100,000 year ice age cycle linked to orbital periods and sea ice


Earth’s orbital variations and sea ice synch glacial periods

The Southern Hemisphere has a higher capacity to grow sea ice than the Northern Hemisphere, where continents block growth. New research shows that the expansion of Southern Hemisphere sea ice during certain periods in Earth's orbital cycles can control the pace of the planet's ice ages. CREDITJung-Eun Lee / Brown University

The Southern Hemisphere has a higher capacity to grow sea ice than the Northern Hemisphere, where continents block growth. New research shows that the expansion of Southern Hemisphere sea ice during certain periods in Earth’s orbital cycles can control the pace of the planet’s ice ages. CREDITJung-Eun Lee / Brown University

PROVIDENCE, R.I. [Brown University] — Earth is currently in what climatologists call an interglacial period, a warm pulse between long, cold ice ages when glaciers dominate our planet’s higher latitudes. For the past million years, these glacial-interglacial cycles have repeated roughly on a 100,000-year cycle. Now a team of Brown University researchers has a new explanation for that timing and why the cycle was different before a million years ago.

Using a set of computer simulations, the researchers show that two periodic variations in Earth’s orbit combine on a 100,000-year cycle to cause an expansion of sea ice in the Southern Hemisphere. Compared to open ocean waters, that ice reflects more of the sun’s rays back into space, substantially reducing the amount of solar energy the planet absorbs. As a result, global temperature cools.

“The 100,000-year pace of glacial-interglacial periods has been difficult to explain,” said Jung-Eun Lee, an assistant professor in Brown’s Department of Earth, Environmental and Planetary Studies and the study’s lead author. “What we were able to show is the importance of sea ice in the Southern Hemisphere along with orbital forcings in setting the pace for the glacial-interglacial cycle.”

The research is published in the journal Geophysical Research Letters.

Orbit and climate

In the 1930s, Serbian scientist Milutin Milankovitch identified three different recurring changes in Earth’s orbital pattern. Each of these Milankovitch Cycles can influence the amount of sunlight the planet receives, which in turn can influence climate. The changes cycle through every 100,000, 41,000 and 21,000 years.

The problem is that the 100,000-year cycle alone is the weakest of the three in the degree to which it affects solar radiation. So why that cycle would be the one that sets the pace of glacial cycle is a mystery. But this new study shows the mechanism through which the 100,000-year cycle and the 21,000-year cycle work together to drive Earth’s glacial cycle.

The 21,000-year cycle deals with precession — the change in orientation of Earth’s tilted rotational axis, which creates Earth’s changing seasons. When the Northern Hemisphere is tilted toward the sun, it gets more sunlight and experiences summer. At the same time, the Southern Hemisphere is tilted away, so it gets less sunlight and experiences winter. But the direction that the axis points slowly changes — or precesses — with respect to Earth’s orbit. As a result, the position in the orbit where the seasons change migrates slightly from year to year. Earth’s orbit is elliptical, which means the distance between the planet and the sun changes depending on where we are in the orbital ellipse. So precession basically means that the seasons can occur when the planet is closest or farthest from the sun, or somewhere in between, which alters the seasons’ intensity.

In other words, precession causes a period during the 21,000-year cycle when Northern Hemisphere summer happens around the time when the Earth is closest to the sun, which would make those summers slightly warmer. Six months later, when the Southern Hemisphere has its summer, the Earth would be at its furthest point from the sun, making the Southern Hemisphere summers a little cooler. Every 10,500 years, the scenario is the opposite.

In terms of average global temperature, one might not expect precession to matter much. Whichever hemisphere is closer to the sun in its summer, the other hemisphere will be farther away during its summer, so the effects would just wash themselves out. However, this study shows that there can indeed be an effect on global temperature if there’s a difference in the way the two hemispheres absorb solar energy — which there is.

That difference has to do with each hemisphere’s capacity to grow sea ice. Because of the arrangement of the continents, there’s much more room for sea ice to grow in the Southern Hemisphere. The oceans of the Northern Hemisphere are interrupted by continents, which limits the extent to which ice can grow. So when the precessional cycle causes a series of cooler summers in the Southern Hemisphere, sea ice can expand dramatically because there’s less summer melting.

Lee’s climate models rely on the simple idea that sea ice reflects a significant amount of solar radiation back into space that would normally be absorbed into the ocean. That reflection of radiation can lower global temperature.

“What we show is that even if the total incoming energy is the same throughout the whole precession cycle, the amount of energy the Earth actually absorbs does change with precession,” Lee said. “The large Southern Hemispheric sea ice that forms when summers are cooler reduces the energy absorbed.”

But that leaves the question of why the precession cycle, which repeats every 21,000 years, would cause a 100,000-year glacial cycle. The answer is that the 100,000-year orbital cycle modulates the effects of the precession cycle.

The 100,000-year cycle deals with the eccentricity of Earth’s orbit — meaning the extent to which it deviates from a circle. Over a period of 100,000 years, the orbital shape goes from almost circular to more elongated and back again. It’s only when eccentricity is high — meaning the orbit is more elliptical — that there’s a significant difference between the Earth’s furthest point from the sun and its closest. As a result, there’s only a large difference in the intensity of seasons due to precession when eccentricity is large.

“When eccentricity is small, precession doesn’t matter,” Lee said. “Precession only matters when eccentricity is large. That’s why we see a stronger 100,000-year pace than a 21,000-year pace.”

Lee’s models show that, aided by high eccentricity, cool Southern Hemisphere summers can decrease by as much as 17 percent the amount of summer solar radiation absorbed by the planet over the latitude where the difference in sea ice distribution is largest — enough to cause significant global cooling and potentially creating the right conditions for an ice age.

Aside from radiation reflection, there may be additional cooling feedbacks started by an increase in southern sea ice, Lee and her colleagues say. Much of the carbon dioxide — a key greenhouse gas — exhaled into the atmosphere from the oceans comes from the southern polar region. If that region is largely covered in ice, it may hold that carbon dioxide in like a cap on a soda bottle. In addition, energy normally flows from the ocean to warm the atmosphere in winter as well, but sea ice insulates and reduces this exchange. So having less carbon and less energy transferred between the atmosphere and the ocean add to the cooling effect.

Explaining a shift

The findings may also help explain a puzzling shift in the Earth’s glacial cycle. For the past million years or so, the 100,000-year glacial cycle has been the most prominent. But before a million years ago, paleoclimate data suggest that pace of the glacial cycle was closer to about 40,000 years. That suggests that the third Milankovitch Cycle, which repeats every 41,000 years, was dominant then.

While the precession cycle deals with which direction the Earth’s axis is pointing, the 41,000-year cycle deals with how much the axis is tilted. The tilt — or obliquity — changes from a minimum of about 22 degrees to a maximum of around 25 degrees. (It’s at 23 degrees at the moment.) When obliquity is higher, each of the poles gets more sunlight, which tends to warm the planet.

So why would the obliquity cycle be the most important one before a million years ago, but become less important more recently?

According to Lee’s models, it has to do with the fact that the planet has been generally cooler over the past million years than it was prior to that. The models show that, when the Earth was generally warmer than today, precession-related sea ice expansion in the Southern Hemisphere is less likely to occur. That allows the obliquity cycle to dominate the global temperature signature. After a million years ago, when Earth became a bit cooler on average, the obliquity signal starts to take a back seat to the precession/eccentricity signal.

Lee and her colleagues believe their models present a strong new explanation for the history of Earth’s glacial cycle — explaining both the more recent pace and the puzzling transition a million years ago.

As for the future of the glacial cycle, that remains unclear, Lee says. It’s difficult at this point to predict how human contributions to Earth’s greenhouse gas concentrations might alter the future of Earth’s ice ages.


357 thoughts on “100,000 year ice age cycle linked to orbital periods and sea ice

    • It’s so sad that I was expecting it at the end. You get a well thought out paper, presented well, then there has to be a random scare guess in at the end about CO2.

      • Apparently he has a mortgage.
        I don’t accept their theory, everyone knows that the closure of the Central American Seaway is the root cause of our malaise and to end this misery we’ll have to build a few more Panama Canals and salt up the Pacific.

      • The E.U. would object to opening up Panama because that would mess up their Gulf Stream climate. Anyway, it wouldn’t do much good if you’re going to leave the Drake Passage open.

      • Yes, the bottling up of the Atlantic/Pacific oceans so they meet only at Antarctica (a very very slender opening!) is a huge reason we have Ice Ages. The true mystery is, why these all, everyone of them, end suddenly and why they are all so short.

      • EMS,
        The Antarctic ice sheets formed at the Eocene/Oligocene Epoch boundary when deep ocean channels opened between Antarctica and South America and Australia, c. 34 Ma. The sheets waxed and waned during the Miocene, during which the long term trend was a cooling and drying earth.
        Northern Hemisphere ice sheets formed when the Isthmus of Panama fully closed the Interamerican Seaway, c. three million years ago, at the end of the Pliocene.
        So our current ice age or ice house results from plate tectonics, as too have at least some if not all prior ones. But the ice fluctuations, such as glacial and interglacial phases, within ice houses are largely driven by celestial mechanics, plus some terrestrial phenomena.

      • Give the girl a chance.
        The gratuitous mention of CO2 at the end is surely forgiveable, given the universal interest in the subject right now.
        I’d be interested to know what the model setup is that relates precession, insolation and
        sea ice extent. Can anybody who understands (I don’t) explain it? Is the algorithm constructed in response to the understood glaciation timetable, or is it derived independently? If the former, it looks rather similar to the speculations about albedo changes due to northern hemisphere land ice sheets, and might be consistent with that.

      • There can be no question that ‘interference patterns’ arising from the interactions between the various orbital and axial variability results in the ebb and flow of interglacial periods (which are the exception to the rule of being in an ice age). I didn’t even think this was new information as it’s the unavoidable consequence of superposition in the energy domain (i.e. 1 Joule + 1 Joule = 2 Joules), moreover; Milankovitch did reference hemispheric asymmetry as a contributing factor which really only matters relative to precession.
        It seems to me that most of Canada, the US East coast, Europe and Russia buried under many km of ice is a lot more catastrophic than a few cm of sea level rise or a few tenths of a degree of warming. And it’s not like this inevitable fate is unexpected or unprecedented …

      • I’ll wager that CO2 was added to the paper to get it through peer review after several warmist inner-circle reviewers rejected the paper without it. It weakens what is a very suggestive argument on albido by orbital mechanics being the main driver of glaciation and a good explanation of why the regime change happened to change which orbital drivers were in the driver’s seat. – Of course, not being the editor or a peer reviewer on the paper, this is all a guess

    • OK Let’s assume, for the sake of discussion, that human contributions are zero. What then do her models predict? I am sure she knows the answer.

      • Excellent Michael.CO2 is irrelevant. The allegation regarding CO2 is nonsense because ECS ~= zero.
        The real question is when will the new Ice Age begin? Does the paper say or not? If not, piffle.
        No prediction suggests no confidence in one’s hypothesis.
        Prediction is also entirely safe in this case, because nobody here will be alive to check it (I hope – if the next Ice Age starts that soon, we have a big problem – get out the water bombers and fill them with carbon black – it’s time to adjust global albedo.).
        Best, Allan

      • Allen,
        ECS is not zero, but it is small and somewhere between 1.0 W/m^2 and 1.6 W/m^2 of incremental surface emissions (about 0.2C to 0.3C at the current average temperature) per W/m^2 of incremental solar input (forcing).
        The basic problem with ECS is expressing it as a temperature change per change in input power, which is a non linear metric designed specifically to obfuscate. It’s more properly expressed as W/m^2 of power leaving the surface per W/m^2 entering it.

      • Indeed, this is a question that begs to be asked: when is the next ice age due to start, assuming no human interference? If their model is correct, it should be able to make that prediction easily. Such a prediction would be very useful. As I understand it, this current interglacial period is already longer than the previous one. (?) If their prediction would be that the next ice age would start “soon” (i.e., within the next 500 years), then that would dampen a lot of the anxiety about global warming. People would think global warming is a good thing, keeping the ice ages away.
        I believe if there was no global warming controversy they would have naturally included a prediction in their paper. Not including it makes me think they didn’t think the prediction would go over well with the establishment.

      • The Holocene, at 11,400 years, has so far been shorter than the Eemian, usually given as 16,000 years.

      • Actually, what I want to see are the currently relied upon models run with static CO2 – i.e., assume zero increase in CO2 – what do the models say would have happened since, say, 1950 – is it realistic? Is it desirable? Does anyone know if anyone has done this with one or more of the GCMs?

        • ‘So how do you really feel about the 3C”
          The 3C number is the 0.8C per W/m^2 since 3.7*0.8 is about 3C. Anything more than about 1.1C for doubling Co2 is completely bogus.

        • Another issue I have with the 3C number is that they have tried to cast sensitivity as being specific to doubling CO2, which is complete BS since what they really mean is that doubling CO2 is EQUIVALENT to 3.7 W/m^2 of incremental, post albedo, solar input. What they call the ‘sensitivity factor’ is the proper metric which specifies the warming (or cooling) per 1 W/m^2 increase (or decrease) in actual forcing, where only the Sun is properly considered a forcing influence. It’s all just part of the obfuscation meant to emphasize CO2 at the expense of science.

    • Her statement is an entirely reasonable statement on the subject that has dominated discussion of climate change for the last thirty years. She’s saying, “we don’t know”. That doesn’t get her any brownie points from the warmists, and apparently only gets her snarky snide comments from the anti-warmists.
      This is just science people – not politics. That’s what we all ought to applaud at all times.

      • No…I agree with Michael. I am also sure she knows the answer to what her model is predicting. There is only one reason to withhold that information…it would upset the powers that be!
        If her model shows more warming, she would just come out and say it, for it would further enhance the threat from man-made global warming and she would be a hero of the left. Her career would be set and she could go on a speaking tour around the world with healthy compensation.
        So it is safe to assume that her model indicates global cooling ahead and in the fairly near future. If it was 5,000 years from now, the AGW paradigm would be safe. If it shows cooling in the next few hundred years, it would make the warming paradigm a mute point, which would upset a large number of scientists, advocates and environmental groups.
        I think it is safe to say that that she won’t say because her model shows global cooling is on the horizon.

    • Except for simply the scientific understanding, giving CO2 any role here is completely spurious.
      CO2 emissions by man have been rising logarithmically over the last 50+ years while atmospheric CO2 has been increasing essentially linearly. If we are have no effect on atmospheric CO2, then we are having no effect on global temperatures. Done and Period!
      The same is true for the other “radiative” (nicknamed “greenhouse gases” for political reasons. In addition, the other radiative gases are in much too low concentrations to have any detectable effects on anything.

    • Except for simply the scientific understanding, giving CO2 any role here is completely spurious.
      CO2 emissions by man have been rising logarithmically over the last 50+ years while atmospheric CO2 has been increasing essentially linearly. If we are have no effect on atmospheric CO2, then we are having no effect on global temperatures. Done and Period!
      The same is true for the other “radiative” (nicknamed “greenhouse gases” for political reasons. In addition, the other radiative gases are in much too low concentrations to have any detectable effects on anything.

    • I also do not accept her theory. It offers no explanation as to why there is a rapid 10 degreee rise in temperature over just a few thousand years, yet the decline back into an ice age takes tens of thousands.

  1. “As for the future of the glacial cycle, that remains unclear, Lee says. It’s difficult at this point to predict how human contributions to Earth’s greenhouse gas concentrations might alter the future of Earth’s ice ages.”
    Oh come on! Take a stab at it. NOAA, NASA & HADCRUT have no problem putting the frighteners on. sarc off.

  2. Finally, something other than gas. They still have way to trek though. The Pliocene-Early Pleistocene pattern reflects the 40 KY pattern, but it also shows a very steady cooling trend.

  3. An interesting point is made by Patrick Moore about the decline of CO2 through the glacial cycles. Every ~ 100,000 years each new glaciation brings on LOWER levels of CO2. It’s a trend. The trend of declining CO2 goes back millions of years to before this glacial period. Its cause: CO2 hungry plants combined with a steady lessening of CO2 producing volcanic activity on the cooling (interior) earth. During the last glaciation we reached an all time low of ~ 180ppm. Juniper fossils from the La Brea tar pit and other evidence shows that that level of CO2 caused severe stress to plants: http://www.pnas.org/content/102/3/690.full?sid=5e3bdf35-c2a6-4fe7-b336-eea3917571f2
    Moore makes the shocking point that the trend of declining CO2 is likely to continue and we’re quickly headed for CO2 reaching apocalyptically low levels where all plants and most animals die. Yet … Human CO2 emissions could actually forestall Armageddon by millions of years.
    Here’s Moore’s video where he discusses the coming low CO2 apocalypse:

    • So true Eric.
      For the sake of the planet and all that will live on it n the future, we absolutely MUST get over this moronic ANTI-CO2 agenda.
      200ppm is dangerously low, and even the current 400ppm is barely sufficient.
      CO2 and H2O are the basis of ALL LIFE ON EARTH…
      .. and the sooner people come to realise this BASIC FACT the sooner the planet can progress as it should.
      Raising CO2 levels to 700ppm or preferably 1000ppm MUST become an major priority.
      But before that can happen, the Global Warming scam/agenda must be dead and buried, with a great big stake through its heart, like the EVIL vampire that it is.

      • Remember that EVERYTHING follows the “Goldilocks Principle”; “too much”, “too little”, and “just right”. I don’t pretend to know exactly where CO2 levels are in this respect, but I would wager that we’re closer to “just right” than we are to “too little”.

      • Ken,
        Science does know what level of CO2 is just right. That would be the level in commercial greenhouses, ie 900 to 1300 ppm, at which concentrations C3 plants (including all trees and most crops) flourish. The world would green even further than it already has, thanks to more beneficial plant food in the air. If that also happened to make earth a little warmer, that too would be a good thing, as early AGW advocates Arrhenius and Callendar believed.

      • It’s amusing to speculate that in future man may finally master fusion and use the vast energy resource to break down limestone for the locked up CO2 in order to replenish our atmosphere. Perhaps mankind’s first purposeful act of Terra-forming.

      • Ken, where do you get the idea that .04% is “just right”? are you afraid the proliferation of flora at .1% will will photosynthesise away the atmospheric CO2 too fast, or what?

      • Ken, in the past when CO2 levels ranged from 5000ppm to 7000ppm, then the amount of CO2 was way, way too much?

