The Cause of Interglacials
What’s caused our current interglacial?
Numerous theories exist on what caused our current interglacial. Most explanations greatly oversimplify the cause to a “temperatures increased, so ice melted”, and fail to consider when, how or why the ice melted where it did, and why it didn’t somewhere nearby. For example, during the Oldest Dryas some ice sheets melted vigorously in both the Northern Hemisphere (e.g. western Canada) and in the Southern Hemisphere (Patagonia), while others didn’t and still haven’t (Greenland, Antarctica).
Does Earth default to glacials?
Right: Antarctica ice core data versus Age. Source: Wikipedia. Left: Imbrie et al., 2006 SPECMAP temperature proxy data versus age. Data
Antarctica temperature data (above left) seem to indicate that glacials last much longer on average than interglacials. But Antarctic temperature data are not indicative of global temperatures: a substack post shows that during the Younger Dryas Antarctica warmed, Greenland cooled, and global temperatures dropped slightly. The right graph, Imbrie et al’s 2006 SPECMAP data, provides a more globally representative view of the temperature variations during the last 5 interglacial-glacial cycles, and demonstrates that the temperature proxy was above average roughly 50% of the time, consistent with the way averages are defined. More interesting is that the temperature proxy appears to alternate between 50 ka periods of ~1 and ~-1.
The abrupt termination of a glacial therefore requires an energetic “disruptor” of the glacial status quo, a physical process that globally causes a step-change in heat. The 100 ka (ka = 1000 years) periodicity of the temperature graphs above reveals this disruptor is almost certainly being modulated by cyclical changes in the Earth’s orbit (orbital forcings).
Milankovitch Cycles
In the 1920’s Milutin Milanković hypothesized that Earth’s orbital variations cause changes in solar insolation (solar irradiation) that in turn drive climate changes. These orbital variations include:
- eccentricity (mainly ~405 ka periods, but also ~95 ka and ~124 ka)
- axial tilt (~41 ka periods)
- precession (~25.7 ka periods)
Legions of researchers over the past 100 years have tried – and failed – to tie these orbital variations to Northern Hemisphere (NH) solar insolation variations that peak at the Last Glacial Maximum (LGM). Cycles with shorter periods (tilt & precession) have the greatest effect on local solar insolation, but would cause more frequent interglacials than what is observed. Combining all forcings into a single insolation model also brings no joy. Muller and MacDonald[1] summarize the problem:
“the abrupt termination of the ice ages preceded warming from insolation, an effect we refer to as ‘‘causality problem.’’”
In other words, (combinations of) Milankovitch cycles don’t cause a step-change in NH solar insolation around the time of the LGM.
Temperature proxy variations of the Antarctic EDML ice core compared to Milankovitch-modeled summer insolation changes. Source: [2]. YD=Youngest Dryas, OD=Oldest Dryas
The graph above is fairly typical: the slow change in Earth’s orbital variations causes a gradual multi-millenial change in NH solar insolation, while the abrupt termination of the glacial status quo requires a forcing that was highly disruptive around the time of the LGM (22,000 BP). It’s evident that NH solar insolation variations could not have caused the severe Oldest Dryas melting episodes, such as the Lake Missoula megafloods that peaked around 18,500 BP (attributed to geothermal melting) or the New York glaciers around 19,000 BP (attributed to increased Atlantic ocean heat) or the “stepped warming” in the Southern Hemisphere (SH) that rapidly melted the Patagonia ice sheet between 17,500 – 17,150 BP[3]. The graph above does indicate that solar insolation plays an important role as “pacemaker”[4]: once a glacial is abruptly pushed into an interglacial the increasing solar insolation prevents a return to the glacial status quo.
Note that some authors claim interglacials are caused by orbital eccentricity (OE) variations, an idea that was robustly debunked by Muller and MacDonald[1]:
- OE variations result in solar insolation changes that are far too small to be significant
- OE’s main period is ~400 ka rather than ~100 ka; 400 ka cycles are absent in most climate records (see graphs below)
- a full resolution spectral analysis of climate records
“shows that the 100-kyr period is a single, narrow peak, a simple pattern that strongly confirms an astronomical origin”
In other words: solar insolation variations didn’t cause our current interglacial, which in hindsight is unsurprising: due to ice’s high albedo only 10-20% of any (small) solar insolation increase is absorbed, while a true disruptor must cause a vigorous melt and a swift retreat of the ice cover, after which the solar insolation pacemaker can cause further vigorous melting.
