This was a true warm period. Most of the ice was melted. Polar bears became grizzlies again. Toronto was like Florida. The tropics were as hot as ever. No mass extinctions, humans were happily evolving.
All this was done by ocean currents. Not a speck of carbon being burned. Yet, the article goes on only about coastal cities being drowned if this were to happen now. Most likely co2 was a bit higher because of the warm water, and that's why life thrived.
ps. polar and grizzly bears are like coyotes and wolves in Ontario. They regularly split and merge.