Sea-level riseDynamic atolls give hope that Pacific Islands can defy sea rise

By Paul Kench

Published 21 April 2014

It is widely predicted that low-lying coral reef islands will drown as a result of sea-level rise, leaving their populations as environmental refugees. New evidence, however, now suggests that these small islands will be more resilient to sea-level rise than we thought. The new findings suggest that, rather than being passive lumps of rock that will be swamped by rising seas and eroded by storms, the islands are dynamic structures that can move and even grow in response to changing seas. Although the islands may survive into the future, the changes could still affect issues like fresh water and agriculture, potentially making life on these islands much more difficult than it is today.

It is widely predicted that low-lying coral reef islands will drown as a result of sea-level rise, leaving their populations as environmental refugees. But new evidence now suggests that these small islands will be more resilient to sea-level rise than we thought.

That is not to say that these tiny nations won’t face significant environmental challenges. Built of sand and shingle and lying just 1-3m above the current sea level, coral reef islands in the central Pacific and Indian Oceans are considered among the most vulnerable places on Earth.

The new findings suggest that, rather than being passive lumps of rock that will be swamped by rising seas and eroded by storms, the islands are dynamic structures that can move and even grow in response to changing seas.

But although the islands may survive into the future, the changes could still affect issues like fresh water and agriculture, potentially making life on these islands much more difficult than it is today.

Long-term island formation
We have closely examined how reef islands formed over the past 5,000 years in response to past changes in sea level, in a bid to find out how islands might behave in the future. In our most recent study, we show that Jabat Island in the Marshall Islands, central Pacific, was created 5,000 years ago as sea level rose to 1.5m above its present level.

Since that time, sea levels have fallen once more, leaving the island much higher relative to the current sea level. Over the coming century, future sea-level rise will simply reoccupy the levels under which the island formed. This finding is consistent with our case studies in the Great Barrier Reef and the Maldives, which show that islands can form under a range of sea-level conditions including rising, falling, and stable.

Together, these studies show that sea level alone is not the main factor that controls the formation and subsequent change of reef islands. These processes also depend on the surrounding coral reef generating sufficient sand and shingle to build islands.

Changes over the past century
We also looked at how islands have physically changed over the past sixty to 100 years. Our study sites are in regions of the Pacific Ocean where sea level has been rising at more than 2mm per year for the past five decades.