level rise in NWHI.
This would involve redistributing sand to increase the size and stability of vulnerable islands in a process known as beach nourishment, Baker says.
"If this were done in the NWHI, it could help preserve key islands and the species which depend upon them," he said.
"Any such work should only be undertaken after very careful planning to ensure no harm is done in the process."
The Northwestern Hawaiian Islands are currently being considered as the 14th and largest national marine sanctuary in the U.S. Final designation is expected next year.
The NOAA says federal sanctuary status would give the islands and their wildlife enhanced protection in terms of enforcement, research, and funding.