Oceans’ surface pH-value as an example of a reversible natural response to an anthropogenic perturbation

Abstract

The anthropogenic emission of carbon dioxide (CO2) has influenced the pH values of the oceans’ surface. Observations show that for several decades, the surface pH value is declining with a simultaneously rising CO2 concentration. It is an important question to understand to what extent this process is reversible. Hence, in this study, the atmospheric carbon dioxide (CO2) partial pressure from 1850 to 2020 is derived from the chemical composition of the seawater, the mass action law, Henry’s law, and published literature data on the relevant equilibrium constants. A single exponential relaxation or equilibration time τ = 52 ± 10 years (or half-time of 36 ± 7 years) accounts for the anthropogenic perturbation due to emissions. The model is based on reversible mechanisms and simultaneously represents the atmospheric CO2 volume fraction with a standard deviation of 7 ppm and the oceans’ surface pH values. Projections until 2100 for various emissions include the possibility of recovery within decades.