Orbital inclination – the forgotten orbital forcing
The invariable plane of our solar system is a plane perpendicular to the angular momentum vector of the solar system, which is approximately equal to the orbital plane of Jupiter. Muller and MacDonald[1] demonstrate that orbital inclination (OI) variations in the invariable frame generate cycles with 100 ka periodicity that match temperature cyclicity very well (see graphs below), so conclude that OI drives glacial cycles. Zhou et al.’s[5] cross-wavelet spectrum between Asian monsoon rainfall and geomagnetic field strength similarly exhibits a strong coherency at the ~100 ka period, but only minor, perhaps insignificant coherency at classic Milankovitch insolation frequencies, despite their climate records showing distinct 23 ka (precession) periods.
Left: Spectral power of temperature proxy data (top 2), and eccentricity (middle) and inclination models (bottom) Source: [1] Right: Cross-wavelet spectrum of geomagnetic and climate proxies. Source: [5]
At this point many will be thinking that this type of reasoning is piling heresy (OI forcing) on top of heresy (solar insolation variations don’t cause interglacials) on top of heresy (orbital forcings drive geomagnetic field variations). But the evidence is undeniable: Earth’s global average surface temperature, Asian monsoon rainfall and geomagnetic field variations show a strong 100 ka periodicity that almost certainly was caused by OI variations, while there is no plausible explanation on how solar insolation changes can modify the geomagnetic field.
Orbital Inclination Forcing
In the invariable frame Earth’s OI variations follow a 100 ka period whereby its values cycle between ~1º and ~3º[1], implying that its forcing reverses (changes sign) at its minima and maxima, 1º and 3º resp.: OI forcing reverses when Earth’s orbital inclination shifts from approaching the invariable plane (3º → 1º) to moving away from it (1º → 3º), and vice versa.
Muller and MacDonald temperature proxies (ocean drilling project site 607 (top) and the SPECMAP compilation (bottom))versus age. Annotated lines are when OI = ~1º (local minimum, blue) and ~3º (local maximum, red)
A plot of Muller and MacDonald’s[1] temperature proxies demonstrates that the switch from approaching the invariable plane to leaving it (blue lines; OI = ~1º, local minimum) is followed by a 50 ka period of cooler temperatures, while a warmer period follows the switch from leaving to approaching (red lines; OI = ~3º, local maximum). Temperature variations therefore follow a rectangular function (step function): OI forcing causes 50 ka periods of warming and cooling. Note the Muller and MacDonald’s 1997 SPECMAP version was updated by Imbrie et al. in 2006, but that the updated version shows similar fluctuations and is based on more and better data.
0-300 ka interval Top left: Imbirie et al.’s SPECMAP data, Top Right: Guyodo Valet 1999 Geomagnetic Intensity variations. Data. Bottom (repeat): Orbital Inclination variations according to Varadi et al, 2003. Data. Annotated lines: min (blue) and max (red) OI.
Geomagnetic intensity and global temperature graphs (above) both show a strong 100 ka periodicity, with peaks lagging OI peaks by either a 1/4 period (temperature) or a 1/8 period (geomagnetic intensity).
Autocorrelation functions for: Top left: the Imbrie et al., 2006 global temperature proxy. Top right: Guyodo Valet 1999 geomagnetic intensity data. Bottom: Varadi et al. 2003 OI data
The autocorrelation of the SPECMAP data confirms the data resembles a 50 ka step function: significant positive autocorrelation for lags up to 20 ka, and significant negative autocorrelation for lags between 30 ka and 70 ka, with the switchover around 25 ka (1/4 period). The temperature data behave as a 100 ka period step-function with discontinuities every 50 ka that are concurrent with the OI minima and maxima. OI peaks and troughs follow a predictable 100 ka period cosinusoidal function. The geomagnetic intensity data follow a fairly complex 12.5 ka (pos) + 37.5 ka (neg) + 12.5 ka (neg) +37.5 (pos) period function, which is the result of a multivariate OI dependency (see below).
