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Summary
At the end of the Pliocene epoch, about 2.6 million years ago, a sustained period of global cooling coincided with the growth of continental ice sheets over Europe and North America. Since then, these ice sheets have periodically grown and collapsed more than 50 times, driving global sea level fluctuations of more than 100 m. What caused this bipolar glacial world? On page 847 of this issue, Woodard et al. (1) show that the ice sheets began to grow gradually before 2.7 million years ago. This gradual buildup led to a more efficient heat transport between the Atlantic and Pacific abyssal oceans, thus resulting in an Atlantic cooling.
