These are the very last days of July, 2013. If we don’t stop and capture the sunshine and the gentle trade winds, the scented leaves and the birdsong, it will be over in a matter of hours and we will be neck-deep in the warm beach sands of August. But that is true only until it is no longer true. In fact, the clock is ticking towards that day when the warmth of July will be a thing of the past.
In fact, if we fast forward 11,000 years, it will be winter in July. And it won’t happen because of anything anyone has ever done or will ever do. It will happen because of something called General Precession.
Ah, the sound of sleigh bells jingling in the bright cold air of a summer that has come once again to the denizens of a beautiful Earth, celebrating yet another summer vacation indoors while the snow plows work mercilessly, clearing away the streets so that folks can go out and visit with friends while enjoying their favorite things, such as crisp apple strudels and warm woolen mittens.
So what is this general precession thing that causes winter to occur in July? Well, it’s not really a thing but rather, more like an action. Wikipedia describes it as the change in the orientation of the rotational axis of a rotational body (the Earth) in which the second Euloer angle is constant. ~ Wikipedia 
Now, I don’t know about you, but that’s just nonsensical blathering to me. However, since it is rather important to me to understand why my favorite time of the year is going to eventually become cold and unappealing, I am going to try to figure this out using my less-than-stellar Taobabe brains. So let’s break it down into its components.
This is the WHAT and the HOW:
So what the heck is a Euloer angle? How do you even pronounce that? Is it someone who delivers eulogies?
I didn’t think it was that simple—but in this case, it really is simple. Notice that this spinning top has one point (at the bottom) that does not move. It’s dead stuck in one spot. This is the Euloer angle, and it is constant because it never moves.
Now, take a look at its opposite end (at the top). That one is moving all over the place. The movement is so wide that it causes a serious wobble to the sphere. That is what is meant by a change in the orientation of the rotational axis.
Now let’s get into the WHY:
If it was just the Earth, spinning by its lonesome, with only its gravitational weight to make it bulge here and there (see my previous post Lumpy Bumpy Humpty Dumpty), the effect of its planetary precession would be so small, we would barely notice it. In truth, the Earth is part of a whole system of other bodies, weighing in and contributing to that gravitational pull, and this pull is ridiculously strong.
Consider that our very own Moon (aka Luna), is just about one of the biggest moons to be found in our solar system, and then consider that Earth is a rather small potato when compared to all the other giants orbiting the Sun, and we have a strange anomalous relationship between a rather small planet and a rather large satellite.
That lunar pull is so strong that it actually causes Earth to bulge out around its midsection. Add the gravitational pull of the mighty Sun to this equation and the Earth’s equatorial region is completely squashed out of shape.
With both the Moon’s and the Sun’s combined gravities exerting their influence on the Earth, they collectively yank her chains, so to speak, and Earth’s spin becomes noticeably wobbled and teetered.
The action of Sun and Moon on poor Earth is what is known as the lunisolar precession and it is about 500 times greater than planetary precession alone. And before you even have to ask, yes all the other planets exert their pull as well, but their influence is slight compared to the lunisolar precession’s pull so I have decided to leave them out of the mathematical equation.
Mathematical equation? Did I just say that dreaded ‘M’ word?
Why, yes—yes I did, but only because I don’t have to do the hard work of calculating this horrid thing out to its bitter end. I am simply going to let smarter people do the math and then point to it and say, “See? That’s how it works.”
- Gm = standard gravitational parameter of the perturbing body
- r = geocentric distance to the perturbing body
- C = moment of inertia around Earth’s axis of rotation
- A = moment of inertia around any equatorial diameter of Earth
- C − A = moment of inertia of Earth’s equatorial bulge (C > A)
- δ = declination of the perturbing body (north or south of equator)
- α = right ascension of the perturbing body (east from vernal equinox).
No need to look at the equation closely. I swear, the numbers work out correctly.  (I stole it from Wikipedia so it must be correct. N’est ce pas?). Anyhoo, onto bigger and better things.
This is the WHEN:
The Earth’s precession is very, very, slow. How slow? From start to finish, it is a 26,000 year cycle. We have already passed the half-way point of this latest precession cycle, which happened two-thousand years ago (give or take a few years). In other words, right around the time Jesus was born, we hit mid-cycle.
We are now moving into the second phase of the cycle, which means our summers will eventually get colder and colder until it becomes winter in July, 11,000 years from now.
Yes, this will happen.
No, this has nothing to do with CO2 or human-created global warming.
It does not matter what we do or don’t do, and it doesn’t matter if we’re even around to watch it happen.
It will simply happen when the time comes for it to happen because it is a natural and rhythmic cycle which exists outside of and beyond our sphere of influence.
It has been in existence since the world began and it will not end until Earth is subsumed by the Sun (or is otherwise destroyed due to some cataclysmic event beyond our imagination).
Of course, we’ll all be safely dead by then, so this won’t really have much of an impact on us—-except for a couple of OTHER things about Earth’s movement, which I am a bit more concerned with.
You see, general precession is just one of three Earth cycles that a gentleman by the name of Milutin Milankovitch has so very kindly mapped out for us back in 1920.  Even though we won’t be around to witness the next precessional winter in July, the other two cycles will be interesting to live through, as they are coming ’round the bend in short order.
(…to be continued)
The “cold phase” exists only during the (minority) Ice House conditions from which we are experiencing a brief interglacial break. Most of the time, Earth’s average temperature is about 10°C higher, in Hot House mode. Life abounds during those multi-hundred-million year long periods. Probably has more to do with continental drift and the resulting ocean circulation than precession.
