See Comments down arrow

The Milankovitch mystery, or, wobbly science

29 May 2024 | OP ED Watch

Here at CDN we get a variety of interesting correspondence and we appreciate it. Most of it, anyway. Including when an alert viewer asked about Milankovitch Cycles, which seem important to some long-run natural climate cycles (yes, those again) during the most recent Ice Age, which appears to have started either 2.6 or 33 million years ago depending if you demand significant ice at both poles or only one. And the question got us thinking about Serbian geophysicist Milutin Milanković who challenged climate orthodoxy a century ago despite not being a “climate scientist” as some would define the term, by arguing that a series of wobbles in the Earth’s motion had a major impact on long-run climate because they altered the amount and impact of incoming solar radiation. And if so you’d think it would always have been true… and that alarmists wouldn’t be so determined now to pooh-pooh the concept of major solar influence.

The Milankovitch matter is a mathematical mess because our planet’s motion is variable in three main ways: eccentricity, obliquity and precession. Uh, that’d be that the orbit varies between nearly circular and slightly elliptical over about 400,000 years if you believe Wikipedia and 100,000 if you believe NASA, and when the orbit is less round there’s more seasonal variation. Also that it wobbles on its axis on roughly a 41,000-year cycle, and the more it tilts, the more sunlight hits high altitudes in summer, also increasing seasonal variation. And that its ellipse around the sun shifts in roughly a 26,000 year cycle, meaning that it’s sometimes nearer Sol in Northern Hemisphere winter and sometimes in Northern Hemisphere summer which matters because there’s more land in the Northern Hemisphere and land absorbs more heat than sea.

Got it? Well, not entirely, because there’s also apsidal precession and orbital inclination. You can Google that stuff. And should if you think climate change is “simple physics” in this or any other way.

Collectively the impact is clearly significant. In its page on “Milankovitch (Orbital) Cycles and Their Role in Earth’s Climate”, NASA says this pioneering climate skeptic:

“examined how variations in three types of Earth orbital movements affect how much solar radiation (known as insolation) reaches the top of Earth’s atmosphere as well as where the insolation reaches. These cyclical orbital movements, which became known as the Milankovitch cycles, cause variations of up to 25 percent in the amount of incoming insolation at Earth’s mid-latitudes (the areas of our planet located between about 30 and 60 degrees north and south of the equator).”

Before letting you slide into heresy, they offer a handy “further reading on why Milankovitch cycles can’t explain Earth’s current warming here”. And it’s a bit of a wobbly circle since the main point is that while climate is complex and multifactorial, they know it’s CO2 because they know it’s CO2:

“Today, however, it’s the direct input of carbon dioxide into the atmosphere from burning fossil fuels that’s responsible for changing Earth’s atmospheric composition over the last century, rather than climate feedbacks from the ocean or land caused by Milankovitch cycles.”

QED. They also say the cycles operate over the long term and this warming happened fast. But who knows what tipping points a long-term cycle might trigger? After all, when the glaciers retreat, they do it fast as part of a long-term cycle. So for our part we’re more open-minded.

Speaking of glaciers, Milankovitch cycles are generally thought to explain why and when they come and go. And if it’s true, then one possible answer to the question we started with is that they’ve operated a lot longer but unless you’re in an ice age, as the planet has been for 2.6 million years (the Pleistocene) or by some counts 33 million, since significant polar ice first appeared at both poles when the Pleistocene started but before that at the South Pole at the “Eocene-Oligocene Boundary”, they might indeed have caused temperature to fluctuate but not in a way that sent glaciers galloping one way or the other, so their proxy footprint was smaller.

Too small to see, in fact. How would you begin to determine whether Milankovitch Cycles were happening during, say, the Cretaceous? What proxies would you even go looking for?

Here it’s important to note that, despite NASA’s dogmatic assertion, we do not have good paleo evidence of the sorts of short-term temperature fluctuations that typically happen on Earth. The alarmists are united in asserting that the warming of, as NASA put it, “over 1 degree Celsius (1.8 degrees Fahrenheit)” since 1850 is so rapid as to indicate some sort of unnatural shock. But it’s bad science to say so. Even the famous ice core bubbles take decades, even centuries to form, and back further than a million years or so we’re using other stuff like fossils and geological formations that cannot possibly give us a sense of what’s happening in one century.

Mind you the historical record suggests that things like the Medieval Warm Period ended quite suddenly, and the Little Ice Age saw dramatic ups and downs. And decent geological evidence says at the start and end of the “Younger Dryas” reversal of the early Holocene warming, temperature may have shot down then up by 5C in a century or even less, completely naturally.

We don’t want to get too polemical here. Instead we want to quote NASA that Milankovitch Cycles:

“provide a strong framework for understanding long-term changes in Earth’s climate, including the beginning and end of Ice Ages throughout Earth’s history.”

Oops. We’re going to get polemical here because this statement is, regrettably, blatantly and brazenly false. The planet has seen roughly five total ice ages, the Huronian, Cryogenian, Andean-Saharan, late Paleozoic, and Quaternary. Maybe. But remember the first hypothesized period with significant ice at least at the poles, the Huronian, is estimated at 2.4 to 2.1 billion years ago. We’re working with faint proxy traces here.

