Equilibria of Atmosperic CO2, Dissolved CO2 Carbonate, Carbonate Ions, Boric Acids and Boric Ions.

pH
logarithmic partial pressure of CO2 in micro- atmospheres

Solid vertical line shows concentration at pre-industrial levels (@ 1850).
Dashed vertical line shows present values CO3-2 + B(OH)4- are depleted as aqueous CO2 increased due to increases in atmospheric CO2.