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Just how ‘Sapiens’ in the world of high CO2 concentrations?

Posted on 17 November 2014 by Marcin Popkiewicz

Editorial note

Reader comments elicited by this article call attention to several problems with the path taken to arrive at its central conjecture. We appreciate this feedback and note:

1. The author's key support for claims (cited as "D. Robertson, 2006") is not available.

2. Research results on cognitive effects of CO2 are quite complicated and often inconsistent, insufficiently conveyed here. This leads readers to conclusions lacking circumspect informational foundations.

In the interest of transparency we're not altering the original text. We urge readers to pay attention to the above items of concern which together call into serious question the article's core hypothesis, which can fairly be described as overstated and under-supported.

High concentration of CO2 reduces man's intellectual abilities

Did you ever experience being at a lecture or a meeting in a room where you felt tired, your eyes were closing and no matter how hard you tried you could not concentrate? The reason did not have to be a boring subject or a mediocre lecturer – it is a common experience caused by high concentration of carbon dioxide in the air of a crowded and poorly ventilated conference room or a classroom.

People exhale carbon dioxide. If the room is crowded, small and poorly ventilated, the concentration of carbon dioxide in the air grows. When in turn we inhale such air, the carbon dioxide contained in it gets dissolved in our blood and reacts with water to create carbonic acid [H2CO3], which, in turn dissolves into ions of hydrogen [H+] and bicarbonate [HCO3]. Increase in the concentration of hydrogen ions increases blood acidity and creates electrolyte imbalance, causing increased discomfort and decline in intellectual performance. We feel tired, numb and less capable of any mental or physical effort.

Blood pH vs CO2 concentration

Figure 1. Changes in blood acidity level (pH coefficient) as  a function of CO2 concentration in the air we breathe (expressed in number of CO2 molecules per million - ppm). Increase of CO2 concentration in the atmosphere from 280 ppm in the preindustrial era to the current approximately 400 ppm reduces pH of our blood by 0.1 (which is equivalent to acidity increase by 30%). Effective ventilation of buildings becomes more difficult (D. Robertson, 2006).

The threshold of well-being

Building norms are supposed to prevent problems related to poor ventilation. 5000 ppm during an 8-hour workday is typically considered to be the safety threshold. However staying below this level should not be equated with guaranteed comfort and lack of health effects. People start complain about the air quality around 600-800 ppm and the number of complaints greatly increases above 1000 ppm. Various international norms suggest 600 ppm as a maximum CO2 level for a very good air quality, 600 to 1000 ppm is considered good air quality and 1000-1400 ppm is regarded as acceptable (EN 13779, CDC, IDPH, IAQUK, OSHA, EngineeringToolBox). However, CO2 concentrations above 1000 ppm is often interpreted (OSHA, ASHRAE) as a reason for a need to improve building ventilation.

Carbon dioxide and our ability to solve complex problems

So far it has often been assumed that elevated CO2 concentration was a proxy for other harmful pollutants. However, it turns out that CO2 itself may be the culprit.

Studies show that while at elevated carbon dioxide concentrations we can effectively perform simple tasks, our ability to solve complex problems, strategic thinking and initiative quickly degrades.

In the 2013 study, researchers from the University of Berkeley (Fisk et al., 2013, method description) conducted an experiment in which participants took part in a decision-making test - a computer game simulating the management of an organization experiencing a series of problems and crises. The test consisted of three parts, lasting 2.5 hours each, carried out in random order under identical conditions - except for the concentration of CO2, which was set to different levels of, respectively, 600 ppm, 1000 ppm and 2500 ppm.

Researchers found that breathing air with a CO2 concentration of 1000 ppm causes a measurable decline in intellectual capacity. At a concentration of CO2 at the level of 2500 ppm, the initiative and strategic thinking of the participants has declined to a dysfunctional level. Similarly impaired was the ability of the participants to use the available information and the breadth of approach.

The effect of CO2 concentration on peoples' decision abilities

Figure 2. The effect of CO2 concentration on peoples' decision abilities Fisk et al., 2013.

World like a badly ventilated office

In fact, it is not surprising that for concentrations above 600-800 ppm we observe a decline in our intellectual capacity. We have evolved in a climate in which the concentration of CO2 in the atmosphere (since the time of Australopithecus) has varied in the range of 180-300 ppm.

Because of burning of coal, oil and gas, we emit CO2 into the atmosphere and thereby raise its concentration, currently to about 400 ppm. Such high concentrations of carbon dioxide as today have not existed for many million years - possibly more than 10 million years ago (Tripati 2009 [full version]). Continuation of the decades-old trend of burning more and more fossil fuels will lead to an increase in the concentration of CO2 in the atmosphere by the end of the century to a level of 1000 ppm, and later possibly to 2500 ppm or even more.

CO2 emissions and concentration 3000AD

Figure 3. CO2 emissions (a) and its atmospheric concentration (b) for various emissions scenarios  Zickfeld et al., 2013.

Even during the lifetime of many of us the concentration of carbon dioxide in the atmosphere will reach a level not seen since tens of millions of years ago. Currently living species of mammals, birds, and we ourselves - Homo Sapiens - have never had to deal with such high concentrations of carbon dioxide.

Less intelligent man

Gradually, to the known effects of carbon dioxide emissions – like climate warming and ocean acidification – we will be forced to add impairment of our higher mental functions. Faced with the rising complex problems of our civilization, requiring the ability to analyze complex information, undertake initiatives and strategic planning - we place ourselves at a profound disadvantage, perhaps at a literally dysfunctional level.

