42,000 Years Ago A Massive Geomagnetic Shift Plunged A Warm Earth Into An Ice Age…But CO₂ Didn’t Budge

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A groundbreaking new study in Science suggests warm interglacial-like conditions (surface temperatures within 1°C of today’s) persisted from 54 to 42,000 years ago even though CO₂ levels idled around 200 ppm at that time. A sudden geomagnetic shift that intensified galactic cosmic rays and cloud formation and reduced ozone levels ~42,000 years ago resulted in global-scale cooling, rapid glacier advance, disappearing water sources (lakes), plummeting sea levels, and a catastrophic peak in large animal extinctions.

In the 20 thousand years between about 55 and 35 thousand years ago, the agreed-upon paleoclimate CO₂ reconstructions suggest concentrations hovered around 200 ±10 ppm (Kohfeld and Chase, 2017). It was during this phase, however, that a 33-author new study (Olsen et al., 2021) suggests abrupt and dramatic changes in the Earth’s magnetic field (for example, a “10-fold decrease in the cosmic ray cut-off rigidity”) about 42,000 years ago “drove synchronous global climate” from interglacial-like conditions (with surface temperatures within 1 to 1.5°C of today’s 54 to 42 ka) to a fully glacierized state.

The catastrophic consequences of this Grand Solar Minima-induced global-scale “pervasive and widespread cold conditions” and “greatly reduced surface temperatures” resulted in tens of meters of sea level fall, the disappearance of lakes and fresh water sources, the North American Laurentide ice sheet advancing more than 1,000 kilometers within just a few thousand years, and the consequent destruction of megafaunal (i.e., wooly rhino, mammoth, bison) habitat that led to their extinctions.

It has previously been thought that the entire ~90,000-year interval sandwiched between the last interglacial ~120,000 years ago and the Holocene (11,700 years ago to present) had gradually and slowly dipped into glacial conditions over the course of many millennia, and that human perturbations were responsible for the last glacial peak in megafaunal die-offs. But since the extinctions occurred 10 to 15 thousand years after it was still warm enough for anatomically modern humans (AMH) to occupy sites north of the Arctic circle from 55 to 50 thousand years ago, the authors suggest it was far more likely Grand Solar Minima-induced habitat destruction centered around the dramatic climate shift 42,000 years ago is responsible for the demise of large mammalian species.

So, once again, the paleoclimate record affirms pervasive and “synchronous global climate shifts” occur without any obvious contribution from atmospheric CO₂ concentration changes.

Image Source: Cooper et al., 2021 and Supplemental Data

Some key quotes from the paper and supplemental materials:

“geomagnetic field minima ~42 ka, in combination with Grand Solar Minima, caused substantial changes in atmospheric ozone concentration and circulation, driving synchronous global climate shifts that caused major environmental changes, extinction events, and transformations in the archaeological record”

“geomagnetic excursions can alter latitudinal temperature gradients through drastic increases in cosmic radiation and decreased ozone concentrations”

“a warm period from 54 to 42 ka within the last glaciation [with] annual temperatures within 1°C to 1.5°C of those today”

“a weakening of the magnetic field intensity to <28% of current levels during the reversed phase of the Laschamps [led to] a return to periglacial conditions that occurred at 42.23 ±0.2 ka”

“a 10-fold decrease in the cosmic ray cut-off rigidity”

“pervasive and widespread cold conditions” “greatly reduced surface temperatures”

“the LIS [Laurentide Ice Sheet] expanded rapidly from a local minimum at 42 ka…the ice sheet may have expanded >1000 km by ~39 to ~37 ka”

“the magnitude of large mammal faunal change across the Laschamps exceeded that which occurred across the Pleistocene-Holocene transition”

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9 responses to “42,000 Years Ago A Massive Geomagnetic Shift Plunged A Warm Earth Into An Ice Age…But CO₂ Didn’t Budge”

  1. bonbon

    Do the Authors cite Svensmark and/or Shaviv on aerosol formation?

    1. Petit_Barde

      “In its 10 years of operation, CLOUD has made several important discoveries on the vapours that form aerosol particles in the atmosphere and can seed clouds. Although most aerosol particle formation requires sulphuric acid, CLOUD has shown that aerosols can form purely from biogenic vapours emitted by trees, and that their formation rate is enhanced by cosmic rays by up to a factor 100.”


      Not even a word about Svensmark on the CERN presentation, while all the CLOUD experiment was driven to verify the Svensmark hypothesis (and they showed he was right).

      It’s all politics and bigottery because Kirkby did a presentation (can be seen on youtube) where he clearly cited Svensmark’s work.

      1. Petit_Barde

        Kirkby citing Svensmark’s work in the Q&A session of his CLOUD presentation :


        1. Yonason

          Not the same as citing him in a paper to credit him as an important contributor to/inspiration for the work. As you write, “It’s all politics and bigottery.”

          I don’t know yet if that’s the same video I watched several years ago, but in the one I saw, Kirkby seemed very nervous when discussing Svensmark, as if fearful of saying the wrong thing in front of his colleagues, and then relieved when he could move on.

          Very smart people can be as ignoble as anyone else, and sometimes even more so.

