<p>There looks like legitimate cause <em>for further study</em>, preferably by scientists breathing air under 950 ppm <span class="math-container">$\small\mathsf{CO_2}$</span> (<a href="https://ehp.niehs.nih.gov/doi/10.1289/ehp.1510037" rel="nofollow noreferrer">this study</a> showing a 15% decline in cognitive ability at this level). </p>

<p>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 (<a href="https://soa.cmu.edu/vivian-loftness" rel="nofollow noreferrer">Vivian Loftness</a>) 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 <span class="math-container">$\small\mathsf{CO_2}$</span> levels is not known, but could be significant - this, along with impacts more generally at levels that are within the range of possible <span class="math-container">$\small\mathsf{CO_2}$</span> concentrations people now living can expect outdoors needs more study.</p>

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

CC BY-SA 4.0
2019-11-06T00:37:04.457Z
That is significantly more scary than I had expected! I asked about the relation of cognitive ability to CO₂ at [psychology.se]: https://psychology.stackexchange.com/q/24392/4799
Volker Siegel
CC BY-SA 4.0
2019-11-06T17:50:38.847Z
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.
KRyan
CC BY-SA 4.0
2019-11-06T18:53:19.307Z
@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".
Volker Siegel
CC BY-SA 4.0
2019-11-06T20:25:06.180Z
@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.
Ken Fabian
CC BY-SA 4.0
2019-11-07T09:31:08.430Z
"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.
Denis de Bernardy
CC BY-SA 4.0
2019-11-06T00:15:32.710Z
2020-01-04T19:06:06.390Z
2020-01-04T19:06:06.390Z
Ken Fabian
<p>Two recent studies tend to contradict the 2016 study mentioned in Ken Fabian's answer.</p>
<p><a href="https://www.ncbi.nlm.nih.gov/pubmed/29789085/" rel="noreferrer">Acute Exposure to Low-to-Moderate Carbon Dioxide Levels and Submariner Decision Making</a> (June 2018) reports:</p>
<blockquote>
<p>METHODS:</p>
<p>Using a subject-blinded balanced design, 36 submarine-qualified sailors were randomly assigned to receive 1 of 3 <span class="math-container">$\small\mathsf{CO_2}$</span> 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.</p>
<p>RESULTS:</p>
<p>There were no significant differences for any of the nine SMS measures of decision making between the <span class="math-container">$\small\mathsf{CO_2}$</span> exposure conditions.</p>
</blockquote>
<p><a href="https://www.ncbi.nlm.nih.gov/pubmed/31240239" rel="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 shares an author with the 2016 study, finds:</p>
<p><a href="https://i.sstatic.net/oefxV.png" rel="noreferrer"><img src="https://i.sstatic.net/oefxV.png" alt="enter image description here" /></a></p>

CC BY-SA 4.0
2019-11-08T16:41:36.017Z
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."
Roland Pihlakas
CC BY-SA 4.0
2019-11-08T16:53:12.243Z
@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."
DavePhD
CC BY-SA 4.0
2019-11-08T16:56:36.200Z
@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).
DavePhD
CC BY-SA 4.0
2019-12-06T22:57:29.093Z
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.
Ken Fabian
CC BY-SA 4.0
2019-11-08T15:18:18.083Z
2020-01-04T19:07:04.240Z
2020-06-18T08:25:19.090Z
DavePhD
<p>The NASA has recently lowered their recommendation for astronauts on the ISS from 7000 ppm to 5300 ppm <span class="math-container">$\small\mathsf{CO_2}$</span></p>

<blockquote>
  <p>NASA has continued to lower <span class="math-container">$\small\mathsf{CO_2}$</span> exposure levels for ISS astronauts, down from 5.3 mm Hg (7000 ppm) to “4 mm Hg [under 5300 ppm] more recently.”</p>
</blockquote>

<p>see <a href="https://thinkprogress.org/its-taking-less-co2-than-expected-to-cause-health-risks-in-astronauts-7af09e82b83/" rel="nofollow noreferrer">https://thinkprogress.org/its-taking-less-co2-than-expected-to-cause-health-risks-in-astronauts-7af09e82b83/</a></p>

<p>Newer studies even recommend lower values</p>

<blockquote>
  <p>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 <span class="math-container">$\small\mathsf{CO_2}$</span>, 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.”</p>
</blockquote>

