Regensburg 2007 – wissenschaftliches Programm

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SYEE: Symposium Energy and Extraterrestrial Influences on the Climate

SYEE 1: Symposium: Energy an Extraterrestrial Influences on the Climate

SYEE 1.2: Hauptvortrag

Dienstag, 27. März 2007, 10:15–11:00, H46

The Astronomical Theory of Palaeoclimates — •Michel Crucifix — Institut d’Astronomie et de Géophysique Georges Lemaître, Université catholique de Louvain, 2, Chemin du Cyclotron, B-1348 Louvain-la-Neuve, Belgique

Links between climate and Earth’s orbit have been proposed for about 160 years. Two decisive advances towards an astronomical theory of palaeoclimates were Milankovitch’s (1941) canon of incoming solar radiation (insolation) and findings, in 1976, of a double precession frequency peak in marine sediment data consistent with celestial mechanics. This lecture is divided in two parts : (1) it outlines the formalism behind the calculation of Earth’s orbital elements (2) it summarises the present status of the astronomical theory of palaeoclimates. For example, we know since Milankovitch that ice volume variations are largely determined by northern hemisphere summer insolation. Indeed, low summer insolation allows snow fell in winter to survive the summer and accumulate from one year to the next, causing glacial inception. However, this first-order description is not fully satisfactory. The climate response to the astronomical forcing is highly non-linear, and the difficulty is to identify and characterise the mechanisms causing non-linearity. Some are known since Milankovitch (the snow-albedo feedback), others were largerly discussed during the eighties (the isostatic response); at last, some are not well understood, yet (the response of atmospheric carbon dioxide). The lecture comments on different strategies to progress : comprehensive general circulation models, models of intermediate complexity, and palaeodata assimilation schemes.