Earth’s climate system is ever-evolving. When heat-trapping greenhouse gases block solar radiation from being reflected back into space, its effect is felt on Earth as temperatures warm and temperatures soar.
As Europe’s largest semi-enclosed sea, the Mediterranean is particularly at risk from climate change. Numerous marine species are already experiencing range shifts that will have serious repercussions for their populations and ecosystems.
Climate Change
The Mediterranean Sea is extremely vulnerable to climate change. Although past changes, such as during an ice age and Holocene period, have seen dramatic shifts, current changes are much faster and more dramatic than historical ones.
Population growth in Mediterranean countries is one of the key indirect drivers of climate and environmental changes (Map 2). Urbanization, industrial activities and overexploitation of ecosystem services result in elevated pollution levels; diverting water for agricultural uses compromises the hydrological cycle.
High levels of atmospheric CO2 lead to acidification of surface waters, with adverse impacts on benthic and pelagic organisms with calcareous body parts like corals and mussels. Furthermore, Mediterranean fisheries are extremely vulnerable to climate-induced shifts of commercial species and stocks; vulnerability analyses must therefore be completed at both country and species levels for all stocks or species of commercial importance in the Mediterranean.
Water Resources
As one of the world’s water crisis hot-spots, Mediterranean areas are highly vulnerable to climate change. Over recent years, mean annual temperatures have been increasing at an exceedingly rapid rate, coupled with decreasing precipitation that will result in more frequent drought periods and eventually lead to less available freshwater supply.
Studies suggest that, under a business-as-usual scenario, freshwater availability should decline by at least 25% in most arid and semiarid catchments of the Mediterranean basin by 2050 (Fig. 3). Withdrawals for irrigation purposes should remain at current levels in most southern rim catchments while increasing by 10-40% on its northern rim (such as Greece or Ebro and Buyuk-Menderes catchments).
Increased water temperatures also facilitate the establishment of numerous non-native, invasive species which will have profound ecological and socioeconomic consequences in the area, particularly for native Mediterranean fish and shellfish (Cramer et al., 2019).
Sea Level Rise
As a semi-enclosed sea, the Mediterranean Sea is very susceptible to climate change. It contains extreme oligotrophic waters that are becoming depleted of their vital nutrients due to the inflow of warm surface Atlantic water through Gibraltar Strait.
Rising temperatures are leading to increased thermal expansion of ocean water, causing sea level to rise. Furthermore, melting land ice (terrestrial ice melt or GIA) also contributes to this phenomenon and thus raises sea levels further.
Regional climate models have generated future scenarios for the Mediterranean Sea that show potential sea-level rises of up to 9.8/25.6 cm between 2040-2050 due to both steric and GIA effects.
Coastal communities and rural populations across the Mediterranean region are facing serious difficulties when it comes to water supply, with increased evaporation and declining rainfall placing immense strain on natural and managed water resources. Many resources have already been overextracted; furthermore, reduced river flows hinder replenishing groundwater aquifers.
Adaptation
The Mediterranean Sea is being plagued by numerous climate change impacts that are having detrimental effects on marine biodiversity. Seawater temperatures are rising faster than global averages and leading to marine heat stress that has resulted in mass mortality events among benthic organisms with calcareous parts such as corals, pteropods, and sponges. Furthermore, coastal areas are subject to intense development and tourism that has an adverse effect on their ecosystems.
As climate change impacts have grown more extreme over the years, species have various adaptive mechanisms available to them for adapting to its effects, such as acclimatization over multiple generations, genetic adaptation and short-range shift. Unfortunately, however, such processes are often difficult to apply within Mediterranean environments where steep ecological gradients exist. It is essential to recognize, address and adapt to these trends quickly in order to avoid further damage and potential losses (Hidalgo et al. 2022a). For effective implementation this requires flexible management policies as well as gradual transition from risk identification through risk identification into implementation of adaptation measures (Hidalgo et al. 2022a).