I think the level of carbon dioxide in the air is high enough to reduce the intelligence of humans. This has nothing to do with climate change.

Except that both mean we should reduce CO₂.

I never heard of that, surprisingly, but deducted that from simple known facts. I hope I'm missing something.

Maybe my idea is just wrong? It's simple enough to explain here:

Elevated CO₂ levels in office air reduce the cognitive ability of office workers, that is well established.
That is measurable by experiment. Complaints about drowsiness start at about 1000 ppm CO₂ in air.
Reduction in cognitive ability does happen with drowsiness, almost by definition.

The level of CO₂ is currently a significant fraction of 1000 ppm, about 409 ppm as of November 2019.

The CO₂ level in a typical western indoor working environment raises by multiple 100 ppm over the day, exhaled by people breathing in the working environment.

With an increasing base level, an increasing level in workplace air reaches a fixed threshold sooner, because CO₂ levels are additive.

The base level does increase. Therefore a level of CO₂ that reduce the cognitive ability of humans is reached earlier in a working day.

If the base level is higher, base level plus the additional CO₂ in office air reach a level that reduces cognitive ability sooner during a work day.

This happens globally in many workplaces.

That is true for any values of base concentration, threshold concentration and maximum of increase during a day that are of the same order of magnitude. This estimation is optimistic, because it assumes that the effect has a sudden onset at a level that causes obvious symptoms.

To summarize the central points: Some CO₂ concentration exists that has negative effects. An offset in base air concentration results in an offset in the workplace concentration. That means the detrimental concentration is reached more often. For this to be true, the exact numbers are not even relevant.

Ok, what's wrong with that deduction?
I really hope there is something wrong.

If this is a reason to care about the level of carbon dioxide in common air, it is completely independent of climate change, an alternative motivation to do exactly the same thing. That seems very relevant to me.

co2 levels

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    $\begingroup$ This is very interesting and I was not aware of this, but is it really about Earth Science? If your question is, "are CO₂ levels likely to reach level x by year y", then that would be an Earth Science question; but if it is "are CO₂ levels at level x impacting cognitive ability", then that is better for your question on neuroscience. $\endgroup$ – gerrit Nov 6 '19 at 9:43
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    $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – gerrit Nov 6 '19 at 21:19
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    $\begingroup$ Awesome to see someone else picked up on this. I thought and saw exactly the same thing a while ago. $\endgroup$ – The_Sympathizer Nov 8 '19 at 3:11
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    $\begingroup$ @The_Sympathizer - Ok, if we do, we hallucinate at least not alone... But by now, I have seen enough papers that indicate this is reality. I'm a rational person, but I'd prefer it were not, in this case. But still, something is odd. I mean, it is not something obscure. That CO₂ has a negative effect is often discussed, in scientific papers and elsewhere. All that's different here is that all these symptoms set in earlier and therefore are present for a longer time. All. $\endgroup$ – Volker Siegel Nov 8 '19 at 3:27
  • $\begingroup$ @The_Sympathizer - Maybe the "All." makes it just too scary to reflect it. $\endgroup$ – Volker Siegel Nov 8 '19 at 3:29

There looks like legitimate cause for further study, preferably by scientists breathing air under 950 ppm $\small\mathsf{CO_2}$ (this study showing a 15% decline in cognitive ability at this level).

Because it is not known what mechanisms are involved in this decline in cognitive ability it is not clear if there are threshold levels, with step changes in impacts or if the effect is linear, but changes at below 950 ppm is indicated and subtle impacts at much lower level seem likely, with one leading expert (Vivian Loftness) on Health, Productivity, and the Quality of the Built Environment suggesting atmospheric levels above 600 ppm would be cause for concern about cognitive effects. For people with poor cognitive abilities potential impacts of $\small\mathsf{CO_2}$ levels is not known, but could be significant - this, along with impacts more generally at levels that are within the range of possible $\small\mathsf{CO_2}$ concentrations people now living can expect outdoors needs more study.

