/ co2

CO2 is Poison

You may have seen the recent report about surpassing 400ppm for good. You've certainly heard about how CO2 is the main culprit behind climate change. Odds are you haven't heard that the greatest threat from rising carbon dioxide levels may in fact be to our health.

To be clear, CO2 is poison (just like Oxygen or water are) at high enough levels. The trick is figuring out what levels (and for how long) cause a detrimental health effects in humans. Perhaps you remember the tense scene in Apollo 13 where Houston has to figure out a way for the astronauts to scrub the gas from their crippled capsule. High levels of CO2 cause something called hypercapnia (what NASA was so worried about) that causes a variety of symptoms eventually leading to death. Fortunately for those of us here on earth (and not living in submarines - this is also a concern for the US Navy), hypercapnia is very rare and only occurs at extremely high levels. OSHA has stringent recommendations on safe levels of exposure to avoid the disease. But what about health effects at lower levels?

For most of human history, CO2 was only 280ppm-320ppm, much lower than even the well ventilated averages of today over 400ppm. Cities have even higher levels due to weather patterns and greater amounts of traffic (500-600ppm is not uncommon). I myself run a CO2 measuring station (among other air quality markers) and see ranges from as low as 380ppm on a rare and very clear and breezy day to as high as 680ppm during less favorable weather conditions.

Indoors, the numbers are even worse. I have another CO2 measurement device indoors and I never see lower than 500ppm and often wake up to 1500ppm in my bedroom (even with a fan and some plants to help reduce this). My anecdotal findings aren't unusual and in fact may be on the low side. A Texas study found classrooms had an average carbon dioxide reading of over 1000ppm with many at 2000ppm and as much as a fifth over 3000ppm. The more you look into this data, the more you find that this is fairly typical for offices, homes, and the other places we spend most of our time.

Yeah, these levels are as much as 10 times higher than what we humans evolved to survive under, but they're a far cry from the 30,000+ ppm that concerns OSHA, right?

Well, yeah, but that's not the whole picture. For starters, extremely high levels are a concern for short periods of time, but the effect of carbon dioxide is cumulative in part, and extended exposure to lower levels can also have a detrimental effect. Up until recently, there was very little research in this area (extended exposure of low to midrange carbon dioxide levels) with most of it being limited to NASA and the US Navy looking for safe exposure levels for months long missions. The figure they ultimately came to was anything below 5000ppm was considered safe, though NASA had plenty of reports of astronauts complaining about headaches and feeling sluggish at levels much lower than that.

Well okay, that's much lower than the OSHA figures, but still not anything close to even the high readings in classrooms and indoor environments. Nothing to worry about, right? That was certainly the predominant feeling (and still is for much of the world today) until the past few years when a number of new pieces of research came out and revealed that CO2 levels not much higher than our current global average have dramatic impacts on our cognitive abilities (particularly decision making), affect our mental state, and may even be linked to increases in obesity, cancer, and other neurological conditions.

Health Risks

In the early '80's, doctors started noticing people working in certain buildings suffered from a variety of maladies including headaches, lethargy, lack of concentration, and general poor performance. These symptoms would disappear shortly after leaving the office/classroom/whatever in which these individuals came down with the problems. A flurry of explanations followed blaming the "disease" on everything from toxic mold to ADHD. Eventually, doctors and scientists narrowed the cause down to poor ventilation and termed the disease "Sick Building Syndrome." They concluded that a variety of poor air quality markers (VOCs, CH20, and particulates) were to blame and CO2 (which they knew was harmless below extreme levels) was simply used as a marker of how well ventilated the air was (below 600ppm was excellent, 600ppm-1000ppm was good, and so on).

While VOCs, CH20, and other pollutants are undoubtedly dangerous, recent studies seem to prove that the greatest impact may be from that "benign" gas CO2 - and it's only going to get worse.

