...that I remember when atmospheric CO2 was under 300ppm.

. . . by which I mean any of our species.

...I think that our species will survive. We are very clever individually and in small groups. If Earth can sustain life, there will be people who figure out how to survive, imo. It may not be many and they may be (almost certainly will be) miserable, they'll survive.

That said, not sure that people in 2150 or 2300 will be doing much work on tracking atmospheric trace gases, or will even remember how that works.

And the last pound of each ton we emit won't be absorbed by natural systems for +/- 25,000 years - data points that seem to get, uh, overlooked, in press release "news" about "carbon sequestration" and "direct air capture".