The timing of interglacials

By Andy May

P. C. Tzedakis and co-authors have just published a new paper in the February 23, 2017 issue of Nature entitled “A simple rule to determine which insolation cycles lead to interglacials.” The paper introduces new rules for defining interglacial periods in the geological record. They come up with the same interglacial periods that Javier identified in his post Nature Unbound I: The Glacial Cycle.

The Earth has been in an ice age for the last 2.6 million years, Javier defined an ice age as:

“… any period when there are extensive ice sheets over vast land regions, as we see now.”

Tzedakis, et al. note that

“The fundamental property that underlies the concept of an interglacial is high sea-level.”

The higher sea-level is a result of melting a significant amount of land-ice during the interglacial. We are currently in the “Quaternary Ice Age,” which is either the coldest or the second coldest period in the last 500 million years as can be seen in figures 1 and 2. These are the most popular temperature reconstructions of the past 540 million years. Ice ages (or a collection of closely spaced continental glacial periods) have occurred in the geological record roughly every 150 million years in the Phanerozoic. The cause of these cold periods is not known, but we are clearly in one now.

Figure 1, source Veizer, et al., 1999 and Wikipedia

Figure 2, Phanerozoic temperatures, source Geocraft

The current (Quaternary) ice age is punctuated by warm periods, called interglacials. These warm periods are identified in the geological record by rising sea level. They persist for about 15,000 years on average and are typically 4° to 5°C warmer than the preceding glacial period, with the difference much larger at the poles than at the equator. Glacial periods are much longer than interglacials, and are the norm for the Quaternary, the warm interglacials are the anomaly. As discussed in Nature Unbound I and in Tzedakis, et al., 2017, we have had 13 interglacial periods in the past one million years. These are identified with red bars in Figure 3 (Javier’s figure 12).

Figure 3, Orbital obliquity increases, which correlate to July insolation peaks at 65°N, are colored. Red identifies successful interglacials and blue identifies a failure. The labels are MIS numbers. Low late-glacial temperatures (red circles below the blue dashed line) stimulate interglacials. High insolation at 65°N, the green circles above the green dashed line also stimulate interglacials. MIS 13 is an anomaly. Source Nature Unbound I.

The same interglacials are identified, with slightly different nomenclature, in figure 2 (our figure 4) of Tzedakis et al. The numbers in figure 3 and across the top of figure 4 are the Marine Isotope Stage (MIS) number, the odd numbers refer to “interstadials” which are warmer periods, separating the even numbered “stadials” or cooler periods. Notice that both Tzedakis et al. and Javier find more than one interglacial in MIS 7 and 15. We are currently living in MIS 1. Some interstadials are significant enough (as judged by the rise in sea level) to be labeled interglacials and some are not. One of the problems in Quaternary geology is how to objectively tell a true interglacial period from a common interstadial. Javier and Tzedakis, et al. have different criteria, but come to very similar conclusions.

Figure 4, Obliquity peaks are shaded in gray, the black line is the caloric summer half-year insolation at 65°N, the red circles are insolation maxima nearest the onset of interglacials, black diamonds are continued interglacials, light blue triangles are failed interstadials. The orange line is the δ18O stack representing temperature. The upper numbers are MIS numbers for interglacials and the lower are kyrs (thousands of years) before present or the number of a continued interglacial or a failed interstadial. The “Mid-Pleistocene Transition” toward lower-frequency higher-amplitude glacial cycles is apparent near MIS 38/37. Source Tzedakis, et al., Nature, 2017.

Javier’s methodology for identifying interglacials begins with locating every period of rising obliquity which creates a window that can initiate an interglacial. Fewer than half of these periods results in an interglacial. Next, he looks for the periods where summer insolation at 65°N exceeds 550 W/m2 and where the temperature of the preceding glacial period is below 4.55 0/00 δ18O. δ18O is a common proxy for atmospheric temperature because the colder it gets, the less 18O is found in glacier ice . The boundaries and the resulting classification are shown in figure 3.

Tzedakis (2017) uses a different methodology that results in the same set of interglacials for the past one million years. The methodology is summarized in figure 5.

Figure 5: Temperature peaks for the last 2.6 million years separated into successful interglacials (red dots), failed interglacials (blue diamonds), continued interglacials (black diamonds) and uncertain assignments (open symbols). The dashed black line separates successful interglacials from unsuccessful interstadials with only two misclassifications (59 and 63). The ramp in the dashed line is the “mid-Pleistocene transition.” Source: Tzedakis, et al., 2017.

Figure 5 plots effective energy required to cause an interglacial versus time. As can be seen more effective energy is required to initiate an interglacial over the past 600,000 years than before 1.5 million years. In figure 4, interglacials (red dots) were more frequent and more regular before 1.5 million years ago, when they corresponded to the obliquity cycle of 41,000 years. Peak summer solstice insolation at 65°N is a function of the 21,000-year precession cycle. But, rising obliquity enhances the “caloric half-year insolation at 65°N” which is more relevant to ice loss. Prior to 1.5 million years ago, every other insolation peak at 65°N was boosted by increasing obliquity and an interglacial would occur. The idea of “caloric summer half-year insolation” originated with Milanković.

More recent interglacials occur about 100,000 years apart, meaning more insolation peaks are skipped now than before 1.5 million years ago. Thus, recent glacial periods are longer now and average ice volume is larger today than in the past. The ramp between the two horizontal lines is the mid-Pleistocene transition (MPT). Effective energy is computed using equation one from Tzedakis, et al., 2017. It is computed using the caloric summer half-year insolation peak at 65°N in (GJ/m2) and the time since the previous interglacial period. Tzedakis, et al. explain including the time since the previous interglacial in terms of ice stability. That is, the longer the ice has existed and the thicker it is the more unstable it is.

Why current interglacials require more effective energy to initiate is not known. Tzedakis, et al. list several possible reasons, but do not offer a preferred theory. Why current glacial periods are more severe today than prior to 1.5 million years ago, is also not known.

Clark, et al. 2006 have noted that the severity of glacial periods and the total land-ice volume increased dramatically after the mid-Pleistocene transition. The additional land-ice present now, versus before the MPT, represents a decrease of 50 meters of sea-level equivalent. While land-ice volume increased after the MPT, the area covered with ice did not, suggesting that average land-ice thickness increased. Clark, et al. (2006) also estimate a decrease in in global deep-water ocean temperature of 1.2°C currently, relative to the pre-MPT period of 41,000 year glaciations. Thus, we are not only in a major ice-age, we are also in the coldest part of the current ice age.

So, although Javier and Tzedakis, et al. used different criteria they did identify the same interglacials for the past million years. Tzedakis et al.’s method is able to classify all but two interglacials correctly for the past 2.6 million years and their method only uses orbital forcing and elapsed time as input. This last point is important as they found no need to incorporate either CO2 concentration or δ18O records. This suggests that glaciations are caused solely by astronomical forcing, although the reason for the MPT is unclear. Tzedakis, et al. is also important because they seem to have resolved most, if not all, outstanding problems with the original Milanković theory.

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187 thoughts on “The timing of interglacials

      • Remember the immovable object vs the irresistible force.
        Well, imagine both are incorporated into one entity, that being a 2 kilometer thick glacial wall slowly advancing upon your city or farm.

      • Paul Belanger – immovable object and irresistible force are mutually exclusive; each disproves the other.

      • What happens when an irresistible force meets an immovable object?

        You go buy a better dictionary.

      • It’s an immovable object from the perspective of the glacier.
        It’s an irresistable force from the perspective of everyone else.
        Come now, didn’t y’all ever learn relativity.

    • I just remember screaming “We’re still in an ice age, you idiot!” and the realizing I was talking to my computer.

    • Dang, beat me too it! Bill Nye the science guy should deny this fast. HELP: I’m over the sea so he is not known to me, what are his qualifications? is he special needs but allowed on TV under a democratic equal opportunity STEM programme promoting silly ties?? I am too stupid to conect the treads in what he says, or the logic behind it. No facts are harmed in his assertions, because none are used. Nearly as mad as “Doctor” Jeff Patterson, the mad as a box of frogs osteopath from Wisconsin and BBC go-to expert radiobiologist (because the UK has no expert radiobiologist or radiation physicists who will support its prejudices available in the science correspondent pool, of course……………)

      BTW, IF we are not to become Neanderthal 2.0 in the next ice age, or even 3.0?, I suggest we will need to be all sustainable nuclear powered – fast fission and maybe Thorium before the ice age after – and moved to where the ice isn’t to maintain a developed civilisation, or many Billions will die early and not be replaced. Building walls won’t help. Renewable enrgy sources can’t support the developed 11 Billion stable population we expect to arrive at, and the fossil fuels WILL be well gone in 10,000 years, for sure, we did a pretty good number on them in the last 200 years, noise in the real passage of planetary time. Go figure.

