Guest “I couldn’t make this sort of schist up if I was trying” by David Middleton

H/T to Robert Bissett…

Drop in Greenhouse Gas Caused Global Cooling 34 Million Years Ago, Study Finds
August 6th, 2021, 6:00AM / BY Abigail Eisenstadt

[…]

A paper published in the journal Nature Geoscience confirms that a drop in carbon dioxide around 34 million years ago caused Earth to enter a period of global cooling, called an icehouse state.

[…]

In the past, scientists were unsure why the Eocene Oligocene transition happened. For a while, they thought it was because of a change in the Antarctic ocean’s currents. But that theory gradually grew out of favor.

“The question has always been what was driving this change,” said Naafs.

Through climate modeling, the researchers found that only a decrease in carbon dioxide could have led to such a big temperature drop in the geologically short span of 300,000 years.

[…]

Smithsonian Magazine

This is from the paper:

Two main mechanisms have been proposed as drivers for this greenhouse-to-icehouse transition: (1) changes in Southern Ocean gateways, leading to the thermal isolation of Antarctica and onset of the Antarctic Circumpolar Current7,8; and (2) a decline in atmospheric pCO2 driving the cooling and build-up of continental ice sheets9–11. Different mechanisms have been invoked to explain this drawdown in pCO2, including a shift from shelf to basin carbonate fractionation12, driving the deepening of the calcite compensation depth13, possibly associated with increased weathering and/ or a perturbation in organic carbon fluxes14. A different hypothesis identifies the intensification of silicate weathering, linked to the tectonic deepening of the Drake Passage and the strengthening of the Atlantic meridional overturning circulation, as the primary mechanism15.

Laurentano et al, 2021

Where do I start?

  • Models can’t confirm anything.
  • We pretty well know that the “thermal isolation of Antarctica and onset of the Antarctic Circumpolar Current” occurred approximately 34 million years ago.
  • We pretty well know that the abrupt cooling at Eocene-Oligocene boundary was coincident with the “thermal isolation of Antarctica and onset of the Antarctic Circumpolar Current”
  • Estimates of Paleocene-Eocene atmospheric CO2 vary widely depending on the method of investigation.

This is from my college meteorology text book:

FORECASTING THE FUTURE. We can now try to decide if we are now in an interglacial stage, with other glacials to follow, or if the world has finally emerged from the Cenozoic Ice Age. According to the Milankovitch theory, fluctuations of radiation of the type shown in Fig. 16-18 must continue and therefore future glacial stages will continue. According to the theory just described, as long as the North and South Poles retain their present thermally isolated locations, the polar latitudes will be frigid; and as the Arctic Ocean keeps oscillating between ice-free and ice-covered states, glacial-interglacial climates will continue.

Finally, regardless of which theory one subscribes to, as long as we see no fundamental change in the late Cenozoic climate trend, and the presence of ice on Greenland and Antarctica indicates that no change has occurred, we can expect that the fluctuations of the past million years will continue.

Donn, William L. Meteorology. 4th Edition. McGraw-Hill 1975. pp 463-464

The Antarctic ice sheet likely began to form prior to the sudden drop in temperature, allegedly caused by a drawdown in atmospheric CO2… Indicating that the onset of cooling probably preceded the onset of CO2 drawdown.

Figure 1. High Latitude SST (°C) From Benthic Foram δ18O (Zachos, et al., 2001) Click to enlarge (older is toward the bottom) .

This is from my historical geology text book:

Suggestion that changing carbon dioxide content of the atmosphere could be a major factor in climate change dates from 1861, when it was proposed by British physicist John Tyndall.

[…]

Unfortunately we cannot estimate accurately changes of past CO2 content of either atmosphere or oceans, nor is there any firm quantitative basis for estimating the the magnitude of drop in carbon dioxide content necessary to trigger glaciation.  Moreover the entire concept of an atmospheric greenhouse effect is controversial, for the rate of ocean-atmosphere equalization is uncertain.

Dott, Robert H. & Roger L. Batten. Evolution of the Earth. McGraw-Hill, Inc. Second Edition 1976. p. 441.

While a great deal of progress has been made since 1976 in estimating changes of past CO2 content, it is still not accurate enough to draw the conclusion that CO2 has been a major climate driver over the Phanerozoic Eon.

Paleocene-Eocene CO2 estimates range from 400-800 ppm to 2,000-3000 ppm. The drawdown that allegedly caused the geologically sudden cooling at the onset of the Oligocene can’t even be properly quantified.

