Constraining ocean dynamic sea level projections along the coast of the Netherlands

Ocean dynamic sea level (ODSL) is the local height of the sea surface above the geoid. It is computed by atmosphere-ocean coupled general circulation models from the coupled model intercomparison projects (CMIP). In many places it is one of the most important components of sea level projections for the coming century. However, because it depends on climate dynamics, there is a low agreement between climate models. Moreover, the difficulty to estimate ODSL from observations has resulted in IPCC AR5 and AR6 sea level projections using CMIP5 and CMIP6 outputs without model selection nor bias correction.

 

We use multiple lines of evidence to constrain ODSL along the coast of the Netherlands: ocean reanalyzes, sea-level budget closure using tide gauges and satellite altimetry observations, and direct integration of steric sea level change from observed temperature and salinity together with an estimation of wind influence on sea level.

 

We find that CMIP6 overestimates ODSL change along the Dutch coast and that this overestimation is not only related to the overestimation of global mean temperature increase. Based on the emergent constraint framework, we provide improved ODSL projections with reduced uncertainty and an increased level of confidence.