    • Bill Nye being the “Science Guy” is like Adolph Hitler being the “Human Rights Guy.” Bill Nye is less than clueless about science. Much like the Wizard of Oz, “pay no attention to that man behind the curtain.”

      • Glad we agree that we are STILL in a macro scale “ice age”. Little of the rest of this stuff works for me. What is the physical meaning of a “failed interglacial”? Uncomfortably similar to “failed warming” from CO2.

        What it means is you don’t have your finger on the real pulse. It means there are fibrillations not accounted for. Don’t try to apologize with chaos. That’s just another word for “we don’t know Jack”.

    • Brad, the delta 18O is measured primarily from calcite rather than from ice. The calcite (CaCO3) is formed from sea ice by a variety of marine organisms, most notably foraminifera. Changes in the 18O content of sea water are recorded effectively instantaneously by the change in the content of shell material. This material is deposited on a continuous basis on the sea floor. It is recovered later by scientists. They get continuous records by extracting drill cores from the sea floor. The record goes back many millions of years.

      The change in the 18O content of fossil shell material is basically a proxy for ocean volume. The lighter isotopes of oxygen (16O and 17O) end up preferentially in ice on the land, and the heavier isotope (18O) preferentially stays in the ocean. If you can determine the change in ocean volume then at the same time you have determined the change in land-based ice volume.

      This work has been repeated thousands of times in all the worlds oceans and marginal seas. So it is well replicated. What is more, the work can be carried out for different depth levels within the ocean. For instance there are foraminiferal species that live exclusively on the ocean floor, others that float near the surface as planktonic species and still others that live at intermediate depths. Further, there are species that prefer colder water (nearer the poles) and species that prefer warmer water. So the nature of oceanic water can be sliced and diced in many different ways using the chemistry of the shells of fossilised foraminifera. There is a huge amount of scientific literature on the subject.

      • “The change in the 18O content of fossil shell material is basically a proxy for ocean volume.”

        Overstated, but an important point. Dilution matters, and it has not been factored to the best of my knowledge.

  1. None of this matters now, because we are in the Anthropocene. We humans are now in control of the climate. Amazing, innit.

    • You’re right, we are in control. We can save the world with this melody! The bozo below is the UN bureaucrat who tried to refuse the Rebel (Canadian skeptic journalism outlet) media accreditation for COP22 Marrakech last fall.

      • Made it about 45 seconds into that before I stopped it, it was either that or lobotomize myself
        Perhaps this will make it better

      • You have a strong stomach Brian, I lasted about 5s after the singing started.

        Now if you’ll excuse me I have some vomit to clean up.

      • Bryan and Greg,
        C’mon guys, you didn’t even get as far as the real puke-worthy totalitarian and socialist stuff!

      • Jerome,
        My experience is that peddlers of repugnant ideologies don’t like having debates so they disable comments. The CBC does the same thing on all their videos!

      • I can’t imagine allowing anyone to see me like that–humiliating myself. They have no sense of self–could not have or they’d be lobotomizing themselves!

      • LOL. I listened to the whole thing. I was waiting for a sign giving away their Scientology orientation but it never happened. It did provide me with a new benchmark for weird.

      • Exploding schoolchildren and now they’re terrifying the kiddies with their horror movie version of Peter Pan and Tinkerbell. Is there no limit to the depths these people plumb?

      • Vuk, did not know that. Another useful fact gleaned from learned commenters here. And to think (not PC) I was taught they were Eskimos, and one was just an Eskimo.

      • Two totally different peoples, surely?

        Eskimos are hardy Arctic hunters who live in igloos, drive dog sledges, make their own clothes and tools from animal furs, skins and bones, and dine raw seal and whale meat.

        Inuit, by contrast, tend to be diabetes-prone Arctic couch-potatoes who live in kerosene-heated houses, drive gasoline-fueled snowmobiles, wear synthetic clothes made in China and ordered online from half a continent away, dine on imported food grown using chemical fertilizers, and—if the Greenpeace ads are anything to go by—spend a lot of their spare time complaining about how everyone else’s fossil fuel use is destroying their pristine Arctic environment.

      • Well then, Vuk, it is inuks. Unix guys said inux. Emacs nerds wanted inucsen, but were told to fo.

      • The Inuit of Greenland and eastern Canada are Eskimos, just as are the Inuktitut of northern Alaska and Yupik of western Alaska and Siberia. Aleut aren’t. There is no indigenous word for Eskimo covering all these linguistic and cultural groups.

      • Hugs hi
        I’m the last person to be arbiter on the finer points of the English language.
        Wikepida says:
        “Inuit (pronounced /ˈɪnu.ɪt/ or /ˈɪnju.ɪt/; Inuktitut: ᐃᓄᐃᑦ, “the people”[6]) are a group of culturally similar indigenous peoples inhabiting the Arctic regions of Greenland, Canada and Alaska.[7] Inuit is a plural noun; the singular is Inuk
        And here you can read what was said to me when I transgressed on the matter https://wattsupwiththat.com/2017/02/24/claim-air-pollution-may-have-masked-mid-20th-century-sea-ice-loss/#comment-2436485

    • nope, that’s the other way round : Earth’s rotation is slowing down, days used to to be shorter, so there were more day in a year. 380 during cretaceous. 400 during Carboniferous. etc.

      And we have fossil proofs of that, too.
      Even wikipedia knows that (Earth’s_rotation).

  2. It’s actually the Nyeocene where Party objectives and presentation style matter much more than objectivity.

  3. Changing the definition of scientific terms to suit an hypothesis is anti-scientific. To count as interglacials, warm interval should be separated by glacial phases. Double peak interglacials are the same interglacial unless at least 40,000 years of ice sheet advance intervenes.

    Also, by the definition of “any period when there are extensive ice sheets over vast land regions, as we see now”, earth has been in an ice age for 34 million years, not just 2.6 million. That is an unjustifiably Northern Hemispherocentric view. Ice sheets extended over Antarctica from the Oligocene Epoch, long before the Plestocene glaciation of the NH.

    • This is a very valid point. Antarctica is exceptional in that it is surrounded by ocean, whereas the Arctic ocean is surrounded by land, but still it is a huge continent and has been covered in ice for 35 million years. It would seem our definition should be changed to vast northern hemisphere land regions covered in ice. Although that only applies to the continents in their current configuration. Either way, there are only 4 such periods in the last half billion years.

      • Dunno. The Pleistocene glaciation is periodic, earlier ~41ky and later ~100ky. Antarctic glaciation is quasi permanent because of its tectonic position at the South Pole. Very slow to change. A distinction with a difference. It is understanding the cause of the Pleistocene periodicy that is the interesting problem addressed by Javier and this new paper. But until the 41-100 shift can be explained, dunno that we have a convincing answer. As for Pleistocene onset ~2.4mya, the most compelling explanation I have seen is tectonic closure of the ocean gap between N and S America when the Ithmus of Panama formed. Which suggests that somehow, ocean circulation is a major player.

      • The East and West Antarctic ice sheets fluctuate, just as have those in the NH for the past 2.6 million years. In interglacials, usually only the Greenland ice sheet and mountain glaciers remain there.

        But Antarctica isn’t that different. During the Miocene, its ice sheets retreated substantially.

        IMO an ice age is when there are continental ice sheets. This has been fairly rare during the Phanerozic, at most perhaps one third of the time. And counting.

        There have been long epochs without even montane glaciers of which to speak.

      • Ristvan,

        But until the 41-100 shift can be explained

        An explanation exists. Whether it is the right one or not is a different matter.
        The planet has been progressively cooling for many millions of years. Until the Mid-Pleistocene Transition the energy provided by the combined effect of high obliquity and high Northern summer insolation was enough to get the planet out of glacial conditions every single obliquity cycle.

