Newly discovered African ‘climate seesaw’ drove human evolution

Posted: June 1, 2021 by oldbrew in atmosphere, climate, Cycles, ENSO, History, research, weather
Tags:

Walker_neutral

Generalized Walker Circulation (December-February) during ENSO-neutral conditions. Convection associated with rising branches of the Walker Circulation is found over the Maritime continent, northern South America, and eastern Africa. [Credit: NOAA Climate.gov — drawing by Fiona Martin]

El Niño and 100,000 year glaciation/climate cycles feature prominently in this research. The Walker circulation has been described as ENSO’s atmospheric buddy.
– – –
While it is widely accepted that climate change drove the evolution of our species in Africa, the exact character of that climate change and its impacts are not well understood, says Phys.org.

Glacial-interglacial cycles strongly impact patterns of climate change in many parts of the world, and were also assumed to regulate environmental changes in Africa during the critical period of human evolution over the last ~1 million years.

The ecosystem changes driven by these glacial cycles are thought to have stimulated the evolution and dispersal of early humans.

A paper published in Proceedings of the National Academy of Sciences (PNAS) this week challenges this view.

Dr. Kaboth-Bahr and an international group of multidisciplinary collaborators identified ancient El Niño-like weather patterns as the drivers of major climate changes in Africa. This allowed the group to re-evaluate the existing climatic framework of human evolution.

Walking with the rain

Dr. Kaboth-Bahr and her colleagues integrated 11 climate archives from all across Africa covering the past 620 thousand years to generate a comprehensive spatial picture of when and where wet or dry conditions prevailed over the continent.

“We were surprised to find a distinct climatic east-west ‘seesaw’ very akin to the pattern produced by the weather phenomena of El Niño, that today profoundly influences precipitation distribution in Africa,” explains Dr. Kaboth-Bahr, who led the study.

The authors infer that the effects of the tropical Pacific Ocean on the so-called “Walker Circulation”—a belt of convection cells along the equator that impact the rainfall and aridity of the tropics—were the prime driver of this climate seesaw.

The data clearly shows that the wet and dry regions shifted between the east and west of the African continent on timescales of approximately 100,000 years, with each of the climatic shifts being accompanied by major turnovers in flora and mammal fauna.

“This alternation between dry and wet periods appeared to have governed the dispersion and evolution of vegetation as well as mammals in eastern and western Africa,” explains Dr. Kaboth-Bahr. “The resultant environmental patchwork was likely to have been a critical component of human evolution and early demography as well.”

The scientists are keen to point that although  was certainly not the sole factor driving early human evolution, the new study nevertheless provides a novel perspective on the tight link between environmental fluctuations and the origin of our early ancestors.

Full article here.

Comments
  1. saighdear says:

    Ok it’s unusually WARM for start of June ( rolling month – then maybe MAY, still) and I’m glad to come in early to phone for spare parts and get out of the sun, but: BUT! “archives from all across Africa covering the past 620 thousand years ” eh? sunstroke anyone? is this ecospeke for something?

  2. Curious George says:

    “Glacial-interglacial cycles strongly impact patterns of climate change..”
    Climate change strongly impacts patterns of climate change. I just love science.

  3. oldbrew says:

    Researchers ‘identified ancient El Niño-like weather patterns as the drivers of major climate changes in Africa.’
    – – –
    And modern ‘El Niño-like weather patterns’ do what – something similar, possibly?

  4. ivan says:

    integrated 11 climate archives from all across Africa covering the past 620 thousand years is that the new form of climate speak for ‘we worked up some computer models and then used then to in other computer models to get the answer we wanted’?

  5. bonbon says:

    As usual the absolute difference between man and beast is to be hidden at all costs, fire.
    Mankind headed direct to the Arctic, not huddled in warm equatorial yuppie hotels.
    Why, pray tell?
    And more importantly, as various have shown, not by ‘foot’, rather by sail. The great oceans were conquered. See the famous Olmec heads in stone :
    https://en.wikipedia.org/wiki/Olmec_colossal_heads
    Or the modular spears found in Okhotsk.
    Sure man noted the vagaries of weather and climate, and acted thereon. This drives Greta’s benefactors to distraction!

  6. JB says:

    “it is widely accepted that climate change drove the evolution of our species”

    That width does not include me, and I don’t see how acceptance makes fact. More nonsense from Phys.org

  7. tom0mason says:

    “The ecosystem changes driven by these glacial cycles are thought to have stimulated the evolution and dispersal of early humans.”

    Oh right. Of course during the glacial cycle (or maybe during the decline to, or the rise out of a glacial freeze) nothing else could be happening, eh? Couldn’t be cosmic rays stimulated the evolution could it? Or the knock-on effect from the changes in cosmic rays impacting the Earth’s ecology.
    Towards the end of this video at https://www.climateclips.com/the-cloud-factor/ Professor Nir Shaviv says it with how the sun progresses around the galaxy.

