The world has changed.
Humans may not have had the power to change the globe so drastically on our own, but we didn’t really need to. We just needed enough power to start the process. Feedback loops did the rest, including many that we never even recognized before we set them into motion, pushing the world quickly into a new equilibrium. Global temperatures have risen dramatically, the ice caps have melted, and the seas have risen 216 feet, carving out new coastlines.
The feedback loop kept on intensifying until the cloud regime itself broke down. The new cloud regime that immediately began to form covered most of the earth in clouds most of the time, reflecting much of the sun’s heat and finally beginning to stabilize the rising temperatures. It rains a great deal more, as the new, hotter earth evaporates more water into the atmosphere. Powerful storms occur more frequently, and often rage longer and more violently.
Life has proven most resilient, though. Great evolutionary leaps tend to follow mass extinctions. Warmer climates and increased rates of mutation can spur faster evolution as well. The end of the old world brought all three at once. Four hundred years might not leave enough time for plants and animals to change drastically, but the incredible changes in bacteria and fungi can still have profound effects. What happens when one species of fungus begins to metabolize radioactive material? Or when the bacteria living inside one species’ guts evolve to digest plastic?
In accordance with Bergmann’s rule, warm-blooded animals (including humans) have gotten somewhat smaller in this warmer world, while the increased carbon dioxide in the atmosphere has provided for more plants, which in turn have put more oxygen into the atmosphere, allowing insects and reptiles to grow much larger.