<p><a href="https://www.airspacemag.com/daily-planet/why-living-space-can-be-pain-head-180951507/" rel="nofollow noreferrer">https://www.airspacemag.com/daily-planet/why-living-space-can-be-pain-head-180951507/</a></p>

<p>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. </p>

CC BY-SA 4.0
2020-02-18T21:39:50.967Z
Excellent. There is also this [2016 study](https://orbit.dtu.dk/en/publications/human-responses-to-carbon-dioxide-a-follow-up-study-at-recommende) which finds no evidence of physiological response with CO2 levels up to 5000ppm.
M Juckes
CC BY-SA 4.0
2019-11-12T10:07:41.520Z
2020-01-04T19:07:54.283Z
2020-01-04T19:07:54.283Z
asmaier
<p>You are being alarmist. <span class="math-container">$\small\mathsf{CO_2}$</span> 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 <span class="math-container">$\small\mathsf{CO_2}$</span> levels have existed since time immemorial, but were rarely high enough to produce the cognitive deficiency you speak of. If raised <span class="math-container">$\small\mathsf{CO_2}$</span> 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. </p>

<p>Carbon monoxide (CO) is far more of a danger than <span class="math-container">$\small\mathsf{CO_2}$</span>, 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 <span class="math-container">$\small\mathsf{CO_2}$</span>, but where combustion is inefficient the <span class="math-container">$\small\mathsf{CO_2}$</span> is mixed with carbon monoxide. <span class="math-container">$\small\mathsf{CO_2}$</span> 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.       </p>

CC BY-SA 4.0
2019-11-05T22:50:07.173Z
I'm not trying to be alarmist, I changed the word "panic" to "worry" in the title. CO is not exhaled by humans in significant quantities, it is directly toxic, and while interesting, it is unrelated to the question.
Volker Siegel
CC BY-SA 4.0
2019-11-05T22:54:14.083Z
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.
Volker Siegel
CC BY-SA 4.0
2019-11-05T23:01:47.147Z
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.
Michael Walsby
CC BY-SA 4.0
2019-11-05T23:02:50.207Z
The problem is that it is an offset. The level in my lung increases by the same difference as the base level, independent of what that is. Say the base level is 400 ppm, and my metabolism adds 1000 ppm to my lungs. It makes a difference to have 400+1000 = 1400 ppm or 410+1000 = 1410 ppm in the lung.
Volker Siegel
CC BY-SA 4.0
2019-11-05T23:17:27.917Z
CO is exhaled by humans in minute amounts because it is used as a signal molecule in the body. It will get into the lung by diffusion in irrelevant amounts. For practical purpose, nothing is exhaled. Apart from that, CO is acutely toxic, no doubt. The level of CO₂ in workplace air increases from a source not creating CO, but that is not even relevant. The problem is that any level is increased by an increasing base level. So if there is any problematic level at all, it is reached more often. I hope to be proven wrong, but I do not see how?
Volker Siegel
CC BY-SA 4.0
2019-11-06T12:25:09.733Z
https://static.skepticalscience.com/images/co2_10000_years.gif Looks like we have a 140 ppm rise, about a fifth of what's needed for drowsiness. It would be surprising if it had no adverse effects, but I guess it's easy to mitigate
JollyJoker
CC BY-SA 4.0
2019-11-06T13:13:55.613Z
"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.
Richard Tingle
CC BY-SA 4.0
2019-11-06T14:18:34.397Z
"employers would soon find a way" But only if they knew about it - and productivity is notoriously hard to measure.
jpa
CC BY-SA 4.0
2019-11-06T19:38:07.273Z
@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.
StackOverthrow
CC BY-SA 4.0
2019-11-06T23:04:12.600Z
... And if CO2 will be close to even 800 ppm, disastrous consequences of global warming will be still more immediate danger. Consequences of such warming likely will be substantial decline of human population, increase of plant activity and in few dozen thousands of years all will be OK. Until then, less so.
Peter M. - stands for Monica
CC BY-SA 4.0
2019-11-08T10:06:52.140Z
@Friddy A level of 400 ppm, or the current base level of 410, is no problem at all. But it's about the offset: The concentration for every single negative effect is reached earlier by an offset! If a person got sleepy at 1000 ppm, that happens after 600 ppm increase when the base level is 400 ppm. But when the base changed by only 100 ppm, the sleepiness occurs now after an 500 ppm increase.
Volker Siegel
CC BY-SA 4.0
2019-11-08T10:11:12.327Z
@PeterM.-standsforMonica Sounds realistic, unfortunately. But that means it is even more valuable to have this completely separate motivation to fight climate change, that may motivate different people.
Volker Siegel
CC BY-SA 4.0
2019-11-12T22:50:41.120Z
CO2 has similar effects to CO but much higher levels are needed. Both bind to hemoglobin and reduce the ability of oxygen to bind to those sites. CO2 is removed relatively efficiently by the lungs but higher atmospheric levels of CO2 reduce the amount of oxygen in the blood. CO binds more strongly and thus is more toxic.
haresfur
CC BY-SA 4.0
2019-11-05T22:42:39.053Z
2020-01-04T19:10:31.637Z
2020-01-04T19:10:31.637Z
Michael Walsby
<p>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 <span class="math-container">$\small\mathsf{CO_2}$</span> level increase that much but still, I'm no expert... So I checked.</p>

