Abstract
The period in question lasted around ten millennia, from 21 000 to 11 600 years before present (BP: before present). It was long enough for slow variations in the Earth's orbit to have had an influence on climate. Indeed, the geometry of the Earth's orbit and its position during its annual revolution evolve according to cycles linked to the attraction of the Sun and other planets. The eccentricity of the orbital ellipse varies according to cycles of around 100 000 and 400 000 years. Obliquity, i.e. the angle of inclination of the Earth's axis of rotation in relation to the ecliptic plane, follows a cycle of around 41 000 years. Climatic precession, expressed by the angle between the position on the orbit of the spring equinox and that of perihelion, the closest point to the Sun, varies with periods close to 19 000 and 23 000 years. As the Earth-Sun distance is modulated by eccentricity, the climatic precession parameter takes both orbital parameters into account.
These variations in the geometry of the Earth's orbit combine to produce seasonal and latitudinal variations in insolation. These fluctuations in regional and seasonal insolation are the primary cause of the glacial-interglacial cycles of the Pleistocene epoch. The Pleistocene-Holocene transition is characterized by an increase in summer insolation at high latitudes in the Northern Hemisphere. Around 11 500 years BP, maximum obliquity and minimum Earth-Sun distance at the summer solstice favored the melting of ice caps in North America and Europe.
The glaciations had a huge impact on the global carbon cycle, which responded by lowering atmospheric levels of greenhouse gases such as carbon dioxide, methane and nitrous oxide. Covariations inCO2, CH4 and N2Ohave amplified glacial cycles, particularly deglaciation phases such as the last one before the Holocene.
