“There is no constant exponential rising CO2-concentration since preindustrial times but a variing CO2-content of air following the climate. E.G. around 1940 there was a maximum of CO2 of at least 420 ppm, before 1875 there was also a maximum.” (Source)
agere_contra also posted the same thing.
During the period in which the Earth’s second major atmosphere was composed of more than 96 percent or 98 percent CO2 and before the advent of aerobic lifeforms, the atmospheric concentrations of CO2 could be described as somewhere in the order 886,000 ppm or 998,000 ppm versus 300 ppm to 400 ppm or a little more in recent ages. What is even more amazing, the Earth’s second atmosphere at that time was upwards of 100 times greater in mass than at present. So, where did all of those gigatons of CO2 go when ti was removed from the Earth’s second atmosphere to create a third atmosphere? Aerobic plant life voraciously ate the CO2 and deposited it into the Earth’s Lithosphere, biospahre or decomposed it into life giving oxygen.
Bottomline, aerobic lifeforms are still voraciously removing CO2 from the Earth’s atmosphere at rates which keep the plant life perpetually on the brink of CO2 deprivation.