We should remember that even during the adjacent times (the Paleocene and Middle Eocene) temperatures were about 8C higher than they are now, and large mammals (some of the largest ever) evolved during those times.

The decrease in size probably had more to do with the chaos wrought by whatever unknown event caused the thermal maximum than with the temperature itself.

To make this all more relevant: I'm not saying that climate change won't be disruptive. It will. I'm just saying we can adapt and endure. And I think we should plan for that, because we clearly aren't going to stop it.

It is interesting that with climate change, the public debate is mostly about 'is it man-made?' as if it'd just become a non-issue if it was. It's debating a fundamental point while we need practical solutions or even just concepts to cope with all sorts of interconnected problems on the entire spectrum of what we as humans are able to address - from microorganisms to geopolitics. While at this point, nobody is sure what will happen, societies will get a clearer picture of the imminent consequences over the next decades. At the moment, everyone seems to be waiting.