THE INCEPTION OF MODERN ACCELERATED RATES OF SEA-LEVEL RISE

The sea-level variability over the Common Era (last two millennia) has been widely recognized as being crucial for understanding the present and future climate responses to anthropogenic forcing. Here, we use Common Era sea-level reconstructions to address the debate regarding the exact timing of when the modern rates of sea-level rise exceed Common Era background rates. Identifying the timing of the inflection between the Common Era background and modern rates is crucial to define target climate thresholds for the future. However, a substantial range of suggested dates for the inflection persists depending on the types sea-level data and dating methods used and their associated errors.

Here, we use a global database of instrumental and proxy sea-level records from Common Era to examine the precise timing and spatial variability of the beginning of accelerated rates of sea-level rise due to human influence, which has implications for the interpretation of underlying driving mechanisms. The proxy records are from over 30 regions around the world using proxies such as foraminifera, diatoms, testate amoebae, coral microatolls, archeological evidence, and sediment geochemistry. We develop a new component in a spatiotemporal model to examine the timing of accelerated rates of sea-level rise and standardize the records to minimize the influence of the differing sea-level and chronological resolution. We examine whether the timings among regions are nonsynchronous, which would suggest at a regional cause for rapid sea-level rise, such as ocean dynamical change or thermal expansion. In contrast, a synchronous timing might signal forcing by mass balance change of ice sheets and/or glaciers.