Estimating Recent Global Sea Level Changes

Abstract

An empirical model for sea level trends over several decades is set up such that it is consistent with the global pattern of Local Sea Level (LSL) trends observed by the global network of tide gauges. The forcing factors taken into account are steric sea level variations, present-day ice load changes, and post-glacial rebound. Model parameters are determined in a least squares fit of the model to the LSL trends. The model allows the determination of the contribution of each factor to the global average LSL trend.

Here we compare the solutions for two different LSL trend sets, namely one determined without and one with taking into account local atmospheric forcing at the tide gauges (denoted here as T1 and T2). From the globally given model, the global average trend over the last 50 years in LSL is found to be of the order of 1.05 ± 0.75 mm/yr and 1.20 ± 0.70 mm/yr for T1 and T2, respectively. For T1, the contribution of the Antarctic and Greenland ice sheets to the global average are 0.39 ± 0.11 mm/yr and 0.10 ± 0.05 mm/yr, respectively and for T2 0.31 ± 0.16 mm/yr and 0.16 ± 0.03 mm/yr, respectively. Using T1, the contribution from steric change is clearly identified and found to be at least 0.2 mm/yr with the most likely value being close to 0.35 mm/yr. For T2, there is no correlation between the spatial pattern of the observed LSL trends and the steric sea level trends, and the steric contribution to the global average turns out to be equal to zero. This result indicates a very high correlation between the local atmospheric forcing and the thermosteric sea level changes, which may be the result of a feedback of temperature changes in the upper layer of the ocean into the air pressure and wind field over the ocean.