Volume 12, Number 22: 3 June 2009 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