A gradual change is more likely to have caused the Mid-Pleistocene Transition than an abrupt event

The Mid-Pleistocene Transition (~1.2–0.8 million years) corresponds to a time interval when high-amplitude ~100,000 years glacial–interglacial cycles replaced the more subdued ~40,000 years glacial–interglacial cycles. Whether it was triggered by physical processes affecting the climate system at a specific time interval or more gradually over the course of the Pleistocene, is still an open question. Here we use an original approach based on conceptual modelling to identify the temporal structure of the Mid-Pleistocene Transition controlling factors. By comparing our new simulations of global ice volume changes with existing paleo-reconstructions over the past 2 million years, we find that it is more relevant to simulate the Mid-Pleistocene Transition with a gradual-rather-than-abrupt change in the climate system. Our results support the hypothesis that a progressive decrease in atmospheric carbon dioxide concentrations throughout the Pleistocene played a key role in triggering this major climatic transition.