    Just a thought.

  8. tom0mason says:

    Ooops and my apologies.

    Please(!) can you remove the copyrighted video from my comment above and insert the web site where I found it — https://www.climateclips.com/the-cloud-factor/

    [mod] done

  9. oldmanK says:

    From tom0mason says: June 2, 2021 at 9:35 am
    Video at 06:10 shows a graph the base line of which is in 100Myr. A cycle is more than 100Myr. The changes to human civilisations flowed and ebbed at much closer periods than that. Actually, when seen over a period of ~8000 years the most appropriate cycle is the 980 Eddy.

    The subject article covers 620,000 years, IMO too wide and far a vista for meaningful results. On the other hand by following the Eddy cycle, peaks were turning points. 3550bce was near one, when the Sahara dried abruptly (but still relatively an unknown period, except that it was a peak for megalithic Malta). The following Eddy peaks were 2700bce. > Akkad/Sumer; 1750bce > Babylonian/Mycenaean; 800bce> Punico/Greek. We are third peak down the time-line.

    Eddy roots: points of collapse. Eight periods between ~6150bce (Doggerland) and 1680ce LIA. 3195bce was one such collapse, and there is evidence of considerable geological rearrangement in the Med, which explains partly why the Sahara did not flourish again. And the beginning of the end for the megalithic civilisation which came with the following root; the 4k2 event (2345bce).

  10. tom0mason says:

    Thank [mod].
    oldmanK one part of video shows Professor Nir Shaviv pointing out (at about the 5 minute mark) that our solar system has been moving through a minor arc of the milky-way. How long has the solar system been doing this, I don’t know — a few 100,000 years? Would this minor arc have ripples on the times scales you have outlined, again I don’t know.
    Either way I’m still left wondering, could variations in cosmic rays, and therefore solar variations, stimulate some aspects of evolution and climate?

  11. oldmanK says:

    tom0mason: the video at 06:10 shows a graph with period in excess of 100Myrs. Even one glacial cycle from the past 450,000 years, of circa 100ky per cycle is far too long.
    The ripples can be seen here https://www.linkedin.com/pulse/predictability-past-warm-periods-renee-hannon/ They are abrupt shifts, showing as jagged lines, somewhat chaotic, on the sawtooth shape of a glacial cycle.

  12. tom0mason says:

    oldmanK,

    The ripples to which I suggest is the ripples (variations in density) within the minor arc of the milky-way this solar system is moving through. Yes I can see that Professor Nir Shaviv IS talking about a much larger time scale, I AM NOT!
    I am speculating about the ripples(variations) in matter density within the minor arc Professor Nir Shaviv says we are in, and how maybe, they could be affecting the solar output and cloud formations on Earth.
    My question was how long have we been in this minor arc, so far I am unable to find an adequate answer.

  13. oldmanK says:

    tom0mason’
    OK. Actually it did occur to me you likely were following such train of thought.
    I do not mean to flog a point, but your speculative ‘question’ can be placed in a perspective that can be populated further with available info. To be clear, my aim is to find the source of a strong driver that, based on the last 8000 years, has impacted humanity for good and bad (as I indicated above).

    Example: the last 12000 years are known, an early part of a glacial cycle (vide charts in Dr R Hannon link). The previous ~400kyrs cover four such glacial cycles. How can the minor arc of the milky way dictated such forcing? Can some correlation be perceived? It is not in the video. Same way there is no answer in the subject matter of this thread, eg quote:”– wet and dry regions shifted between the east and west of the African continent on timescales of approximately 100,000 years,–“. Those are glacial cycles. There is evidence of shifts in Africa on much narrower time periods than that. In fact there are evidence in dated African sediment that correlate to the 980 yr period.

    So, like the blessed robin that adopted my small garden, you turn every leaf maybe you find the grub that does it.

  14. oldbrew says:

    Various theories, but the ‘100,000-year problem’ is still with us.

    https://en.wikipedia.org/wiki/100%2C000-year_problem

  15. oldmanK says:

    Just to be clear, I seek answers. That said, from oldbrew’s link
    quote “The 100,000-year problem (“100 ky problem”, “100 ka problem”) of the Milankovitch theory of orbital forcing refers to a discrepancy between the reconstructed geologic temperature record and the reconstructed amount of incoming solar radiation, or insolation —- ” The 100kyr orbital eccentricity I don’t question, but the backward extrapolation of Newcomb’s obliquity I question a lot. Milankovitch theory is based on such an extrapolation.

    I have an interest in this – declared-. GF Dodwell perceived abrupt changes to obliquity; I found that evidence. Seen in that perspective one can also understand clearly the words of ancient writers on the matter; Plato, Herodotus, Mela, Berossos,;
    Equally in that perspective insolation would be unknown and possibly quite different from what it is assumed.
    Then again the 100kyr signal referred to in the subject article (no data source given) seems to be from an ecological source and is likely of glacial origin, not direct orbital as in Wiki statement.

