Astronomical theory and orbital forcing

Berger, A. [UCL] Yin, Qiuzhen [UCL]

The Astronomical Theory of paleoclimates aims to explain the climatic variations occurring with quasi-periodicities situated between tens and hundreds of thousands of years. Such variations are recorded in deep-sea sediments, in ice sheets and in continental archives. The origin of these quasi-cycles lies in the astronomically driven changes of the latitudinal and seasonal distribution of the energy that the Earth receives from the Sun. Milutin Milankovitch extensively published about the theory between 1920 and 1950, but the relationship between the astronomical parameters, insolation and climate, had already been suggested in the early part of the nineteenth century. The evolution of ideas from the early times to the present day is reviewed, but most of this chapter deals with the calculation of the astronomical forcing, explaining both the long-term variations of eccentricity, obliquity and precession and their impacts on insolation. The behavior of the daily insolation is described and compared to the behavior of the insolation received during the astronomical and caloric seasons.