        At the MPT the planet became so cold that obliquity+precession did not provided enough energy. A third factor become necessary. This factor is represented at Tzedakis et al., 2017 as ice sheet instability that accumulates over time (b∆t in their article). It is made by every ice sheet melting positive feedback factor that increases over time and over the build up of huge ice sheets. It includes CO2, dust, continental shelf ice that is melted by rising sea levels, albedo…

        This factor becomes big enough to help trigger an interglacial every two obliquity cycles with only one exception, MIS 3 due to low precession. When eccentricity is high enough this factor is dispensed and the planet goes back briefly to a 41 Kyr interglacial periodicity (MIS 7e, 7c, 15a, and 15c).

      • Javier, thanks for the reply. I read your previous post with great interest. Understand your reasoning. Am simply not yet convinced. Reason is that a slow cooling should not necessarily lead to a sudden switch. (Although I proved a sharp strange attractor transition both modeled and empirically observed in a paper published in 1991). I dont think glaciation periods necessarily evidence strange attractors in the technical mathematical chaos sense, as they evidence none of the other typical indicia (like period doubling, bifurcation,…). The experimental factory example did.
        Highest regards in any event. Enjoy your posts.

      • Except that it was not a sudden switch, Ristvan. We make it look sudden due to our mental and language categorization, by defining limits that are in reality progressive differences.

        Do we say that MIS 39, MIS 41 and MIS 51 are interglacials or interstadials? Clearly the MId-Pleistocene Transition was not a switch but a very long process that saw both some interglacials becoming cooler and some becoming warmer.

      • Very informative discussion.
        It may be possible to “explain” the MPR as a transition between two different modes of periodically forced nonlinear/chaotic oscillation, such as a transition between strong and weak forcing. The system gradually moves out of the state of sensitivity to Milankovich forcing as glaciation slowly deepens. Thus eventually there could be continuous glaciation without interstadials for some tens of millions of years.

      • Ptolemy2,

        Thus eventually there could be continuous glaciation without interstadials

        Except that the Earth does not appear to have been cooling for the past 0.6 Myrs. We seem to have reached a limit or whatever caused the Ice Age is no longer intensifying.

      • Javier
        Thanks. I guess each tick is 200k years, each dotted line a million?
        I am struck by the pattern resemblance between the Quaternary temperature record and that of Arctic ice in the last few decades (if you invert one of them so there time directions are the same):

        Some underlying chaotic-nonlinear fractal dynamic is at work.

      • is it possible the weight of northern hemisphere ice in a glacial period could have an effect on precession . i suspect this may well be easily answered by more informed commentators so apologies if this has already been dismissed.

      • is it possible the weight of ice in the northern hemisphere could have an effect on precession ? apologies if the answer to this is well known, i have a feeling it will be to more informed commentators.

      • @Javier

        Except that the Earth does not appear to have been cooling for the past 0.6 Myrs. We seem to have reached a limit or whatever caused the Ice Age is no longer intensifying.

        but it looks to have started some 2 million years ago, and that I want to remind you that the oceans play a great role in the storing and then moving vast quantities of water around, and the Isthmus of Panama hadn’t been around for long(this as an example, not necessarily the culprit), and ocean levels would matter.

        Maybe enough water has gotten trapped in Antarctica even in the mild periods water stopped overflowing what bridge had formed. That would greatly impact water circulation, and heat distribution.

        Can you guys use your muck to determine changes in ocean currents? You’d want to look at the muck on both sides of the isthmus, when water flowed across, the flora would change, and when it broke they’d diverge again.

      • Javier,

        Great chart. Thanks.

        The late Pliocene cooling (before onset of Pleistocene glaciations c. 2.6 Ma) is interesting, happening before the complete closure of the Inter-American Seaway by the Isthmus of Panama. The cold event at c. 3.3 Ma is especially noteworthy, as is the previous lesser one.

        I recall long ago reading that a small ice cap might have existed on southern Greenland in the Pliocene, perhaps thanks to more precipitation falling as snow.

        Bill Illis is definitely on to something about the northern movement of the NH continents, but also oceanic circulation would have been affected while the IAS was shoaling before being completely closed. I’ve also read that it might have briefly reopened c. 1.8 Ma.

    • I might add that the Ordovician and Carboniferous ice ages were restricted to the SH, yet no one claims that they don’t count.

      Thus, it IMO makes no sense to date the Cenozoic ice age from the Pleistocene Epoch, in which ice sheets grew in the NH, rather than from the Oligocene, when they spread across Antarctica in the SH.

      • GM, not trying to pick nits. But I have fundamental problems with all deep paleoclimate comparisons. Neither the continents nor their positions were the same thanks to plate tectonics. The plant and animal life was very different. (Example: carboniferous era likely began with evolution of lignin, which enabled tall woody plants. It likely ended with evolution of white fungi capable of digesting lignin. A span of ~60my to lay down most major coal deposits.)

      • Ristvan,

        No nits to pick. Either the earth has ice sheets or it doesn’t, as during most of the Phanerozoic.

        When there are ice sheets, as during the Ordovician-Silurian, Carboniferous-Permian and Cenozoic glaciations, our planet is in an ice age. All of those occurred with land over the South Pole. During the missing Mesozoic ice age, land was close, but no cigar.

        By the same definition applied to those previous two Phanerozoic ice ages, our present one must have started 34 Ma. It didn’t begin 2.6 Ma, but just spread to the NH then.

    • GM
      Yes, double peak interglacials happened at around 200k and 600k years ago.

      As discussed in Nature Unbound I and in Tzedakis, et al., 2017, we have had 13 interglacial periods in the past one million years. These are identified with red bars in Figure 3 (Javier’s figure 12).

      So there have really been 11, not 13 interglacials since the MPR.

      Both these two-headers occurred at times of maximal peaks in the 400k year modulation of eccentricity amplitude. There’s some causal link there even though eccentricity is out of fashion ad a Milankovich cycle.

    • Changing the definition of scientific terms to suit an hypothesis is anti-scientific.

      Except that there is no accepted definition of interglacial to be changed. The distinction between an interglacial and an interstadial is more of a degree than clear cut, since there are cool interglacials and warm interstadials.

      The identification of interglacials that I made for the past 800,000 years was confirmed independently but published earlier by:
      Past Interglacials Working Group of PAGES (2016), Interglacials of the last 800,000 years, Rev. Geophys., 54, 162–219, doi:10.1002/2015RG000482.
      http://onlinelibrary.wiley.com/doi/10.1002/2015RG000482/full

      This working group is formed by:
      A. Berger1, M. Crucifix1, D. A. Hodell2, C. Mangili3, J. F. McManus3, B. Otto-Bliesner4, K. Pol5, D. Raynaud6, L. C. Skinner6, P. C. Tzedakis7, E. W. Wolff2, Q. Z. Yin1, A. Abe-Ouchi8, C. Barbante9, V. Brovkin10, I. Cacho11, E. Capron5, P. Ferretti9, A. Ganopolski12, J. O. Grimalt13, B. Hönisch3, K. Kawamura14, A. Landais15, V. Margari7, B. Martrat13, V. Masson-Delmotte15, Z. Mokeddem3,16, F. Parrenin6, A. A. Prokopenko17, H. Rashid18, M. Schulz19, and N. Vazquez Riveiros15

      So I would say that it is supported by the main experts at this time.

      MIS 7e, 7c, 15a, and 15c are separate interglacials because they belong to separate obliquity cycles. Their distances are not anomalous for interglacials during the Early Pleistocene when the 41 kyr cycle dominated.

      Regarding how long we have been in an ice age, that depends again on the definition. If you use the geological definition that is represented in the figure 1 of this article from Vezier, it looks like this glacial period, at least in comparison with Phanerozoic average temperatures, has extended far longer than 2.6 Myr.

      • IMO, by definition, an interglacial has to be preceded and followed by a glacial, ie 40 to 120K years of ice sheet advance. Maybe there needs to be a different term for a double peak millennial scale warming besides interglacial or interstadial.

      • That’s your definition, GM, but if you check the Early Pleistocene you will reject many interglacials there. If the obliquity cycle lasts 41 kyr and interglacials last 10-15 kyr, it follows that the average glacial in the Early Pleistocene has 26-31 kyr. That’s not too much time to get seriously cold considering that cooling after interglacials is quite slow.

