Milankovitch proposed in the 1920’s that Ice-Ages would be periodic and caused by 3 periodic variations in the Earth’s orbit. These 3 periodic changes are:
Eccentricity, approximately 100,000 years. (Eccentricity is something I can definitely relate to). This is the only periodic change that actually affects the amount of sunlight reaching the Earth, and not by very much — I think by less than 1/10th of a percent, so really, none of these periodic changes in the Earth’s orbit should matter at all, to first order !
Obliquity, approximately 41,000 years. (I might also relate to this, as some have said that I and my writings can be somewhat oblique, but I’m not exactly sure what it means to be oblique, but it’s probably not good); and
Axial Precision or Wobble, approximately 23,000 years (something I can definitely relate to especially after an amount of 100 Proof Kentucky Bourbon which I’ve been sipping while writing this [can you tell ?]).
Below is a link to a website which shows these three period variations in the Earth’s orbit with nice moving-graphics:
https://climate.nasa.gov/news/2948/milankovitch-orbital-cycles-and-their-role-in-earths-climate/
Hays et al. confirmed the Milankovitch Cycles in their seminal 1976 publication in the respected journal, Science:
Variations in the Earth’s Orbit: Pacemaker of the Ice Ages (https://www.whoi.edu/cms/files/hays76sci_268464.pdf).
So, why is this not completely accepted ? It sure doesn’t seem as though it is.
Some may believe verification by Hays et al. to not be so convincing — they did quite a bit of massaging of the mud core data, and presented their findings in the “frequency domain” rather than the “time domain”. Figures showing frequency spectra are not convincing, let alone understandable to most people.
If one does an internet search today on the Milankovitch Cycles, you are left with the impression that, well, maybe there is something there, but scientists are still very uncertain about many things.
You certainly don’t find any climatologists confidently predicting when the next Ice Age will occur; and
data are usually displayed in a way that would make anyone wonder if there is really anything there or not, e.g., the Milankovitch Cycles as presented by Wikipedia [By Incredio - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=6930545:
Figure 1. Milankovitch Cycles as shown in Wikipedia. Convincing, or just head scratching ?
Anyway, I was curious as the when the next Ice Age would occur — we are already about 12,000 years into the present Inter-Glacial, which is about how long we might expect it to last. So, I created a number of simple programs using the Milankovitch Cycles to predict the next Ice Age, which I shall present and discuss in my next posting. (I’m trying to keep these things short).
Happy Holidays,
TimE.