Earth atmosphere is 21% O2 vs. 0.04% CO2 (up from ~0.03% CO2 prior to the human era.) Had all the gigatons of CO2 pumped into the atmosphere by human activities

Earth atmosphere is 21% O2 vs. 0.04% CO2 (up from ~0.03% CO2 prior to the human era.) Had all the gigatons of CO2 pumped into the atmosphere by human activities instead been O2, the effect would be negligible.