The decline in intelligence, although difficult to detect on such a long time scale in individuals, can have a huge impact on the whole population. This is illustrated by the figure below, showing the effect of lowering IQ by 5 points. With CO2 concentrations increasing to 1000 ppm, 2000 ppm and possibly even higher, one may wonder what would be the decline in our IQ.

IQ distribution

Figure 4. Comparison of normal distribution of IQ in a population and comparable population for which the IQ was lowered by 5 points. (Source: PSR)

Average IQ is 100 and 95% of the human population have an IQ between 70 (people with IQ lower than 70 are treated as mentally handicapped) and 130 (individuals with higher IQ are considered intellectually talented). Lowering IQ by 5 points, from the average of 100 to 95 – seemingly a small change – will cause a 40% rise in the number of people mentally handicapped and 60% decrease of the highly talented group. We need our intelligence and we should do our best to protect it. Similar effects would be observable in our physical performance – for example establishing new records in sports competitions may become increasingly difficult and rare.

The current standard for harmful CO2 concentrations applies to buildings – places where we stay for a while, then go out for a breath of fresh air. Breathing the fresh air, we have the opportunity to restore our body's proper level of blood acidity. But with unabated emissions we will become continually exposed to higher CO2 concentrations, not only in buildings, which will become less safe, but also outside. Some research suggest first adverse effects of carbon dioxide at a constant (lifelong) exposure of only 426 ppm (D. Robertson, 2006).

Even under the most optimistic possible scenarios of emission reductions CO2 concentration in the atmosphere reaches 550 ppm, which is above the safe threshold. Most scenarios of emissions reduction project reaching atmospheric CO2 concentrations of the order of 750-900 ppm. Taking into account typically higher concentrations of CO2 in buildings, it follows that we will be forced to permanently reside in conditions widely considered to be harmful to health, even by the undemanding ventilation standards.

Increased concentrations of CO2 lead to metabolic acidosis and an array of adverse health effects, going far beyond lowered intelligence. Moreover, due to global warming induced heat-waves people may be forced to spend long periods indoor, in poorly ventilated environments, where ambient CO2 levels will be very high, further endangering their health (D. Zappulla, 2013).

Some people find solace in the fact that in conditions of high concentrations of carbon dioxide plants will fare better. Well, we are not plants. Nevertheless, if people insisting on unlimited burning of fossil fuels have their way, we may end up intellectually a lot closer to plants.

[Updated on February 5, 2024 to add the green box at the top cautioning readers on shortcomings with this article.]

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Comments 1 to 48:

  1. Wow. Had not heard of anything like this. Wonder what Watt and the rest think about this?

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  2. How much more difficult is it to ventilate  a building when the incoming air is 450 ppm instead of 350 ppm?  It would obviously require more air to keep levels below 600 ppm using 450 ppm to ventilate.  Ventilating with 550 ppm?  How difficult is this?  Any input from building engineers?

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  3. This astounds me!  But I'm going put some plants near my desk and try reading it again....

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  4. "Some research suggest toxic effects of carbon dioxide at a constant (lifelong) exposure of only 426 ppm (D. Robertson, 2006).

    Even under the most optimistic possible scenarios of emission reductions CO2 concentration in the atmosphere reaches 550 ppm, which is above the safe threshold."

    CO2 toxic at 426 ppm?  Really?  That's a pretty extraordinary claim.  

    I'm sure you've got some actual evidence to back that up... as opposed to mere speculation, or assertion.

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  5. "man's"?

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  6. I'm afraid I'm going to have to side with Russ here. Lifetime toxicity at 426ppm sounds like a bit of a stretch. I just browsed through the paper by Robertson and it doesn't look to me like the research supports such a claim. The paper states:

    Such a situation is unlikely to be tolerable for a lifetime by humans (and other mam- mals with the possible exception of seals) without dete- rioration in general health along with serious curtailing of physical activity presently taken as normal.

    But I don't see how Robertson can possibly quantify that based on the information he's presenting. 

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  7. I also have to voice skepticism on the Robertson paper. What kind of journal exactly is "current science"?

    It seems to me that, on severl;a occasions, he starts from a plausible premise but then draw conclusions formulated in drastic language when we are still only in the realm of possibility. I know quite well the effects of a high partial pressure of CO2 in the body, which I have to watch for routinely in my job with various kinds of patients in respiratory failure. However, I do not see that he truly has the data to support some of his assertions.

    Nonetheless, it is true that forcing the entire terrestrial biome to endure a spike of 200 ppm in a couple of centuries is one heck of an experiment. I find it extremely irresponsible but that's another debate.

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  8. It is unfortunate that the Berkeley experiment did not include a baseline for behaviour with CO2 concentrations of 400 ppm. That may have provided some evidence regarding the potential consequences for long term exposure to elevated concentrations.

    However, 600 ppm may be an appropriate baseline for the potential indoor concentrations when the best quality of 'fresh air' to improve indoor air quality is 400 ppm. And it is clear that capability was diminished on a number of measures when the concentration increased.

    So, although the claimed long term consequence of 426 ppm is in question there would be less doubt about the potential negative long term consequences of being indoors too much of the time now that the likely indoor air concentration is above 426 ppm and increasing.

