We also found effects of CO2 (a proxy for ventilation) on cognitive function. For every 500ppm increase, we saw response times 1.4-1.8% slower, and 2.1-2.4% lower throughput.
Which is why you open a window: Atmospheric CO2 is at around 410ppm. And rising, yes, by around 2-3ppm/a. So I suppose it's making us around 0.02% slower per year, going by those figures.
We need to curtail emissions, but not because atmospheric CO2 is affecting cognition.