The principle response in the near term is improving air quality in buildings, with raised atmospheric $\small\mathsf{CO_2}$ levels most significant with respect to rates of $\small\mathsf{CO_2}$ buildup and the required air replacement by ventilation systems. There are ample reasons to commit to actions that reduce emissions and $\small\mathsf{CO_2}$ rise in the atmosphere, but better understanding of all the potential consequences is worthwhile.

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    $\begingroup$ That is significantly more scary than I had expected! I asked about the relation of cognitive ability to CO₂ at Psychology & Neuroscience: psychology.stackexchange.com/q/24392/4799 $\endgroup$ – Volker Siegel Nov 6 '19 at 0:37
  • $\begingroup$ We probably don’t need the scientists to be breathing air of any particular concentration of CO; what we’d really need is subjects breathing said air. :P Typo aside, great answer: +1. $\endgroup$ – KRyan Nov 6 '19 at 17:50
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    $\begingroup$ @KRyan You are right, of course. A single sample does not allow for any meaningful result. We need at the bare minimum 10 scientists to draw a conclusion of their reaction. Oh I would so love to see that paper "The effect of carbon monoxide on scientists". $\endgroup$ – Volker Siegel Nov 6 '19 at 18:53
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    $\begingroup$ @KRyan - that was me half joking; seems important that scientist doing such studies don't have impaired cognitive abilities. A double blind study of different scientists doing double blind studies under varying CO2 levels? I suspect that good methodology is crucial when studying something they may be subjected to themselves. I think the 600ppm threshold is suggested because in the 600 - 750 range people start to notice poorer air quality; something physiological is happening but it is not necessarily - yet - poorer cognition. $\endgroup$ – Ken Fabian Nov 6 '19 at 20:25
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    $\begingroup$ "preferably by scientists breathing air under 950ppm CO2" -- judging by cursory googling, it's not uncommon for office buildings to have 1000ppm or more, so that may be asking too much. $\endgroup$ – Denis de Bernardy Nov 7 '19 at 9:31

Two recent studies tend to contradict the 2016 study mentioned in Ken Fabian's answer.

Acute Exposure to Low-to-Moderate Carbon Dioxide Levels and Submariner Decision Making (June 2018) reports:


Using a subject-blinded balanced design, 36 submarine-qualified sailors were randomly assigned to receive 1 of 3 $\small\mathsf{CO_2}$ exposure conditions (600, 2500, or 15,000 ppm). After a 45-min atmospheric acclimation period, participants completed an 80-min computer-administered SMS test as a measure of decision making.


There were no significant differences for any of the nine SMS measures of decision making between the $\small\mathsf{CO_2}$ exposure conditions.

Effects of acute exposures to carbon dioxide on decision making and cognition in astronaut-like subjects NPJ Microgravity. (June 2019) 5: 17, which shares an author with the 2016 study, finds:

enter image description here

  • $\begingroup$ From the abstract of the second study: "These outcomes, which conflict with those of other studies, likely indicate differing characteristics of the various subject populations and differences in the aggregation of unrecognized stressors, in addition to CO2, are responsible for disparate outcomes among studies. Studies with longer exposure durations are needed to verify that cognitive impairment does not develop over time in crew-like subjects." $\endgroup$ – Roland Pihlakas Nov 8 '19 at 16:41
  • $\begingroup$ @RolandPihlakas yes, and the full text says: "Clearly, the...relationship between CO2 concentration and performance on the SMS that was demonstrated in earlier studies4,5 was not replicated in this study, which included concentrations within the ranges used in those earlier studies ... Our findings at 2500 and 5000 ppm diverge from those anticipated by the findings of earlier studies that demonstrated substantial effects of CO2 upon performance on the SMS at lower concentrations4,5 but the absence of an effect at 2500 ppm replicates the finding of Rodeheffer11 at that concentration." $\endgroup$ – DavePhD Nov 8 '19 at 16:53
  • $\begingroup$ @RolandPihlakas So the common author, Usha Satish, of the two "earlier studies" and the 2019 study seems to be retracting her earlier conclusions and agreeing with Rodeheffer (the first reference in this answer). $\endgroup$ – DavePhD Nov 8 '19 at 16:56
  • $\begingroup$ I'm not sure submariners or astronauts - highly trained and task oriented with clear tasks set in front of them - can be considered representative of people at large. Just as intern doctors may do exceptionally long shifts without sleep and remain focused we can expect plenty of other people, less highly trained and less motivated, would make serious mistakes. Those with poor cognitive ability and unaware of raised CO2 levels may test more poorly at CO2 levels that don't affect high achievers. I don't think the study cited is definitive any more than the one I cited in my answer is. $\endgroup$ – Ken Fabian Dec 6 '19 at 22:57

