55 million years or so ago, the Earth got darn hot for 150 K years or so. Probably due to CO2. Anyway, a bunch of species went extinct, but others just got smaller. I can see that happening with our current warming episode. I picture a future with tiny people - I imagine them as looking a bit like hobbit sized versions of David Brooks or Lumo. The tall descendants of basketball players and my line will have gone extinct.
The human species might bifurcate in two, the peaceful descendants of liberals and hippies living above ground and eating flowers. The conservatives will have moved underground, out of sight of Sun and Moon, and will be called Morlocks, or if you want them to rhyme with the flower people, the Eloi, just call them Luboi.