Caldeira Lab Research:Ocean acidification and ocean carbon cycle

Effects of carbon dioxide and climate change on ocean acidification and carbonate mineral saturation

Long Cao, Ken Caldeira, & Atul K. Jain

An investigation of whether or not the degree of temperature changed cause by excess CO2 emission is related to changes in acidity and aragonite saturation in the ocean. This study was done by comparing three different models working with the same amount of CO2 emissions: one under a constant climate, one with a change of 2.5 degrees, and another with a change of 4.5 degrees. The results indicate a small correlation.

Cao L., K. Caldeira and A.K. Jain, Effects of carbon dioxide and climate change on ocean acidification and carbonate mineral saturation, Geophysical Research Letters 34 (5): Art. No. L05607, 2007.

Different climate sensitivities and their effect on pH and mineral saturation: When climate sensitivity was raised, carbon concentration and pH reduction were both slightly amplified. The change in aragonite saturation was slightly reduced. These results suggest a slight correlation between increasing temperature and the other effects of climate change.

Specific results of changed climate sensitivity: In each run of the model, the decrease in pH was slightly larger. The decrease in aragonite saturation, however, was smaller.


We use an earth system model of intermediate complexity to show how consideration of climate change affects predicted changes in ocean pH and calcium carbonate saturation state. Our results indicate that consideration of climate change produces second-order modifications to ocean chemistry predictions made with constant climate; these modifications occur primarily as a result of changes in sea surface temperature, and climate induced changes in dissolved inorganic carbon concentrations. Under a CO2 emission scenario derived from the WRE1000 CO2 stabilization concentration pathway and a constant climate, we predict a 0.47 unit reduction in surface ocean pH relative to a pre-industrial value of 8.17, and a reduction in the degree of saturation with respect to aragonite from a pre-industrial value of 3.34 to 1.39 by year 2500. With the same CO2 emissions but the consideration of climate change under a climate sensitivity of 2.5°C the reduction in projected global mean surface pH is about 0.48 and the saturation state of aragonite decreases to 1.50. With a climate sensitivity of 4.5°C, these values are 0.51 and 1.62, respectively. Our study therefore suggests that future changes in ocean acidification caused by emissions of CO2 to the atmosphere are largely independent of the amounts of climate change.