The NASA has recently lowered their recommendation for astronauts on the ISS from 7000 ppm to 5300 ppm $\small\mathsf{CO_2}$

NASA has continued to lower $\small\mathsf{CO_2}$ exposure levels for ISS astronauts, down from 5.3 mm Hg (7000 ppm) to “4 mm Hg [under 5300 ppm] more recently.”

see https://thinkprogress.org/its-taking-less-co2-than-expected-to-cause-health-risks-in-astronauts-7af09e82b83/

Newer studies even recommend lower values

Law’s paper is the first serious look into the subject, and her team’s recommendation is to go even lower, to 2.5 mm Hg. They found that “for each 1-mm Hg increase in $\small\mathsf{CO_2}$, the odds of a crew member reporting a headache almost doubled.” Their recommended level of 2.5 mm would, according to the paper, “keep the risk of headache to below 1%, a standard threshold used in toxicology and aerospace medicine.”


But these values are still 5-10 times as high as the average value in the atmosphere. So if the studies on astronauts are correct, there should be no reason to worry.


Even if your concern is interesting the "fact" you bourght up seems surprinsing to me. With ventilation and open windows, it seems strange to me that $\small\mathsf{CO_2}$ level increase that much but still, I'm no expert... So I checked.

After a bit of research I found this article which talk about the 15% drop in cognitive function in office with 1000 ppm (which Michael Walsby bourght up in his answer) and a link to the study from where those data are from.

I went straight at the conclusion of said article and from what I read, it seems to be more about an increase in test score based on environment quality (mostly air quality and mold from what I read) and this make a big difference.

The result could be because of an alarming $\small\mathsf{CO_2}$ level that is corrected with a ventilation improvement, or it could just be because the air is easier to breath so student are less stressed out. From what I see, the study only talk about a link between environment quality and performances at different tests. It does not conclude anything about $\small\mathsf{CO_2}$ level, which means that the article which was talking about the 15% decrease in cognitive ability probably over-interpreted the article.

I haven't done more research but I think your concern is probably a wrong interpretation of some articles doing a wrong interpretation of studies that are too fiew to draw a clear conclusion. It's still an interesting topic though but without more studies it's just speculation from what I see.

  • $\begingroup$ Of course, if anything I assume is not actually true. Let me know any specific point that you think is not or may not be true. Regarding "Elevated CO₂ levels in office air reduce the cognitive ability of office workers, that is well established." This is about an elevated CO2 level, which excludes the situation with ventilation. If there are any other negative effects or pollutants that reduce test scores, that does not contradict what I write: It is only relevant whether an increased CO2 level has an additional negative effect. $\endgroup$ – Volker Siegel Nov 6 '19 at 16:38
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    $\begingroup$ I do not think about any specific person, but about globally all people in the situation. The sum of small changes makes the problem relevant. We can assume that, at any point in time, a number of people are in a workplace or classroom that is not well ventilated. Let us assume some lower bound. Do you agree that the number of people are more than 100,000? I would estimate more than a million, but we just ignore that. I claim: If it is true that 100000 people experience a reduction of their cognitive ability by 5%, that is a fact that is negative in some objective way. Do you agree? $\endgroup$ – Volker Siegel Nov 6 '19 at 16:47
  • $\begingroup$ Any study related to this question is very interesting. But a central part of my argument is that it is completely independent of any study. The deduction is there in the question, completely. I could try to write it down more like a mathematical proof. $\endgroup$ – Volker Siegel Nov 6 '19 at 16:51
  • $\begingroup$ There is a phenomenon called 'sick building syndrome', which refers to the fact that some buildings, especially offices, have poor air quality which affects workers performance. Pollutants such as paint fumes and/or traffic fumes seem to be responsible.. $\endgroup$ – Michael Walsby Nov 6 '19 at 20:28
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    $\begingroup$ @Louis Schuck - I lack the expertise to properly assess the methodology but from its intro - "we assessed cognitive function after a full-workday exposure to CO2 while holding other variables constant" says to me they tried to address CO2 specifically. I would say it is more than mere speculation but not yet definitive. Clearly people do manage to do their jobs in raised CO2 but maybe less than optimally. More study needed. $\endgroup$ – Ken Fabian Nov 6 '19 at 20:57

