Cognition as a Function of CO2 Concentration

Background on CO2

There really hasn't been enough research on the cognitive impact of elevated CO2 levels. Right now, atmospheric CO2 levels are around 410 ppm, but the level inside buildings is often as high as 2,000 ppm, and inside aircraft can be as high as 5,000 ppm. Levels below 20,000 are very safe from having people suffer physical harm. OSHA requires workplaces to be below 5,000 ppm.

But people often feel less comfortable above 1,000 ppm, which is the level below which the US Navy tries to keep submarines.

According to the IPCC, in the RCP 8.5 "business as usual" scenario where we fail to make any effort at all to reduce green house gas emissions, we are expected to be at 1,200 ppm of CO2 in the atmosphere by 2100.

Research Papers:

Usha Satish et al, 2012

Usha Satish et al, 2012 found noticeable cognitive impairment at 1,000 ppm, but much more significant impairment at 2,500 ppm. No measurement was taken for CO2 levels between those two values. The experiment was done double-blinded, and care was taken to ensure that the only gas whose concentration varies was CO2. The experiment had only 24 test subjects, mostly university students.

Zhang and Wargocki, 2015

Zhang and Wargocki, 2015, with 25 test subjects, averaging 23 years old, conflicted with Satish et al.'s findings. The experiment was very similar, but they observed no significant cognitive impairment, even at 3,000 ppm, of CO2 alone. But they did find impairment when they elevated the levels of other gases that are normally present in rooms crowded with breathing human beings. It appears that perhaps the cognitive testing in this study may have been less thorough than that in Usha Satish et al.

Allen, Satish, et al, 2016

Allen, Satish, et al, 2016 was more in-depth than Satish et al, 2012. The number of test subjects was still only 24, but they weren't all college students this time, they were mostly professionals of a variety of ages. Tests were done on a range of CO2 levels from atmospheric to around 1,500 ppm, and showed that by 1,500 ppm, impairment was quite significant.


These 3 papers don't agree with one another, and all three of them have pretty small sample sizes. It may be that the study that failed to reproduce the result found by the other two was not testing cognition in as much detail. The results of 2 out of 3 are that anticipated RCP 8.5 "business as usual" CO2 levels by 2100 will be starting to inflict a cognitive deficit on the whole human race, many of whom are not terribly bright to begin with. This is a very, very important issue, and more studies with larger sample sizes are badly needed.

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Bill Chapman