Currently, the Earth is in an icehouse climate state. About 34 million years ago, ice sheets began to form in Antarctica; the ice sheets in the Arctic did not start forming until 2 million years ago. Some processes that may have led to our current icehouse may be connected to the development of the Himalayan Mountains and the opening of the Drake Passage between South America and Antarctica but climate model simulations suggest that the early opening of the Drake Passage played only a limited role, while the later constriction of the Tethys and Central American Seaways is more important in explaining the observed Cenozoic cooling.{Zhang, Zhongshi & Nisancioglu, Kerim & Flatøy, F. & Bentsen, M. & Bethke, I. & Wang, H.. (2009). Did the opening of the Drake Passage play a significant role in Cenozoic cooling?. } Scientists have been attempting to compare the past transitions between icehouse and greenhouse, and vice versa, to understand where our planet is now heading.