Probabilistic surface reconstruction of coastal sea level rise during the twentieth century

We present a new surface reconstruction procedure based on the Bayesian inference method for coastal relative sea level variation during the twentieth century. Average rates are computed from tide gauge records. Models based on a Voronoi tessellation adapt to the level of information which proves well suited to the strong heterogeneity of data. Each point of the reconstructed surface is defined through a probability density function, a format particularly well adapted to this climate-related datum. The resolution of reconstructed surfaces strongly varies among the six large regions considered and within a given region. Anomalous sea level variations recorded locally are shown to reflect either anthropogenic effects or well-identified fast tectonics. For a poor data coverage, these can cause a problematic distortion of the reconstructed surface. Europe, North America, Australia, and Africa present a single trend with a decreasing precision of the reconstructed surface as a function of resolution of the tide gauge record. The most prominent feature in Europe is the pronounced uplift of Fennoscandia. Coasts of United States have the best resolution in North America and present stronger rates of sea level rise on the Atlantic than their European counterparts. Australia (especially in the North) and Africa are poorly resolved. Asia and South America depart clearly from this trend: a relatively uniform rise is obtained for Asia in spite of a good tide gauge record. Conversely, the reconstructed surface for South America presents an exceptional degree of roughness, at odds with a relatively poor record. Overall, this method not only offers a new assessment of sea level change (validating earlier results) but also quantifies the reliability of estimates.