Paper Reviewed
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.

From time to time, concerns emerge in the global warming debate that rising atmospheric CO2 is directly harming human health and/or impairing cognitive performance. In a prior review we addressed the former concern by highlighting the work of Liu et al. (2017), who evaluated acute health symptoms and physiological responses of human subjects exposed to carbon dioxide levels of 400 and 3000 ppm, finding no adverse link between them. In the present review we examine the latter claim by analyzing the work of Rodeheffer et al. (2018), who investigated the influence of acute exposure to high levels of atmospheric CO2 on human cognitive performance and decision making.

The work was conducted on 36 submarine-qualified sailors at the Naval Submarine Medical Research Laboratory's Genesis hypo/hyperbaric chamber, in which test subjects were exposed 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 that responses to their pre- and post-test questionnaires revealed that 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, even at values more than 36 times the present CO2 concentration of the atmosphere (15,000 ppm) Rodeheffer et al. were "unable to detect any decrements in decision-making performance."

In commenting on their findings, the researchers 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)." Consequently, it would appear that society has little to fear with regard to the impact of elevated levels of atmospheric CO2 on human cognitive performance and decision making. There simply is no negative impact!

References
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.

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.

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.