<p>According to <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3548274/" rel="nofollow noreferrer">Is CO2 an Indoor Pollutant? Direct Effects of Low-to-Moderate CO2 Concentrations on Human Decision-Making Performance</a> <em>Environ Health Perspect</em>. 2012 Dec; 120(12): 1671–1677: </p>

<p>of 9 different cognitive tests performed at 600ppm (green), 1000ppm (blue) and 2500ppm (red) several show very marked decrease in scores at higher C02 concentration.  </p>

<p><a href="https://i.sstatic.net/g7U8f.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/g7U8f.jpg" alt="enter image description here"></a> </p>

<p>Authors summarized findings as: </p>

<blockquote>
  <p>Relative to 600 ppm, at 1,000 ppm CO2, moderate and statistically significant decrements occurred in six of nine scales of decision-making performance. At 2,500 ppm, large and statistically significant reductions occurred in seven scales of decision-making performance </p>
</blockquote>

<p>Four years after the above was published, the negative effects of carbon dioxide were confirmed in <a href="https://ehp.niehs.nih.gov/doi/10.1289/ehp.1510037" rel="nofollow noreferrer">Associations of cognitive function scores with carbon dioxide, ventilation, and volatile organic compound exposures in office workers: a controlled exposure study of green and conventional office environments.</a> <em>Environ Health Perspect</em> (June 2016) 124:805–812, which was mentioned on Earth SE by Ken Fabian, although there is one common author Usha Satish.  </p>

<p>On the other hand, a very recent article <a href="https://www.ncbi.nlm.nih.gov/pubmed/31240239" rel="nofollow noreferrer">Effects of acute exposures to carbon dioxide on decision making and cognition in astronaut-like subjects</a> <em>NPJ Microgravity</em>. (June 2019) 5: 17, which also has Usha Satish as an author, tends to contradict the above: </p>

<p><a href="https://i.sstatic.net/oefxV.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/oefxV.png" alt="enter image description here"></a></p>

CC BY-SA 4.0
2019-11-08T14:36:56.100Z
Oh... That makes what I was thinking about significantly more scary... Proportional to the significance reflected in the diagrams... Secular [bleep*]! (*American English)
Volker Siegel
CC BY-SA 4.0
2019-11-08T15:01:00.547Z
@VolkerSiegel I added data from a very recent study might lessen your fear.
DavePhD
CC BY-SA 4.0
2019-11-08T15:08:23.507Z
Thanks for trying to lessen it, but it just came to my mind that there is one group which is dramatically affected by it: Families in poor regions where all members of the family share one small room - including children doing homework. I would expect dramatic buildup there. Not good.
Volker Siegel
CC BY-SA 4.0
2019-11-08T15:10:05.007Z
@VolkerSiegel This is another very recent article that found no negative effect https://www.ncbi.nlm.nih.gov/pubmed/29789085/ They tested all the way up to 15,000ppm
DavePhD
CC BY-SA 4.0
2019-11-08T15:14:54.950Z
Up to 15000 ppm sounds suspicious, because somewhere around 2000 ppm is the onset of sleepiness, and I am quite sure that sleepiness does have a negative effect. (I did not read it yet)
Volker Siegel
CC BY-SA 4.0
2019-11-08T15:15:55.953Z
@DavePhD Thank you for including the contrary result. That original result by Satish et al is absolutely ridiculous.
Bryan Krause
CC BY-SA 4.0
2019-11-08T15:18:30.117Z
@VolkerSiegel Make sure you aren't getting your decimal places in the wrong place. 2000 ppm is 0.2%, not 2%. 2000 ppm CO2 is not the onset of sleepiness.
Bryan Krause
CC BY-SA 4.0
2019-11-08T15:29:35.270Z
@BryanKrause I did mean 2000 ppm. I did check my random source, and it is of limited trustworthiness, as it is a company selling CO2 meter devices: https://www.kane.co.uk/knowledge-centre/what-are-safe-levels-of-co-and-co2-in-rooms
Volker Siegel
CC BY-SA 4.0
2019-11-08T15:34:46.340Z
I think there may be a significant difference between performance in decision making versus more general cognitive performance.
Volker Siegel
CC BY-SA 4.0
2019-11-08T15:37:36.303Z
@VolkerSiegel Some of the confusion may be because CO2 is used as sort of a canary gas in studies of indoor air quality. If 2000 ppm CO2 is associated with any symptoms, it's because it's measured in a real-world setting where the actual cause is a different chemical - maybe CO, maybe VOCs, etc.
Bryan Krause
CC BY-SA 4.0
2019-11-08T15:39:11.900Z
"Effects of acute exposures to carbon dioxide on decision making and cognition in astronaut-like subjects" refers to a comparison where a difference is found between the effect of "pure CO2" and "exhaled CO2". Which makes no sense, and lets me think there may be other relevant processes involved.
Volker Siegel
CC BY-SA 4.0
2019-11-08T15:39:59.510Z
Zhang, X., Wargocki, P., & Lian, Z. (2016). Human responses to carbon dioxide, a follow-up study at recommended exposure limits in non-industrial environments. Building and Environment, 100, 162-171. is another negative result, showing even 5000 ppm CO2 doesn't cause sleepiness.
Bryan Krause
CC BY-SA 4.0
2019-11-08T15:41:32.330Z
Let us [continue this discussion in chat](https://chat.stackexchange.com/rooms/100824/discussion-between-bryan-krause-and-volker-siegel).
Bryan Krause
CC BY-SA 4.0
2019-11-08T14:26:13.623Z
2019-11-08T14:59:27.660Z
2019-11-08T14:59:27.660Z
DavePhD
<p>The cognitive ability of humans is varies with the concentration of CO₂ in breathing air. But how does it vary?</p>

