I recently asked a question about whether there were studies on the effects of reduced CO2 level air and got what sounds like a good answer:

Are there studies on the effect of reduced CO2 levels on human cognition?

The answer posted to the above question states that there is no reason to expect low inhaled CO2 levels to even make a difference in the relative levels of CO2 in the lungs, with are ~100x higher than in the ambiant air. This seems like a rational argument.

But with further thought that argument seems inconsistent. If average CO2 levels in the air are around ~400ppm, just 3x that number, ~1200ppm, is known to be associated with drowsiness and complaints of poor air quality (if my research is correct).

If the argument above holds, that reducing CO2 levels in the air from ~400ppm to ~0ppm, isn't going to significantly affect the ratio of CO2 in the lungs, then why doesn't that argument hold also with a seemingly small increase of 3x CO2 levels in the air (as compared to the 100x levels in the lung already)?

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    $\begingroup$ The US Navy has tried to replicate the (highly dubious) results claimed by some recent "Green" buildings research (which is the stuff you're referring to, even if you don't say it explicitly). The Navy replication study failed to find any differences whatsoever in their replication. Non-replicable research gets published in psychology all the time, alas. Also the "Green" building research contradicted decades of prior research on the matter. $\endgroup$ Mar 31, 2019 at 17:42
  • $\begingroup$ Thanks, that's a really good reference, that's the kind of stuff I was hoping to find with this question, you should post that as an answer. I am interested in the references to the decades of prior research. I'm not an expert in this field, so I look to places like wikipedia and stack exchange to cue into it, and I've been seeing contradictory publications. $\endgroup$ Apr 1, 2019 at 17:49

1 Answer 1


3X atmospheric CO2 does not have appreciable cognitive impact.

Indoor air typically is already much higher in CO2, especially in a room full of people, because they are all breathing out CO2. It would not be unusual to find 2-3X atmospheric CO2 inside.

In the answer to your previous question, I referred to much higher concentrations that do have appreciable impact. For example, at 100X normal atmospheric concentration, the concentration in the air is similar to the normal concentration in the lungs, such that CO2 builds in the lungs and dissolved levels increase in the bloodstream.

  • $\begingroup$ So is a site like this is publishing incorrect information? dhs.wisconsin.gov/chemical/carbondioxide.htm, they state that: "1,000 - 2,000 ppm: level associated with complaints of drowsiness and poor air." $\endgroup$ Feb 19, 2019 at 20:01
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    $\begingroup$ @davidparks21 They're being super safe for safety's sake. They aren't publishing incorrect information, they are publishing guidelines for keeping building air overturned. If CO2 levels inside are rising to 1000-2000 ppm, probably the building air isn't turning over much. There could be lots of other things in the air, and particular individuals who already have breathing problems (i.e., the CO2 in their blood is already high) could have symptoms. $\endgroup$
    – Bryan Krause
    Feb 19, 2019 at 20:05
  • $\begingroup$ I see a variety of numbers published that are hard to disentangle here. On this wikipedia page: en.wikipedia.org/wiki/Carbon_dioxide#Toxicity, I note two quotes, (1) "In concentrations up to 1% (10,000 ppm), it will make some people feel drowsy and give the lungs a stuffy feeling.[115]", which seems to support this line of reasoning, and (2) "A study of humans exposed in 2.5 hour sessions demonstrated significant effects on cognitive abilities at concentrations as low as 0.1% (1000ppm) CO2 likely due to CO2 induced increases in cerebral blood flow.[121]", which seems to question it. $\endgroup$ Feb 19, 2019 at 20:15
  • $\begingroup$ Bryan is right, I think. The level of CO2 is used as a measure of indoor air quality because it is convenient, not because CO2 is toxic at these concentrations. There are probably confounding factors in studies which find a correlation between CO2 level and effects on cognitive function at 1000ppm. Studies controlling the level of O2 and other confounding factors have found have found no dose-response for CO2 under 2000ppm. $\endgroup$ Apr 27, 2021 at 11:25

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