As for CO2 counts, we know the Siberian traps produced some of the largest flood basalts ever in earth history, estimates are from 1 to 4 million cubic meters of material, ( Iceland produced 12km and altered global temperature) sealing the lower atmosphere in a shroud of gas and dust, and probably brought about an extinction event unparalleled in geologic times. So the numbers are quite possible over a short period, and better known as spikes.
The charts and graphs we have today are based on long term periods and averages, and at best can be interpreted with a good margin of + - effects, and as data becomes more abundant, this will eventually narrow down exact times and dates.
I believe oceanic evaporation to be the key workings in climate balance, even in the midst of geological upheaval. So looking back at what has transpired in previous times, we have never experienced anything on a scale of these events, and yet the world has cleaned up after itself in a manor we have yet to understand.
As I have repeated several times, we have not yet reached the end of this current interglacial period, and to speculate what little effect we have as humans seems a bit futile in the face of previous cataclysm's, and the earths astounding ability to deal with them.