[<1/1,000,000th%]

CO2 is already just 3/10,000 ths of the atmosphere.

Of course if they could get rid of it all, we would die from lack of oxygen just before all plant life became extinct.

[palmer]

CO2 is already just 3/10,000 ths of the atmosphere

That's what it would be without mankind. Instead it is 4/10,000.

Your second statement is correct. Somewhere below 2/10,000 plants start dying off. We are in a geological era of very low CO2 and anything we add is helpful.