This work assesses the effect of long-term changes in the wave climate on the optimal sizing and performances of oscillating water column wave energy converters along the coastline of the Mediterranean basin. Trends are evaluated based on the projections of future wave climate to 2100 delivered by the Climate Data Store of the Copernicus Climate Change Service under representative atmospheric emission scenarios. The capture width of the device under different wave conditions is computed using an empirical model capable of predicting the device performance with acceptable accuracy and limited computational time. The optimal geometry of the device varies significantly across different geographical locations, with maximum values of chamber size along the north African coasts and western Sardinia and Corse, and minimum values in the Adriatic and Aegean Seas. Long-term changes in the wave energy resource result in moderate modifications of the optimal geometry, with relative variations between present and future scenarios up to 10% of the size. The annual energy production of the device in the projected scenario would significantly increase in most geographical locations, potentially contributing to reducing the levelized cost of energy and favouring the economic competitiveness of this technology.