Earth’s Ice Ages

By Andy May

The phrase “Ice Age” is poorly defined and often abused, so let’s first define the climate state during most ice ages. It is called “Icehouse Earth.” The earth is in an icehouse state when either or both poles are covered in a thick, permanent icecap (Scotese 2015). Today, both poles are covered in ice year-round, so you may be surprised to learn this is very rare in Earth’s history. In fact, out of the last 550 million years, the earth has had permanent ice caps on one or both poles only nine percent of the time.

An “Ice Age” is best defined as a geologically (or millions of years long) long period of low temperatures. This usually results in the presence of continental and polar ice sheets and alpine glaciers. We are currently living in the Quaternary Ice Age, this is only the fifth significant and severe ice age in Earth’s known history, and, so far it has lasted about 2.6 million years (technically 30+ million years ago when permanent ice appeared on Antarctica). It is the most severe ice age in the Phanerozoic, the geological name for the past 550 million years. Ice Ages are rare, but humans evolved during one, so it seems normal to us.

Figure 1. Christopher Scotese’s geological interpretation of Phanerozoic global temperatures in degrees C. The vertical line on the right side, labeled “PAW” is a projection of possible anthropogenic warming according to a pessimistic IPCC climate model. In 2016 the actual global average surface temperature of the Earth was about 14.5 degrees C. as marked on the plot, in 2019 the temperature is slightly lower at 14.35 degrees according to NASA GISS. The names of the major ice ages were added by the author. After (Scotese 2015)

As Figure 1 makes clear, the “normal” or “optimum” global average temperature of the Earth is 19.5 degrees C. or 67 degrees F. This is over 5 degrees C. (9 degrees F.) warmer than today. Over the past 550 million years, the Earth has normally been in the green area of Figure 1, the “Greenhouse” or optimal temperature regime. There are five periods when the Earth became very warm with average surface temperatures of more than 24 degrees C. or 75 degrees F. This area is called “hothouse” and is shaded in red in Figure 1. The blue area in Figure 1 is called the “icehouse” and we are living in the fourth or fifth icehouse period. Normally the Karoo Ice Age is considered one icehouse period, but it briefly returns to greenhouse conditions in the middle. The sharp cooling period labeled “KT Impact Winter” occurred 66 million years ago and was caused by a large asteroid striking the Earth near the Yucatan Peninsula in southern Mexico. The ejecta, which included a lot of SO2, from the crater caused a sudden cooling of the Earth and the extinction of all large animals, including the dinosaurs. This impact also marks the end of the Cretaceous Period and the beginning of the Tertiary. It is not considered an Ice Age, as it is too brief. In this article, the Jurassic-early Cretaceous Cool period will be considered an ice age, although the temperatures were not low enough to enter the icehouse state for any significant period.

The maximum swing in temperature in Figure 1 is from 13 degrees to 28 degrees C. or an increase of 15 degrees C. (27 degrees F.) between 280 million years ago and 250 million years ago. This is from the depths of the Permo-Carboniferous icehouse to the peak of the Triassic hothouse. Tropical temperatures change more slowly than polar temperatures, compare Figure 1 to Figure 2.

Figure 2. Change in global temperature in the tropics from Scotese. Over the past 550 million years there has been a steady decline in temperatures, but over the past 20 million years the tropical temperatures have increased 0.7 degrees C, whereas global temperatures have decreased four degrees into the last glacial maximum (LGM) 19,000 years ago and then increased two degrees to the present day. Source: (Scotese 2015).

As shown in Figure 2, the global temperature of the tropics (roughly 23.5 degrees north latitude to 23.5 degrees south latitude) varies less than the average global temperature of the entire Earth’s surface (see Figure 1). This means that the temperatures in the polar regions vary a lot from warmer periods to cooler periods. In the cooler periods, like our current ice age, the polar temperatures are low enough for ice to survive the summer months and thus, form permanent ice caps. Ice reflects more solar radiant heat than the soil or ocean under it, which amplifies the cooling.

With today’s configuration of the continents, the tropics are mostly covered with ocean water, which has a very high heat capacity, which means a lot of thermal energy is required to change the ocean water temperature. This characteristic of the oceans, plus the cooling effect of water evaporating from the ocean surface, carrying considerable thermal energy away as latent heat, reduces, or dampens, changes in tropical temperatures. But, even when the continents are clustered around the equator, the temperature change in the tropics is less than at the poles. Christopher Scotese has made a terrific animation of both plate movement and ice ages coming and going in the Phanerozoic that can be viewed here. Figure 3 is a screenshot from the animation showing the position of the continents 204 million years ago, in the Late Triassic. At this time, the land masses cover a lot of the tropics and the tropics are less than three degrees warmer than today (Figure 2). Yet, the average surface temperature is eight degrees warmer, implying that the polar temperatures are much higher than today. There are no ice caps on either pole at this time.

Figure 3. The continental land masses 204 million years ago according to Christopher Scotese. There are no ice caps on either pole.

When viewing Scotese’s animation, one must consider that sea ice normally leaves no geological record. Evidence of glaciation, such as striations (“striae,” Figure 4) on rock surfaces or anomalous boulders (“erratics, “Figure 5) that were carried large distances inside glaciers are not preserved, normally, from sea ice. In recent times, in the North Atlantic, icebergs, calved from Greenland, can carry erratics out into the ocean that can be seen in subsea cores. But, interpreting these requires considerable knowledge about currents and the nature of the rocks under the ice in Greenland that we do not have for older glaciations. It also requires that the sediments containing erratics be preserved. Older rocks are not preserved on ocean floors due to plate subduction in ocean trenches.

Figure 4. Glacial striae in Central Park, New York. Source: The Gates of Lodore.
Figure 5. Erratic boulders in The Netherlands, they were transported by glaciers from Norway. Source: Michielverbeek.

What causes ice ages? They occur roughly every 150 million years, as we can see in Figure 1. Notice that I am including the Jurassic-early-Cretaceous cool period (see Figure 1) as an “ice age,” even though it did not reach icehouse conditions. One possible explanation relies on the hypothesis that the amount of galactic cosmic rays striking the Earth varies as the solar system traverses the arms of the Milky Way, which it does roughly every 135 million years, plus or minus 25 million years (Svensmark and Svensmark 2017). The theory suggests that when more high-energy cosmic rays strike the Earth, more low-level clouds form. Low-level clouds cool the planet because they reflect more thermal energy than they trap under them. This reduces the warming effect of solar radiation (Svensmark, et al. 2017). This effect is one of the possible reasons that low solar activity and reduced solar wind in the eleven-year solar cycle minima cause the Earth to cool. A strong solar wind and high solar activity, during solar cycle maxima, reduce (attenuate) the cosmic rays in space before they strike the Earth, cloud cover goes down and temperatures go up, and vice-versa (Svensmark 2019). A definitive causal link has not been demonstrated to everyone’s satisfaction, although the work by Henrick and Jacob Svensmark is quite convincing. We consider the theory very intriguing, but still controversial.

Figure 6. The Solar System orbits the center of the Milky Way galaxy and passes through spiral arms roughly every 150 million years. Currently the Solar System is at the edge of the Sagittarius Arm of the galaxy. The Solar System also moves up and down relative to the Galactic Plane and its position up or down is not known very accurately. Source: Physics Forums.

If the cosmic ray and climate link is true, it could explain why ice ages occur. The density and energy of cosmic rays is higher in the Milky Way arms because there are more stars there (Shaviv 2002). So, the theory suggests that each time the solar system crosses a galactic arm, an ice age could be triggered. This idea was originally developed by Edward Ney of the University of Minnesota (see here) and the details of the theory are explained well by Nir Shaviv (Shaviv 2003). Shaviv also explains that variations in cosmic ray density is recorded in meteorites and that these variations correlate well with the known ice ages and with computed solar system galactic arm transits.

Ice ages are glacial periods, or periods of glacier advances, that are interrupted by periods of glacial retreat, called interglacials. We are currently living in an ice age interglacial we call the Holocene, see Figure 7. The forces and mechanisms that cause glacial advances and interglacials within an ice age are understood reasonably well and are well described by Javier, here and here. A plot of Antarctic temperatures, interpreted from ice cores, for the past 750,000 years is shown in Figure 7. The interpretation was done by Ryu Uemura and colleagues (Uemura, Motoyama and Masson-Delmotte 2018).

Figure 7. Antarctic temperature deviation from today. The global average temperature today is about 14.5 degrees C. or 58 degrees F. After (Uemura, Motoyama and Masson-Delmotte 2018).

Discussion

The Earth’s normal or optimum global average temperature over the past 550 million years is about 19.5 degrees C. or 67 degrees F. according to the temperature reconstructions done by Christopher Scotese. The normal state of the Earth’s climate is called the “Greenhouse” state, in this state there are no permanent, year-round ice caps on the North or South poles. But, in the past 550 million years there have been four, long anomalously cool periods we call Ice Ages. In three of these cool periods we entered icehouse conditions where there were permanent, year-round ice caps on one or both poles. We are currently living in the most recent ice age; we are also in icehouse conditions and have permanent ice on both poles. In the past 550 million years we have been in icehouse conditions about nine percent of the time and the current icehouse is one of the most severe in that period.

There is no general agreement on why the Earth has ice ages or why they appear in a roughly regular pattern. But, as Nir Shaviv has shown there is some evidence that the position of the Earth, relative to the arms of the Milky Way Galaxy, correlates with the occurrence of Ice Ages in our history. It also correlates with cosmic ray density. High cosmic ray density and energy also correlate with the ice ages and low cosmic ray energy correlates with warmer periods as shown by Shaviv’s meteorite studies. Henrik Svensmark provides us with a mechanism for creating additional low level, cooling clouds, as cosmic ray density and energy increases. Cosmic rays increase when the solar system is in the Milky Way galactic arms because there are more exploding stars in the arms, and they are the source of cosmic rays.

Experiments at the Large Hadron Collider (CERN) were used to create a model of cosmic ray/atmospheric ion collisions. The model suggested that cosmic rays have a minimal effect on cloud formation. However, subsequent experimental and theoretical work by Svensmark and Svensmark has suggested the model is flawed. In our judgement, while the cosmic ray/climate connection is far from proven, it is still a viable hypothesis and worth considering.

Works Cited

Scotese, Christopher. 2015. Some Thoughts on Global Climate Change: The Transition from Icehouse to Hothouse. PaleoMap Project. https://www.researchgate.net/publication/275277369_Some_Thoughts_on_Global_Climate_Change_The_Transition_for_Icehouse_to_Hothouse_Conditions.

Shaviv, Nir. 2002. “Cosmic Ray Diffusion from the Galactic Spiral Arms, Iron Meteorites, and a possible Climatic Connection?” Physical Review Letters 89. http://old.phys.huji.ac.il/~shaviv/articles/PRLice.pdf.

Shaviv, Nir. 2003. “The Spiral Structure of the Milky Way, cosmic rays, and ice age epochs on Earth.” New Astronomy 8: 39-77. http://old.phys.huji.ac.il/~shaviv/articles/long-ice.pdf.

Svensmark, H., M. B. Enghoff, N. J. Shaviv, and J. Svensmark. 2017. “Increased ionization supports growth of aerosols into cloud condensation nuclei.” Nature Communications 8. https://www.nature.com/articles/s41467-017-02082-2.

Svensmark, Henrick, and Jacob Svensmark. 2017. “The Connection between Cosmic Rays, Clouds, and Climate.” London: GWPF. https://www.thegwpf.com/content/uploads/2018/03/SvensmarkLondon2018.pdf.

Svensmark, Henrik. 2019. Force Majeure: The Sun’s Role in Climate Change. GWPF. https://www.thegwpf.org/content/uploads/2019/03/SvensmarkSolar2019-1.pdf.

Uemura, R., H. Motoyama, and V. Masson-Delmotte. 2018. “Asynchrony between Antarctic temperature and CO2 associated with obliquity over the past 720,000 years.” Nature Communications 9. doi:https://www.nature.com/articles/s41467-018-03328-3.

285 thoughts on “Earth’s Ice Ages

  1. Our present, Cenozoic Ice Age (Oligocene to Holocene Epochs) hasn’t yet equaled the Carboniferous-Permian Ice Age in duration.

    The northern polar regions probably didn’t have an ice cap in the Oligocene and Miocene Epochs, but a small one might have formed on Greenland in the Pliocene. Vast continental ice sheets, as on Antarctica since the Oligocene, didn’t build up in the Northern Hemisphere until the Pleistocene.

    • Ummm.. not one person alive can tell us what the temperatures of the earth WERE, more than back to about 1800. All these statements of temps are just assumptions, [made up facts], which the authors needed to make up..to support their conclusions!
      Nobody can even tell how old the earth is …bks all the age “measurements” depend upon many more ASSUMPTIONS. Look…”scientists” use “age measurements” …stuff like carbon 14 or uranium to lead ratios and so forth, but C14 is only good for about 15,000 years at best, and things like uranium to lead ratios depend upon assumptions.. [more made up facts]
      ie, If a man tells you a thing is a million years old by Ur to Pb ratios, ask him to tell you HOW TH he knows what the % of Ur was ‘back then’ and how he knows where all that uranium went and how he knows that some uranium did not just get washed out of that rock..and how he knows that the radon (a breakdown product of Ur) did not just diffuse out of that rock, etc. Ask questions like these and you just blew his theory. . Remember..when the first assumption enters, true science leaves, and things then become a belief..a..religion.
      Good grief folks..this article is like Gretta Thumb-in-mouth science.

      • Fred762, Not one person alive can tell you the precise average temperature of the Earth yesterday, much less in 1800. I suggest you read Chris Scotese’s report (link in the text) to see how he made Figure 1. Then you can discuss it intelligently.

        All global average temperature estimates are estimates. If you question them, please read their report so you can say something halfway relevant.

      • Uranium-lead dating doesn’t need to know how much lead there was to start. It’s based on the present ratio. U decays radioactively at a steady rate, thus any sample of U and Pb in the rock can date it.

        I don’t know why creationists have such a hard time understanding this simple physical fact. Whether the rock contained a ton or a gram of U to start doesn’t matter. The ratio of U to Pb does.

  2. It’s interesting that mainstream climate scientists are really just number crunchers, statistics-sophists and computer jocks (not to mention total incompetents and bald-faced liars – but I digress…), and the more compelling climate scientists are (among other things) astrophysicists. The galactic arm theory is quite fascinating.

    • icisil,
      Good points, but I would add atmospheric physicists to your list of real climate scientists, this would include Richard Lindzen and William Happer. I’ve never considered computer modelers to be real scientists, and I used to be a petrophysical computer modeler before I retired. I took the data and theories that real geologists, engineers and geophysicists gave me and created a numerical model to generate consistent mappable values for them. I would also tell them when their ideas didn’t make any quantitative sense on occasion. I never considered creating an alternative reality like these so-called “climate scientists” are trying to do.

    • The really “compelling climate scientists” (interesting concept) are our palaeoclimatologists, if you think about it. But Al Gore’s opinions are given more weight!

  3. There may be another cause for ice ages. Variation in atmospheric pressure. Mind that all atmospheric gasses, also N2 and O2, are part of complex cycles and changes in those cycles may change the sink capacity of the amount of that specific gas. Variation in total atmosphere gasses changes the depth of the atmosphere and the lapse rate takes care of the rest, altering the basic surface temperature. I will not mention Nikolov and Zeller and spoil Willis’day.

    • Andre — If there is an effect of varying “amount” of atmosphere, it is due to changes in the “optical depth” (opacity) of the atmosphere to radiation from the absorbing gases in the atmosphere.

      With a transparent atmosphere (say N2, O2, and Ar), it would not make any difference. N&Z don’t have a basic grasp of either high school physics or math.

      • Actually, changing the mass and chemical composition of the atmosphere changes the temperature at which the surface temperature will cause convection and remove heat from the planet more quickly. link

        • N2 and O2 form 99% of the atmosphere, and this has not changed significantly for a VERY long time. As diatomic molecules, their Cp specific heats are virtually identical (20.7 and 20.8 J/mol/K, respectively), so there will not have been any significant change in the -g/Cp adiabatic lapse rate over relevant time frames.

