I don’t need to look at studies in other people, I notice and feel the effects directly at high CO2 levels, such that I can tell when it it too high before checking the meter.
I’d need to look at the study, but I also suspect the submariners would be used to high CO2, and also not experienced enough in doing focused creative or knowledge work for impaired abilities there to be detectable.
Please consider the possibility that you can accurately detect increased CO2 (it increases your breathing rate almost instantly for example) without it causing impairement.
Even if you are right and there is no objectively measurable impaired abilities, the things I can detect directly are themselves extremely undesirable.
I feel irritable, and fatigued/sleepy when CO2 is high. Increased breathing rate by itself activates an undesirable sympathetic nervous system response, that anyone can notice immediately with deliberate breathwork.
Also, it seems likely to me that the same poor air exchange that leads to high co2 causes respiratory disease to spread more rapidly, and with a higher initial viral titer.
I’d need to look at the study, but I also suspect the submariners would be used to high CO2, and also not experienced enough in doing focused creative or knowledge work for impaired abilities there to be detectable.