His point is that irrespective of what we do now, (including population reduction and immediate adoption of a zero carbon economy) we’ve passed the point of no return for some of the macro global feedback systems.
Notably this includes melting permafrost greenhouse gases, which makes anthropogenic global warming inputs look like a drop in the ocean.
I don’t fully share his completely apocalyptic view, but I suspect in a few hundred years time competition for diminishing/ unavailable resources will make the earth a pretty unrecognisable place if we were to look at it from our current viewpoint. Perhaps we’ll see a genetic bottleneck of our own making in the future?
Planet will be fine of course, and life will most certainly find a way, but it might not be our life.