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Two questions really.

The Quaternary glaciation has been ongoing for 2.58 million years, as far as I know mainly meant to be caused by the Panama Isthmus separating the Pacific and Atlantic and also various Milankovitch forcings. Thus began the cycle of glacial and interglacial.

Assuming anthropogenic global warming does not abort this entirely and force a transition back to permanent hothouse, is there any educated guess we can make at how much time the glaciation has left before the cycle ends and the northern ice sheets melt permanently? The only figure I've seen was on the order of ten million years, and it wasn't by anyone with any qualifications.

Also - the cycle length of glacial-interglacial switched from 41kyr to 100kyr 1.25 million years ago. As the cycles continue (ignoring AGW for a moment) could this change happen again, the other way? Do we have a good enough grasp on the factors involved to give a date for any such future transition?

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    $\begingroup$ Hi. Good questions, frequently asked and answered not just in here. Choose one question and perform a little prior search, that'll make answering much easier and better. Edit: and don't make too many assumptions as they only get in the way of a good answer :-) $\endgroup$
    – user35846
    Commented Nov 3 at 8:29
  • $\begingroup$ This "question" asks two rather distinct questions; questions should ask one question. Unfortunately, both questions asked are currently unanswerable. Scientists disagree to this day on the cause of the Mid Pleistocene Transition. When/if the current 100 ka cycle will revert to a 41 ka cycle: who knows? Regarding the end of the Quartenary: That too is another who knows? $\endgroup$
    – David Hammen
    Commented Nov 4 at 2:38
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    $\begingroup$ I’m voting to close this question because both questions raised in this question are currently unanswerable, and will remain unanswerable for a long, long time. $\endgroup$
    – David Hammen
    Commented Nov 4 at 2:39
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    $\begingroup$ They are not unanswerable, answers about the future are just never exact. But the question should be split and reworked according to "How to ask a good question". $\endgroup$
    – user35846
    Commented Nov 4 at 7:41

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It took 60 million years for the earth from green- to ice house, in several steps and with interruptions. The closing of the isthmus between the Americas created the Gulf Stream that brought moisture to the north, thus enabling the build-up of ice sheets. At the time orbital parameters (Milankovic cycles) started to control the spread and retreat of ice sheets in the north.

The south is a different thing.

"[...] how much time the glaciation has left before the cycle ends and the northern ice sheets melt permanently?"

The northern ice sheets disappeared at the end of the Pleistocene and the onset of the Holocene, they are gone except for Greenland and glaciers in mountains. Greenland has been ice free once in the Pleistocene, meaning its cover is fragile. If we continue on the current path with fossil fuels/thermal power generation it could be ice free in centuries.

https://www.pnas.org/doi/10.1073/pnas.2407465121

https://www.nature.com/articles/s41586-020-2742-6

The Himalayas as an iconic example for the melting of mountain glaciers could loose up to 80% of their ice until 2100.

https://www.smithsonianmag.com/smart-news/himalayas-could-lose-two-thirds-its-glaciers-2100-180971415/

The Arctic could be ice free during summer (except for remnants along the coast lines) before mid-century.

https://www.nature.com/articles/s43017-023-00515-9

Antarctica is a completely different thing and will need a separate answer. Also note that these answers reflect current knowledge and may be adjusted in both directions, for instance on profound changes in the AMOC.

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  • $\begingroup$ This doesn't answer either question, (1) When will the Quaternary glaciation end, and (2) When, if ever, will the glacial periods switch from the current 100000 year cycle back to the former 41000 year cycle. $\endgroup$
    – David Hammen
    Commented Nov 4 at 12:48

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