Crosscorrelation functions between: Top: temperature and geomagnetic intensity; Bottom left: OI and temperature; Bottom right: OI and geomagentic data
Cross-correlation plots (above) reveal that temperatures lag the OI by 25 ka: the temperature highs (interglacials) occur middle in the period when OI is decreasing from ~3º to ~1º. The geomagnetic data show a more complicated relationship with OI, due to a dependent variable – Outer Core temperature (see next substack post)- also covarying with OI. This causes the geomagnetic intensity peaks to precede the OI peaks by a 1/8 cycle (12.5 ka) and its troughs to precede OI troughs by 12.5 ka, resulting in a phase-shifted 12.5 + 37.5 ka period cyclicity.
The solar wind and solar particle events – the forgotten solar power source
Solar insolation is by far the most powerful energy source that reaches Earth, which is why many climate modelers habitually ignore all other energy sources. Other significant solar power sources include:
- The solar wind, a sun-emitted stream of charged particles that delivers a fairly constant average Earth-incident 4 – 6 TW of power
- Solar particle events (SPE), some of which delivered estimated power pulses of up to 30,000 TW during the OD. Powerful Earth-incident SPE’s occurred around 18,600 years ago (start Oldest Dryas) , 14,800 BP (start Bøllling-Allerød) and 17,600 BP, around the time of the “stepped warming” that occurred in Patagonia.
Solar wind and SPE power largely consists of the momentum and magnetic energy of their charged plasma stream particles. Their flowpaths mainly follow the heliomagnetic field lines, whose interplanetary azimuths and incidence angles fluctuate (figure below) around and in the solar equator plane that itself is at a ~7º angle to the invariable plane[9]. Average Earth-incident SPE and solar wind energy would therefore be maximal if Earth’s orbit was wholly in the solar equator plane, but would be significantly reduced if Earth had an orbital inclination of 90º. An increasing OI – away from the solar equator/invariable plane – therefore reduces incident solar wind and SPE power, while a decreasing OI – towards the plane – increases incident power. Next week’s substack post discusses how these power variations cause geomagnetic field strength, geothermal heat flux and surface temperature variations.
The heliospheric current sheet that results from the influence of the Sun’s rotating magnetic field on the plasma in the interplanetary medium (SPE’s & solar wind). Source: Wikipedia
Other proposed causes of interglacials
At this point many readers will be thoroughly disappointed that their favorite theory on the cause of the last glacial period end has not been discussed. Most of these theories depend on solar insolation variations pushing Earth’s climate into an interglacial, although the above discussions demonstrate that such a reliance is incompatible with the undeniable OI forcing. Vieira et al. 2012[10] claim:
“the maximum change in the average TSI [due to OI forcing] over timescales of kyrs is 0.003 Wm-2”
For completeness’ sake:
- Ocean currents: ocean currents played an important role during the melting of the ice sheets as a horizontal advector of cold and warm. But a change in horizontally advected heat requires either a large change in albedo or solar insolation around the time of the LGM, so in essence requires an additional end-of-glacial cause.
- Cosmic Rays: a theory proposed by Kirby in 2004, who agrees that orbital forcings are responsible for glacial cycles, and also agrees that the classic Milankovitch cycles and solar insolation are not responsible. He attributes the end of the last glacial period to variations in cosmic rays (modulated by the heliomagnetic field) and their effect on cloud formation. The theory relies on three speculative and contentious assumptions:
o Abrupt step changes in cosmic rays occurring with 100 ka periodicity
o Cloud formation is affected by cosmic ray variations
o Increased cloud formation causes global warming. Clouds reflect solar insolation energy, but also help retain Earth-surface emitted thermal energy, and as such have been invoked as the possible cause of both the beginning and end of glacial periods. A recent study indicates that clouds[7]
“have a large net cooling effect on the planet”
So are an unlikely cause of an interglacial.
- Dust: this idea was popularized by Ellis and Palmer[3] in 2016. It relies on four highly speculative assumptions: 1) that a reduction in atmospheric CO2 caused a massive areal die-back of plants, mainly at high altitudes, 2) that this plant die-back caused desertification, 3) that winds transported desert dust onto the ice sheets, and 4) that this dust caused an albedo decrease that caused melting.
