After 1750 and the onset of the industrial revolution, the anthropogenic fossil component and the non-fossil component in the total atmospheric CO 2 concentration, C(t), began to increase. Despite the lack of knowledge of these two components, claims that all or most of the increase in C(t) since 1800 has been due to the anthropogenic fossil component have continued since they began in 1960 with "Keeling Curve: Increase in CO 2 from burning fossil fuel." Data and plots of annual anthropogenic fossil CO 2 emissions and concentrations, C(t), published by the Energy Information Administration, are expanded in this paper. Additions include annual mean values in 1750 through 2018 of the 14 C specific activity, concentrations of the two components, and their changes from values in 1750. The specific activity of 14 C in the atmosphere gets reduced by a dilution effect when fossil CO 2 , which is devoid of 14 C, enters the atmosphere. We have used the results of this effect to quantify the two components. All results covering the period from 1750 through 2018 are listed in a table and plotted in figures.These results negate claims that the increase in C(t) since 1800 has been dominated by the increase of the anthropogenic fossil component. We determined that in 2018, atmospheric anthropogenic fossil CO 2 represented 23% of the total emissions since 1750 with the remaining 77% in the exchange reservoirs. Our results show that the percentage of the total CO 2 due to the use of fossil fuels from 1750 to 2018 increased from 0% in 1750 to 12% in 2018, much too low to be the cause of global warming.

We thank Schwartz et al. for their significant comments. While we do recognize the reality of exchange of CO 2 among the atmosphere and reservoirs, it was not our intent to attempt to develop a model that considered these, nor do we believe this was necessary for our purposes. Our intent was to develop a useful model that incorporated the CO 2 molar concentration in 1750, C(0), its associated 14 C specific activity, S(0), the concentration value at t years past 1750, C(t), and its associated 14 C specific activity, S(t), for the purpose of quantifying the annual mean anthropogenic fossil-derived CO 2 in the atmosphere, C F (t). Pertinent exchanges between the atmosphere and CO 2 reservoirs produce results that are observed in the atmosphere. There have been claims that correlations between anthropogenic fossil-derived CO 2 and measurable statistics, including d 13 C and D14C, show that C F (t) constitutes most or all of the CO 2 that has been added to the atmosphere. We were not able to find any determination of the values of the anthropogenic fossil component, and this deficiency is what provided the impetus for our work.We began with a baseline assumption that the long-term preindustrial molar concentration was fixed and constant, changing significantly only as additional inputs to the atmosphere from possible natural and manmade sources later took place. Exchange among the reservoirs was inconsequential for our work, except for the possible residual effects of bomb

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