co2 material safety data sheet says 5000 ppm is max allowable for an 8 hour work day. [1]
co2 levels (appear to) have a direct impact on cognition [2], specifically strategy and information usage.
Ecoene had levels around 2000ppm. It'll be interesting to see if we overshoot or undershoot. Sensitive people start noticing effects at around 1k, perhaps as high as 2k for insensitive people. 2-5k "Headaches, sleepiness and stagnant, stale, stuffy air. Poor concentration, loss of attention, increased heart rate and slight nausea may also be present." [3]
I don't think there have been any studies of long term exposure to 2k+ ppm (with no recovery time). as far as i know, nobody has to deal with that level of exposure for months or years. It's likely not good. But, as you say, not Venus.
[1] https://www.airgas.com/msds/001013.pdf
[2] http://ehp.niehs.nih.gov/15-10037/
[3] https://www.kane.co.uk/knowledge-centre/what-are-safe-levels... (not a great source, but plausible)
Have we really reached the point where it's necessary to claim political correctness before embarking upon a discussion?
Do you think it's necessary in order to have your opinion taken seriously, or to avoid moral opprobrium?
In geologic time frames, we are likely to be entering a domain where glaciation entirely disappears, including in Antarctica. The world was last here ~34M years ago, and sea levels were 200ft (60m) higher. I'm sure anyone reading this understands that this will have huge impacts on our day to day, including the drowning of most of the today's population centers.
(If anyone is curious, research the Eocene, the era that likely has the best predictive power for what will be happening to our climate over the next few thousand years). Just imagine it running in reverse, at a greatly accelerated rate.
And if you're wondering how we might avoid this fate, from an engineering perspective we need to recreate something like this: https://en.wikipedia.org/wiki/Azolla_event