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    I recommend this article:

    Toxicity of carbon dioxide: a review

    I just began to read it, but I quote:

    "Volunteers were exposed to 1.5% CO2 over a period of 42 days, and acid base balance and changes in electrolyte metabolism were studied


    although there were some minor modifications of the pH and serum level of the electrolytes, the experimental conditions were well tolerated"

    However, it is said also that intermittent high levels of CO2 are much less well tollerated.

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  10. Comparing exposure over a 75 years span with exposure over a mere 42 days doesn't really tell us anything about long term exposure. For one the effects could be at least somewhat cumulative like we are now finding out about radiation exposure.

    I think they should redo this study with Climate Change Deniers and non-Deniers ..... I have a sneaking suspicion the 'stupidity threshhold" Deniers is closer to 350 ppm ..... Just a hunch and it certainly would explain a lot

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    Moderator Response:

    [JH] Please keep it civil.

  11. Figure 1 is extremely suspect. It lacks data points and has no indication of uncertainty.  I'll bet the particpants in "From Peru"'s reference did not use that figure in advance to extrapolate to determine their likely blood pH!  :-)  The result is nonsensical, but nonetheless the figure indicates a horrifically acidic blood pH, which of course did not arise.

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  12. ianw01@11, Figure 1 has data points in the original version in the linked paper.  Further, the range of variation given for 2005 represents the uncertainty in blood pH given the CO2 concentration in that year.  Intuitively, projecting that range across the entire graph gives a partial estimate of uncertainty.

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  13. Figure 1 is suspect for more reasons than just its data points and uncertainty.

    It depicts a linear relationship between atmospheric CO2 and blood pH, which is entirely at odds with reality.

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  14. Russ R @13, following your link I found that the equation you refer to as "reality" is in fact an approximation.  Further, it is an approximation that is close to linear across most of it range, and where it departs significantly from linearity, it often also becomes very inexact (with real values approximating to linear).  Therefore, for you to draw you conclusion you need to show that:

    1)  the Henderson Hasselbalch equation does not approximate to linarity across the range shown in Fig 1; and

    2) If the Henderson Hasselbalch equation does not approximate to linearity across that range, that it is in fact accurate across that range (which is not a given).

    Absent that, your comment amounts merely to a slogan.

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  15. Trying to understand this one better. It does sound like mammals have the capacity to buffer these effects. That's what is bothering me about the graph. The H-H equation sounds pretty standard, and the normal range indicated on the graph also seems to be well accepted. What I'm not yet buying is the idea of long term toxicity at atmospheric concentrations of CO2 over 400ppm.

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  16. One clue here is, if there were a serious human toxicity issue one would think that would have been a key element of the EPA findings on carbon emissions. 

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  17. Rob @15 & 16, I am certainly not claiming the toxicity claim to be correct.  I have merely pointed out that two "rebutals" of the graph have failed to actually do any rebutting.

    My concern with the graph is that it is cited to Robertson 2006, but Roberston 2006 merely claims, "The estimated toxic level of carbon dioxide in the atmosphere under lifetime exposure is 426 ppm (Figure 1)4", where reference 4 is Roberston (2001).  I have been unable to find a public domain copy of Roberston (2001); and the graph merely shows the fall in blood pH with rising abient CO2 concentrations.  While falling pH can lead to acidosis, the argument as to why that should have lifetime consequences at 426 ppmv ambient CO2, and what the level of the purported toxic effects are is not accessible to me.  Certainly the graph does not establish it.

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  18. From the reading I've done it appears that there are very few studies of <1000ppm CO2 long term health effects - given that such experiments might have to run for significant portions of a human lifespan, and that brief exposures to ~10,000ppm, while dehabilitating, have reversible effects. Long term exposure to somewhat raised CO2 may, however, have significant health effects due in part to long term acidosis. 

    Despite the paucity of literature on low level exposure, I did locate Satish et al 2012Is CO2 an Indoor Pollutant? Direct Effects of Low to Moderate CO2 Concentrations on Human Decision-Making Performance. They studied decision-making performance at in blind tests for several CO2 levels:

    At 1,000 ppm CO2, compared to 600 ppm, performance was significantly diminished on six of nine metrics of decision-making performance. At 2,500 ppm CO2, compared to 600 ppm, performance was significantly reduced in seven of nine metrics of performance, with percentile ranks for some performance metrics decreasing to levels associated with marginal or dysfunctional performance.

    Business As Usual scenarios point to ~1000ppm by 2100. I would opine that this is not good. 

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  19. Tom...  I didn't think you were making that claim at all. My comment wasn't specifically directed at your comment. What you're saying is exactly what I'm also thinking. The claim of toxicity under lifetime exposure is dubious at best.

    I did find one EPA document that discusses toxicity levels as part of comments on the EPA findings to suggest there is no evidence to support that position.

    9.1.2 Carbon Dioxide; Comment/Response (9-8)

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  20. KR... That's still a far cry from "lifetime toxicity at 426ppm." 

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  21. This all seems terribly difficult to square with the performance of the crews routinely enduring significantly higher CO2 levels in submarines and spacecraft. Have a look at chapter 3, "Carbon Dioxide", in Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants (Washington, DC: The National Academies Press, 2007,, from which I take all the quotes below.

