Well, this is a problem. Right when you think the science might be kinda sorta settled, you find out it isn’t and there’s a boat load of “issues”.
I’ll start with a “money quote” from a paper, then fill in with the path I took to reach it and a bit on kinds of geomagnetic changes. (A small departure from my usual order of ‘as encountered’).
First off, the Money Quote. RPI is Relative Paleo Intensity (of magnetism in sediments) in this quote; not the cute little computer board ;-)
RPI lows often coincide with the end of interglacial or interstadial stages. The geomagnetic moment loss (330%) over the last two millennia deduced from archeomagnetic results (e.g. [38,39]) might foreshadow the next excursion for the end of our present interglacial, even though this loss started 2200 years ago from an exceptionally high geomagnetic moment value.
So we had a big run up in magnetic strength during the warmth of the Roman Optimum, and it’s been wobbly downhill since, and we ran smack into the Little Ice Age toward the end of it. Now we’ve poked our head up out of the frost on a counter cyclical wobble, and the mag field is also just now turning quite weak ( as in a ‘crossing zero in a few decades’ level of quite weak ) just as the sun goes quiet (exceptionally quiet as in grand minimum quiet if it keeps up being down…). And this paper asserts that low magnetic excursions tends to ‘coincide’ with the end of interglacials.
Somehow “oh dear” doesn’t quite capture it…
Yes, yes, I know. It’s Yet Another Scare The Children Story until more vetting and a lot more “Dig Here!” is done. And, as I’ve kinda sorta avoided the whole “magnets and hand waving done it” topic areas, I’m very deficient in background on this particular topic (and I’ve “poo pooed” more than once over “magnets do it” type statements in the past…without decent reason… other than charlatans using “magnets” far too often and tainting the well…)
A couple of Terms and Background
Ice Ages and Glacials stuff:
“Ice Age” is a problematic term. Formally it means long intervals of cyclical glaciation and warming oscillations. We are, presently, in an Ice Age. Many folks use Ice Age to talk about the frozen periods during an Ice Age so will talk about when the last Ice Age ended 12,000 years ago. Technically that is not correct. It didn’t end. Yes, the ice melted, but that’s the end of a Glacial Period during an ongoing Ice Age. We drop back into ice Real Soon Now in geologic terms. This warm time is called an “interglacial” since it’s a bit of warm in the middle of a frozen sandwich…
To make that less of an issue (and since most folks don’t really care about when Ice Ages cycle, them being many millions of years long and more millions of years between each other) I usually only talk about our current (and ongoing) Ice Age. Then, I’ll call frozen times an Ice Age Glacial and the warm times an Interglacial (or sometimes holocene warming). If you really want to talk about prior Ice Ages, start with the information here:
and be ready to think in terms of many millions of years. Otherwise, I’m talking about our present Ice Age that has had several Ice Age Glacial intervals of about 100,000 years each and several interglacials of about 10,000 years each. No more than a couple of million years all told is my maximum time horizon here. One, and only one, Ice Age with several frozen Ice Age Glacial periods, the last one ending about 12,000 years ago.
Be aware that during Ice Age Glacials there are frequent (in the geologic sense) warm spikes to almost as warm as now. These are called Interstadials. (Just like during warm times, a cold spike is called a stadial).
Stadials and interstadials are phases dividing the Quaternary period, the last 2.6 million years.
Stadial are colder periods and interstadials are warmer. Each phase has a Marine Isotope Stage (MIS) number, working backwards from the present, with stadial having even numbers and interstadials odd numbers. Thus the current Holocene is MIS1 and the most recent ice age is MIS2.
Stages are divided into warmer and colder intervals. Interglacial 5e (the Eemian), the hottest of the last million years, was the oldest interstadial of MIS5, with MIS3 and MIS1 being interstadials and MIS2 and MIS4 being colder stadials. In glacials a and c are stadials and b and d are warmer interstadials. Thus MIS 6a, 6c and 6e are stadials and 6b and 6d are interstadials.
Generally, stadials endure for a thousand years or less, interstadials for less than ten thousand years, interglacials for more than ten thousand and glacials for about one hundred thousand.
The Bølling Oscillation and the Allerød Oscillation, where they are not clearly distinguished in the stratigraphy, are taken together to form the Bølling/Allerød interstadial, and dated from about 14,700 to 12,700 years before the present.
Greenland ice cores show 24 interstadials during the one hundred thousand years of the Wisconsin glaciation. Referred to as the Dansgaard-Oeschger events, they have been extensively studied, and in their northern European contexts are sometimes named after towns, such as the Brorup, the Odderade, the Oerel, the Glinde, the Hengelo, the Denekamp, etc.