<p>After a bit of research I found this <a href="https://www.lesswrong.com/posts/DtQzYXBTwaWXbhCoS/stale-air-high-co2-may-decrease-your-cognitive-function" rel="nofollow noreferrer">article</a> 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.</p>

<p>I went straight at the conclusion of <a href="https://www.gwern.net/docs/co2/2015-stafford.pdf" rel="nofollow noreferrer">said article</a> 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.</p>

<p>The result could be because of an alarming <span class="math-container">$\small\mathsf{CO_2}$</span> 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 <span class="math-container">$\small\mathsf{CO_2}$</span> level, which means that the article which was talking about the 15% decrease in cognitive ability probably over-interpreted the article.</p>

<p>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.</p>

CC BY-SA 4.0
2019-11-06T16:38:35.867Z
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.
Volker Siegel
CC BY-SA 4.0
2019-11-06T16:47:52.133Z
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?
Volker Siegel
CC BY-SA 4.0
2019-11-06T16:51:24.067Z
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.
Volker Siegel
CC BY-SA 4.0
2019-11-06T20:28:36.947Z
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..
Michael Walsby
CC BY-SA 4.0
2019-11-06T20:57:16.947Z
@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.
Ken Fabian
CC BY-SA 4.0
2019-11-06T16:26:08.497Z
2020-01-04T19:08:41.567Z
2020-01-04T19:08:41.567Z
Louis Schuck
<p>I don't doubt that CO<sub>2</sub> 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 <a href="https://psychology.stackexchange.com/a/24414/24666">noise</a>.</p>

<p>Therefore I believe that the impact of CO<sub>2</sub> 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 <strong>lasting</strong> effect on the cognitive performance), and keeps being a problem the whole day.</p>

CC BY-SA 4.0
2019-11-08T02:20:11.887Z
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.
RonLugge
CC BY-SA 4.0
2019-11-08T03:37:32.673Z
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.
Volker Siegel
CC BY-SA 4.0
2019-11-08T03:45:10.547Z
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?
Volker Siegel
CC BY-SA 4.0
2019-11-08T04:22:21.957Z
I asked a question that could be answered by this answer at Psychology & Neuroscience: "What can reduce the cognitive abilities in a common workplace?" https://psychology.stackexchange.com/q/24412/4799
Volker Siegel
CC BY-SA 4.0
2019-11-08T10:27:11.963Z
@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.
Dmitry Grigoryev
CC BY-SA 4.0
2019-11-08T10:44:58.590Z
My experience is that young people love noise, indeed, some could be called noise addicts. They flock into pubs and clubs with dangerous noise levels which would be illegal without ear defenders if they occurred in a factory. Most of them seek out the noisiest part of the pub, and if it's not noisy enough for them they start shrieking and bellowing to add to the decibels. This might make a suitable research project for a psychologist. It is a recent phenomenon in UK, it didn't happen 50 years ago.
Michael Walsby
CC BY-SA 4.0
2019-11-08T11:27:31.670Z
@MichaelWalsby It's an interesting remark, but I think pubs and clubs are hardly representative of places where you need to max out on cognitive abilities.
Dmitry Grigoryev
CC BY-SA 4.0
2019-11-07T13:16:52.173Z
2019-11-08T10:20:21.993Z
2019-11-08T10:20:21.993Z
Dmitry Grigoryev
<p><span class="math-container">$\small\mathsf{CO_2}$</span> 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 <span class="math-container">$\small\mathsf{CO_2}$</span> in some way affects us is not likely.</p>