<p>A very high concentration causes sleepiness, and sleepiness is a state of reduced cognitive ability.</p>

<p>That means it does vary, but I think there is no sudden onset of the reduction.</p>

<p>I would be interested in, ideally, a function of some experimental correlate of cognitive ability by level of CO₂, but any theoretical or experimental information about the shape of the function is interesting.</p>

<p>I'm aware that the signal to noise ratio in an experimental measurement is high, but qualitative results are the most important.</p>

CC BY-SA 4.0
2019-11-06T11:41:07.557Z
[This review](https://www.researchgate.net/publication/268377763_Cognitive_responses_to_hypobaric_hypoxia_Implications_for_aviation_training) might help formulate an answer.
got trolled too much this week
CC BY-SA 4.0
2019-11-07T12:38:25.680Z
Are you sure the CO2 is relevant? I read your [related question](https://earthscience.stackexchange.com/q/18390/1087) as well, and it seems far more likely that the effects you are measuring are not caused by the increase of CO2 concentration but instead are caused by the decrease of relative oxygen concentration that will be caused by the CO2. In other words, increase of any non-oxygen atmospheric gas concentration would have the same effect. The drowsiness comes from a lack of oxygen AFAIK, not from an increase of CO2.
terdon
CC BY-SA 4.0
2019-11-08T14:11:01.867Z
@terdon oxygen concentration is 209500ppm.  Just adding 1000ppm of another gas would only reduce oxygen to ~209300ppm.
DavePhD
CC BY-SA 4.0
2019-11-08T14:28:10.560Z
@terdon I found it counter intuitive myself,  and had expected it should all be about oxygen. I do not yet understand the exact interaction, but there is one very strong hint: Oxygen is transported by hemoglobin, but carbon dioxide is also transported  by hemoglobin, it connects in a different way thought. It could be that the CO2 somehow competes with O2 on hemoglobin, with CO2 having priority, which should be the case in the bloodstream. Too much CO2 is possibly more problematic than not enough oxygen, because CO2 makes the blood acidic.
Volker Siegel
CC BY-SA 4.0
2019-11-08T14:45:54.953Z
@VolkerSiegel what you describe is about carbon _monoxide_ (CO) not dioxide (CO2). That does indeed compete with oxygen for the 4 hemoglobin binding sites. But apparently, CO2 concentration [is the main sensor for respiration](https://chat.stackexchange.com/transcript/message/52471409#52471409), so there is indeed something that can detect it.
terdon
CC BY-SA 4.0
2019-11-08T14:46:14.853Z
@DavePhD yes, but I was thinking we might be hypersensitive. Turns out I was wrong.
terdon
CC BY-SA 4.0
2019-11-08T14:58:19.630Z
@terdon - Wait, it turns out it was CO2 indeed: Carbon dioxide does interact with hemoglobin and oxygen, described by the Bohr effect.
Volker Siegel
<cognitive-psychology><cognitive-neuroscience><brain>
How does intelligence or general cognitive ability vary with level of CO₂?
Volker Siegel
# How does intelligence or general cognitive ability vary with level of CO₂?

