I’m sure there are a handful of species that will be well placed to rapidly increase in population, but it seems like that would be the exception not the rule. Not only does the species itself need to withstand the higher temps and acidity, its food chain does as well (or it needs a replacement food chain that does). What about its predators and the rest of the ecosystem? If they aren’t keeping pace then you can have runaway population growth which causes its own issues (e.g. algae bloom induced dead zones).
The rate of change is just so fast relative to what evolutionary biology generally has to deal with. These things usually play out over thousands or tens of thousands of years, not decades.
Historically, half the population died in infancy or childhood. They didn’t reproduce. Another significant chunk of the population, in Christian countries at least, became priests, monks, or nuns and mostly didn’t reproduce. Genetic diversity got along just fine.
This. While indeed life, uh, finds a way, it’s often on timescales that are an eternity compared to human society.
In the meantime, there can and has been mass extinctions.
Yes. The mere fact a new ecological niche opens up doesn’t mean it gets filled soon. It will get filled eventually, but “eventually” can be measured in millennia.
A similar thing happens with a volcanic eruption. The phrase “rich volcanic soil” is practically a cliche. Lotta folks don’t realize that that soil takes a few hundred to a few thousand years to develop from the shiny fresh just-cooled lava. Happens faster in wetter climes, and slower in dryer ones.
If an eruption buries your farm, you won’t be growing anything on that land again. Nor will your descendants be for a very long time.