CC BY-SA 4.0
2019-12-05T02:50:57.760Z
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.
RBFOLLETT
CC BY-SA 4.0
2019-12-06T16:16:37.427Z
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.
RBFOLLETT
CC BY-SA 4.0
2019-12-06T17:28:28.010Z
I rest my case:   https://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.
RBFOLLETT
CC BY-SA 4.0
2019-12-07T01:03:08.977Z
@RBFOLLETT Let me emphasize this is not an effort to demonize CO2! If this problem does not exist, I will find that out at some point, and the later that is, thee more it hurts. Especially if I would have convinced others it exists at that time. That would directly harm the public understanding about the relevance of CO2 in relation to climate change, because it adds complexity by adding a whole new branch to the complex topic. Also, that CO2 has various beneficial effects is not disputed by anybody, it is just not the topic here.
Volker Siegel
CC BY-SA 4.0
2019-12-07T01:20:17.677Z
@RBFOLLETT Please take a look at the answers of my question "How does intelligence or general cognitive ability vary with level of CO₂?" at https://psychology.stackexchange.com/q/24392/4799 in Psychology and Neuroscience.
Volker Siegel
CC BY-SA 4.0
2019-12-03T18:18:52.123Z
2020-01-04T19:09:31.857Z
2020-01-04T19:09:31.857Z
RBFOLLETT
<p>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.  </p>

<p>Except that both mean we should reduce CO₂.</p>

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

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

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

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

<p>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.  </p>

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

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

<p>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.</p>

<p>This happens globally in many workplaces.  </p>

<p>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.</p>

<p>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.</p>

<p>Ok, what's wrong with that deduction?<br>
I really hope there is something wrong.</p>

<p>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.</p>

<p><img src="https://climate.nasa.gov/system/resources/detail_files/24_co2-graph-061219-768px.jpg" alt="co2 levels"></p>

CC BY-SA 4.0
2019-11-06T09:43:23.313Z
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](https://psychology.stackexchange.com/q/24392/4799).
gerrit
CC BY-SA 4.0
2019-11-06T21:19:41.797Z
Comments are not for extended discussion; this conversation has been [moved to chat](https://chat.stackexchange.com/rooms/100770/discussion-on-question-by-volker-siegel-co-level-is-high-enough-that-it-reduces).
gerrit
CC BY-SA 4.0
2019-11-08T03:11:04.470Z
Awesome to see someone else picked up on this. I thought and saw exactly the same thing a while ago.
The_Sympathizer
CC BY-SA 4.0
2019-11-08T03:27:29.847Z
@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.
Volker Siegel
CC BY-SA 4.0
2019-11-08T03:29:01.817Z
@The_Sympathizer - Maybe the "All." makes it just too scary to reflect it.
Volker Siegel
CC BY-SA 4.0
2019-11-08T09:21:07.190Z
Surely if this was the case, we'd notice Idiocracy happening in real life... you may have a point.
Comic Sans Seraphim
CC BY-SA 4.0
2019-11-09T21:57:29.707Z
@gerrit - I agree that this is not really a question for Earth Science. The reputation points I've gotten for my answer are not the point. The climate change issue is difficult to contain and constrain to specific areas of science or study and I do think it is a good question - just not specifically an Earth Science question.
Ken Fabian
CC BY-SA 4.0
2019-11-09T23:19:32.833Z
@gerrit - ironically the rep points I'm getting might get me the privilege of being able to cast a close vote on questions like this. The right place for questions around climate change, with its implications that cross disciplines isn't entirely clear.
Ken Fabian
CC BY-SA 4.0
2020-02-12T17:55:44.467Z
@gerrit My perspective leading me to associate it with earth science is that it depends on CO2 concentration in air and somehow gives it a fundamental relevance completely independent of climate change. The neurological part seems to be pretty clear, and its details are actually not relevant (it changes thresholds only, but they are not explicit anyway)
Volker Siegel
<climate-change><greenhouse-gases>
CO₂ level is high enough that it reduces cognitive ability. Isn't that a reason to worry?
Volker Siegel
# CO₂ level is high enough that it reduces cognitive ability. Isn't that a reason to worry?

