the climate has always changed.... it is a natural occurrence

About 40 million years ago this area, which is today called Wadi Al-Hitan (or “Whale Valley”), was underwater and populated by early whales like this Basilosaurus. Basilosaurus was up to 18 metres long and was the first whale to reach truly gigantic size and become fully adapted to the watery world, having evolved from a terrestrial ancestor.

Always has. Climate fluctuation is the main driver of all extinction and evolutionary events.

Pretty sure it started when the earth was a ball of molten stone being bombarded by asteroids.