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High-resolution Modelling of Sea-level Projections - A Necessity or a Luxury Problem?

Satellite-observed sea-level measurements indicate an ongoing increase of the global mean sea-level since the satellite era. Global mean sea-level rise threatens low-lying coastal regions and these regions will benefit strongly from sea-level projections to adapt their coastal protection infrastructure. Current sea-level projections are based on climate models in which ocean-eddy processes are parameterized. In these climate models, sea-level variability and the present-day climate state strongly deviate from available observations.  Here we will investigate the effect of ocean model resolution on sea-level variability and sea-level projections. We analyze a version of the Community Earth System Model (CESM) in which ocean-eddy processes and interactions are resolved by the model. The results of the eddying version of the model are compared to a non-eddying version of the same model. First, we will briefly analyze the sub-annual variability in both versions of the model and compare the results with available observations. Next, we force both models under an idealized forcing scenario (1% pCO2) for 100 years. In the forcing experiment, we investigate regional (Caribbean) and global mean sea-level projections, together with an analysis and comparison of CMIP6 models. The results indicate that realistic sea-level projections can only be obtained by using ocean-eddying models.