Re: Personally, I wish someone would follow through on the other side of the story...
Our goal is survival, just like any other lifeform. Luckily, along with rats and cockroaches, we are exceptionally good at it. That's why we're the most widespread species and most numerous of comparable size in planetary history. Even Lystrosaurus didn't dominate its ecosystem the way we do.
I completely agree that the current interglacial works well for humans (our variety at least), but that's not a stable state. Left to its own devices, in a few millennia, the interglacial would end, and major glaciation would sterilize Northern Europe and North America all over again. Our accidental climate engineering may be postponing this (a logical corollary), but (as far as I know), the error bars on the models for all this are very wide and the end game may still be the same.
The best course of action for a planetary dictatorship of philosopher-kings, serving the interests of the species and unmoved by the parochial concerns of current generations and national borders is as obvious as it is irrelevant. That's not the geopolitical system we have, and no system we do have (especially not a democracy) is ever going to behave that way.
That being the case (premise), how do we adapt? We can (and did) live from the Arctic to the middle of the Sahara without the support of modern technology and trade. I simply cannot take seriously the suggestion that the mid-Eocene (extreme, verging on hyperbole given the models) would be beyond us.
I think more discussion and consideration of this possibility would be useful, without it jumping overboard into histrionics at the first opportunity.
What do I mean by that? Well, if you wipe out 99.999% of the human population you are *not remotely close* to achieving an extinction. See "Toba Catastrophe". Even if that causal theory is wrong, the genetic signature is clear: something shrank the effective human population to the ten-thousands in that (very recent) timeframe and we're back to 8bn today.
We are not going extinct by our own hand. We aren't smart enough. We are also not going to stop climate change. We aren't united enough. But what we are smart enough to do (I contend) is survive anything we are capable of causing.