Left: Profiles of microparticle (dust) concentration. Source: [6]. Right: Sea Level Rise Curve. Source: Wikipedia
Ruth et al. [6] however show a 100-fold decrease in dust concentrations from the LGM (1 ppm) to the Holocene (10 ppb; 1 µg/kg = 1 ppb), indicating dust concentrations are inversely proportional to melting. For example, the large Bølling-Allerød (BA) “Meltwater Pulse 1A” occurred when dust levels were around 10 ppb, a concentration that is multiple orders of magnitude too low to have an impact on ice albedo.
- CO2
Atmospheric CO2 versus age. Top: last 800 ka (Source: [3]), Bottom: Since LGM (Source: [8]) Red: Antarctic temperature. Blue: global composite temperature. Yellow: CO2.
A too perfect correlation exists between atmospheric CO2 and Antarctic temperature, while very poor correlations exist between CO2 variations and most other parameters: global temperatures, Greenland temperatures, sea level rise, melting events, etc. Additionally, no step change occurs around the time of the LGM, and CO2 increases were minimal at the time of the severe Oldest Dryas melting in Patagonia or Western Canada. Shakun et al.[8] agree that:
“CO2 did not initiate deglacial warming”
So atmospheric CO2 in effect also likely functioned as a “pacemaker”.
A previous substack post documented that ocean warming around the time of the LGM caused Antarctic sea ice cover to melt and Antarctic onshore temperatures to rise. A recent study has shown that sea ice helps remove CO2 from the atmosphere, or conversely release CO2 during melting, suggesting that Antarctic sea ice melting drove CO2 increases rather than vice versa, or that the CO2 measured in Antarctic ice core gas bubbles represents the volume of calcium carbonate crystals that formed at the time of ice formation.
Conclusions
Orbital Inclination Forcing drove and is driving the glacial – interglacial cycles: the last 5 glacial-interglacial cycles show a good, statistically significant correlation between variations in Earth’s orbital inclination, and global temperature and geomagnetic intensity variations. Earth’s orbital inclination variations only vary solar insolation by (an insignificant) 0.003 Wm-2 [10] so the main conclusion is: solar insolation variations are not causing the glacial-interglacial cycles. Which – oddly – reflects the IPCC conclusion (that I agree with) that solar insolation variations are not causing our current global warming episode. But here’s the rub: IPCC model only 2 natural forcings, solar insolation and volcanics. The latter acts mainly to limit solar insolation (volcanic ash). Which unequivocally demonstrates that the IPCC climate models are missing a major climate forcing, one that varies with orbital inclination. The IPCC models cannot reproduce the last 10 major climate change episodes, the glacial-interglacial and interglacial-glacial transitions.
References
[1] Muller, R. and MacDonald, G., 1997, Spectrum of 100-kyr glacial cycle: orbital inclination, not eccentricity. PNAS, 94, 8329-34 .
[2] Williams, C.,et al., 2010, Deglacial abrupt climate change in the Atlantic Warm Pool: A Gulf of Mexico perspective, Paleoceanography, 25, PA4221, doi:10.1029/2010PA001928.
[3] Ellis, R. and Palmer, M., 2016, Modulation of ice ages via precession and dust-albedo feedbacks, Geoscience Frontiers, doi: 10.1016/j.gsf.2016.04.004.
[4] Hulton, N. et al., 2001, The Last Glacial Maximum and deglaciation in southern South America. Quaternary Science Reviews, 21, 233-241, 10.1016/S0277-3791(01)00103-2.
[5] Zhou, W. et al., 2023, Eccentricity-paced geomagnetic field and monsoon rainfall variations over the last 870 kyr, PNAS, 120, https://doi.org/10.1073/pnas.2211495120
[6] Ruth, U. et al., 2003, Continuous record of microparticle concentration and size distribution in the central Greenland NGRIP ice core during the last glacial period, J. Geophys. Res., 108, 4098, doi:10.1029/2002JD002376, D3.
[7] Ramanathan V. and Inamdar, A., 2006, The radiative forcing due to clouds and water vapor. In: Kiehl JT, Ramanathan V, eds. Frontiers of Climate Modeling. Cambridge University Press, 119-151.
