Sea-level change is one of the most concerning climate change and global warming consequences, especially impacting coastal societies and environments. The spatial and temporal variability of sea level is neither linear nor globally uniform, especially in semi-enclosed basins such as the Mediterranean Sea, which is considered a hot spot regarding expected impacts related to climate change. This study investigates sea-level trends and their variability over the Mediterranean Sea from 1993 to 2019. We use gridded sea-level anomaly products from satellite altimetry for the total observed sea level, whereas ocean temperature and salinity profiles from reanalysis were used to compute the thermosteric and halosteric effects, respectively, and the steric component of the sea level. We perform a statistical change point detection to assess the spatial and temporal significance of each trend change. The linear trend provides a clear indication of the non-steric effects as the dominant drivers over the entire period at the Mediterranean Sea scale, except for the Levantine and Aegean sub-basins, where the steric component explains the majority of the sea-level trend. The main changes in sea-level trends are detected around 1997, 2006, 2010, and 2016, associated with Northern Ionian Gyre reversal episodes, which changed the thermohaline properties and water mass redistribution over the sub-basins.

Sea-level science has seen many recent developments in observations and modelling of the different contributions and the total mean sea-level change. In this overview, we discuss (1) the evolution in IPCC projections, (2) how the projections compare to observations and (3) the outlook for further improving projections. We start by discussing how the model projections of 21 st century sea-level change have changed from the IPCC AR5 report (2013) to SROCC (2019) and AR6 (2021), highlighting similarities and differences in the methodologies and comparing the global mean and regional projections. This shows that there is good agreement in the median values, but also highlights some

Sea level on the northwestern European shelf (NWES) varies substantially from year to year. Removing explained parts of interannual sea level variability from observations helps to improve estimates of long-term sea level trends. To this end, the contributions of different drivers to interannual sea level variability need to be understood and quantified. We quantified these contributions for the entire NWES by performing sensitivity experiments with a high-resolution configuration of the Regional Ocean Modeling System (ROMS). The lateral and atmospheric boundary conditions were derived from reanalyses. We compared our model results with satellite altimetry data and used our sensitivity experiments to show that nonlinear feedbacks cause only minor interannual sea level variability on the shelf. This indicates that our experiments can be used to separate the effects of different drivers. We find that wind dominates the variability of annual mean sea level in the southern and eastern North Sea (up to 4.7-cm standard deviation), whereas the inverse barometer effect dominates elsewhere on the NWES (up to 1.7-cm standard deviation). In contrast, forcing at the lateral ocean boundaries results in small and coherent variability on the shelf (0.5-cm standard deviation). Variability driven by buoyancy fluxes ranges from 0.5-to 1.3-cm standard deviation. The results of our sensitivity experiments explain the (anti)correlation between interannual sea level variability at different locations on the NWES and can be used to estimate sea level rise from observations in this region with higher accuracy. Plain Language Summary Sea level on the continental shelf northwest of Europe is rising in the long term but is also varying strongly from year to year. This makes it difficult to determine the rate of sea level rise from observations. To improve long-term trends computed from sea level observations, the causes of short-term sea level variability need to be understood. Therefore, we test the influences of different components of the atmosphere and ocean on year-to-year sea level variability, using a numerical ocean model for northwestern Europe. We find that the varying strength and direction of winds causes large variability of sea level in the southern and eastern North Sea. In other places on the continental shelf, sea level variability is mainly influenced by the variability of atmospheric pressure. We also find that the ocean outside our model domain drives small and uniform sea level variability on the continental shelf and that there is a moderate influence of solar radiation, precipitation, and evaporation. Our results help to understand how sea level varies at different locations in northwestern Europe and to obtain better estimates of the rate of long-term sea level rise.