The present atmospheric concentration of carbon dioxide has not been exceeded during the past 420,000 years, and possibly not during the past 15 million years. The present sustained rate of increase is unprecedented, at least during the past 20,000 years (Prentice et al., 2001). This rise is expected to continue, leading to significant global temperature increases by the end of this century. It is very likely that the partial pressure of CO2 (pCO2) in the surface ocean will double over its pre-industrial value by the middle of this century. Accompanying surface ocean pH changes three times greater than those experienced during the transition from glacial to interglacial periods are predicted, which could have profound impacts on marine organisms and ecosystems.