[MathMonkeyMan]

I don't know the mechanism, but: https://www.google.com/search?q=co2+cognitive+impairment

[ekianjo]

This has the hallmark of confounding factors. There is no way you can design a study to control for CO2 alone vs other trace contaminants in the air.

[UniverseHacker]

In that case it wouldn't matter much to an individual making personal decisions about their environment. Either way, an environment with enough outdoor air exchange to keep CO2 low would avoid these effects.

But hypothetically, what other trace contaminants would you expect to be so universally correlated with CO2 in different environments that they could account for repeatedly observing these effects in different studies? That seems implausible.