The chemical process of
ocean acidification is relatively straightforward, although there is substantial
regional and seasonal variability in ocean pH.1 As
the term ‘ocean acidification’ suggests, when CO2 dissolves in the oceans it
reacts with H2O to form an acid, carbonic acid.2 The
oceans are naturally alkaline and the pre-industrial pH of the oceans was
around 8.1.3 The ocean pH has now
declined by 0.1, such that the oceans are more acidic today than at any time in
the last half-million years.4 Moreover,
ocean pH may fall by up to 0.5 units by 2100 if CO2 emissions are not
This process results in
substantial changes to the carbon chemistry of the oceans. Hydrogen ions
released in the formation of carbonic acid combine with carbonate ions in the
water to form bicarbonate, removing substantial amounts of carbonate ions from
the water which are essential for the formation of a range of marine organizations.6
There has been a ten percent decline in carbonate concentrations compared to
pre-industrial levels, 17 and these are projected to decrease by 50 percent by
1 B. I. McNeil and R.J.
Matearb, “Southern Ocean acidification: A tipping point at 450-ppm atmospheric
CO2”, 105 Proceedings of the National Academy of Sciences (2008).
2 J. C. Orr et al.,
“Anthropogenic ocean acidification over the twenty-first century and its impact
on calcifying organisms”, 437 Nature (2005), 681.
3 O. Hoegh-Guldberg et al.,
“Coral reefs under rapid climate change and ocean acidification”, 318 Science
5 Royal Society, Ocean
acidification due to increasing atmospheric carbon dioxide (2005), in Rachel Baird, op cit, 4.
7 B. Rost and U. Riebsell,
“Coccolithaphores and the biological Pump: responses to environmental changes”,
in H. R. Thierstein and J. R. Young (eds.), Coccolithophores: from molecular
process to global impacts (Berlin: Springer, 2004), 99.