          • With a transparent atmosphere (say N2, O2, and Ar), it would not make any difference.

            No. The mass of the atmosphere matters a lot.

          • So exactly how does the “mass of the atmosphere matter[] a lot”?

            The static pressure from the weight of the atmosphere (mass in a gravitational field) cannot transfer ANY energy to the surface, because it is not actually moving the surface downward. (Energy transfer is the force multiplied by the distance over which the force acts, and here the distance is zero.)

            And a transparent atmosphere permits the surface to radiate directly to deep space.

          • So exactly how does the “mass of the atmosphere matter[] a lot”?

            1 – The Earth is a rotating sphere, not a disk. The poles, for instance, do not receive as much energy as the equator. They don’t heat as much as the equator.
            2 – The atmosphere is heated by the surface by conduction. Don’t believe that? If so, you’ve never designed a heat sink.
            3 – Convection will move heat poleward.
            4 – The mass of the atmosphere determines the surface temperature at which convection will occur.
            5 – Conduction and convection remove heat from the equator in addition to that which is removed by long wave radiation.
            6 – Some folks don’t believe it but the atmosphere can transfer heat to the surface. That’s exactly what happens in an ice covered arctic and is why the environmental lapse rate is upside down there.

          • Bob:

            I’ve designed plenty of heat sinks, and because of that I know that heat sinks also have to reject the thermal energy they get from the object they are cooling to the ambient environment. I often add fans to aid in this second step in my designs.

            (I recently fielded a call from a scientist who was complaining that his motor – with integral fins for heat sinking – kept overheating in the vacuum chamber he was using.)

            A transparent atmosphere has NO way of doing this second step because it has nothing to conduct TO in its ambient environment.

            Therefore, such an atmosphere cannot over the long term steadily remove heat from the surface. It must overall transfer as much heat to the surface as it accepts (of course in different places and/or times).

            (Natural) convection occurs when the magnitude of the negative lapse rate exceeds the adiabatic rate (-g/Cp). The mass of the atmosphere does NOT determine this. You need to brush up on some basic physics – look up “unstable lapse rate”.

          • I’ve designed plenty of heat sinks …

            And I’ve melted solder with a blast of hot air.

            The atmosphere can remove heat from the equator and dump it at the poles and, yes, heat the ground. The atmosphere itself can heat up. In fact, the temperature of the atmosphere can be predicted based on its chemical composition and its mass.

          • Bob:

            You still have not explained your assertion that the mass of the atmosphere matters (by itself).

            I already explained that the environmental lapse rate determines when convection occurs, not the pressure from mass.

            Now you say that “the temperature of the atmosphere can be predicted based on its chemical composition and its mass.” I’d like to see that equation, especially one that does not include the radiative inputs, outputs, and absorptive/emissive properties of the atmosphere.

      • Try that again, in English. A 5 bar atmosphere is much better insulation than a 1 bar one, say 5 X better….

        • If you are talking about conductive insulation, that’s not true at all. With the near total vacuum of space, there is nothing to insulate from, as the atmsophere cannot not conduct to space at all.

          If you are talking about radiative insulation, opacity (i.e. absorbing gases) IS radiative insulation.

          • Something is missing in your comment. If O2 and N2 don’t radiate to space then the only way to eliminate their heat is by conduction to water vapor and CO2 and then to space by radiation.
            This means water vapor and CO2 provide the only way to cool the earth. Wouldn’t this mean we want to increase these gases?

          • Jim:

            Gases that don’t emit IR also don’t absorb IR (Kirchhoff’s Law). So an atmosphere just of N2 and O2 would permit all surface IR to pass directly to space.

            Yes, the IR-active gases in the atmosphere – primarily H2O and CO2 – do radiate to space. But they also absorb IR from the surface. And – here is the key – they radiate at lower temperatures than the surface does, and therefore with lower intensity.

            An analogy using (primarily) conductive heat transfer: If you put on a jacket on a cold day, you are still losing thermal energy (heat) through the jacket. But your surface is conducting to the relatively warmer inside of the jacket instead of directly to the colder ambient. This is how the jacket “keeps you warm” while at the same time providing a path for your heat loss to ambient.

          • Doesn’t answer or alter my comment. A 5 bar atmosphere may well be more than 5 X as insulative with 100% ish humidity.

          • Chas:

            You aren’t disagreeing with me. A 5 bar atmosphere with 100% humidity has a lot more optical depth (opacity to IR) than a comparable 1 bar atmosphere, and as I said above, opacity is radiative insulation.

            But it’s only because of the increased IR absorption. This would not happen in a transparent atmosphere.

          • I guess you missed my point. Do O2 and N2 absorb heat from CO2 and water vapor? If they absorb heat, say by conduction, then how is that heat transferred to space? If radiation is then only way heat can be lost, doesn’t it have to go through CO2 and water vapor?

          • Jim: Let’s try this again. If a CO2 or H2O molecule in the atmosphere absorbs an IR photon and goes into an excited state, it is about 1000 times more likely to transfer that energy to an N2 or O2 molecule through a collision than it is to re-emit a photon first.
            But in the continual collisions that occur in the atmosphere (about once per nanosecond at STP, IIRC), occasionally a CO2 or H2O molecule will be put in an excited state for a period where it can emit an IR photon, so energy can be transferred to space.
            But at heights where this photon stands a good chance of making it to space, it is usually much colder than the surface, reducing the chances of this and resulting in a lower intensity of radiation of those wavelengths. This has been verified by satellite measurements.
            And to repeat, in an atmosphere without IR-active gases, all the surface radiation makes it directly to space.

    • Changing the pressure distribution also changes the ability of air to hold water vapor. Together with a lower temperature there will be much more snow.

    • Andre, I agree that’s a possibility (very generally, greater pressure = higher surface temps). Unfortunately there doesn’t seem to be a reasonable method of determining past atmospheric pressure, tho we can estimate composition to some extent (% of N2, O2, CO2, etc).

      • beng135:

        You state that (very generally, greater pressure = higher temps)

        What is the reason that this happens?

        Anybody?

        • Burl,
          Yes, I can tell you why. It is because temperature is really a measurement of energy density. If you have X amount of energy in a volume of gas, and then compress it, you still have X amount of total energy. But the density of the gas, and hence the energy density (temperature), goes up. It’s really just that simple.

  4. Earth’s normal or optimum global average temperature
    Why is that temperature ‘optimum’?
    BTW: The averaged energy density of Galactic Cosmic Rays [in our Milky Way Galaxy] is greater than that of starlight. Integrated over the whole Galaxy, their total energy amounts to a non-negligible fraction of the rest-mass energy of the stars themselves. GCRs arrive at Earth almost exactly isotropically [not depending on direction] suggesting that there is not any significant variation with location within the Galaxy, making the ‘spiral arm crossing’ hypothesis unlikely.

    • Leif,
      #1. The greenhouse temperature range is where most species evolved and lived and 19.5 is the middle of that range. It is optimal because most species in the Earth’s modern history (last ~550 million years) are better suited to it than any other temperature range. Today we are too cold, this is easily seen in the mortality statistics, we are much more likely to die in the winter than in the summer.

      See figure 1 here: https://andymaypetrophysicist.com/2017/12/18/climate-related-deaths-and-insecurity/

      • People have spread over the Earth, living their lives in all climatic zones except the ice caps. This leads to the erroneous belief that the present climate and average temperature is normal or even optimal. Not so. Without technology in the form of fire, clothing, shelter humans in their natural state can only be comfortable near the equator. Living there would just about eliminate AGW, assuming that’s a real thing.

        “The thermoneutral zone describes a range of temperatures of the immediate environment in which a standard healthy adult can maintain normal body temperature without needing to use energy above and beyond normal basal metabolic rate. It starts at approximately 21 degrees Celsius for normal weight men and at around 18 degrees Celsius for overweight[5] and extends towards circa 30 degrees Celsius. Note this is for a resting human and does not allow for shivering, sweating or exercising.”

        21C close to the 19.5C to the Greenhouse mid range temperature. 70F to 86F we can do pretty well without clothing; maybe a loin cloth to facilitate social interaction. Those are the temperatures we seek out for winter vacation. Hawaii, don’t forget your swim suit! While ending the ice age would cause problems we probably ought to do it, if we can.

        • Robert
          You said, “… living their lives in all climatic zones except the ice caps.” That’s not quite true. People have long lived in the northern Arctic region using only resources available to them from the local environment. The early European explorers of Antarctica adapted the ways of northern Arctic dwellers, such as fur coats with parkas, skis, and dog sleds. If Eskimos had been able to get to Antarctica, they probably would have been able to survive there.

          Also, it is my understanding that early Europeans who explored Tierra del Fuego reported that the natives were able to sleep nude in temperatures below freezing. Similarly, Australian aborigines wore little in the way of clothes and were able to survive freezing temperatures.

          • It is reported that the North American First Nations people in Southern Canada (a broad stretch) had incredible tolerance to cold and wore little we would consider adequate clothing even in mid-winter.

            I don’t think we have any idea how that was accomplished.

          • “If Eskimos had been able to get to Antarctica, they probably would have been able to survive there.”

            No. I have some Arctic experience, and before visiting Antarctica I too thought of it as something rather like e. g. Northeast Greenland or Nordaustlandet on Svalbard.

            It isn’t. It is much, much worse.

            Remember that there are vast areas even in Arctic Canada and Greenland where Eskimos were unable to settle or survive. The eskimos in eastern Greenland, Prince William Island and Ellesmere Island died out during the Little Ice Age.

            However I do think that Eskimos transplanted to South Georgia would have been able to survive.

            And Tierra del Fuego is positively balmy in comparison. True, it is very wet and stormy, but never really cold.

          • There is a you tube video out there of a guy handling a winter night in mother but a loin cloth — no tools, no prep.

            So, modern man isnt completely ruined.

          • tty

            You said, “Remember that there are vast areas even in Arctic Canada and Greenland where Eskimos were unable to settle or survive.” There has to be food available to survive. While the earliest explorers of Antarctica were using cold weather clothing not really different from Eskimos or Europeans in northern Scandinavia, the Antarctic interior has no animal life to eat. Any inhabitants would have had to stay close to the shoreline, where the temperatures are not as severe.

            My point about Tierra del Fuego was that the natives survived sub-freezing temperatures essentially nude. Humans are really quite robust, given time to adapt.

      • As Figure 1 makes clear, the “normal” or “optimum” global average temperature of the Earth is 19.5 degrees C. or 67 degrees F.

        I was also surprised by the assertion that the “average” temperature ( by which we have to assume you are referring to the mean since you do not define it ) is “normal”. In what way? From the graph it seems this is a rapid transitory state. For something to be the norm it would have to be like that most of the time or at least in state more of the time than any other ( ie the median, not the mean ).

        It is optimal because most species in the Earth’s modern history (last ~550 million years) are better suited to it than any other temperature range.

        Says who?

        I agree that warmer than current values are probably more suited to life but where you get the evidence that the mean of the temperature range is the “optimum”?

        Neither do I get why you are adopting Scotese’s silly “ice house” terminology. We are living in an interglacial stade of an ice age, we are not living in an “ice house”.

        • It’s a valid concept. The current Ice House began about 34 Ma. Ice ages happen during ice house intervals.

          • No the Quaternary ice age began 34 million years ago. Glaciations happen during ice ages.

            There is no need for a new term to describe the same thing.

            Unnecessarily changing and redefining terminology just leads to confusion and imprecision.

          • The term is valid because ice ages do not always occur during ice houses. The most recent example was the Mesozoic ice house, in which no ice sheets or caps formed, just perhaps a few mountain glaciers.

            Both Paleozoic ice houses suffered ice ages. The Ordovician-Silurian ice age was short but deep. The Carboniferous-Permian was long and deep, like our present ice age during the Cenozoic ice house.

      • Optimal might also be considered the state where life has not been completely or nearly completely eliminated from large portions of the planet surface, as is the case when the polar regions are frozen solid all year around.

      • Andy
        And, it isn’t just humans. While some animals living in hot deserts, such as the Sahara, are near their thermal regime upper limits, for mid-latitudes, mortality is greater in the Winter than Summer for almost everything. Even animals adapted to polar regions are more likely to die of extreme cold than extreme ‘warmth.’

        • Clyde, Nicholas, John and Greg,
          Thanks for the discussion, it is interesting and informative. For myself, I like Scotese’s terminology. The greenhouse conditions are certainly normal for the life on earth, I do not detect any objection to that. Icehouse and hothouse, but especially icehouse (like today) are abnormal and cause extinctions. I still think it is logical to conclude that the middle of the greenhouse state is optimal. I understand the objections, lack of direct evidence, etc. But it is a logical conclusion, using the principle of natural selection, that the temperature where nearly all species (not phyla!) evolved would be the optimal temperature.

    • Leif, Your question #2: Shaviv disagrees with you and believes that the cosmic ray density and energy in the spiral arms is higher than between them. See Shaviv, 2002 in the references. There are many other references that discuss this idea, but Shaviv goes into considerable detail and offers a lot of evidence.

      • Shaviv disagrees with you and believes that the cosmic ray density and energy in the spiral arms is higher than between them
        1: Disagreement is not evidence.
        2: Neither is belief.
        3: If the density is higher in spiral arms, then we would expect to see a higher
        flux in the direction of the arms, contrary to observations [isotropy].
        4:The cosmic ray flux has been high the past two cycles, yet temperatures have soared.

        • “suggesting that there is not any significant variation with location within the Galaxy”

          Goose, meet gander.

          Suggesting is not evidence either.

        • Magnetic fields impact the direction of GCRs, so the belief that GCRs should be coming preferentially from the direction of the arms is not supported.

          Temperatures have soared? On what planet?

        • Temperatures on Earth have not soared during the past two cycles, ie ~22 years.

          The peak of the 1998 Super El Nino was insignificantly higher than that of the 2016 El Nino. A statistical push, with flatness in between.

          Since February 2016, Earth has cooled dramatically.

          Where is a warming effect, let alone “soaring” temperature?

          • John Tillman

            “The peak of the 1998 Super El Nino was insignificantly higher than that of the 2016 El Nino. A statistical push, with flatness in between.”

            Well when I look at the MEI index I wouldn’t pretend it was ‘insignificantly higher’:

            https://www.esrl.noaa.gov/psd/enso/mei/img/meiv2.timeseries.png

            “Since February 2016, Earth has cooled dramatically.”

            Aha. Where did you obtain this information from?
            Maybe when looking at

            http://www.drroyspencer.com/wp-content/uploads/UAH_LT_1979_thru_December_2019_v6-1536×886.jpg

            or something similar?

            How, do you think, could UAH’s anomaly level bypass its highest level since 1979 within only a couple of years?

            When a series begins with a very high value, isn’t it unlikely to expect the series trend to be anything else than negative?

            I propose you to look at the two El Nino periods 1997-2001 and 2015-2019, when they are displayed relative to their respective begin (through subtracting, in both series, the first anomaly from all of them):

            https://drive.google.com/file/d/1y1zmzMt_1gD5jxCOH13UVYvbocYulbNz/view

            You think it’s restricted to the lower troposphere? So what!
            Let’s look at the surface:

            https://drive.google.com/file/d/1B1fmSRnfC_TIRUYI6eQs2JeSFRHxhXqL/view

            You see that the recent period (2015-2019) behaves exactly as the previous one (1997-2001), at the surface as well as in the LT.

            Rgds
            J.-P. D.

          • John Tillman”

            “The peak of the 1998 Super El Nino was insignificantly higher than that of the 2016 El Nino”

            Both were man-made events caused by large reductions in the amount of anthropogenic SO2 aerosol emissions, due to Clean Air efforts.

            And the cooling that peaked in the early 1970’s was caused by increased levels of anthropogenic SO2 aerosol emissions.

            The point is that decreased atmospheric SO2 levels will cause warming, and increased SO2 levels will cause cooling.

