One of the important points that emerges from the material Pekka has cited above (and it’s also in my article) is that for the most vulnerable marine organisms, the calcifiers, pH is less important than carbonate saturation. They are only loosely correlated, and so a hazardous decline in carbonate saturation can occur with only a small pH change. Conversely, if atmospheric CO2 concentrations rise very slowly (e.g., over many thousands of years), carbonate concentrations can be maintained fairly well even in the face of a declining pH. For this reason, the current rate of ocean acidification is more likely to reduce carbonate saturation than even greater changes in some past eras that occurred very slowly.
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