      • Ken’s ‘Goldilocks Principle’ has an excellent pedigree in the biological sciences, and poses a few philosophical questions as well (the ‘anthropic principle’ has long fascinated me). Perhaps it is better to look at it the other way round. Optimum CO2 is very likely to be the present level – because it is the best level for the plants that exist today. If CO2 levels were more than halved, we wouldn’t necessarily have fewer plants, nor more stressed plants. Just different plants, living in their own goldilocks world.

      • mothcatcher
        January 27, 2017 at 8:46 am
        Four hundred ppm is far from the best level for plants which exist today. Two or three times higher would be ideal for C3 plants, the most significant to humans.
        The important angiosperms (flowering plants) evolved under much higher CO2 levels, for example. They had probably been around for a long time earlier, but became suddenly abundant in the Cretaceous, when earth was much warmer (maybe four degrees C hotter) and CO2 was four or five times higher than now.

    • we’re quickly headed for CO2 reaching apocalyptically low levels where all plants and most animals die.

      Quickly as in tens to hundreds of million years. Besides it could be postponed by plants adaptation to lower CO2 levels (like C4 plants).
      Your alarmism is way over-hyped. Mammalian species last an average of perhaps 2 million years. It is not that we are not going to be around, our species is not going to be around to die for lack of CO2, har har.

      • >>Besides it could be postponed by plants adaptation
        >>to lower CO2 levels (like C4 plants).
        But C4 plants are not well adapted to cold condition, which is why extra-tropical trees and most of the grasses are still all C3. So low CO2 still causes great problems to agriculture and nature, even at the 180 ppm level.

      • “Mammalian species last an average of perhaps 2 million years. It is not that we are not going to be around, our species is not going to be around to die for lack of CO2, har har.”
        Humans aren’t just another “mammalian species”. Even with our relatively fledgling genetic capabilities, we’re at the point where we can eliminate unwanted mutations. I’m sure there’ll be genetic drift as humans spread across the galaxy, but in principle there’s reason to think that some humans even a billion years in the future will be pretty well unchanged from humans of today. I expect machine augmentation will be a much more significant trend.
        In short, homo sapiens is exceptional.

      • Javier
        So you reckon plants are going to evolve a way to thrive at 100 ppm CO2?
        That’ll happen around the time we humans evolve the ability to fly around like Iron-man.
        Your reflexive conformity to alarmist dogma might paint you as a moderate “skeptic” but here you’re plain wrong.

      • Ptolemy,
        Plants capable of surviving at CO2 levels below 100 ppm already have evolved, the C4 and CAM plants.
        The problem is that they tend to be tropical. Corn (maize) varieties can be grown as far north as Canada, but it’s an exception among C4 crops.
        “C3 plants include trees, bushes and shrubs, and their leaves and fruits; most vegetables; cool-season grasses and grains such as timothy, alfalfa, wheat, oats, barley and rice; soybeans; non-grassy herbs and forbs.
        “C4 plants are warm-season or tropical grasses and sedges and their seeds, leaves or storage organs like roots and tubers. Well-known sedges include water chestnut, papyrus and sawgrass. C4 plants are common in African savannas and deserts. C4 grasses include Bermuda grass and sorghum. C4 grains include corn and millet.
        CAM plants include tropical succulent plants such as cactus, salt bush and agave.”
        Potatoes are also C3 plants.
        The Pleistocene megafauna of the steppe-tundra relied heavily on forbs, which must have been stressed at 180 ppm CO2.

      • Botanists believe C4 adaptation has evolved independently about 40 times in the last few million years. It is the only way to explain why it appears in so many distinct genre and families. The pressure to evolve C4 must be enormous. If this pressure continues in the next glacial periods, pretty soon (geologically), most plants will be C4 or some other CO2 efficient mechanism.
        Ironman flies in an nonphysical way for thousands of km without any apparent need for fuel deposits, using tiny rockets. We are not going to fly that way any time soon.

      • C4 plants may well evolve to cope with colder temperatures. They do not do so today because under those conditions they can’t cope with competition from better-adapted C3 plants. Or maybe a third pathway wil open, given the long timescales involved.

      • we’re at the point where we can eliminate unwanted mutations. I’m sure there’ll be genetic drift as humans spread across the galaxy, but in principle there’s reason to think that some humans even a billion years in the future will be pretty well unchanged from humans of today.

        Either you don’t believe in evolution or you don’t understand how evolution mechanisms act. Evolution doesn’t stop for as long as there is differential reproduction of individuals. We are evolving now. Our brains are becoming smaller for the past 10,000 years. Our digestive systems are changing. Evolution never stops. Even if our species does well, there wont be any humans in two million years. It will be a different species, or several, as different from us as we are from Homo habilis. Or we could very well go extinct as most hominin species have done.

      • Eric,
        All plants won’t die under 150 ppm.
        C4 and CAM plants keep working, however poorly, down to very low CO2 levels.

      • No Eric,

        We’re talking about CO2 levels going below 150ppm where ALL plants would die. And a timetable of hundreds of thousands of years, not tens of millions.

        We are talking AVERAGE CO2 levels. Scientists had to go to remote places to measure CO2 levels because there is so much variability that plants today are exposed to much lower and much higher CO2 levels over the course of a single day. When CO2 levels were low during last glacial maximum, plants didn’t die, they grew more slowly. But we know ecosystems continued working fine at 180 ppm, because there was no mass extinction. It doesn’t even look like we lost a significant number of species. Your alarmism that at 150 ppm everything is going to die is not supported by evidence.
        And the scale is millions of years if you care to look at the rate of change of CO2 in geological past according to evidence and Geocarb III.
        It is in the human nature to look at things and develop alarmist unreasonable fears about the future. A cursory look at the long list of past unfounded fears should vaccinate us against that, but it doesn’t. Christianity was founded on the belief that the end of the world was coming soon. And frankly the Phanerozoic reduction in CO2, that is currently being partially reversed is probably the absolute least of our worries.

    • ‘Yet … Human CO2 emissions could actually forestall Armageddon by millions of years.’
      You see the good Lord put us here to release all that locked up carbon in the ground so it could combine with the oxygen to keep the Garden of Eden healthy. Whoda thunk it listening to all those Devil’s disciples eh? Praise the Lord and pass the keys to the new Heavenly V8 chariot.

        . . It is found that even an increase by a factor of 8 in the amount of CO2, which is highly unlikely in the next several thousand years, will produce an increase in the surface temperature of less than 2°K. However, the effect on surface temperature of an increase in the aerosol content of the atmosphere is found to be quite significant. An increase by a factor of 4 in the equilibrium dust concentration in the global atmosphere, which cannot be ruled out as a possibility within the next century, could decrease the mean surface temperature by as much as 3.5°K. If sustained over a period of several years, such a temperature decrease could be sufficient to trigger an ice age!
        * * *
        Fig. 1 [omitted]. Change in tropospheric temperature as a function of the amount of CO2 in the atmosphere. The dashed curve is computed for constant surface absolute humidity, and the solid curve is for the case in which the surface relative humidity is maintained constant. Note that the rate of temperature increase diminishes with increasing CO2 in the atmosphere.
        * * *
        From our calculation, a doubling of CO2 produces a tropospheric temperature change of 0.8°K (12). However, as more CO2 is added to the atmosphere, the rate of temperature increase is proportionally less and less, and the increase eventually levels off. Even for an increase in CO2 by a factor of 10, the temperature increase does not exceed 2.5°K. There¬fore, the runaway greenhouse effect does not occur because the 15μm CO2 [solar radiation] band, which is the main source of absorption, “saturates,” and the addition or more CO2 does not substantially increase the infrared opacity of the atmosphere. But if the CO2 concentration in the atmosphere becomes so high that the total atmospheric pressure is affected (which will require a CO2 increase by a factor of 1000 or more), then the absorption bands will broaden and the opacity will in¬crease, and the temperature may start to rise so rapidly that the process could run away (13). However, this appears to be only a remote possibility for Earth, even on a geological time scale, as a large buildup of CO2 in the atmosphere will be severely restrained by its interaction with the oceans, the biosphere, and the crust (14).
        (From “Atmospheric Carbon Dioxide and Aerosols: Effects of Large Increases on Global Climate,” by S.I. Rasool and S.H. Schneider [of the Goddard Institute of Space Studies], Science Magazine, vol. 173, 9 July 1971, pp. 138-141.

    • I agree Eric. I corresponded with Patrick many years ago on CO2 starvation, and posted on wattsup and elsewhere since about 2008 – here is one such post.
      I have since learned more about C3, C4, and CAM plants, btu the problem is still much the same.
      Best to all, Allan
      (Plant) Food for Thought (apologies – written too late at night)
      1. “As CO2 is a critical component of growth, plants in environments with inadequate CO2 levels – below ~200 ppm – will cease to grow or produce.” (2017 Note – I would now write ~150ppm not 200ppm)
      2. “The longest ice core record comes from East Antarctica, where ice has been sampled to an age of 800 kyr BP (Before Present). During this time, the atmospheric carbon dioxide concentration has varied by volume between 180 – 210 ppm during ice ages, increasing to 280 – 300 ppm during warmer interglacials…
      … On longer timescales, various proxy measurements have been used to attempt to determine atmospheric carbon dioxide levels millions of years in the past. These include boron and carbon isotope ratios in certain types of marine sediments, and the number of stomata observed on fossil plant leaves. While these measurements give much less precise estimates of carbon dioxide concentration than ice cores, there is evidence for very high CO2 volume concentrations between 200 and 150 myr BP of over 3,000 ppm and between 600 and 400 myr BP of over 6,000 ppm.”
      Questions and meanderings:
      According to para.1 above:
      During Ice ages, does almost all plant life die out as a result of some combination of lower temperatures and CO2 levels that fell below 200ppm (para. 2 above)? If not, why not?
      Does this (possible) loss of plant life have anything to do with rebounding of atmospheric CO2 levels as the world exits the Ice Age (in combination with other factors such as ocean exsolution)? Could this contribute to the observed asymmetry?
      When all life on Earth comes to an end, will it be because CO2 permanently falls below 200ppm as it is permanently sequestered in carbonate rocks, hydrocarbons, coals, etc.?
      Since life on Earth is likely to end due to a lack of CO2, should we be paying energy companies to burn fossil fuels to increase atmospheric CO2, instead of fining them due to the false belief that they cause global warming?
      Could T.S. Eliot have been thinking about CO2 starvation when he wrote:
      “This is the way the world ends
      Not with a bang but a whimper.”
      Regards, Allan 🙂

  4. Of course the question that should be asked, is why if the main cycle is around 20,000 years long, we don’t have ice-ages every 20,000 years. And the answer is very simple: orbital cycles are merely a trigger for some other mechanism. In other words, the main period is not set by the orbital cycle, but instead the small changes due to an orbital cycle just “take us over the edge”.
    (See Caterpillar effect for my own take on it).

      • One small problem re insolation during variable distances from the sun on earth’s elliptical orbit, the actual difference is too small to measure (NH winter, sun is closest) , although it “should” be significant. Willis noted this in one of his articles. Something else is happening in the atmosphere or the ocean surface response to attenuating the effective heating expected.

    • No – the answer is in the article above. It is the combination of precession and the maximum of eccentricity which creates the conditions for maximal southern sea ice growth. Please read the whole article – not jsut the intro then dive off into your theory-de-jour.
      This article confirms that classic Milankovich is quite adequate to explain glacial cycles (with the paradigm of a periodically forced nonlinear oscillator) and the menagerie of alternatives – that you always get on these threads – are just muddled thinking.

      • Those cycles always existed and didn’t cause Ice Ages up until the earth’s ocean circulatory system was greatly reduced when North and South America joined up.

      • EMS,
        Yes, Milankovitch cycles have always existed. NH ice sheets formed when the Americas were joined, altering oceanic circulation. SH ice sheets however had already long existed, again due to oceanic circulation.
        It’s common to consider that the current ice age began in the Pleistocene, because of NH glaciations, but it really started in the Oligocene, 34 Ma, with Antarctic glaciation.

      • No – the answer is in the article above. It is the combination of precession and the maximum of eccentricity which creates the conditions for maximal southern sea ice growth. Please read the whole article – not jsut the intro then dive off into your theory-de-jour.
        Err, my ‘de-jour theory’ is an entire peer-review paper. And the article above is wrong, because it still cannot explain the missing precessional cycles. If interglacials are modulated by precession, then ALL the strong precessional-insolation cycles should produce an interglacial, and they do not. Ergo, my friend, the paper cited here is so incomplete it is totally wrong.

      • Gloateus, EMS
        You tectonists seek to explain Antarctic glaciation by OPENING of a seaway and Arctic glaciation by CLOSING.
        Antarctica was glaciated very nicely on the Carbo/Permian when the continents looked like this:
        Meridional ocean heat movement is what must be restricted, not zonal flow. The Bearing Strait is more important than the Isthmus of Panama.

      • Gymno,
        Why is it a problem that Oligocene Antarctic glaciation was caused by the formation of deep channels in the Southern Ocean and the Pleistocene NH glaciations by the formation of the Isthmus of Panama?
        The fact is that those glaciations followed those events, and there are good geophysical, atmospheric and oceanographic reasons why the tectonic events would have had those effects.
        The Carboniferous glaciation also took place when there was land over the South Pole. In that case, ice sheets spread from there to lower latitudes. Antarctica didn’t need to be isolated from other continents. Antarctica already had glaciers in the Eocene, but they didn’t form ice sheets until after the formation of the Southern Ocean.

      • And, speaking of the Ordovician glaciation, its Milankovitch cycles are well-recorded and obliquity ruled then, too. From “Stratigraphy” last year:
        Milankovitch cycles in the Juniata Formation, Late Ordovician, Central Appalachian Basin, USA
        Linda A. Hinnov and Richard J. Diecchio
        ABSTRACT: The Juniata Formation is a thick succession of prevalently red, cyclically bedded arenites, wackes, and mudrocks found in the Upper Ordovician of the Central Appalachian Basin, USA. In outcrops close to the study area, the Juniata cycles predominantly have the characteristics of regressive tidal flat deposits. Long and continuous well logs of the subsurface Juniata provide an unparalleled opportunity to investigate Milankovitch controls on the cyclic deposition. In the Preston 119 well, northern West Virginia, a 2700-ft long gamma-ray well log provides a high-resolution proxy of terrigenous siliciclastic flux to the northern Central Appalachian Basin shoreline, from the early Maysvillian (Reedsville Shale) to the Ordovician/Silurian transition (Tuscarora Sandstone). The gamma-ray cycles provide strong evidence for sea level oscillations forced by Milankovitch cycleswith a dominant obliquity component. The strong obliquity signal is reminiscent of the obliquity forcing of Oligocene climate and sea level following the glaciation of Antarctica. The Late Ordovician world analogously experienced glaciation of Gondwana, which straddled the South Pole; this may have involved ice sheet dynamics that generated obliquity-paced sea level oscillations that affected Late Ordovician shorelines worldwide. This Milankovitch-forced glacio-eustatic record from eastern North America joins other suspected Milankovitch-forced successions reported from the Late Ordovician of northern Africa, northwestern Australia, Scandinavia, and northeastern and eastern-central North America.

      • I’m with CO2isnoEvil that the ice core records are the best data available on the long term climate. As yet, there is nothing to show that the current warm period is out of line with anything in the past.
        The important features I see in the Law Dome C record are:
        1) just about every warming period happened very abruptly in geological terms- it took as little as 1-2000 years for the temperature to climb as much as 15degC.
        2) In most cases the temperature immediately began to drop in fits and starts, sometime very large fits of cold followed by re-warming to some extent.
        3) The latest warming shows up at ~15,000 years. Like a couple of other previous peaks, it has not started a steady drop as yet.
        4) All the low temperatures were within 5degC or so. The last cold period just before the current warm period spent an extended period right down near the bottom of the chart for 20-25,000 years at ~-8degC anomaly.
        5) The latest warming period is by far not a record. 3 of the 4 temperature rises that broke the 0degC anomaly spent roughly 10-20,000 years above 0.
        6) The fourth peak back spent multiple thousand years around 280-300ppm.
        7) The only ‘anomaly’ in the graph is the current era 326ppm of CO2 in the recent past. Not having read a detailed account of how this number was obtained and that it is in the recent part of the core it may have been contaminated by diffusion before turning to solid ice.
        My congratulations to all the scientists that obtained and analyzed this ice core in exemplary scientific fashion.

    • Of course the question that should be asked, is why if the main cycle is around 20,000 years long, we don’t have ice-ages every 20,000 years. And the answer is very simple: orbital cycles are merely a trigger for some other mechanism.

      The answer is even simpler than that. The main cycle is not the 20,000 cycle. It has never been. Precession doesn’t drive the glacial cycle.

      • “The main cycle is not the 20,000 cycle. It has never been.”
        Correct. The most visible cycle is from the variability in the tilt of the Earth’s axis which is about a 40K cycle, which was the period of glaciations prior to about 500K years ago. How deep an ice age gets depends on the relative phases of the other orbital effects. It just happens that the 40K effect has been roughly aligning with the 100K effect during the last 500K years, but the alignment has been slipping away and is why this interglacial is several degrees cooler and significantly longer than the last one.

      • CO2,
        Except that the Holocene hasn’t yet lasted longer than the Eemian, though it well might. Much longer if the eccentricity advocates are right.
        But it has been cooler than the Eemian, despite lack of a Neanderthal industrial age.

      • co2isnotevil,
        I agree, but

        is why this interglacial is several degrees cooler and significantly longer than the last one.

        The Holocene is on track to last the average duration of an interglacial, as the Eemian lasted.
        In my opinion the Holocene wasn’t warmer because summer 65°N insolation has been about 20 W/sq m lower than Eemian, which is a lot, and because Holocene deglaciation was sabotaged by the Younger Dryas.

      • Javier,
        IMO the Dryases might have been more pronounced than similar fluctuations during prior terminations because there was more ice after the long Wuerm/Weichselian/Wisconsin glaciation, especially with its pronounced glacial maximum. This meant larger meltwater fluxes when ice dams retreated or broke, disrupting ocean circulation more.