            Similarly, increased atmospheric SO2 levels from large volcanic eruptions will cause cooling, and when they eventually settle out, warming to pre-eruption levels, or , usually a bit higher, occurs.

            The ~300 year Medieval Warm Period was characterized by few large (VEI4, or larger) volcanic eruptions, and the resultant warming due to low atmospheric SO2 levels melted most of Earth’s glaciers

            The following ~600 year Little Ice Age was characterized by frequent large volcanic eruptions (with a few warm intervals of decreased volcanic activity interspersed within), and the elevated SO2 level from the eruptions cooled temperatures, resulting in the formation or enlargement of glaciers, which are now melting because of the reduced volcanic activity since the end of the LIA.

            Thus, there is really no mystery about Earth’s Ice Ages. They are simply the result of periods of elevated SO2 levels from extensive volcanism, probably triggered to a large extent by plate tectonics.

            Can anyone refute any of my scenario?

          • Burl Henry

            Good point.

            I recall this rather tremendous series of huge volcano eruptions I read years ago about, which all happened before the Maunder Minimum:

            – 1257 Samalas, Indonesia, VEI 7
            – 1280 Quilotoa, Andes VEI 6
            – 1452 Kuwae, Vanuatu, VEI 6+
            – 1477 Bárðarbunga, Island, VEI 6
            – 1563 Agua de Pau, Açores, VEI 5
            – 1580 Billy Mitchell, Solomon Island, VEI 6
            – 1586 Kelut Island, VEI 5
            – 1600 Huaynaputina, Peru, VEI 6
            – 1641 Mount Melibengoy, Phillipines VEI 6
            – 1650 Kolumbo, Greece, VEI 6
            – 1660 Long Island, Papua New Guinea, VEI 6

            with in addition between them, about 35 eruptions with VEI up to 4. I had this list too some years ago but it went lost.

            An interesting paper about this:

            Abrupt onset of the Little Ice Age triggered by volcanism and sustained by sea‐ice/ocean feedbacks

            Gifford H. Miller, Áslaug Geirsdóttir & al.

            https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2011GL050168

          • Bindion,

            Super El Ninos don’t last four years.

            Burl,

            IMO warm and cool cycles are better explained by solar activity. The MWP suffered just one or two mild solar minima, while the LIA three or four much deeper ones.

            Volcanic activity can’t explain either interval’s WX. The effect of even the biggest eruptions doesn’t last long enough, and the location of the volcano matters a lot.

            If the LIA date from c. AD 1400 to 1850, and the MWP from c. 950 to 1400, then the former did suffer more VEI 6 or 7 eruptions than the latter (earlier), but each interval experienced just one magnitude 7 event.

          • John Tillman

            As I anticipated, you didn’t understand my comment. Maybe you were too much busy with own thoughts…

            The comment evidently wasn’t about how long the Ninos last.
            It was about a comparison of two periods.

            Try again, with somewhat more attention.

          • Commenter Tillman thinks he knows everything, and manages to show:
            “Comparison of duration of Ninos or Ninas doesn’t signify.”

            He still didn’t understand the graph.
            So what.

            In my native tongue we say: “Le comportement autoritaire ne reflète en aucune manière une quelconque autorité.”

        • Dr Svalgaard, certainly the closer you are to supernovae or other high-energy systems (or in an area of greater density of), the greater the CR flux.

        • For what it’s worth, as I am very much a layman astrophysicist, I agree. My understanding is that “Cosmic Rays” originate in supernovae from throughout the cosmos, not limited to our galaxy, and hence come equally from all directions.

          One might speculate that some large astronomic structures, eg the supermassive black hole at the center of the galaxy, might cause a cosmic ray “shadow”. Is there any evidence for this?

      • Andy, am I to understand that the solar system drifts across spiral arms and isn’t simply a star within a particular arm? Surely it is slave to the gravitational forces and galactic rotational momentum that give form to the arm itself (and the galaxy). Perhaps ambiguity in the decriptive language gives this impression.

      • Despite of good contra-arguments, I would assume that truth is much closer to Dr. Svalgaards view than the one Dr. Shaviv proposes.
        Reason is simple; there are thousands or even millions of stars in the areas of the galactic arm that sun might be traversing through. Most of these stars if not all, have strong magnetic field deflecting GCRs in various directions. Further more, the galactic arm itself may have a collective magnetic flux of its ‘own’ due to presence of so many local magnetic sources, repelling the GCRs away from the arm. Therefore I would argue that ‘the cosmic ray density in the between spiral arms is higher than within the arm itself’.

        • Vuk, the most powerful (fastest) cosmic rays, that have the strongest effect on the earth’s atmosphere, are the least affected by magnetic fields.

    • Further to your questions #2, from Shaviv 2002, page 41: “CR’s are believed to originate from supernova remnants. … they should predominantly reside in spiral arms, where most massive stars are born and shortly thereafter die.”
      There are numerous references in the text.

      • GCRs move almost at the speed of light and quickly escape the spiral arms to diffuse all through the Galaxy leading to the observed isotropic distribution.
        There are numerous references in the text
        A large number of references to an erroneous idea does not make it right.

        • Leif, Your arguments lack any supporting evidence or references, they ring very hollow. Simple assertions will not fly here.

          • The problem is that there are too many unknowns (maybe unknowables).

            Shaviv (2002, 2003) proposed that the occurrence of ice‐age epochs on the Earth was influenced by the solar system crossing through the spiral‐arms of the Milky Way. In the diffusional model of Shaviv, variations in GCR fluence between the regions within and outside of the spiral arms may be up to a factor of three. The GCR flux is higher in galactic spiral arms than in interarm regions due to higher supernova rates and/or closer proximity to supernovae explosions. He proposed, by assuming four galactic spiral‐arms for the Milky Way, a spiral crossing period for the solar system of ~140 Ma. Shaviv also argued that this periodicity is seen in the GCR exposure age histogram for iron meteorites. Although some studies were supportive (e.g., Wallmann 2004; Gies and Helsel 2005), many subsequent investigations have questioned the original hypothesis. First, Sloan and Wolfendale (2013b) calculated GCR intensity variations between spiral‐arm and interarm regions to be in the range 10–20% and not more than 30%, that is, far less than the factor of three assumed by Shaviv (2002, 2003). In addition, the calculated periodicity depends on the number of galactic spiral‐arms. While there are indeed some arguments that the Milky Way has four spiral‐arms (e.g., Vallée 2017), there are also some arguments for a two‐armed spiral in the Milky Way (Drimmel 2000). If true, the periodicity of the GCR intensity variations would be closer to 280 Ma and would no longer be in accord with periodic Earth climate changes. Using new data on the structure of the Milky Way, Overholt et al. (2009) argued for a nonsymmetric galaxy and concluded that the timing of the crossing of our solar system through galactic spiral‐arms is most likely irregular. A second and motivating rationale for the present study are questions about the interpretation of the meteorite data by Shaviv (2002, 2003). For example, Rahmstorf et al. (2004) argued that Shaviv misinterpreted the iron meteorite data (see also Wieler et al. 2013). Going one step further, Alexeev (2016) used the same data set as Shaviv (2002, 2003) but reinterpreted the data by fully considering uncertainties for the cosmic ray exposure (CRE) ages and using the now accepted chemical grouping for iron meteorites. Doing so, he found no indications for a periodicity of 140 Ma in the CRE age histogram but he found slight indications of a periodicity in the range 400–500 Ma. Jahnke (2005), using the same data set, found no indications for any periodic signal in the CRE age histogram for iron meteorites.

            Smith et al., 2019
            https://onlinelibrary.wiley.com/doi/full/10.1111/maps.13417

            The problem with meteorites is that the error bars in dating them are too large, we don’t really know how long it takes our Solar System to orbit the Milky Way and we can’t even be certain of what the exact spiral arm configuration is. This is why I suggested a paleoregolith coring program on the Moon. Basalt can usually be dated with fairly decent accuracy. It might be possible to construct a Protozoic record of the GCR flux from Lunar basalts. This might tell us if there is a clear periodicity. Mare basalts range in age from 3.9 to 3.2 BY, a span of 700 MY. If there’s a 140-150 MY periodicity, it should be detectable in lunar basalts.

          • David, More data is definitely needed. Shoot for the Moon!

            More seriously, it is a hypothesis, one with some data supporting it, but still a hypothesis.

          • I think it’s the only coherent hypothesis for the apparent periodicity of ice ages and 1st order sea level cycles.

          • To repeat:
            Wieler et al.: https://link.springer.com/article/10.1007/s11214-011-9769-9:
            “The very long-lived radioactive nuclide 40K allows to assess the GCR flux over about the past one billion years. The flux over the past few million years has been the same as the longer-term average in the past 0.5–1 billion years within a factor of ∼1.5. However, newer data do not confirm a long-held belief that the flux in the past few million years has been higher by some 30–50% than the very long term average. Neither does our analysis confirm a hypothesis that the iron meteorite data indicate a ∼150 million year periodicity in the cosmic ray flux, possibly related to variations in the long-term terrestrial climate.”

            So: no good evidence for the claim of the present post as is well-known.

        • Do not fight the observations. What the heck caused the earth to cool for millions of years repeatedly?

          There must be an explanation for everything that physically happens.

          Ice house periods are cold periods for millions of years. There must be a physical cause that can explain cold periods that last for millions of years and recur.

          We know that ice house periods cannot be explained by changes in atmospheric CO2. (See reference below as CO2 and temperature changes absolutely do not positively correlate with each other.) This finding is a hard paradox for CAGW and possibly AGW.

          One physical advantage of the theory that galactic cosmic rays (high mostly high speed protons) varying when the solar system passes through the galaxy’s arms theory, is it can explain cold periods that lasted from millions of years and that reoccur.

          The second advantages is the authors presents meteorite analysis that supports their assertion that GCR has varied at the period in times when the ice house ages did occur.

          https://www.mdpi.com/2225-1154/5/4/76

          The Relationship between Atmospheric Carbon Dioxide Concentration and Global Temperature for the Last 425 Million Years

          Of 68 correlation coefficients (half non-parametric) between CO 2 and T proxies encompassing all known major Phanerozoic climate transitions, 77.9% are non-discernible (p > 0.05) and 60.0% of discernible correlations are negative.

          Marginal radiative forcing (∆RF CO2 ), the change in forcing at the top of the troposphere associated with a unit increase in atmospheric CO 2 concentration, was computed using MODTRAN.

          The correlation between ∆RFCO2 and linearly-detrended T across the Phanerozoic Eon is positive and discernible, but only 2.6% of variance in T is attributable to variance in ∆RF CO2 . Of 68 correlation coefficients (half non-parametric) between ∆RF CO2 and T proxies encompassing all known major Phanerozoic climate transitions, 75.0% are non-discernible and 41.2% of discernible correlations are negative.

          Spectral analysis, autoand cross-correlation show that proxies for T, atmospheric CO 2 concentration and ∆RF CO2 oscillate across the Phanerozoic, and cycles of CO 2 and ∆RF CO2 are antiphasic.

    • Leif,

      Do you have any observations that support your claim that GCR is constant in the galaxy and does not increase by a factor of five when the solar system passes through the galaxies arms?

      This is a link to the paper which you appear to have not read. The paper includes analysis of 50 meteorites to determine past GCR levels.

      This analysis of 50 meteorites finds that GCR did vary by a factor of five and periodicity of the change in GCR’s effect on the meteorites varies with the same periodicity of the earth’s climate changes.

      Obviously there is a physical reason for the occurrence and periodicity of the ice house periods.

      http://old.phys.huji.ac.il/~shaviv/Ice-ages/GSAToday.pdf

      This is link to the rebuttal written by the authors of the CAGW critism of the meteorite analysis method.

      “It is certainly true that the complete meteoritic data includes clusters of meteorites of the same type, and that such clusters are most likely the result of a single parent body breaking up into many small pieces, but this is totally irrelevant.

      “As detailed in Shaviv [2002] and Shaviv [2003], in order to neutralize this effect, a modified meteoritic data set is generated (using 80 K-dated Iron Meteorites) where clusters of meteorites of the same Iron group classification are replaced with one having an average age.

      Thus, the clustering can either be because of a variable CRF, or, simply because parent bodies tend to break up more often periodically. However, it is not likely that single bodies generated each of the clusters, since each cluster is now comprised of meteorites that are all of different Iron group classification.”

      Irrespective, even if the CRF were constant, and even if the origin of the clusters were single heterogeneous asteroids, each giving rise to a heterogeneous cluster, we still find that the periodic pattern in the “celestial” signal correlates with the pattern in the terrestrial one!

      Moreover, independent evidence in the Iron meteorite data, based on comparison of different exposure dating methods, clearly shows that the CRF over the past 10 Ma must have been 30% higher than was the average over the past 1000 Ma [Lavielle et al. 1999]. If it was variable recently, it is unlikely that it was constant before.

      Plus, the astronomical understanding of the origin and diffusion of cosmic rays in the galaxy predicts that the CRF should be variable. It is therefore not surprising that it is observed, as predicted, in the meteoritic data.

      The periodicity in the exposure ages of meteorites, which includes now also exposure ages based on Cl, is described in figure 1. As clearly evident from the figure, the meteorites cluster periodically. This is highly unlikely to be a random fluke.

      • The paper rather stresses that no significant variation has been established and any conclusion must await more data from an expanded lunar exploration. The paper cites Wieler et al.: https://link.springer.com/article/10.1007/s11214-011-9769-9:
        “The very long-lived radioactive nuclide 40K allows to assess the GCR flux over about the past one billion years. The flux over the past few million years has been the same as the longer-term average in the past 0.5–1 billion years within a factor of ∼1.5. However, newer data do not confirm a long-held belief that the flux in the past few million years has been higher by some 30–50% than the very long term average. Neither does our analysis confirm a hypothesis that the iron meteorite data indicate a ∼150 million year periodicity in the cosmic ray flux, possibly related to variations in the long-term terrestrial climate.”

        So: no good evidence for the claim of the present post.

    • Leif#1 ‘optimum’, I noted that too. Poor word choice. MOR value, but it never stays there, it just visits passing through on its migrations. Although at one point it then goes back instead of forward. Beats me.

      “making the ‘spiral arm crossing’ hypothesis unlikely”. Shaviv’s paper was interesting, but not convincing, despite all the equations, since he isn’t even sure of what a spiral arm is. But if it is/was a shock wave big enough to create stars, I could imagine it might affect the earth’s temperature.
      His figures 10 and 11 are accessible for those who glaze over at math.

      Andy’s Figure 1 is also interesting for the “KT Winter” blip — a huge sharp impact on temperature and then it immediately goes right back to where it was. If that was not a tipping point (and it wasn’t), then nothing is.

      • Very good point, I’ll make a note of that.

        Looks like the most convincing evidence of a strongly dominant negative feedback.

    • “GCRs arrive at Earth almost exactly isotropically”

      Sounds like a good criticism of the essential theory of earth being directly affected by some kind of proximity based galaxy GCR variation. Yet one must account for the variation in GCRs arriving at earth over time as found in studies perhaps in time with passing through galaxy arms.

      One argument might be some effect from passing through galaxy arms not directly due to proximity-based GCR variation; but instead may be an effect on the solar wind via whatever proximity-based mechanisms cause variations in that. Oh oh!

    • Andy
      Thanks for the important and helpful article.

      The greenhouse temperature range is where most species evolved

      With respect, I believe this is incorrect. All 19 phyla of multicellular organisms established their body plans and evolved during the Cambrian and Ordivician. All but one of these arose during the “Cambrian explosion” from 540-510 million years – a period of less than 30 million years. During all this time the earth was in the Cambrian hothouse climate.

      By time the earth cooled into the “Greenhouse” climate, major phylum level evolution was over. Only minor adjustments followed. CO2 levels were ~10,000 ppm during this time. All calcified phyla (corals, bryozoans, shelled molluscs, Echinodermata etc.) evolved and thrived under these conditions. And now we are asked to believe that increase in CO2 from 280 to ~500 ppm CO2 is going to acid-corrode marine calcified organisms? It makes no sense.

