In accommodation to my last question, we are now transferring from meteorology to ecology.
Today, tropical rainforests take up only 3% of the world's surface, yet they take up half of the plant and animal species (that we know of--if Blue Planet II were to be taken into consideration, it's that deep-sea habitats are not as barren as once thought.)
During the Eocene epoch, such habitats had filled up all of the Earth's continents. Today, half of the world's species varies in translation between three and 50 million species. Now, in an alternate Earth where the 21st century in the Common Era is as hot as it was 50 million years ago, what would happen to those 50 million species? Would they multiply into a higher number of new species? Or would the global jungle give those original 50 million more territory to claim?