      • Gloateus,
        the Dryases might have been more pronounced than similar fluctuations during prior terminations because there was more ice after the long Wuerm/Weichselian/Wisconsin glaciation, especially with its pronounced glacial maximum. This meant larger meltwater fluxes
        It is certainly a possibility. However one would expect a faster sea level rise prior to or coincident with the YD if large meltwater pulses (MWP) were involved. That was not the case. YD showed a reduction in sea level rise rate (figure D below from Lambeck 2014), and MWP 1A took place several thousand years before, and MWP 1B afterwards.
        It is likely that several factors contributed to create the conditions for the YD. We know that there was a low of the 2400-yr Bray Solar cycle at ~ 12800 BP, as the cosmogenic isotopes record reveals. That would be the first red arrowhead in the figure.
        However the effect of a 2400-yr solar low is not so long. Due to IRD deposition it looks like YD is related to Heinrich events, but we do not know what causes Heinrich events. The duration is adequate for a Heinrich event, and it ends in a D-O oscillation at 11,700 BP that it is at the right periodicity point for its 1470-yr beating.
        The YD doesn’t register much in sea level rise, and in LR04 benthic stack, and it is much less conspicuous in Antarctic records, Its importance is very much influenced by its very strong presence in Greenland records that don’t extend past the Eemian. If analog YD-like events have taken place at other deglaciations we might not know. The resolution of our records goes down a lot when they get older than 150,000 years.

      • IMO sea level didn’t rise despite the meltwater because the colder climate caused ice growth soon after the pulse.
        There are some good explanations for Heinrich events which would also apply to the Dyrases.
        If the meltwater came in part from floating ice shelves, the effect on sea level would also not be noticed despite the influx of a lot of cold fresh water into the oceans.

      • If the meltwater came in part from floating ice shelves, the effect on sea level would also not be noticed despite the influx of a lot of cold fresh water into the oceans.

        That is a better argument for why we wouldn’t see it.

        There are some good explanations for Heinrich events which would also apply to the Dyrases.

        Do you have any info on that? I am interested. The three theories that I know (from Hemming 2004), binge-purge, meltwater pulse, or ice shelf collapse do not look very capable of explaining the prior cooling and glacier growth that accompanies the early phase of Heinrich events.

      • Javier,
        Info, not so much. Opinions, yes.
        Mine is akin to the suggestion of Alley, et al, 2006. It has always seemed to me that expansion of the ice sheets alone can account for the iceberg armadas. During cold, stadial intervals, the sheets just get as big as the can without large edge chunks calving into the sea.
        Alley, R.B., Dupont, T.K., Parizek, B.R., Anandadrishnan, S., Lawson, D.E., Larson, G.J. and Evenson, E.B. 2006. Outburst flooding and the initiation of ice-stream surges in response to climatic cooling: a hypothesis. Geomorphology 75: 76-89.
        Another hypothesis, after Flückiger, et al, 2006, has to do with oceanic processes rather than the land ice itself.
        Flückiger, J., Knutti, R. and White, J.W.C. 2006. Oceanic processes as a potential trigger and amplifying mechanism for Heinrich events. Paleoceanography 21: PA2014.
        From 2011:

    • Again, this is a layman’s question, but if we’re talking about an orbital cycle – basically a much larger cycle being a major influence on long-term climate trends – rather than small changes you suggest resulting from the Earth’s own orbit, what about the effect of even larger orbits, such as the solar system’s position in the larger galaxy, and that sort of thing?
      If you’re a flea on a dog, the dog has a (fairly) stable internal climate, but the dog itself might run through the snow, or jump in a stream, or lay down in front of the fireplace – the flea will experience a wide range of effects, which actually has little to do with the dog’s own changing metabolism.

      (Griff asked me to fill in for him – NOT!!!)

      • Yah and in terms of Arctic ice coverage history is the last 40 years. The planet warms and cools cyclically correlating with solar cycle changes.
        Fortunately/Unfortunately the solar cycle has been interrupted. The cooling will start when coronal holes on the sun abate.
        The coronal holes create repeating solar wind bursts. The solar wind bursts create a space charge differential in the ionosphere which in turn causes there to be potential different between the poles and the equatorial region. The potential difference causes a current flow which changes the cloud amounts and cloud properties in both regions which in turn causes warming at both locations. The solar wind burst mechanism is called electroscavenging.
        Enric Palle calculated in a 2008 paper that based on observed changes in cloud cover that the warming caused by cloud changes in the 40 to 60 latitude regions was 7 watts/m^2 as compared to 3.5 watts/m^2 for the incorrect assumed warming for a doubling of atmospheric CO2.
        After months and months of talk about the warm Pacific blob there is now a cold Pacific blob which of course is not mentioned in the liberal press.

      • ‘After months and months of talk about the warm Pacific blob there is now a cold Pacific blob which of course is not mentioned in the liberal press.’
        And soon SH summer is over without recharging its ocean batteries to full capacity .

  5. A long and slow depletion of Earth atmosphere could also be a cause of Earth getting gradual colder last 30 million years?

  6. But does this paper say anything about the current state of the poles? I’m wondering if this cycle they found also explains sea-ice levels, considering we should be somewhere near the end or bottom of the cycle?

  7. Why do they have to destroy their work with that stupid CO² rider at the end. It’s not a bad stab and there is something to a model that could predict the underlying effect of the M Cycles. There should be some fairly simple mathematics behind this work that they could use to explain their conclusions.
    Hopefully this will be the last of such poor papers on the subject

    • ‘Why do they have to destroy their work with that stupid CO² rider at the end.’
      Well you’ve gotta throw in a bit of settled science when you’re out there busily discovering new stuff. That’s the way science works nowadays.

      • You are correct: it that makes the whole article more questionable. Cogent science doesn’t benefit from the CO2 argument.

  8. Not sure I’m buying this. Every temperature reconstruction I’ve seen shows an abrupt transition from a glacial period into an interglacial period occurring at approximately 100K years, then a brief stay at warm temperatures before a long slow decline into glaciation. Glaciation is the norm, not the exception. This paper seems to have it backwards. They would need an explanation for why temperatures rise suddenly every 100,000 years, stay there for a few thousand years, and drops back down into glacial periods for the rest of the 100K year cycle. ,

    • Absolutely. Not only are warm cycles short they are very sudden. And the warmest part of the warm cycles aren’t at the middle, they are at the beginning and the warm surges get less and less warm as things cool down after around 10,000 years or so.

    • I’ve always had this as an explanation, it’s my thoughts, so hey.
      This is Co2. My thinking is with a freezing point about 70F colder than water, if the planet lost it’s water vapor (ie it froze) you’d have the lower temp ghg’s in the atm.
      With co2, say at the end of the interglacial all the vegetation sucks all the co2 out of the atm, and with a touch of a cold spell. you get a lot of polar ice, and less water vapor, cascades into a frozen earth, and the oceans cap a lot of the co2 in the oceans and under ice. Now, this last a long time, the little water just isn’t enough to kick the water cycle off. slowly, over time volcanism converts trapped carbon into a higher and higher level of co2, at some point co2 starts to warm the oceans/ice and it finally kicks the water cycle off, and it wakes up again.
      Co2 props up water, but once water takes over, it takes over.

      • That’s why humanity is doing brilliant work by returning CO2 where it belongs, in the atmosphere. A green planet will eventually like a cancer kill the body it feeds on. Luckily this planet has volcanic activity because without it we would probably look like Mars.

  9. Well, yes…
    We know Milankovitch cycles affect arctic sea ice: the low in the Eemian was entirely down to the then cycle…
    but now we have record low sea ice extent/thickness/volume and a change in weather patterns and in the winter too, not just at minimum.
    and there isn’t any Milankovitch cycle influence and this is lower than the last sea ice cycle in the 20s through 40s and it is not recovering and it is trending down.
    so what do we say is the cause of the current state and trend of the arctic sea ice?
    climate change caused by human CO2.
    There is no other causation in operation, is there?

        • What changes of any magnitude the temperature has only risen 0.9 degrees C since 1880. Like man where’s my shorts. I’m sweating to death. 🙂 Get a grip people

      • But that’s the whole point, it isn’t normal weather.
        The arctic has and has had all winter an enormously anomalous temperature… and a series of huge storms. Svalbard just saw its first year averaging above 0 C temps (reords from 1912). Alaska had its third year with a new temp record high.

      • What’s a short period of time and what’s the normal weather Chris? Forgive me if it’s a dumb question but I’m a bit slow at getting my head around these time spans and cycles just at present, so I need someone with the smarts to spell it out for me.

      • Griff, I’m not sure if you read the article, but they mostly mention the southern hemisphere sea ice as being the main player. Until this year, southern hemisphere sea ice was running at record highs. Let’s see what it does the next few years.
        Also, there hasn’t been anywhere near as much warming in the southern hemisphere, particularly near the pole.

      • John, for a couple of years it ran at record highs -and there was an explanation for that in a shift in wind patterns/currents (which can be traced back to…). This year its below the long term trend by a large amount.
        and you don’t offer an explanation or comment on the very real effects we do see in the arctic. The two poles are very different environments…

      • observa – 30 years is usually considered as sufficient to call it a climate trend rather than weather. We’ve had 37 of the sea ice satellite record (and a decade where ice has not recovered to its pre-2007 level)

      • “Normal weather” …. what a meaningless concept (no offense intended, Matt)!
        How can anyone claim to know what “abnormal weather” looks like? Assuming such a chimera actually existed, it seems to me, you would need impeccable, real-time global data going back to the beginning of the current interglacial to determine this.
        We don’t have that data and never can have it. We can’t even determine if the data we have from the past 100 years is reliable. (Apparently not, since it has to be “adjusted.”)
        “Normal” weather therefore cannot be defined. That’s the beauty part of Climate Change(TM): it is only nominally data-dependent. In fact, it is barely data-constrained at all.
        Normalcy is the hobgoblin of little minds.

      • “But that’s the whole point, it isn’t normal weather.”
        So what is ‘normal weather’, genius?
        “30 years is usually considered as sufficient to call it a climate trend rather than weather. ”
        Only because that was the number of years that showed a warming trend when they chose it.

      • Griff, you know it was for more than a couple of years. It was almost a decade. Also, it hasn’t shown signs of any long term decrease in the satellite record. The loss of 2016 was a single event and it didn’t impact how the ice usually shrank (or make it worse) the remainder of the season. Now, I admit freely, if that keeps on happening and it becomes a new trend, it is concerning, but if it is a blip and southern sea ice keeps on as it was, you would need to admit that is is at least a distinct possibility that southern hemisphere sea ice (which was keeping the anomaly globally steady or in positive) is a much bigger player than the northern hemisphere . Therefore, it would be pure speculation to be putting things out there like “Well, we won’t have an ice age again, because of CO2. Look at the arctic”

      • “”But that’s the whole point, it isn’t normal weather.””
        You’re absolutely right….
        What we would call cold is the set point for this planet…
        …warm is not normal

    • I have no argument whatever that we have warmed the planet with CO2. But I am still a very strong CAGW skeptic.

      • “I have no argument whatever that we have warmed the planet with CO2. But I am still a very strong CAGW skeptic.”
        Wow, Evan, saying that here will usually have you figuratively tarred and feathered for such impertinence. However, it is a valid and sensible point, you must have at least a healthy share of Welsh genes and ancestry!

      • Evan Jones, I completely disagree. CO2 is NOT a driver of temperature, over any time frame that you chose, the change in temperature has ALWAYS happened in advance of the change in atmospheric CO2 concentrations.
        Saying that changes in atmospheric CO2 concentrations drives temperature is analogous to saying:
        “The tail wags the dog.”
        or my favorite;
        “Lung cancer causes smoking.”
        Furthermore, only in a lab environment can it be demonstrated that CO2 can even be minutely considered a “greenhouse” gas.
        How do you explain 7,000 ppm CO2 during the Cambrian with global temperatures that were very conducive to plant and animal life.
        How do you explain a glacial event (ice age) near the end of the Cambrian (450 million years ago) with atmospheric CO2 concentrations TEN TIMES current (4,000 ppm vs. 400 ppm).
        How do you explain a glacial event at the end of the Jurassic (144 million years ago) with atmospheric CO2 concentrations FIVE TIMES current (2,000 ppm vs. 400 ppm).
        CO2 does not drive temperature. It physically cannot, the First Law of Thermodynamics very clearly demonstrates this.

      • Gareth, why do you find it necessary to lie about what others have been saying?
        Is your own position really that weak that you have to create strawmen in order to convince yourself that your life is worth living?

      • This is a competition in throwing darts: Turn your dart board to the side that shows radial segments numbered randomly from 1 to 20 and start throwing!
        Your SWAG system to determine how much humans have warmed the planet with CO2 is now in place!
        (And if you accidentally hit a high number, say 18-20, you can publish and get funding from the CAGW trough).
        I’m not kidding folks: the argument isn’t about whether humans have contributed to warming, the argument is HOW MUCH.
        Is it 0.003%? 0.03%? 0.3%? 3.0%? 6.0% 12.0%? (The first three numbers aren’t even on the dart board, sorry–but if you’re a lousy shot and miss the dart board completely, that guess may be the actual amount.)
        Get your dart board and start tossing away.

      • RockyRoad, there is no correlation whatsoever that demonstrates that CO2 changes the atmospheric temperature.
        And even at peak CO2, at 7,000 ppm, if you consider that to be a BIG number, then what about the other 993,000 ppm, isn’t that a REALLY BIG number?
        So please tell me how, at a measly 400 ppm, that this TRACE molecule in our atmosphere (and that is all that CO2 has EVER been) can somehow magically, mysteriously, dominate the other 999,600 ppm.
        Truly a miracle molecule, but not for THAT reason. The miracle is that all plant life can extract that one molecule out of 2,500 for plant life/growth. That is the miracle, not how it can physically impose its will on the other 2,499 molecules that exist along side it.

      • That’s my point, Darrel.
        Did you read the description of my SWAG (Scientific Wild Ass Guess) dart board “calculator”?

      • Duly noted and thank you for the response.
        There are times (and some on this site would say lots of times) where I am not the sharpest knife in the drawer. D’oh!

    • There is no other causation in operation, is there?
      Oh Dear.
      How Sad.
      Never Mind.
      Griff, a complete believer in Climate change based on feedback, is apparently unaware of how causality in time delayed negative feedback governed systems actually works.
      He can’t even get to the simple case that e.g. blowing over the mouthpiece of a flute ’causes’ sounds.
      These wild fluctuations in the air pressure at the flute holes have to be ’caused’ by something eh griff?
      It couldn’t be that massive amounts of energy moving from the equator towards the poles where they get radiated away into space, moving past mountains and ocean basins and shelves and coasts and the like, don’t do so smoothly and linearly in the way someone who has never even got past O level mathematics can understand, but are subject to eddies, turbulence, and all sorts of ‘noisy’ variations in flow…
      I probably blame Tony Blair and Socialism for making people with less than half a brain – but brimming with ’emotional intelligence’ – think that they can actually understand mathematics that leaves top PhD graduates in applied maths stumped.
      Perhaps we need to add a days lesson in ‘self causation’ to the average snowflake syllabus.
      Sometimes Griff, its enough to say that the trickle of verbal diarrhoea emerging from someone’s mouth isn’t caused by anything other than that is simply the way they are made.

      • @ Leo Smith
        “I probably blame Tony Blair and Socialism for making people with less than half a brain – but brimming with ’emotional intelligence’ – think that they can actually understand mathematics that leaves top PhD graduates in applied maths stumped”.
        That’s a pretty breathtaking statement to make there Leo in light of the fact that the vast majority of climate scientists ( yes, with Doctorates etc) actually support standard climate science, while the opposing charge is led by far fewer people with scientific credentials as well as people like Monckton who lets face it, is not the sharpest knife in the draw. By the way, if you had any understanding of UK politics you would be aware that Blair was not a socialist in any real measure, he just had some socialist ideas such as universal healthcare and education. Willis would never class such people as socialists.

      • I don’t see any causation for the change (increased melting, continuing decline) referenced in what you wrote.
        Its not variation, its a clear trend down. And a change from the past.
        when something changes and heads determinedly in a new direction, there’s a reason for it, a cause.

      • A trend of 30 years is meaningless, not in a world with known climate cycles that range from 70 to several hundred years.
        You are seeing what your handlers tell you see. As always.

      • Griff,
        You couldn’t forecast the amplitude of a Sine wave. Your linear extrapolations are worse than useless.

    • Griff,
      You are understandably mistaken about what is going on, because you lack a long term perspective.
      Climate variability is subdued during interglacials and it is much higher during glacial periods. As the world cools down, climate variability increases. We know of similar warming periods at the end of other interglacials. A warming period is expected after every significant cold period, so that is what we got.
      We have helped warm the world with our emissions, but we mistakenly think that all the warming is due to that, when a big part is still the natural reaction to the Little Ice Age.
      We are lucky to be at the position marked by the asterisk. Conditions are likely to be nice for a few centuries. Glacial inception could take place in about 2000 years.
      If you think that is not the case you just have to compare our interglacial with the average of seven previous interglacials.

      • The long term trend should be we are heading slowly into the next glaciation… except we torpedoed that one and put it off a few thousand years.
        you offer no explanation for the rapid and continuing downward trend in the last century, increasing in recent decades.
        why this? why now?

      • >>As the world cools down, climate variability increases.
        Yes, Javier, but you do not understand why. The answer is that the Achilles-heel of an ice-age world is albedo. If you can darken the ice it will melt very rapidly, as you know. So the answer to all these problems is not simply orbital cycles, it is dust and albedo – as I explain in my post below:

      • Griff,

        The long term trend should be we are heading slowly into the next glaciation… except we torpedoed that one and put it off a few thousand years.

        So some believe. But they are the type of people that always think that this time is different (just because they are there). It never is. The next glaciation will arrive on schedule.

        you offer no explanation for the rapid and continuing downward trend in the last century, increasing in recent decades.

        You mean upward? I already did. It is part natural and part anthropogenic. Isn’t it obvious to everybody?

        why this? why now?

        Again you lack long term perspective. For about 400 years since the bottom of the LIA it is the turn of warming. That is why, and why it is now. In about 200-300 years it will be the turn of cooling. If the cooling doesn’t arrive then, I will be surprised.

      • Succinct presentation, Javier!
        But Griff will fail to understand it…. he will again focus on the short term.
        There is none so blind as he who will not see!

    • Griff says, “and there isn’t any Milankovitch cycle influence and this is lower than the last sea ice cycle in the 20s through 40s”
      Do you have the data? Can you post it?

      • Griff,your link has some nice pictures and information in it,but utterly fails to make the case from 1850 onward,since the data resolution is very low and coverage of the region spotty.
        Your claim of a record low is absurd,since YOU have been shown MANY TIMES,by published science research,that the Arctic for a few THOUSAND years had little to no Summer ice.
        Stop being a liar!