    The OP suggests "dysfunctional" initiative and basic strategy at 2500 ppm CO2. Alert the navy! "Data collected on nine nuclear-powered ballistic missile submarines indicate an average CO2 concentration of 3,500 ppm with a range of 0-10,600 ppm..." (p. 47)

    There are studies from the 1990s to suggest a lowest observed adverse effect level of 25,000 ppm for visual effects (p. 53). In a study from 1974, "CO2 at 40,000 ppm for 2 weeks did not affect performance on multiple tests of cognitive function in physically fit young airmen" (p. 54)

    As for buffering of blood pH: "CO2 exposures as low as 7,000 ppm can lower blood pH by up to 0.05 units, but even at high exposures, renal compensation seems to occur in healthy subjects. In a 30-day exposure to CO2 at 20,000 ppm, there was an average pH change of only 0.01 units" (p. 51) Again, that is hard to square with the OP's claim that the rise from preindustrial has lowered blood pH by 0.1.

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  22. The pH graph is from an article by D. S. Robertson in Current Science, which bills itself as India's leading multidisciplinary science journal. For the "data", the graph credits another article by the same D. S. Robertson  published in the Elsevier journal Medical Hypotheses in 2001, "The rise in the atmospheric concentration of carbon dioxide and the effects on human health" ( doi:10.1054/mehy.2000.1256). Scopus suggests this was Robertson's first published article, followed in short order by a further 11 papers in Med. Hyp. on a variety of topics up to 2005, during which period he published nothing in any other journal. It's way past bedtime here, so I'm not reading it tonight, but it sounds speculative at best, and I don't think this was a well-considered post.

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  23. Christian Moe @21, thank you.  That book seems like a very definitive reference on the subject.  Recommended maximum levels are set out in Table 3-3 (page 60):

    "TABLE 3-3 Emergency and Continuous Exposure Guidance Levels for Carbon Dioxide
    Exposure Level
    U.S. Navy Values (ppm)
    NRC Recommended Values (ppm)

    1 h

    24 h

    90 days
    Abbreviations: CEGL, continuous exposure guidance level; EEGL, emergency exposure guidance level; h, hour; NRC, National Research Council; ppm, parts per million."

    Formating was not preserved in my cut and paste, so in explantion, the values are in order the current (2001) Navy maximum concentration standards, the recommended new standard by committee, and the National Research Council recommended values for, in turn, 1 hour, 24 hour and 90 day exposures.  The report does not some minor adverse effects that are ignored because they clear up on return to normal atmospheric conditions.  If atmospheric CO2 levels were to rise to 7,000 ppmv, these minor conditions would not clear up, and may become worse with prolonged exposure.  Never-the-less, it seems clear that CO2 will not have direct toxic effects on humans at concentrations achievable in this century, or likely even with BAU in the next.  Mild toxic levels could be achieved from a determined effort to burn all fossil fuel reserves (which can raise CO2 concentrations to 10,000 ppmv if carried through) but that is likely not a realistic scenario, nor one that need be considered in the short term even if it were in that there must be a significant time in which that route could be avoided.

    I do not think these results challenge those of Fisk et al 2013, however.  They types of effects shown by Fisk 2013 are too sutble for consideration by NRC subcomittee, and would fall into the category they considered as not relevant because the effects are not permanent after return to normal (380 ppmv) CO2 concentrations.  They would become relevant if normal CO2 concentrations rose to 2500 ppmv or (perhaps) even 1000 ppmv.  I think reliance on Robertson 2006 was a mistake, but that the rest of the article is interesting and informative, and has not been challenged by anything you have uncovered.

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  24. I am skeptical of this article.

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  25. Tom Curtis @23,

    I agree that the NRC findings do not seem to challenge those of Fisk et al 2013 directly. Fisk et al sought to measure capabilities that the pencil-and-paper tasks in the 1974 study in all likelihood did not. I take back the comment that they are difficult to reconcile.

    Think about the wider context of submarines, though. If the findings of Fisk et al are correct and widely applicable, the U.S. Navy (and its Soviet counterpart) spent the Cold War entrusting its most critical missions, its weapons of absolute last resort, to crews with significantly impaired "decision-making performance" – below average at utilizing information and taking a broad approach, and dysfunctionally deficient in initiative and basic strategy. Come to think of it, given what was at stake, it's sort of astonishing that the NRC study doesn't record any studies of decision-making under elevated CO2. So I guess it's conceivable that these functions really are badly impaired, and that the Navy didn't know, or didn't let on that they knew.

    Still, it's easy to agree with Fisk et al that:

    The strength of the effects at 2,500 ppm CO2 is so large for some metrics as to almost defy credibility, although it is possible that such effects occur without recognition in daily life. Replication of these study findings, including use of other measures of complex cognitive functioning and measures of physiologic response such as respiration and heart rate, is needed before definitive conclusions are drawn.

    The Zappulla reference sets off my alarm bells in much the same way as Robertson's. Two of Zappulla's four publications on Scopus, including the one referenced here, are book chapters published by academic vanity press Nova Publishers.

    I'll go out on a limb and disagree with you, something I rarely do. I don't think the article is informative. It does tell about an interesting, actually, an astonishing study. But the potential for misinformation outweighs the information. It ignores the study's caveats about needing replication before conclusions can be drawn, sandwiches it between speculative claims from sources of low credibility and a thought experiment about lowered IQ (not observed). The casual reader is left with the take-away message that rising CO2 will make us stupid, an extraordinary claim not supported by extraordinary evidence. I rely on SkepticalScience to be more skeptical than this.