One of the first alarming papers on the subject appeared in Medical Hypotheses in 2001 and was furthered by a follow up article in General Science in 2006. The paper begins with the alarming announcement that "to date, no one has considered that the rise in CO2 in the atmosphere is a direct threat to human life, i.e. the gas may well have long-term toxic effects." The paper's author, D. S. Robertson, makes a simple but terrifying point. Our blood must exist within a narrow pH range for human survival. Too alkaline and we develop alkalosis and too acidic we develop acidosis - both harmful and potentially fatal conditions. The concern is that rising CO2 levels has an almost linear relationship to the acidity of our blood. To illustrate this, examine figure 1 (data from Robertson).

The chart makes it abundantly clear that as CO2 levels rise (with 550ppm considered the absolute best case scenario), so will the acidity of our blood. What health conditions might this create? Well, mild acidosis can result in headaches, confusion, tiredness, tremors, restlessness, and sleepiness - all classic symptoms associated with short term exposure to elevated CO2 levels (beginning at about 600ppm for sensitive individuals and by 1000ppm for almost everyone). Oh, and medical science considers a pH of about 6.8 the lower limit for life. This may be a chart showing human extinction in the worst case scenario. Remember though, while this was published in a peer reviewed journal, it represents an extremist, contrarian view and should be taken with a grain of salt.

But of course it doesn't end there.

A 2013 study furthered the CO2 and pH link, and found that increased carbon dioxide levels are linked to osteoporosis (something predicted by Robertson in their earlier studies) as well as sleep apnea and even increased body fat. Yes, rising CO2 may be contributing to the obesity epidemic. Further studies have found links to reduced fertility, asthma, and even erratic behavior. One study found that CO2 levels of 1000ppm and higher can cause biological changes similar to smoking.

But where the research really gets concerning is in a number of papers linking elevated carbon dioxide levels to drastic decreases in cognitive functioning. The first major publication in this area was a 2012 research study from Berkeley followed by a second larger, confirmatory 2015 study from Harvard which found a 15% average decrease in cognitive tasks performed at 940ppm vs 500ppm. The effect was even worse at 1400ppm with a 50% decrease in performance. Take a look at the results:

The baseline to take away from this? On average, a 400-ppm increase in CO2 was associated with a 21% decrease in a typical participant’s cognitive scores across all domains after adjusting for participant. That means as we climb towards 680ppm (probably by 2050-2075) which 400ppm above the pre industrial revolution levels, we will have decreased the cognitive capabilities of humanity by 21%. The effect is even worse considering most strategic decision making occurs within offices that have CO2 levels often above 1000ppm. This makes a brighter future where we innovate out of the mess we created seem less and less likely.

Little research has been done on how this affects young, still growing minds. But researchers have identified classrooms as a place of extremely high CO2 levels with 2000ppm being common and 3000ppm and above not at all rare. This may be responsible for behavioral issues, poor concentration, poor performance, and even absences according to several research papers. I'm not hopeful on whether developmental problems are being introduced.

Of course, the worst part of all this is that as global CO2 levels climb higher, it will prove harder to keep these interior levels low. Worst case scenario predictions expect us to surpass 1000ppm global average outdoor level by 2100 (and many scientists claim that this official number may even be too low). With new links to low level exposure CO2 toxicity constantly being made, it’s becoming increasingly clear that climbing CO2 levels aren’t just dangerous for increasing global temperatures (and the mess that goes along with that), but may be actively poisoning us directly.


Allen JG, MacNaughton P, Satish U, Santanam S, Vallarino J, Spengler JD. 2016. Associations of cognitive function scores with carbon dioxide, ventilation, and volatile organic compound exposures in office workers: a controlled exposure study of green and conventional office environments. Environ Health Perspect 124:805–812; http://dx.doi.org/10.1289/ehp.1510037 [PDF]

Bierwirth, P. N. "Effects of rising carbon dioxide levels on human health via breathing toxicity - A critical issue that remains unapprehended." (2015). Retreived from: http://grapevine.com.au/~pbierwirth/co2toxicity.pdf [PDF]

Fisk, William J.(2014). Is CO2 an Indoor Pollutant? Higher Levels of CO2 May Diminish Decision Making Performance. ASHRAE JOURNAL, 55, 3, 84-85, March 2013. Lawrence Berkeley National Laboratory: Lawrence Berkeley National Laboratory. LBNL Paper LBNL-6148E. Retrieved from: http://escholarship.org/uc/item/6gm6t5zc [PDF]