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

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](https://climate.nasa.gov/system/resources/detail_files/24_co2-graph-061219-768px.jpg)

**Tags:** climate-change, greenhouse-gases

> **Comments:**
> **username_1**: 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](https://psychology.stackexchange.com/q/24392/4799).  
> **username_1**: Comments are not for extended discussion; this conversation has been [moved to chat](https://chat.stackexchange.com/rooms/100770/discussion-on-question-by-username_0-co-level-is-high-enough-that-it-reduces).  
> **username_2**: Awesome to see someone else picked up on this. I thought and saw exactly the same thing a while ago.  
> **username_0**: @username_2 - 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.  
> **username_0**: @username_2 - Maybe the "All." makes it just too scary to reflect it.  
> **username_3**: Surely if this was the case, we'd notice Idiocracy happening in real life... you may have a point.  
> **username_4**: @username_1 - I agree that this is not really a question for Earth Science. The reputation points I've gotten for my answer are not the point. The climate change issue is difficult to contain and constrain to specific areas of science or study and I do think it is a good question - just not specifically an Earth Science question.  
> **username_4**: @username_1 - ironically the rep points I'm getting might get me the privilege of being able to cast a close vote on questions like this. The right place for questions around climate change, with its implications that cross disciplines isn't entirely clear.  
> **username_0**: @username_1 My perspective leading me to associate it with earth science is that it depends on CO2 concentration in air and somehow gives it a fundamental relevance completely independent of climate change. The neurological part seems to be pretty clear, and its details are actually not relevant (it changes thresholds only, but they are not explicit anyway)  

---

## 7 answers

### Answer by username_4 on 2019-11-06. Score: 40

There looks like legitimate cause *for further study*, preferably by scientists breathing air under 950 ppm $\small\mathsf{CO\_2}$ ([this study](https://ehp.niehs.nih.gov/doi/10.1289/ehp.1510037) 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](https://soa.cmu.edu/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.

> **Comments:**
> **username_0**: That is significantly more scary than I had expected! I asked about the relation of cognitive ability to CO₂ at [psychology.se]: https://psychology.stackexchange.com/q/24392/4799  
> **username_5**: 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.  
> **username_0**: @username_5 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".  
> **username_4**: @username_5  - 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.  
> **username_6**: "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.  

---

### Answer by username_7 on 2019-11-08. Score: 8

Two recent studies tend to contradict the 2016 study mentioned in username_4's answer.

[Acute Exposure to Low-to-Moderate Carbon Dioxide Levels and Submariner Decision Making](https://www.ncbi.nlm.nih.gov/pubmed/29789085/) (June 2018) reports:

> METHODS:
>
> 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.
>
> RESULTS:
>
> 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](https://www.ncbi.nlm.nih.gov/pubmed/31240239) *NPJ Microgravity*. (June 2019) 5: 17, which shares an author with the 2016 study, finds:

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

> **Comments:**
> **username_8**: 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."  
> **username_7**: @username_8 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."  
> **username_7**: @username_8 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).  
> **username_4**: 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.  

---

### Answer by username_9 on 2019-11-12. Score: 5

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.”

<https://www.airspacemag.com/daily-planet/why-living-space-can-be-pain-head-180951507/>

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.

> **Comments:**
> **username_10**: Excellent. There is also this [2016 study](https://orbit.dtu.dk/en/publications/human-responses-to-carbon-dioxide-a-follow-up-study-at-recommende) which finds no evidence of physiological response with CO2 levels up to 5000ppm.  

---

### Answer by username_11 on 2019-11-05. Score: 2

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.

