Timescales of Anthropogenic and Total Carbon Dioxide (CO2) in the Atmosphere

The author has enhanced the original one dimensional semi-empirical atmosphere-ocean-biosphere model 1DAOBM based on the four-box presentation. The improved 1DAOBM-2 contains two major parameters, which have been tuned to adjust the total CO2 net flux rate and the anthropogenic net flux rate from the surface ocean into the deep ocean based on the observed values. The surface ocean part is based on the known dissolution chemical equations according to Henry’s law depending on the atmospheric CO2 concentration and the surface ocean temperature. Simulations have been used to calculate the dynamic responses to the step changes from the actual fossil fuel rate to zero in 1964. The results show that the anthropogenic CO2 decay rate follows very accurately the observed decay rate of radiocarbon 14C having the residence time of 16 years. This is the expected result according to nature of anthropogenic CO2 in the system of the atmosphere, the ocean and the biosphere. The decay rate of the total CO2 in this system is much longer having the residence time of 55 years matching the adjustment time of 220 years. The simulations of the atmospheric net CO2 rate by 1DAOBM-2 from 1960 to 2013 confirms the earlier results that the coefficient of determination r2 = 0.75 (r2 = 0.81 eliminating the Pinatubo eruption effects). The simulations also show that the present anthropogenic CO2 fraction in the atmosphere is 8.0%, and it explains the observed δ13C value of -8.4‰ extremely well. The problem of the sink between the ocean and the biosphere could not be solved totally. A mass balance study shows that before 1956, the ocean and/or the biosphere acted as a source for the total CO2 increase in the atmosphere and thereafter as a sink. This study suggests that the division ratio between the ocean and the biosphere is 60% / 40% for the period from 1750 to 2013. The high correlation between the ocean uptake and the net increase of the total atmospheric CO2 strongly indicates that the ocean has been the sink after 1956.