Greenhouse and Icehouse Earth - Causes of Transition

Causes of Transition

During periods of transitions from greenhouse to icehouse, and vice versa, there has been much mass extinction across the planet ("99.99% of all life that has ever existed is extinct"). The Eocene, which occurred between 53 and 49 million years ago, was the Earth's warmest temperature period for 100 million years. However, this "super-greenhouse" soon became an icehouse by the late Eocene. It was believed that the decline of CO₂ caused this change, though there are possible positive feedbacks, or added influence that contributes to the cooling.

The best record we have for a transition from an icehouse to a greenhouse period where plant life exists is during the Permian Epoch that occurred around 300 million years ago. In 40 million years a major transition took place, causing the Earth to change from a moist, icy planet where rainforests covered the tropics, into a hot, dry, and windy location where little could survive. Professor Isabel Montanez of University of California, Davis, who has researched this time period, found the climate to be "highly unstable" and "marked by dips and rises in carbon dioxide".