If look it up ; there is no set theory on the cause. Just wondering then; if somebody has thoughts on why any ice age would manifest at all.
To do with the Earth's changes in tilt and orbital parameters I would suggest...Other aspects such as the Chandler wobble may also play a part, in conjunction with other variable aspects of the tilt.
The Chandler wobble is a wobble in the tilt of the Earth's axis over relatively short periods: https://en.wikipedia.org/wiki/Chandler_wobble In retrospect, this slight short period wobble would not contribute too much to the comings and goings of ice ages. https://www.sciencedaily.com/releases/2013/08/130807134127.htm The explanation for the cyclical alternation of ice and warm periods stems from Serbian mathematician Milutin Milankovitch (1879-1958), who calculated the changes in Earth's orbit and the resulting insolation on Earth, thus becoming the first to describe that the cyclical changes in insolation are the result of an overlapping of a whole series of cycles: the tilt of Earth's axis fluctuates by around two degrees in a 41,000-year cycle. Moreover, Earth's axis gyrates in a cycle of 26,000 years, much like a spinning top. Finally, Earth's elliptical orbit around the sun changes in a cycle of around 100,000 years in two respects: on the one hand, it changes from a weaker elliptical (circular) form into a stronger one. On the other hand, the axis of this ellipsis turns in the plane of Earth's orbit. The spinning of Earth's axis and the elliptical rotation of the axes cause the day on which Earth is closest to the sun (perihelion) to migrate through the calendar year in a cycle of around 20,000 years: currently, it is at the beginning of January; in around 10,000 years, however, it will be at the beginning of July.
Paddoby's facts in post four are more about the "modulation of probability of an Ice Age starting" than a direct cause of when it does. This is because of the strong positive feed back a decade or so of more than average snow can cause (less solar absorption, for a decade, is the actual "trigger" of a new ice age). This statistical fluctuation making decade or more of lower solar absorption needs to occur roughly when it is re-enforced by the Milankovitch cycles. If it does not then the possible ice age within the Milankovitch cycle may not occur. They are not guaranteed to make an ice age, but often do. Why ice ages do not occur with astronomical precision.
From what I've read on the subject. No one knows why we got into this ice age, nor how nor when we will exit it. And many disagree as to when it started. https://en.wikipedia.org/wiki/Antarctic_ice_sheet meanwhile: Australia and Antarctica separated about 40mybp Did the ice age start with the glaciation of antarctica? Did the ice age start with the glaciation of the northern hemisphere? One hypothesis that seems plausible is that as we drift in and out of our galactic arm we are exposed to different amounts of cosmic radiation. The more radiation supposedly equals more clouds which reflect the solar radiation cooling the earth while producing more precipitation producing snow and further cooling the planet. Alternately, little is known about the long term behavior of our sun. It may have long term quiet periods which are causal to the initiation of an ice age. If so, then when we witness periods like the last grand solar maximum, during the last 1/2 of the last century, we were still not seeing the long term average of the sun's output. Alternately it may have to do with the varying gravitational forces as we circle the galactic center as the galaxy hurtles toward the great attractor. If so: Then we would expect to see evidence of an ice age roughly every 225-250 million years. However, if our timeline understanding is correct, ice ages seem to occur roughly every 150 million years. If one of these estimates is wrong, then maybe we have a whole new ballgame? The field seems rife with stray hypotheses and guess work. Feel free to join in.
