If Earth were deglaciated, it would have overall higher biodensity, despite the fact that the land area would be smaller.
It might have better biodiversity as well, although a colder Earth could also generate that... it certainly creates more varied ecozones.
The problem isn't the climate, but the climate
change.The disruption to the environment is the problem, not the environment itself.
During those past periods of climate instability, life had all the time and an entire world in which to find new survival solutions.
You don't have an entire world to find 'survival solutions' if your habitat disappears off the face of the map.
We've pretty much penned in or fenced out anything that can't live alongside us, We're quite an obstacle that life hasn't had to contend with before.
I think you overestimate physical human footprint on the planet. It isn't like there's "cities, no wildlife" and "farms, no wildlife" and then "postage-stamp sized pieces of land- wildlife".
When the climatic chips are down we'll eat anything that moves and there's a lot of us on this planet.
When the 'climatic chips' are down, I can think of a lot of things humans could eat... wildlife really isn't in the top items on the list.
Unless perhaps you are in a severely third-world nation.
