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Modeling perspectives on the mid-Pleistocene transition

The Quaternary is the most recent geological period, covering the past ~2.6 million years. It is characterized by the presence of glacial-interglacial cycles associated with the cyclic growth and decay of continental ice sheets in the Northern Hemisphere. Climate variations during the Quaternary are best seen in oxygen isotopes measured in deepsea sediment cores, which represent variations in global ice volume and ocean temperature (Lisiecki and raymo 2005). These data show clearly that there has been a general trend towards larger ice sheets and cooler temperatures over the last 3 million years, accompanied by an increase in the amplitude of glacial-interglacial variations and a transition from mostly symmetrical cycles with a periodicity of 40,000 years (40 kyr) to strongly asymmetric 100-kyr cycles at around 1 million years ago (Fig. 1a). The ultimate causes of these transitions in glacial cycle dynamics still remain debated.