Addendum to post #20 above.
Safe CO2 Levels
10,000 ppm, about 30X the outdoor air concentration, is considered safe for indoor breathing for an 8-hour period. 30,000 ppm,
90X the outdoor concentration, is considered safe for 15 minutes indoors. Outside of some manufacturing operations, this concentration is almost nonexistent. The only other situation where CO2 could get dangerously high would be something like a group of miners trapped in a cave-in in a small space with no ventilation, for days or weeks. Serious danger starts at 30K ppm and higher. (The well-reported 2010 Chilean miner cave-in had them down there for ten weeks, and all 33 survived.)
So all the Chicken Little screeching about high CO2 in the atmosphere is complete nonsense. The Earth is a self-regulating system, and never in its 4.5 billion year history has there ever been a CO2 problem--with the exception of very roughly the first billion years or so, when the planet had no life at all. Once plants evolved and started producing oxygen, the atmosphere very slowly started changing into something breathable. And it has been so ever since.
Sources
https://www.health.state.mn.us/commu...oxins/co2.html
https://www.britannica.com/topic/evo...sphere-1703862