      • It’s not my definition. It’s the definition on its face and has been for 150 years. “Inter” means between. The derivation and etymology of the geologic term could not be more clear.

        An interglacial is a warmer interval between glacial advances. An interstadial is a warmer interval within a glacial episode.

        Change it if you want, but know that you are revising usage now practiced in three different centuries, plus the blatant plain meaning of the term, inter-glacial. That’s making up your own definition to suit your needs and desires. I happen to agree with you on the most important Milankovitch cycle, but object to such revisionism in scientific nomenclature.

      • It’s the definition on its face and has been for 150 years. “Inter” means between. The derivation and etymology of the geologic term could not be more clear.

        Except that everybody thought that there had been only four glacial periods until the 1960’s. My school science book in the early 70’s still had them: Gunz, Mindel, Riis, and Würm.

        We know better now what an interglacial is or isn’t than we knew for those past 150 years. Cesare Emiliani was the scientist that worked them out and named them wit the MIS numbers. Small problems are still being identified and corrected. That’s why the PAGES consortium tried to unify the criterion.

        MIS 7e is a short interglacial, but MIS 7c, 15a and 15c have the average length of an interglacial. Sticking them together makes for very anomalous interglacials. A 70 kyr interglacial? I think not.

        The old incorrect classification led to the inexistent 100 kyr cycle with its associated problems:
        – The 100 kyr problem
        – The stage 5 or causality problem
        – The symmetry of glaciations and deglaciations problem.

        Almost everybody thought that Milankovitch theory was incomplete or wrong. This fixes it. The metric is not 65°N summer insolation, but half year caloric energy or total summer energy at 65° N integrated over all days for which insolation exceeds 350 W m−2. A measure of whole summer energy at high latitudes.

      • Javier

        My school science book in the early 70’s still had them: Gunz, Mindel, Riis, and Würm.

        Does your school book use expressions such as greenhouse Earth, hothouse Earth, Icehouse Earth?

        Do you have any idea when such expressions came into popular usage?

        One of the problems is that expressions may over the course of time become terms of art, without properly defining the expression and identifying the precise distinction between it and different but somewhat similar expressions. This is of course the point that Gloatius is getting at with interglacials and interstadials.

      • Richard,

        One of the problems is that expressions may over the course of time become terms of art, without properly defining the expression and identifying the precise distinction between it and different but somewhat similar expressions.

        I understand GMs point, but interglacials where not defined in precise terms because there was no need. Only the late Pleistocene ones were known, and the dating was imprecise. In fact those four glacial periods do not correspond to the last four glacial periods. Some of them were actually stadials.

        GM’s definition has never been official. He won’t find them in writing with the exact terms he has used. What was not a problem a few decades ago to describe Late Pleistocene interglacials from the past 350,000 years became a problem when it had to describe nearly 50 interglacials in the past 2.6 Myrs.

      • Javier,

        I’m old enough to recall when it was discovered that there might have been more than 20 Pilo-Pleistocene glaciations, which can now be called all Pleistocene thanks to moving the Gelasian from the Pliocene to Pleistocene, so that it begins 2.6 rather than 1.8 Ma.

        But I also remember learning the difference among stadials, interstadials and interglacials. The definition was clear. It applies regardless of the number of ice sheet advances.

      • GM,

        The definition was clear.

        Then you won’t have a problem providing a citation about what an interglacial is or isn’t, according to you.

        I have already provided a link to the Past Interglacials Working Group of PAGES (2016), that support my view. They have an entire chapter on how to define an interglacial with a table with different methods with advantages and disadvantages. They say:

        “a more specific definition of an interglacial as an interval within which the distribution of Northern Hemisphere ice resembled the present (0 ± 20 m), i.e., there was little Northern Hemisphere ice outside Greenland, with periods of significantly greater ice volume (sea level passing below approximately -50 m compared to present) before and after the interglacial period.

        Using our sea level definition, MIS 7a-7c and 7e, and also MIS 15a and 15e are all equally prominent within their respective stages, and as we do not assume a particular periodicity, they are all included in our intergla-
        cial roster,”

        The key here is just the opposite of what you say: “we do not assume a particular periodicity”. They are not trying to push a hypothesis, they are just letting the data speak for itself. Revolutionary.

    • Surely, with continental drift, Antarctica wasn’t where it is today, 34 million years ago, therefore wouldn’t have been covered in ice? Paleogeological evidence suggests it was once tropical!

      • Antarctica hasn’t moved much since the Oligocene (34 Ma), but South America and especially Australia and New Zealand, formerly attached to Antarctica, have moved a lot. Ice sheets started building up on Antarctica after the formation of deep channels in the Southern Ocean. They receded a bit in the Miocene, when the channel under the Drake Passage shoaled again for a while.

        Antarctica wasn’t tropical in the Mesozoic Era (252-66 Ma), but was temperate boreal most of the time. Hard to have tropics when it’s dark for months on end.

      • Hard to have tropics when it’s dark for months on end.

        Animals and plants adapted to months of very little light. It is too bad that their remains are buried under kilometers of ice and out of our reach. They all died out when the continent froze. Emperor penguins are the last survivors of Antarctica.

      • Yet we have a surprisingly good sample of Mesozoic and early Cenozoic Antarctic animals, whose climate was definitely not tropical. Giant “amphibians” took the place of crocodilians. Dinosaurs and of course birds were diverse. The Cenozoic mammals were marsupials, not surprisingly.

        The oldest known Antarctic dinosaurs are Early Jurassic Glacialisaurus, a genus of massospondylid sauropodomorph, from the central Transantarctic Mountains, and the tetanuran theropod Cryolophosaurus, aka “Elvis”, from Mt. Kirkpatrick. The other three genera are all from the Late Cretaceous: the ankylosaur Antarctopelta and iguanodonts Morrosaurus and Trinisaura. Thus both suborders of Order Saurischia (Theropoda and Saurodomorpha) and of Order Ornithischia (Thyreophora and Ornithopoda) are represented.

        There are also lots of Australian dinosaurs, which would then have lived at high latitudes, from Middle Jurassic to Early and Late Cretaceous times.

      • Also Adélie, Chinstrap and Gentoo penguins on the continent itself, with seasonally the long-distance migratory arctic tern and some other breeders. Plus the odd Weddell seal which might haul out on land there instead of fast ice.

  4. Looking at one of the graph lines in figure two, I believe I see some active geoengineering in our future–CO2 supplementation

  5. Last paragraph of post is interesting if true. The data is quite noisy. Lack of explanation for the MPT and the sharper transition from ~41ky to ~100ky glacials suggest that there must be more to the story. One possibility is the glacial dust hypothesis changing albedo. Also need to look at oceans. Bering and Sundra straits become dry land during a glacial. Dogger bank connected Britain to Europe so English Channel was closed. I think we dunno, and an exercise in mostly peak fitting may not suffice .

  6. Svensmark and Shaviv have a hypotesis about why there are more iceages the last couple of million years. More cosmic rays and more cloud cover and therfore colder, because we are inside a small spiral arm of the Milkyway.

      • The dust/albedo conjecture is based on an imperfect correlation, lacks explanatory power for interglacial distribution (happens when it happens), and as CO2 fails to distinguish between cause and effect. Not to mention that it has an insolvable problem to explain 41k interglacials when the world was warmer and had more CO2, and hence much less dust yet a lot more interglacials.

    • IMO that’s not what they argue.

      Clearly, there were more ice ages in the Neoproterozoic Era of the Proterozoic Eon, ie most of the time, than during the Phanerozoic Eon. Ditto the Paleoproterozoic Era.

      They instead find cosmic causes for the quasicyclical occurence of ice houses.

    • There is only an ice age when there is a large landmass at or near the poles that is above sea level.

      Glaciers do not build up and flow towards to the equator on the ocean, only on the land.

      That makes land at or near the poles, the number 1 prerequisite.

      Northern Hemisphere glacial cycles started when Greenland and Northern Europe, moved just that little bit farther north so that they became succeptible to the Milanokovitch Cycles. Greenland, for example, has moved northwest about 800 kms in the last 55 million years.

      • Bill,

        That makes land at or near the poles, the number 1 prerequisite.

        Yes, it is necessary to have landmasses at or near the poles to have an ice age. But is it sufficient?

