This is interesting from a catastrophist point of view – at https://tallbloke.wordpress.com/2023/05/17/study-warm-ice-age-changed-climate-cycles/ … this gets to the nitty gritty of a strange consensus idea, the switch from a 45,000 year glacial cycle to a 100,000 year glacial cycle. I have often pondered if these cycles were computer driven. Initially, they weren’t as Milankovitch used maths to estimate the changes caused by the orbit of the earth around the Sun. He was an incredible guy but his painstaking research was rejected for many years, only becoming acceptable in the late 1950s as a result of the discovery of magnetic stripes on the sea floor of the Atlantic. It was used to bolster the Ice Age theory in combination with isotopic analysis of plankton shells on the sea floor that seemed to suggest periodic coolings and warmings. The Milankovitch theory was used to anchor the isotopic data – creating a thoroughly uniformitarian timescale of the waxing and waning of the ice sheets. No one nowadays questions, seriously, the idea of ice ages every 100,000 years, even though that equates roughly with the journey of the Sun around its barycentre.
The full study is at https://www.nature.com/articles/s41467-023-38337-4 … and the researchers make plain they used computer simulations and this leads to some nagative comments at the first link. The new claim is that approximately 700,000 years ago, or 7 times 100,000 year cycles on the uniformitarian column, a ‘warm ice age’ permanently changed the climate cycles on earth. Contemporary with this event, polar glaciation expanded. Over the next 700,000 years Ice Ages persisted at 100,000 years intervals, whereas before 700,000 years ago the earth was dominated by 45,000 year cycles [although that figures varie by a few thousand years depending on the source]. This is now an embedded consensus theory in mainstream science. It is also an unresolved problem. Why and how did it happen. The new study is an attempt to answer that problem.
In geological terms 700,000 years ago marks the end of the Middle Pleistocene period. There must have been something going on at that time in order to become a boundary marker on the geological column. The last 700,000 years comprise the Late Pleistocene. Obviously, computer simulation cannot determine what happened at the boundary, as the answer can only stem from what is fed into the computer in the first place. So, what was the nature of the change?
The researchers suggest that higher moisture content in SW Europe combined with the growth of forests in the Mediterranean basin, together with an enhanced summer monsoon in East Asia, presumably China, may have created enough precipitation to form larger ice caps. On the other hand, if the poles were situated somewhat differently to those of today, the Mediterreanean could have been temperate and China could have been closer to the equator. The ice caps could simply have moved geographically. We might then ask what else was going on at approximately 700,000 years ago? This is roughly when the Earth is said to have fully reversed its magnetic signature – permanently. Unlike the Laschamp event at 40,000 years ago, the magnetic field did not revert back to its previous position. North became North once more. At 700,000 years ago, the North may have become the South – and stayed that way. Does it involve a physical reversal of the earth – flipping over, or does it more likely involve a new position of the poles, after a period of dipole wobble. The Laschamp event coincided with mass die offs of mammals, including Neanderthals and Denisovans. It was a symptom of a bigger event, in other words, some sort of catastrophe. The same is probably true of the 700,000 years ago magnetic reversal – which is why it marks the boundary of the Middle and Late Pleistocene periods. A catstrophic event could not of course permanenlly cause a change in Ice Age frequency. The question then is could a more moist ice age leading up to 700,000 years ago, achieve that change.
Also, worth mulling over, these 100,000 year glacial periods are very odd. Around 50,000 years ago Europe had a savannah like environment, and was warmer than it is today, or did mammoth and lions roam in a cold environment? During the Late Glacial Maximum, 30,000 to 16,000 years ago, roughly so, N W Europe had an ice sheet, as did NE North America. It was also very cold in SE Australia – but warmer in Patagonia. Are 100,000 year glacial cycles real – or contrived?