Dynamic response of the Mediterranean Sea surface circulation at various global warming levels: A multi-model approach

Changes in the Mediterranean circulation patterns due to global warming may have strong socio-economic and environmental impacts. Here, we analyze the future evolution of the Mediterranean surface circulation under different levels of global warming (from 1°C to 4ºC) with respect to the preindustrial period. To this end, we use a set of 18 multi-decadal simulations (7 historical and 11 scenario projections) from a set of seven coupled regional climate system models of the Med-CORDEX initiative. For the first time, global warming levels are used to assess impacts of climate change on the Mediterranean Sea, allowing us to combine CMIP5 (RCP2.6, RCP4.5 and RCP8.5) and CMIP6 (SSP5-8.5) scenarios in a multi-model and ensemble approach. Most of the models show an accurate representation of the surface circulation in the historical period, although biases in the mean SSH and wind stress are observed. In terms of variability, we show that a minimum horizontal resolution of ~11 km is necessary to reproduce the dominant eddy-driven dynamics. The circulation is mainly driven by geostrophic currents, while Ekman currents are about one order of magnitude smaller than the mass-driven circulation. We find a linear relationship between the mean absolute dynamical response and the global warming level. The mean surface circulation shows the strongest response in the Balearic Sea, the Gulf of Lions, the southern Adriatic and along the Mid-Mediterranean Jet. Furthermore, our results suggest that future changes in the Mediterranean circulation variability will be primarily associated with a general increase of high-frequency processes (eddies), while the seasonal cycle and interannual variability will play a secondary role.