        2. bonbon

          Svensmark replied to Kirkby – he found they actually did show aerosol production up to a very specific size and then modeled aerosol growth using CERN’s computing facilities. In other words the extrapolation was done numerically, and incorrectly. There is a youtube video on this . How do aerosols of 2nm grow to 50nm, a million times mass factor, to become actual clout condensation nuclei.

          1. bonbon

            https://www.thegwpf.com/content/uploads/2018/03/SvensmarkLondon2018.pdf Page 22

            I have the full video, but online it is cut at 35min. The CCN info is at 45min…

  2. William Astley

    The Laschamp geomagnetic field reversal occurred at time in which the planet was in glacial cold conditions.

    Therefore the drop in the magnetic field strength from 50% of current to 6% of current magnetic field strength (reversed) and then back up to 28% before recovering, of the geomagnetic field and the drop in magnetic field strength occurring for 1000 years …

    Would if it occurred now cause abrupt cooling (say a drop of 2C for 1000 years).

    The Laschamp reversal occurred during the glacial period and it did not cause more cooling, as the GCR mechanism was at saturation. These geomagnetic reversal events….

    Are caused by something. It is not an internal liquid change in the earth that causes the earth’s magnetic field to reverse for a 1000 years. The geomagnetic field theory now cannot explain the observations. The speed of the change is impossible to physically cause by liquid velocity or direction changes, even if there was a physical explanation as to what could cause a liquid core change.

    We are missing the what causes the geomagnetic answer/concept.

    The geomagnetic field changes are forced and very rapid. And the geomagnetic field strength changes correlate with the temperature changes.

    A paper published 15 years ago by a pair of Japanese researchers determined that the geomagnetic field strength spikes/peaks, increasing when the earth’s orbit is most extencentric, every 100,000 years.

    The geomagnetic field strength increased in strength by a factor of two during this interglacial phase. It was lower by a factor of two during this glacial period. And interestingly the geomagnetic field strength during the glacial period increased and decreased correlating with the D-O warming.

    French fired tile analyses (100,000 tiles) determined that in the last 1500 years geomagnetic field is changing abruptly every 200 years and 500 years, the North pole location abruptly changes and the geomagnetic field strength changes.

    So there is evidence that there is small, large, and abrupt climate change forcing mechanism (not internal to the earth) that is changing the geomagnetic field. The implications of that logical fact are ignored because the cause logically is the sun.

    It is interesting that there is a solar system anomaly that was discovered and confirmed by multiple satellite analyzes. The orbits of the planet’s are decreasing as if the sun was gaining mass. The sun should if it is a simple fusion star, loss mass due to e=MC^2 and more importantly due to the solar wind. This is not due to a measurement error. The measured change is large and consistent year by year.

    Excerpt from the paper:
    “Laschamps Excursion (hereafter Laschamps)— a recent, relatively short-duration (<1000 year) reversal ~41 thousand years ago (ka) (4). Sedimentary and volcanic deposits indicate a weakening of the magnetic field intensity to <28% of current levels during the reversed
    phase of the Laschamps and, notably, as little as 0 to 6% during the preceding transition as polarity switched (Fig. 1 and supplementary
    materials) (1, 2, 5)."

    1. Bruce Williams

      Like all electron flow in a heated medium the change in the electron flow path which causes the earths magnetic field can be changed significantly by a change in local pressure gradients in the material if under pressure, changes in material makeup, and in local temperature changes any place in the material.
      Nothing in the earths crust, mantle, outer or inner core is homogeneous enough in material content such that the resistivity would allow electrons to flow randomly. Their temperature is also not homogeneous enough to make only the resistivity be what directs the current flow even if the plumes never moved and the mantle “loops” never changed. The circulating currents would still be changed as the core heat escaped to the surface and then to space as well as the change if there is no heat transfer in the out from the vents and volcanoes. So the changing magnetic field can be caused both by reduced pressure as lava outflows through vents and volcanoes, the associated changes in temperature as the local pressure is reduced, the change in the core temperature as its rate of heat transfer changes, changes in mantle motion, and several other physical factors. It can also be redirected by changes in thickness of the crust as internal plumes push up against the mantle (if not fully penetrating the crust) and thin the mantle and thus allow more heat to escape to the surface and its inverse effect of the plume solidifying as it cools when it no longer moves up into the mantle at certain spots.
      As far as the sun, the activity on the sun can cause the solar wind to push the magnetic field in different directions, causing the external path of the earths magnetic field to shift, causing a “pressure” on the internal field to follow that change which can cause multiple effects. Exactly how much of an effect I have never seen published or anyone trying to calculate it but it is there to some unknown degree. Keep in mind it should be small(?) considering the solar wind pushes the magnetic field in a cone like pattern in a 360 degree wobble every 24 hours as the earth rotates.
      Don’t know if this is what you were working on or if you have already accounted for it?

  3. bonbon

    Clearly we live near a variable star.

    The best way to look at this is bring cosmology back to the lab as Dr. Lerner of LPPFusion says – plasma in our service.

    In other words striving for fusion energy will clear this up.

    After all the cosmos strove over eons for this energy source, so we should strive after happiness (faster) in this way (as stated in the US Preamble).

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