    • Argumentum ad Ignorantiam.
      “climate change caused by human CO2” is not the default.
      “There is no other causation in operation, is there?”
      Lack of evidence for one cause is NOT evidence for another.

      • No human caused climate change is not the default…
        but it is the only explanation that fits when you see the default setting – none of the known standard causes- doesn’t produce the results we now see.

      • No Griff, it isn’t the only explanation that fits. We’ve seen a millennial cycle for the past 3-4 thousand years and with a positive AMO sitting on top of it we have everything we need to explain the changes. Of course, given this solid explanation all we ever see is you ignoring it. Why is that?

      • I love it when Griff displays his ignorance.
        First the troll declares that this isn’t Argumentum ad Ignorantiam, then he declares that it must be CO2 because no other explanation fits.
        Griff, you have started off my day on a high note.

    • Far from record low sea ice. It has been lower than now for most of the Holocene and prior interglacials.
      Arctic sea ice is down from 1979, but that was near or at the height for the past century. Antarctic has been gaining for most of the past 40 years.

    • Griff
      The core of your scam is to argue that just because paleo proxies of the distant past have low resolution, this means that climate was constant back then. An absurd fiction – “we cant see the high frequency variation back then so there was no high frequency variation back then”. It’s depressing how many folks fall for it.

    • And the Antarctic (home of 90% of the glacial ice mass on the planet) is growing, on average, by 82 billion tonnes/year.
      And the Greenland ice mass is growing.
      And the glacier on Mt. St. Helens, WA, is growing.
      And glaciers expand and contract, ALL THE TIME!
      Here is a fascinating link from one of the very few climate experts on the planet, however since you are so deeply immersed in only considering what is happening in a single location on the planet, I understand completely if your perception on this topic does not allow you the permission to read something that completely contradicts your “beliefs”:
      Here is a slightly modified extract that is worthy of reading, irrespective of your level of “permission” Griff:
      CO2 is plant fuel, and they only reason that we are here is due to the fact that white rot fungi evolved to produce the enzymes that can digest lignin and coincident with that, was the end of the coal making era approximately 270 million years ago. There was no guarantee that fungi or any other decomposer species would develop the complex of enzymes to digest lignin, and if this did not occur, CO2 concentrations would have continued to drop to 150 ppm, at which point the majority of plant generation would have stopped, and the earth could have very well been a sterile planet for all life.
      Griff, I have yet to hear from you (not that I ever will but don’t fret, I will continue to destroy your singular focus on a small piece of the planet) with regards to why out wonderful planet was able to not only sustain life, but for it to flourish with historical CO2 concentrations that were 3 to 10 times higher than current, and you cannot comprehend that our atmosphere is so very complex, that focusing on a single trace molecule and on a single area of the planet is so insanely absurd …..
      And to answer a question posed of you in a previous topic, I personally prefer the “real” equation to the “ideal” one, however in the case of our atmosphere, z will be very close to 1 over the entire P range, so “ideal” is sufficient ……

    • Griff January 27, 2017 at 2:34 am
      “but now we have record low sea ice extent/thickness/volume and a change in weather patterns and in the winter too, not just at minimum.”
      No we don’t.
      You keep citing graphs based on guesstimates of an Arctic which has few actual temperature instruments.
      This link shows a failed attempt by the Russians to ship cargo.
      The link is from Ice Age Now.
      Oh and Griff, I hope that you and your little sea ice graph had no influence in their decision to try the passage.
      I hear that the “Wet Affairs” desk rolled directly into the new and improved KGB. (FSB&SVR)

    • Griff, when you fixate on CO2, does the diseconomy of strangling its release ever trouble you, or do you deny the economic and political power it gives to the few while inflicting waste and hardship on the many? If you are asking about other possible causes of warming, perhaps even some that don’t persistently lag temperature in sufficiently long and detailed records, you should know better.

  10. “The 100,000-year pace of glacial-interglacial periods has been difficult to explain,” said Jung-Eun Lee

    It is difficult to explain because it is a mathematical artifact of averaging complicated by the irregularities in the glacial cycle. When you actually go and measure the distance between interglacials, what comes out is a cycle driven by obliquity, not precession or eccentricity, at multiples of 41,000 years.
    Interglacials are separated by 82,000 years since the Mid-Pleistocene transition. Previously they were separated by 41,000 years but the world got too cold and started skipping one interglacial. When eccentricity is very high the world goes briefly back to 41,000 years. Sometimes the conditions that have to align for producing an interglacial do not align properly and the interglacial comes a little early or late, affecting its length (MIS 11, MIS 7a), or doesn’t come at all (MIS 3) producing a glacial period of 123,000 years.

    In terms of average global temperature, one might not expect precession to matter much.

    And it doesn’t. The correlation between temperatures and precession is lower than the correlation between temperatures and obliquity.

    “Precession only matters when eccentricity is large. That’s why we see a stronger 100,000-year pace than a 21,000-year pace.”

    Precession matters all the time since the Mid-Pleistocene Transition, because obliquity requires its help to produce an interglacial. When eccentricity is high an interglacial is produced at every obliquity cycle thanks to the effect of precession being higher.

    So why would the obliquity cycle be the most important one before a million years ago, but become less important more recently?

    Yes, why? The answer is that obliquity has the same importance. Occam’s razor is honored. We do not need a different theory for interglacials in the Early and Late Pleistocene.
    They are once again mistaking the effect (sea ice expansion) for the cause.
    If interested in the Glacial Cycle, check my article at Climate Etc., available here as a pdf:

    • That is hugely disingenuous, Javier,
      To get the Eemean glacial period down to 82 ky you have linked it to MIS 7c, which is NOT considered to be an interglacial. Which is preceded by a small 20 ky gap which is clearly precessional. And the marker over MIS 9 is also clearly wrong, because the preceding glacial period was 95 ky long. Measure it on the following graph.
      Anyway, your assertion that obliquity modulates interglacials doubly falls flat on its face because the interglacials clearly do not align with the obliquity cycle. Look at the obliquity cycles 255 ky ago and 170 ky ago, which were clearly passing by each other like ships in the night, and nothing to do with each other at all. Look also at the obliquity cycles 170 ky and 50 ky ago, which had almost no effect on temperature.
      Graph of obliquity (blue) vs interglacial temperature (red).
      So even if you want to champion obliquity as the primary cause of interglacials, you are stuck in the same position as Prof Jung Lee (author of this paper) and all the other precessionalists – because not every cycle causes an interglacial. And until you can explain those failed cycles, you have a non-theory that has fallen off its perch and is probably pining for the fjords.
      The answer to this conundrum is, of course, dust. As I explain in my post below.

      • Ralph,
        You share with the authors of this study mistaking the effect for the cause. We know that dust is produced by deep glacial conditions, so the correlation is explained.
        Explaining why not every obliquity cycle produces an interglacial is very easy. Don’t forget that in the early Pleistocene every obliquity cycle produced an interglacial, when dust was not playing any role, as deep glacial conditions were not reached.
        In the late Pleistocene several conditions must be aligned to overcome the cold inertia of the planet. If they don’t take place the obliquity does not produce an interglacial. I explained it very clearly in my article at Climate Etc.
        A summary of conditions is in this figure:
        Figure 12. A simple model of interglacial determination based on obliquity, insolation, and temperatures. Top, A window of opportunity takes place every time obliquity increases, marked with a colored bar, red when an interglacial results and blue when not. Middle, Insolation is proposed to promote interglacial conditions when above the red dashed line at 520 Wm2, during the second half of the window (red circles), or directly result in an interglacial when above the green dashed line at 550 W/m2(green circles). Bottom, Low temperatures are proposed to promote interglacial conditions when below the blue dashed line at 4.55 ‰ δ18O during the first half of the obliquity window (red circles). Numbers on top are periods of increasing obliquity with red numbers indicating an interglacial produced by favorable conditions (red circles), blue numbers indicate an interglacial was not produced due to unfavorable conditions (blue circles), and green numbers indicate interglacials produced by very high insolation despite unfavorable temperatures (green circles). MIS 13 (window 13) cannot be explained by this model, thus the question mark.

      • Ralph,
        In the abstract of your recent paper, you meant “a critical” minimum “of about 200 ppm”, not ‘minima’, which is plural:
        We present here a simple and novel proposal for the modulation and rhythm of ice-ages and interglacials during the late Pleistocene. While the standard Milankovitch-precession theory fails to explain the long intervals between interglacials, these can be accounted for by a novel forcing and feedback system involving CO2, dust and albedo. During the glacial period, the high albedo of the northern ice sheets drives down global temperatures and CO2 concentrations, despite subsequent precessional forcing maxima. Over the following millennia more CO2 is sequestered in the oceans and atmospheric concentrations eventually reach a critical minima of about 200 ppm, which combined with arid conditions, causes a die-back of temperate and boreal forests and grasslands, especially at high altitude. The ensuing soil erosion generates dust storms, resulting in increased dust deposition and lower albedo on the northern ice sheets. As northern hemisphere insolation increases during the next Milankovitch cycle, the dust-laden ice-sheets absorb considerably more insolation and undergo rapid melting, which forces the climate into an interglacial period. The proposed mechanism is simple, robust, and comprehensive in its scope, and its key elements are well supported by empirical evidence.

      • >>you meant “a critical” minimum “of about 200 ppm”.
        Err, yes, quite possibly. But do remember that there is more than one critical minimum. Confused? I am…

      • >>Figure 12. A simple model of interglacial determination
        >>based on obliquity, insolation, and temperatures
        Javier, your fig 12 is a bit of a nonsense. You are comparing obliquity with Milancovitch insolation – but obliquity is already included in Milankovitch insolation. So you are conflating the obliquity function twice.
        You then seem to indicate that rising obliquity can only cause an interglacial when the temperature is cold, but you do not explain why. What is the difference? And you still fail to explain the interglacial warming 240 ky ago, which has no obliquity associated with it at all.
        Of course the real reason for low temperatures initiating an interglacial, is that CO2 concentrations also came down. It was low CO2 and the resulting dust that initiated the interglacial, not obliquity.

      • but obliquity is already included in Milankovitch insolation.

        Obliquity is not included in Milankovitch insolation, as this is insolation measured at 65°N at the summer solstice. Obliquity affects both poles symmetrically and increases the entire melting season energy, not just 21st of June peak energy.

        rising obliquity can only cause an interglacial when the temperature is cold, but you do not explain why.

        This is an observation, not an explanation. But essentially every negative feedback factor becomes stronger when at an extreme temperature. They all cooperate towards a faster warming when the melting starts. Dust is just one of them.

        you still fail to explain the interglacial warming 240 ky ago, which has no obliquity associated with it at all.

        MIS 7e and MIS11, the short interglacial and the long interglacial explain themselves when you look at their astronomical signature. MIS 11 started too early respect the obliquity cycle and MIS 7e too late, and that explains their unusual length. Before MIS 7e started it was barely cold enough at the right time according to the obliquity cycle, but the very high eccentricity 240 kyr ago gave enough push to precession for a late start. Since it still ended when obliquity came down after the usual lag, it became a short interglacial.
        It is explained at the article at Climate Etc. and here:

  11. The first question that occurs is ‘Does this enable a prediction of when the next ice age is due to start ?’
    Scientific theories are validated by their prediction, and this is one question we would really like to be able to answer. Another ice age is due sometime, and that’s one type of climate change that we really should worry about – if it’s coming anytime soon.

    • Depends on what do you understand for soon. Is it 2000 years soon to you? For theory validation most scientists are not keen on waiting 2000 years to be vindicated.

  12. Why is there no graph showing where we are in the cycles, along with a projection of where we are going on a time scale?

  13. but now we have record low sea ice extent/thickness/volume and a change in weather patterns and in the winter too, not just at minimum.

    We do not have record low sea ice. Since we know very little about the Southern Hemisphere, there may be some speculation or conjecture as to whether the MWP, or the Roman Warm Period or the Minoan Warm Period were truly global, or whether they were limited to the Northern Hemisphere.
    But we know as fact that the MWP, and the Roman Warm Period and the Minoan Warm Period all happened, as far as the Northern Hemisphere was concerned, and we know as fact that during those periods, Arctic sea ice, Ice in and around Greenland, ice/glacification in and around Norway were much lower than today.
    But also recently, ie., during the 20th century there was less ice in and around the 1940s.
    And from Ogi et al’s recent paper on greenland temperatures:
    And the recent reconstruction of North Atlantic Sea temperature:
    There have been many papers published these past couple of years that suggest that today is no warmer than it was around the 1940s in and around high latitudes in the Northern Hemisphere.
    There is nothing unprecedented about today’s level of ice in and around the Arctic basin.

    • “We do not have record low sea ice…”
      But we do for the period of recent human history and very probably for the period since the Eemian.
      we have the satellite record and very good records for the period before it… for example all existing records from 1850 have recently been collected and analysed from thousands of sources and we can see that current extent is much lower than any period since 1850.
      and the trend is down.
      We have less sea ice than would be the case without human caused warming, humand caused warming is contributing to its continued decline.
      and that matters, because declining sea ice impacts the climate further…

      • Griff,
        There is zero evidence that human GHGs have had any effect whatsoever on sea ice extent. If they did, the Antarctic would have declined since 1979 along with the Arctic.
        Ice is low this year because of the super El Niño, not people.
        Sea ice since 1979 is not in any way unusual. It’s normal for a warming cycle coming out of a cooling cycle like the LIA.
        As noted, sea ice has been lower for most of the Holocene and prior interglacials, to include the Eemian.
        Besides which, less drift ice is a good thing, as for that matter is more CO2.

      • Griff, I try to make sense of what I read. When argument boils down to assertions of “It is,” “It isn’t,” we can make progress, because the issue (whichever it is) is well defined. Based on what you just wrote, do I understand that you reject the accuracy of the Hasholt 2016 graph cited by Mr. Verney?

      • OK, my second blunder this week. Because Mr. Verney introduced the Hasholt graph with the line:
        But also recently, ie., during the 20th century there was less ice in and around the 1940s.
        I mis-read it as a graph of ice extend. But it is clearly labelled as a graph of temperature. Sorry bout that…

      • Sorry, I was not as clear as I could have been.
        As far as I am aware, prior to the satellite era, there is no quality data on the extent of sea ice since there was no easy way to track it, and the existence of which disappears as ice melts and is covered up as ice reforms.
        One is therefore left to infer the extent of ice from temperature records, and this is the approach adopted. There is an assumption that the extent of ice is largely a function of the prevailing temperature, but weather patterns, particularly wind, can play a significant role at least over short periods. Ocean currents play a role but warm ocean currents usually influence land coastal temperature records so to some extent land temperatures pick up on the changeability of ocean currents.
        So what I set out was temperature records.
        Of course what we do know is that the Northern hemisphere cooled significantly from the highs of the late 1930s/1940 , viz:
        The global cooling scare was built upon the back of the large fall in Northern hemisphere temperatures (variously assessed to be between 0.5 to 0.8deg C) and the growing extent of sea ice in the Arctic which reached a peak in the early 1970s (1873/4).
        Thereafter, of course, there has been a decline in Arctic sea ice but given the temperatures that we have today, in and around the Arctic basin, are broadly no warmer than they were back in the 1940s, and given that North Atlantic Sea temperatures are not as warm as they were in the 1940s, it is reasonable to infer that the extent of sea ice that prevails today is not significantly lower than that in the 1940s, and every reason to suspect that there may well have been less Arctic sea ice in the 1940s.
        Of course we also know that the Skate and the Nautilus both surfaced at the North pole in the 1950s without dynamiting the ice..
        And it is worth looking at the Seadragon and Skate in 1962, and the amount of open water:
        Compare the above photograph to the photographs of the three subs surfacing in 1987 where there is a lot less open water.
        These photographs were taken in different months, so a great deal of care needs to be taken ovr reading too much into matters
        But as I say, conditions today, are not unprecedented even comparing with last century. One does not have to go back to the conditions of the say the MWP or the roman Warm period etc.

      • MarkW, that’s actually hundreds of log reports and observations and records from Denmark, Russia Norway, US cold war submarines etc etc etc … a complete collection of the available evidence, carefully sorted and evaluated, and it is valuable, accurate and full data.
        You might note that is ALL the data we have. And nowhere in ALL the data is there a lower point than now: there are many, many, many higher points.

      • Chimp.
        No. Just no.
        Arctic and antarctic are different ice environments. They don’t respond in the same way.
        We don’t have the same conditions as produced the Eemian, but have the lowest ice since.

      • Griff,
        No, no and no-no.
        Present ice is very far from the lowest since the Eemian.
        As stated, for most of the Holocene, summer ice has been much lower than now. For thousands of years.
        How this fact escaped you, I don’t know. You must have intentionally ignored the reality revealed by all the evidence, which is abundant.
        Yes, the Arctic and Antarctic are different environments, but the air above them has about the same number of CO2 molecules. Explain please why Antarctic sea ice has surged since 1979, if man-made CO2 be the alleged cause for Arctic sea ice decline (which of course it isn’t).

      • Griff,
        I guess you missed this blog post:
        Not only was Arctic sea ice extent much lower during the Holocene Optimum, c. 8200 to 5000 years ago, but also during the Egyptian, Minoan, Roman and Medieval Warm Periods.
        Also before the HO, during the breakdown of perennial sea ice cover:
        “Arctic Ocean sea ice proxies generally suggest a reduction in sea ice during parts of the early and middle Holocene (∼6000–10,000 years BP) compared to present day conditions. This sea ice minimum has been attributed to the northern hemisphere Early Holocene Insolation Maximum (EHIM) associated with Earth’s orbital cycles. Here we investigate the transient effect of insolation variations during the final part of the last glaciation and the Holocene by means of continuous climate simulations with the coupled atmosphere–sea ice–ocean column model CCAM. We show that the increased insolation during EHIM has the potential to push the Arctic Ocean sea ice cover into a regime dominated by seasonal ice, i.e. ice free summers. The strong sea ice thickness response is caused by the positive sea ice albedo feedback. Studies of the GRIP ice cores and high latitude North Atlantic sediment cores show that the Bølling–Allerød period (c. 12,700–14,700 years BP) was a climatically unstable period in the northern high latitudes and we speculate that this instability may be linked to dual stability modes of the Arctic sea ice cover characterized by e.g. transitions between periods with and without perennial sea ice cover.”
        What was unusual in the Holocene was the greater sea ice extent of the LIA, which you somehow imagine to have been “normal” for this interglacial.