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  26. If I say this article is bollocks, I'll be moderated out, so I won't, but...

    The graph of association between atmospheric CO2 and blood pH can only be from (very) short term experiments on raising CO2 and measuring blood pH. It has no relevance to how the body buffers and stabilises blood pH over a longer term (which might even be as short as hours or days.  It's therefore simply irrelevant to a conversation about human response to century-long changes in CO2.

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  27. Martin Audley @28,

    Far as I can tell, the graph is not from any measurements of blood pH at all. There are none in Robertson 2006 and none in the cited data source, Robertson 2001. The 2001 paper does some calculations, apparently based on the premise that the hydrogen ion concentration in the blood changes proportionally with the atmospheric CO2 concentration. No idea how he got from there to the linear graph, though.

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  28. Tom Curtis @14,

    "your comment amounts merely to a slogan."

    Slogan?  Are you serious?

    The chart depicts a perfectly linear relationship between blood pH and atmospheric CO2.  There are two blatantly obvious reasons that this contradicts reality.

    1. First, pH a logarithmic scale.  
    2. Second, blood is a buffered solution.

    Here's what the logarithmic H-H relationship looks like over that range, without even considering the buffering effect (i.e. HCO3 held constant):

    I wouldn't say that "approximates to linearity".  Would you?  And that's entirely ignoring the buffering effect, which would further limit the pH change.

    If you want to dispute the validity and accuracy of the H-H equation which you claim "is not a given", be my guest.  Those are some mighty fine straws you're grasping at.

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  29. Being something of an old git, I cannot but help thinking of Apollo 13 whenever I hear/read about the decidely unwelcome effects of elevated CO2 levels.

    A quick Google check turned up the following reference which may be of interest to some readers. The title of the piece is "Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants" and it is on the National Acadamies Press.

    The section in question deals with Carbon Dioxide - although I'm sure the very idea of regarding CO2 as a contaminant will raise some hackles. The opening paragraph reads as follows...

    Carbon dioxide is the major expired by-product of human metabolism; if not effectively controlled, it can rapidly accumulate to dangerous concentrations in spacecraft atmospheres. On earth, the outdoor CO2 concentration is typically about 0.03%, and average indoor air contains CO2 in the range of 0.08% to 0.1% (IEQ 2006). In nominal spacecraft operations, the CO2 concentration is typically about 0.5%, but the concentration approached 2% during the troubled Apollo 13 mission (Michel et al. 1975). Carbon dioxide can also enter the atmosphere of a space habitat from accidental combustion of materials, from operation of payloads that use CO2 as an intravehicular propellant, and from use of the fire extinguisher, which, on the U.S. segment of the International Space Station (ISS), is CO2.

    From the above numbers, anyone who spends most of their time indoors is already experiencing CO2 levels somewhere in the 800 - 1000 ppm(v) range as their default exposure. Until the Lithium Hydroxide scrubbers in the Apollo 13 Command Module were "persuaded" to fit into the Lunar Module, the levels in Aquarius were pushing 20,000 ppm.

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  30. Thank you all for valuable remarks and links. Yes, it's debatable, how elevated CO2 concentrations influence our ability to process information. I also agree that it's quite possible that Robertson's opinion is too extreme. It's true that our bodies have strong balancing mechanisms, buffering us from too strong blood acidification and enabling us to function under such conditions, allowing us to perform simple or routine tasks. But, as research of Fisk et al (as well as ventilation norms and observation of crowded meeting rooms, who wake up after a short draught) suggest, CO2 concentration of 1000 or 2500 ppm seems to hamper our information processing and strategic thinking abilities.

    In case of submarine crews their extensive training allows them to perform their duties on a routine level, mostly without real need for learning "on the fly". Their officers, who have to make such decisions, have high intellectual abilities - even if one's IQ decreases from 130 to 125 pts (or even 120), he still will be a highly intelligent and capable individual.

    Maybe we don't have to worry much. Maybe. But none of the research cited answers this question in a direct and unambiguous way. It would be much better to be sure, by performing experiments similar to Fisk et al., but with a much better statistics and longer exposures time for various CO2 concentrations. Then we would know whether after staying at high CO2 concentrations for a long time we will adapt without any measurable loss to our IQ or not.

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  31. Anecdotal evidence, but...

    A friend of mine who spent his twenty in the navy, mostly in the sub service, told me that the low O2 and high CO2 levels were preferred because they _did_ slow the sailors down mentally, leading to more time in the bunks and less energy to cause trouble in confined quarters. After all, damage control and many other duties require rote learning, not considered decision making. Follow The Book, don't reinvent it.

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  32. Peru's point @9 about intermittency matters. Fisk et al's test subjects were exposed to elevated CO2 concentration for a 2.5-hour period, and the test was administered over the latter half of that period. Their bodies would have little time to adjust. That's fine for Fisk et al's purposes, looking at office-building conditions. They draw no conclusion about the effects of permanently elevated atmospheric CO2, and I don't see how such conclusions can be drawn on the basis of their study. As Marcin admits in @30, studies of long-term exposure would be required. That would have been a fitting conclusion to an article seeking to relate this study to global change.

    Why the speculations about IQ? Are there studies that find elevated CO2 lowers IQ? Fisk's didn't test IQ.

