The ocean plays a major role in the uptake of carbon dioxide emitted from fossil-fuel burning, helping to moderate future climate change. However, the addition of the gas to the ocean alters marine chemistry by increasing acidity, posing a threat to shelled organisms and their predators.

Long Cao of the University of Illinois and colleagues sought to quantify the effect of climate change on ocean acidity and on the calcium-carbonate minerals.

Using an Earth system model, the researchers found ocean pH declines by 0.31 units by the end of this century are likely if atmospheric carbon dioxide concentrations continue on a trajectory that ultimately stabilizes at 1,000 parts per million.

That increase in acidity, the scientists determined, occurs regardless of how much of a global warming-related temperature rise takes place as carbon dioxide builds up to that concentration.

The research by Cao and Atul Jain of the University of Illinois, along with Ken Caldeira of the Carnegie Institution in Stanford, Calif., is reported in the journal Geophysical Research Letters.