An anonymous reader writes: Is there a CO2 — level sense that says “be calm, you sleep in a chamber”, “be active, you are outdoors”, similarly to the circadian rhythm? Or is it because atmospheric CO2 makes the blood PH decline sharply already? A study says “the exposure — response between CO2 and cognitive function is approximately linear across the concentrations used in this study,” which were in the range 500 ppm — 1500 ppm. 600 ppm is exceeded already in large cities and prognosed everywhere in several decades. Is the coal industry going to make the idiocracy real?