How has a near doubling of atmospheric CO2 not affected our respiration?

Question

CO2 is basically poison within the context of our respiration. How has there been no serious biological/performance implications from such a drastic change in atmospheric composition? Obviously as a percentage of atmospheric makeup, CO2 is extremely low, but I would assume that the relative figures are what matters here.

heavyset_go · Accepted Answer

Atmospheric CO2 concentration is ~0.04%. When you exhale, your breath contains a CO2 concentration of ~3.8%.
Acidosis occurs in humans at atmospheric CO2 concentrations of ~5%.
Looking at statistics of indoor CO2 concentrations, it seems that offices, classrooms and under ventilated spaces often have CO2 concentrations reaching 2%.
I'd posit that there is probably an order of magnitude of leeway in regard to increasing atmospheric CO2 concentration affecting human respiration.

thedevindevops · Answer

Also of note - we don't have an extensive history of human resting pulse & respiration over generational time (primarily because modern medicine isn't old enough)