CO2 is only 0.03 % of atmospheric air
(concentrations beyond 9%, which is 300 times the normal one in air!)
CO2, which usually is hardly toxic, can reach crazy levels : a quarter of a million tons in Cameroun 1986 Lake Nyos resulted in 2000 deaths by suffocation. This is because it can at very high partial pressures displace O2, hence reducing its concentration : death is more due to hypoxia than to hypercapnia.
VAAS is an anxiety/panic rating scale
All CO2 can induce, at 300 times the normal concentration, is slight anxiety
Pr J. Lovelock, key alarmist on climate change, admits in April 2012 "I made a mistake"