    I concede that my argument from incredulity @25 about naval nuclear submarine crews was not compelling. I guess reduced "initiative" could be seen as a feature rather than bug when you've got a tin can of young males confined handling the world's most dangerous weapons — in line with KR's anecdotal evidence @31. And though you'd care about anything degrading the decision-making performance of officers hunting and being hunted by other submarines, they'd start from a very high baseline performance, as Marcin pointed out @30, and could count on the other side breathing at least as much CO2.

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  33. How fast dioxygen decrease with respiration in a room of 10m² with 1 person ? 

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  34. In response to the questions posted by posters:

     Chronic Respiratory Carbon Dioxide Toxicity: a serious unapprehended health risk of climate change


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    Moderator Response:

    [RH] Shortened link.

  35. Craig Idso and others of that ilk have been commenting on a study by Rodeheffer et al (2018), who fail to replicate the effect on the same measure of cognitive ability. However, they are using a different population, and I think shorter exposure. Maybe submariners have become habituated to high carbon dioxide levels, or maybe the sample size is too small. The lack of reported effect on comfort might suggest some acclimatisation.

    Allen et al (2015) (free full text) is strongly supportive of the cognitive effect. There's also a new review by Kenichi Azuma et al (2018): 'Effects on cognitive performance begin at 1000 ppm during short-term exposure', but other physiological variables at 500ppm.

    Our brains and circulatory systems did indeed evolve in a high-O₂, lower CO₂ world, so this seems plausible, but needs more research. When contrarians ask about the direct human health effects, it is usually a distraction from what is healthy for the climate and biosphere.

    Rodeheffer CD, Chabal S, Clarke JM, Fothergill DM. Acute exposure to low-to-moderate carbon dioxide levels and submariner decision making. Aerosp Med Hum Perform. 2018; 89(6):520–525

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  36. I registered just to make this comment.  I agree with many of the earlier comments - this is a a very problematic post.   It would be prudent to remove anything associated with the Robinson article.  It is clearly not a peer-reviewed work - regardless of its stated affiliation.  Leaving stuff like this up is not good for SkepticalScience. BTW, there is a very relevant July 2019 review article in Nature Sustainability, "Direct human health risks of increased atmospheric carbon dioxide" Jacobson, Kler, Hernke, et. al. 

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  37. Ancillary to the above comment (but not necessarily in approval of it), the paper by Jacobson et al 2019 is here.

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  38. Here's a link to the full text of the Jacobson et al 2019 paper

    Perhaps this old thread is picking up again?

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  39. Not to detract from the general argument, but as noted by other posts, Figure 1from D. Robertson is a little off. What D. Robertson overlooks in his calculations is that arterial CO2 partial pressure in the human bloodstream, as it is in most mammals, is a significantly higher than what it is in ambient atmosphere. That means a percentage rise in CO2 in the atmosphere makes for a much smaller percentage rise of CO2 concentration in the bloodstream. In short at low CO2 levels the effect is a whole lot less. Not until CO2 levels reach about 1000ppm in the does the change become notable in the bloodstream. That means the effects of CO2 will not be notable in the human body until around 1000ppm (ok, maybe around 600ppm for a few canaries among us.) Nevertheless, direct impact of CO2 on the human body should still be a big concern because 1000ppm CO2 in the atmosphere will be what we see by the end of this century if the world keeps on the course that it is presently on. Now consider fish whose arterial CO2 pressures are generally an order of magnitude less than that of mammals. They will see the effects much earlier, and most likely by the end of the century will die off significantly. Also, while plants do thrive on a little extra CO2, with atmospheric CO2 concentrations over 1000ppm they tend to die off. So, what we may see is that fish and plants will die back first leaving humans without sufficient means for sustainment. For a more concise treatment of the subject please refer to, “ Carbon Dioxide’s Direct Impact on Down-Regulating the Human Species”, by R.E. Stumm, published in Science of the Total Environment, 19 September 2023.* *


    Also check out the video short “The Die Back” on Rumble** **

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  40. Res01 @39 :

    Agreed ~ as stated in a number of comments [2014 onwards] earlier in this thread, this whole question of CO2 physiological danger is overblown.

    The original research article was of poor quality and poor experimental methodology, and hence poor conclusions.  Or so I gather from others' comments [for me, the linked Robertson article showed as Page Not Found].   I would also argue from basic principles of bodily homeostasis, that whatever transient mental incapacitation (minor, I gather) would occur for a few hours at higher ambient CO2  ~ the body would respond (by increased renal excretion of acid) in the longer run, with the effect of raising the blood pH back to the normal range.

    No need for any alarm, for man nor beast (nor fish).

    Res01 ~ pehaps you might be kind enough to comment specifically on that R.E.Stumm  article, and also the "Die Back" video you mentioned.   I am unclear whether you mean they are alarmist or not.

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  41. Eclectic @40,

    Thank you noting my post.

    I am not sure if you read the RE Stumm article*, or watched the movie,  but the calculations made by Stumm in his article shifts the curve by Robertson over a bit, but generally confirms what is being said here by M. Popkiewicz; the CO2 physiological danger is not being overblown. If we are not already done in by climate change, the direct effects of CO2 on us and other life forms will start haunting us around the end of the century.  I suppose it depends on one's age if this is alarmist or not. If you're a senior with no kids like I am who is going to check out in a few years anyways then the whole subject is simply academic. However, if I were a twenty something or younger who may likely otherwise live to see the end of the century, I'd be freaking out right now.

