Wow I didn't realize that submarines and the ISS had such a high level of CO2. I feel noticeably worse when CO2 is above 2000ppm in my house. I've always wanted to have an artificial CO2 scrubber for when the windows are closed, but energetically I would probably be better off opening the windows and heating or cooling the air to compensate. Do submariners and astronauts have impacts to their cognitive abilities from this elevated rate?
Whether there are cognitive effects is not clear, but it definitely affects their mood and their sleep. It's a touchy subject since astronauts don't like to publicly complain. Scott Kelly talks about it pretty openly in his book; reading between the lines of tech papers on next-generation life support you get the impression that crews insist levels need to get below 2000 ppm for long-duration missions.
