According to Wikipedia: ‘The 100,000-year problem refers to the lack of an obvious explanation for the periodicity of ice ages at roughly 100,000 years for the past million years, but not before, when the dominant periodicity corresponded to 41,000 years. The unexplained transition between the two periodicity regimes is known as the Mid-Pleistocene Transition, dated to some 800,000 years ago.’ Of course the Wiki page then attempts to bring in CO2, for no obvious reasons except their desire to do so. But this study takes a different route, ignoring CO2.
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Editor’s summary (@ Science.org):
During the Mid-Pleistocene Transition, between ~1.2 million and 700 thousand years ago, the length of Earth’s glacial cycles changed from ~41,000 years to ~100,000 years, but the reason for this shift is not clear. An et al. combined climate and ice sheet records to show that growth of the Antarctic ice sheet and the associated expansion of Southern Ocean sea ice caused northern high-latitude cooling, more vigorous moisture transport to the Northern Hemisphere, and subsequent rapid growth of the Northern Hemispheric ice sheet, thereby triggering the Mid-Pleistocene Transition. —Jesse Smith
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<a href="https://phys.org/news/2024-08-link-asymmetric-polar-ice-sheet.html"Phys.org says:
Joint research led by Professor An Zhisheng from the Institute of Earth Environment of the Chinese Academy of Sciences has revealed the pivotal role of the growth of the Antarctic ice sheet and associated Southern Hemisphere sea ice expansion in triggering the mid-Pleistocene climate transition (MPT).
It has also shown how asymmetric polar ice sheet evolution affects global climate.
The MPT refers to a shift in Earth’s climate system between about ~1.25–0.7 million years ago, marking a shift to more pronounced and regular glacial-interglacial cycles.
While providing insight into the rapid expansion of the Northern Hemisphere ice sheet since the mid-Pleistocene, this study also challenges numerous hypotheses regarding the origin and mechanisms behind the MPT.
Results of the research were published in Science, titled “Mid-Pleistocene climate transition triggered by Antarctic ice sheet growth.”
Due to the importance of the MPT for the evolution of Earth’s ice sheet dynamics over the last ~1.25 million years, such hypotheses have been debated and discussed frequently in the journals Nature and Science over the last decades.
“This study contributes to our understanding of the question ‘What causes ice ages?’—one of the 125 frontier scientific problems raised by Science in 2021,” said Professor An, also a member of Chinese Academy of Sciences (CAS) and Foreign Associate of the National Academy of Sciences, U.S.
This work also illustrates how processes in the Earth system define and change characteristics of glacial-interglacial cycles, their dynamics, and their length.
Integrating geological records with numerical climate simulations, this study reveals the history of the asymmetric evolution of ice sheets in both hemispheres and the associated response of the Earth’s climate system.
The findings indicate that 2–1.25 million years ago, the ongoing growth of the Antarctic ice sheet and the associated expansion of sea ice in the Southern Hemisphere triggered a temperature drop and water vapor boost in the Northern Hemisphere through the modified cross-equatorial pressure gradient and meridional overturning circulation.
These changes thus fostered the development of the Arctic ice sheet and ultimately caused a shift in Earth’s glacial cycles from ~40,000 years to ~100,000 years.
By examining the changes in ice volume across both hemispheres, this work highlights the profound impact of the asymmetric evolution of polar ice sheets upon global climate, particularly on the climate of the Northern Hemisphere.
Full article <a href="https://phys.org/news/2024-08-link-asymmetric-polar-ice-sheet.htmlhere.
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Image: Ice core sample [credit: Discovering Antarctica]
via Tallbloke’s Talkshop
August 2, 2024 at 03:29AM
Iowa Climate Science Education 