I don't see how it can be about oxygen. In the paper I linked, I think they directly add relatively pure carbon dioxide. And the total concentration is 0.1%. So the concentration of oxygen in the air is not really changing.
The texas natural experiment seems like an especially convincing complement to the more artificial setting, thanks for pointing it out.
If you look into this I will leave open the offer to buy certificates after the prize. So far not many takers on the prize, this comment is currently in the lead based on the literature review, not sure if there will be takers closer to the cutoff.
(aside from the sample size)
The sample size is small, but given the effect size I don't think it even matters that much. The error seems like less than a factor of 2.
taken at face value, with reasonable estimates of how much rooms differ from day to day or week to week, CO2 levels would explain a lot or maybe most of variability in IQ tests or cognitive performance!
This looks right to me (well "a lot," I don't think "most"), I assume that something is wrong. An obvious possible culprit is their cognitive test.
It's also unlikely to be about oxygen because oxygen levels that reach the brain in a healthy person depend almost entirely on the amount of saturated haemoglobin, which is 95-100% of Hb in someone without serious lung heart or haemoglobin defects. This means that variability in O2 availability is more dependent on one's iron level than breathing/air effects. (I disclaim that I haven't yet looked into literature about O2 chemistry and supply to the brain so may be wrong)
The CO2 hypothesis at least makes some sense because bloodstream CO2 levels vary a bit....
One or two research groups have published work on carbon dioxide and cognition. The state of the published literature is confusing.
Here is one paper on the topic. The authors investigate a proprietary cognitive benchmark, and experimentally manipulate carbon dioxide levels (without affecting other measures of air quality). They find implausibly large effects from increased carbon dioxide concentrations.
If the reported effects are real and the suggested interpretation is correct, I think it would be a big deal. To put this in perspective, carbon dioxide concentrations in my room vary between 500 and 1500 ppm depending on whether I open the windows. The experiment reports on cognitive effects for moving from 600 and 1000 ppm, and finds significant effects compared to interindividual differences.
I haven't spent much time looking into this (maybe 30 minutes, and another 30 minutes to write this post). I expect that if we spent some time looking into indoor CO2 we could have a much better sense of what was going on, by some combination of better literature review, discussion with experts, looking into the benchmark they used, and just generally thinking about it.
So, here's a proposal:
Some clarifications:
(Thanks to Andrew Critch for mentioning these results to me and Jessica Taylor for lending me a CO2 monitor so that I could see variability in indoor CO2 levels. I apologize for deliberately not doing my homework on this post.)