The grandiose name “Milankovitch theory” purports to account for the recurrence of the ice ages. In fact, it is more correct to call it the “Milankovitch hypothesis” or better, conjecture - especially as few astronomers that I know accept it. On that note, we can examine how it's basically been disproven as a valid theory. That is to say, an entity that is capable of making verifiable predictions based on a self-consistent hypothesis.
Milankovitch proponents claimed decades ago that a geological proxy climate record revealed the same temporal cycles manifested in the three orbital parameters: eccentricity, obliquity, and precession. All this was intended to substantiate the so-called Milankovitch theory which asserts these three distinct cycles are applicable to Earth's orbital motion.
To fix ideas the eccentricity (a) describes the shape of Earth's orbit around the Sun, said by the Milankovitch proponents to vary from near circular (as it is now) to more elliptical, with a period of 96,000 years. The obliquity (b) is the tilt of the Earth's axis of rotation with respect to the orbital plane, and oscillates with a period of 41,000 years - according to Milankovitch proponents The precession (c) combines the spin of Earth's orbital axis and its orbital path over time, producing a 21,000 year cycle, again according to Milankovitch proponents.To my knowledge no proponent has actually made predictions that have verified the 3 cycles' connection to the geological proxy record. Technically, one would also expect such predictions to come out of a dynamic model from celestial mechanics - not one dependent on sea floor topography or geology. These are two distinct sciences after all. (Paleo-climatology, i.e. based on marine micro-fossils, is also distinct from celestial mechanics.) What we have then is not a theory but a conjecture.
Missing such theoretical connections it's relatively easy to disprove this conjecture, focusing on just one cycle. We can then examine the putative change in the eccentricity e, which is currently at 0.0167 but which Milankovitch adherents claim can reach e = 0.07. (Elongating the orbit so as to influence climatic factors, e.g. see this video demonstration:
But what would it take to change the shape of the Earth's current orbit, to the one proposed by Milankovitch supporters? How much energy would be required? We can use the equation for the total energy of the orbit, in terms of the eccentricity, e, and the dimension of orbit known as the semilatus rectum,: r o (= b 2 /a) and the other familiar parameters for Newtonian orbit computations, e.g.
D E » 1.9 x 10 42 J
This is an enormous amount of energy input. WHERE does it come from? HOW is it produced? What is the time evolution - in energy increments- leading to the final more eccentric orbit? The Milankovitch adherents who adopt the work of a Serbian civil engineer, provide us no answers. How can they when they are working from reconstructed sea floor geology findings and not celestial mechanics per se?
Given the preceding we should acknowledge that there are significant problems with that Serbian civil engineer's hypothesis that bid us to exercise much more caution, i.e. before adopting it without qualification. Especially given its reversed engineered construction from geological data, to arrive at a celestial mechanics format requiring new orbital elements. Or conferring the benediction of an origin in celestial mechanics, as opposed to geology. One major issue was raised in a paper by Daniel B. Karner and Richard A. Muller 2 which pointed out a number of serious problems, inconsistencies associated with the Milankovitch hypothesis.
Thus, while one can certainly appreciate Prof. Maslin’s article, it is also worthwhile to be aware of the problems to do with the underlying hypothesis, most of which I suspect were engendered by the origins in sea floor geologic data..
But what would it take to change the shape of the Earth's current orbit, to the one proposed by Milankovitch supporters? How much energy would be required? We can use the equation for the total energy of the orbit, in terms of the eccentricity, e, and the dimension of orbit known as the semilatus rectum,: r o (= b 2 /a) and the other familiar parameters for Newtonian orbit computations, e.g.
The objective is to find the change in energy E, i.e. when the eccentricity is altered from 0.0167 to 0.07. This turns out to be approximately:
D E » 1.9 x 10 42 J
This is an enormous amount of energy input. WHERE does it come from? HOW is it produced? What is the time evolution - in energy increments- leading to the final more eccentric orbit? The Milankovitch adherents who adopt the work of a Serbian civil engineer, provide us no answers. How can they when they are working from reconstructed sea floor geology findings and not celestial mechanics per se?
