Looking at the CO2 concentration per year chart: how long until we've got Spaceballs' "Perri Air" to avoid cognitive impairment? Anyone already experimenting with getting their indoor air closer to the (extrapolating a bit) ~250-280PPM of the pre-industrial atmosphere? This'd be a step farther than people who vent in outdoor air to keep indoor air from creeping even higher due to respiration and such.
Ventilation (or lack of it, due better sealing that prevents continuous ventilation through cracks) will have much more impact than background concentration.
