This is perhaps the most terrifying idea I’ve encountered in the last 10 years. Humans evolved in a lower CO2 environment. Our lungs are adapted for optimal gas exchange in that environment. At what point do we start literally suffocating?

And this would creep up on us very slowly. Not only would we not notice, but we’d lose our ability to notice. It’d be like the whole species slowly descending into dementia.

Most of what I’ve seen suggest that the effect starts really kicking in around 1000ppm. But as outdoor levels rise, indoor levels, which are usually higher, rise too. They can already hit those levels.

If we keep burning more and more carbon outdoor levels could hit that by the 22nd century.

If we start getting here we need to put away the green moralistic finger wagging and start looking at ways to suck CO2 out of the air like it’s an emergency. Things like ocean seeding or huge scale industrial scrubbers powered by solar or nuclear power, or all of the above.

This is a far scarier possibility than just climate change. The only thing scarier than this is the clathrate gun, which luckily seems to be considered unlikely by most climate scientists (at least unless we get to really insane CO2 levels like thousands of ppm).