Given the preceding we should acknowledge that there are significant problems with that Serbian civil engineer's hypothesis that bid us to exercise much more caution, i.e. before adopting it without qualification. Especially given its reversed engineered construction from geological data, to arrive at a celestial mechanics format requiring new orbital elements. Or conferring the benediction of an origin in celestial mechanics, as opposed to geology. One major issue was raised in a paper by Daniel B. Karner and Richard A. Muller 2 which pointed out a number of serious problems, inconsistencies associated with the Milankovitch hypothesis.
Specifically the authors – after assessing the data from numerous sources (e.g. U-Th dating from the Devil’s Hole cave in Nevada) found that the Devil’s Hole data indicated a shift in d 18 O to interglacial values and was “essentially complete by 135 ka but the Northern Hemisphere summer insolation hadn’t yet warmed to the point when it would have triggered anything extraordinary, let alone a glacial termination” Adding: “We call this discrepancy the causality problem”:
- The authors conclude (op. cit.):
“The standard Milankovitch insolation theory does not account for the termination of the Ice Ages.”
Adding that:
“We can conclude that models that attribute the terminations to large insolation peaks (or equivalently to peaks in the precession parameter)…are incompatible with the observations.”
Equally significant, perhaps, Richard A. Muller has pointed out in a separate paper 3 that “the spectral shapes predicted by the Milankovitch theory do not match those in the spectrum and bispectrum of the data..”
In addition, Muller notes that the net forcing associated with clouds, i.e. about 30 W/m 2 is substantially greater than the rms variations in insolation. This leads him to conclude:
“The changes in cloud cover could be more important than the changes in Milankovitch parameters.”
Finally, Puetz et al4, employed a “universal cycle model” – using a Universal Wave Series (UWS) with cycles in the kyr range - to show that orbital tuning limits independent and objective testing of an empirical hypothesis like that of Milankovitch. In effect, while Milankovitch offers a “seductively elegant solution to the problem of age-stratum mapping”, its template remains a trap for selection effects (and data bias) to enter. This results in a condition, as it pertains to the Milankovitch hypothesis, whereby:
”Reporting bias occurs when articles mention favorable results from orbitally tuned records, which are supportive of the Milankovitch theory, while failing to mention unfavorable results from un-tuned versions of the same records.”
The reason is clear given that (ibid.): “Statistically significant positive results that support a desired outcome are more likely to be published in high impact journals.”
Thus, while one can certainly appreciate Prof. Maslin’s article, it is also worthwhile to be aware of the problems to do with the underlying hypothesis, most of which I suspect were engendered by the origins in sea floor geologic data..
My contention then is if there is no independent confirmation of the Milankovitch hypothesis from celestial mechanics proper, the whole conjecture falls apart. (Or if you prefer, the "theory
is disproven.) I cn here the Milankovitch proponents screaming already: "But what do you expect us to do then?"
is disproven.) I cn here the Milankovitch proponents screaming already: "But what do you expect us to do then?"
Easy. Provide us with the model, or even just a numerical simulation, showing how the three orbital parameters evolve over time t to yield the temporal cycles suggested by the marine microfossil studies?
In effect, leaving out the geological data, show us how Earth's orbit changes its parameters to yield the temporal cycles claimed by Maslin, as well as Hays et al, and oh yes, Milankovitch.
References:
1. J.D. Hays, J. Imbrie, N.J. Shackleton, Science 194, 1121 (1976)
2.Daniel B. Karner, Richard A. Muller, A Causality Problem for Milankovitch, Science, 288, 2143 (2000)
3. Richard A. Muller, Limitations and Failures of the Milankovitch Theory, poster paper, American Geophysical Union Fall Meeting (2001)
4. Stephen J. Puetz, Andreas Prokoph, Glenn Borchardt, Evaluating Alternatives To The Milankovitch Theory, Journal of Statistical Planning and Inference, 170, 158 (2016)
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