        I would guess not according to these maps:

      • Javier, I think the answered the question we’ll enough in the next set of comments below – glacial rebound and suppression versus sea level. The other prerequisite (among some others I imagine) is that the main ocean gyres are not cycling close enough to the coast to keep the landmass warm enough in the summers to melt the snow such as was the case with Antarctica from 80 Mya to 33.6 Mya shown below. The Pacific and Antarctic Ocean gyres cycled right up to Antarctica until there was enough separation from Australia and South America and the Antarctic Circumpolar Current started up.

      • Bill Illis February 28, 2017 at 3:45 pm
        “That makes land at or near the poles, the number 1 prerequisite.”
        To me it seems the number one prerequisite would be deep oceans cold enough to allow ice to form at all.
        Around 84 mya the deep ocean temps peaked around 18K above present levels. Only when they cooled sufficiently ice sheets started to form on Antarctica (~35mya).
        Just 2,5mya deep ocean temperatures where low enough for ice sheets to form in the NH.
        see http://onlinelibrary.wiley.com/store/10.1029/2011JC007255/asset/supinfo/jgrc12191-sup-0010-fs09.pdf?v=1&s=79e93e124ca1fd8a33753fc667ff17deaa20b3e6

        Reason for the high temperatures imo the Ontong Java event (possibly 100 million km^3 magma) plus a few smaller ones.

      • To me it seems the number one prerequisite would be deep oceans cold enough to allow ice to form at all.

        I have repeatedly made that point when discussing the temperature of the planet. I consider it incorrect not to take account of how very cold the deep ocean is not withstanding circa 4 billion years of Solar + DWLWIR (if the latter adds anything at all). This planet is a water world. It is this that determines the climate on this planet.

        It is the coldness of the deep ocean that comes back to bite when ice ages form. If the deep ocean was say 10 or 12 degrees, there would be so much energy contained within it that, by way of conduction and convectional currents, the surface ocean would never freeze, and would always provide warmish coastal waters.

        It is only perchance that we see the sea surface temperatures that we observe today. They will not forever remain because of the coldness of the deep ocean.

        I do consider that the position of land masses to also be an important factor.

      • @richard verney March 1, 2017 at 1:46 am
        ” I consider it incorrect not to take account of how very cold the deep ocean is not withstanding circa 4 billion years of Solar + DWLWIR (if the latter adds anything at all).”
        Even solar is not able to warm the deep oceans. Look at any set ofseasonal temperature profiles, below ~200m NO solar influence anymore. The sun DOES warm the mixed surface layer, that prevents water warmed at the ocean floor to reach the surface, except at high latitudes where the surface is cold enough.
        Also realize that the deep oceans are cold to human standards (body temperature).
        Their temperature is ~275K, already well above the infamous 255K. This is the base temperature on which the sun starts its warming.

        Without cooling at high latitudes the geothermal flux alone would warm ALL ocean water from freezing to boiling in just 500.000 years.

      • ” If the deep ocean was say 10 or 12 degrees, there would be so much energy contained within it that, by way of conduction and convectional currents, the surface ocean would never freeze, and would always provide warmish coastal waters.”
        This is the climate that existed in the Cretaceous, after the warming by (mostly) the Ontong Java event.
        Deep ocean temperatures up to 18K warmer then today.

      • Ben Wouters, deep ocean temperatures were not 18C above today’s level 84 million years ago.

        People have played around with the dO18 isotope to temperature formula and/or not used it properly. When these incorrect formulae are used for even older times, they have temperatures getting up to 40C above today’s level for 400 million years ago for example. I have a chart which demonstrates this if you want to see it. It is a miscalibration problem.

        84 Mya was only about 7C warmer.

      • @Bill Illis March 1, 2017 at 4:11 am
        “84 Mya was only about 7C warmer.”
        I’m not qualified to argue on this subject. My numbers are based on this article:
        http://onlinelibrary.wiley.com/doi/10.1029/2011JC007255/full
        and eg.
        https://phys.org/news/2006-02-warmer-hot-tub-atlantic-ocean.html
        The last articles surface temperatures require the deep oceans to be a lot warmer than 7C above present.

        The Phanerozoic graph at 400 mya shows Earth just coming out of a deep ice age. Do you disagree with this graph?

        Regardless all this, I’m convinced that the deep ocean temperatures have been and still are completely set by geothermal energy in all its forms.

      • You have a number of people who have deliberately miscalibrated the dO18 isotope to temperature formula variously calling it the “Deep-Ocean” or “Ice-Free Ocean” or “Polar Ocean” etc. In addition, there is another step which is required for the very old dO18 isotopes and that is to detrend it which they almost never do.

        They normally only do it with Zachos 2001 dO18 isotope database because it is only goes back to 67 million years but there are databases of the same datasources which goe back even 2.4 billion years ago.

        This is what happens when you extend the databases back in time using this miscalibrated formula.

        No Carboniferous or Ordovician ice-ages in the past. Tropics oceans boiling in some places in deep time. Fake Temperatures.

      • Ben,

        Yes there was a brief (maximum 30 million years, but probably less) but intense ice age at the Ordovician-Silurian boundary (~450-420 Ma), called the Andean-Saharan glaciation, when CO2 was around 4500 ppm, ie more than 11 times present level.

      • @Bill Illis March 1, 2017 at 4:59 am
        Assuming your graph shows DEEP ocean temperatures, it gives anomaly in C.
        Present anomaly -5C, around 90mya +10C. Difference 15C. I’m fine with that number iso 18C.

      • Ben

        Thanks your further comments. I am unsure that we differ significantly.

        This planet was born hot, is gradually cooling but still very geologically active. What base temperature do you consider that this planet would have simply because of its geological activity, and why do you claim 255K as the base temperature?

        Which of the many theories do you favour for the Ontong Java event, and why?

      • Richard,

        You didn’t ask me, but the Louisville Hotspot has not been conclusively ruled out.

      • Ben Wouters March 1, 2017 at 5:18 am
        @Bill Illis March 1, 2017 at 4:59 am
        Assuming your graph shows DEEP ocean temperatures, it gives anomaly in C.
        Present anomaly -5C, around 90mya +10C. Difference 15C. I’m fine with that number iso 18C.
        —————————————

        Present anomaly is 0.0C (-5.0C is the last few glacial maximums). 90 Mya +8.0C . PETM +6C (often quoted as high as 20C which is also based on this fake calibration).

      • Also note that the Deep Ocean temperature is rarely much different that 0.0C. In the ice ages, it might get to -0.5C, today it is +0.5C and 100 Mya it was probably closer to +3.0C.

        The Deep Ocean temperature is determined by what is the coldest densest water on the planet. And this is the polar oceans in the wintertime when there is zero sunlight for 6 months. They should have never called it Deep Ocean. The Oceans have always been stratified with the deepest parts coming from the coldest places on the planet at the time.

      • I should also note the dO18 isotopes from deep time mostly come from foraminifera plankton shells which mostly live in shallows waters. So they accumulate dO18 isotopes when they are growing and when they die, they fall to the ocean floor and become part of the sea floor cores where these dO18 isotopes are gathered from.

        So, the isotopes do NOT reflect deep ocean temperatures.

      • @richard verney March 1, 2017 at 5:21 am
        A rocky planet in outer space with a geothermal flux of 100 mW/m^2 would have a surface temperature of ~30K to radiate the 100 mW/m^2 away.
        Add the sun and the temperature goes up to ~197K, being the average surface temperature of our moon, with albedo .11
        The reason for our extremely high temperatures are the oceans. Preheated close to boiling during their creation and kept warm ever since by the geothermal flux (GF) plus occasional massive magmatic events like the Ontong Java (OJ) one.
        I’m mostly interested in the amount of magma that erupted. OJ produced possibly 100 million km^3 according to this study: http://www.sciencedirect.com/science/article/pii/S0012821X06002251
        I used it mostly for the nice round number ;-)
        With the GF more or less maintaining the deep ocean temperatures, the OJ event had the potential to warm ALL ocean water ~100K..

        Role of the atmosphere is just reducing the energy loss to space. With our current temps and no atmosphere earth would radiate ~400 W/m^2. Atmosphere reduces this to just ~240 W/m^2.
        No warming by a GHE, just an Insulation Effect.

