The timing of Pleistocene glaciations from a simple multiple-state climate model

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The Earth's climate over the past million years has been characterized by a succession of cold and warm periods, known as glacial–interglacial cycles, with periodicities corresponding to those of the Earth's main orbital parameters; precession (23 kyr), obliquity (41 kyr) and eccentricity (100 kyr). The astronomical theory of climate, in which the orbital variations are taken to drive the climate changes, has been very successful in explaining many features of the palaeoclimate records1. Nevertheless, the timing of the main glacial and interglacial periods remains puzzling in many respects2,3,4,5. In particular, the main glacial–interglacial switches occur approximately every 100 kyr, but the changes in insolation forcing are very small in this frequency band. Similarly, an especially warm interglacial episode, about 400,000 years ago7, occurred at a time when insolation variations were minimal. Here I propose that multiple equilibria in the climate system can provide a resolution of these problems within the framework of astronomical theory. I present two simple models that successfully simulate each glacial–interglacial cycle over the late Pleistocene epoch at the correct time and with approximately the correct amplitude. Moreover, in a simulation over the past 2 million years, the onset of the observed prominent 100-kyr cycles around 0.8 to 1 million years ago is correctly reproduced.

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Figure 1: Schematic structure of the multiple-state system used.
Figure 2: Results from the first idealized model (middle curve).
Figure 3: Results from the second model (thick middle curve).
Figure 4: Same as Fig. 3 but with a time-varying threshold vmax.


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We thank S. Clemens and to M. Raymo for encouragement and comments on this Letter.

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Correspondence to Didier Paillard.

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