      • Phil Salmon, So your argument is that evolution stopped at the end of the Cambrian explosion? I find this very hard to accept. What species living today, evolved in final form in the Cambrian?

        • Andy,

          Check your reading comprehension. It is clear to me that Phil is explicitly NOT saying that evolution stopped at the end on the Cambrian explosion. He refers to “major phylum level evolution”.

          Further, he is not countering your argument, he is countering the argument of the alarmists that say stupid things like 2 degree temperature increases and ocean “acidification” are going to end life on the planet.

          Personally, I think you are both right. It is amazing that no new phyla have developed in the last 450 million years. (Competition is a bitch?)

          Andy is certainly correct to point out that very few species have evolved during Icehouse Earth conditions. Further, most of these species are close relatives of existing species.

          I certainly agree with Andy’s major premise that WARMER IS BETTER from our current state.

        • Phil and Pillage, What threw me was he was complaining about my mention of species with a comment about phyla. I was discussing species evolution and he switched to phylum evolution. Apples and oranges. Anyway, regardless of the complaints in the comments, I stand by my statement that greenhouse conditions are optimal, and since 19.5 degrees is the center of the greenhouse range it is the optimal global average temperature for life on Earth. That is where modern life evolved and that is where they prefer to be. It is unclear how many extinctions occurred under hothouse conditions, but a lot of extinctions have occurred in icehouse conditions, maybe most of them. Mortality, both human and animal, is much higher in colder temperatures than warm temperatures. I think I’m on firm ground here.

        • Andy, PI
          Thanks for your replies.
          I guess my use of “incorrect” was too strong. I instinctively trace species origination back to their parent phylum and thus to the Cambrian explosion. But although the anatomical scope of evolution has been narrowing, the rate and fecundity of generation of new life species has remained vigorous over the whole Phanerozoic.

          I guess in a very general, conservative, parsimonious way it is safe-ish to conclude from Scotese’ graph that the median temperature of 19.5 is at least comfortable, and at least within an optimal range.

          But the habitable range is evidently wide, from hothouse to icehouse. And the Cambrian explosion – where most phyla originated – was in a hothouse, so how could that not be optimal?

        • Some recent research may contradict my argument that the phylum level diversification of the Cambrian explosion implies an idyllic climate. It may have been far from idyllic. Evolution is a strange thing, and very unusual circumstances are required for major changes. Isolation is required for instance. It might even be the opposite – idyllic and productive ecosystems may favour fine tuning only of evolving life forms but major change requires something else – something more stressful.

          Recent research has shown that the Cambrian explosion happened as soon as oxygen levels rose high enough to allow it, as the world recovered from the deep almost global Cryogenian glaciations. Careful palaeontology along Siberian river beds has shown that the Cambrian explosion of new multicellular life forms was associated with bursts of oxygenation of air:

          https://www.sciencedaily.com/releases/2019/05/190506111436.htm

          This was intermittent, so many life forms also went extinct as oxygenation ended at particular locations. It’s likely that there were discreet “refuges” of oxygenation separated spatiotemporally by nonoxygenated areas. This is a perfect scenario for life to evolve fundamentally different body plans and phyla. Eventually the whole atmosphere remained stably oxygenated and the separate refuges joined into a common living space. But the initial separation into “bubbles” could have been needed to generate the fundamental diversity.

          This scenario of intermittent oxygenation was far from idyllic so can’t be considered as optimal. But it was good that it happened, I guess.

          • IMO, the “explosion” was similar to the Triassic “explosion” of apparently new forms. In both cases, the explosion followed a major mass extinction event, ie the end-Ediacaran and end-Permian.

            What makes the Cambrian stand out is the increase in size and hardness of bodies, plus proliferation of senses in predators and their prey.

            It appears that an approximately 50% increase in O2 to about 25% of present level occurred during the preceding Ediacaran, driven by tectonics.

            https://www.nature.com/articles/s41467-019-10286-x

          • While it is off the topic of optimum temperatures and different climate cycles, what about the arguments regarding species presented in the video interview, supposedly based on current understanding of molecular biology and probability theory? Obviously, a great many species have come into existence so either the information presented is wrong (in what way?) or something else is at work. Please ignore the speculation presented about ‘what else’. My question is only about the arguments regarding the expressed difficulty of new species appearing.

          • Phil Salmon, Thanks for an interesting series of comments, very informative. Reading them, I perceive that the origination of complex phyla, as in the Cambrian, might have different environmental requirements than the preservation of species. By that I mean that optimal conditions for species is defined as the conditions that lead to fewer extinctions. These are the conditions that preserve existing species. Very different than the creation of new phyla.

          • Andy,

            There is no difficulty in the appearance of new species. As simply a consequence of reproduction, speciation can’t help but happen.

            New species are observed in the wild, created in the lab and can speciations found in nature can be recreated in the lab.

            No “mathematical” objections to these facts can possibly exist.

          • Andy and Phil
            I think that we need to make a distinction between multicellular forms evolving in the oceans and on land. The temperature ranges and rates of change are different for the two environments. Also, I seem to remember that some oceanic Precambrian forms became extinct before the Cambrian Explosion and certainly before the land was colonized.

          • John Tillman: No “mathematical” objections to these facts can possibly exist.

            Clearly you did not listen to the argument. It is rather more specific and rigorous than can be explained away by any general belief. The fact that a great many species existed, exist, and seem to continue to appear is not disputed. It is rather about the mechanism, the reasons that the generally accepted idea of random gene mutations cannot explain the observed facts.

            Clearly new species are not simply a result of reproduction. How many human bodies does it take to make that clear, not to mention termites? If a new species appears from reproduction, something very different had to occur in that one in umpteen billion times, or that one in a trillion trillion times.

          • AndyHce,

            I’ve listened to the same garbage for decades. It’s all based on a willfully ignorant false assertion as to how biology works.

            Each base pair is not individually reshuffled at each new generation, as the paid liars whose lies you’ve bought into know very well.

      • Phil,

        I think you mean animal phyla not “organisms”. The exact number which date from the Cambrian, rather than, say, the Ediacaran or Ordovician, is now subject to debate, but your general point remains valid, in the present state of our knowledge.

        However, countless animal classes, families, orders, genera and species have evolved since the Cambrian, not to mention fungi and plants, the latter of which didn’t exist in the Cambrian, plus protists, bacteria and archaea.

        • You are correct. Since my comments are always held in purgatory, I didn’t see your comment before making my one below.

          • Mine usually are, too. But on other rare occaisions, appear promptly.

            The cyberspace gods must be appeased, as so capricious.

      • It sounds extreme to say evolution “stopped” after the Cambrian explosion, and of course evolution never stops, species are continually evolved (closing sentence of Darwin’s Origin of Species). However I’m referring to the top level of taxonomic classification, the phylum or basic body plan. There are 19-20 of these, including the chordates, the molluscs, Annelida, arthropods, Cnidaria, echinoderms, nematodes, and a dozen other so others. No new phylum has arisen after the Ordovician AFAIK. Evolution now fine-tunes existing plans. This term “fine” has a specific meaning including what look like quite big changes. For instance within the tertiary over just a few million years evolution changed a cow into a whale. Both mammals. And made us out of old world monkeys.

        • Closer to a hippo than a whale, but point taken. An artiodactyl.

          You may well be right about no new animal phyla since the Ordovician, but please consider plants. Lots of phyla in the Silurian, et seq. I’m not qualified to comment on fungi, which were important in colonizing the land.

        • A couple points on evolution & “optimum conditions” — the “life expectancy” of a species is only on the order of 1 x 10^6 yrs; geologic epochs are measured in 10^7 or 8 yrs. The Optimum conditions for any given species are the ambient conditions while it’s in existence. If the conditions change, the species dies out or adapts. We might more meaningfully talk of Optimum Conditions for a whole biome. The best for tundra flora & fauna are not the best for a tropical rain forest biome, etc…..One might be tempted to say warmer conditions are “better” because there is more biodiversity, but in the event of a rapid change in conditions, it’s the generalist species that will provide the diverse pool of genes more likely to lead to adaptation & survival than the restricted gene pools of the highly specialized species.

          Back to astronomy: Our Sun wanders thru the galaxy on an orbit independent of the spiral arms? WUWT? Why are we so special?

          • Guido, Good point, although I think species may have a larger “life expectancy than one million years. One million years may be the average in an icehouse, but I think it is much longer in greenhouse conditions. Either way, given what we know about evolution and geological history, “optimum” for life on the earth’s surface, should be close to the average greenhouse temperature.

          • The standard estimate of the duration of an animal species is two million years, but some of course are shorter and others apparently much longer.

            It’s doubtful however that seeming “living fossils”, such as Oz lungfish and one or more tarsier species, could actually produce viable offspring with their ancestors of ten million years ago.

          • Guido, Andy, John
            I can echo your comments that species take about one million years to fully speciate into a new species from an evolutionary “parent”. Furthermore, the average lifetime of a species, once evolved, is again about a million years.

            This is an average of course, some survive much longer e.g. sharks, horseshoe crabs, others less.

    • Frisch and LaViolette separately put forward the theory that the start of the interglacial coincided with entry into a region of interstellar clouds.

      Previously, during past ~3 Myrs, the sun traveled between the spiral arms of the galaxy. See https://arxiv.org/abs/astro-ph/0601356v1, keywords “Local Bubble” and “Local Fluff”, and https://arxiv.org/abs/physics/0503158v1

      These theories do not depend upon a steady-state cosmic ray flux, but rather upon the frequency of extreme cosmic ray events.

      Entry into a spiral arm of the galaxy may also be significant due to proximity to near-earth supernovea (we would likely be further away, otherwise). See http://arxiv.org/abs/astro-ph/0110162v2

      • Been waiting for someone to bring this up.

        There is a self-described nuke physicist / engineer James Marusek who writes at the Impact blog who is of the opinion that crossing galactic arms brings the solar system in close proximity to multiple large stars and in turn multiple close supernovae over the course of a few millions of years. These bump up the incoming cosmic ray flux which cool the earth in times of quiet sun via the mechanism that Svensmark has described.

        If this guy is right, it is not crossing the arm, but the increased proximity to close supernovae and in turn the increased cosmic ray flux when they pop. Cheers –

        http://www.breadandbutterscience.com/

    • “GCRs arrive at Earth almost exactly isotropically [not depending on direction] suggesting that there is not any significant variation with location within the Galaxy, making the ‘spiral arm crossing’ hypothesis unlikely.”

      That was my thinking, too.

    • There is a lot of geological data regarding cosmic ray intensities on earth (14C and 10Be isotopes). The sun’s magnetic field has also a crucial role in modulating the amount of particles that reach the earth’s atmosphere. That this radiation appears to be currently isotropic does not mean that this is/was always true. It is even very probable that when our solar system travels through a high density region of our galaxy, that the cosmic ray intensity does increase since the amount of exploding stars in “close proximity” increases.

    • We are in an ice age now, so that would mean, according to the theory, that we are in a spiral arm now.
      If we are in an arm now, it may be difficult to say what is happening elsewhere.
      Would we not expect to see them coming from all sides if we are immersed in an arm?

    • Leif, I agree. During this solar minimum, earth has received more cosmic radiation due to the diminished solar magnetic field. This has increased earth’s average cloud cover, but it’s not clear if the radiation does this directly by ionizing air molecules or if it’s a byproduct of changing the pH of our atmosphere, the way hydrogen sulfide makes clouds out of humidity, or some other process like the creation of carbon 14 . Cosmic radiation levels found here:
      https://spaceweather.com
      Another angle that has not been considered is the efect of hydrogen gases like methane and ammonia on our oxygen atmosphere. (from our Sun or distant stellar explosions that fill the Local Fluff that the Solar system passes through) For example, northern lights when the sun is not active.
      https://spaceweather.com/archive.php?view=1&day=05&month=12&year=2019
      Whether it’s a coronal mass ejection, or interstellar gas caught in our magnetic field, the hydrogen burns producing water causing our ocean levels to rise. Very slow process normally, but there may be situations that occur, as described in the Noah story, that the burning gases remove oxygen from our atmosphere as it converts it to water, lowering the air pressure becoming colder to the point that the endless rain turns into snow that covers the earth in an ice age such as the woolly mammoth suddenly being covered in 100 feet of ice . (not liquid water as tradition insist but frozen water. The ark was a thick walled square shelter on the side of a mountain, not a boat)
      If the solar system passed through a thick interstellar gas cloud that dimmed the sun, converted our thick atmosphere into water, and covered mars with frozen gases (just like Europa and other outer moons) of which only Mars polar ice caps are remaining. This would also explain why earth has so much nitrogen. This is a plausible scenario that doesn’t involve comets, volcanoes, cosmic radiation, etc.

    • Vuk, These cycles are still with us, but they work on very short time frames, less than 120,000 years. They account for the occurrence of glacials and interglacials within an ice age, not the ice age itself.

      • Thanks Andy, just wanted to bring in name of my compatriot.
        I am admirer of Milutin Milankovic, not least that my university lectures took place in the same Belgrade university theatre where Milankovic gave his lectures in the subject of Applied Mathematics more than half a century earlier. However I’m toying with an alternative hypothesis based on the ‘helium flare’ cycles of about 100ky periodicity releasing ‘asymmetrically’ additional solar energy in less than 10ky, while both numbers have physical basis and are consistent with the temperature changes characterising the glacial cycles. As the sun is not very consistent with its sunspot ’magnetic flare’ cycles length (up to 15% variability) it is reasonable to assume that the ‘helium flare’ cycles variability could be of a similar degree.

        • Except that before the mid-Plesitocene transition, the cycles matched the 41,000 year tilt cycle.

          The transition to an apparent ~100,000 year cycle may best be understood, as Javier has it, as the average of 82 K and 123 K, ie two or three tilt cycles, as Earth has cooled, so that some nascent interglacials are stillborn as interstadials within continuing glaciations, rather than seeing life as fullblown interglacials.

    • Milankovitch cycles are flicker (OK, periodically forced, but still flicker)

      Flickering as an early warning signal

      Dakos V, van Nes EH, Scheffer M. Flickering as an early warning signal. Theoretical Ecology. 2013 Aug 1;6(3):309-17.

      Abstract

      Most work on generic early warning signals for critical transitions focuses on indicators of the phenomenon of critical slowing down that precedes a range of catastrophic bifurcation points. However, in highly stochastic environments, systems will tend to shift to alternative basins of attraction already far from such bifurcation points. In fact, strong perturbations (noise) may cause the system to “flicker” between the basins of attraction of the system’s alternative states. As a result, under such noisy conditions, critical slowing down is not relevant, and one would expect its related generic leading indicators to fail, signaling an impending transition. Here, we systematically explore how flickering may be detected and interpreted as a signal of an emerging alternative attractor. We show that—although the two mechanisms differ—flickering may often be reflected in rising variance, lag-1 autocorrelation and skewness in ways that resemble the effects of critical slowing down. In partic- ular, we demonstrate how the probability distribution of a flickering system can be used to map potential alternative attractors and their resilience. Thus, while flickering systems differ in many ways from the classical image of critical transitions, changes in their dynamics may carry valuable information about upcoming major changes.

    • Vuk: “Whatever happened to the Milanković cycles?”

      I wondered the same thing. I think probably they are covered by: “The forces and mechanisms that cause glacial advances and interglacials within an ice age are understood reasonably well and are well described by Javier, …”

    • Milankovitch theory that changes in solar insolation at 65N caused, the glacial/interglacial cycle, is a dead theory, not part of the solution.

      (A key observation that killed Milankovitch is the recent discovery that both hemispheres are cooling and warming in synchronism. That does not make sense as the solar insolation varies oppositely for the two hemispheres.) See reference below.

      There are more than at least a dozen paradoxes (observations that cannot be explained by Milankovitch’s theory.)

      The following is a partial list of some of the problems with the theory.

