Increasing atmospheric CO₂ concentrations lowers oceanic pH and carbonate ion concentrations, thereby decreasing the level of saturation of calcium carbonate [Feely et al., 2004]. This acidification will eventually lead to undersaturation and dissolution of calcium carbonate in parts of the surface ocean. Besides affecting the global carbon cycle, these changes threaten marine organisms that form their exoskeletons out of CaCO₃, which are essential components of the marine food web [Orr et al., 2005]. We investigate magnitude and pattern of ocean acidification due to increasing atmospheric CO₂ concentrations and global warming, both for the recent past and the near future, using the reduced complexity, Bern 2.5-D physical-biogeochemical climate model and a series of CO₂ emission scenarios and CO₂ stabilization profiles provided by the Intergovernmental Panel on Climate Change (IPCC). The focus of the study is on the impact of global warming and induced ocean circulation changes on the projected oceanic pH and carbonate ion reductions.