      • “and why do you claim 255K as the base temperature?”
        My mistake, the base temperature before the sun does its warming magic is the temperature of the DEEP oceans, presently ~275K.

      • Bill Illis March 1, 2017 at 5:28 am
        “Present anomaly is 0.0C (-5.0C is the last few glacial maximums). 90 Mya +8.0C . PETM +6C (often quoted as high as 20C which is also based on this fake calibration)”
        Bill Illis March 1, 2017 at 4:59 am: graphic ‘Bill Illis’ temperatures

        Bill, I know you are often right. But still I am interested in which calibration you are using and how you do know that your (?) calibration (or the calibration you are using) is correct?

      • Wim Röst:

        I am using the same calibration that has been used in all “serious” efforts at reconstructing the history of the Earth’s climate. One thing I used which is slightly different is that I am using a higher resolution of 1M year Gaussian smooth where most of the others were done with a 50M year smooth or one was a 3M year smooth.

        The first of these was done by Jan Veizer.

        https://www.researchgate.net/profile/Louis_Francois/publication/12199006_Evidence_for_decoupling_of_atmospheric_CO2_and_global_climate_during_the_Phanerozoic_eon/links/09e4150aa8d25d618f000000/Evidence-for-decoupling-of-atmospheric-CO2-and-global-climate-during-the-Phanerozoic-eon.pdf

        Then Shaviv and Veizer.

        https://www.geosociety.org/gsatoday/archive/13/7/pdf/i1052-5173-13-7-4.pdf

        Then Royer and Berner.

        https://www.geosociety.org/gsatoday/archive/14/3/pdf/i1052-5173-14-3-4.pdf

        At some point in the middle of this mix, Christopher Scotese produced a simpler version of it which he has updated a little recently.

        https://www.researchgate.net/publication/275280922_Phanerozoic_Global_Temperature_Curve

        And then Robert Rohde had a version which was on Wikipedia for a long time and I copied his methodology except I moved to a shorter resolution time-line. He was operating a section on Wiki called Global Warming Art which was a very good source at the time. The original earlier pages seem to be missing now but here is one of them from 2010.

        Since these efforts, the usual crowd from RealClimate and Hansen and others decided to distort it.

      • @Bill Illis March 1, 2017 at 4:11 am
        “Ben Wouters, deep ocean temperatures were not 18C above today’s level 84 million years ago.
        84 Mya was only about 7C warmer.”
        I went trough this paper again: http://onlinelibrary.wiley.com/doi/10.1029/2011JC007255/full
        As far as I can judge it it makes a solid impression. Doesn’t go further back then 107 mya and is definitely about DEEP ocean temperatures.
        The 18K higher temperatures are easily explainable just by the Ontong Java event, possibly 100 million km^3 magma, capable of increasing the temperature of ALL ocean water ~100K.

      • Bill Illis March 1, 2017 at 9:57 am
        WR: Thanks for the explanation Bill. Like everyone I expect(ed) every scientist to do the calibration as carefully as possible.

        Doing the wrong calibration and knowing you are wrong is nothing else but misleading people. And misleading politicians. And media. After a fundamentally wrong calibration all scientific ‘results’ are worthless and they are directing people into the wrong direction. No good decision can be made on bad results.

        Some very intelligent people seem to know how to trick everyone, just by ‘tuning’ ‘some specific elements’. Hidden for the eye of most of us.

      • Bill Illis March 1, 2017 at 5:40 am
        “So, the isotopes do NOT reflect deep ocean temperatures.”

        WR: Bill, next question. Which proxy do you think is representing deep ocean temperatures best?

      • Wim Röst March 1, 2017 at 3:30 pm
        Bill Illis March 1, 2017 at 5:40 am
        “So, the isotopes do NOT reflect deep ocean temperatures.”
        WR: Bill, next question. Which proxy do you think is representing deep ocean temperatures best?
        ——————-

        Well, there is no proxy for it except how much ice is there at the poles in the time-period in question and what is the coldest temperature that water gets to at the poles in the time-period in question.

        Deep ice age: Deep ocean temperatures: -1.0C

        Moderate ice age (as in the last 28 glacial maximums in the last 2.7 million years): -0.5C

        Modern temperatures and lots of sea ice in the winter: 0.5C

        Moderate temperatures as in minimal or no sea ice/glaciers: 1.5C

        Hothouse climates (Cretaceous, Pangea/Permian, Devonian, Cambrian): 3.0C

        Snowball Earth (635 Mya, 715 Mya, 2.2 Bya, 2.4 Bya): -1.0C

        I imagine you notice there no 18Cs in there. This is based strictly on the physics of the density of water and what we know today about how the deep ocean water forms and what it does.

      • @Bill Illis March 1, 2017 at 4:34 pm

        Well, there is no proxy for it except how much ice is there at the poles in the time-period in question and what is the coldest temperature that water gets to at the poles in the time-period in question.

        see http://www.ucmp.berkeley.edu/fosrec/Wetmore.html
        In the study i linked that gave the ~18C peak they use specifically the benthic foraminifera. Those are the ones that live in or near ocean floors. Only a few species seem to be planktonic (floaters ;-)
        Means probably that you have to select the planktonic ones first, before making a reconstruction of eg surface temperatures.

    • While no longer in memory, our journey within our galaxy, surely passes through great dust clouds, which to lesser or greater degree, may hinder our own sun’s effects on its planets. Or did I miss a dismissal of that question?

  7. ‘The cause of these cold periods is unkown’. No it isn’t. It’s having a landmass at one or both poles which allows ice to accumulate and thus affect the albedo of the planet .

      • The northern hemisphere landmasses are just that little bit far enough North now due to continental drift so that they are succeptible to the Milankovitch Cycles in the last 2.7 million years. Move Greenland another 200 kms northwest as will happen in the next 10 million years, and the ice age is permanent.

        (Unless the weight of the glaciers pushes it far enough down into the mantle so that the whole sub-continent goes below sea level. At that point, the ocean comes in and the glaciers are gone again. This can then introduce another level of periodicity where glacial rebound or depression will be the determining factors rather than Milankovitch. There are tens of millions of year when Gondwana did not have glaciers only because the glaciers had depressed the land below sea level by so much for long periods of time so that when it finally rebounded above sea level finally, the glaciers can back again and promptly pushed it back down again. ie. little evidence of glaciation (430 Mya to 360 Mya) although there was continental landmass over the south pole. Antarctica appears to be big enough and centred over the pole enough so that it is not succeptible to this other glacial cycle periodicity. Greenland has not suffered from this either but its central land region is also below sea level right now – only the coastal areas are above. But the Barents Sea, Kara Sea, Hudson Bay, Arctic Archipelago sea lanes, Laptev Sea and the East Siberian Sea are substantial continental shelf regions which have been depressed below sea level by past glaciations and are subsequently free of glaciers today but someday … they will rebound back again and they will be glaciated all over again).

  8. A friendly reminder: EVERY ice age interstadial and interglacial without exception ended when obliquity dropped below 23.5 degrees…NO EXCEPTIONS. You have been warned.

    • Correct, dscott,

      No interglacial has survived the end of the obliquity cycle. Some people are breathing too much CO2 if they think it will be different this time.

      • So, when does obliquity drop below 23.5 degrees, or do you believe a different number is appropriate, Javier?

      • Don B,

        According to my calculations, glacial inception, the time when continental ice fails to melt back and the cooling accelerates, could take place at any time between 2000-5000 years from now. And the cooling is progressive over several tens of thousands of years. Nothing to worry about.

      • Bill,

        I don’t see that in the numbers

        It is not exactly a precise tilt. It is that no interglacial survives the downward phase of obliquity. You can check Figures 3 and 4 from Andy May’s article above.

  9. Interesting that the two papers come to the same conclusion. What I don’t see is of more interest to me, and that is when does the interglacial end? Or did I miss something in the paper?

  10. Ice age? According to IPCC, sulphur hexafluoride, SF6, is a GHG which is 23900 × more effective than CO2. It is also very inert, so extremely long-lived. Estimated atmospheric lifetime of 800–3200 years. We’d need to add 5 billion tonnes of it to the atmosphere to get 1ppm. That should warm the putative ice age up. The main problem is: mass insanity that would result as millions of greens see red. I’m not sure society could cope with that scale of madness. Here are the IPCC’s other scary GHGs: http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2s2-10-2.html

  11. North Atlantic configuration has changed in the last 20+ MY with the appearance of Iceland, where the oldest rocks above sea level are estimated to be around 15 MY.
    Most recent series of interglacials is more likely to be caused by changes in the intensity of the n> Atlantic currents, while the Milancovic cycles hade role of a ‘trigger mechanism’.

