The Baltic Sea is a semi-enclosed sea with a positive freshwater balance due to runoff from a catchment area which is four times the sea surface area. As the mean water depth is only 54 m, temporal variations in stratification and currents are large compared to other seas, making the Baltic Sea vulnerable to global change. About 85 million people live in the catchment basin, and the intensive agriculture, especially in the southern part, is mainly responsible for the release of nutrients into the watershed and subsequent transport towards the sea. As a consequence, the Baltic Sea today suffers from severe environmental problems due to eutrophication,
Multi-model ensemble simulations for the marine biogeochemistry and food web of the Baltic Sea were performed for the period 1850–2098, and projected changes in the future climate were compared with the past climate environment. For the past period 1850–2006, atmospheric, hydrological and nutrient forcings were reconstructed, based on historical measurements. For the future period 1961–2098, scenario simulations were driven by regionalized global general circulation model data and forced by various future greenhouse gas emission and air- and riverborne nutrient load scenarios (ranging from a pessimistic ‘business-as-usual’ to the most optimistic case). To estimate uncertainties, different models were applied
Assuming the IPCC greenhouse gas emission scenarios, the multi-modal ensemble simulation found that water temperatures at the end of this century may be higher and salinities and oxygen concentrations may be lower than ever measured since 1850. There is also a tendency of increased eutrophication in the future, depending on the nutrient load scenario. Although cod biomass is mainly controlled by fishing , climate change together with eutrophication may result in a biomass decline during the latter part of this century, even if less fishing occurs.
Despite shortcomings of the models, this study suggests that climate change will have considerable impacts on the future Baltic Sea, which will change significantly compared to the past 150 years. More information is needed to raise public awareness of the possible impacts of climate change on marine ecosystems.