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Why is the 100,000-year climate cycle difficult to explain using eccentricity alone?

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Map showing the extent of the Laurentide, Cordilleran, and Greenland ice sheets during the Wisconsin glaciation, roughly 100,000 to 11,000 years ago. The Laurentide Ice Sheet covers most of present-day Canada and parts of the northern United States in light blue, the Cordilleran Ice Sheet covers the Pacific Northwest in teal, and the Greenland Ice Sheet is marked in purple. Modern international and state or provincial boundaries are outlined for reference. — Pleistocene Epoch Ice sheets during the Wisconsin glacial episode penetrated deep into North America.

The 100,000-year climate cycle is difficult to explain using eccentricity alone because the magnitude of the eccentricity cycle is considered too weak to account for the significant climatic changes observed during the Pleistocene Epoch.12

While eccentricity is one of the three primary Milankovitch cycles that influence the distribution of solar radiation on Earth, it is the weakest of the three parameters. Scientists note that the relatively small variations in radiation caused by orbital parameters are insufficient on their own to drive the massive shifts between glacial and interglacial periods.123

Consequently, researchers believe that complex feedback mechanisms—such as changes in albedo, atmospheric carbon dioxide concentrations, and the dynamics of large continental ice sheets—must act to amplify these orbital signals. Other theories suggest that major reorganizations of the ocean-atmosphere system, particularly involving deep oceanic currents in the Atlantic Ocean, may play a critical role in pacing these cycles.13