Again: During past, intense periods of global warming, why didn't allegedly positive feedbacks turn the Earth into a permanently uninhabitable fireball?

Giant Fossil Ants Linked To Global Warming - insciences

During the Eocene Epoch, many plants and animal species migrated between Europe and North America via continuous land across the Arctic, bridging the two continents. But the mystery is how did these ancient giant ants pass through a temperate Arctic climate — too cool for them?

The researchers suspect that the key is in the brief, but intense episodes of global warming that happened around this time. They appear to have created periodic opportunities for hot climate life to pass between continents through the Arctic. Archibald calls them brief openings of a physiological gate to cross the physical land bridge.