The key bit here is to notice that Climate Changes. A Lot. It always has. It always will. It has nothing to do with what people do. It changes all on its own, thank you very much. With periods from tens of thousands of years down to hundreds of years. It gets hot spikes during glacial times. It gets cold spikes during warm times. It just bounces around. But we bag, tag, and classify them with names and numbers and such. Except for “climate scientists” who insist they don’t exist, or don’t matter, or both…
Now, when the papers and links talk about magnetic changes aligned with the end of an interstadial, you know what they are talking about. It means it got cold… The interstadial was warmer, like now, and it ended with a drop into cold (like will happens when the present interglacial ends).
Magnetic Field is generally going to be talking about the geomagnetic field of the Earth. It changes. Some changes are more periodic than others, but change it does. It strengthens, weakens, and wanders around. Folks have decided to class those changes into groups based on how much geography they impact and how long they last (and if the field flips to the opposite orientation and stays there a long time, called a ‘reversal’). Just realize that any notion that the magnetic field of the planet is a stable reliable thing is, from the very start, a broken view. It’s more of a writhing twisting flipping thing. Just on such a long geologic time scale that we tend to not notice. (Unless you are a pilot of a plane or ship. Then you know the North Pole has been headed from mid-Canada when I was a kid 1/2 century ago over toward Siberia at an ever increasing rate… and that something “odd” happens to the mag fields near South America and off of Bermuda… so use your GPS there…)
Jerk is the shortest length of change. Excursion lasts longer and covers more turf. Reversal is the longest and biggest change and can last tens of thousands of years.
In geophysics, a geomagnetic jerk or secular geomagnetic variation impulse is a relatively sudden change in the second derivative of the Earth’s magnetic field with respect to time.
These events were noted by Courtillot and others in 1978. The clearest ones, observed all over the world, happened in 1969, 1978, 1991, and 1999. Data before 1969 is scarcer, but there is evidence of other global jerks in 1901, 1913, and 1925. Other events in 1932, 1949, 1958, 1986, and 2003 were detected only in some parts of the world. These events are believed to originate in the interior of the Earth (rather than being due to external phenomena such as the solar wind); but their precise cause is still a matter of research.
The name “jerk” was borrowed from dynamics, where it means the rate of change of the acceleration of a body, that is, the third derivative of its position with respect to time (the acceleration being the second derivative); or, more specifically, a sudden and momentary spike (or dip) in that rate.
Jerks seem to occur in irregular intervals, in the average about once every 10 years. In the period between jerks, each component of the field at a specific location changes with time t approximately as a fixed polynomial of the second degree, A t2 + B t + C. Each jerk is a relatively sudden change (spread over a period of a few months to a couple of years) in the A coefficient of this formula, which determines the second derivative; and usually in B and C coefficients as well.
The strength of each jerk varies from location to location, and some jerks are observed only in some regions. For example, the 1949 jerk was clearly observed at Tucson (North America, long. 249.17°), but not at Chambon la Forêt (Europe, long. 2.27°). Moreover, the global jerks seem to occur at slightly different times in different regions; often earlier in the Northern hemisphere than in the Southern hemisphere.
Those are bit more often and more pedantic than I care to explore right now, but realize that they happen. Just out of the blue, a sudden shift, for just a while, and in just some places, mostly… As to why:
“Why? Don’t ask why. Down that path lies insanity and ruin. -E.M.Smith”.
Unlike my usual behaviour of following that with “Exploring why…”, I’m going to follow my own advice on this one and “let it go”. Theories are all over the place. I chalk it up to the unstable nature of magnetic fields in swirling rotating conducting liquids.
A geomagnetic excursion, like a geomagnetic reversal, is a significant change in the Earth’s magnetic field. Unlike reversals however, an excursion does not permanently change the large-scale orientation of the field, but rather represents a dramatic, typically short-lived decrease in field intensity, with a variation in pole orientation of up to 45 degrees from the previous position.
These events, which typically last a few thousand to a few tens of thousands of years, often involve declines in field strength to between 0 and 20% of normal.
Excursions, unlike reversals, are generally not recorded around the entire globe. This is partially due to them not being recorded well within the sedimentary record, but also because they likely do not extend through the entire geomagnetic field. One of the first excursions to be studied was the Laschamp event, dated at around 40,000 years ago. Since this event has also been seen in sites around the globe, it is suggested as one of the few examples of a truly global excursion.
