Most of the cognitive work is done inside buildings, where concentrations are higher anyway, so looking at atmospheric CO2 is almost irrelevant. You can have a

Most of the cognitive work is done inside buildings, where concentrations are higher anyway, so looking at atmospheric CO2 is almost irrelevant. You can have a properly ventilated building at 1000 atmospheric CO2, and end up with an indoor concentration of 1200ppm; likewise many buildings today have concentrations of 2000+ppm with atmospheric CO2 hovering around 400. That's not to say it's not going to get worse and much worse. But it will take a few human generations to get to that point.