Box 7.3, Figure 1. (a) Atmospheric CO2 emissions, historical atmospheric CO2 levels and predicted CO2 concentrations from the given emission time series, together with changes in ocean pH based on horizontally averaged chemistry. The emission time series is based on the mid-range IS92a emission scenario (solid line) prior to 2100 and then assumes that emissions continue until fossil fuel reserves decline. (b) Estimated maximum change in surface ocean pH as a function of final atmospheric CO2 pressure, and the transition time over which this CO2 pressure is linearly approached from 280 ppm. A: Glacial-interglacial CO2 changes; B: slow changes over the past 300 Myr; C: historical changes in ocean surface waters; D: unabated fossil fuel burning over the next few centuries. Source: Caldeira and Wickett (2003). Reprinted with permission from Macmillan Publishers Ltd: Nature, Caldeira and Wickett (2003), copyright (2003).