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).