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Current and Rising Atmospheric CO2 Concentrations Pose No Threat to Human Health

By -- October 3, 2022

“… breathe easy. Atmospheric CO2 is not causing, nor will it ever cause, and direct threat to your health or cognitive performance.”

Almost all trace elements and compounds, even beneficial ones, can be poisonous if ingested or inhaled in large enough concentrations. So, what about carbon dioxide (CO2)? Do we have to worry about any deleterious health effects as its atmospheric concentration continues to climb?

As an answer to the above questions, consider the work of the following four research teams, two of which focused on human physiological responses to elevated levels of CO2 and two of which focused on human cognitive responses.

Liu et al. (2017)

Liu et al. (2017) examined the performance, acute health symptoms and physiological responses of human subjects exposed to both ambient (403 ppm) and elevated (3025 ppm) atmospheric CO2. Measured physiological parameters included skin temperature, eardrum temperature, heart rate, blood pressure, end-tidal partial CO2, arterial blood oxygen saturation and body weight. Respiratory ventilation rate was also calculated, and biomarkers in the subject’s saliva were measured to test for stress-related changes in their bodies.

Additionally, the subjects were assessed for their “thermal sensation, thermal comfort, acceptability of the thermal environment, acceptability of the air quality, odor intensity, sleepiness, self-estimated work performance and the intensity of dry nose, dry throat, aching and dry eyes, and dry skin, as well as headache, difficulty in concentrating and thinking clearly, wellbeing, mood, fatigue and dizziness.” When all was said and done, the authors’ analysis revealed “increasing [the] CO2 concentration to 3000 ppm at 35°C did not cause changes in any of the measured responses.”

Publishing their work in the journal Advances in Experimental Medicine and Biology — Neuroscience and Respiration, Monsé et al. (2019) investigated the physiological effects of long-term exposure to elevated CO2 in miners who had experienced repeated exposure to high CO2 levels on a regular basis. In all, 93 miners were examined for the study. Each worked in the potash mines of the Werra-Fulda district in Hesse, Thuringia and Saxony-Anhalt in Germany for a minimum of two years. All miners underwent medical examinations directly before and after underground shifts that subjected them to CO2 levels ranging from near-ambient to 15,000 ppm. Specific examinations included testing of thoracic and abdominal organs, laboratory analyses of blood, urine and lung function.

Results of the medical examinations, in the words of the authors, “failed to reveal any signs of acute and chronic health hazard of potash mining related to [elevated levels of CO2 in] the workplace.” More specifically, they report that “there were no pathological alterations or short-term adverse effects of CO2 exposure” on blood gas content, adding that “all measured values remained within reference values.” Additionally, they found “no evidence of any appreciable influence on lung function of CO2 exposure in potash miners, nor any pulmonary impairment comparing pre/post work shift conditions regardless of the [CO2] exposure severity.”

Rodeheffer et al. (2018)

Focusing on the influence of acute exposure to high levels of atmospheric CO2 on human cognitive performance and decision making, Rodeheffer et al. (2018) exposed 36 submarine-qualified sailors at the Naval Submarine Medical Research Laboratory’s Genesis hypo/hyperbaric chamber to one of three atmospheric CO2 levels (600, 2500 or 15,000 ppm) over a period of approximately 2.5 hours.

Following a 45-minute acclimation period, the subjects participated in an 80-minute computer-administered test (the Strategic Management Simulation) that “collects performance and decision-making data through the presentation of simulated real-world scenarios” and which was developed to “measure both cognitive and behavioral responses to varying executive functioning task demands.” In addition, the participants completed a pre- and post-test air quality control questionnaire in which they were asked several questions regarding the quality of the test chamber environment.

In discussing their findings, Rodeheffer et al. report responses to their pre- and post-test questionnaires revealed perceptions of air quality did not significantly differ among the three CO2 exposure levels and that test subjects did not experience differences in their level of physical discomfort or alertness. With respect to the results of the Strategic Management Simulation (SMS) tests, the four scientists report that statistical analysis of the means across the three test conditions showed “no trends or indicators that performance was at all affected by elevated CO2 exposure,” adding that the test subjects “did not experience any deficits in decision-making ability, as measured by performance on the SMS test.”

