[michael9423]

> 1000 ppm is at the level where us apes have measurable reduction in reaction time and other cognitive impairments.

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.

If you add 1000ppm CO2 to fresh air, it actually boosts cognition due to the Bohr effect.

[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.

[Hugsun]

> The experiments that showed this were confusing correlation with causation.

What nonsense.

https://www.nature.com/articles/s41893-019-0323-1

From the paper: "All studies measured the effects of exposure to artificially raised (pure) CO2"

Some studies showed no effects (for the given task) while others showed a reduction in performance.

[michael9423]

Thank you for that paper. It shows that the proposed negative effects of CO2 do not exist.

Let's take the study by Rodeheffer. Even 15,000 ppm CO2 in the atmosphere did not change the results of a thorough 90-minute test. If this is not indicative of the benignancy of CO2, I don't know what is.

Let's take the another study by Allen that showed "SMS performance was 15% lower for 945 ppm and 50% lower for 1,400 ppm relative to 550 ppm"

This was not a controlled study, but just an association study in different buildings. All the studies that use a good setup do not report marked lowering of cognitive function.

Then you can look at the paper by Herczeg and the mental performance is not really much different between 600 and 4000 ppm - merely 5% difference in errors found in the test. With only few participants, this is not significant. Since this is a short-term study, adaption to higher CO2 levels needs to be considered.

[Hugsun]

Thank you for your patience. I looked at the Rodeheffer study which does indeed conclude that CO2 has no effect on cognitive function (among submariners). I have updated my beliefs accordingly.

The nature paper does suggest that it's concerning so I have not ruled out the option of high CO2 exposure negatively affecting humans. I'll have to look into this more at some point.

Your comments have suggested you are, so I'm assuming with low confidence you are biased towards these things being positive, or much less negative than the scientific community thinks.