[supergauntlet]

The GP obviously doesn't mean that 1000+ ppm CO2 is toxic, they mean that the changes to the environment it would cause are less than ideal for humans to thrive.

[shawnb576]

1000ppm decreases human cognitive ability by ~20%. It's hard enough to deal with these problems with the brainpower we have.

[1] https://ehp.niehs.nih.gov/doi/10.1289/ehp.1510037