Discomfort only kicks in under more extreme conditions. We're talking about very mild asphyxiation that is not noticeable but degrades mental and physical perfo

Discomfort only kicks in under more extreme conditions. We're talking about very mild asphyxiation that is not noticeable but degrades mental and physical performance. CO2 outdoors has gone from about 280ppm to 420ppm in the last hundred years. If we kept going for another century it could approach 1000ppm, which is where you start seeing these effects. The scary question is whether there is any effect at 420ppm. We don't think so, but very marginal effects are hard to detect. Yet a global loss of an average of 5 IQ points would have significant large scale effects on society. It's also possible that it doesn't affect all people equally, since most things don't. There have been times in Earth's history where CO2 concentrations were in the thousands of ppm, but there were no humans then.