So an “excursion” can be a few thousand years and might be global, or maybe not. It’s big. Much bigger than a “jerk”, but maybe not global all the time. Left a bit unclear by “jerk” vs “excursion” is what happens in the 100s of years range… The Wiki then goes on to explore “why” in some depth. Be prepared for lack of understanding…
Scientific opinion is divided on what caused geomagnetic excursions.
The dominant theory is that they are an inherent aspect of the dynamo processes that maintain the Earth’s magnetic field. In computer simulations, it is observed that magnetic field lines can sometimes become tangled and disorganized through the chaotic motions of liquid metal in the Earth’s core. In such cases, this spontaneous disorganization can cause decreases in the magnetic field as perceived at the Earth’s surface. In truth, under this scenario, the Earth’s magnetic field intensity does not significantly change in the core itself, but rather energy is transferred from a dipole configuration to higher order multipole moments which decay more rapidly with the distance from the Earth’s core, so that the expression of such a magnetic field at the surface of the Earth would be considerably less, even without significant changes in the strength of the deep field. This scenario is supported by observed tangling and spontaneous disorganizations in the solar magnetic field. However, this process in the sun invariabily leads to a reversal of the solar magnetic field (see: solar cycle), and has never been observed such that the field would recover without large scale changes in field orientation.
The work of David Gubbins suggests that excursions occur when the magnetic field is reversed only within the liquid outer core; reversals occur when the inner core is also affected. This fits well with observations of events within the current chron of reversals taking 3–7000 years to complete, while excursions typically last 500–3000 years. However, this timescale does not hold true for all events, and the need for separate generation of fields has been contested, since the changes can be spontaneously generated in mathematical models.
A minority opinion, held by such figures as Richard A. Muller, is that geomagnetic excursions are not a spontaneous processes but rather triggered by external events which directly disrupt the flow in the Earth’s core. Such processes may include the arrival of continental slabs carried down into the mantle by the action of plate tectonics at subduction zones, the initiation of new mantle plumes from the core-mantle boundary, and possibly mantle-core shear forces and displacements resulting from very large impact events. Supporters of this theory hold that any of these events lead to a large scale disruption of the dynamo, effectively turning off the geomagnetic field for a period of time necessary for it to recover.
Except for recent periods of the geologic past, it is not well known how frequently geomagnetic excursions occur. Unlike geomagnetic reversals, which are easily detected by the change in field direction, the relatively short-lived excursions can be easily overlooked in long duration, coarsely resolved, records of past geomagnetic field intensity. Present knowledge suggests that they are around ten times more abundant than reversals, with up to 12 excursions documented within the current reversal period Brunhes–Matuyama reversal.
You would think they could have just said “nobody knows”…
I’m preserving the rest of this wiki here since W.W.C. has a habit of rewriting anything that gets linked to climate change and isn’t ‘CO2 Friendly’…
Due to the weakening of the magnetic field, particularly during the transition period, greater amounts of radiation would be able to reach the Earth, increasing production of beryllium 10 and levels of carbon 14. However, it is likely that nothing serious would occur, as the human species has certainly lived through at least one such event; Homo erectus and possibly Homo heidelbergensis lived through the Matuyama reversal with no known ill effect, and excursions are shorter lived and do not result in permanent changes to the magnetic field.
The major hazard to modern society is likely to be similar to those associated with geomagnetic storms, where satellites and power supplies may be damaged, although compass navigation would also be affected. Some forms of life which are thought to navigate based on magnetic fields may be disrupted, but again it is suggested that these species have survived excursions in the past. Since excursion periods are not always global, any effect might well only be experienced in certain places, with others relatively unaffected. The time period involved could be as little as a century, or as much as 10,000 years.
Possible relationship to climate
There is evidence that geomagnetic excursions may be associated with episodes of rapid short-term climatic cooling during periods of continental glaciation (ice ages).
That last line cites this article:
Possible relationships between changes in global ice volume, geomagnetic excursions, and the eccentricity of the Earth’s orbit
Michael R. Rampino1
1NASA, Goddard Institute for Space Studies, 2880 Broadway, New York, New York 10025
A possible relationship between major changes in global ice volume, geomagnetic variations, and short-term climate cooling has been investigated through a study of climate and geomagnetic records of the past 400,000 yr. Calculations suggest that redistribution of the Earth’s water mass can cause rotational instabilities that lead to magnetic excursions; these magnetic variations in turn may lead to rapid coolings through several proposed mechanisms. Such double coincidences of magnetic excursions and sudden cooling and glacial advance at times of major ice-volume changes have occurred at about 13,500, 30,000, 110,000, and 180,000 B.P. The last four and possibly five times of maximum eccentricity of the Earth’s orbit were closely followed by magnetic excursions; catastrophic cooling and rapid ice buildup accompanied several of these excursions. Thus, Milankovitch cycle parameters may lead to glaciation through both insolation changes and geomagnetic effects on climate.