http://arxiv.org/pdf/1302.1492.pdf Why could ice ages be unpredictable? Submitted to Climate of the Past on the 4th February 2012. Abstract It is commonly accepted that the variations of Earth’s orbit and obliquity control the timing of Pleistocene glacial-interglacial cycles. Evidence comes from power spectrum analysis of palaeoclimate records and from inspection of the timing of glacial and deglacial transitions. However, we do not know how tight this control is. Is it, for example, conceivable that random climatic fluctuations could cause a delay in deglaciation, bad enough to skip a full precession or obliquity cycle and subsequently modify the sequence of ice ages? To address this question, seven previously published conceptual models of ice ages are analysed by reference to the notion of generalised synchronisation. Insight is being gained by comparing the effects of the astronomical forcing with idealised forcings composed of only one or two periodic components. In general, the richness of the astronomical forcing allows for synchronisation over a wider range of parameters, compared to periodic forcing. Hence, glacial cycles may conceivably have remained paced by the astronomical forcing throughout the Pleistocene. However, all the models examined here also show a range of parameters for which the structural stability of the ice age dynamics is weak. This means that small variations in parameters or random fluctuations may cause significant shifts in the succession of ice ages if the system were effectively in that parameter range. Whether or not the system has strong structural stability depends on the amplitude of the effects associated with the astronomical forcing, which significantly differ across the different models studied here. The possibility of synchronisation on eccentricity is also discussed and it is shown that a high Rayleigh number on eccentricity, as recently found in observations, is no guarantee of reliable synchronisation. 4 Conclusion The present article is built around the paradigm of the ‘pacemaker’, that is, the timing of ice ages arises as a combination of climate’s internal dynamics with the variations of incoming solar radiation induced by the variations of our planet’s orbit and obliquity. This is not the only explanation of ice ages, but this is certainly one of the most plausible. In this study we paid attention to the dynamical aspects that may affect the stability of the ice age sequence and its predictability. First, the astronomical forcing has a rich harmonic structure. We showed that a system like the van der Pol oscillator is more likely to be synchronised on the astronomical forcing as Nature provides it than on a periodic forcing, because the fraction of the parameter space corresponding to synchronisation is larger in the former case. A synchronised system is Lyapunov stable, so that at face value this would imply that the sequence of ice ages is stable. However, —this is the second point– even if the dynamical structure of the Pleistocene climate was correctly identified, there would be at least two sources of uncertainties : random fluctuations associated with the chaotic atmosphere and ocean and other statistically random forcings like volcanoes; and uncertainty on system parameters. In theory both types of uncertainties point to different mathematical concepts: path-wise stability to random fluctuations in the first case, and the structural stability in the second. In practice, however, lack of either form of stability will result in similar consequences: quantum skips of insolation cycles in the succession of ice ages. This was the lesson of Figure 10. It was shown here that, compared to periodic forcing, the richness of the harmonic structure of astronomical forcing favours situations of weak structural stability. To preserve stability, the richness of the astronomical forcing has to be compensated for by large enough forcing amplitude. Out of the seven models tested here, we ignore which one best captures ice ages dynamics. The overwhelming complexity of the climate system does not allow us to securely select the most plausible model on the sole basis of our knowledge of physics, biology and chemistry. Consequently, while we have understood here how and why the sequence of ice ages could be unstable in spite of available evidence (astronomical spectral signature; Rayleigh number), estimating the stability of the sequence ice ages and quantifying our ability to predict ice ages is also a problem of statistical inference : calibrating and selecting stochastic dynamical systems based on both theory and observations, which are sparse and characterised by chronological uncertainties. A conclusive demonstration of our ability to reach this objective is still awaited.
Has to do with glacial and intergacial periods within this ice age. Too many people confuse the phrase "ice age" with the phrase "glacial period". Can we agree that we are now within an interglacial period within an ice age that has existed for at least 2.8 million years? So milankovitch cycles only correlate to episodes within this ice age? Unless, you think that the milankovitch cycles are/were significantly different when the world was not in an ice age. Whither hence?
Please Register or Log in to view the hidden image! Your statement that "The field seems rife with stray hypotheses and guess work" is somewhat extreme to put it mildly. There are many logical reasons, including the Solar systems orbital parameters around the central SMBH at the center of the MW galaxy. imho it's probably a combination of all aspects of tilt, Earthly motions/solar system motions and such. In time, as our geographical and cosmological data increases, more certainty will be forthcoming.