> **Comments:**
> **username_0**: I'm not trying to be alarmist, I changed the word "panic" to "worry" in the title. CO is not exhaled by humans in significant quantities, it is directly toxic, and while interesting, it is unrelated to the question.  
> **username_0**: 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.  
> **username_11**: 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.  
> **username_0**: The problem is that it is an offset. The level in my lung increases by the same difference as the base level, independent of what that is. Say the base level is 400 ppm, and my metabolism adds 1000 ppm to my lungs. It makes a difference to have 400+1000 = 1400 ppm or 410+1000 = 1410 ppm in the lung.  
> **username_0**: CO is exhaled by humans in minute amounts because it is used as a signal molecule in the body. It will get into the lung by diffusion in irrelevant amounts. For practical purpose, nothing is exhaled. Apart from that, CO is acutely toxic, no doubt. The level of CO₂ in workplace air increases from a source not creating CO, but that is not even relevant. The problem is that any level is increased by an increasing base level. So if there is any problematic level at all, it is reached more often. I hope to be proven wrong, but I do not see how?  
> **username_12**: https://static.skepticalscience.com/images/co2_10000_years.gif Looks like we have a 140 ppm rise, about a fifth of what's needed for drowsiness. It would be surprising if it had no adverse effects, but I guess it's easy to mitigate  
> **username_13**: "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.  
> **username_14**: "employers would soon find a way" But only if they knew about it - and productivity is notoriously hard to measure.  
> **username_15**: @username_13 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.  
> **username_16**: ... And if CO2 will be close to even 800 ppm, disastrous consequences of global warming will be still more immediate danger. Consequences of such warming likely will be substantial decline of human population, increase of plant activity and in few dozen thousands of years all will be OK. Until then, less so.  
> **username_0**: @Friddy A level of 400 ppm, or the current base level of 410, is no problem at all. But it's about the offset: The concentration for every single negative effect is reached earlier by an offset! If a person got sleepy at 1000 ppm, that happens after 600 ppm increase when the base level is 400 ppm. But when the base changed by only 100 ppm, the sleepiness occurs now after an 500 ppm increase.  
> **username_0**: @username_16 Sounds realistic, unfortunately. But that means it is even more valuable to have this completely separate motivation to fight climate change, that may motivate different people.  
> **username_17**: CO2 has similar effects to CO but much higher levels are needed. Both bind to hemoglobin and reduce the ability of oxygen to bind to those sites. CO2 is removed relatively efficiently by the lungs but higher atmospheric levels of CO2 reduce the amount of oxygen in the blood. CO binds more strongly and thus is more toxic.  

---

### Answer by username_18 on 2019-11-06. Score: 2

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](https://www.lesswrong.com/posts/DtQzYXBTwaWXbhCoS/stale-air-high-co2-may-decrease-your-cognitive-function) which talk about the 15% drop in cognitive function in office with 1000 ppm (which username_11 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](https://www.gwern.net/docs/co2/2015-stafford.pdf) 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.

> **Comments:**
> **username_0**: 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.  
> **username_0**: 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?  
> **username_0**: 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.  
> **username_11**: 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..  
> **username_4**: @username_18 - 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.  

---

### Answer by username_19 on 2019-11-07. Score: -1

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](https://psychology.stackexchange.com/a/24414/24666).

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.

> **Comments:**
> **username_20**: 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.  
> **username_0**: 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.  
> **username_0**: 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?  
> **username_0**: I asked a question that could be answered by this answer at Psychology & Neuroscience: "What can reduce the cognitive abilities in a common workplace?" https://psychology.stackexchange.com/q/24412/4799  
> **username_19**: @username_20 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.  
> **username_11**: My experience is that young people love noise, indeed, some could be called noise addicts. They flock into pubs and clubs with dangerous noise levels which would be illegal without ear defenders if they occurred in a factory. Most of them seek out the noisiest part of the pub, and if it's not noisy enough for them they start shrieking and bellowing to add to the decibels. This might make a suitable research project for a psychologist. It is a recent phenomenon in UK, it didn't happen 50 years ago.  
> **username_19**: @username_11 It's an interesting remark, but I think pubs and clubs are hardly representative of places where you need to max out on cognitive abilities.  

---

### Answer by username_21 on 2019-12-03. Score: -1

$\small\mathsf{CO\_2}$ 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.

> **Comments:**
> **username_21**: 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.  
> **username_21**: 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.  
> **username_21**: I rest my case:   https://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.  
> **username_0**: @username_21 Let me emphasize this is not an effort to demonize CO2! If this problem does not exist, I will find that out at some point, and the later that is, thee more it hurts. Especially if I would have convinced others it exists at that time. That would directly harm the public understanding about the relevance of CO2 in relation to climate change, because it adds complexity by adding a whole new branch to the complex topic. Also, that CO2 has various beneficial effects is not disputed by anybody, it is just not the topic here.  
> **username_0**: @username_21 Please take a look at the answers of my question "How does intelligence or general cognitive ability vary with level of CO₂?" at https://psychology.stackexchange.com/q/24392/4799 in Psychology and Neuroscience.  

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