[8] Shakun, J. et al., 2012, Global warming preceded by increasing carbon dioxide concentrations during the last deglaciation. Nature 484, 49–54, https://doi.org/10.1038/nature10915
[9] Balogh, A. et al., 2008, The Heliosphere through the Solar Activity Cycle. Springer, 286 pp.
[10] Vieira, L. et al., 2012, How the inclination of Earth’s orbit affects incoming solar irradiance, Geophysical Research Letters, 39, doi:10.1029/2012GL052950
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Corona Hotspot
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Watch Valentina Zharkova if you want to know what will happen next https://www.youtube.com/watch?v=tgMK2QIw-YE and read my blog.
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Richard
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The last ice age, when glaciers covered Canada , the US and Asia – the Arctic was similar to today with seasonal open waters – geothermal anyone !
Reply
Jerry Krause
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Hi Koen and Richard,What do either of you know about “leads” and their causes? (https://follow.mosaic-expedition.org)
Have a good day
Reply
Koen Vogel
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Hi Jerry, obviously not a lot. I spent a few minutes to find something on leads at the mosaic-expedition, but couldn’t: your comment is a bit too cryptic. BTW the article lost its hyperlinks and I would like to pass on the CO2-ice one to anyone who’s interested:
https://www.sciencedaily.com/releases/2014/09/140922110424.htm
@ Richard: yes, geothermal. That’s where I’m going with this on my substack
https://thinkandhammer.substack.com/publish/posts/detail/141265454?referrer=%2Fpublish%2Fposts%2Fpublished
where on 8 March I’ll publish the physics behind this, and on 15 March will publish some examples of the forcing in action, such as the Little Ice Age, the 4.2 ka event, etc. I’ll also send copies to PSI for publishing here.
Reply
Jerry Krause
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Hi Koen,
Thanks for the reply. L”leads” A cracks which spontaneously form in the 6ft+ thick Arctic ice. These leads allow seals to live most beneath the ice and polar bear to live on the ice during the winter-spring seasons. I will allow you and other PSI readers explain how it is these cracks spontaneously form? A clue is the most obvious is most difficult to see. You should allow this dumb academic stump you guys who know so much.
Have a good day
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S.C.
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Hi Jerry. I have not heard of this phenomenon before, that is of spontaneous cracks in 6′ ice, but I don’t mind taking a stab.
The first possible culprit to come to mind is pressure from the sea below. Water, especially at extreme temperatures, definitely has the power. Another potential suspect is tidal forces from the sun, moon, or other nearby objects. Tides are related to orbital planes and thus, on topic with the essay. Could explain why you decided to post about it here, but i digress.
I will guess both. Tidal forces cause pressure waves in the cold, dense seawater. When pressure that’s trapped under the ice gets a boost from wave building interference patterns, a six feet sheet doesn’t stand a chance, does it?
Well, that was fun. Thanks, keep em coming.
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Jerry Krause
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Hi S.C.,
It would seem the pressure mechanisms you suggested would flood the surface of the ice around the crack. But that isn’t reported by the Mosaic scientists. Do you agree with my reasoning? But thanks for you effort. My proposed is obvious as yours was. Take another shot.
Have a good day
Reply
S.C.
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I agree that water would rise up to the surface in that scenario.
Are the cracks oriented in a predictable manner? For example, do they form in a generally north/south or east/west direction. As long as they are far enough from the pole to make such a distinction, that could be a clue to the source ice-cracking force. And if they are more or less random, that may eliminate another possibility.
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Jerry Krause
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Hi Richard,
Have no idea to whose comment you are referring. Please clarify.
Have a good day
Reply
JJerry Krause
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Hi S.C.,
Thanks for sticking with me. Another clue–some children who play on a Well equipped playground could explain the cause.
Have a good day
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S.C.
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Are you talking about centripetal force? As the northern seas rotate around the pole, the force would be persistent. I don’t know for sure, but it seems that clues to the idea’s veracity should exist in the orientation of the cracks, hence my previous question. Of course, even small wobbles in at the poles during rotation could stir the pot, so to say. Despite the huge number of variables involved, I still think a pattern would exist, though.