      • Griff,
        Note in Charctic graph that, as predicted, low Arctic sea ice this year from El Niño is headed back into the normal zone.
        You still have not provided a shred of evidence for your ludicrously false, baseless assertion that present Arctic sea ice is lowest since the Eemian.
        Nor told us why Antarctic sea ice set record highs up to 2014, if CO2 is responsible for lower Arctic ice after the abnormally high year 1979.
        Antarctic and Arctic ice were affected by the super El Niño but that effect is fading.
        Besides which, lower ice is good, not bad. Same as higher CO2. Double or triple present CO2 would be better.

  14. I can’t find an on-line version of the full article. We will have to see the math here.
    It is actually a plausible mechanism but the southern sea ice would have to increase to encompass a huge area (much, much larger than today) and then melt-back very little in the summer.
    Basically, the southern sea ice has to increase by an amount which would drop global temperatures by about 3.0C or so. That would be enough to interrupt the summer snow melt in the far northern latitudes and then glaciers build up etc.
    My Albedo calculator says that winter southern sea ice would have to get to almost 45S and summer sea ice would have be at least no lower than 50S or so. I don’t think the southern Milankovitch Cycles produce this kind of southern sea ice. A blurry image of the ice extent in the preview function for the article does not show it getting that far.
    And then we have to see if the southern Milankovitch Cycle downdips match the timing. We need to see all that.

    • Even at the LGM, let alone at NH ice sheet initiation, Antarctic winter max extent reached only 48 to 60 degrees S, depending upon sector. The lower latitude figure was for the Atlantic and western Indian Oceans, so ice may have engulfed Tierra del Fuego, which extends down to 55 S.

    • Seems to me that if southern sea ice grow enough to measurably cool the whole planet, then northern sea ice and land based ice would also start to expand which would increase the amount of cooling.
      We wouldn’t have to rely on southern sea ice all by itself to cause all of the cooling.

    • I changed my mind, this is not a plausible scenario.
      The ice ages always begin when there is big downdip in higher northern summer solar insolation. The 4 big downdips here that kicked off the last 4 ice ages are equivalent to when solar insolation at 75N falls below 440 W/m2 on June 21 (summer solstice) which is more-or-less the level that is needed to melt the winter snow.
      Your winter snow melts out when the solar insolation gets to this level in the spring whatever that date is. At 75N, the summer solstice has about 530 W/m2 so we are nowhere near the level it takes. Eureka Canada at 80N loses its snow in early June and it comes back in early September. That, again, is 3 months of no snow which is nowhere near the level of starting another ice age.
      Once the glaciers get set-in at 80N and 75N, they start to reflect more and more sunshine until the ice age is inevitable.
      It takes 2 or 3 good upturns in the summer Sun of the Milankovitch cycles to break the back of the glaciers. It is a complete fluke that they are roughly 100,000 year long in the last 3 or 4 ice ages. The 100,000 eccentricity Cycle is not correlated to that 100,000 time-frame at all. There is Zero correlation.
      What is the most weird thing about the ice ages is that glaciers have no business being all the way down to Chicago. I mean there is no way that should really happen. The summer Sun here is a good 400 W/m2 higher than is needed to melt the winter snow or a glacier, even in the deepest downturns of the Milankovitch. It is only because everything north of it has Albedo of 75% to 90% that it can be cold enough in Chicago in the summer to let the glaciers get there and stay there for any period of time. Even 65N NEVER has a low enough decline to let glaciers exist here, even on Greenland.
      Northern solar insolation at 75N is where the make or break sunshine varies enough so that there are periods when the sea ice and the winter snow does not melt.

      • The 4 big downdips here that kicked off the last 4 ice ages are equivalent to when solar insolation at 75N falls below 440 W/m2 on June 21 (summer solstice) which is more-or-less the level that is needed to melt the winter snow.

        Your conjecture fails at MIS 19 that with very similar northern summer insolation levels to ours got its glaciation, as every interglacial.
        It is obliquity with a lag of several thousand years due to thermal inertia what determines glacial inception. Regardless of northern summer insolation levels.
        We have for example MIS 7c, 215,000 years ago. MIS 7c got its glacial inception with the surprising amount of 530 W/sq m of 65°N summer insolation, 200,000 years ago.
        It really demonstrates that 65°N summer insolation is irrelevant for glacial inception. When obliquity says it is time to go glacial, it is time to go glacial. And once you go glacial you don’t come back regardless of insolation, obliquity, or whatever, until everything gets properly aligned after going through a very cold glacial maximum. With low eccentricity like now, once we go glacial it will be at least 70,000 years before the next interglacial.

      • 65N versus 75N.
        Like I said, 65N never gets below the threshold. The event starts at 75N where solar insolation can get low enough.
        So at 65N at MIS19, solar insolation falls to 480 W/m2 and the winter snow doesn’t survive the summer but at 75N you can can expect it to be 40 W/m2 lower and the sea ice and the snow doesn’t melt out in the summer.
        Today, 75N is up to 560 W/m2 or so. The key is that once the snow and sea ice melts out in early June, now the full force of the Sun gets to have its effect.
        Eureka Canada at 80N has a world-class climate research station. The solar radiation tower shows the data. Solar gets to 530 w/m2 at its peak. By early June, the snow melts and the full force of the Sun hits at that time. So, this is the true “sweet-spot” for the ice ages. Once the SW Down falls a moderate amount and the SW UP never falls and the SW Down – UP never gets to high levels the ice age is starting. These are REAL measurements.

      • >>What is the most weird thing about the ice ages is that glaciers
        >>have no business being all the way down to Chicago. I mean there
        >>is no way that should really happen.
        You are forgetting the power of albedo. When the albedo hits 0.95, your 400 W/m2 becomes 20 W/m2. So now you know why ice sheets continue to extend, despite subsequent up-turns in Milankovitch insolation.
        What you now need is a way of preventing that high albedo, to create an interglacial. And the mechanism that does that is dust, as I have explained elsewhere on this thread.

      • Here is another visual to show one why there is just a small strip at the far northern latitudes that are the make or break location.
        Look at the axial tilt changes. The more the tilt, the more the chance that the snow has to melt in the summer because the summer sun is just that little bit more overhead. (it is a good thing there is a tilt at all because without it, the ice and snow at the poles would never melt and the Earth would just be a white ice-ball.)
        But look at the Earth surface where the two lines 22.1 degrees and 24.5 degrees are. The difference between where the two intercept the Earth surface is so small. 22.1 degrees ice-age on; 24.5 degrees ice-age off. The two points are only a several hundred kms apart.
        The summer solar forcing in the summer varies between where you live and a community which is just a few hundred kms north of you. Like 3 hours drive. That is how tiny the differences are. It ONLY matters at the 75N-80N where these few hundreds kms difference of solar energy can be the make or break factor. (There’s more in the Milankovitch Cycles of course but this is the Major one – it was the key driver between 2.7 million years ago and 1.0 million years ago).

      • If all it took was tilt, then we’d be headed for the next glaciation within 10,300 years.
        Obliquity is currently 23.44 degrees and decreasing at a rate of about 0.013° per century. (23.44 – 22.1 = 1.34 / .013 = 103 x 100 = 10,300.)
        Of course ice sheet inception can occur before the lowest tilt angle, ie 22.1 degrees.

      • Like I said, 65N never gets below the threshold. The event starts at 75N where solar insolation can get low enough.

        There is no threshold. Here you have the comparison at 75°N:
        So on that small difference you justify that MIS 19 got a glaciation but the Holocene won’t get it?
        Everybody gets fixated on W/sq m, as if that was all. The climate however shows us that a lot of the effects do not depend on W/sq m. Precession determines the differential insolation on both hemispheres determining the position of the ITCZ, and the effect is huge enough to decide if the Sahara is a desert or a savanna. Obliquity determines the equator-polar gradient that decides on the poleward transport of meridional heat and humidity. That heat transport is not included in the calculations of W/sq m.
        And we do know that when the obliquity cycle turns down and obliquity decreases, interglacials come to an end with a lag of about 6500 years. Anybody claiming an exception for the Holocene should first find an exception for this rule, and explain why it doesn’t apply to the Holocene.

  15. Hmm, wrong on most counts I fear.
    For a start there is NO 100 ky glacial-interglacial cycle. It is a 90 ky or a 115 ky cycle, which matches the precessional cycle very well. Here is a table of the last fice ice ages.
    Precession cycles (kyr) … Cluster length (kyr) … Ice-age duration (kyr)
    23, 21, 26, 22, 25 …………..117 ………………………..117
    23, 22, 23, 24, 23 …………..115 ………………………..115
    21, 21, 27, 22 ………………….91 …………………………90
    16, 22, 15, 17, 22 …………….92 …………………………90
    25, 20, 22, 17, 21 …………..105 …………………………99
    So we can see that the ~100 ky eccentricity cycle is important, but not pivotal. Lee says: “When eccentricity is small, precession doesn’t matter”. But this is completely wrong.
    Look at the following diagram (by Mike Palmer). The central blue plot is eccentricity, the top orange plot is precession-insolation (Milankovitch cycles). Note that the precession peaks 290 ky, 170 ky, 105 ky and 80 ky ago did NOT cause an interglacial, depite them being enhanced by high eccentricity. In fact, the cycle 170 ky ago that failed completely, was greater than the cycle 240 kya ago that did cause an interglacial.
    High Milankovitch insolation is NOT the sole cause of interglacial initiation. So what is? The answer is dust. As you can see in the following graph, every interglacial is preceded by dust, which lowers the albedo of the northern ice sheets and allows the ice to melt, and the interglacial to proceed.
    Please see the following paper which explains everything. And yes CO2 is vital for interglacial warming – but only when it gets too low.

    • So what causes dust? I speculate in a comment below. And what makes dust go away? It gets rained out. Think thermofluid dynamics in a very very very large pot of water with the heat source above combined with the plain old water cycle. Clouds during discharge, clear sky during recharge, dust because of low humidity while the oceans recharge.

      • Desertification causes dust. Loess deposits in China from this cover vast areas and are hundreds of meters thick. A lot of dust arises during glacial retreat exposing unvegetated ground covered in deposits of gravel sand and silt/clay that are products of the grinding of bedrock by kilometer+ moving ice sheets. I mapped crescent-shaped sand dunes in the bush of northern Manitoba sourced from the retreating ice sheet.

      • >>So what causes dust?
        Just as Gary says, the lack of CO2 caused the appearance of CO2 deserts (instead of aridity deserts) in the Gobi region of China and Mongolia. This is why the NE Asia region never had any ice sheets, despite the cod weather there – it was always too dusty.
        And the reason the dust stopped as soon as the interglacial started, is that Co2 concentrations started to rise and C3 grasses repopulated the Gobi (C4 plants cannot live on the Gobi).
        And the reason the interglacial continued to warm, is that there was already 10,000 years of dust embedded in the ice sheets, and these continued to concentrate on the surface as the ice melted.
        It is quite a comprehensive theory.

      • What causes dust? Wind. What does the wind also do? Turning the cold oceans upside down. The cold surfaces don’t evaporate water. Therefore it is dry and the windy circumstances blow the remaining dust on the icy areas.
        But what caused wind? Notice that interglacials start after the lowest temperatures in the preceding Glacial. When the oceans are turned ‘upside down’, the coldest surface (!) circumstances will exist. The lack of vegetation (lack of CO2, cold, enhanced water shortages) can cause lower winter season temperatures on ‘land’ and colder nights on ‘land’. While the tropical seas remained warm and the land cooled down, the temperature gradient rose. As soon as the temperature gradient rises, wind speed rises. As wind speeds rises, cold upwelling will be enhanced, sea surface will cool, evaporation will be lowered, vegetation will diminish even more, dust will be abundant and wind also, dust will be transported to the ice and snow and the big melt can start. As soon as temperature goes up, the temperature gradient will diminish and upwelling will slow down, making it possible that the sea surface temperatures rise. Retreating snow and ice enhance the distance between snow and the equator, diminishing the temperature gradient and lowering the wind speed once more. The surface will be in a continued ‘heat gain’ modus, raise melt etc. etc.

      • >>What causes dust?
        Bare ground. This was recently barren ground, just like 1930s ‘dust-bowl America’. Unlike deserts, where the fine material has long since been blown away, newly barren areas are full of microscopic particles just waiting to be taken aloft.

      • >>Wind. What does the wind also do?
        But the data suggests otherwise.
        From the analysis of dust grain-size, it has been established that conditions were windier upon the Gobi plateau (where the glacial dust came from). However, the data also suggests that wind strengths on the ice sheets did not change. Which is logical, as the peak wind change will be close to the ice sheet termini, in lower latitudes.
        So although more dust was lifted by stronger winds, it was not carried far and most settled upon the Loess Plateau. So the main reason for increased dust on the ice sheets, was a much greater desert area – caused by the CO2 deserts.

    • Thanks for the link. That will be some good reading for me this weekend.
      PS. Happy new year to all the folks celebrating it this weekend.

    • Ralf
      Maslin and Ridgewell also consider the apparent 100,000 year pacing of recent interglacials to be in fact a complex result of precession cycles, not eccentricity, although they concede a possible “pacing” role to eccentricity:
      again this is all understandable in the context of a weakly periodically forced nonlinear oscillator.

      • >>Maslin and Ridgewell consider … recent interglacials to be
        >>a complex result of precession cycles
        Yes, but Maslin was also trying to push the CO2 agenda, citing 240 ppm of CO2 is a ‘critical threshold’? (A tipping point.) This is an abridgement of my letter to Maslin, which greatly upset him.
        So where in the graph below is the transition from normal cooling to ’tipping point’ cooling? It is not there, is it. There is no tipping point in ice age cooling, and so your suggestion is wrong. … And your quote above, and implied in the Daily Mail article, is the complete opposite of what you acknowledge in your 2015 paper. At the beginning of your 2015 paper you quote the prevailing wisdom that … (ice ages progress due to ice-albedo) ……
        So you have already found the true feedback agent, that operates long before 240ppm CO2. So why attempt to force CO2 into the argument, and leave albedo out of your discussion and conclusions? Where is the logic in that? Especially since the albedo feedback is orders of magnitude stronger than CO2, when calculated regionally and annually. Is it sImply because CO2 HAS to be there, according to the consensus? Is that the reason? If so, it is a poor one. Yet you must yourself have doubts, because your 2016 paper does not mention CO2 at all.
        More importantly, you have still not addressed the MOST IMPORTANT aspect of the post-MPT glacial cycle – the missing interglacials. If CO2 were the primary climate feedback, then why does the all-powerful CO2 not assist and promote an interglacial at EVERY precessionary cycle in the NH. You cannot explain that deficiency, with the simplistic CO2 approach.
        However, the one feedback mechanism that DOES increase before each interglacial, and not in-between, is dust. And dust is the primary ingredient in the albedo feedback mechanism. Ergo, my friend, it is dust and albedo that control interglacial modulation, not CO2.
        I did not get a coherent reply that addressed the issues I raised, just a complaint that my letter was too forthright.

        • ralfellis,
          “I did not get a coherent reply that addressed the issues I raised, just a complaint that my letter was too forthright.”
          And this response is surprising? It’s been my experience that the more definitively the alarmist POV is deconstructed, the more hostile and incoherent their responses become. Schlesinger and others have demonstrated this to me within the last few days. The pathological denial of any physics, data or hypothesis that disputes a high sensitivity is as anti-scientific as it can be, yet this logical flaw is endemic among those highly vested in the status quo. Schlesinger even suggested that I need psycho analysis for suggesting that if Mars had 1 ATM of O2/N2, the CO2 concentration would be over 6000 ppm in response to his claim that there’s not enough CO2 on Mars to make it warm.
          BTW, Schlesinger (Cess and Hansen) are largely responsible for the incorrect application of Bode’s control theory to the climate system that provided the theoretical foundation for a high sensitivity and which led to the formation of the IPCC. I made him aware of the errors nearly a decade ago and will be happy to testify at his trial.

      • Ralf
        Yes I thought the CO2 homily in that M&R paper was out of place in an otherwise useful study. It is sad to witness the moment when a scientist steps over the line from curiosity and inquiry into cynical politicing. Also depressing to see how badly scientists respond to criticism of their work even when it is delivered confidently and personally. I have seen this myself. (Your letter made a clear scientific point and was a fair comment.)
        Perhaps the way science works is that any view or hypothesis that a scientist advances becomes an all-consuming circus of self promotion and fundraising that they become so heavily invested in that contradiction is seen as an existential threat.

  16. I look at this paper and I cannot process all the variability. I am attracted to solar influence despite the persistent criticism that it doesn’t have any measurable effect. Well, it seems that there is something there.
    The posting is stained with incredulity IMO, despite my interest in the subject, by the concluding statement wrt AGW matters. Other critics raise this issue as well.
    …stay curious…

  17. http://siberiantimes.com/other/others/news/n0857-blow-to-northern-sea-route-as-voyages-of-two-icebreakers-are-broken-by-ice/
    “But now a spokesman for Rosmorport has announced the icebreakers will delay a return until probably May or early June. ‘The vessels will remain for the winter because of the very heavy severe ice conditions,’ he said.”
    “Emergencies Ministry officials denied the situation was an emergency. ‘A winter stop is a good practice for preventing accidents related to complex ice situation,’ said a source”

    • Is that intended to show the ice is getting thicker/recovering/an ice age is on the way?
      The reason they were out there at all is that climate change is opening up the N sea route for longer and the Russians are putting in the infrastructure to take advantage of that. They just commissioned an LNG icebreaker tanker for the N sea route… replaces pipeline use through europe. Note it isn’t intended to break the ice full time, its just that with permanently decreasing ice it can operate safely for longer on that route now.

  18. Absorbed incoming solar radiation integrated annually is the same for the two hemispheres, independent of eccentricity. Therefore, if cooling is caused by radiation reflected by excess sea ice in the Southern hemisphere, it remains to be explained why the Northern hemisphere reflected more as well.

  19. “Much of the carbon dioxide — a key greenhouse gas — exhaled into the atmosphere from the oceans comes from the southern polar region. If that region is largely covered in ice, it may hold that carbon dioxide in like a cap on a soda bottle.” CO2 is a minor greenhouse gas when compared to water vapor …

    • Since there are major currents in the oceans. Water that is under southern sea ice now, won’t be in a few years. I’m not seeing sea ice as being a capable of keeping CO2 locked up in water. Not long term.
      As Kaiser points out, sea ice does prevent evaporation, which would keep water out of the air over the ice cap, and that would aid in heat loss.