      1) The observational effects of that are found in the paleo record is physically impossible for changes in solar insolation at 65N to explain.

      The effect in the climate record is an order of magnitude too high and there is evidence of abrupt change, both hemispheres (same periodicity) not gradual change.

      https://news.wisc.edu/glacial-records-depict-ice-age-climate-in-synch-worldwide/

      Glacial records depict ice age climate in synch worldwide

      “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.”

      People who talk as if Milankovitch theory is alive use it to super there claim that there is some unknown super amplification mechanism that amplifies, solar insolation changes, when required but does not amplify at other times to cause climate oscillation in response to a large volcanic eruption.

      The Younger Dryas super abrupt cooling period (12,900 years before present) at which time the planet when from interglacial warm to glacial cold, with 80% of the cooling occurring in less than a decade, and the cold period lasting 1200 year ….

      … solar insolation at 65N was maximum for this cycle at the time of occurrence of the Younger Dryas abrupt cooling.

      … solar insolation at 65N is now the same as it was during the coldest part of the last glacial period.

      2) Unexplained change from a 41,000 year cycle to 100,000 year cycle. How does one explain the observation that the glacial/interglacial cycles started with a cycle periodicity of 41,000 years in duration and then 1.6 millions ago the cycle time changed to a cycle of 100,000 years (90,000 years glacial and 10,000 years interglacial.)

      http://en.wikipedia.org/wiki/Milankovitch_cycles#/media/File:Five_Myr_Climate_Change.svg

      2) Orbital eccentricity is the weakest of the orbital cycle modulation on insolation. Why does it dominate for the last 1.6 million years?

      3) The stage 5 glacial was terminated 10,000 years before the insolation change. There is no cause for that change. There is no back up forcing mechanism to terminate glacial periods.

      4) There is evidence in the paleo climate data of cyclic abrupt climate change. (Heinrich events, such as the 12,900 years BP Younger Dryas abrupt cooling event.) There is no forcing mechanism that explains the cyclic abrupt climate changes.

      5) The glacial and interglacial periods end abruptly. The paleo record supports the assertion that the mysterious cyclic abrupt climate forcing function terminates both the glacial and interglacial period.

      6) The cycle abrupt climate change cools both the Southern Hemisphere and the Northern hemisphere synchronously. This does not make sense at the Southern Hemisphere has maximum insolation in the summer when the Northern Hemisphere has minimum insolation in the summer.

        • Yes, however, that fact does not bring life to Milankovitch’s theory. There are dozens of observations that disprove Milankovitch’s theory.

          It is physically true that due to there being more land than ocean in the north hemisphere as compared to the Southern Hemisphere and the Northern hemisphere will amplify a forcing change.

          Think physical cause, not amplification.

          The paleo record shows glacial periods and interglacial periods end abruptly, not gradually.

          Milankovitch’s mechanism is slow and cannot produce rapid abrupt large cyclic climate changes.

          For example:

          The Younger Dryas (YD) abrupt climate change is an example of what the true mechanism must be physically able to cause cyclically. i.e. There are more YD examples in the paleo record.

          The earth 12,900 years ago when from interglacial warm to glacial cold with 80% of the cooling occurring in less than a decade and the cold period lasting for 1200 years.

          The YD cooling period occurred when summer solar insolation at 65N was maximum. he issue is what is the cause of the glacial/interglacial cycle and what is the cause of the cyclic warming and cooling that occurs with a periodicity of 1200 years with the same periodicity in glacial and interglacial period.

          … and from your link.

          “The perihelion is when the Earth is closest to the sun and that currently takes place in January.”

          So based on Milankovitch’s theory, currently summer solar insolation at 65N is minimum. So we should be in an ice age now if Milankovitch’s theory was correct.

        • This analysis shows that orbital position is not driving the cyclic climate change that is observed.

          Orbital position appears to amplifying or inhibiting a forcing mechanism that is cyclic and that comes in a small, medium, and super large version.

          https://www.sciencedirect.com/science/article/abs/pii/S0277379104000575

          Quantitative estimate of the Milankovitch-forced contribution to observed Quaternary climate change

          A number of records commonly described as showing control of climate change by Milankovitch insolation forcing are reexamined.

          The fraction of the record variance attributable to orbital changes never exceeds 20%.

          In no case, including a tuned core, do these forcing bands explain the overall behavior of the records.

          At zero order, all records are consistent with stochastic models of varying complexity with a small superimposed Milankovitch response, mainly in the obliquity band.

          Evidence cited to support the hypothesis that the 100 Ka glacial/interglacial cycles are controlled by the quasi-periodic insolation forcing is likely indistinguishable from chance, given the small sample size and near-integer ratios of 100 Ka to the precessional periods.

          At the least, the stochastic background‘‘noise’’ is likely to be of importance.

        • William Astley
          Your arguments are somewhat contradictory as you oppose Milankovitch forcing but concede pacing by the obliquity cycle. Which is hard to deny since every single interglacial since the mid Pleistocene transition/revolution coincides with a 6500 year lagged obliquity peak (thermal inertia). Or is the alignment in this figure coincidence arising from noise?

          https://curryja.files.wordpress.com/2017/04/figure-35.png

      • William Astley wrote and quoted:
        “Glacial records depict ice age climate in synch worldwide.
        . . . 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.’ ”

        These statements are inconsistent with the Scotese animation that is linked in the above article. Reference the interval of about 330 to 280 Ma . . . there is a huge disparity between the large ice cap around the Earth’s southern pole while at the same time there is no ice coverage around the Earth’s northern pole.

  5. Causes of icehouse climate, all of the following, in interaction.
    1. Cosmic rays
    2. Milankovitch cycles
    3. Plate tectonics – when the land prevents efficient mixing of equatorial and polar waters, then icecaps can form.

    • LarryD,
      The Milankovich cycles are too short to affect the ice ages, but they do affect the internal structure (glacial and interglacial lengths).

      #3 doesn’t cause ice ages, but it helps. I think when ocean circulation is maximal, it might prevent the formation of ice caps.

      • #3 might be a bigger factor. It seems that reductions in ocean heat transport efficiency, driven by plate tectonics, played a pretty big role in the onset of the Cenozoic ice age in the Late Eocene to Early Oligocene and also led to regime changes within this ice age (Pliocene to Pleistocene, Mid-Pleistocene to Late Pleistocene).

        That said, Shaviv’s hypothesis is definitely plausible.

      • LarryD and David,
        This is the configuration of the continents during the Triassic hothouse and after the Karoo Ice Age.
        250 Ma

        I do think #3 helps, but it alone obviously cannot cause an ice age. Given the Cenozoic it may make an existing ice age more severe. In the case of the Jurassic-early K cool period, perhaps good circulation prevented icehouse conditions.

        • Then we need to lobby NASA to make a paleoregolith coring project part of the Artemis Program.

          The Moon as a Recorder of Nearby Supernovae
          Ian A. Crawford
          Department of Earth and Planetary Sciences, Birkbeck College, University of London
          i.crawford@bbk.ac.uk

          Abstract
          The lunar geological record is expected to contain a rich record of the Solar System’s galactic environment, including records of nearby (i.e. ≤ a few tens of parsecs) supernova explosions. This record will be composed of two principal components: (i) cosmogenic nuclei produced within, as well as radiation damage to, surface materials caused by increases in the galactic cosmic ray flux resulting from nearby supernovae; and (ii) the direct collection of supernova ejecta, likely enriched in a range of unusual and diagnostic isotopes, on the lunar surface. Both aspects of this potentially very valuable astrophysical archive will be best preserved in currently buried, but nevertheless near-surface, layers that were directly exposed to the space environment at known times in the past and for known durations. Suitable geological formations certainly exist on the Moon, but accessing them will require a greatly expanded programme of lunar exploration.

          https://arxiv.org/ftp/arxiv/papers/1608/1608.03926.pdf

        • Also, Antarctica wasn’t over the South Pole then, and no land made it to the North Pole, either.

      • Ice ages occur when there is land over one (as now) or both poles, so tectonics do matter, IMO.

        Milankovitch cycles vary in length from axial precession’s period of 25,771.5 years to eccentricity’s major component period of 413,000 years, but also some shorter, yet still long, components. The probably most important cycle is axial tilt, with period of 41,000 years.

    • Larry

      One shouldn’t confuse glacial periods – “ice ages” in Andy West’s sense – with the glacial-interglacial flicker that occurs during an individual ice age such as the current Pleistocene.

      Glacial-interglacial flicker is a transitional phenomenon that occurs at the boundary of a transition into or out of an ice age. The system flickers between the greenhouse and icehouse attractors.

      As evidence of this, there is geological evidence of glacial-interglacial flicker at the end of the Cryogenian ice ages about 600 million years ago, before the Cambrian:

      https://www.nature.com/articles/ngeo2502

  6. Unfortunately omitted from this (almost) comprehensive analysis, is the effect of planetwide glaciation on different layers within the Earth.

    Under heavy glaciation that results in ice retention at the poles, the kilometers upon kilometers depths of ice causes the spin rate of the planet to increase. This results in differential rotational speed between the surface layers and the iron rich core; a magneto rotor/stator effect that forms the basis of, and creates the Earth’s magnetic field.

    So during heavy glaciation, the core is trying to “catch up” to the rotational speed of the surface; the catching up limited by the heavy viscosity of the in between layers.

    When the ice blanket over the polls diminishes at the ending of ice ages, the surface spin rate slows down, and at the crossover rate of surface versus core, the magnetic field flips, as it is now the core who spin rate exceeds that of the surface.

    We are presently in the latter phase where the spin rate of the core still exceeds that of the surface. But the differential is diminishing, and the current accentuated polar drift is just one piece of that evidence. The Song-Richards July 18 Nature report is another.

    A diminishing Sun and Ewing-Donn Arctic opening, resulting in Polar Easterlies “Ocean Effect” land ice accumulation around the Arctic looks to be the onset of the following Ice Age. Surface spin rate will then overtake the core, flipping the field, and adding another key to the keyboard of the piano key effect. Of course the Svensmark cosmic ray effect speeds up the process!

    • I doubt that those kilometers of ice would speed the rotation of the earth by more than a second or two, and it would take thousands of years for the full affect to be felt.

      The diameter of the earth at the equator is almost 6400km, while the drop in ocean levels is only a couple of hundred meters.
      This is partially compensated for by those kilometers thick ice sheets.

    • Honest noob question here: how exactly does ice accumulation at the poles cause the earth’s crust to gain angular momentum and / or velocity?

  7. My thoughts are that ice ages happen because the surface temperatures of the oceans. Surface temperatures of oceans means water vapour, more water vapour means more heat kept in. Today there is little place for warm water to create dense water that will go to the bottom of the ocean and create a warm planet everywhere. Because cold waters from Antarctica and Arctic are pushing cold water down to the bottom later to come back up creates a colder top layer. If the Panama Isthmus wasn’t created then the oceans could circle and keep a warm top but with it closed off the warm water doesn’t and you have cold water coming up on the west coasts of NA and SA from the rotation of the planet cooling the planet. The closed off Africa position without any shallow waters also doesn’t help. If you want to warm the planet to prevent the next deep glaciation just blast a waterway through Panama and let it free flow which the waters can then become dense enough in a high enough volume to not have 90% of the ocean being between 1-3 degrees. It would take millions of years to warm like it did to cool. But like any of us will see this.

    • Many scientists have theorized that during the last major ice age, sea level was low enough that the Bering Strait became a land bridge, which allowed people from eastern Asia to migrate to North America without using boats or ships. This land bridge may have extended as far south as today’s Aleutian Islands.

      But if the Bering Strait was dry, there would be no exchange of water between the cold Arctic and the warm Pacific, meaning that the northern Pacific Ocean along the southern coast of Siberia / Alaska might actually have been warmer during the last Ice Age than now, resulting in a mild, damp climate along the “land bridge”, which would be at low elevation, since it is underwater now. This could have provided a favorable climate for human settlement while vast areas of North America were under more than a kilometer of ice.

      As the glaciers melted and this coastal plain was flooded, people living there would be forced to migrate southeastward along the west coasts of Canada and the USA to find habitable land.

      Another interesting point from the article–if neither pole was ice-covered for 91% of geological history, how did polar bears survive the lack of ice?

  8. I should’ve added that the Nils-Axel Mörner Rotational Eustasy effect will serve to drain the Arctic Ocean, blocking ingress of warm water that keeps the Arctic Ocean Ice free during the Ice age’s build-up. Once that happens, the Arctic Ocean freezes over and the Ice Age ends, slowing spin rate, etc., etc.

  9. The Genesis account describes regarding the forming of earth’s atmosphere: “And God went on to say: ‘Let an expanse come to be in between the waters and let a dividing occur between the waters and the waters.’ Then God proceeded to make the expanse and to make a division between the waters that should be beneath the expanse and the waters that should be above the expanse.”—Gen. 1:6, 7.
    This expanse and water above is the Thermosphere. The earth was tropical in climate before the Flood.
    When the vast water canopy was released somehow this along with waters under the surface to come up from the ground caused the Earth wide Flood and caused the so called Ice Age when the Green house effect was broken. Is not true they have found 1000.s of Wooly Mammoths some with the flesh still edible with green vegetation in their mouths instantly frozen on the permafrost in Siberia?

    I suggest you read these two articles I think you will find them very infromitive
    https://wol.jw.org/en/wol/d/r1/lp-e/1968520

    https://wol.jw.org/en/wol/d/r1/lp-e/101975401#h=19:0-20:484

    Its too bad the communist professors in the Universities only have one agenda.

    • The Bible doesn’t say “expanse”. It says “raqiya”, which is an onomatopoetic word meaning “something pounded out”, akin to but not cognate with English “racket”. Hellenistic Hebrew scholars in Alexandria in the last centuries BC who translated the OT into Greek (the Septuagint or “Apostles’ Bible”) rendered it as “stereoma”, which Jerome put into Latin as “firmamentum”, hence “firmament” in the KJV. IOW, a solid dome covering the flat Earth.

      The dome had openings through which passed the Sun and Moon on their appointed rounds over the Earth, and through which fell rain, snow and other storehouses of precipitation, with levers operated by God. The singing host of stars hung from it.

        • Yet another terrible, tendencious translation. The KJV variously translates the same word as “circle” and “circuit”, meaning the “edge” of the earth:

          “It is He who sits above the circle of the earth, And its inhabitants are like grasshoppers, Who stretches out the heavens like a curtain, And spreads them out like a tent to dwell in.”

          Here we see the then current idea of God, as a larger than human being, but anthropomorphic, like the Greek, Roman and Norse gods, who sits on the edge of the flat Earth, looking down on us insect-like mortals.

          If this passage indeed means circle, as it almost certainly doesn’t, then, great, the flat Earth is shaped like a round plate.

          Elsewhere in the Bible, the flat Earth has corners, so is rectangular or square rather than circular.

          Even in the New Testament, long after classical pagans knew that the Earth is a sphere, from a high place Satan shows Christ all the kingdoms of the earth, which is of course impossible on a sphere.

          From Genesis to Revelations, the Bible is a flat Earth document, as the Early Church Fathers rightly insisted. Then Augustine argued that propagation of the faith was more important than biblical literalism. Thus, he argued for interpreting the Bible in ways acceptable to educated pagans.

          Calvin recognized that Genesis was wrong, in that there was not water above the Earth and below it. To him, this wasn’t a problem, since he was interested in biblical theology not “science”. He argued that the obviously false “scientific” bits were written so that ancient, uneducated pagans could understand it.

          • Flat earth? Are you kidding me?
            It takes so much more BLIND faith to believe in the science thats being pushed today than God’s word.

            The word circle can also mean Or “sphere.”

        • Sorry, but no one associated with the Jehovah’s Witnesses can possibly have any credentials.

        • Besides which, your useless link cites no scholar, so how could whatever credentials she or he has be evaluated?

          • Oh sorry, I meant Spiritual Credentials. Its funny, the Pharisees said the same thing about Jesus and his disciples..
            Jesus throughout his ministry constantly condemned the religious leaders of the day for their traditions and so called knowledge.
            READ Matt. chapter 23.

