Oceans Become More Acidic as Atmospheric CO₂ Increases

Increases in atmospheric CO₂ lead to more absorption of CO₂ by the global oceans, which creates carbonic acid. Caldeira and Wickett (2003) calculated future pH levels of the global oceans that would result from projected future atmospheric CO₂ concentrations and concluded that pH decreases (increased acidity) of 0.77 would follow from atmospheric CO₂ concentrations of 1900 ppm. From the paleoclimate record of atmospheric CO₂, Caldiera and Wickett (2003) concluded that anthropogenic CO₂ will reduce oceanic pH to levels well below any that have occurred in the past 300 million years.

Reference

Caldeira, K., and M. E. Wickett, 2003: Anthropogenic carbon and ocean pH. Nature, 425 365.