This increase in the ocean's hydrogen ion concentration corresponds to a reduction in pH, or an increase in acidity. (metlink.org)
If the surface ocean pCO2 concentrations continue to increase in proportion with the atmospheric CO2 increase, a doubling of atmospheric CO2 from preindustrial levels will result in a 30 % decrease in carbonate ion concentration and a 60 % increase in hydrogen ion concentration. (realclimate.org)
pH is an indicator of acidity by measuring the hydrogen ion concentration. (lbah.com)