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Puzzling Evidence: Glacial Deposits and the Cause of Ice Ages
  • Alice Doughty
Alice Doughty
University of Maine

Corresponding Author:[email protected]

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The cyclical pattern of glaciations (about every ~100,000 years in the past million years in isotope records) suggests an external forcing, such as changes in the amount of sunlight (insolation) reaching areas on the cusp of glaciation (e.g., ~65° latitude) during the season when ice is most likely to melt (summer). Alternatively, ice ages could be caused by insolation triggering changes within the Earth’s climate system that alter carbon dioxide and ice sheet size, leading to globally synchronous climate change. The key to testing these hypotheses is knowing the timing and magnitude of past temperature change. Mountain glaciers tell a slightly different story about past climate change. Strand et al. (2022, https://doi.org/10.1029/2022PA004423) contribute a new moraine chronology from an understudied region in Mongolia showing that the glacier reached a maxima 10,000 years prior to the lowest CO2 level and peak in global ice volume, and that massive glacier retreat was underway millennia prior to any of the proposed climate drivers. Their moraine chronology is in agreement with those from the Southern Alps of New Zealand, which is located in the opposite hemisphere and maritime climate rather than continental. Here, I review the results from Strand et al. (2022) in the context of ongoing advances in the methods and moraine chronologies from the last glacial cycle. The issue remains that we do not have a clear understanding of the cause of ice ages and the strength of feedbacks within Earth’s climate system.