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Sinking Islands: Fact or Fiction?

Biribo, N. and Woodroffe, C.D. 2013. Historical area and shoreline change of reef islands around Tarawa Atoll, Kiribati. Sustainability Science 8: 345-362.
According to Biribo and Woodroffe (2013), "low-lying reef islands on atolls appear to be threatened by impacts of observed and anticipated sea-level rise," noting that "widespread flooding in the interior of Fongafale on Funafuti Atoll, in Tuvalu, is often cited as confirmation that 'islands are sinking' (Patel, 2006)." But is this really the case?

In an attempt to find out, Biribo and Woodroffe examined changes in shoreline position on the majority of reef islands on Tarawa Atoll, the capital of the Republic of Kiribati, by analyzing "reef-island area and shoreline change over 30 years determined by comparing 1968 and 1998 aerial photography using geographical information systems."

In describing their findings, first of all, the two Australian researchers state that the reef islands of Tarawa Atoll "substantially increased in size, gaining about 450 ha, driven largely by reclamations on urban South Tarawa, accounting for 360 ha (~80% of the net change)." And of the 40 islands of North Tarawa, where population is absent or sparse, they report that "25 of the reef islands in this area showed no change at the level of detection, 13 showed net accretion and only two displayed net erosion." In addition, they indicate that "similar reports of reef island area increase have been observed on urban Majuro, in the Marshall Islands, again mainly related to human activity," citing Ford (2012). And they say that "a recent analysis of changes in area of 27 reef islands from several Pacific atolls for periods of 35 or 61 years concluded that they were growing (Webb and Kench, 2010)," likely "as a result of more prolific coral growth and enhanced sediment transport on reef flats when the sea is higher," under which conditions they note that "shorelines will actually experience accretion, thus increasing reef island size (Kinsey and Hopley, 1991)."

Biribo and Woodroffe conclude that "despite the widely held perception that reef islands around the perimeter of coral atolls are eroding and will disappear as a consequence of sea-level rise resulting from global warming, this study shows that the total area of reef islands on Tarawa Atoll has increased over recent decades," just as it has also done on many other reef islands.

Additional References
Ford, M. 2012. Shoreline changes on an urban atoll in the central Pacific Ocean: Majuro Atoll, Marshall Islands. Journal of Coastal Research 28: 11-22.

Kinsey, D.W. and Hopley, D. 1991. The significance of coral reefs as global carbon sinks - response to Greenhouse. Palaeogeography, Palaeoclimatology, Palaeoecology 89: 363-377.

Patel, S.S. 2006. Climate science: a sinking feeling. Nature 440: 734-736.

Webb, A.P. and Kench, P.S. 2010. The dynamic response of reef islands to sea-level rise: evidence from multi-decadal analysis of island change in the central Pacific. Global and Planetary Change 72: 234-246.

Archived 5 November 2013