Oceans in Crisis - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 186

carbonate and bicarbonate ions already dissolved in the water,
shifting the balance away from carbonate towards bicarbonate. It is
the carbonate in the ocean waters that is the feedstock for those
organisms—molluscs, corals, foraminifera, sea butterflies—that build
skeletons of calcium carbonate. The less dissolved carbonate there is,
the more difficult it is for these organisms to build their skeletons. But
how big is this problem?
The answer is that it is absolutely enormous. The statement of the
scale of the problem that made everybody sit up was published in
2003, in a 'brief communication' to the journal Science by Ken Caldeira
and Michel Wickett, scientists at the Lawrence Livermore Laboratory
in California. 109 They devised a computer model that tracked the
release of carbon dioxide from the present into the future under a
'business as usual' scenario—that is, assuming that we will burn our
way through most of our fossil fuel resources over the next few cen-
turies. They modelled the carbon emissions from the air into the
oceans, based on the way that carbon dioxide partitions between
atmosphere and ocean (which is moderately straightforward) and the
way it then travels through the oceans. This second factor is a little
trickier, involving knowledge of how ocean waters circulate to carry
the carbon dioxide, but in essence the carbon dioxide will build up
first in shallow water and then be carried into deep water. Let this
experiment run, they said, and the pH of the water will drop by as
much as 0.77 of a pH unit. To put that into context, this would be a
greater change than any seen in the last 300 million years at least—
with the possible exception, they added, of 'rare, catastrophic events
in Earth's history'.
Already, the pH of seawater is one-tenth of a percentage point lower
than it was before humans started burning fossils fuels in earnest at
the beginning of the Industrial Revolution. That may not sound very
much: it is a drop from a pH of 8.4 to 8.3, and the water is still well