We investigate climate-related processes causing variations of the global mean sea level on interannual to decadal time scale. We focus on thermal expansion of the oceans and continental water mass balance. We show that during the 1990s where global mean sea level change has been measured by Topex/Poseidon satellite altimetry, thermal expansion is the dominant contribution to the observed 3 mm/yr sea level rise. For the past decade, exchange of water between continental reservoirs and oceans as well as glaciers and ice sheet melting may account to up 1 mm/yr. This suggests that there is a missing contribution which counterbalances the 1 mm/yr eustatic contribution. Dam building and irrigation associated with anthropogenic activities appear able to cancel out the effect of ice melting and land water change. For the last four decades, thermal contribution is estimated to about 0.5 mm/yr, with a possible accelerated rate of steric sea level rise during the 1990s.