Dynamic atolls give hope that Pacific Islands can defy sea rise

Using comparisons of historical maps, aerial photographs and satellite images, we have been able to test the hypothesis that central Pacific Islands have begun to erode away in response to this sea-level rise.

One example is the reef islands in Funafuti Atoll, Tuvalu, in the central Pacific. Our study found that most of these islands either remained stable in size or grew larger over the past few decades, in spite of rising sea levels.

Another of our studies found that islands in Nadikdik Atoll, Marshall Islands, have been rebuilt over the past century despite being destroyed by a typhoon in 1905. All of this shows that reef islands are able to grow under current climate conditions.

Dynamic islands
This suggests that coral islands are very dynamic landforms that adjust their shape and position on reef surfaces over decades. Low-lying islands are built by the action of waves and currents, which deposit sand and gravel at the shoreline. Just like any beach, as wave and current processes change, island sand and shingle is mobilized and deposited elsewhere on the shoreline. Through this ongoing process islands can change their shape and migrate across reef surfaces.

We are now aiming to work out the scale and speed of these changes — which will be crucial for helping island communities to adapt to the rising seas. One question is whether islands can build vertically to keep pace with rising sea levels.

Our results suggest that islands can grow upwards when waves wash over them during storms or tsunami, depositing sand in the process. This suggests that islands may be able to withstand rising sea levels and increased storminess – although life on those islands may be very different to today.

What does this mean for small island nations?
On the face of it, this is potentially good news for Pacific communities. The islands they call home may be less vulnerable than is commonly thought.

But our findings also suggest that although the islands may not be swamped by rising seas, they are likely to change in size and shift their position on the surface of reefs. The rate of these changes may also increase as sea level rises.

This raises questions for their ongoing habitation. How will physical changes to the islands affect drinking water supplies, and how will communities need to adapt their farming practices? Questions about island change must be addressed urgently in order to inform decision making and secure the future of Pacific nations.

Paul Kench Professor, School of Environment at University of Auckland. This story is published courtesy of The Conversation (under Creative Commons-Attribution/No derivatives).