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There was a study which focused on pilots...

https://www.hsph.harvard.edu/news/press-releases/carbon-diox...

The results are very interesting to say the least:

The findings showed that the pilots were 69% more likely to receive a passing grade on a maneuver when CO2 levels were 700 ppm compared with 2,500 ppm. When CO2 levels were 1,500 ppm, the pilots were 52% more likely to successfully perform a maneuver than when CO2 levels were 2,500 ppm. When the researchers compared the difference in pilot performance at 700 ppm and 1,500 ppm, the difference was not statistically significant, but they did find that pilots were more likely to successfully perform some of the most difficult maneuvers at the lower CO2 level. The study also found that the negative effects of CO2 on flight performance became more pronounced the longer the pilots were in the simulator.