Letters

Island outlook: Warm and swampy

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Science  19 Sep 2014:
Vol. 345, Issue 6203, pp. 1461
DOI: 10.1126/science.345.6203.1461-a

In his In Depth News story “Warming may not swamp islands” (1 August, p. 496), C. Pala argues that “coral reefs supporting sandy atoll islands will grow and rise in tandem with the sea,” based largely on studies that showed stable Pacific-island area over recent decades (14). He suggests that recent land losses are driven mostly by bad choices and that islanders are being affected “for the same reason as millions of people on the continents: because they live too close to shore.” We disagree with these conclusions.

Pala bases his arguments on (i) evidence that reefs can build vertically at 10 to 15 mm/year, a rate far exceeding the anticipated rate of sea-level rise, and (ii) sequential air photographs that document stable island areas despite rising sea level. An analysis of the early literature (i.e., pre-1999) revealed 22 articles reporting much lower reef-accretion rates—0.60 to 7.89 mm/year, averaging 3.54 (see supplementary materials). More recent reviews similarly conclude that rates of 10 to 15 mm/year are much too high for Holocene reef building (58). Recent declines in coral cover can only slow accretion in the future.

Flooding on Ejit Island in Majuro.

PHOTO: ALSON KELEN

Naomi Biribo has noted that “widespread erosion along the ocean and lagoon shorelines is primarily due to human activities” (3). However, the same paper also attributes 90% of the increase in island area on South Tarawa to reclamation projects (i.e., no inherent ability to keep pace with sea level naturally). Island area may not provide an adequate measure of either changing sediment volume or the susceptibility of the island to flooding, erosion, or drowning. It is possible that erosion of sand from higher marginal areas and redistribution to lower shorelines elsewhere on the island can increase island area, even in the face of declining sediment volume.

Pala's sources describe islands building seaward 4800 to 4500 years ago (3, 9), a pattern opposite to the island retreat that is occurring today. If rising sea level is to be discounted, then a mechanism to explain this recent reversal must be identified. Also, fewer corals making calcium carbonate and stronger storms removing at least some of it will likely reduce sediment availability.

We also take exception to laying the sole blame at the feet of islanders who have occupied these fragile islands for millennia. Human communities living on atoll islets often depend on thin aquifers, agroforestry, and freshwater wetland taro production. Saltwater intrusion and flooding destroys otherwise sustainable food and water sources (10), making islands unlivable long before drowning.

Certainly the situation has been exacerbated by poor choices, and politics is rarely the best lens for viewing natural phenomena. Adapting to either sea-level rise or more frequent inundation often involves ill-placed engineering solutions that require substantial volumes of sand and rock that would be better left in place to protect coastlines and contribute to island sediment budgets. The meteorological instability that comes with rising temperatures, the likely increase in erosion and storm surge, islands constantly retreating from the sea, dwindling groundwater supplies, decreasing rainfall, and rising sea level will all have disproportionate impacts on populations that are least responsible for the global carbon emissions that are at the heart of these changes.

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