  20. Conceded Milutin Milankovitch had more than such models – he was used to think for himself.

  21. Hmmmm. Dust. What causes dust. Lack of humidity. Oceans provide humidity. So if humidity is low for a long time, oceans have gone into net recharge mode. They are not evaporating heat, they are absorbing heat. Which would lead to dust, thus limiting what solar insolation is available, prolonging the amount of time needed to warm up the oceans enough that heat begins to escape again. I still must return to the oceans themselves as a slow discharge/recharge battery that both causes and then interacts with atmospheric water vapor and airborne dust to create a cyclical stadial/interstadial jagged oscillation mildly impinged upon be orbital mechanics. CO2, a bit player, rides along.

  22. Now for something completely different. (from me)
    Climate change skeptics say that fluctuations in the earth’s climate are caused by variations in the output of the sun. Alarmists respond by stating that variations in solar luminosity and the average solar constant of 1,368 W/m^2 are too small to make much difference. They are both correct and yet both of those explanations are inaccurate and incomplete.
    What both sides forgot to mention is that the earth does not orbit in a nice average circle, but in an ellipse:
    1) closer to the sun at perihelion, 1/4/17, and hotter with a solar non-constant of 1,415 W/m^2,
    2) and farther at aphelion, 7/3/17, and colder with a solar non-constant of 1,323 W/m^2
    3) for a total variation of 92 W/m^2.
    What both sides also forget to mention is that because of the tilted axis and spherical shape the total insolation incident on a horizontal surface at the top of the atmosphere at any given point, e.g. 40 N latitude, fluctuates by around 670 W/m^2 solstice to solstice. What are the consequences of that large fluctuation? Winter and summer which the earth has survived for thousands of millennia.
    Per IPCC AR5 between 1750 and 2011, 261 years, assuming all natural processes remained constant (not necessarily valid) the atmospheric concentration of carbon dioxide rose due to by default human processes, i.e. fossil fuel and land use changes, from 278 ppm to 391 ppm. The consequence to the atmospheric heat balance of 261 years’ worth of that additional carbon dioxide was a warming of 2 W/m^2. (IPCC AR5 SPM.5)
    If the 92 W/m^2 fluctuation due to orbit and a 670 W/m^2 fluctuation due to tilt and shape have no catastrophic consequences what should we reasonably expect from 2?
    BTW 1,415, 1,323, 92, 670 W/m^2 are real numbers based on real physical parameters, real math, and confirmed by real measurements. IPCC’s 2 W/m^2 is based on a conceptual model such as Kiehl-Trenberth’s power flux graphic diagram, i.e. a ball suspended in a hot fluid, with no consideration of orbit, tilt, night and day, and bearing no resemblance to the actual earth.

    • Another point is that the earth moves faster when it is closer to the sun, so it spends less time at perihelion than it does at aphelion.

  23. The frigid waters around the Antarctic are the biggest global sink for CO2, never a source. Seasonal sea ice expansion does not change the area of that sink but shifts it to the north. CO2 being delivered to the South pole via the upper atmosphere from the tropics has to travel further over ice to open water during Antarctic winter causing a slight increase in concentration during that time.
    In contrast, the big sink in the north is nearly covered with ice during the northern winter and CO2 being delivered there builds up to maximum concentration values. When the ice melts in summer, the frigid waters suck up every molecule that reaches it. We don’t need to wait 100,000 years to see this effect, but it is nice to know that nature behaves similarly on much longer time scales. The water cycle controls the CO2 cycle.

  24. The assertion that summer insolation changes at 65N due to the earth’s orbital changes, which is referred to as Milankovitch’s theory, somehow causes the glacial/interglacial cycle, is an urban legend.
    A paradox is an observation (cyclic abrupt climate change in the paleo record for example) that cannot be explained by a theory. When there are piles and piles of paradoxes a field of science should be in crisis. Climate science is in crisis.
    An obvious observation that refutes Milankovitch theory is the Younger Dryas abrupt cooling event 12,900 years ago, at which time the planet when from interglacial warm to glacial cold with 70% of the cooling occurring in less than a decade. The Younger Dryas abrupt cooling event lasted for 1200 years.
    There is a massive cyclic forcing function (hint it’s the sun and hint the sun causes a massive change to the earth’s geomagnetic field which in turn causes long term cooling, the self exciting theory for the generation of the geomagnetic field is also a urban legend) that has not been taken into account.
    Currently summer insolation at 65N is the same as the coldest part of the last interglacial.
    Greenland Ice Sheet Temperatures Last 100,000 years
    It is interesting that the Dansgaard/Oescheger cyclic warming and cooling ‘events’ have a characteristic period of 1470 years which has continued with same periodicity from the last glacial period into the current Holocene interglacial period.
    As there are cosmogenic isotope changes that are concurrent with all of the Dansgaard/Oescheger events (also referred to a Bond events named after Gerald Bond who tracked 23 of the cycles) and the Heinrich events it is obvious a specific solar cycle change is causing what is observed.
    Are at least 12 different observations and analysis results that support the assertion that insolation changes at 65N are physically not capable of causing the temperature changes observed in the paleo record and did not cause what is observed. The following is a sample of the paradoxes which disproof the theory.

    Milankovitch believed that decreased summer insolation in northern high latitudes was the dominant factor leading to glaciation, which led him to (incorrectly) deduce an approximate 41 ka period for ice ages.[18] Subsequent research[19][20][21] has shown that ice age cycles of the Quaternary glaciation over the last million years have been at a 100,000-year period, leading to identification of the 100 ka eccentricity cycle as more important, although the exact mechanism remains obscure.

    1) 100,000 year problem

    The 100,000-year problem is that the eccentricity variations have a significantly smaller impact on solar forcing than precession or obliquity – according to theory- and hence might be expected to produce the weakest effects. However, the greatest observed response in regard to the ice ages is at the 100,000-year timescale, even though the theoretical forcing is smaller at this scale.[10] During the last 1 million years, the strongest climate signal is the 100,000-year cycle. In addition, despite the relatively great 100,000-year cycle, some have argued that the length of the climate record is insufficient to establish a statistically significant relationship between climate and eccentricity variations.

    2) Southern Hemisphere cools cyclically at the same time as the Northern Hemisphere

    Glacial records depict ice age climate in synch worldwide
    “During the last two times in Earth’s history when glaciation occurred in North America, the Andes also had major glacial periods,” says Kaplan.
    The results address a major debate in the scientific community, according to Singer and Kaplan, because they seem to undermine a widely held idea that global redistribution of heat through the oceans is the primary mechanism that drove major climate shifts of the past.
    “Because the Earth is oriented in space in such a way that the hemispheres are out of phase in terms of the amount of solar radiation they receive, it is surprising to find that the climate in the Southern Hemisphere cooled off repeatedly during a period when it received its largest dose of solar radiation,” says Singer. “Moreover, this rapid synchronization of atmospheric temperature between the polar hemispheres appears to have occurred during both of the last major ice ages that gripped the Earth.”

    3) Stage 5 problem (Causality Problem)

    The stage 5 problem refers to the timing of the penultimate interglacial (in marine isotopic stage 5) that appears to have begun ten thousand years in advance of the solar forcing hypothesized to have caused it (also known as the causality problem)(putative effect precedes cause).

    4) Effect exceeds cause

    The effects of these variations are primarily believed to be due to variations in the intensity of solar radiation upon various parts of the globe. Observations show climate behavior is much more intense than the calculated variations.

    5) The unsplit peak problem

    The unsplit peak problem refers to the fact that eccentricity has cleanly resolved variations at both the 95 and 125 ka periods. A sufficiently long, well-dated record of climate change should be able to resolve both frequencies.[15] However, some researchers[who?] interpret climate records of the last million years as showing only a single spectral peak at 100 ka periodicity.

    6) The transition problem

    The transition problem refers to the switch in the frequency of climate variations 1 million years ago. From 1–3 million years, climate had a dominant mode matching the 41 ka cycle in obliquity. After 1 million years ago, this switched to a 100 ka variation matching eccentricity, for which no reason has been established

    7) Identifying dominant factor

    Milankovitch believed that decreased summer insolation in northern high latitudes was the dominant factor leading to glaciation, which led him to (incorrectly) deduce an approximate 41 ka period for ice ages.[16] Subsequent research[17][18][19] has shown that ice age cycles of the Quaternary glaciation over the last million years have been at a 100,000-year period, leading to identification of the 100 ka eccentricity cycle as more important, although the exact mechanism remains obscure
    The Earth’s orbit is an ellipse. The eccentricity is a measure of the departure of this ellipse from circularity. The shape of the Earth’s orbit varies in time between nearly circular (low eccentricity of 0.000055) and mildly elliptical (high eccentricity of 0.0679)[3] with the mean eccentricity of 0.0019 as geometric or logarithmic mean and 0.034 as arithmetic mean, the latter useless. The major component of these variations occurs on a period of 413,000 years (eccentricity variation of ±0.012). A number of other terms vary between components 95,000 and 125,000 years (with a beat period 400,000 years), and loosely combine into a 100,000-year cycle (variation of −0.03 to +0.02). The present eccentricity is 0.017 and decreasing.

    • William Astrology
      An obvious observation that refutes Milankovitch theory is the Younger Dryas abrupt cooling event 12,900 years ago, at which time the planet when from interglacial warm to glacial cold with 70% of the cooling occurring in less than a decade. The Younger Dryas abrupt cooling event lasted for 1200 years.
      Not so. A few chaotic fluctuations and flip-flops between the glacial and interglacial attractors do not in any way refute Milankovich. If they do, then they refute the whole peleton of solar and astrophysical alternative cyclical theories also.
      Your own figure that you posted – the temperatures in Greenland over the last 100,000 years – makes it clear that the YD is nothing at all exceptional – it is simply one – the last one – out of about 20 “microinterglacials” that took place during the previous glacial interval. Microinterglacials are sometimes called DO (Dansgaard-Oescher) events.
      How many posts does one have to plough through in which every tiny twitch and inflection of the graph needs its own unique external forcing? What is so taboo about saying the obvious, that it’s simply a weakly periodically forced nonlinear oscillator?
      Think of the bigger picture and it becomes still more obvious. Earth has been cooling for at least 40 million years, and now we are just entering glaciation for the last 3 million years. So earth is finely balanced on the threshold between glacial and interglacial. Like any dissipative open system with chaotic dynamics, it is characterised by islands of stability in the probabilistic topology that are called “attractors”. Glacial and interglacial are attractors. As the abundant literature on chaotic experimental systems such as the Belousov-Zhabotinsky reaction (in all its forms including thin film) shows, chaotic oscillation can be periodically forced from the outside. Where the periodic forcing is weak or of comparable magnitude to the system’s own internal fluctuations, then the resulting wavetrain becomes very complex and the forcing signal is mixed with internally generated oscillations. The climate of the last 2-3 million years is as clear an example of this as one could ever hope to find.
      There are many natural systems that during a gradual transition from one state to another, flip between the two states during a short transitional period, such as fish shoals or flocks of birds flipping between random milling and coordinated emergent-pattern swarming.
      It is my prediction that every major glacial period in earth’s history, such as the Marinoan, Varangian, Saharan-Andean (end-Ordovician) also both began and ended with transitional periods of glacial-interglacial flipping. Why would they not? The long term trend we are in is for gradually deepening glaciation, as the above article states. So the transitional period of glacial-interglacial flip-flopping wont last forever – eventually there will be permanent and deep glaciation for a few tens of millions of years.
      The fact that the pacing of interglacials has only loosely followed the obliquity cycle (3-1 mYa) and eccentricity (last million years) is because it is weak periodic forcing, mixed with internal chaotic oscillation. The fact that the forced oscillation is chaotic also means that it does not slavishly follow a fixed threshold, and the timing also varies. The oceans posess their own chaotic oscillations which occur over century and millenial timescales, and ocean circulation and mixing, the immediate cause of all climate change, is under weak external periodic forcing of the Milankovich cycles.

    • >>An obvious observation that refutes Milankovitch theory is
      >>the Younger Dryas abrupt cooling event 12,900 years ago
      There is good reason to believe that the YD was caused by an meteorite impact. See the mystery of the Carolina Bays, discussed here before.
      And good reason to believe that the sudden D-O events during the last ice age were caused by continent-wide forest fires. Especially as these temperature excursions hardly show up in the SH.

      • Gosh, Ralph,
        You really subscribe to any wacko conjecture you come about.
        Younger Dryas a meteoritic effect? D-Os caused by periodic forest fires?
        Younger Dryas has all the aspect of being a mild late Heinrich event, similar to H3. It ends in a sudden warming accompanied by heavy Ice Rafted Debris in the North Atlantic, as Heinrich events do.
        And we have a pretty good idea of what caused D-O events if you bother to read the ample bibliography on the matter, and it wasn’t dust, or ashes, or fires, or extraterrestrial beings.

      • >>You really subscribe to any wacko conjecture you come about.
        I think you are losing the plot, Javier.
        It was not me who suggested fires for D-O events, it was Fischer et al in “Millennial Changes in North America Wildfires….”. They demonstrated quite clearly that D-O events were strongly linked with fire combustion products.
        To me this is logical. I have already demonstrated that the greatest feedback is albedo, not CO2. And the two most common elements that will change ice sheet albedo are dust and soot. Ergo, Javier, the continental fire theory is probably correct.

      • Ralf,
        There is no reason to imagine an impact at the YD, as there is not a scrap of evidence for one.
        D/O and Heinrich, the Dryases and 8.2 Ka events all are caused by melting ice and ocean circulation, just as were the similar events in all prior glaciations. Bond cycles during interglacials are also due to ocean oscillations.

      • ” I have already demonstrated that the greatest feedback is albedo, not CO2.”
        You have demonstrated nothing of that sort.

      • Ralph,
        You have it backwards.
        D/O events led to more vegetation and less ice, so there was more biomass to burn.
        Your own citation from Nature Geoscience, Fischer, et al, makes this point. It doesn’t say what you claim, ie that wildfires caused the D/O events. The warmer intervals caused more vegetation to grow in areas from which ice retreated. Also probably longer growing season when warmer.
        Millennial changes in North American wildfire and soil activity over the last glacial cycle
        Climate changes in the North Atlantic region during the last glacial cycle were dominated by the slow waxing and waning of the North American ice sheet as well as by intermittent, millennial-scale Dansgaard–Oeschger climate oscillations. However, prior to the last deglaciation, the responses of North American vegetation and biomass burning to these climate variations are uncertain. Ammonium in Greenland ice cores, a product from North American soil emissions and biomass burning events, can help to fill this gap. Here we use continuous, high-resolution measurements of ammonium concentrations between 110,000 to 10,000 years ago from the Greenland NGRIP and GRIP ice cores to reconstruct North American wildfire activity and soil ammonium emissions. We find that on orbital timescales soil emissions increased under warmer climate conditions when vegetation expanded northwards into previously ice-covered areas. For millennial-scale interstadial warm periods during Marine Isotope Stage 3, the fire recurrence rate increased in parallel to the rapid warmings, whereas soil emissions rose more slowly, reflecting slow ice shrinkage and delayed ecosystem changes. We conclude that sudden warming events had little impact on soil ammonium emissions and ammonium transport to Greenland, but did result in a substantial increase in the frequency of North American wildfires.

      • Javier,
        So it appears.
        There is no need to invoke extraterrestrial or terrestrial gods on machines to account for climatic observations. The climate system itself, ie oceanic and atmospheric interactions, plus celestial mechanical modulation of solar activity, with some tectonic elements, adequately explain most phenomena.

      • Ralf
        The YD bolide impact hypothesis was thoroughly discredited in this recent post here:
        As for forest fires increasing NH temperatures by as much as 10 C – come on Ralf! You’re better than that.
        Both the Bolling-Alerod and the previous microinterglacials were likely to have been excursions of the AMOC (linked to its salinity-downwelling feedback instability) – thus as Javier points out they appear only in the Greenland i e core records, not the Antarctic:

      • ;-). True.
        But at least we can debate several scenarios, without getting arrested on trumped up RICOH charges…..

  25. Okay, I sort of got blasted for my writing critique of another article here at WUWT, which had as much to do with my ignorance as it did to to with the author’s presentation. Still, I gotta risk getting blasted again, so here goes:
    My first annoyance with this article, as with any article, is a clickable link to PAY-WALLED original research. This seems pretty useless to me, so why do it. A broken link, okay fine, that can be fixed. But a pay-wall link seems like free marketing for the journal, which might not be the intent of the author, but, unfortunately it is the effect on the reader.
    Say I click on the link that says Geophysical Research Letters. What does that do for me ? It takes me to page that refers me to another page that refers me to another page that shows the cost of accessing the article. I wasted my time, in other words, when I was trying to understand the article in which the link appeared, by seeing the original research upon which the article was based.
    Yeah, yeah, I know, I’m such a whiner ?
    On another, related note (and perhaps putting my neck further in a noose of highly trained minds here in this field of study), here was my attempt at a similar article some years back (since someone requested a sample of my attempts at writing in another post):
    I realize, by YOUR standards here, that my attempt there might be underwhelming, flawed, amateurish. I even quote some of the names I think I have seen here in the WUWT comments.
    Anyhow, as usual, no guts, no glory.

    • Oh no, and now I must face the wrath of William Astley. (^_^) … as I endure the torture of his ripping my amateurish article to shreds.
      Live and learn. Living is not so hard. Learning, on the other hand, …

  26. A Scotsman named Croll wrote about this in the late 1800’s. That’s why they are sometimes known Croll Milankovich cycles.

  27. Nickolas. I was hoping to find out why the shape of earth’s orbit changes. Judging from your comment I thought you could explain it for me.

    • William Astley’s point 7) in his post above covers some of the orbital information…
      Also remember the earth is tilted… that tilt, its inclination may be toward or away from the sun, over time…

      • Currently the NH tilts away at perihelion, closest, so away and close offset the heating a bit. The SH tilts toward at perihelion making for double hotness.
        At aphelion, farther, the NH tilts towards, but colder orbit and warmer tilt off set. SH tilts away and gets double coldness
        Milankovitch says that in half of 26,000 year or so the earth will precess in its orbit to the point that the arrangement will be 180 degrees, NH tilted closer at perihelion, double hotness and SH away, offset, at perihelion.
        All of this fluctuation is bound to change the heating/cooling and behavior of the climate and biosphere and orders of magnitude more than GHGs/CO2.
        Why an ellipse? Well, I understand that’s not always the case. Need to go back to the original science, Newton, Kepler, Copernicus, et.al.

