CO₂ — research review 2

...and that’s where the human evidence often differs from the lab. Take indoor CO₂ levels. There's a lot of talk about how even slightly elevated CO₂ impacts our brains.

Right, you hear people linking it to "brain fog" and all sorts of cognitive issues. But what do the clinical trials actually show?

Well, a study in Environmental Health Perspectives in 2012, for example, exposed participants to varying CO₂ concentrations. They found significant decrements in cognitive function—things like decision-making and strategic thinking—at levels above 1000 parts per million, or ppm. Some tasks were impaired even at 600 ppm compared to baseline outdoor air.

So there is evidence for impairment, but at what point does it become significant for most people in common indoor spaces? We're not usually hitting 1000 ppm in a typical office, are we?

Many offices, schools, and homes can exceed 1000 ppm, especially in poorly ventilated spaces with several occupants. But it's important to remember that the most dramatic impairments in that 2012 study, and others like it, were seen at much higher levels, sometimes exceeding 2500 ppm.

So the "brain fog" at slightly elevated levels might be overblown compared to the actual data, even if higher concentrations are clearly detrimental. What about long-term effects? Does chronic exposure to moderately elevated CO₂ have cumulative impacts that these acute studies might miss?

That's a crucial unknown. Most studies are short-term exposures. We simply don't have robust human evidence yet on the cumulative effects of, say, 800 ppm over months or years. The current evidence mostly points to acute, high-level effects.