There is considerable current concern that the ongoing rise in the air's CO2 content is causing a significant drop in the pH of the world's oceans in response to their absorption of a large fraction of each year's anthropogenic CO2 emissions. It has been estimated, for example, that the globe's seawater has been acidified (actually made less basic) by about 0.1 pH unit relative to what it was in pre-industrial times; and model calculations imply an additional 0.7-unit drop by the year 2300 (Caldeira and Wickett, 2003), which decline is hypothesized to cause great harm to calcifying marine life such as corals. But just how valid are these claims?
Whenever the results of theoretical calculations are proposed as the basis for a crisis of some kind or other, it is always good to compare their predictions against what is known about the phenomenon in the real world. In the case of oceanic pH, for example, Liu et al. (2009) write in an important new paper that "the history of ocean pH variation during the current interglacial (Holocene) remains largely unknown," and that it "would provide critical insights on the possible impact of acidification on marine ecosystems." Hence, they set about to provide just such a context.