They might thrive, if and only if, they can move to an area where they have their needed heat, water and light exposures. If atmospheric CO2 is 5x or 10x everything will need to be migrating an awful lot of miles northwards. To soils and locations that may not be suitable for ph or mineral reasons. Plants almost certainly can't migrate fast enough for current rates of change, let alone more. So there's agriculture screwed.

At or above 1,000ppm, or 2.5x current outside levels, human performance starts to decline. People will complain of drowsiness and stuffiness. Those levels can occur in buildings already. I don't look forward to a future where opening a window for fresh air delivers stuffiness, and inside buildings rise commensurately.

Who knows how many pollinating species will go extinct, and at what levels, as they can no longer breathe enough to fuel their activities.