    *The R.E. Stumm article unfortunately is behind a paywall. However a preprint that is not too significantly off from the peer reviewed published article can be found at  Recommend reading as it should answer your questions on CO2 impact on human body physiology.

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  42. Thanks, Res01 @41  (and forgive my perhaps over-courteous usage of a capital letter for your moniker ~ that is simply my customary literary style).

    Time is precious in this modern age . . . and so, no  ,  have not read the OP's Robertson  paper [the link showed as Page Not Found]  nor the Stumm  paper [unlinked].    Yes, it is quick to read a paper's Extract; and where that is insufficiently informative, still it is usually possible to skim through the body/conclusion of a paper to identify the salient points.   But it's even better if one can "Cut To The Chase".

    All the same, there is so much information "out there" on the internet ~ that the SkS  website staff have created a Comments Policy which requests all commenters to respect readers' time . . . by giving a sufficiently detailed relevant description/summary of (linked) citations.  Whether the citation/link is an actual scientific paper or simply a journalistic article.

    # That request applies in Spades, to video links (even if the video is only 5 minutes long).   As you know, videos can be a great time-waster.   That's why a summary of the video's message and significance can be a great help to the flow of the discussion happening in the thread here.

    Res01 ~  I particularly ask for your deeper discussion of the essential science of this topic of "CO2 impact" on human (and animal) bodies.  That is because I fear that a major mistake is being raised (and I would be pleased to be corrected if I am wrong about that).

    Evolution has designed the body to operate at a specific set point (or very narrow range)  of acidity/pH.   You can temporarily disturb that pH by hyperventilating (to raise the pH)  or by re-breathing into the classic paper bag (to lower the pH).   But in the long run, it is the kidney (as mentioned earlier)  which maintains the body's day-by-day acidity level.   Renal function is vital !

    And it is (as yet) unclear to me if Robertson / Stumm / and other sources, have made allowance for those basic facts of physiology.   Are they making a giant blunder ~ or am I making a blundering assessment of their warnings?   Please discuss.

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  43. A modest suggestion  [ not Modest Proposal ] :-

    In the absence of any information to the contrary during the past 8 days in this thread, I would like to suggest that this O.P. from 2014 be marked with a prominent note of Warning or Caution for readers.

    The O.P. starts well, by evidencing mild impairment of human intellectual function at an ambient (air) level of 1000 ppm of CO2.   Fortunately, a reversible impairment.

    But in the final 4 paragraphs, the O.P. implies that we humans should be alarmed, medically, at the prospect of a terrestrial atmospheric CO2 level of even 426ppm - 900ppm.    (The O.P. also links to the [bookish]  D.Zappullo~2013 ,  wherein is discussed major health problems from air CO2 of 5,000ppm - 30,000ppm.)

    However, in actuality,  an ambient CO2  426ppm-900ppm level would be swiftly compensated inside the body (within hours to days) through the activity of the kidneys which possess routine mechanisms to normalize total body acidity.   The adverse planetary effects of high CO2 are an entirely separate matter.

    SkS staff may wish to consider adding an up-front note, such as :-

    CAUTION : parts of this 2014 post are very misleading.


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  44. Eclectic:

    I think your concern is misplaced.

    This paper, from 2015 finds concentrations of CO2 in classrooms in New York at levels up to 1591 ppm.  They report teachers had more headaches the higher the concentration of carbon dioxide.  Obviously students are negatively affected.  Since background levels have increased since then you would expect classroom levels to increase.

    I taught in Florida.  Our classrooms are more crowded and often the air conditioning systems do not work.  I woud expect classroom conentrations to be hgher in Florida.  New York spends more on classroom maintenance than most states so I would expect New York data to be lower than most other states.

    If the external CO2 concentration increases that has a disproportionate on inclosed space concentrations.  If you are diluting the internal space with 300 ppm air the internal concentration stays lower than when you dilute the internal space with 450 ppm air.  Anywhere there are crowded buldings the concentration of CO2 becomes severely elevated.  Theatres, crowded offices, manufacturing areas all have elevated CO2.  Restaraunts that use gas stoves are severely affected.  

    The external air in cities is not 425 ppm.  This paper reports an hourly average of CO2 in Salt Lake City USA as high as 700 ppm in 2016.  I would expect other locations to be higher.

    Even 1000 ppm affects how people work and feel.    Most of us do not live on the top of Mauna Loa where the air is well mixed. (They delete the data when hgh CO2 air from the volcano mixes in).  You are looking at outside air.  The spaces where people work and live have increased carbon dioxide and exceed the limits that affect people.

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  45. Michael @44 , I must modestly disagree with you.

    Yes, there is a real concern about the adverse effect of high local ambient CO2 levels in classrooms, submarines, and other enclosed spaces.   A perfectly valid concern, for health and intellectual performance (and most especially the performance of crew in a nuclear-armed submarine ! ).

    But please read again through the O.P.  ~ and note the panicky crescendo in the final few paragraphs.   [quote] "... we may end up intellectually a lot closer to plants."

    Sure, that was an expression of dramatic hyperbole ~ but hyperbole more fitted to a rally of Extinction Rebellion adherents, than to the sober annals of SkepticalScience.   Even in the comments thread, some seem to have taken that apocalyptic message seriously.   And I am thinking the propagandists at WUWT  would take it even further, as an example of them thar crazy Alarmists.

