CO2 emissions from humans cannot change net global average CO2 concentration nor its rate of change. CO2 concentration and its partial pressure in air and ocean surface are controlled by Henry’s Law, Le Chatelier’s principle and the Law of Mass Action. Henry’s partition ratio of CO2 gas between ocean surface and in the air above that surface is an intensive property of matter which is independent of the source of the CO2 and the amount of CO2, like CO2’s molecular weight. Henry’s partition ratio is not a constant. Henry’s coefficient varies with temperature. The solubility of CO2 gas (and all other atmospheric gases) in ocean and all water is a function of temperature. The residence time of CO2 in the atmosphere is an irrelevant statistic, having zero effect on net global average atmospheric CO2 concentration.
CO2 partial pressure in air and net global average concentration of CO2 in air and CO2 flux in both directions are dominantly functions of the surface area of ocean above and below 25.6 C. In local conditions, salinity, alkalinity and conditions above and below the surface also affect the ratio; for example winds, currents or storms above warm (>25.6C) surface deplete the surface water of aqueous CO2 gas, or biological activity in the water such as phytoplankton can cause local under-saturation (with respect to the Henry’s partition ratio for the local SST) of aqueous CO2 gas in the surface waters. Simultaneously, conditions in other locations, such as rotting biological material in an estuary, create over-saturation of aqueous CO2 gas in ocean surface with respect to the Henry’s Law partition ratio for the SST there, resulting in CO2 emission flux at the surface. Globally averaged, alkalinity, salinity, winds and currents cancel out. This leaves CO2 flux in both directions, emission from ocean surface and absorption into ocean surface, as a function the area of ocean surface above or below SST of 25.6 C as the determining value. Since around 1918, area of ocean surface SST above 25.6 C has been slowly increasing. This very fortunate circumstance for life on earth is the cause of the slowly increasing trend in net global average CO2 concentration such as measured at Mauna Loa. Perturbations to this trend such as human emissions, volcanic emissions, seasonal differences between ice cover and photosynthesis in northern and southern hemisphere, etc. are rapidly re-balanced and the trend returns to the average Henry’s Law equilibrium condition based on SST. There is 30 to 50 times more aqueous, non-ionized CO2 gas in ocean surface than in the air above the surface, depending primarily on surface temperature.
Over-saturation of aqueous CO2 gas in ocean surface in excess of the Henry’s partition ratio for a given SST results in increasing the hydration reaction of the CO2 into either carbonic acid or bicarbonate ions, which in turn removes the CO2 gas from the Henry’s Law phase state equilibrium reaction. Removal of aqueous CO2 gas from the Henry’s equation changes the ratio, which requires additional CO2 gas flux into ocean surface. When the aqueous CO2 over-saturation condition continues, then carbonates precipitate as solid in ocean or are incorporated into organisms as shell.
Net global average CO2 concentration today is the same as it would be if humans never existed. Higher atmospheric CO2 concentration would benefit all plants and life, but CO2 concentration is controlled by the various natural processes such as humidity, clouds, solar and planetary cycles, affecting insolation of ocean surface, as well as oceanic and atmospheric currents.