Ocean Acidification

The pH of the oceans will remain alkaline (greater than 7) even after atmospheric CO2 is tripled.

MISNOMER: “Acidification” means turning a solution acid; i.e., changing pH to 7 or lower.

DEFINITION: pH is the negative logarithm (base 10) of hydrogen ion concentration, in (moles H+) / (Kg solution)


  • The oceans are presently alkaline (pH greater than 7) at pH 8.2
  • The oceans absorb nearly 50% of man-made carbon emissions
  • Absorption by the oceans of CO2 will lower, but not acidify, oceanic pH.
  • Not only doubling, but quadrupling existing CO2 (400 ppm) will not acidify the oceans, but will lower pH to above 7 (will remain alkaline).

pH various Temps

The method for calculating pH of seawater used here is from MacKenzie and Lerman, “Carbon in the Geobiosphere”, Springer 2006, p. 125.

Below is data from Hawaii (pCO2 is partial pressure of CO2 in millionths of atmospheres):


The blue line following the red shows Henry’s Law is in effect.


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