Past and Future Sea-Level Changes in French Polynesia

Abstract

Among the various adverse effects of climate change, sea-level rise is expected to increase the severity and frequency of flooding events impacting the vulnerable, low-lying islands of French Polynesia. It has long been understood that sea-level changes are not spatially uniform, yet this aspect is not taken into account in the decision-making. Notably, no projections of future sea level have been produced specifically for this region so far, partly because the processes driving sea-level changes remain poorly constrained. To approach the issue, we present a detailed reconstruction of sea-level changes for the mid-to-late Holocene, based on the observation of coral proxies. This dataset is then used to calibrate a sea-level model in order to estimate the contribution of glacial isostatic adjustment to regional sea-level changes and to infer past variations in global ice volume. Building upon this baseline and exploiting recent outputs of climate models, we project that in a “worst-case” scenario, sea level would rise 1.05 meters by 2100 in French Polynesia, exceeding the value adopted in the French adaptation strategy by 0.45 meters. We conclude that spatial variability of sea-level rise should be considered in future risk studies for this and other regions.