Ocean acidification caused by the uptake of carbon dioxide (CO2) by the ocean is an important global change problem (Kleypas et al. 1999; Caldeira and Wickett 2003; Doney et al. 2009). Ongoing ocean acidification is closely linked to global warming, as acidification and warming are primarily caused by continued anthropogenic emissions of CO2 from fossil fuel burning (Marland et al. 2008 ), land use, and land-use change (Strassmann et al. 2007). Future ocean acidification will be determined by past and future emissions of CO2 and their redistribution within the earth system and the ocean. Calculation of the potential range of ocean acidification requires consideration of both a plausible range of emissions scenarios and uncertainties in earth system responses, preferably by using results from multiple scenarios and models. The goal of this chapter is to map out the spatiotemporal evolution of ocean acidification for different metrics and for a wide range of multigas climate change emissions scenarios from the integrated assessment models (Nakićenović 2000; Van Vuuren et al. 2008b). By including emissions reduction scenarios that are among the most stringent in the current literature, this chapter explores the potential benefits of climate mitigation actions in terms of how much ocean acidification can be avoided and how much is likely to remain as a result of inertia within the energy and climate systems. The longterm impacts of carbon emissions are addressed using so-called zero-emissions commitment scenarios and pathways leading to stabilization of atmospheric CO 2. Discussion will primarily rely on results from the cost-efficient Bern2.5CC model (Plattner et al. 2008) and the comprehensive carbon cycle– climate model of the National Centre for Atmospheric Research (NCAR), CSM1.4-carbon (Steinacher et al. 2009; Frölicher and Joos 2010). The magnitude of the human perturbation of the climate system is well documented by observations (Solomon e t al. 2007). Carbon emissions from human activities force the atmospheric composition, climate, and the geochemical state of the ocean towards conditions that are unique for at least the last million years (see Chapter 2).