Thanks for your observation. Could you please cite the sources for the information you just posted so that I can go and learn something new? Thanks!
I am going to stand by my assertion unless you can come up with facts that can support your argument. Temperature measurements going back hundreds of thousands of years support the long-ice-age/brief-warm-interglacial periods. Here is a link to a graph of that temperature fluctuation which shows brief warm periods and very long cold periods.
“Our climate has experienced much more dramatic change than the Little Ice Age,” says Cook. “Over the past 400,000 years, the planet has experienced ice age conditions, punctuated every 100,000 years or so by brief warm intervals. These warm periods, called interglacials, typically last around 10,000 years.” ~ John Cook.
I’ll get around to digging up some refs. In the meantime, look over any paleogeology text covering the past few billion years. The last 4-5 million, with its glaciation and interglacials, is an exception to the rule, not the rule.
Ice ages are hardly exceptions to the rule. “Rocks from the earliest well established ice age, called the Huronian, formed around 2.4 to 2.1 Ga (billion years) ago during the early Proterozoic Eon.” ~ wikipedia. Since the Earth is only 4.54 billion years old, this means ice ages have been occurring at steady and regular rates for more than half of Earth’s timespan.
If you state something, please be willing to back up your assertions with some forms of evidence. I try to do this with all my postings because I know that my words may not have much weight, but the words of scientists and professionals in their fields of work, although they may not necessarily be 100% accurate (nothing ever is, but it’s the best we can hope for in this ever-changing world we live in) at least, they come from a more informed source.
Sure, but they’re the minority, and generally pretty deadly. The good times are the warm times.
Brian, for the past two billion years or more, it’s been cycling 100,000-year glacial periods, alternated by 10,000-year interglacials. We have been cold far more often than we have been warmth.
And yes, I agree with you that cold is far far deadlier than warm, and that the warm spells are the good times. But I’m trying to get you to comprehend that once we get back into the coldness, it won’t be a short interval, it will be around a hundred-thousand years of cold.
False. That 100,000 year cycle is very recent, only a few million years old. In fact even then it was about 41,000 years/cycle for a while. As I said, get a good geology book.
Whatever made you think you had to tell me the next cold period will be 100,000 yrs long?
The precession theory is of limited applicability. What was it up to during, say, the Triassic?
Brian, the graph that you pointed me to shows CO2 concentrations, which was then calculated to reflect temperature changes that are suppose to follow the rise and fall of CO2. For the longest time, everyone thought this was true. However, within the last seventeen years, we have detailed recordings of CO2 levels rising sharply upwards, but Earth’s temperature has remained basically stable, plateauing and even going downwards. If we were to track temperature changes with the amount of CO2 in the atmosphere, our seas would be boiling at this time (which it is not). If you are going to use good reference, make it up-to-date, because scientific understanding and discovery changes very quickly.
As for the General Precession part of your rebuttal, I never did say that it was the ONLY thing to affect Earth’s climate. It is only ONE of many factors which, when in alignment with each other, cause various things to happen. In one of my posts, I also talked about lunar, as well as solar influence, including sun spots (and the lack thereof) which influences cloud cover. I will do a more in-depth posting on that in the near future.
The most important thing to grasp from all this is that when it comes to global climate change, it is never ONE SINGLE INDICATOR that causes changes. It is most likely to be a combination of many factors, converging into a single point which marks the event horizon.
There is NO observational evidence, in paleohistory or currently, to indicate that CO2 is anything other than a trailing indicator of temperature.
A fascinating document:
Click to access WarmAudit31.pdf
No observational evidence? Are you positive about that? Here is a scholarly paper published in Climate by Dr. Syun-Ichi Akasofu which talks about that very same issue. It is rather long and involved, but it does allow for download of the PDF.
Abstract: The rise in global average temperature over the last century has halted since roughly the year 2000, despite the fact that the release of CO2 into the atmosphere is still increasing. It is suggested here that this interruption has been caused by the suspension of the near linear (+ 0.5 °C/100 years or 0.05 °C/10 years) temperature increase over the last two centuries, due to recovery from the Little Ice Age, by a superposed multi-decadal oscillation of a 0.2 °C amplitude and a 50~60 year period, which reached its positive peak in about the year 2000—a halting similar to those that occurred around 1880 and 1940. Because both the near linear change and the multi-decadal oscillation are likely to be natural changes (the recovery from the Little Ice Age (LIA) and an oscillation related to the Pacific Decadal Oscillation (PDO), respectively), they must be carefully subtracted from temperature data before estimating the effects of CO2.
Groan. Where, in that pile of circular mental faeces, is there any observational evidence (which is what I was referring to)?
The paper takes observed temperature readings and makes a scientific projection based upon trajectories. Obviously, you can’t have an observational evidence for future projections. You can only have conjectures, but not all conjectures are weighted the same. Some are based on nothing and others are based upon past trends. There is no other method (except getting into a time machine and going into the future yourself) to determine future trends.
One of the better projections/predictions. The evidence I was referring to is any past prediction which has been confirmed (preferably a unique one which other factors could not and did not provide.) CO2 warming has failed to provide any so far, and in AR5 is backing off even guesstimating sensitivity, since the past numbers have produced models which “run too hot”, universally, Not even one which is too cool! If they were just imprecise, that’s almost impossible. They are systematically flawed.
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