You are being alarmist. $\small\mathsf{CO_2}$ levels vary considerably from place to place, but as you know, the average level is just over 400 ppm. You have a higher level than that in your own lungs at this moment, so it is far too low to cause mental problems. Places with raised $\small\mathsf{CO_2}$ levels have existed since time immemorial, but were rarely high enough to produce the cognitive deficiency you speak of. If raised $\small\mathsf{CO_2}$ levels were significantly reducing the efficiency of their workforce, employers would soon find a way of piping fresh air to them. Perhaps opening the windows would be enough.

Carbon monoxide (CO) is far more of a danger than $\small\mathsf{CO_2}$, as it cuts off the supply of oxygen to the brain, and worldwide, thousands of people die of CO poisoning each year. It comes from the same sources that produce $\small\mathsf{CO_2}$, but where combustion is inefficient the $\small\mathsf{CO_2}$ is mixed with carbon monoxide. $\small\mathsf{CO_2}$ can become dangerous when levels increase beyond about 3 percent by volume, but this rarely happens. Humans can tolerate levels much higher than 400 ppm without ill effect.

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    $\begingroup$ What you say does not contradict my argument. It is not about a difference that is directly apparent in a working environment. It is about a difference that could be experimentally measured. Even if it is small, it is relevant, as it has an effect to many people globally. $\endgroup$ – Volker Siegel Nov 5 '19 at 22:54
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    $\begingroup$ So far as I know, CO is not exhaled by humans except when they have breathed it in. It is related to the question in so far as it comes from the same sources as CO2 but is far more dangerous, and does indeed damage the brain. In minute amounts its effects could be confused with those of large quantities of CO2. $\endgroup$ – Michael Walsby Nov 5 '19 at 23:01
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    $\begingroup$ "You have a higher level than that in your own lungs at this moment, so it is far too low to cause mental problems" This statement seems odd, isn't that obviously true, always. As your lungs take whatever the ambient CO2 is and add some more CO2 to it. $\endgroup$ – Richard Tingle Nov 6 '19 at 13:13
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    $\begingroup$ "employers would soon find a way" But only if they knew about it - and productivity is notoriously hard to measure. $\endgroup$ – jpa Nov 6 '19 at 14:18
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    $\begingroup$ @RichardTingle And a higher concentration in the ambient air might not proportionally increase the concentration in your lungs. Instead, it might hinder your lungs' ability to exchange it, resulting in a similar concentration in your lungs and a higher concentration in your blood, which is what really matters. $\endgroup$ – user560822 Nov 6 '19 at 19:38

I don't doubt that CO2 has the potential to impact cognitive abilities and that poor air quality really affects many people. However, if we consider all factors impairing cognitive abilities in a typical office environment, the elephant in the room is the noise.

Therefore I believe that the impact of CO2 on cognitive abilities doesn't hit the news because it's not as significant as other factors such as the noise. It only starts to be a problem half-way though the day if ventilation is inadequate, whereas noise becomes a problem for most people even before they arrive to work (loud noise has lasting effect on the cognitive performance), and keeps being a problem the whole day.

