Prove it!
Oh, and what about the levels BEFORE man?????
At 415 ppm, STILL a pretty low percentage of the atmosphere, and people are a LONG ways from passing out due to its effects on the body’s physiology.
Some might be fainting from hysteria, though.
Water vapor is about a hundred times as concentrated in the atmosphere, on average, at any given time, and has VASTLY more effect on either heat absorption or heat dissipation over a 24-hour period (strangely enough, just about EXACTLY the length of one earth day).