    • Earth’s orbit is elliptical because of the gravitational attraction of Jupiter and other solar system bodies besides the sun. It also of course wobbles on its axis, ie precesses, and changes tilt. There is as well precession of perihelion, but that is considered to have only a minor effect on climate.

  28. It’s a breath of fresh air – actually considering external forces affecting climate. Now, after first trashing the CO2 based muddle, we can begin to construct a rational climate model. This has been mentioned, but when dealing with events on scales of tens of thousands of years you must consider plate tectonics. How were the land masses arranged then? Perhaps a future refinement, but please omit the CO2 genuflexion.

  29. MODS
    A comment of mine is presently in moderation. When you post it please will you correct a typo appearing immediately before the 2nd image.

    …and the growing extent of sea ice in the Arctic which reached a peak in the early 1970s (1873/4).

    The date in parenthesis should be 1973/4
    many thanks.

  30. This theory sounds a lot like many others I have heard. I think the dust theory poster here some months back seemed to fit better.

  31. Firmly tongue in cheek it is worth pointing out that Milankovitch was not always the darling of consensus science. He was a pal of Wegener for example and a bit of a maverick. However. he lived in a time when it was impossible to get out of the straightjacket of mainstream theory and recognised that all it takes to create an ice age is a tilt in the axis of rotation. My theory for what it is worth is that he created a situation where he got the necessary tilt in the orbit of the earth by coming up with a lengthy series of cycles, and the 100,000 years cycle was the longest which is why mainstream adopted his scheme in the 1950s as it was possible to glue it together with their other pet theories, such as the magnetic stripes on the floor of the Atlanti, and the discovery that foraminifera also displayed a cycle of around 100,000. Rhodes Fairbridge however suggested the sun went around it barycentre at just short of 100,000 years – so does the foraminifera (and its changes in oxygen isotopes) really have anything to do with ice ages? I find it strange on this blog that so many people are willing to rubbish climate science and co2 levels but are fully prepared to accepted equally dodgy other consensus theories – as if it is the truth. Is it too much for the brain to think in terms of more than one anomaly? What if Milankovitch just wanted to create a tilt in the earth – but mainstream would not allow the earth to shift from its axis of rotation. Would he have been forced to come up with a tilt that fitted the mainstream agenda? It’s an interesting question and we shall never know the answer. I am of course chucking a stone into the waters. We really should not toe the consensus line in any science – which is the point I wish to make. Not unless it has been indisputably verified. As far as I can see Ice Ages have not been verified as even foraminifera data has come under attack in some quarters – and Plate Tectonics, you might remember, is stridently supported by none other than Naomi Oreskes. That should tell you all you want to know. It is a consensus theory. Why do people accept that and blow cold air at global warming?

    • Hi, Carol.
      Your point is well made. Plenty of denizens here will clutch at anything that seems to be an alternative to CO2 as a cause of climate change, and make of it much more than can be justified with our present state of knowledge. Unfortunately, warmists then seize upon this willing credulity to dismiss the whole sceptic postion. I, too, wish we could confine ourselves to a critique of the CO2 paradigm, but I guess it isn’t going to happen.
      That said, there are some really interesting things that emerge when we go off at a tangent – worth a separate blog in their own right. A few of these you see immediately above your post (Ralfellis, Ptolemy, Javier). So we shouldn’t be too displeased, but feeling guilty at spending so much time here

    • Earth’s axis completes one full cycle of precession approximately every 26,000 years. At the same time, the elliptical orbit rotates more slowly. The combined effect of the two precessions leads to a 21,000-year period between the astronomical seasons and the orbit.

    • >>Current estimates place it at around 26,000 years instead
      As Gloateus said, you have to factor in apsidal precession too. And even with this, the precessional cycle is highly variable, from 15 ky to 25 ky. Which is why it was so difficult for Milankovitch to calculate, before the advent of computers.

      • Gloateus and Ralf,
        Thanks for your enlightening information.
        Having just calculated the period of the combined axial and orbital rotation cycles myself, I can confirm that it comes to roughly 21,000 years.
        However, I was somewhat bemused to learn that the orbital (“apsidal”) motion is referred to as “precession” when it would have to be “procession” (i.e. in the same direction as the planets move in their orbits, which is opposite to the direction of axial precession) to produce a 21,000-year combined cycle. If the orbit really was precessing in the same sense as the Earth’s axis, the period of the combined cycles would be 34,000 years or thereabout.
        Factoring in Ralf’s point about the extreme variability of the combined cycles as well, I find myself drowning in a boundless sea of mathematical uncertainty, which I dare say provides infinite wiggle-room for a climate modeler to speculate in.

  32. There are major problems with the Milankovich/Croll hypothesis that no model is going to solve. For example, (1) 40 years ago John Mercer pointed out that if the M/C theory is correction, glaciations and interglaciations in the Northern Hemisphere should be out of phase with those in the Southern Hemisphere (he called this the ‘fly in the Milankovitch ointment), (2) the deep sea core record is largely undated, so it was stretched or contracted until it matched the astronomical record and then (lo and behold), because the two curves matched, the Milankovitch theory must be true, (3) the discovery of abrupt, full scale climate changes from full glacial to interglacial in a hundred years or so (D/O events) dealt the Milankovitch a death blow because orbital changes couldn’t possibly change back and forth that rapidly, (4) we now know from isotope dating of glacial deposits in both hemispheres that abrupt, short term, fluctuating climate changes occurred simultaneously in both hemispheres and could not be caused by slow orbital variations, and on and on.
    No computer model can overcome these contradictions to the Milankovitch/Croll theory.

    • Don,
      Those aren’t problems for the celestial mechanical hypothesis.
      Glacial and ice sheet advances can and do overlap in both hemispheres, but initiating colder climate can start in either and affect the other with a lag.
      Ice core records are well dated, and they confirm the hypothesis.
      Rapid climatic fluctuations don’t need to be explained by the hypothesis. Celestial mechanics explain the onset and demise of glaciations. They needn’t explain what happens during them. D/O and Heinrich events are due to sudden freshwater flows into the oceans, whether from meltwater or iceberg armadas.

      • “Gloateus,
        “Those aren’t problems for the celestial mechanical hypothesis.”
        Of course they are.
        “Glacial and ice sheet advances can and do overlap in both hemispheres, but initiating colder climate can start in either and affect the other with a lag.”
        You’re missing the point rather badly here–THERE IS NO LAG!
        “Ice core records are well dated, ”
        No–the Greenland GISP2 is well-dated by annual layering, but it only extends back 100,000 years so doesn’t help with 100k cycles. The Antarctic cores are very poorly dated.
        “and they confirm the hypothesis.”
        No, they do not (see above)
        “Rapid climatic fluctuations don’t need to be explained by the hypothesis.”
        Of course they do–they are real and prove that full glacial/interglacial climate changes
        have occurred repeatedly within a few hundred years, far too abrupt to be caused by M/C.
        “Celestial mechanics explain the onset and demise of glaciations.”
        No they do not–for all of the reasons stated previously.
        “They needn’t explain what happens during them. D/O and Heinrich events are due to sudden freshwater flows into the oceans, whether from meltwater or iceberg armadas.”
        No they are not–if this were true, there would be a lag between hemispheres, but recent extensive isotope dating of glacial deposits in both hemispheres prove that there is no lag at all.

      • Don,
        Nope. All the evidence says you’re wrong as to both the lag and the celestial mechanical cause of NH glaciation:
        The Milankovitch theory of climate change proposes that glacial–interglacial cycles are driven by changes in summer insolation at high northern latitudes. The timing of climate change in the Southern Hemisphere at glacial–interglacial transitions (which are known as terminations) relative to variations in summer insolation in the Northern Hemisphere is an important test of this hypothesis. So far, it has only been possible to apply this test to the most recent termination because the dating uncertainty associated with older terminations is too large to allow phase relationships to be determined. Here we present a new chronology of Antarctic climate change over the past 360,000 years that is based on the ratio of oxygen to nitrogen molecules in air trapped in the Dome Fuji and Vostok ice cores. This ratio is a proxy for local summer insolation, and thus allows the chronology to be constructed by orbital tuning without the need to assume a lag between a climate record and an orbital parameter. The accuracy of the chronology allows us to examine the phase relationships between climate records from the ice cores and changes in insolation. Our results indicate that orbital-scale Antarctic climate change lags Northern Hemisphere insolation by a few millennia, and that the increases in Antarctic temperature and atmospheric carbon dioxide concentration during the last four terminations occurred within the rising phase of Northern Hemisphere summer insolation. These results support the Milankovitch theory that Northern Hemisphere summer insolation triggered the last four deglaciations.

      • Gloateus,
        I’ve shown real-time physical data for synchronous glaciations in both hemispheres, no lag between hemispheres, and climate reversals too abrupt to be caused by M/C. Nothing you have said provides any evidence to the contrary (‘dating’ of ice cores by ‘orbital tuning’ is not really dating–you need independence measurement (such as annual dating in GISP2) for real chronology.

      • Don,
        You´ve mentioned isotope data here, but haven´t provided the data. No doubt you have elsewhere, but so far my link is the only source in our discussion.
        Dating ice and sediment cores can be difficult, but with enough different methods and using well constrained checks such as volcanic eruptions, the results are good enough for government work, ie climatological purposes.

      • Gloatus,
        I assumed that anyone serious about the cause of climate change would be familiar with the literature, but considering the vastness of the literature, perhaps I presume too much. If you intend to defend the M/C hypothesis, you will need to be aware of the negative evidence (real, physical evidence) that I referred to above. As a start, I would recommend the new Elsevier volume, “Evidence-based I Climate Science.” It has a lot of isotope data and other information by 15 authors. Then you can follow up with references in the papers there. I hope you do this, as I think it will sharpen the issues for you.
        Having spent a lifetime dating sediments and working with ice core isotopes, I can tell without equivocation that “the results are good enough for government work, ie climatological purposes” is not good enough.

      • Don,
        Presumably specialists in celestial mechanics and paleoclimatology who have concluded that Milankovitch cycles regulate ice sheet inception are at least as conversant with the literature as you. So I’d like to see your evidence that they are wrong.

    • Good points Dr. E. If the models are able to distinguish changes in the relative influence of the three cycles, they should be able to pinpoint the onset of the next ice age. Yet, the paper makes no such claims.

      • Rob,
        Many scientists have made predictions based upon M cycles. Those who conclude that eccentricity dominates predict that the Holocene will be a very long interglacial. Those, like Javier, who consider other parameters more important, predict it will last only a few thousand more years, being shorter than the Eemian, the previous interglacial.

      • Gloateus,
        My point does not concern the relative strength of one cycle vs another, as the paper claims to have discovered which cycle dominates when. If the models in question have no predictive skill, the we have to assume claims of discovering a cipher to which cycle dominates when, are tenuous at best.

    • Don,
      (1) Obliquity is in phase in both poles. Obliquity is the main responsible factor for interglacials. Glacial periods are the default situation of being in an ice age and don’t need explaining.
      (2) The deep sea core record is dated by magnetic inversions. No adjustment needed to support obliquity driven interglacial cycles.
      (3) D-O events have nothing to do with the glacial cycle, and they are not global in nature as they do not show in Antarctic records.
      (4) Abrupt climate changes take place all the time in the proxy records. The 8,2 kyr event, the 4.2 kyr event, Heinrich events, Bond events, D-O events. Why should the orbital theory have to explain them all?
      I am very surprised by the simplicity, lack of depth, and lack of evidence of your arguments.

      • Javier,
        “1) Obliquity is in phase in both poles. Obliquity is the main responsible factor for interglacials. Glacial periods are the default situation of being in an ice age and don’t need explaining.”
        ‘Glaciations don’t need explaining’?? I hope you don’t really believe such nonsense.
        “(2) The deep sea core record is dated by magnetic inversions. No adjustment needed to support obliquity driven interglacial cycles. ”
        Deep sea cores have ONE magnetic reversal in the past million plus years, and you consider that enough for chronology?
        “(3) D-O events have nothing to do with the glacial cycle, and they are not global in nature as they do not show in Antarctic records.”
        Your ignorance is showing here–they have everything to do with glacial cycles and they do indeed show in both Antarctic and Greenland records.
        “(4) Abrupt climate changes take place all the time in the proxy records. The 8,2 kyr event, the 4.2 kyr event, Heinrich events, Bond events, D-O events. Why should the orbital theory have to explain them all?”
        M/C doesn’t have to explain every climatic variation, but because D/O events (especially the Younger Dryas) show that global climates can shift from full glacial to full interglacial in a few hundreds years, they are far too abrupt to be cause by orbital variations.
        “I am very surprised by the simplicity, lack of depth, and lack of evidence of your arguments.”
        Then you need to read the literature and educate yourself–you obvious don’t know much about the issues.

      • In explanation……
        Javier likes to use Huybers’ home-made marine-core chronology, which was indeed centered around magnetic reversals some 900 ky apart. It uses none of the other chronological pegs that the ice core chronology depends upon, and is therefore the most unrelaible ice age chronology on the market.
        Javier likes this chronology because it was made to support Huybers’ obliquity theory, which Javier subscribes to. So he is clinging to a self-fullfilling prophesy, which is not exactly science.

      • Don,
        (1) Perhaps you are unaware that the planet has been cooling for the past several million years to the point that now it spends 90% of its time in a default glacial state characterized by extensive continental ice sheets.
        Nobody knows the cause of that multi-million year cooling, but when the conditions that give rise to an interglacial end, the planet slides naturally to a glacial state.
        “Deep sea cores have ONE magnetic reversal in the past million plus years, and you consider that enough for chronology?”
        Pardon me, but we have Brunhes, Matuyama, Jaramillo, Olduvai, Kaena, Mammoth, Gilbert, Cochitl, Nunivak, Sidufjall, and Thvera in the past 5 million years. That’s enough to know what orbital periodicities we are talking about. For the past 800,000 years we can compare with Antarctic ice cores. The match is quite good as this figure from Varga 2015 shows:
        (a) is LR04 benthic record, and (b) is EPICA Dome C in Antarctica. Do you get lost there?
        And the dating of ice cores is quite good with a very small error.
        (3) It is your ignorance that shows. DO-events do not appear neither in Antarctic records, nor in benthic records. You have a syndrome known as “Greenland climate represents global climate.”
        (4) “D/O events (especially the Younger Dryas) show that global climates can shift from full glacial to full interglacial in a few hundreds years”
        DO-events and YD do not represent a shift from full glacial to full interglacial. They affect mainly the northern hemisphere with some teleconnections affecting Antarctica. DO events do not register and YD barely in the global benthic record.
        “Then you need to read the literature and educate yourself–you obvious don’t know much about the issues.”
        I think I have read the literature in more depth than you and I know more about these issues than you do.
        I already published a very in depth article about the glacial cycle with very extensive literature review at Judith Curry’s blog Climate Etc.
        And I am sending a new one about the Dansgaard-Oeschger cycle today, that if approved will appear shortly at the blog.
        Read them and learn.

      • Ralph

        Javier likes to use Huybers’ home-made marine-core chronology, which was indeed centered around magnetic reversals some 900 ky apart. It uses none of the other chronological pegs that the ice core chronology depends upon, and is therefore the most unrelaible ice age chronology on the market.
        Javier likes this chronology because it was made to support Huybers’ obliquity theory, which Javier subscribes to. So he is clinging to a self-fullfilling prophesy, which is not exactly science.

        That’s a lie. In the methods part of my article it says and shows very clearly that I am using EPICA Dome C chronology.
        You are the one that subscribes to alternative explanations like forest fires for D-O events, meteorites for the YD, and dust for interglacials.
        Your own figure clearly shows that temperatures and interglacials follow the obliquity cycle when the thermal inertia of the planet is taken into consideration.
        Thanks for your help in making my point.

      • Javier,
        Your graph also show how variable are the glacials as well as the interglacials, both in duration and temperature.
        The last glaciation was a biggie, including two full tilt cycles between the obliquity peaks associated with the Eemian and Holocene. These stillborn interglacials were instead merely major interstadials within the glacial.

      • Yes, Gloateus,
        The planet is so cold that 9 of the last 20 obliquity cycles resulted in aborted interglacials.
        Yet here we are, near the end of an interglacial, worried that the planet might warm too much. What a curious species we are.
        According to my calculations, the next obliquity cycle will also fail, so we are looking towards at least 70,000 years of glaciation. Large parts of the world will become uninhabitable.

      • Javier,
        Except that in a few thousand years, when high latitude snow no longer melts in summer, we can help it along with soot, if not indeed giant, fusion-powered blow driers or front-end loaders dumping it in trucks to be hauled to warmer climes.

      • Yes that wall that Trump is building will prove an obstacle when – Day after Tomorrow style – US citizen fleeing glaciation are trying to cross into Mexico.

  33. Warmists do love their theories about how sea ice (or lack of) is a big climate driver. Tail wagging the dog.

    • >>Tail wagging the dog.
      Not necessarily. The feedback effects of ice-albedo are orders of magnitude greater than the feedback effects of CO2.

      • ralfellis,
        “The feedback effects of ice-albedo are orders of magnitude greater than the feedback effects of CO2.”
        Yes, except it is incorrect to characterize this as ‘feedback’, moreover; we are close to minimum ice now, so the potential cooling effect is far, far larger than the potential warming effect based on the current state of average ice.
        Average ice coverage is about 12-13% of the surface. 2/3 of the planet is covered by clouds, thus on average, only 1/3 of the ice, if it all melts, will decrease the net albedo. The difference in reflectivity between average ice (40%) and no ice (7%) averages about 240*(.4-.07) = 80 W/m^2. Calculating the global effect of ice disappearing altogether is 80 * .125 * 1/3 resulting in an average of 3.3 W/m^2 across the globe and this doesn’t include the fact that the portions of the planet covered by ice get less Sun than average. Adding 3.3 W/m^2 to the 3.7 W/m^2 of forcing said to arise from doubling Co2 only adds up to less than half of the power required to sustain a 3C increase (> 16 W/m^2 of incremental surface emissions).
        During ice ages, nearly 1/3 of the planet is covered by ice resulting in 80 * 1/3 * 1/3 is an average reduction of nearly 9 W/m^2 whose global temperature influence is about 2-3C (or 7.2C if you believe the absurdly high sensitivity claimed by the IPCC). Of course, they assume a high sensitivity to make a case for CO2, not realizing that the ice albedo effect is similarly increased far beyond reason. I would be remiss to not point out that at lower CO2 concentrations and lower temperature, the incremental effect (cooling or warming) from CO2 is far larger than it is today.

