Is the Evolution of Climate a Four-beat Waltz?

Considering the different forcing factors that drive climate evolution, we can divide Earth History in three periods. The first one - at a timescale of billions of years — for which the major forcing factor is the Sun luminosity. Its increase corresponding to 7% by billion years is crucial for the planet temperature, the hydrology and the carbon cycle. For the second one - at a timescale of tens of million years — tectonics is acting on both plate motion and carbon cycle (Ramstein et al. Tectonics, 2019). It is a pivotal parameter to explain climate changes. Last but not least, for the third one — at a timescale of tens to hundreds of years — the main factor driving climate is the evolution of the astronomical parameters on a timescale ranging from tens to hundreds of ka. All these timescales are embedded (Ramstein, Surveys in Geophysics, 2011) and the interaction of their respective evolution explains the regulation of climate throughout Earth's History except during short periods, such as the snowball Earth (Donnadieu et al. Nature, 2004; Ben et al. Nature Geoscience, 2015). We will discuss how the different regulation and feedback mechanisms have made the Earth habitable since 3.7 Ga (first imprint of life on Earth). These are the three classical natural periods of time of our complex system, which drive climate changes at geological time scale and they can be thought of as the beats in a three-beat waltz. Today, however, Humans have become a planetary climate forcing factor. In the last two centuries, fossil fuel combustion — by drastically and rapidly increasing the amount of GHG in the atmosphere — is deeply modifying the climate. It can be seen as the fourth beat of the waltz.