Is the Ice Sheet Collapse Inevitable? What Ancient Ice Reveals About Our Future

Scientists from the Mann Research Group drove a climate model both forward and backward in time and discovered significant path dependence in the development of Plio-Pleistocene glaciations.
The climate modeling community has been particularly vexed by the glacial and interglacial cycles over the past three million years, during which the Northern Hemisphere alternated between periods with and without extensive ice sheets.

From about 1.25 million to 750,000 years ago—in the Pleistocene epoch—a change in glacial cycles called the Mid-Pleistocene Transition (MPT) occurred. During this time, glacial/interglacial cycles shifted from occurring every 41,000 years to every 100,000 years, with an increase in the amplitude and asymmetry of the cycles. Scientists are working to understand why these changes happened, considering that insolation forcing—variation in energy that Earth receives from the sun—does not on its own explain the change.