Studies of the Long-term Change of Global Mean and Regional Sea Surface Height

Sea level change could have profound impacts on our society. We report here on three related sea level change problems. First, a variety of regression models have predicted different rates for global mean sea level rise over the past century. Some of these models are accelerating and others are not. We ask whether we can distinguish between these using a new nonparametric noise model that we have developed. Simulations show that we can, and further imply that GMSL is rising at an accelerating rate. Second, historical global mean sea level is reconstructed from tide gauges that are located along coastlines and islands, but over the past 25 years we also have data from satellite altimeters that give global coverage. This raises the question as to whether there are differences between coastal and open-ocean sea level trends. Linear sea level trends from tide gauges, with and without vertical land motion corrections, are compared with the trends derived from altimetric observations in the nearby open ocean. The globally averaged trend difference is not significant, but at the regional scale there are possibly significant differences in some areas. These trend comparisons highlight the importance of having accurate estimates of vertical land motion for correcting tide gauge records. Finally, in contrast to global mean sea level change, which reflects ocean volume changes, regional sea level variations are mostly associated with water volume redistribution. Earlier work in the Northeast Pacific suggests that wave propagation and local damping are the two main mechanisms that might account for large-scale, low-frequency sea level variability, but these studies have reached conflicting conclusions. We develop a novel sea level model driven by wind, buoyancy and eddy forcing and including both mechanisms to examine their relative roles in the Northeast Pacific. The diagnosis demonstrates that temporal damping is more important to the sea level response than propagation over most of the Northeast Pacific, while propagation plays a role in the southwest portion of the study region where the stresses associated with mesoscale eddies dominates