So more for the “things that make you go hmmmmm” department….
Finally, there is what most folks think about when talking about magnetic field changes. A full on reversal where the orientation “flips” North for South and gets stuck that way for tens of thousands or millions of years:
A geomagnetic reversal is a change in a planet’s magnetic field such that the positions of magnetic north and magnetic south are interchanged.
The Earth’s field has alternated between periods of normal polarity, in which the direction of the field was the same as the present direction, and reverse polarity, in which the field was the opposite. These periods are called chrons. The time spans of chrons are randomly distributed with most being between 0.1 and 1 million years with an average of 450,000 years. Most reversals are estimated to take between 1,000 and 10,000 years. The latest one, the Brunhes–Matuyama reversal, occurred 780,000 years ago. A brief complete reversal, known as the Laschamp event, occurred only 41,000 years ago during the last glacial period. That reversal lasted only about 440 years with the actual change of polarity lasting around 250 years. During this change the strength of the magnetic field dropped to 5% of its present strength. Brief disruptions that do not result in reversal are called geomagnetic excursions.
The wiki then indulges a lot of history description and a load of the currently scientifically endorsed speculation about “why” and some of “what happens”. Maybe. They think. Fun to read, sometimes…
The bottom line is that there’s a whole lot of change happening in magnetic fields over time, and you don’t need a full on “reversal” to have magnetic fields dropping quite low and moving around. Kind of like what is happening now…
So narrowing back in on the recent times, we have that above referenced paper about magnetic changes, weakening, and cold periods.
Is the paper with the “money quote” from the top in it (though near the bottom of it). It goes to some pains to look at sediment cores from near Portugal and does a load of “fancy math” to smooth without averaging and with little data loss. I’ve not read it all in enough detail, nor given it enough ‘think time’ to know if the method is really sound. On a ‘top read’ it looks OK. But it is different from the usual, so ought to be pondered a bit more.
At any rate, they find a correlation between some kinds of magnetic field weakening / changes and onset of the end of warm periods (both interglacials and interstadials).
Geomagnetic moment variation and paleomagnetic excursions since 400 kyr BP: a stacked record from sedimentary sequences of the Portuguese margin§
Nicolas Thouveny a;,Julien Carcaillet a,Eva Moreno a,Guillaume Leduc a, David Ne¤rini b
a CEREGE, Europo“le Me¤diterrane¤en de l’Arbois, P.O. Box 80, Aix en Provence Cedex 4, France
b Centre d’Oce¤anologie de Marseille, Case 901, Luminy, 13288 Marseille Cedex 9, France
Received 23 December 2002; received in revised form 26 November 2003; accepted 4 December 2003
A paleomagnetic study was performed in clayey-carbonate sedimentary sequences deposited during the last 400 kyr on the Portuguese margin (Northeast Atlantic Ocean). Declination and inclination of the stable remanent magnetization present recurrent deviations from the mean geomagnetic field direction. The normalized intensity documents a series of relative paleointensity (RPI) lows recognized in other reference records. Three directional anomalies occurring during RPI lows chronologically correspond to the Laschamp excursion (42 kyr BP),the Blake event (115^122 kyr BP) and the Icelandic basin excursion (190 kyr BP). A fourth directional anomaly recorded at 290 kyr BP during another RPI low defines the ‘Portuguese margin excursion’. Four non-excursional RPI lows are recorded at the ages of the Jamaica/Pringle Falls,Mamaku,Calabrian Ridge 1,and Levantine excursions. The RPI record is characterized by a periodicity of V100 kyr,paleointensity lows often coinciding with the end of interglacial stages. This record sets the basis of the construction of an authigenic 10Be/9Be record from the same sedimentary sequences [Carcaillet et al.,this issue].
A 2004 Elsevier B.V. All rights reserved.
