Ocean Sci., 16, 743–765, 2020 https://doi.org/10.5194/os-16-743-2020 © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License. The climate change signal in the Mediterranean Sea in a regionally coupled atmosphere–ocean model Ivan M. Parras-Berrocal 1 , Ruben Vazquez 1 , William Cabos 2 , Dmitry Sein 3,4 , Rafael Mañanes 1 , Juan Perez-Sanz 2 , and Alfredo Izquierdo 1 1 Instituto Universitario de Investigación Marina (INMAR), University of Cádiz, Puerto Real, Cádiz 11510, Spain 2 Department of Physics and Mathematics, University of Alcalá, Alcalá de Henares 28801, Spain 3 Alfred Wegener Institute for Polar and Marine Research, Bremerhaven 27570, Germany 4 Shirshov Institute of Oceanology, Russian Academy of Science, Moscow, Russia Correspondence: Ivan M. Parras-Berrocal (ivan.parras@uca.es) Received: 26 April 2019 – Discussion started: 3 May 2019 Revised: 4 March 2020 – Accepted: 3 May 2020 – Published: 25 June 2020 Abstract. We analyze the climate change signal in the Mediterranean Sea using the regionally coupled model REMO–OASIS–MPIOM (ROM; abbreviated from the re- gional atmosphere model, the OASIS3 coupler and the Max Planck Institute Ocean Model). The ROM oceanic compo- nent is global with regionally high horizontal resolution in the Mediterranean Sea so that the water exchanges with the adjacent North Atlantic and Black Sea are explicitly sim- ulated. Simulations forced by ERA-Interim show an accu- rate representation of the present Mediterranean climate. Our analysis of the RCP8.5 (representative concentration path- way) scenario using the Max Planck Institute Earth System Model shows that the Mediterranean waters will be warmer and saltier throughout most of the basin by the end of this century. In the upper ocean layer, temperature is projected to have a mean increase of 2.7 ◦ C, while the mean salinity will increase by 0.2 psu, presenting a decreasing trend in the western Mediterranean in contrast to the rest of the basin. The warming initially takes place at the surface and propa- gates gradually to deeper layers. Hydrographic changes have an impact on intermediate water characteristics, potentially affecting the Mediterranean thermohaline circulation in the future. 1 Introduction The Mediterranean Sea is expected to be among the world’s most prominent and vulnerable climate change “hot spots” (Giorgi, 2006; Cramer et al., 2018). As such, the region is an optimal case study site to test new approaches to bridge the gap between science and society by using a sound scientific basis of climate information which is applicable to a broad range of vulnerable sectors. The Mediterranean is a regional sea surrounded by Africa, Europe and Asia and divided into two subbasins (eastern and western) through a sill that does not exceed 400 m depth between Sicily and the African continent. The freshwater balance in the Mediterranean basin is negative since the evaporation exceeds precipitation and river runoff (Sanchez- Gomez et al., 2011). This deficit is compensated for by a net inflow of water through the Strait of Gibraltar and the Dardanelles. The region is located in a transitional area be- tween tropical and midlatitudes and presents a complex orog- raphy and coastlines, where intense air–sea and land–sea in- teractions take place. These intense air–sea interactions to- gether with the inflow of Atlantic Water drive the Mediter- ranean thermohaline circulation (MTHC) (Fig. 1), suggest- ing that atmosphere–ocean regionally coupled models (AOR- CMs) could be conducive to the study of atmospheric and oceanic processes in the Mediterranean Sea. Different AORCMs with typical horizontal resolutions of 25–50 km in the atmosphere and 10–20 km in the ocean have been developed to study the climate of the Mediterranean Published by Copernicus Publications on behalf of the European Geosciences Union.