The rate and acceleration of the global mean sea level revisited

Since nearly 3 decades, high-precision satellite altimetry allows us to precisely measure the mean sea level evolution at global and regional scales. In terms of global mean, sea level is rising at a mean rate of 3.2 mm/yr. The altimetry record is also suggesting that the global mean sea level rise is accelerating. However, the exact value of the acceleration and even its mere existence are still debated. Determination of the global warming-related sea level rate and acceleration are somewhat hindered by the interannual signal caused by natural climate variability. During the recent years, several studies have shown that at interannual time scale, the global mean sea level is mostly due to ENSO-driven land water storage variations. But thermal expansion fluctuations may also contribute. Thus, to isolate the global warming signal in the global mean sea level, we need to remove the ENSO-related interannual variability. For that purpose we use the Water Gap Global Hydrological model developed by the University of Frankfurt for land water storage as well as GRACE space gravimetry data on land and empirical models based on ENSO indices. We also extract the ENSO-related signal in thermal expansion. After removing the total interannual variability signal due to both mass and steric components, we compute the evolution with time of the ‘residual’ rate of sea level rise over successive 5-year moving windows, as well as the associated acceleration. Using time series of thermal expansion and ice sheet mass balances, we also estimate the respective contributions of each component to the global mean sea level acceleration.