            As far as making an accurate as possible translation of the Bible, if you go on the web site, JW.org you will see a header that says English. Its a drop down menu and on the left you will see 1006 languages. Now if they can make a website that automatically Translate to 1006 languages plus Sign language I think they can figure out how to get the proper sense from the original Hebrew, Aramaic and Greek languages!
            There is nothing in the world like it, for free!
            REV 22:16
            “‘I, Jesus, sent my angel to bear witness to you about these things for the congregations. I am the root and the offspring of Davidu and the bright morning star.’”v
            17 And the spirit and the bridew keep on saying, “Come!” and let anyone hearing say, “Come!” and let anyone thirsting come;x let anyone who wishes take life’s water free.y

          • Translation credentials are based upon scholarship, not spiritual belief.

            The word in Isaiah doesn’t mean “sphere”. Ancient Hebrew had a word for “ball”, which is never used to describe Earth.

            Biblical cosmology is standard ancient Near Eastern, with a flat Earth covered by a dome. In the Egyptian version, the Sun traveled under the Earth to get back to the “place of his rising”. This wasn’t possible in the Hebrew version, since Earth was supported by pillars in the “waters beneath”. So the anthropomorphic Sun had to go around the outside of the dome to get back to the tent from which he emerged as a strong man, ready to run his race, or an energized bridegroom.

            https://biblehub.com/psalms/19-5.htm

      • Hey John
        I agree with to a certain extent what other Bible scholars have stated concerning the word Expanse.
        Here is a write up on why JW.s have used the word Expanse when translating the word [Heb., ra·qiʹaʽ]

        Give this a read please. JW.s are not out to deceive anyone but to enlighten!

        https://wol.jw.org/en/wol/d/r1/lp-e/1200001461

        • No you’re not. To deceive is exactly what you’re out to do.

          Your “translation” of the Bible is a pack of lies. Your cult is the enemy of the truth, not “The Truth” as your mendacious, child-abusing, cult masters so falsely claim.

    • Um…yeah. Only a few mammoth carcasses have been found with undigested food in the mouth. Most were not found in this condition. Since only a few have been found like this, the likely explanation is falling through late spring ice or being swept away in floods. In Yakutia, around 140 mammoths were found in a single spot, probably swept there by a flood.

      I wouldn’t recommend taking an ancient Jewish description of the creation of the earth literally because there is abundant scientific evidence that it didn’t happen in six 24-hour days. Likewise there is no scientific evidence of a global flood, and certainly not in the last 6,000 years. That doesn’t invalidate the moral lessons taught in the scriptures, but if you take it literally you’re going to tie yourself in knots.

      An important question to ask when reading those stories is “what was the author trying to convey?” Remember, the author wasn’t God. The authors of the books in the Old Testament were human; some (very few) described a profound spiritual experience, some described an interaction with God or a messenger from God (a few), some described the moral decay of their people, some related the historical events (wars and such) of the time that appeared to fulfill a warning by an earlier prophet, some laid down detailed laws of moral conduct, personal hygiene, property and trade, conflict resolution, religious observances (for their time), some described their spiritual struggles and resolutions lyrically. It makes much more sense when you read it with that understanding and it’s easier to derive and appreciate what they were trying to convey.

      • As the Bible advises: “Test all things; hold fast what is good.”— Thessalonians 5:21 (NKJV).

        There is no qualification to the word “all”; therefore, such testing does NOT exclude the Bible itself nor ANY translation of same.

        The Bible also offer this: “”Professing themselves to be wise, they became fools.” — Romans 1:22 (NKJV)

        I offer that any religious zealot lecturing a scientist—and conversely, any scientist lecturing a religious zealot—be mindful of that second quote.

      • JWs go to great extent to lie shamelessly. They have no spiritual credentials whatsoever.

        However we do have them to thank for the Supreme Court decision Barnette, overturning a contrary decision of just three years prior.

        Where however is there a JW hero to match the Adventists’ Desmond Doss?

        • 1 For 3:18 Let no one deceive himself: If anyone among you thinks he is wise in this system of things, let him become a fool, so that he may become wise.u 19 For the wisdom of this world is foolishness with God, for it is written: “He catches the wise in their own cunning.”v 20 And again: “Jehovah knows that the reasonings of the wise men are futile.”

          I am positive that the science of this world is not going to save you from God’s wrath on this wicked system of things.

          Proverbs 21:30 There is no wisdom, nor discernment, nor counsel in opposition to Jehovah.j

          • I’ll take my chances.

            My bet is that trying to follow Christian precepts beats blasphemous bibliolatry and intolerance.

            Again I ask, what have Jehovah’s Witnesses contributed as a group comparable to their fellow fundamentalists the Seventh Day Adventists, so prominent in, among other fields, medicine, as exemplified by Dr. Carson?

            All you’ve achieved is irritating your neighbors by uninvited doorbell-ringing. How many real Christians have you ever converted to your blasphemous cult, let alone agnostics, atheists of people of other religions, through your annoying intrusions?

          • John, when people have to resort to name calling and derogatory comments to try and win an argument, they lost!

            I’m surprised you didn’t also throw in names like, racists, white supremacists, Nazies etc. about us like all the learned kids coming out the Marxist Indoctrination centers have been taught pushing their Leftists agendas.

          • Craig,

            No name calling. Just the facts, which you can’t handle. Your cult not only mistranslates the Bible on purpose, but shuns those who reject its authoritarian dictates and exposes its protection and promotion of child sexual predators. Please free yourself from the Satanic cult in which you’re trapped.

  10. Based on observations of the evolution of stars similar to out Sun, astronomers believe that the solar energy reaching Earth likely increased by a few percent over the past 500 Myr. This ought to have been sufficient to slowly warm Earth by several degrees, but apparently did not. Other long-term factors are likely involved.

    • Since solar power increases by about one percent per 110 million years, its radiation has grown by some 5% during the Phanerozoic Eon.

      Yes, in the geologically short term, solar output is just one factor in major climatic “house” switches. But in the longer term, it’s a killer.

  11. This is a fascinating theory, except for the fact that it doesn’t include CO2, so therefore is not acceptable to Climate Science.
    The rest of us can appreciate it though.

  12. Perhaps some complex combination of Svensmark and Milankovitch cycles is the more complete answer to long term climate.

  13. One possibility is that the atmosphere gains or loses mass. For instance, it’s much easier to explain dinosaur flight if the atmosphere was denser.

    There’s all kinds of speculation on the web about the thickness of the atmosphere at different times. Usually I provide a link, but there’s so much stuff and it may be contradictory. I don’t know where to start.

    At any rate, the first order approximation to the planet’s surface temperature is based on the mass of the atmosphere and the resulting lapse rates.

    Why would we assume that the mass of the atmosphere is constant? atmospheric escape If we were slowly losing atmosphere, then you would think the planet would be slowly cooling.

  14. Figure 7 is a powerful insightful graph.

    During the last 700,000 years, Antarctica has been usually MUCH colder than present.

    There have been some brief (10-20k year) warm as present intervals, but they are sandwiched in between long (60-100k year) intervals that are COLD.

    Mankind’s climate change concern should obviously contain a fear of global cooling component, especially with 10k year focus.

    Maybe that’s something the catastrophic alarmists can focus on tomorrow…?

  15. I’d be interested to know why there are continental shelves. I have a thought experiment going that they represent the long term continental edges because ice ages are the normal condition of the earth.

  16. I’m having trouble with the word “permanent” used lots of times in the article. If it’s permanent, why is it there only 9% of the time? I suspect you mean that it doesn’t disappear in the summer months, and this is really picking at nits, but it bugs me just the same. Otherwise thanks for the article — I enjoyed it.

    • Sorry, but I meant long-term, many millions of years and they have to be very thick, thousands of feet. Permanent seemed the most appropriate word. I wanted to exclude thin ice caps that only lasted a few decades or centuries. Those happen all the time in geological history.

  17. “causal link has not been demonstrated to everyone’s satisfaction,”

    I always wonder why there is no citing of the Wilson Cloud Chamber (invented around the turn of the 20th Century) in discussions of cosmic rays and clouds. Cosmic ray collisions with molecules in the atmosphere create a variety of atomic particles that were detected and identified as temporary streaks of clouds in the wake of the particles in the cloud chamber. Wilson got a Nobel for it and others got Nobels using it. To me, knowing this gives more credence to Svensmark’s theory. The cloud chamber must have given Svensmark the sctual idea – perhaps he cites it in his papers.

    https://en.m.wikipedia.org/wiki/Cloud_chamber

    • Good point, thanks. I don’t remember the Svensmarks mentioning it, but I haven’t read all of their papers or presentations.

      • In the video, The Cloud Mystery, Svensmark mentions that someone came into his office and mentioned cosmic rays and he immediately thought of an experiment he had done in high school science class with a cloud chamber and that was what gave him the idea that cosmic rays might affect clouds. Start at about the 6:45 time of the video.

      • Most of the criticisms of Svensmark’s theory is that the initial nuclei formed from the GRC collision is many times smaller than the nuclei that form cloud droplets. Around 1987 this was a stumbling block, but further work at CERN has encouraged him in the concept.

    • I’ve wondered that as well. Wilson discovered cosmic rays in his Cloud Chamber accidentally, he was researching cloud formation if I remember correctly.

  18. The arrival of the Antarctic land mass (a craton in geologic speak) over the Southern pole some 30 million years or so ago, along with the simultaneous pushing up to the Himalayan Plateau and ranges was pivotal in the continuing evolution of Earths climate and to biosphere-life as it adapts to existing niches lost and new ones formed. The resulting rearrangements of ocean THC flows, albedo increases due to snow cover, geo-weathering and CO2 removal/sequestration, imbalances in NH and SH land-ocean ratios, and steadily rising ice surface over Antarctica (to over 3000 meters with significant pushing down of the craton into the lithosphere) are all complex factors in how the Quaternary began, maybe with the final straw being the closure of Panama Straits linking two great oceans near the equator and shutting off a balancing heat exchange.

    Thus our global climate today cannot be understood outside the the context of what came before, the geological record as Andy discusses here.

    In consideration of all that has come before, and the current Ice House age we are still in, the idea that an increase of CO2 as a trace gas from 3parts/10,000 to 6 parts/10,000, and that will somehow lead to global mass extinctions/cataclysms should be dismissed as simply ludicrous and recognized as the purely political agenda it is.

    George Carlin’s comedy monologue of “Save the eff’n planet??” comes to mind.

  19. It always surprises me that greens see the earth as static, to be preserved from change. The notion that all is ‘good’ except for the evidence of human occupation has a long history in the Judeo-Christian tradition, going back to the original sin. In the 19th C, Heber wrote:
    What though the spicy breezes
    Blow soft o’er Ceylon’s isle,
    Though every prospect pleases,
    And only man is vile:
    At that time, the vileness could only be treated by conversion to Christianity: now the solution seems to be elimination of 9/10ths of the population. (or not using plastic straws).

    • Fran, Religion is in our DNA, if traditional religions don’t work for some people, they turn to environmentalism. All religions are the same in that “we” [I and my fellow religious believers] are good and will save the planet and our souls by forgiving or converting or fighting/destroying/killing, etc. all who disagree with us. They also all seem to have doomsday predictions, the second coming, climate catastrophe, Shiva takes over, the end days of the Mayas, or some other myth of global destruction. Not sure how much is nature and how much is nurture, but these things have been around as long as man. Look at Gobekli Tepe, they built it to worship in it 12,000 years ago, then buried it when rapid sea level rise started to protect it from the rising water. Rationality always seems to take a back seat to religion.

      • Yes, religion began in part in the hope that the local tribal gods and spirits could not only provide their adherents with sustenance, but help to defeat their enemy tribes in the battles over resources.

      • PS: Yahweh started out as such a chief tribal god, in the “my god can beat your god” vein, before morphing into a monotheistic god, however accompanied by angels, etc. Perhaps under the influence of brief Egyptian monotheism, under King Tut’s strange dad.

  20. “GCRs arrive at Earth almost exactly isotropically”

    Sounds like a good criticism of the essential theory of earth being directly affected by some kind of proximity based galaxy GCR variation. Yet one must account for the variation in GCRs arriving at earth over time as found in studies perhaps in time with passing through galaxy arms.

    One argument might be some effect from passing through galaxy arms not directly due to proximity-based GCR variation; but instead may be an effect on the solar wind via whatever proximity-based mechanisms cause variations in that. Oh oh!

    • It takes distance for a weak magnetic field to affect the direction of a GCR.
      That a location that is well away from any sources would receive GCRs from all directions, does not prove that a location that is surrounded by nearby GCR sources would not receive more GCRs.

  21. “Low-level clouds cool the planet because they reflect more thermal energy than they trap under them.”

    Hmmm, I always thought it was the opposite…

  22. I tend toward Lief’s skepticism. One obvious reason (if we can believe the graph showing the last 750 Ma) is the abrupt changes to interglacial periods and the rather cyclic nature. Since cosmic ray flux is highly dependent on both the proximity and strength of exploding stars in the milky way galactic arms, what are the odds that we would pass through several arms to encounter precisely equivalent flux density changes that trigger both a similar magnitude and periodicity of the interglacials shown in the graph? Is there a force much closer to Earth that might explain this? Perhaps our own star?

    • The idea is that the ~150 million year cycle sets up Icehouse conditions, but other factors determine whether major glaciations occur or not.

      There was for instance a relatively cold interval in the generally balmy to steamy Mesozoic, but tectonic and oceanic conditions weren’t conducive to formation of continental ice sheets. Rather there were montane glaciers and cooler climate, perhaps encouraging the evolution of feathers among dinosaurs.

  23. Making up data – As a geophysicist I hav been known to generate a closing contour of the third kind.

  24. Phil Salmon, So your argument is that evolution stopped at the end of the Cambrian explosion? I find this very hard to accept. What species living today, evolved in final form in the Cambrian?

  25. High solar minimum GCRs didn’t stop the ocean and troposphere from warming in 2019.

    If only Svensmark’s idea worked in the real world…

    • The sort of GCR flux postulated for driving major ice ages isn’t an annual sort of thing. It would be significantly elevated for 10’s of millions of years.

      • One implication of GCR flux significantly elevated for 10’s of millions of years is the solar activity was quite likely very low for long periods, with commensurately long-enduring TSI, with clear cooling implications, together with the long-term orbital changes.

  26. Andy, very nice interesting post.
    Glaciation phases – into and out of are multifaceted complicated processes.
    We know from recent studies that Greenland ice melt and Arctic sea ice extent / volume are primarily controlled by atmospheric ingress primarily by lower and mid latitude convection = atmospheric displacement plus heat. Current science pays no attention to variances to daily, monthly and yearly convection volume patterns. Convection occurs in pulses, not a constant boiling pot process. This has never been considered from what I have read.

    There is the dust theory as a catalyst when moving into inter glacial phase. But what carries the dust to the higher latitudes during this phase, it is the wind – atmospheric ingress at increasing rates from lower latitudes. Yes the dust plays a part of increased surface heat uptake, but the wind has a far greater role for heat transport and sublimation effects. Just look at the rapid changes of surface melt for very short periods (days) in Greenland.

    Some of my own research has been focused on how to identify and quantify convection volume, timing, and the annual hemispherical differences in volume and the many associated downstream outcomes. Some years the NH has a noticeably higher rate that the SH for example, some years the hemispheres are balanced, then vice a versa. 2012 for example had a higher volume of convection in the NH compared to the SH. This convection process has a major role in temperature outcome that people take so seriously. Temperature records are not a very accurate measure of the work done, the effect on climate and the current state and direction. Temperature record should be one of a number of lets say KPI’s
    With best regards
    Martin

  27. Dear Mr. May,

    What a wonderful essay! I’ve been waiting for just this! And Christopher Scotese’s “movie” is excellent.

    The take home for me is that a degree or two or five of warming is nothing to fear. Global warming, should it occur, would be a Good Thing, a boon to all life, a return to normality and the normative Earth.