Hersoug, Lars-Georg, A. Sjödin, and A. Astrup. "A proposed potential role for increasing atmospheric CO2 as a promoter of weight gain and obesity." Nutrition & diabetes 2.3 (2012): e31. Retrieved from: http://www.nature.com/nutd/journal/v2/n3/full/nutd20122a.html [PDF]

Lu, C. Y., Ma, Y. C., Lin, J. M., CY, C., Sung, F. C., & Sung, F. C. Oxidative DNA damage in relation to indoor carbon dioxide, volatile organics and tobacco smoke exposures. Retreived from: https://www.researchgate.net/profile/Fung_Chang_Sung2 [PDF]

Lu, C.-Y.; Ma, Y.-C.; Chen, P.-C.; Wu, C.-C.; Chen, Y.-C. Oxidative Stress of Office Workers Relevant to Tobacco Smoking and Inner Air Quality. Int. J. Environ. Res. Public Health 2014, 11, 5586-5597. Retrieved from: http://www.mdpi.com/1660-4601/11/6/5586 [PDF]

Robertson, D. S. "Health effects of increase in concentration of carbon dioxide in the atmosphere." Current Science 90.12 (2006): 1607-1609. Retrieved from: http://co2gas.nethouse.ru/static/doc/0000/0000/0327/327646.l7oajaotz4.pdf [PDF]

Robertson, D. S. The rise in the atmospheric concentration of carbon dioxide and the effects on human health, Medical Hypotheses, Volume 56, Issue 4, 2001, Pages 513-518, ISSN 0306-9877, http://dx.doi.org/10.1054/mehy.2000.1256.
Retrieved from: http://www.sciencedirect.com/science/article/pii/S0306987700912568 [PDF]

Satish, U., Mendell, M. J., Shekhar, K., Hotchi, T., Sullivan, D., Streufert, S., & Fisk, W. J. (2012). Is CO2 an indoor pollutant? Direct effects of low-to-moderate CO2 concentrations on human decision-making performance. Environmental health perspectives, 120(12), 1671. Retrieved from: http://ehp.niehs.nih.gov/1104789/ [PDF]

Seppänen, O. A., Fisk, W. J. and Mendell, M. J. (1999), Association of Ventilation Rates and CO2 Concentrations with Health and Other Responses in Commercial and Institutional Buildings. Indoor Air, 9: 226–252. doi:10.1111/j.1600-0668.1999.00003.x. Retrieved from: http://onlinelibrary.wiley.com.proxy.library.nd.edu/doi/10.1111/j.1600-0668.1999.00003.x/abstract [PDF]

Sidorin, D.I. "Dynamics of carbon dioxide concentrations in the air and its effect on the cognitive ability of school students". Izv. Atmos. Ocean. Phys. (2015) 51: 871. doi:10.1134/S000143381508006X. Retreived from: http://link.springer.com.proxy.library.nd.edu/article/10.1134/S000143381508006X [PDF]

Shendell, D. G., Prill, R., Fisk, W. J., Apte, M. G., Blake, D. and Faulkner, D. (2004), Associations between classroom CO2 concentrations and student attendance in Washington and Idaho. Indoor Air, 14: 333–341. doi:10.1111/j.1600-0668.2004.00251.x Retrieved from: http://onlinelibrary.wiley.com/doi/10.1111/j.1600-0668.2004.00251.x/full [PDF]

Zappulla, Donatella. Air Pollution: Sources, Prevention and Health Effects., Edition: first edition, Chapter: The CO2 Hypothesis -- The Stress of Global Warming on Human Health: pH Homeostasis, the Linkage between Breathing and Feeding via CO2 Economy., Publisher: Hauppauge, N.Y: Nova Science, Editors: Sethi R., pp.293-313. Retrieved from: https://www.researchgate.net/publication/259791549 [PDF]

Zheutlin AR, Adar SD, Park SK. Carbon Dioxide Emissions and Change in Prevalence of Obesity and Diabetes in the United States: An Ecological Study. Environment international. 2014;73:111-116. doi:10.1016/j.envint.2014.07.012. Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4194141/ [PDF]

Photo by Mark Knobil released under CC BY.