    The grey area is the Greenland-Scotland ridge, average depth around 300m except for the Denmark Strait (~600m) and Faroes Bank Channel (~800m), the two main thoroughfares for the dense, cold sea-floor waters.
    Parts of the ridge are rising due to the postglacial isostatic uplift, and in doing so are more and more obstructing the cold dense sea floor currents outflow from the Arctic basin. Reduced outflow means reduced warm surface water inflow and steady cooling, as it has been the case during the last 7-8 KY.
    Since the ocean level rising (due to the ice melting) is slowing down to a standstill, another thousand or two of years of the uplift, the Arctic will again start its refreezing sequence, causing gradual drop in the sea level, with the depth of the two thoroughfares further decreasing, the result is the end to the current interlacial. Polar jet stream at this stage would be extremely strong and circular with very little or no meandering.
    After 40 or more KY of the ice build up, when the weight of the ice in the north Canada, Greenland and Scandinavia has sufficiently deformed the Earth’s crust along the Middle Atlantic Ridge (boundary between N. American and Eurasian tectonic plates) the Iceland’s volcanoes will go off with a ‘bang’ (occasionally triggered by Milancovic cycles planetary tidal pull).
    At the end of the last ice age the magma flow was more than 100 times current rate, with the Iceland’s volcanoes ejecting into atmosphere huge volumes of ash/tephra, spreading across whole of the Arctic region by strong polar jet stream.

    btw. Iceland’s volcanoes are the world’s most productive, currently about 5% of world activity with 30% of the total ejected mass.
    Sudden reduction in the albedo, due to accumulation of the ash/tephra on the ice, initiates fast melting, the obstruction by the G-S ridge is suddenly reduced by the fast rising sea level (outpacing the the ridge’s postglacial uplift) allowing rapid increase in the cold currents outflow and consequently equally rapid move of the warm surface currents further north into the Arctic ocean, result: interglacial or the sudden end to the Ice Age.
    However, slow but steady postglacial isostatic moving of the parts G-S ridge upwards will again cause the slow but steady cooling and increase the ice accumulation.
    Greenland’s uplift from the postglacial rebound means the island is gaining mass from below and its bedrock is continuously rising. At the same time, it is losing some mass from above as its ice melts. 60% of Denmark Strait is part of Greenland’s bedrock and follows its uplift, while the Wyville Thomson Ridge (closing narrow Faroes channel) is part of the Scotland’s shelf with a similar uplift.

    Are these (glacial/interglacial) cycles are going to go for ever? No.
    Iceland is growing larger and the warm periods’ Greenland’s glaciers are silting Denmark Strait, currently the deposit is up to 1km deep and only 600m below surface. As it happens the most of the Arctic outflow is via DS, just below 50% of the total, see the illustration above. With another 300m of silt, the cold outflow will be reduced to the level where the volume of the replacing warm waters has no sufficient melting effect on the Arctic ice, blocking onset of some future interglacial.
    There is also the East Greenland (cold) surface current generated by fresh river waters flowing into Arctic as well as the sea ice summer melt. However, during the ice ages this current might disappear (freeze) since it is on the surface and of a low salinity.

  12. Referring to your image 1. I believe the last warming period from ~160mya to ~84mya can be linked to large magmatic events totalling around 136 million km^3, capable of increasing the temperature of ALL ocean water ~136K. If confirmed, this would make the cold periods the norm, and only large magmatic events could bring earth out of an ice age.

    See the posts following this one:
    https://wattsupwiththat.com/2017/02/18/stokes-and-the-somehow-theory-of-ocean-heat/comment-page-1/#comment-2432044
    including two links to posts on that other site for details.

    • Mesozoic oceans were indeed kept warm by the volcanism associated with the break of Pangaea and other magmatic events during that era, continuing into the early Cenozoic.

      https://en.wikipedia.org/wiki/List_of_largest_volcanic_eruptions#Effusive_eruptions

      of the eleven largest known effusive eruptions (flood basalts, etc) on this list, eight occurred in whole or part during the Mesozoic Era, one preceded it, at the time of the Permian-Triassic Mother of All Mass Extinction Events, and two followed it.

      Mesozoic

      1. Ontong, Cretaceous Period
      2. Kerguelen, Cretaceous
      5. Caribbean, Cretaceous
      6. Siberian, Permian/Triassic
      7. Karoo, Jurassic
      8. Parana, Cretaceous
      9. CAMP, Triassic/Jurassic
      10. Deccan, Cretaceous/Paleogene

      Pre-Mesozoic

      11. Emeishan, Permian

      Post-Mesozoic

      3. NAIP, Paleogene
      4. Mid-Tertiary, Paleogene

      Note preponderance of Cretaceous eruptions, helping to account for hot tub temperature oceans at that time.

      • @Gloateus Maximus March 1, 2017 at 4:31 am
        “Note preponderance of Cretaceous eruptions, helping to account for hot tub temperature oceans at that time.”
        I have a list of LIP’s at the first link to “that other site”
        I’m convinced we’re looking at the explanation for the high temperatures on earth.
        Once you realize that ALL energy that warmed the deep oceans came from within the earth, the whole GHE disappears. The sun is easily able to increase the temperature of the mixed surface layer a bit above the deep ocean temperatures.to arrive at the observed surface temperatures.
        This mechanism also does away with the Faint Young Sun paradox and may explain the relative rapid exit out of a glacial into an interglacial.

      • How can Solar and DWLWIR heat the deep oceans given that DWLWIR penetrates only matters of microns, and Solar does not penetrate significantly beyond 100 metres and given the very slow rate of deep ocean overturning which overturning is further restricted by salinity/density/pressure stratification?

        It seems to me that the vast amount of heating that goes into the deep oceans most probably comes from below, due to geothermal activity.

      • @richard verney March 2, 2017 at 12:38 am
        “It seems to me that the vast amount of heating that goes into the deep oceans most probably comes from below, due to geothermal activity.”
        No doubt in my mind that ALL thermal energy in the deep oceans came from geothermal activity.
        While cooling down the last 84 million years geothermal flux alone supplied at least 60 times the total OHC (ocean heat content) to the deep oceans.
        But how to convince the rest of the world ;-)

  13. The only climate change humans living in high latitudes ever need to really worry about is when does the present interglacial end?

  14. I’m surprised this paper even got published. It posits a NON -anthropogenic cause for climate change. The CAGW crowd will be very unhappy.

  15. Ignore the ice, measure the sea level (where possible). It should be an easier metric of glacial versus inter-glacial when considering the entire Earth. Sea level should correspond to the total volume (not extent) of land ice, and that is really a better measurement than extent.

    • Except that other factors contribute to sea level besides the amount of water locked up in land ice. Notable among these are ocean temperature and the amount of seafloor spreading volcanic activity.

      • And configuration of the continents. A supercontinent has less continental shelf than a bunch of isolated continents.

  16. The current NH ice age began with the rise of Panama. We could probably end it by blasting through Panama with nukes. Then we’d go back to a period when we were basically in an interglacial all the time. The coming 100K yr glacial period will not be fun. One way or another, people will try to prevent it. Either that or the strongest races will seize Africa and Brazil.

  17. With all those large numbers a person’s life seems so insignificant. It’s a shame how we waste it with wars During the next interglaciation in about 100k years you think they’ll know we’ve ever existed?

  18. Astronomers tell us that the 140-150 million year interval between major glacial periods coincides with the time when the solar system is located in the outer arms of the galaxy. More GCRs due to the proximity of supernovae.

    • The sun is one of the stars that make up the arm of the galaxy. The sun and the arm rotate about the center of the galaxy at the same rate. Why would the position of the sun in the arm change?

      • The stars do not rotate with the arms. The arms are compression artifacts. Like waves in a traffic jam on the freeway. They all slow and bunch up and are “in an arm” then speed up and spread out and are not..

