CLIMATE CHANGE, CORAL REEFS, AND ATOLL SUSTAINABILITY

Although rates of sea-level rise (SLR) and projected 2100 global sea levels span a wide range, models consistently suggest that eustatic sea level will be considerably higher by the end of the century and rates of SLR will far outstrip vertical coral-reef accretion rates, which will have a profound impact on coral reef-lined islands. Atoll islands are low-lying carbonate Holocene features, many of which have maximum elevations of less than 4 m, that support 1000 year-old cultures, yet the amount of land and water available for human habitation, water and food sources, and ecosystems is limited and extremely vulnerable to episodic wave-driven flooding and permanent inundation from SLR. The USGS is leading a multidisciplinary effort to understand how SLR and climate change may impact low-lying atoll islands in Micronesia using field observations and global climate model outputs to drive coupled hydrodynamic and hydrogeologic models for a number of SLR and climate change scenarios. Rising sea levels and climate change will reduce the ability of coral reefs to mitigate wave-driven flooding in the future, leading to more frequent, persistent, and extreme marine flooding and overwash on atoll islands, damaging infrastructure, habitats, and agriculture. More importantly, the increased marine flooding, along with decreased precipitation, will result in salinization of the islands’ limited freshwater drinking supplies with such frequency that the freshwater lenses will not be able to recover. Our findings suggest that such “tipping points” – when the islands can no longer sustain a freshwater lens and thus human habitation – will likely occur in decades, not centuries as previously thought, which will result in significant geopolitical issues when it becomes necessary to abandon and relocate island-states.