Analysis of the Simulation Results of Three Carbon Dioxide (CO2) Cycle Models

The CO2 (carbon dioxide) circulation models referred by the IPCC (Intergovernmental Panel on Climate Change) show that the increase of atmospheric CO2 by 240 GtC (Gigatonnes of carbon) from 1750 to 2011 is totally anthropogenic in nature, which corresponds to the permille value of about -12.5‰, but the observed value is only -8.3‰. The author’s improved 1DAOBM-3 CO2 circulation model shows that the anthropogenic CO2 amount in 2011 is only 73 GtC, satisfying the observed atmospheric permille values from 1750 to 2017. The CO2 circulation between the ocean and the atmosphere has increased the amount of atmospheric CO2 by natural CO2 197 GtC from the ocean, and this explains why the net uptake rate is only 1.9 GtC yr-1. Together with the anthropogenic amount of 73 GtC, the total increase is 270 GtC by 2017, corresponding to the observed atmospheric CO2 concentration. The simulations for 1000 GtC emissions by 2100 have been carried out by three models, including 1DAOBM-3, Bern2.5CC, and the mean model of 15 circulation models (called Joos 2013). The residence time of 1DAOBM-3 is 16 years for anthropogenic CO2 impulse, the same as for the radiocarbon decay time. The decay time of 1DAOBM-3 for the impulse function is about 600 years meaning the residence time of about 150 years only. These values are much shorter than the residence times of two other models, which show that 25±9‰ of any anthropogenic CO2 is still found in the atmosphere after 1,000 years. The reasons have been analyzed. The advantage of 1DAOBM-3 over the other models is that its results are in line with the oceanic and atmospheric observations from 1750 to 2017 but the future simulations include uncertainties due to ocean and biosphere uptake rate models.