Keywords: sedimentary records; geomagnetic ¢eld directions and paleointensity; paleomagnetic excursions; paleomagnetic events;
relationships between the climate and the geomagnetic ¢eld
FWIW, I came to this paper via an archives discussion here:
that has the usual amount of “Does So!” vs “Does Not!” bickering and including some more references to other things too. As a sample of that discussion:
There are a series of papers that support the assertion that geomagnetic excursions cause Younger Dryas magnitude abrupt climate change events. There is a geomagnetic excursion that correlates with the Younger Dryas abrupt climate change and with similar abrupt climate change events. Looking at how the geomagnetic field has changed in the past (the frequency of reversals, the change in the periodicity of excursions during the current ice epoch, and the periodicity of the Younger Dryas type abrupt climate events, the following hypothesis can be formed. The periodicity of the forcing event that causes the geomagnetic excursion is around 12 kyr. The same forcing event (smaller magnitude) causes geomagnetic jerks which are secular geomagnetic field changes (regions on the planet surface that have stronger normal or reversed polarity in reference to the current geomagnetic field configuration. It appears the cyclic event that is forcing the geomagnetic field is external. The field changes are too closely spaced to be due to internal changes in the planet. As the liquid core is conductive rapid field changes in the liquid core induce counter fields in the conductive liquid which inhibits rapid field changes. The Paleoclimatic data shows that the Younger Dryas cooling event occurred over 15 years in three 5 years steps. The entire Younger Dryas cooling event was complete in 40 years. The planet cooled from interglacial warm to within 25% of the glacial temperatures. Temperature in the North America cooled by around 18F. What is interesting is the Younger Dryas is one of a series of similar cooling events, including the termination of past interglacial periods. During the glacial period the external forcing event has less affect on the geomagnetic field and planetary temperature as the planet is already cold and vast regions of the planet’s surface is covered with ice sheets which insulate the planet’s surface from the cyclic forcing event, and planetary temperature is already very cold so increased GCR has less effect. The affect of the external cyclic event that is forcing the geomagnetic event it appears is dependent on the earth’s axis tilt at the time of the event, timing of perihelion, the eccentricity of the earth’s orbit, the distribution of the continents on the surface of the planet, and the area of the planet’s surface covered by ice sheets.
[then links to the paper and has some quoted material]
Sorry but this is really apples and oranges. Yes, there have been an abnormal amount of geomagnetic excurions in the current Lachamps chron, but it has nothing to do with the Younger Dryas stadial. See for instance Guyodo and Valet 1999 which concludes: There is no correlation between these intensity dips and cold climate events, although such a correlation has been suggested. Obviously the Younger Dryas has been associated with a erratic geomagnic reversal, known as the Gothenburg magnetic flip (Morner 1971), but that has only been found in one sediment core in the Botanical garden in Gothenburg. It has never been reproduced, despite vigourous attempts. But there was something wrong with that core. it was broken. Although it has never been officially withdraw, the Gothenburg flip is no longer considered (info oral lecture Prof Cor Langereis). Reference: Morner, R. A., 1971, Late Weichselian paleomagnetic reversal. Nature Physical Science, vol. 234, no. 52, pp. 173-174 (December 27, 1971).
Sorry but this is really apples and oranges. Yes, there have been an abnormal amount of geomagnetic excurions in the current Lachamps chron, but it has nothing to do with the Younger Dryas stadial. See for instance Guyodo and Valet 1999 which concludes: Yohan Guyodo & Jean-Pierre Valet’s 1999 work “cold adjusted” the proxy data base that was used to determine geomagnetic field strength. The “cold adjustment” increased the geomagnetic field strength inferred from the ocean floor sediments during periods when the planet was cold which makes it appear the actual change in geomagnetic field strength did not cause the cooling. Subsequent geomagnetic field intensity proxy analysis used different proxies to find the “archeomagnetic jerks” which are abrupt secular (regional and hemispheric) changes to the geomagnetic field intensity with a periodicity of roughly 400 years. The secular geomagnetic field changes weakens the geomagnetic field temporarily in a specific region and hemisphere and changes the tilt of the field offsetting it from the rotational axis of the planet. The resultant archeomagnetic jerks is caused by the small version of what is forcing the geomagnetic field.
For me, there’s enough here to make it a “Dig Here!” that needs more looking at. I can see things like magnetic excursions, or reversals, from any of: large impacts disrupting fluid flows, from fundamental instability of large rotating blobs of molten metal, and from major solar changes and events. Maybe even some of that Electric Universe stuff.
Yes, asking “Why”…
But it does look like folks have found a connection between low mag field levels and the end of interstadials and interglacials. Given that we are near the end of our interglacial, and the magnetic field of the earth is falling fast, I’d say this needs some closer attention.