      • >>Yes, except it is incorrect to characterize this as ‘feedback’,
        Classical climatologists tie themselves in knots with this terminology, as Hansen did in one of his papers, because forcing and feedback often overlap.
        I term a feedback as anything that is a terrestrial response to a change in forcing. Orbital cycles are obviously a forcing. Since ice-albedo cooling is a response to that initial forcing, I term it as a feedback. Likewise with ice-albedo warming.

        • “Orbital cycles are obviously a forcing”
          Technically, only the Sun forces the climate. If the Sun stopped shining, orbital cycles would be irrelevant. Orbital cycles are not so much a specific forcing, but a modulation and redistribution of solar forcing, much like night and day, except to a lesser extent.
          When the IPCC says doubling Co2 is 3.7 W/m^2 of forcing, what they really mean is that doubling Co2 is EQUIVALENT to 3.7 W/m^2 more post albedo power from the Sun, keeping the system (Co2 concentrations) constant.

          • what they really mean is that doubling Co2 is EQUIVALENT to 3.7 W/m^2 more post albedo power from the Sun, keeping the system (Co2 concentrations) constant.

            I think we have to be cautious, they are both equal to 3.7J/s/m^2. But they don’t necessarily add together because the e of the material they encounter will matter greatly for the 15u photon, and the broadband solar is well absorbed.
            I also think it is possible it only really lights up when a lot of water vapor is condensing, as it has a wide band around 15u and it has to radiate to change to liquid water, and those photons can couple to co2, and vise versa, very laser cavity like. If this is the case I would expect the top of this area would get really bright at 15u.
            It’s also possible its transfer the heat to the surrounding, that it would warm that object, which would have a more BB spectrum, where ~40% can radiate out the optical window,

          • “But they don’t necessarily add together because the e of the material they encounter will matter greatly for the 15u photon, and the broadband solar is well absorbed.”
            This is the whole concept of EQUIVALENCE and since 1 joule does 1 joule of work, this is a convenient metric to be equivalent to. The equivalent forcing attributed to doubling Co2 is adjusted until it’s exactly equivalent to 3.7 W/m^2 of post albedo incident forcing. Climate science puts so many layers of obfuscation when considering the sensitivity, its not all that surprising that it has never been corrected, after all, that was the point of all the obfuscation in the first place.

          • How can they do that? They don’t have any idea what the e is going to be.
            My point is they could actually be putting in 4 times that is, they set e as .25

          • “How can they do that?”
            They guess and they have made a significant mistake, since the definition of forcing sets an instantaneous increase in post albedo input power as the same as an instantaneous decrease in surface emissions passing though the transparent region. All of the former affects the surface temperature, while in LTE, some of the later (about half) ends up escaping out to space.
            Also, the LWIR emissivity and absorption of the surface is close enough to unity that e=1 is a good approximation. The ‘equivalent’ temperature of the surface is defined as the temperature of the surface of an ideal BB whose LWIR absorption is equal to its LWIR emissions. It just happens that this surface is a good proxy for the surface whose temperature we care about making its temperature a very good proxy for the actual surface temperature.

      • As far as short term variations go, this is far more complex.
        It appears that the claim that loss of sea ice will adversely impact upon albedo thereby leading to more warming may be incorrect. There is a recent article on the NASA website that sheds considerable doubt upon the correctness of that assumptions.

        But, as is usually the case with climate processes, that simple description isn’t the whole story: the positive ice albedo feedback may have a competitor. “If the sea ice shrinks,” says Kato, “intuitively we would think that more water is exposed to the atmosphere, and so more water vapor is available to the atmosphere to form clouds. So in addition to changing sea ice, we can kind of guess that something must be happening in the atmosphere over the Arctic, too.” Clouds are bright, too, and an increase in clouds could cancel out the impact of melting snow and ice on polar albedo. (my emphasis)

        See: http://earthobservatory.nasa.gov/Features/ArcticReflector/

  34. To form ice sheets over a mile thick in northern latitudes, there must be a source of humidity to provide the snow to create the ice sheets. Ergo, the Arctic must be relatively ice free for extended periods.

    • The moisture comes from the lower latitudes, where there is no ice. There is no need for the Arctic to be ice free.

      • One reason for the onset of NH Pleistocene glaciations after the closure of the Inter-American Seaway by the Isthmus of Panama was more moisture brought north by the strengthened Gulf Stream.

      • Also Indonesia. Hot off the press, Jan 2017:
        Tectonically induced changes in oceanic seaways had profound effects on global and regional climate during the Late Neogene. The constriction of the Central American Seaway reached a critical threshold during the early Pliocene ~4.8–4 million years (Ma) ago. Model simulations indicate the strengthening of the Atlantic Meridional Overturning Circulation (AMOC) with a signature warming response in the Northern Hemisphere and cooling in the Southern Hemisphere. Subsequently, between ~4–3 Ma, the constriction of the Indonesian Seaway impacted regional climate and might have accelerated the Northern Hemisphere Glaciation. We here present Pliocene Atlantic interhemispheric sea surface temperature and salinity gradients (deduced from foraminiferal Mg/Ca and stable oxygen isotopes, δ18O) in combination with a recently published benthic stable carbon isotope (δ13C) record from the southernmost extent of North Atlantic Deep Water to reconstruct gateway-related changes in the AMOC mode. After an early reduction of the AMOC at ~5.3 Ma, we show in agreement with model simulations of the impacts of Central American Seaway closure a strengthened AMOC with a global climate signature. During ~3.8–3 Ma, we suggest a weakening of the AMOC in line with the global cooling trend, with possible contributions from the constriction of the Indonesian Seaway.

      • Yes, because Holocene snow deposition is much greater than at the LGM.
        But do also remember that the blue Ice Age ice in your diagram is much more compressed than the upper green Holocene ice. Although we have a complete ice record of the ice age, the lower strata have been squeezed to almost nothing, and the bulk of the ice has been forced to the margins, where it can melt.

  35. Because the Milankovic cycles describe physical motions of the
    Earth it is assumed that they could only be ” Earth’s cycles”. But
    this is simply not true. The Milankovic cycles are in fact the sole
    property of the Sun. They are members of an exclusive group of
    frequencies that are characterized by a 360 degree rotation of the
    Sun’s outwardly directed acceleration. They are vector quantities.
    The Earth is blessed with a single large moon, so we inherit the
    accelerations of the Sun as if these cycles were our own. The Earth
    is caught up between the Sun’s accelerations and the pull of its orbiting
    moon. This is where we get our 25772 , 41000, 100000 and 113000 etc.
    year physical motions.
    Milankovic theory as we know it, is completely backwards. It is a solar system
    that loses eccentricity that sends us into an ice-age cycle. Take Jupiter
    as an example: Jupiter accelerates toward its perihelion and decelerates
    toward its aphelion. There is a continual exchange of energy as kinetic is
    tranformed into potential and back again. Without eccentricity this exchange
    does not take place. In our solar system the lowest level of energy that exists
    is when the Sun and the gas giants lose there eccentricity.
    Please visit weathercycles.wordpress
    “The Sun’s acceleration responsible for ice-age cycles?”

  36. In my space dynamics course @ PSU in late 60’s, I was taught the precession cycle was 26,000 years, not 21,000 as mentioned in the article. That’s a 20% discrepancy and would have a significant variance in the harmonics and the ~100k ice age cycle calculations! Doubt the precession cycle has changed that much over past 50 years!

    • Hey Bill,
      You’re absolutely correct, the Earth’s precession rate is about
      25772 years. If the Earth’s elliptical orbit were to also precess at a
      rate of ~113,209 years, this would result in a speeding up of the
      amount of time it takes for the the Earth’s axis to point in the same
      113209 x 25772 / (113209 + 25772) = ~20993 years
      Please visit weathercycles.wordpress
      “Earth’s climate linked to . . . “

    • >>26,000 years
      Yes, but you need to take apsidal precession into account, which reduces ‘seasonal’ precession to 21,000 years. This does not change normal precession, which remains at 26,000 years.
      Do also remember that the ‘seasonal’ precessional cycle (the one that matters for paleoclimatology) is highly variable, ranging from 15,000 to 25,000 years.

      • Thanks Ralph for the correction on seasonal precession.
        I just had surgery last weak and I plead impairment due
        to massive amounts of morphine.

  37. …these glacial-interglacial cycles have repeated roughly on a 100,000-year cycle…
    What they mean by “roughly”?
    And Ice age intensities also “roughly” ?

  38. According to the AGW conjecture CO2 controls the primary greenhouse gas, H2O and greenhouse gases are entirely responsible for the atmospher’s insulation effect which keeps the Earth’s surface 33 degrees warmer on average then it would be without the insulaton effect of the atmosphere. CO2, in connection with other phenomena is also responsible for the ice ages and interglacial periods that we have been experiencing. According to the AGW conjecture it has to be CO2 that is responsible because there is no other explanation. It also must be so because of the 98% scientific consensus that both validates and settles the science and that is what they have been requiring our children to learn in our schools. At first all of this seems logical but upon close examination by someone who has at least some understanding of scientific principals, the AGW conjecture falls apart. Clearly this report shows that there are alternate
    explanations as to the ice ages and interglacial perieods. CO2 need not be part of the explanation. But let us also discuss some of the other points.
    1. According to the AGW conjecture CO2 controls H2O because the additional warming that CO2 produces causes more H2O to enter the atmosphere which causes more warming beccause H2O is also a greenhouse gas with LWIR absorption bands. Actually, molecule per molecule, H2O is a stronger IR absorber than CO2. If the AGW conjecture were true then a random increase in H2O itself would be enough to set off an unstable warming cycle that would end with the oceans boiling over and the Earth’s atmosphere becoming more massive than that of Venus but that does not happen. The reality is that H2O is really a net coolant in the Earth’s atmosphere exemplified by the fact that the wet lapse rate is significantly lower than the dry lapse rate. So this part of the AGW conjecture falls apart. Another fact that the AGW conjecture ignores is that more heat energy is moved from the Earth’s surface, which is mostly some form of H2O, to where clouds form via the heat of vaporization then by both convection and LWIR absorption band radiation combined, according to some popular models. A major problem with the AGW conjecture is that it is based on only a partial understanding of science.
    2. As derived from first principals the surface of the Earth is 33 degrees C warmer than it would otherwise be due to the action of the heat capacity of the atmosphere and gravity. In a sense one can consider this to be a convective greenhouse effect. 33 degrees C is what is calculated and what is observed and it has nothing to do with the LWIR absroption properties of so called greenhouse gases. An additional radiant greenhouse effect caused by the LWIR absorption properties of greenhouse gases has not been observed anywhere on Earth or anywhere in the solar system for that matter. The radiant greenhouse must therefore be science fiction as must be the AGW conjecture.
    3. Scientists never registered and voted on the the AGW question so the 98% conensus is nothing more than wishful thinking by those that make their living from pushing the AGW conjecture. Such a consensus is meaningless anyway because science is not a democracy. The laws of science are not some form of legislation. Scientific theories are not validated through a voting process. This consensus business in politics and not science. Something must be really wrong if consensus has to be used as an arguement.
    4. The AGW conjecture also ignores the fact that good absorbers are also good radiators. Heat energy transfer via convection and conduction dominates over heat transfer by LWIR absorption band radiation in the troposphere. There have been no practical applications where CO2 is used as an insulator. If CO2 really affected climate then the increase in CO2 over the past 30 years should have caused at least a measureable increase in the dry lapse rate in the troposphere but such has not happened. After more than 2 decades of effort the IPCC has been unable to narrow the range of their guesses as to the climate sensivity of CO2 one iota. I am sure that they would not want to even enterain the idea that the climate sensivity of CO2 is really zero or very close to zero as some researchers have found.

  39. This thesis leaves a lot unanswered.
    It is well know that it is the combination SUM insolation of 100, 41, & 21 kyr cycles that correlate with hemisphere TOA insolation.
    But, the authors suggest that it is during times when the southern hemisphere (SH) is cooler in summer, meaning the SH is tilted away, that SH sea ice grows. These are also the times when the northern hemisphere (NH) receives more insolation.
    Proxy data show that major glaciations began when the NH received less summer insolation and the SH glaciation occurred at similar times. This is when the SH received more insolation, just opposite from what the authors suggest.
    Then they suggest that the change-over between 41 kyr glaciation cycles to 100 kyr cycles began because of the cooling of the globe, but they do not explain why.

  40. “sea ice in the Southern Hemisphere…. that ice reflects more of the sun’s rays back into space, substantially reducing the amount of solar energy the planet absorbs. As a result, global temperature cools.”
    And since the sea ice around Antarctica seems to be growing, we are going to face another ice age any minute.
    We’re doomed.

    • Yup. Mesoproterozoic, about 1.3 billion years ago:
      Carbonate strata of the Mesoproterozoic Wumishan Formation in the Jixian area near Tianjin are ~3300 m thick and were deposited over some 100 million years (from ~1310±20 Ma to ~1207±10 Ma). Metre-scale cycles (parasequences) dominate the succession. They are generally of the peritidal carbonate type, and mostly show an approximately symmetrical lithofacies succession with thick stromatolite biostromes and small thromboliteoncolite bioherms constituting the central part and tidal-flat dolomites forming the upper and lower parts. Lagoonal-supratidal dolomitic shales with palaeosol caps make up the topmost layers. The boundaries of the Wumishan cycles are typically exposure surfaces, and there is abundant evidence for fresh-water diagenesis.
      Widespread 1:4 stacking patterns indicate that the individual Wumishan cycles are sixth-order parasequences, with 4 parasequences constituting one fifth-order parasequence set. Locally, 5–8 beds or couplets, can be discerned in some of the cycles. The regular vertical stacking pattern of beds within the sixth-order parasequences, forming the fifth-order parasequence sets, are interpreted as the result of environmental fluctuations controlled by Milankovitch rhythms, namely the superimposition of precession, and short and long-eccentricity. The widespread 1:4 stacking pattern in the cyclic succession, as well as the local 1:5–8 stacking patterns of the beds within the cycles, suggest that the Milankovitch rhythms had similar ratios in the Mesoproterozoic as in the Phanerozoic. Based on the cycle stacking patterns, 26 third-order sequences can be distinguished and these group into 6 second-order, transgressive-regressive megasequences (or sequence sets), all reflecting a composite, hierarchical succession of relative sea-level changes.

      • Ptolemy,
        Yup, especially with the 41 K tilt cycle. In rocks from both the Proterozoic and Phanerozoic Eons, as I now know. Dunno about the Archaean.

      • Looking back billions of years, this paper studied the evolution of Milankovitch cycles and the earth-moon system (earth spinning faster when the moon was closer) by comparing stripes in Banded Iron Formations and other Archaean and Proterozoic sediments with a set of theoretical Milankovitch and tidal frequencies:

      • IMO it makes sense that the tilt cycle is the most important. After all, it is earth’s obliquity to its axis which gives us our seasons. Changes in this angle can affect climate as well.

    • I agree with your article, It is the water cycle responding to solar radiation that is controlling the skin surface temperature of the earth. Because there is so much water in all it’s phases, skin surface temperature is closer to measured dew/frost point than it is at atmospheric temperature measured a couple of meters above the surface. The surface (skin) will radiate at that temperature. Also, the tops of clouds radiate at the temperature at which they are caused by condensation or evaporation. The energy exchange associated with CO2 radiation is a drop in the bucket compared to the energy exchange in these processes. Atmospheric concentrations of CO2 are just going along for the ride. Water cycles are controlling atmospheric CO2 cycles. Annual sea ice cycles are just one of these controlling factors.

  41. Javier,
    Your article at Curry’s site states that Milankovitch is wrong about insolation at 65 N, but in the wider sense of the impact of celestial mechanics on climate, he and his predecessors were right.
    The debate is over which orbital and rotational cycles are most important. I’m with you on tilt, but the other cycles have an effect, as you demonstrate, as do other factors. But it appears well supported IMO that obliquity primarily rules.

    • I also find it convincing that the mid-Pleistocene transition from 41 to (apparently) ~100 millennia-long glacial phases can be explained simply by a world grown colder, with ~100K as the rough average of 82 and 123K years.

  42. I like interglacials and wish that this one would live up to the previous…ie about 2-3C warmer than today. Let’s go Earth, you-can-do-it!

    • Plate tectonics set the stage for the glaciations by separating Antarctica from South America and Australia about 34 million years ago and by connecting the Americas some three Ma.

  43. The Earth/Moon system is a binary relationship.
    The Earth’s inside is made up of layers having variable densities.
    This allows its iron core to rotate independent of the outer layers
    and the outer crust. During inter-glacials the iron core not only rotates
    but wobbles and presses outward. This is what gives us geomagnetism,
    geomagnetic jerk, length of day, plate tectonics, volcanic activity and
    magnetic field production.
    The Milankovic cycles are in fact accelerations of the Sun directed in
    specific directions (vector quantities). When the Sun loses its acceleration
    the Earth’s iron core loses its wobble. Magnetic field production is diminished
    and much of the heat that is associated with an active inner core is lost.
    Plate tectonics and volcanic activity are reduced.

    • The eccentricity of earth’s orbit owes to the gravitational attractions of Jupiter, Saturn and other celestial bodies in the solar system.

  44. The various hemispheric difficulties that scientists have experienced in using insolation from the Milankovitch rhythms to explain glacial/interglacial episodes disappear when one realizes that insolation probably isn’t the operative mechanism after all. Gravity probably is. It is well known that tidal effects from Moon correlate well with volcanic eruptions. It’s therefore likely that Milankovitch rhythms are effective in stimulating and repressing the hair-trigger mechanism of sea floor spreading and its attendant volcanism, of which there are basically two kinds: far-plate edge explosive andesitic and near-plate edge non-explosive basaltic. The former are well known to cause global cooling through stratospheric aerosol formation, whereas the latter, which emit hydrogen chloride and bromide, but don’t form aerosols, can cause global warming through ozone layer depletion, allowing a greater influx of solar UV-B. This, then, could be the real cause of the glacial/interglacial oscillation. More on this in Chapter Three of “The Real World, a Synthesis” on amazon.com.

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