    But I am not so much interested in the final paragraph, as in the build-up evident in those lattermost paragraphs.   Even in the sly reference to D.Zappulla,2013  ~ a reference which actually discusses effects at CO2 ambients in the range 5,000 - 30,000 ppm.   Golly !

    The O.P. starts with matters of technical interest . . . but then gradually slides into unwarranted alarmism.   And it entirely fails to mention the human body's well-evolved compensation system [the kidneys].

    I do not wish to see the O.P. deleted  ~ but suggest a prominent CAUTION for the casual reader.

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    As various people have remarked (thanks to all for your productive and tactful critique) this article's overall theme and especially conclusory speculation do not seem sufficiently supported by citations of directly pertinent literature. We're taking a closer look at the topic so as to formulate a responsive, fair and kindly means of remedy

    Update: article is now caveated with points of concern via editorial note.
    . --Skeptical Science Team

  46. Skeptical Science Team, Eclectic @42, et. al, 

    Recent paper by P. Bierwith (2024)*  notes, "There is now substantial evidence that permenant exposure to CO2 levels in the future will have significant effects on humans." The article goes on to summarize recent findings; all of which generally support the subject article here.  I find though the article does contain a few "technical errors" as it was written with the knowledge as it was best known a few years back, it is in no way unnecessarily "alarmist."  The problem I believe is that to some the subject itself is "alarmist", and in truth it should be. 

    To address Eclectic's concern a bit more succinctly; the human body's CO2 compensary mechanisms have been considered in the papers being questioned. Basically, though the body can compensate for very high levels of CO2 for short periods of time, eventually these mechanisms will "give out" over time as one is continually immersed in even mildly elevated levels of CO2; the effect becoming noticeable around 800-1200 ppm. The general effects are bone dimeneralization, calcification of soft tissues, and neurological agitation which will give rise to a range malidies not favorable for human health and well being.


    *P. Bierwith, (2024), "Long-term carbon dioxide toxicty and climate change: a critical unapprehended risk for human health. Australian National University.

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  47. Res01 @46 : thank you for resuming the conversation of 2023, and the mention of the new [2/2024] paper by Dr P. Bierwirth (please note the second "r" in Bierwirth).

    His 2024 Abstract quotes: "Protein malfunctions in cells due to elevated CO2 and associated low pH has [sic] the potential to cause threats to life including cancer, neurological disorders, lung disease, diabetes, etc.      ... overexpression of carbonic anhydrase, the enzyme that catalyses CO2 in the body, causes calcification in the kidneys arteries and tissues, along with other diseases and this may be an existential threat."

    Please excuse my adding of underlining emphasis, in the above.  The body of the paper does not really add much, I think, to earlier comments on the topic.  # It is all rather breathless [please forgive my feeble attempt at a pun, of sorts].

    Looking at the bigger picture, we see that the dinosaurs survived millions of years of "high" ambient CO2.   Were their bodily proteins shaped by evolution to perform satisfactorily at high CO2 levels ~ or did their kidneys simply compensate for high CO2 ?   We don't know ~ and yet we know that the dinosaurs did survive and thrive.

    Is there any experimental evidence to support Dr Bierwirth's gloomy comments about long-term CO2 exposure?   # Well, for what it's worth, there is a 3-month study in mice, by C. Wyrwoll et al (2021).  Gestation through to 3-months of age.   Despite some slight ambiguity in the Abstract, they quote: "There were no clear anxiety, learning, or memory changes.  Renal and osteological parameters were minimally affected."  [my emphasis]


    If there be some clear-cut evidence of failure of the mammalian body to make (renal or other) adjustment/compensation in high ambient CO2, then I would be pleased to learn of it.

    At SkS , we all know the potential of increasingly severe adverse effects of higher atmospheric CO2 levels.  But these dangers are terrestrial, rather than physiological, for mammals.

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  48. On reflection, I believe my @47 comments (on Dr Bierwirth's paper) were lacking the bluntness that our readers deserve.

    His 2024 Abstract shows a notable Red Flag, in his mention of the phrase "existential threat"  ~ a phrase which is not only rather panicky, but is fashionably overused nowadays for subjects ranging from imminent nuclear holocaust . . . through to a possible world shortage of cocoa.

    A second Red Flag is his lengthy laundry list of "potential"  threats of a wide range of nasty diseases ~ cancer; calcification in the kidneys; diabetes; etcetera.

    A third Red Flag is his attribution of all these diseases to a combination of elevated CO2 in association with  low pH.   Actually, such a combination is a brief/transitory situation when CO2 is high  ~ for (as I and others have pointed out, earlier in this thread) the body's kidney function does correct the low pH in the medium & long term.

    Which leaves us with his dubious claim about "protein malfunctions".

    In short, it seems Dr Bierwirth paints with a very broad brush and also draws a very long bow.   Not only that ~ but some of his other papers seem to have a similar flavor.

    All well and good if Dr Bierwirth has supportive evidence ~ but for the meantime, I think we should all remain most skeptical.


    # Obviously, we cannot expect controlled experiments in humans with exposure to years of elevated ambient CO2.   The mouse experiment (mentioned above) was a controlled study using mice in 890ppm CO2 versus mice living in half that level.   The gestation & first 3 months of life might perhaps equal 5 - 10 years of human equivalence.   Still, it is only about 110 days in absolute terms ~ and that might explain the absence of adverse findings in the "high CO2" mice, despite the rapid pace of mouse physiology.

    And that fits with other evidence, of mice and men . . . and dinosaurs. 

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