  • $\begingroup$ I don't think your 'well known' fact is entirely accurate -- or well known. Or rather, I think it's a dangerous oversimplification. Some people have trouble concentrating in excessive quiet. Heck, I remember a study that showed that quiet classical music can assist in learning mathematics. Might not sound important -- but I deal with (and in fact am, in the case of Autism) a lot of people with various mental 'disabilities' like ADHD, Autism, etc etc. Keeping in mind that stuff like this is a generalization is important. $\endgroup$ – RonLugge Nov 8 '19 at 2:20
  • $\begingroup$ That is all true and very relevant. But this is specifically about the first sentence. It in no way contradicts what you describe. It is a small additional effect that makes any CO₂ related symptom a little stronger or more common. A single person does not notice the difference, because the normal variation is too large. But over a large number of people, I am sure it can be measured (similar things were measured already) with statistical significance. Even for moderate groups, like 200. $\endgroup$ – Volker Siegel Nov 8 '19 at 3:37
  • $\begingroup$ We should keep this answer here, as a reader finding the question may look for this information too. Maybe it could also fit the site for psychology? $\endgroup$ – Volker Siegel Nov 8 '19 at 3:45
  • $\begingroup$ I asked a question that could be answered by this answer at Psychology & Neuroscience: "What can reduce the cognitive abilities in a common workplace?" psychology.stackexchange.com/q/24412/4799 $\endgroup$ – Volker Siegel Nov 8 '19 at 4:22
  • $\begingroup$ @RonLugge Any statistical study is a generalization by definition. I believe there are more people (myself included) who would be disturbed by music than those who would benefit from it, otherwise WHO would have recommended playing music in schools during classes. $\endgroup$ – Dmitry Grigoryev Nov 8 '19 at 10:27

$\small\mathsf{CO_2}$ levels in the lungs of a human can reach levels as high as 70,000 ppm under normal breathing while the concentration of our breath out is normally 40,000 ppm. The numbers skyrocket well over 100,000 ppm when we exert ourselves or hold our breath. To even suggest that an extra 200 ppm or even 1000 ppm of $\small\mathsf{CO_2}$ in some way affects us is not likely.

  • $\begingroup$ To quickly equalize wild throwing around of random numbers, here official numbers on the toxicity of CO2: cdc.gov/niosh/idlh/124389.html. This is concerning, no question. $\endgroup$ – user18411 Dec 3 '19 at 18:48
  • $\begingroup$ Nobody is suggesting you can breath in 40,000 ppm CO2 and not be affected but the numbers above are scientific fact for exhaled breath. The point is that our lungs are exposed to high levels of CO2 EVERY TIME we breath in and out with no ill affect as long as we continue to breath. CO2 is not toxic, the lack of oxygen is the problem. Short term exposure to 70,000 ppm CO2 happens in our lungs 15 times a minute every minute of our lives, we just replace it every time we breath in. $\endgroup$ – RBFOLLETT Dec 5 '19 at 2:50
  • $\begingroup$ Everybody here is aware of the breathing apparatus, but people are talking about a permanent offset, not a short term exposure. Iow with an elevated atmopsheric CO2 level one would reach toxic levels more often and continuously, resulting in reduced cognitive abilities and possible more grave consequences, not only to humans. Lung-breathing is pretty effective but has its limits ... $\endgroup$ – user18411 Dec 5 '19 at 11:25
  • $\begingroup$ Seriously, try holding your breath, do you not think the concentration of CO2 within your lungs starts to climb dramatically above the normal 70,000 ppm. Swimmers and divers constantly hold their breath for minutes at a time and are exposed to massive concentrations of CO2 as the O2 is converted with no ill effects. I will say it again CO2 IS NOT TOXIC, it is the reduction of O2 that affects cognitive abilities. Studies of pilots and altitude confirm this. Your efforts to demonize CO2 in this way is ridiculous, it is responsible for all life on earth so get over it. $\endgroup$ – RBFOLLETT Dec 6 '19 at 16:16
  • $\begingroup$ I rest my case: smart-breathe.com/carbon-dioxide. It seems human life began on earth with concentrations of CO2 in the 200,000 ppm range which did decline rapidly overtime. In fact the lungs in the human body had to adapt to the lower CO2 concentrations to survive. Hyperventilation shows what happens to the body when it does not get enough CO2 and proves just how important CO2 is to our body to maintain our health. The very blood that flows through our veins is dependent on CO2 for good health. IT IS NOT TOXIC to the human body and obviously we have the ability to adapt to it. $\endgroup$ – RBFOLLETT Dec 6 '19 at 17:28

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