        The compression wave travels independent of the stars, or the cars…

      • The spiral arms do not rotate as material objects. They are brightly-lit markers of a density wave passing through, as shown by C.C. Lin. The wave leads to star formation. After a while the stars burn out but a new set of stars appears to continue outlining the density wave. If the spiral arms were rotating as material objects, they would get “wound up” over time since the inner parts of the Galaxy rotate faster than the outer parts. This was an unsolved problem for >50 years (Boltzmann took a shot at it) because the astronomers were under the impression that they had to duplicate the spiral arm formation using multiparticle (star) models. Lin was a fluid dynamics guy and treated the Galaxy as a fluid (dust, not stars) so was able to imagine a density wave passing through the fluid.

        E.M. Smith has the right idea below, just add to it that the stars have finite lifetimes so the spiral arms mark the passage of the density wave.

      • Or – it’s dark matter that makes the spiral arms rotate with speed at the outside only slightly less than at the inside.

        A wave of star formation can only explain a single rotation. Stars live too long i.e. several billion years, and the rotation time is only 1-2 hundred million. Soon it would just be a smooth disc.

  19. “Figure 5 plots effective energy required to cause an interglacial versus time. As can be seen more effective energy is required to initiate an interglacial over the past 600,000 years than before 1.5 million years.”
    Per the articles below, ice coverage starts by Milankovitch and precession cycles and is only ended when CO2 levels drop enough to cause plant die off/desertification with blowing dust covering the ice and causing warming/melting. This implies that extreme cold with mile thick glaciers in the northern hemisphere is the norm that is only broken by a lucky accident of nature. This also implies that ice soot coverage along with some minor CO2 warming may be needed to keep the earth from entering the next long term ice age.
    https://wattsupwiththat.com/2016/06/28/new-paper-modulation-of-ice-ages-via-precession-and-dust-albedo-feedbacks/
    http://www.sciencedirect.com/science/article/pii/S1674987116300305

    • BFL,

      Insolation change over time from a high point to a low are far larger than the postulated CO2 warming effect. CO2 will not stop a new Glaciation from happening.

  20. To Javier: The figure 3 is done with the intention of micromizing the visibility of results,
    done to avoid a clear comparison with GISP2. If someone maintains that a 41,000 cycle does produce warming and cooling periods, then he has to give, for the last 300,000 years, at least a curve discussion (i.e. giving dates of maxima and minima, amplitudes, high and bottom peak temperature levels. …When was the present high 41,000 peak in the Holocene, from when on temps will drop into the next glacial, according to the 41,000 2-degree Earth tumble cycle? Why is insolation given at 65 N, leaving out insolation at 65 South? To hide that both values even out?
    Major error, as usual: The glacial-interglacial sine curve is the exclusive result of the SUN MOTION, producing the circular Earth orbit going into an elliptical Earth orbit, and vice versa again, THUS a PULSATION of the the orbit, with an “Einschnürung” of the orbit up to 3%. This is astronomical knowledge, see also the “Klimawandel”-booklet of Rahmstorf. ….Therefore, the 100,000 and 41,000 year peaks are Sun motion results and have NOTHING in common with a 41,000 year (coincidence) of the Earth tumble cycle, which can be smoked in the pipe..

    • The figure 3 is done with the intention of micromizing the visibility of results,
      done to avoid a clear comparison with GISP2.

      No it is not. That you dare to claim that you know other people’s intentions casts a strong doubt on anything you say.

      If someone maintains that a 41,000 cycle does produce warming and cooling periods, then he has to give, for the last 300,000 years, at least a curve discussion

      To maintain that the 41 kyr cycle determines temperatures to a great extent is the easiest thing. The 41 Kyr band shows up in every frequency analysis of temperatures, it correlates very well if a lag of 6500 years is introduced to account for thermal inertia,

      and in this case it is impossible to mistake cause and effect, as we know the axial tilt does not depend on temperatures.

      The glacial-interglacial sine curve is the exclusive result of the SUN MOTION

      That’s your conjecture. But without some serious scientific articles supporting it like the one from Tzedakis et al., 2017, or Huybers 2006 that we are discussing, your conjecture will not make it too far.

  21. Javier’s methodology for identifying interglacials

    Sorry to be picky. I rarely am because I find it annoying but the use of the word methodology grates with me.

    It’s method. ology is greek for study approx.

  22. Andy your conclusion regarding likely cause is unsupported. Simply eliminating other causes cannot be the sole criteria for suggesting another one. Mechanism is key here.

    Without speculating on cause I see the graph displaying some sort of pump. Almost like inhale exhale behavior. At times the rythym is somewhat irregular, not an uncommon feature of breathing. Inhaling and exhaling heat pops up for me. Is there a substance on Earth that can absorbe heat and then exhale it? Of course there is. The oceans. Finding out what drives that process, and it is likely related to thermal dynamic properties of a very large finite volume open container being heated from the top down by the solar spectrum, would be fruitful. Its teleconnections with the atmosphere may help model this seesaw quite well.

    • The oceans contain and distribute most of the heat energy on the surface of the Earth, actually 99.9% of it. So they play a huge role in the process of glaciation and de-glaciation, no doubt about it. But, while they transport heat energy they do not create it or emit much of it to space. That is why the ultimate cause of the glacial cycles is astronomical. Heat energy transport by the oceans is part of the mechanism, not a cause.

    • Pamela Gray
      The El Nino Southern Oscillation is an oceanic cycle with a period of 1-3 years.
      The Atlantic Multidecadal Oscillation has about a half century or 60 year period, also from oceanic circulation, the AMOC.
      Interhemispheric bipolar seesawing, responsible for the Younger Dryas interval, operates on a timescale of around 1000 years – the cycle time approximately of the global ocean deep circulation (OHC).
      However there is no oceanic period or resonance that could operate on a timescale of 10,000 to 100,000 years. There are no cyclic processes whose interval is nearly long enough .

      • Overturning currents is not what I am speculating on. Heat capacity is. The teleconnections between our atmosphere and oceans may have a phase switch related to heat capacity maximum. I am talking about the drop to the stadial trench. That drop could be a net ocean recharge regime that while the storage battery is gaining depleted heat, we are left out in the cold. The reverse which is rather steep and not like the sputtering fall appears to be a net ocean discharge regime thus beniffiting flora and fauna which re-greens the planet.

  23. There were, after all, some correct aspects in the last few scenes of “The Day After Tomorrow.” They got the causal factors wrong but some of the effects they probably got right.

  24. Too many analyzing glacial cycles simply take proxy evidence as to when interglacials occurred (easier to time than the glacials) and try to match them to one or more of the cycles changing orbital insolation. (Javier likes to use only obliquity.) Such comparisons are incomplete.
    First, the insolation SUM of all orbital cycles (~21, ~41, & ~100 kyr) must be used, not just one. It is the SUM that determines far NH insolation and temperature. Second, unless the insolation decrease at high northern latitudes (>60N) is sufficiently large to act as a cold trigger for significant growth of land ice, the insolation cooling alone will just be countered by southern hemisphere heat (which is receiving greater insolation) moving to the north. Now is an example. 65N latitude has lost ~35 watts/m^2 insolation over the past 9 kyr, but no glaciation has begun. It is not cold enough.
    Only for those large NH insolation changes where land ice grows, NH ice and land albedo increases (enhancing the reduced NH insolation), and thus decreasing warm Atlantic currents into the Arctic, does a new glacial period begin. So any specific orbital cycle (individual cycle or cycle SUM) must first meet this minimum and then the Earth must show a minimum response before glaciation begins. Orbital cycles only begin glaciation; other processes are required to actually accomplish it.

    • Agree with your speculation. It could be an ocean heat capacity mechanism responding to this sum by a regime shift between two phases: net recharge and net discharge. I speculate on this because we already see this mechanism on a short term scale with El Niño and La Niña shifts. Finally that there are many intrinsic cycles at short and medium time scales is no proof there are none at much longer scales.

  25. `Interglacial` sea-level appears to be at the heart of the matter. Yet, sea-level during the odd numbered `interglacials` is not hefinitively known. Despite the apparent faith in a `known` `last-interglacial` sea-level, the fact remains that the complexity of ascertaining it, even within a broad band, remains unknown. It is time for the `experts` to acknowledge this.

    • Extent of land ice determines sea level. What causes the water cycle to be so interrupted that the land cannot return the water to sea because the water freezes over land before it makes its way back to the oceans?

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