    Africa provides better data. See https://www.youtube.com/watch?v=BHCk1I_8igU from 30:00 on. The dates of abrupt changes are the same I have indicated above. In a parallel video (PBS -Skeletons of the Sahara prt2 of 5 at 02:43) gives a series of dates of sedentary habitation with abrupt change/termination dates, some of which correlate precisely to the Eddy inflection points.

  16. tom0mason says:

    Thank-you both oldmanK and oldbrew for the insight and information.
    I shall have to think on some more but as you both point out there is the 100,000 year problem.

  17. oldbrew says:

    This abstract briefly outlines the ‘problem’ although the proposed climate feedback ideas are debatable.

    Published: 04 April 2010
    Links between eccentricity forcing and the 100,000-year glacial cycle
    Lorraine E. Lisiecki

    https://www.nature.com/articles/ngeo828

    The supplementary info offers some statistical jiggery-pokery…
    ‘https://static-content.springer.com/esm/art%3A10.1038%2Fngeo828/MediaObjects/41561_2010_BFngeo828_MOESM158_ESM.pdf’

    It ends by saying (ignore line numbers):
    This study proposes that the increase in 100-kyr climate response at the
    199 MPT is largely the result of the combined effects of two long-term trends
    200 (as illustrated by equation 1). First, the long-term cooling trend of the last
    201 5 Myr strengthened ice-albedo and carbon cycle feedbacks, producing an
    202 exponential increase in climate variance. Second, a decrease in the 100-kyr
    203 power of eccentricity at ∼0.8 Ma resulted in long intervals of weak precession
    204 forcing, during which slow climate feedbacks could generate large 100-kyr
    205 glacial cycles without disruption.

    – – –
    ‘Precession forcing’ isn’t defined in the document, but if it’s axial precession then it’s about 25,800 years on average.

  18. oldmanK says:

    A more recent paper. But beware, one can find any number of speculative ‘research’.
    2020 https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2019PA003655
    2015 https://arxiv.org/pdf/1505.02183.pdf

    Quote
    “here are, however, several difficulties in reconciling the Mi-lankovitch theory with observation. Two in particular arise when trying to explain the 100 kyr cycles. The first is the tran-sition from the 41 kyr dominant period in climate variations to a 100 kyr dominant period at the mid-Pleistocene around 1 Myr ago (hereafter “Myr ago” is written “Ma”). The second dif-ficulty is generating 100 kyr sawtooth variations from orbital forcings and climate response mechanisms (Imbrie et al. 1993,Huybers 2007, Lisiecki 2010). On the one hand, and as shown in Figure 1, the onset of 100 kyr power at the mid-Pleistocene transition (MPT) occurs without a corresponding change in the summer insolation at high northern latitudes –”

    A small observation: GF Dodwell perceived that obliquity changed abruptly, and the signal of the change is an exponential superimposed on the secular changes. He proposed a date of 2345bce for that change.
    M Baillie early in 2002 found that date in tree rings https://www.dias.ie/wp-content/uploads/2002/11/tionol2002_baillie.pdf Quote “– the dates 3195 BC, 2345 BC,1628 BC, 1159 BC, 207 BC and AD 540 dropped out of the bog-oak chronology (Baillie and Munro 1988).”
    My delving into megalithic calendar found evidence of change – no clear date- but post 2900 (post 3195 tectonic orientation change) with total civilisation collapse from archaeology at/post 2400bce.

    GF Dodwell was ignored, and questions keep being asked rather that seek out if Dodwell did hit the jackpot. This state of affairs is not explained by any science except psychology and Desmond Morris in the book ‘The Naked Ape’ has an explanation.

  19. oldbrew says:

    How well do scientists understand how changes in Earth’s orbit affect long-term natural climate trends?
    Date: February 7, 2010
    Source: National Oceanography Centre, Southampton (UK)

    Summary:
    The notion that scientists understand how changes in Earth’s orbit affect climate well enough for estimating long-term natural climate trends that underlie any anthropogenic climate change is challenged by new research findings.
    – – –
    The researchers found that the current interglacial has indeed lasted some 2.0-2.5 millennia longer than predicted by the currently dominant theory for the way in which orbital changes control the ice-age cycles. This theory is based on the intensity of solar radiation reaching the Earth at latitude 65 degrees North on 21 June, the northern hemisphere Summer solstice.

    But the anomaly vanished when the researchers considered a rival theory, which looks at the amount of solar energy reaching the Earth at the same latitude during the summer months. Under this theory, sea levels could remain high for another two thousand years or so, even without greenhouse warming.

    “Future research should more precisely narrow down the influence of orbital changes on climate,” said Rohling.

    https://www.sciencedaily.com/releases/2010/02/100205091825.htm
    – – –
    Easier said than done of course, or answers would already be on the table.

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