The second, the ominously-named Cryogenian, which Wikipedia says “may have produced a Snowball Earth in which glacial ice sheets reached the equator” before being ended by CO2, would have destroyed complex life had it not happened between 720 and 630 million years ago before there was any. If it really did create a snowball earth but again we cannot be dogmatic. It’s only “may have” because we’re talking very faint proxy echoes here.

According to our best guesses, there was another from 460-420 MYA and again from 360 to 260 MYA. Then there wasn’t one at the Jurassic-Cretaceous boundary because temperatures dropped significantly but for some reason only half-way to an actual Ice Age. Nobody knows why.

Finally, and we’re rather more certain here, we got the current Pleistocene one starting around 2.58 MYA. Or perhaps 34 MYA, but the reason for the ambiguity there is definition not evidence, because the Antarctic ice sheet began forming around 34 MYA, but major Arctic ice only showed up 2.58 MYA.

Sorry if we’re boring you. But the point is that none of these can plausibly be linked to Milankovitch Cycles. What have they to do with an ice age 2.1 billion years ago, nothing for 1.4 billion years, three in half a billion, then a quarter-billion-year gap? Which is not, you’ll agree, any sort of discernibly rhythmic cycle of any periodicity.

What NASA probably had in mind was glaciations within the current ice age. But when you’re NASA you don’t get a free pass for bungling the terminology. And even so their statement is blatantly wrong, as Milankovitch enthusiasts are painfully aware.

The reason is the so-called “Transition Problem,” again proving Kipling’s point that giving something a long name doesn’t make it better. And the issue here is that for the first million and a half years of the Pleistocene, the pattern of glacials and interglacials was on a 41,000-year cycle, apparently matching the obliquity cycle. Then for the last million it switched to 100,000 years, apparently matching the eccentricity cycle. But why?

Wikipedia tries to sew it up with CO2, of course:

“From 1-3 million years ago, climate cycles matched the 41,000-year cycle in obliquity. After one million years ago, the Mid-Pleistocene Transition (MPT) occurred with a switch to the 100,000-year cycle matching eccentricity. The transition problem refers to the need to explain what changed one million years ago. The MPT can now be reproduced in numerical simulations that include a decreasing trend in carbon dioxide and glacially induced removal of regolith.”

Note that they go back about 500,000 years before the Pleistocene, with a cycle of coolings and warmings that hadn’t yet descended far enough to create glaciations. Unfortunately the seam immediately rips because:

“Even the well-dated climate records of the last million years do not exactly match the shape of the eccentricity curve. Eccentricity has component cycles of 95,000 and 125,000 years. Some researchers, however, say the records do not show these peaks, but only indicate a single cycle of 100,000 years. The split between the two eccentricity components, however, is observed at least once in a drill core from the 500-million year-old Scandinavian Alum Shale.”

And of course the big issue is that 100,000 isn’t 125,000. Gosh. Climate sure is complicated, isn’t it, kids? Almost as if it were non-linear.

Now, as we noted a couple of years ago, one theory is that there was no transition. Rather, Mike Jonas argued on Watts Up With That, it’s actually a 21,000-year “precession” cycle, which seems to show up in Antarctic temperature reconstructions, with every glaciation coinciding with the cycle. But not the reverse because sometimes the 21k cycle doesn’t actually get to a tipping point that unleashes the glaciers, possibly because of how the various longer cycles are interacting to strengthen or counteract one another.

Or maybe it does. Maybe the evidentiary issue is that not every interglacial is as dramatic as the recent Eemian (hotter than the Holocene for reasons no alarmist even wants to try to explain) so it didn’t leave clear proxy traces, and our standard reconstructions underestimate the number of glaciations in the last million years. It wouldn’t be surprising given, again, the blurry nature of the proxies especially as one glacial cycle crunches over the previous one.

Now you get the idea. We don’t know what happened or why. But otherwise it’s all settled. Milankovitch cycles totally explain glaciations and must not be mentioned when the Little Ice Age yields to a long gentle warming. Long complex cycles operate with unpredictable results, but not nowadays because shut up.

We prefer humble curiosity. But then, we’re not “climate scientists”.

4 comments on “The Milankovitch mystery, or, wobbly science”

  1. The problem we have today is that many people get their information from journalists whose understanding of the science of climate change (the real science, not "the science is settled" variety) is no better than theirs, and often worse. It's a case of the blind leading the blind.
    BTW, I had an eccentric Aunt Milankovitch who walked obliquely when she'd had a few drinks. Does this count as precession?
    I've recently set up a Substack channel in which I attempt to demystify technical things, particularly those which are subject to media hysteria. See rogergraves@substack.com

  2. Trough my studies of engineering, I found that the more I studied and learned about a subject, the more aware I was of how little I knew, and the more questions I had about it.
    When I hear somebody saying that the science is settled and that we know it all, I just take note he does not know anything about the subject he is talking about and is just borrowing information he has read from somebody else, who probably knows enough not to open his mouth in public.

  3. Yes Antonio, I have discovered that I am a right wing, blue tie chubby white male when I question the "science".
    Right wing....half correct
    Blue tie....never wear one
    Chubby.... guilty, but I blame vodka

Leave a Reply

Your email address will not be published. Required fields are marked *