Thus, at values more than 36 times the present CO2 concentration of the atmosphere (15,000 ppm) scientists were “unable to detect any decrements in decision-making performance.” And in commenting on their findings, Rodeheffer et al. say they are “in concurrence with more recent research reporting null effects at low-to-moderate levels of CO2 on both the SMS test (Ryder et al., 2017) and on traditional measures of cognitive and neurobehavioral function (Zhang et al., 2016a; Zhang et al., 2016b).”

Scully et al. (2019)

Finally, in another study searching for a link between cognitive performance and CO2 levels, Scully et al. (2019) tested the mental acuity of 22 “astronaut-like” male and female subjects to four different CO2 concentrations (600, 1200, 2500 and 5000 ppm), subjecting them to standardized decision making and cognition tests (the Strategic Management Simulation and Cognition test batteries) routinely conducted on astronauts at the Johnson Space Center.

According to the authors, the experiment revealed “there were no clear dose-response patterns for performance on either [the] Strategic Management Simulation or Cognition” evaluations. More specifically, they report that “performance on most Strategic Management Simulation measures and aggregate speed, accuracy and efficiency scores across Cognition tests were lower at 1200 ppm than at baseline (600 ppm); however, at higher CO2 concentrations performance was similar to or exceeded baseline for most measures” (see Fig. 1).

Figure 1. Mean ± 95% confidence intervals of percentile ranks for Strategic Management Simulation measures at targeted CO2 concentrations. Source: Scully et al. (2019).

Consequently, when considering the full range of CO2 values examined, they conclude that “performance across tests did not differ between baseline (600 ppm) and the higher concentrations.”


The above findings demonstrate that rising atmospheric CO2 levels represent no current direct threat to human health and/or cognitive performance and decision making. And, they will present no realistic threat in the future either; for CO2 levels would need to increase some 36 times above the present concentration before they would even begin to pose a mild health concern. And that value (i.e., 15,000 ppm) will never occur, given it is a factor of ten above the approximate 1500 ppm atmospheric CO2 limit that scientists think is possible if society utilized all of the currently-known fossil fuel reserves on the planet.

So breathe easy. Atmospheric CO2 is not causing, nor will it ever cause, and direct threat to your health or cognitive performance. This is why carbon dioxide has never been considered a criteria pollutant.



Liu, W., Zhong, W. and Wargocki, P. 2017. Performance, acute health symptoms and physiological responses during exposure to high air temperature and carbon dioxide concentration. Building and Environment 114: 96-105.

Monsé, C/. Jettkant, B., Schramm, B.K.H., Broding, H.C., Knappe, M., Michl, M., Hoffmeyer, F., Sucher, K., Brüning, T. and Bünger, J. 2019. Effects of exposure to carbon dioxide in potash miners. Advances in Experimental Medicine and Biology – Neuroscience and Respiration 42: 1-10.

Rodeheffer, C.D., Chabal, S., Clarke, J.M. and Fothergill, D.M. 2018. Acute exposure to low-to-moderate carbon dioxide levels and submariner decision making. Aerospace Medicine and Human Performance 89: 520-525.

Ryder, V.E., Scully, R.R., Alexander, D.J., Young, M., Thomas, G., et al., 2017. Effects of acute exposure to carbon dioxide upon cognitive functions. 2017 NASA Human Research Program Investigators’ Workshop; 23-26 Jan. 2017; Galveston, TX. Houston (TX): NASA Johnson Space Center.

Scully, R.R., Basner, M., Nasrini, J., Lam, C., Hermosillo, E., Gur, R.C., Moore, T., Alexander, D.J., Satish, U. and Ryder, V.E. 2019. Effects of acute exposures to carbon dioxide on decision making and cognition in astronaut-like subjects. Microgravity 5: 17; https://doi.org/10.1038/s41526-019-0071-6.

Zhang, X., Wargocki, P. and Lian, Z. 2016a. Human responses to carbon dioxide, a follow-up study at recommended exposure limits in non-industrial environments. Building and Environment 100: 162-171.

Zhang, X., Wargocki, P., Lian, Z. and Thyregod, C. 2016b. Effects of exposure to carbon dioxide and bioeffluents on perceived air quality, self-assessed acute health symptoms and cognitive performance. Indoor Air 27: 47-64.

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