(Asked by: username_0 on 2019-11-05)

The cognitive ability of humans is varies with the concentration of CO₂ in breathing air. But how does it vary?

A very high concentration causes sleepiness, and sleepiness is a state of reduced cognitive ability.

That means it does vary, but I think there is no sudden onset of the reduction.

I would be interested in, ideally, a function of some experimental correlate of cognitive ability by level of CO₂, but any theoretical or experimental information about the shape of the function is interesting.

I'm aware that the signal to noise ratio in an experimental measurement is high, but qualitative results are the most important.

**Tags:** cognitive-psychology, cognitive-neuroscience, brain

> **Comments:**
> **username_1**: [This review](https://www.researchgate.net/publication/268377763_Cognitive_responses_to_hypobaric_hypoxia_Implications_for_aviation_training) might help formulate an answer.  
> **username_2**: Are you sure the CO2 is relevant? I read your [related question](https://earthscience.stackexchange.com/q/18390/1087) as well, and it seems far more likely that the effects you are measuring are not caused by the increase of CO2 concentration but instead are caused by the decrease of relative oxygen concentration that will be caused by the CO2. In other words, increase of any non-oxygen atmospheric gas concentration would have the same effect. The drowsiness comes from a lack of oxygen AFAIK, not from an increase of CO2.  
> **username_3**: @username_2 oxygen concentration is 209500ppm.  Just adding 1000ppm of another gas would only reduce oxygen to ~209300ppm.  
> **username_0**: @username_2 I found it counter intuitive myself,  and had expected it should all be about oxygen. I do not yet understand the exact interaction, but there is one very strong hint: Oxygen is transported by hemoglobin, but carbon dioxide is also transported  by hemoglobin, it connects in a different way thought. It could be that the CO2 somehow competes with O2 on hemoglobin, with CO2 having priority, which should be the case in the bloodstream. Too much CO2 is possibly more problematic than not enough oxygen, because CO2 makes the blood acidic.  
> **username_2**: @VolkerSiegel what you describe is about carbon _monoxide_ (CO) not dioxide (CO2). That does indeed compete with oxygen for the 4 hemoglobin binding sites. But apparently, CO2 concentration [is the main sensor for respiration](https://chat.stackexchange.com/transcript/message/52471409#52471409), so there is indeed something that can detect it.  
> **username_2**: @username_3 yes, but I was thinking we might be hypersensitive. Turns out I was wrong.  
> **username_0**: @username_2 - Wait, it turns out it was CO2 indeed: Carbon dioxide does interact with hemoglobin and oxygen, described by the Bohr effect.  

---

## 1 answers

### Answer by username_3 on 2019-11-08. Score: 4

According to [Is CO2 an Indoor Pollutant? Direct Effects of Low-to-Moderate CO2 Concentrations on Human Decision-Making Performance](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3548274/) *Environ Health Perspect*. 2012 Dec; 120(12): 1671–1677:

of 9 different cognitive tests performed at 600ppm (green), 1000ppm (blue) and 2500ppm (red) several show very marked decrease in scores at higher C02 concentration.