    The paranoia regarding a possible slight warming is entirely unfounded. So-called scientists who wish to exterminate all the cattle, spew aerosols into the sky, soil the oceans with rust, sequester CO2 in caverns, ban farming, air flight, diesel, gas, coal, and natural gas, and inflict dozens of other crazy expensive “solutions” to a non-problem should be forced to read this essay a hundred times, and be tested on it, and required to memorize key passages.

    Warmer Is Better. Warmer Is Normal. Life Requires Warmth. Those who crave the deep cold are cordially invited to go live in Antarctica or on the Moon.

  28. “and, so far it has lasted about 2.6 million years”

    Much longer. The first continental ice sheet in Antarctica started about 35 million years ago, and Antarctica has been continuously glaciated for about 14 million years.

    It is true that there were no really large continental ice-sheets in the northern hemisphere before 2.6 million years ago (with one exception, see below), but there has been montane glaciers in Greenland-Svalbard and Alaska almost as long as in Antarctica.

    However there was at least one fairly major glaciation in North America, Greenland and Iceland during the Pliocene (MIS M2 c. 3.3 MYA). However this is not talked about by the right-rhinking since it happened during a interval with high CO2 which is supposed to be impossible.

    • tty, You are correct. Technically the most recent Ice Age started 30+ million years ago when the first large continental glaciers developed on Antarctica. I stand corrected.

    • Yup. IMO there’s pretty good support for at least an ice cap on southern Greenland in the Pliocene, and maybe along the NE coast.

      But it took complete closure of the already shoaling Interamerican Seaway to initiate ice sheets in the NH. A shallow version of it might have reopened around 1.8 Ma, which used to be the Pleistocene boundary before the Gelasian Age was, IMO, correctly moved from the Pliocene to the Pleistocene, leaving not much of the former.

      • The highlands of Northeast Greenland were definitely extensively glaciated in the Neogene. The fjords there are the largest in the World and must have taken a very long time to form. And at Scoresby Sound, the largest fjord of all, there are Late Pliocene/Early Pleistocene deposits (Lodin Elv Formation) inside the fjord, so it already existed then.

        • Thanks.

          The fact that much of the Arctic Ocean shore was surrounded by boreal forest during the Pliocene isn’t the whole story. Higher elevations exposed to moisture-bearing winds in the Arctic were indeed icy.

          Fjords, aka “the squiggly bits”!

    • Steven, Go to the source, Chris Scotese’s report for the details and the uncertainty. 54 pages of excruciating details, 15 pages of footnotes, and 13 pages of bibliography. Lots on uncertainty.

  29. It is about time someone actually did an article on the REAL state of the Earth! Pleistocene ice is still around today. Barnes, Greenland, Antarctica? Great job Andy!

  30. In this video, Jasper Kirkby discuses the Cloud findings and states that cosmic rays enhance cloud condensation nuclei when the aerosols are biogenic and says that before the industrial revolution this was the primary way clouds were formed. He goes on to state that they are mostly formed today by sulfuric acid from pollution.

    https://www.youtube.com/watch?v=8M3up6T9Zeg

    However his conclusion would not appear to be the case in the Southern hemisphere, which is the cloudiest part of the earth and where only 10% of its population lives.

    See https://advances.sciencemag.org/content/1/6/e1500157

    “The Southern Ocean (SO) is an expansive and dynamic ocean with rich ecosystems remote from most human influences. It is also the cloudiest region on Earth. These clouds influence the atmospheric and oceanic circulation of the entire Southern Hemisphere and beyond (1), and may help determine the Earth’s climate sensitivity (2). Its remoteness from anthropogenic and natural continental aerosol sources makes the SO a unique natural laboratory for our understanding of aerosol-cloud interactions. Aerosols influence clouds by acting as the cloud condensation nuclei (CCN) on which cloud droplets form, and the resulting concentration Nd of cloud droplets influences the amount of sunlight reflected by clouds (3). Aerosol processes remain a poorly understood influence on clouds (4). Processes regulating the concentration of naturally occurring aerosols, in particular, remain a major source of uncertainty, limiting our ability to quantify the magnitude of the human impact on climate from aerosols (5, 6).

    The rich biological activity in the SO produces a range of biogenic aerosols and aerosol precursor gases (7). Marine biogenic emissions influence atmospheric aerosols in this region, both through primary emissions of organic matter in sea spray aerosol (SSA) (8) and through secondary aerosol formation processes, that is, the condensation of volatile sulfurous and organic compounds (7–9). ”

    So the cloudiest part of the world, where Svensmark’s hypothesis is most likely to be true and having significant effect today is in the part of the world least accessible to humans, and where there are very few land based temperature measurements since 80% of the Southern hemisphere is ocean, and a significant part of the southern land mass is Antarctica.

  31. Well, I like this kind of thing, something that looks back as far as possible and points out several things, e.g.,
    – the Earth is physically active, changing “dry” land shapes on a recurring basis
    – the climate, per the fossil records, changes on a recurring basis with NO interference from anything other than the planet itself
    – and that part about the cause of these and those changes in the climate and what caused them.

    We’re fortunate to have evolved in a Hooman-friendly climate period. Having just watched an informative and interesting video about Neanderthals and H. Sapiens getting together to produce so-called Modern Man, and this during the Pleistocene when things were not really user-friendly, I’m inclined to think we’re lucky to have survived anything at all. No, I have not had my DNA tested to see how much Neandertal DNA I have, but I may do that out of curiosity some day. It might explain why my brother is frequently a colossal jerk. But I digress.

    I’m most interested in the Silurian and Carboniferous periods, which were warm, tropical and heavily oxygenated, which I’ve mentioned before, and what may have brought those to a close. There are still some survivors from the Carboniferous, such as the horsetail reed and shrimp, and I have fossils of both of those. I live where there used to be a river delta that emptied into a shallow ocean of the Carboniferous, north of the what is now the Mazon Creek fossil district near Braidwood, IL, an area awash in coal from that time so long ago. I have a bunch of fossils I found down there. I’m more interested in what ended all of that, than in quibbling over how continental drift was the cause of this or that, or something like that.

    And where was our Solar System when the Silurian and Carboniferous periods were underway, anyway? That was a prolonged time ago, and many species of bugs, including spiders and centipedes, existed back then and still exist today. And was that hyperoxygenation caused by excessive warmth which boosted the plant population and density enormously? Or was it something else? And are we going to face it again, or face extreme cold and heavy precipitation?

    Anyway, I did enjoy that article although I did not see a button to push for what was supposed to be animated.

  32. Am I the only one who doesn’t get this? The primarily driver isn’t cosmic rays, though possibly that may contribute slightly, it’s obvious that continental positions is the overwhelming driver behind long term icehouse or greenhouse eras. Consider what’s happened during the Cenozoic:

    Antarctica sits over the southern polar region with no land around it to the north, allowing circumpolar oceanic circulation to isolate it

    The Northern Hemisphere has a lot of land at subarctic latitudes that have closed off most of the Arctic Ocean

    The closure of the Panama Isthmus, preventing warm Pacific water to get even warmer

    The locations of the Rockies, Cascades, and Himalayas

    Continental drift/development is everything. Other factors may contribute or mitigate, at best.

    • “Am I the only one who doesn’t get this? The primarily driver isn’t cosmic rays, though possibly that may contribute slightly, it’s obvious that continental positions is the overwhelming driver behind long term icehouse or greenhouse eras. ”

      I agree that cosmic rays, is not primary driver of global climate. But cosmic rays probably affect weather and perhaps a significant effect upon global weather.
      But I have question, also, don’t people understand that an Ice Age is about having a cold ocean?
      So “the continental positions” are important in terms of how they produce a cold ocean. Or whether the continental positions produce a warm ocean.

      So we in an Ice Age because we have polar icesheets AND because we have a cold ocean.
      Glaciers {permanent or otherwise} aren’t even a key aspect. A icehouse climate is cold ocean and hothouse climate is warm ocean.
      Our ocean is cold, it’s got average temperature of about 3.5 C.
      In our Ice Age the ocean has been as cold as about 1 C and has been as warm about 5 C

      “As Figure 1 makes clear, the “normal” or “optimum” global average temperature of the Earth is 19.5 degrees C. or 67 degrees F. This is over 5 degrees C. (9 degrees F.) warmer than today. ”

      I would say “normal” is ocean which is 10 C or warmer. And hothouse is ocean 15 C or warmer.

      But I would say with our “continental positions” “normal” is ocean with temperature of 1 to 5 C.
      Regarding this:
      “Figure 1. Christopher Scotese’s geological interpretation of Phanerozoic global temperatures in degrees C. The vertical line on the right side, labeled “PAW” is a projection of possible anthropogenic warming according to a pessimistic IPCC climate model. ” {global average temperature of PAW: 19.8 C}

      I think you might be able to get a global average temperature of 19.8 C, but I think you need a ocean with an average temperature of about 5 C. Or you need to increase the average temperature of the entire ocean by 1.5 C. And that seems pretty much impossible anytime soon. In terms of within 100 hundred it seems possible that ocean could warm by .5 C or our ocean could have average temperature of around 4 C.
      And if ocean become 4 C, that would have fairly dramatic effects. for example with ocean of 4 C, we would have ice free polar sea ice in the summertime.
      And Canada which presently has average temperature of around -4 C, should get it’s average temperature up to around 0 C.
      Also we get about 1 foot of sea level rise due to the ocean thermal expansion.
      And if talking about a few centuries, than the ocean could get average of about 4.5 C and with again very dramatic effects.
      But there no indication that our ocean will warm by .5 C within century or even a few centuries.

      • The ocean can’t possibly warm that much within a few centuries for the very good reason that the turnover time for the deep ocean is on the order of 1,000 years.

        And the ocean can’t warm 5 degrees in a millenium even if the production of NADW stops completely. It would also require that the production of AABW stops, which requires that the katabatic winds off East Antarctica stops, which requires that East Antarctica becomes ice-free at least near the coast.

        Ain’t gonna happen in a millenium or ten.

        • “And the ocean can’t warm 5 degrees in a millenium ”
          Nor cool by 5 C within a millenium.

          I think it is possible that our ocean did cool .5 C within a millenium.
          Or I think think our ocean did cool .5 C or more, since the time of the Holocene climatic optimum:
          “The Holocene Climate Optimum (HCO) was a warm period during roughly the interval 9,000 to 5,000 years BP, with a thermal maximum around 8000 years BP. It has also been known by many other names, such as Altithermal, Climatic Optimum, Holocene Megathermal, Holocene Optimum, Holocene Thermal Maximum, Hypsithermal, and Mid-Holocene Warm Period.”
          https://en.wikipedia.org/wiki/Holocene_climatic_optimum

          And I think it’s possible that within the last 5000 years, the ocean has cooled .5 C or less

          I also think The Little Ice Age may have cooled as much .2 C and the since the LIA the entire ocean may have warmed as much as .2 C. Though ocean may started warming prior to 1800 AD or before the accepted end of LIA which is largely agreed to be about 1850 AD.

          But generally I think 1 C of warming or cooling can occur in about 1000 years, but that quite fast and normally it takes a lot longer to change by 1 C. Or having ocean temperature stay within 1 C for a ten thousand year or longer period is common or ordinary.

          Or if increased CO2 levels can change the ocean temperature by 1 C within 1000 year, it proves that CO2 is a major control knob of global climate.
          And, I don’t think it is. Though CO2 levels such as more than 1000 ppm might warm the Ocean by 1 C within 10,000 years.
          Or it’s 1/10th or 1/1000th of what some people imagine it is.

    • Continental drift/development is everything. Other factors may contribute or mitigate, at best.

      Johne, I don’t think so. Below is the continent configuration 250 Ma during the Triassic hothouse.

      250 Ma

  33. Christopher Scotese has indeed made a terrific animation of both tectonic plate movement and ice ages coming and going. It emphasizes how rare it is over time for Earth to have ice covering at least one pole for any considerable length of time (i.e., for more than one million years continuous).

    Assuming the animation correctly portrays ice coverage in white (I have no reason to believe that it doesn’t), it invites this question: Why, during the peak of the Karoo Ice Age, right around 300 million years ago, when there was a truly massive area of ice around Earth’s south pole, was there no ice coverage at Earth’s north pole?

    I believe the correct answer to that question would show that we understand the primary driver(s) of climate. But as far as I know, we have no good answer. Note that the south pole ice cap of the Karoo Ice Age lasted some 50 million years (from about 330 to 280 Ma) so it would have withstood multiple Milankovitch cycles of any type.

    What created the huge climate asymmetry between Earth’s northern and southern hemispheres for such an extended period of time?

  34. John Tillman:

    “If the LIA date from c. AD to 1850, and the MWP from c. 950 to 1400, then the former did suffer more VEI 6 or 7 eruptions than the latter (earlier), but each interval experienced just one magnitude 7 event”

    The start of the LIA has also been more properly stated to have begun with the VEI7 eruption of Samalas (Rinjani), in 1257, which would include the VEI5 eruption of Katia in 1262, and the string of six VEI5 eruptions of Tarawera (N.Z) in 1310, 1311, 1312, 1313, 1314, and 1315, whose cooling caused the Great Famine of 1315-1317, with ~ 7,500,000 deaths in Europe, alone. It does not require a VEI7 eruption to cause global cooling (even VEI4 eruptions produce measurable cooling, although of a smaller magnitude).

    You also state that “IMO warm and cool cycles are better explained by solar activity ”

    It is IMPOSSIBLE to determine solar activity from proxy measurements at the Earth’s surface , since intervening layers of SO2 aerosols in the atmosphere will cause cooling , which will show up in tree ring measurements, and reduce the flux of incoming incoming cosmic radiation, giving the false impression that the sun’s output has diminished.

    Only since the advent of satellite measurements from above the atmosphere has it been possible to detect changes in solar irradiance

  35. It is far from impossible, indeed the opposite. SO2 from eruptions are short-lived.

    We know that the 1257 eruption didn’t end the MWP because the second half of the next century returned to warmth, despite the Wolf minimum of 1280 to 1350.

  36. Bindidon:

    Re your earlier post of large volcanic eruptions during the LIA.

    “Volcanoes of the World”, 3rd edition (2010) has similar listings, but does not show 3 VEI6 eruptions on your list (1452, 1641, 1650–your data may be more recent), and 3 VEI6 eruptions which are not on your list (1600, 1783, 1809) The listing which follows includes VEI5 eruptions, which can cause significant additional cooling, especially if they erupt during La Nina conditions:

    1257 Rinjani, Indonesia (VEI7)
    1262 Katia, Iceland VEI5
    1280 (?) Quilotoa, Ecuador (VEI6)
    1310 Tarawera, N.Z. (VEI5)
    1311 ” ”
    1312 ” ”
    1313 ” ”
    1`314 ” ”
    1315 ” ”
    1350 El Chichon, Mexico (VEI5)
    1352 Oreafajolkull, Iceland ((VEI5)
    1370 Soufriere, West Indies (VEI?) (Plinian)
    1380 Parker, Philippines (VEI?) (Plinian)
    1440 Soufriere, West Indies (VEI?) (Plinian)
    1450 Pinatubo, Philippines VEI5?)
    1471 Sakura-jima, Japan ((VEI5?)
    1477 Bardarbungua, Iceland (VEI6)
    1480 St. Helens, U.S. (VEI5+)
    1482 ” (VEI5)
    1550 Pago, SW Pacific (VEI?) (Plinian)
    1563 Agua de Pau, Azores (VEI5?)
    1580 Billy Mitchell, SW Pacific (VEI6)
    1586 Kelut, Java (VEI5?)
    1593 Raung, Java (VEI5?)
    1600 Huaynaputina, Peru (VEI6)
    1625 Katia, Iceland (VEI5)
    1630 Furnas, Azores (VEI5)
    1631 Vesuvivus, Italy (VEI5?)
    1632 ” ”
    1640 Komaga-take , Japan (VEI5)
    1641 Parker, Philippines (VEI5?)
    1650 Shiveluch, Kamchiaaika (VEI5)
    1660 Long Island, New Guinea (VEI6)
    1663 Usu, Japan (VEI5)
    1667 Shikostu, Japan (VEI5)
    1673 Gamkoanora, Indonesia (VEI5?)
    1680 Tongkoko, Indonesia (VEI5?)
    1707 Fuji, Japan (VEI5)
    1721 Katia, Iceland (VEI5?)
    1739 Shikotsu, Japan (VEI5)
    1755 Katia, Iceland (VEI5?)
    1783 Grimsvotn, Iceland (VEI6)
    1800 St. Helens, U.S. (VEI5)
    1800(?) Pago, SW Pacific (VEI?) (Plinian)
    1809 Unidentified (VEI6)
    1815 Tambora, Lesser Sunda Is. (VEI7)
    1822 Gallunggung, Java (VEI5)
    1835 Cosiguina, Nicaragua (VEI5)

    In addition to the above list, the reference shows 95 VEI4, VEI4?, and VEI4+ eruptionss.

