To relate the partial pressure of carbon dioxide in the atmosphere to the pH of the ocean, the computer program CO2SYS was used. This program requires various assumptions, which are listed in Table 1.

Table 1. Input Options for Calculation of Atmospheric Carbon Dioxide Concentration and Ocean pH

Note: The input values for alkalinity, salinity, temperature, pressure, silicate concentration, phosphate concentration and pH scale were based on the values used by Bozlee and Janebo, 2008.⁶

The partial pressure of carbon dioxide and the pH of the ocean were calculated using a range of input values for the total inorganic carbon in the surface ocean. The range of values was used because human activity is primarily changing this factor. As human activity produces carbon dioxide emissions, greater amounts of carbon dioxide dissolve into the ocean, causing the total inorganic carbon concentration in the ocean to increase.

Since a range of input values was used for the total inorganic carbon, a range of ocean pHs and partial pressures of carbon dioxide were obtained from CO2SYS. A linear approximation was performed to link the calculated range of ocean pHs to the natural logarithm of the calculated partial pressures of carbon dioxide. In the applet, this linear function was used to calculate the ocean's pH from the natural logarithm of atmospheric carbon dioxide concentration as determined by the slider bar. The function is also plotted in the graph tool, under the tab "CO2 vs pH".