Abstract: On the 102- to 103-year timescale, internal reorganizations of the climate system result in abrupt climatic changes of great magnitude. Although a large body of data has been obtained, the physical mechanisms responsible for these changes are still poorly understood. Instrumental data are too short to fully record the variability of the climate system. Palaeoclimatic records provide estimates of the past atmospheric composition, temperature, precipitation, vegetation, extension of glaciers, and past ocean circulation. On the 104- to 106-year timescale, the astronomical theory of palaeoclimates accounts for most of the reconstructed variations. To cite this article: J.-C. Duplessy et al., C. R. Geoscience 337 (2005).