    Plinian eruptions are explosive eruptions where the VEI has not been determined, as yet, and can range
    between VEI4 and VEI7. They have been included as VEI?, since some may eventually be found be VEI5, or higher.

      • But… let me add a detail or 2:

        – 1600 Huaynaputina, Peru, VEI 6 was on the list;
        – the list was restricted to huge eruptions which occured before Maunder start, due to the context it was published around.

        • Bindidon:

          Thank you for the correction and comment!

          My reference did not include the VEI6 eruption of Kuwae in 1452, or the VEI6 eruption of Kolumbo in 1650, although they are included in the Wikipedia list of large volcanic eruptions, and need to be added to my list.

          Note that within the ~70 year Maunder Minimum there were 11 VEI4 eruptions, 6 VEI5 eruptions, and 2 VEI6 eruptions, which occurred in a climate already cooled by prior large eruptions, worsening their effects.

          They easily explain the cooler temperatures of that era; no need to invoke any supposed change in sunspot activity, which is actually impossible to determine from proxy measurements at the Earth’s surface.

  37. I think of this in terms of external climate forcing at three different scales.
    Milankovic cycles are at the scale of 10,000s to millions of years, caused by orbital eccentricity, obliquity and precession. That stroke of genius has stood the test of a century of time. However, it is insufficient to explain all external climate forcing for all of Earth’s history. Geologists know there is climate change on the scale of 100 millions to billions of years. Nir Shaviv’s idea on the solar system’s position with respect to the spiral arms of the Milky Way Galaxy may be the answer to external climate forcing at the very long scale, which to a geologist is very exciting.
    It is very helpful to understand spectral densities and Fourier analysis to get this. It can be reduced to just superimposed waves of different amplitude, wavelength and phase. Shaviv’s external forcing is long waves, Milankovic external forcing is intermediate waves.
    Neither of these external forcings bear on climate change due to external forcing on the scale of decades to centuries. For that, a new understanding is needed.
    As I like to say, CO2 could in theory cause warming, all else being equal. And that is the problem. All else is not equal. There has been well-deserved skepticism for as long as it has been pushed on the public. Minor changes in oceanic and atmospheric circulation or cloud cover could indeed eclipse CO2 driven warming. Solar variation is a player. But what killed the beast for good in my mind was the assertion on this web site that radiative forcing is not the only thing at work. Thermal transport must be considered. Every weather map shows low pressure zones (warm air rising) and high pressure zones (cold air aloft, sinking). a minor increase in this convection would again eclipse radiative forcing by CO2. Heat is moved by vertical circulation. Hadley cells and Ferrell cells.
    Short-cycle change is occurring. CO2 is playing a role. However, here is another favorite great truth. The Earth’s climate is remarkably stable. If it were not, Earth’s geologic history would be vastly different. There is lots of evidence (and the science of physics) that external forcing has changed climate at all scales periodically, and the explanation is astronomical. Evidence of internal forcing is weak at best.

    • “Heat (energy) is moved by vertical circulation.”

      Atmospheric heat energy is also affected by horizontal movement of air masses. Case is point: watch a massive cold front move across the USA . . . or any other temperate latitude on Earth, for that matter.

  38. Jim January 4, 2020 at 9:23 pm

    Evidence of internal forcing is weak at best.

    Have to disagree. In the period (125-84 mya) leading to the most recent peak temperature around 85 mya at least 135 million km^3 magma erupted into the oceans, delivering enough energy to warm all ocean water 135K. This is on top of the ~100 mW/m^2 Geothermal Flux into the oceans, that “refreshes” the total OHC every 1,5 million years or so.
    It depends on how efficient the Thermohaline Circulation can transport all this energy to (very) high latitudes, the only place where it can be “vented” to the atmosphere/space, whether the oceans heat up or not.
    Since the deep oceans were also (very) warm around ~85 mya, any external “forcing” from outside needs also an explanation on how it can warm deep ocean water.

    • “…Since the deep oceans were also (very) warm around ~85 mya, any external “forcing” from outside needs also an explanation on how it can warm deep ocean water.”

      Since we live in an Ice Age, an immediate concern, is explanation of what is cooling deep ocean waters.

      It seems to me, that ocean which 1 C is unstable and a ocean of 5 C is unstable.
      If 1 C was not unstable, we would have “snowball earths” and if 5 C was not unstable, we would have left the Ice Age, millions of years ago.
      Or Earth is not a planet which has runaway effects, not in our Ice Age and not apparently at anytime on Earth. But one could point to “minor” runaway effects. Or glacier formation seems to have a runaway effect. Or water vapor in the tropics seems to be runaway effect.
      And it seems polar sea ice should have runaway effect. Or having less polar sea ice, seems “to lead” having less polar sea ice, or having more polar sea ice, seems “to lead” to having more polar sea ice.

      So I would guess that over last 1 million years the total amount time spent within .5 K of 1 C ocean is far less than 50,000 years in total and likewise, time spent within .5 of 5 C is far less than 50,000 years.
      And would guess the most of the 1 million year is spent within .5 of 2 C. Mainly because most of time in spent is in glacial periods. But in terms of feeling more certain, I would say you have to be in glacial period if ocean is 2 C, and you have to be in a interglacial period if average temperature of the ocean is 4 C.
      Re:
      “…the only place where it can be “vented” …”
      I generally think ocean warms and Land cools. So, land areas “vent”, and the higher land elevation “vents” more.
      And Antarctica has a high average elevation. And I agree with the general notion that a warming Antarctica is not connected to “global warming”. Or that there factors isolating Antarctica from warming a lot, and being kept cold is something “adding to” global warming. Or Antarctica is venting heat, but it could “somehow” or “potentially” vent a lot more heat {and also remain being a frozen wasteland}.

      • Since we live in an Ice Age, an immediate concern, is explanation of what is cooling deep ocean waters.

        Ice house or Hot house, in both cases the temperatures are way above radiative balance temperature. So in both cases the explanation for the high temperatures is the same: hot deep oceans (currently 275K, maybe ~290K around 85 mya)
        Without occasional warming from gigantic magma eruptions in the oceans, Earth will become colder and colder, like happened in the last 80 my.
        No runaway climate.

        I would say you have to be in glacial period if ocean is 2 C, and you have to be in a interglacial period if average temperature of the ocean is 4 C.

        Seems current Ice Age started when the deep oceans cooled below ~7 C.

        I generally think ocean warms and Land cools.

        Both land and ocean SURFACE can lose energy directly to the atmosphere/space (solar energy almost exclusively.)
        Deep oceans cannot. Every liter of water warmed at the ocean floor has to be transported to mostly Antarctica before it can surface and lose energy to the atmosphere/space.
        https://i0.wp.com/www.uib.no/sites/w3.uib.no/files/styles/content_main_wide_1x/public/w2/at/atlantic-det4.jpg
        https://en.wikipedia.org/wiki/Antarctic_bottom_water#/media/File:Antarctic_bottom_water.svg

  39. There is little reason to believe there are more galactic cosmic rays (GCRs) in the spiral arms. The spiral arms are just density waves where the stellar density is slightly higher. There are more of the bright young stars which is why they appear brighter. GCRs come from high energy astrophysical events, not stars themselves. Since the whole theory is based on a flawed assumption it seems to be worthless?

    • I tend to think spiral arms would have less GCRs.
      But new star formation, can include large star formation with short lifetimes before they supernova. So any region with more supernovas {and/or blackholes} could have more GCRs.
      But nevertheless, I tend to think spiral arms would have less GCRs.
      And I think there are region of galaxy, which Sol could move into and out of that have more GCRs, and I think that we can in the future, we predict where they are, and map our path, Sol has taken and will take in the future.
      We only a few decades into getting somewhat serious and having the technology of detecting GCR and mapping our galaxy and there will be many hypothesises which will tested.

    • kzb and gbaikie, You answered your own question. You wrote: “There are more of the bright young stars which is why they appear brighter.” Bingo! Cosmic rays are mainly generated when massive stars die. This is why there are more GCR’s in the arms, there are more massive stars dying there.

      • Abstract:
        “In the course of our motion through the Galaxy, the solar system has encountered many interstellar environments of varying characteristics. Interstellar medium (ISM) density variations spanning six orders of magnitude are commonly seen throughout the general Galactic environment, and a sufficiently dense cloud within this range has the potential to compress the heliosphere to within one Astronomical Unit (AU). ”
        http://sredfield.web.wesleyan.edu/Kthesis_master.pdf

        Our heliosphere is currently about 100 AU. Well beyond Neptune, and of course the Earth’s distance from Sun is 1 AU.

        Chapter 1
        Introduction
        “Throughout the last 100 years, researchers have speculated on possible connections between our interstellar environment and Earth’s climate. As far back as the 1920’s, Harlow Shapley was suggesting the idea of “Cosmic Seasons” (Shapley 1921), the possibility that periodic mass extinctions and drastic climate changes on Earth could be attributed to the Sun’s passage through different galactic environments in its orbit around the center of our galaxy….”

        …”As we will see, these molecular clouds are dense enough to pose potential hazards to life on
        Earth should the solar system slip through one in its passage around the center of the Galaxy.”

        But I not talking about this, I am thinking of GCR going thru denser regions of space. GCR will past thru a brick wall, but if brick wall is meters thick, it has very low chance going thru.

        https://www.space.com/25434-star-formation-recipe-revealed.html
        “Using data from 16 nearby molecular clouds, each within about 850 light-years of Earth, “we could devise a very concrete recipe for how new stars are born in the interstellar gas clouds,” study lead author Jouni Kainulainen, an astrophysicist at the Max Planck Institute for Astronomy in Heidelberg, Germany, told Space.com. “And the ingredients of this recipe are simple to understand — only those regions in the clouds in which density is higher than about 5,000 molecules per cubic centimeter produce stars, and about a tenth of the gas in these regions collapses into the new stars.”

        And our solar wind varies from 1 to 20 {or more} protons per cubic cm, though generally around 4 to 6 proton per cubic cm. And atmosphere of Moon is about 100 molecules per cubic cm. And low Earth orbit has more atmosphere than the Moon.
        But generally the spiral arms have higher density and clouds so dense you can’t see into or thru them.
        Now if you close to supernova, you are dead. Lets see, what is fairly safe distance:
        “Bottom line: Scientific literature cites 50 to 100 light-years as the closest safe distance between Earth and a supernova. May 11, 2018” So if closer than 50 light years, GCRs are not really the concern- things like atmosphere stripped from Planet and etc are the kinds of problems. Though maybe if there is dense cloud between you and the supernova, they might not be allowing for this particular factor.
        But anyhow, wiki sums it up:
        “Spiral arms typically contain a higher density of interstellar gas and dust than the Galactic average as well as a greater concentration of star formation… The Milky Way’s spiral structure is uncertain, and there is currently no consensus on the nature of the Milky Way’s spiral arms.”

  40. https://en.wikipedia.org/wiki/Galactic_year
    “Estimates of the length of one orbit range from 225 to 250 million terrestrial years”

    “One possible explanation relies on the hypothesis that the amount of galactic cosmic rays striking the Earth varies as the solar system traverses the arms of the Milky Way, which it does roughly every 135 million years, plus or minus 25 million years”

    Earths wobbles and ever changing angle towards the sun will have minor effects, longterm orbit changes of Earth around the sun will have minor effects, output of the sun will have significant effect.

    I’d postulate that one Galactic Year is 150 million years and that the place of our solar system in our galaxy every 150 million years, affected by neighbour solar systems and this local solar systems center of gravity which probably influence both oribital planes and solar irradiation/earth insolation…

    Is what happens.

    As for the clouds, the more there are of them, the less insolation. Correct. But these couds also works as a blanket. Like in less heat escapes the planet?

    In high-pressure weather systems, the earth gets warmer in summers, correct. But also significantly colders in winters. Colder winters building up from icesheets to slush from southpole/northpole and 45 degrees towards the equator. Slush to warm climate from 45 degrees to equator.

    That should also fit nicely as to the expansion of ice sheets to Portland USA, southern France or northern Italy.

    https://en.wikipedia.org/wiki/Ice_age#Glacial_stages_in_North_America
    “During the most recent North American glaciation, during the latter part of the Last Glacial Maximum (26,000 to 13,300 years ago), ice sheets extended to about 45th parallel north. These sheets were 3 to 4 kilometres (1.9 to 2.5 mi) thick.[73] ”

    Oddgeir

  41. I’m not so sure we need to hypothesise about spiral arms. The breakup and collision of continents radically alter oceanic heat transport between the tropics and the poles. The current ice age, for example, initiated when Panama isthmus closed, allowing the present-day Gulf Stream to establish.

    • Absolutely agree. That said, it is difficult to see this action repeat itself every 150 million years?

      Himalayas (arid and cold north, moist and temperate south):
      https://en.wikipedia.org/wiki/Himalayas#Geology
      “About 50 million years ago this fast moving Indo-Australian Plate” (crashed into the Eurasian Plate)

      Andes (arid and cold west, moist and temperate east):
      https://en.wikipedia.org/wiki/Nazca_Plate
      its existence as an independent plate having been formed from the break-up of the Farallon Plate about 23 million years ago. The oldest rocks of the plate are about 50 million years old (crached into the South American plate).

      Off course the climate would not have been the current climate in those regions were it not for tectonics. I doubt however that these tectonics were capable of influencing ice ages (the 150 million year cycle).

      Oddgeir

      • Oddgeir January 8, 2020 at 4:29 am

        I doubt however that these tectonics were capable of influencing ice ages (the 150 million year cycle).

        What would be the recharge time of a major mantle plume once it has left the core and convected all the way to the surface?

        • One more thing: it seems from the plot above that the current Ice Age started when the deep oceans cooled below ~7 C, and became serious for Antarctica with the deep ocean temperature dropping below ~4 C.
          To me it is obvious that Earth is bound to cool down into Ice Ages, unless the deep oceans are heated by gigantic magma eruptions into those oceans.

  42. I agree with the findings of the article, not because I am a scientist. I am an artist with a questioning and analytical mind…. But all the debate here is far more hilarious than a bunch of artists at a critique. Scientists having a pissing contest over data that no one seems to completely agree on. So what does that tell you???? Will there be a day in waking up that scientists will all agree on data pulled from current and historical sources on climate anomalies? Probably not. What can we all agree on? 1. The Earth’s climate is not static. 2. it is difficult to get a complete historic picture without using conjecture. 3. Earth systems are inter-related. 4. No one can really claim the total answer or truth…which could depend on where their funding comes from. 5. The is much we do not know. So while the debate (although smug data crunchers think there is no debate) continues…the Earth has lots of things she needs to happen. Like….cleaning up our Oceans, better farming practices for soil regeneration, fossil fuel independence, as well as better ways for scientists to honor each other’s perspectives… Perhaps some GIS (geographic information systems…management)…you know where you integrate various avenues of data into 3D maps that can show things inter-related that independently would not appear. Guys and gals of Science…pissing contest are irrelevant and NOT HELPFUL.

Comments are closed.