Climate of the Earth: a long term perspective from past to future.

This talk will be divided in two parts. We first we will discuss the regulation processes that made the Earth a habitable planet for 3.5 Billion years. We will explain how temperatures and hydrological cycles remained, most of the time, favorable to the evolution of life. Nevertheless, in this context, a few major accidents occurred, leading during a few Million years, to a "snowball" Earth. But, most of the time, the temperatures on Earth were warm, without any ice sheet. The evolution of more recent climate, since 40 Million years (part of the Cenozoic) is different. Paradoxically, apes and hominins developed in a very cold environment. Since 40 Million years, global temperatures and atmospheric CO2 decreased. This cooling led first to the Antarctica ice sheet onset (34 Million years) and very long time after to the Greenland inception (2.7 Million years). Between these two periods, we will show how climate changes drove the dispersal of our ancestors.  Haven more recently, the cooling has been enhanced since 1 Million years, with 80 % of the time, four ice sheets and a glacial climate. We are now living since 10 000 years in an interglacial period, with only two ice sheets. This warmer period only represents 20% of a glacial/interglacial cycle. Finally, we will discuss the long term (>100 years) possible impact of the human activity.