Decadal Trends in Sea Level Patterns: 1993-2004

Estimates of regional patterns of global sea level change are obtained from a 1◦ horizontal resolution general circulation model constrained by least-squares to about one hundred million ocean observations and many more meteorological estimates during the period 1993-2004. The data include not only altimetric variability, but most of the modern hydrography, Argo float profiles, sea surface temperature, and other observations. Spatial mean trends in altimetric data are explicitly suppressed to isolate global average long-term changes required by the in situ data alone. On large scales, some regions display strong signals although few individual points have statistically significant trends. In the regional patterns, thermal, salinity, and mass redistribution contributions are all important, showing that regional sea level change is tied directly to the general circulation. Contributions below about 900m are significant, but not dominant, and expected to grow with time as the abyssal ocean shifts. Estimates made here produce a global mean of about 1.6mm/y, or about 60% of the pure altimetric estimate, and of which about 70% is from the addition of freshwater. Interannual global variations may be dominated by the freshwater changes rather than by heating changes. The widely quoted altimetric global average values may well be correct, but the accuracies being inferred in the literature are not testable by existing in situ observations. Useful estimation of the global averages is extremely difficult given