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Herb Rose
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Hi S.C.,
Because the Earth is a sphere the speed of the land varies with latitude, going from very slow at the axis to 1000 mph at the equator. Because of the inertia of water the water moves east slower than the land, giving it an apparent westward flow, moving faster as it is closer to the equator.
The atmosphere moves eastward faster than the land (eastward movement of weather systems). Because the surfaces (both underwater and in the atmosphere) are not flat, these two opposite motions create a shearing force that cracks the ice when it exceeds the tensile strength of the ice.
Herb
Jerry Krause
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Hi S.C.,
The “centripetal force” is not an idea. It is an increasing force acting upon every water molecule in the layer of ice (a solid) floating on the liquid water of the Arctic Ocean. The magnitude of the force on these ice molecules is ever increasing away from the axis of the earth’s rotation, and trying to RIP the ice layer apart. The cause of the crack. The is only one direction of this force–away from this axis as the surface rotates every 24 hours a day.
However, we should not forget the variable winds and the localized streams of major rivers which drain the north facing slopes of Russia and Canada.which might create a variable ice thickness. All this action if we forget that the Earth does not ‘STANDSTILL as proven by Galileo’s observations made with his telescope little more than 400 years ago. This is SCIENCE not make believe.
Have a good day
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JaKo
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OK Jerry,
Your vision of centripetal force causing not only cracking of ice but movement of rocks and what-not.
We talked about this over four years ago and I have to remind you of it. The CP force is in perfect balance with Gravitational force through-out the entire planet’s surface — it had all the time it needed to achieve that (~4.5By).
OTOH: If the CP force were of greater relative influence, e.g. if the planet’s rotation were much faster or the planet were much less dense, that planet would look like a flat ellipsoid and not like slightly polar-flattened-sphere as our Earth is. And even then, the forces involved, at the surface, would be in perfect balance again…
It’s amazing as some people stick to their “pet theories” and would not let go despite any and all evidence to the contrary.
You too have a good day, unless you have other plans,
Cheers, JaKo
Reply
Jerry Krause
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Hi JaKo,
Don’t remember this conversation. I don’t understand “Gravitational force through-out the entire planet’s surface — it had all the time it needed to achieve that (~4.5By).” I know I have not written about obvious factors such as the influence of the gravities of the Sun and Moon upon the motions of the ice layer and the liquid water beneath the ice and agree these influence, no matter how seemingly insignificant they may seem to be, do have influences.
But my point is if one ignores that the proven fact that the earth does not standstill, one can never understand the leads (racks) which are clearly an important factor upon the life of seals and polar bears.
Have a good day
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Richard
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I don’t , just the observation that the Arctic had seasonal open waters much like today –
We know volcanoes have had an effect on the ice in the last few decades .
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Richard
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Should say underwater volcanoes !
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Jerry Krause
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Hi Herb
Your comment to S.C. required some pondering. I now conclude you as a child, or adult, never played on a playground “marry-go-around”. and therefore never felt the change in the centrifugal force acting upon your body as you moved from its center to its edge while others are pushing the edge of it ao it is spinning at its maximum rate. The centrifugal force cannot be seen but it certainly can be felt.
Have a good day
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S.C.
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Hi Jerry.
I did not make any of the arguments you seem keen to dispute. I merely stated that CENTRIPETAL based cracking has the potential to leave telltale patterns in the orientation of cracks.
Also, the “force acting upon your body as you moved from its (merry-go-round’s) center to its edge,” is not a force at all. What you perceive to be a force pulling you toward the edge is just your body conforming to the laws of physics.
A body in motion, including a human body, will remain in steady motion until acted upon by an accelerating force. You feel like you are being pulled outward as the velocity vector of the platform below you accelerates (changes direction), but the real reason you firmly plant your feet and hold on with a white-knuckled grip is your struggle to generate friction.
Keep enough friction between you and the platform, and you accelerate with it. The faster the spin, the more the acceleration, the more friction you will need to muster.
At the point you cannot create enough friction (centripetal force), you will devolve back a to simple body in motion, carried over the edge by your inertia (not a force).
Have a soft landing. 😉
Reply
Jerry Krause
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Hi S.C.,
I have never intended to type CENTRIPETAL as you just did. And I just checked my previous comment and found I had typed “centrifugal force” as intended. You need to read more carefully..
Have a good day
Reply