[![enter image description here](https://i.sstatic.net/g7U8f.jpg)](https://i.sstatic.net/g7U8f.jpg)

Authors summarized findings as:

> Relative to 600 ppm, at 1,000 ppm CO2, moderate and statistically significant decrements occurred in six of nine scales of decision-making performance. At 2,500 ppm, large and statistically significant reductions occurred in seven scales of decision-making performance

Four years after the above was published, the negative effects of carbon dioxide were confirmed in [Associations of cognitive function scores with carbon dioxide, ventilation, and volatile organic compound exposures in office workers: a controlled exposure study of green and conventional office environments.](https://ehp.niehs.nih.gov/doi/10.1289/ehp.1510037) *Environ Health Perspect* (June 2016) 124:805–812, which was mentioned on Earth SE by Ken Fabian, although there is one common author Usha Satish.

On the other hand, a very recent article [Effects of acute exposures to carbon dioxide on decision making and cognition in astronaut-like subjects](https://www.ncbi.nlm.nih.gov/pubmed/31240239) *NPJ Microgravity*. (June 2019) 5: 17, which also has Usha Satish as an author, tends to contradict the above:

[![enter image description here](https://i.sstatic.net/oefxV.png)](https://i.sstatic.net/oefxV.png)

> **Comments:**
> **username_0**: Oh... That makes what I was thinking about significantly more scary... Proportional to the significance reflected in the diagrams... Secular [bleep*]! (*American English)  
> **username_3**: @VolkerSiegel I added data from a very recent study might lessen your fear.  
> **username_0**: Thanks for trying to lessen it, but it just came to my mind that there is one group which is dramatically affected by it: Families in poor regions where all members of the family share one small room - including children doing homework. I would expect dramatic buildup there. Not good.  
> **username_3**: @VolkerSiegel This is another very recent article that found no negative effect https://www.ncbi.nlm.nih.gov/pubmed/29789085/ They tested all the way up to 15,000ppm  
> **username_0**: Up to 15000 ppm sounds suspicious, because somewhere around 2000 ppm is the onset of sleepiness, and I am quite sure that sleepiness does have a negative effect. (I did not read it yet)  
> **username_4**: @username_3 Thank you for including the contrary result. That original result by Satish et al is absolutely ridiculous.  
> **username_4**: @VolkerSiegel Make sure you aren't getting your decimal places in the wrong place. 2000 ppm is 0.2%, not 2%. 2000 ppm CO2 is not the onset of sleepiness.  
> **username_0**: @BryanKrause I did mean 2000 ppm. I did check my random source, and it is of limited trustworthiness, as it is a company selling CO2 meter devices: https://www.kane.co.uk/knowledge-centre/what-are-safe-levels-of-co-and-co2-in-rooms  
> **username_0**: I think there may be a significant difference between performance in decision making versus more general cognitive performance.  
> **username_4**: @VolkerSiegel Some of the confusion may be because CO2 is used as sort of a canary gas in studies of indoor air quality. If 2000 ppm CO2 is associated with any symptoms, it's because it's measured in a real-world setting where the actual cause is a different chemical - maybe CO, maybe VOCs, etc.  
> **username_0**: "Effects of acute exposures to carbon dioxide on decision making and cognition in astronaut-like subjects" refers to a comparison where a difference is found between the effect of "pure CO2" and "exhaled CO2". Which makes no sense, and lets me think there may be other relevant processes involved.  
> **username_4**: Zhang, X., Wargocki, P., & Lian, Z. (2016). Human responses to carbon dioxide, a follow-up study at recommended exposure limits in non-industrial environments. Building and Environment, 100, 162-171. is another negative result, showing even 5000 ppm CO2 doesn't cause sleepiness.  
> **username_4**: Let us [continue this discussion in chat](https://chat.stackexchange.com/rooms/100824/discussion-between-bryan-krause-and-volker-siegel).  

---

