[ben_w]

> The experiments that showed this were confusing correlation with causation. High CO2 in rooms is a marker of reduced O2, and a lack of fresh air.

Not to a significant degree. Oxygen is normally around 20.9%, if you raise CO2 levels by 1000 ppm, that goes down to… 20.8%. There's a bigger change to how much O2 you breathe just from the change in air pressure from going up 10 meters.

O2 turning into CO2 becomes lethal at 4%; if O2 concentrations go down in step with that (e.g your breathing causes it) you'll only be drowsy and nauseous from the latter while the former is killing you.

This distinction is also why diving rebreathers work: they remove the CO2, which is toxic much sooner than the mere lack of oxygen.

Also:

Fresh air contains less CO2. In Bohr's day, fresh air meant something like 280 ppm, today that means 440 ppm. If some future atmosphere contains 1000 ppm, that's what "fresh" means in that case.

I'm at least marginally confident you're just misreading the Bohr effect.