Caldeira Lab Research:Ocean acidification and ocean carbon cycle

Comment on "Modern-age buildup of CO2 and its effects on seawater acidity and salinity"

Ken Caldeira, David Archer, James P. Barry, Richard G.J. Bellerby, Peter G. Brewer, Long Cao, Andrew G. Dickson, Scott C. Doney, Harry Elderfield, Victoria J. Fabry, Richard A. Feely, Jean-Pierre Gattuso, Peter M. Haugan, Ove Hoegh-Guldberg, Atul K. Jain, Joan A. Kleypas, Chris Langdon, James C. Orr, Andy Ridgwell, Christopher L. Sabine, Brad A. Seibel, Yoshihisa Shirayama, Carol Turley, Andrew J. Watson & Richard E. Zeebe

Rising atmospheric CO2 concentration will have a direct effect on the acidity of the ocean in the future. In 2006, Hugo A. Loaiciga predicted that rising CO2 levels would decrease ocean pH by .028 and have little to no effect on marine life. Here, the flaws in his argument are shown and a much more serious effect on marine life is predicted.

Caldeira, K; Archer, D; Barry, JP; Bellerby, RGJ; Brewer, PG; Cao, L; Dickson, AG; Doney, SC; Elderfield, H; Fabry, VJ; Feely, RA; Gattuso, JP; Haugan, PM; Hoegh-Guldberg, O; Jain, AK; Kleypas, JA; Langdon, C; Orr, JC; Ridgwell, A; Sabine, CL; Seibel, BA; Shirayama, Y; Turley, C; Watson, AJ; Zeebe, RE, 2007. Comment on "Modern-age buildup of CO2 and its effects on seawater acidity and salinity" by Hugo A. Loaiciga, Geophysical Research Letters 34 (18): Art. No. L18608, 2007.

Predicted ocean pH changes for various temperatures: pH changes predicted by generally accepted and widely-used software show an increase in the acidity of the ocean that is drastically larger than that predicted by Loáiciga.


A doubling of present atmospheric CO2 concentrations (to 760 ppm) may occur by the end of this century in the absence of efforts to diminish CO2 emissions from fossil-fuel combustion [Intergovernmental Panel on Climate Change (IPCC), 2001]. Based on inappropriate assumptions and erroneous thermodynamic calculations, Loáiciga [2006] mistakenly reports that atmospheric CO2 concentrations of 760 ppm will lower the pH of the surface ocean by 0.28 relative to the natural ‘‘mid 18th century’’ conditions. He implies that a drop of this magnitude will have minimal biological impact, neglecting numerous recent experiments and observations showing that this decrease in pH would substantially affect the physiology and health of marine organisms. Here, we focus on two fundamental flaws in the published analysis that invalidate his conclusions: (1) he assumes instantaneous chemical equilibration of the ocean with carbonate minerals although this process is known to take five to ten thousand years and (2) contrary to what is implied by Loáiciga, many marine organisms are sensitive to a pH decrease of 0.2 units.