Now on all continents and islands most of the big animals and plants are humans, domestic animals and cultivated plants. The wild animals and plants, even if they are much more varied, with many thousands times more species than the domestic ones, are much smaller in quantities, with only a few kinds that are non-negligible, e.g. ants, termites, rodents.

So if we will return in a short time to the Paleogene climate, the main question is how this will affect the few dominant animal species, like chicken, humans, pigs, sheep, cattle, dogs and the main cultivated plants, all of which are not adapted to a Paleogene climate and which will not be able to adapt in such a short time.

It is likely that places like Canada, Alaska, Greenland, Siberia, Antarctica might become nicer places where to live and practice agriculture, but the few people who live now there would not welcome invaders coming from places that are no longer habitable.