"As levels of carbon dioxide rose from 550ppm to 945ppm to 1400ppm, subjects’ scores under most headings declined substantially. (Problem-solving ability also seemed to suffer as levels of volatile organic compounds rose.)"
"2,000-5,000 ppm: level associated with headaches, sleepiness, and stagnant, stale, stuffy air; poor concentration, loss of attention, increased heart rate and slight nausea may also be present. > 5,000 ppm: This indicates unusual air conditions where high levels of other gases also could be present."
"Based on preliminary analysis, the global average atmospheric carbon dioxide in 2020 was 412.5 parts per million (ppm for short), setting a new record high amount despite the economic slowdown due to the COVID-19 pandemic."
hmm