Figure 2a. Marine pCO2 (foram boron δ11B, alkenone δ13C), atmospheric CO2 from plant stomata (green and yellow diamonds with red outlines), Mauna Loa instrumental CO2 (thick red line) and Cenozoic temperature change from benthic foram δ18O (light gray line).

Figure 2b. Legend for Figure 3a.

Changes in atmospheric CO2 can’t be clearly tied to the PETMEECO, MECO or MMCO [1], [2]; however a model now suddenly ties it to the one major Cenozoic climate shift that was well-explained by plate tectonics and oceanic circulation changes. Surely they can’t be serious.

Yet climate models, which can’t get anything else right, particularly the Late Pleistocene to Early Holocene, suddenly nail down the Cenozoic ice age…

The models were also out of step with records of past climate. For example, scientists used the new model from NCAR to simulate the coldest point of the most recent ice age, 20,000 years ago. Extensive paleoclimate records suggest Earth cooled nearly 6°C compared with preindustrial times, but the model, fed with low ice age CO2 levels, had temperatures plummeting by nearly twice that much, suggesting it was far too sensitive to the ups and downs of CO2. “That is clearly outside the range of what the geological data indicate,” says Jessica Tierney, a paleoclimatologist at the University of Arizona and a co-author of the work, which appeared in Geophysical Research Letters. “It’s totally out there.”

Science! (as in, “she blinded me with”)

They “solved” the “Holocene temperature conundrum” by simply applying a downwards adjustment to Early Holocene temperatures. Unfortunately for them, it didn’t stay solved.

Figure 3. “A funny thing happened on the way to the Anthropocene.”

For their solution to the “Holocene temperature conundrum” to be valid, much of the melting of the Laurentide ice sheet and the subsequent Neoglaciation would have had to have occurred with very little temperature change. Thankfully, Kaufman et al., 2020 didn’t delete the CPS version of their reconstruction.

Figure 4. CPS with historical climate periods and Neoglaciation (Grosjean et al., 2007), Early Holocene ice extent map (Dyke et al., 2003) and Alps tree line altitude (Bohleber et al., 2021). PAGES 12K: The Ice Age Goeth

References

Bohleber, P., Schwikowski, M., Stocker-Waldhuber, M. et al. New glacier evidence for ice-free summits during the life of the Tyrolean Iceman. Sci Rep 10, 20513 (2020). https://doi.org/10.1038/s41598-020-77518-9

Donn, William L. Meteorology. 4th Edition. McGraw-Hill 1975. pp 463-464

Dott, Robert H. & Roger L. Batten. Evolution of the Earth. McGraw-Hill, Inc. Second Edition 1976. p. 441.

Dyke, A.S., Moore, A. and L. Robertson. [computer file]. Deglaciation of North America. Geological Survey of Canada Open File 1547. Ottawa: Natural Resources Canada, 2003.

Grosjean, Martin, Suter, Peter, Trachsel, Mathias & Wanner, Heinz. (2007). “Ice‐borne prehistoric finds in the Swiss Alps reflect Holocene glacier fluctuations”. Journal of Quaternary Science. 22. 203 – 207. 10.1002/jqs.1111.

Kaufman, D., McKay, N., Routson, C. et al. Holocene global mean surface temperature, a multi-method reconstruction approach. Sci Data 7, 201 (2020). https://doi.org/10.1038/s41597-020-0530-7

Lauretano, V., Kennedy-Asser, A.T., Korasidis, V.A. et al. Eocene to Oligocene terrestrial Southern Hemisphere cooling caused by declining pCO2pCO2. Nat. Geosci. (2021). https://doi.org/10.1038/s41561-021-00788-z

Pagani, Mark, Michael Arthur & Katherine Freeman. (1999). “Miocene evolution of atmospheric carbon dioxide”. Paleoceanography. 14. 273-292. 10.1029/1999PA900006.

Pearson, P. N. and Palmer, M. R.: Atmospheric carbon dioxide concentrations over the past 60 million years, Nature, 406, 695–699,https://doi.org/10.1038/35021000, 2000.

Royer, et al., 2001. Paleobotanical Evidence for Near Present-Day Levels of Atmospheric CO2 During Part of the Tertiary. Science 22 June 2001: 2310-2313. DOI:10.112

Steinthorsdottir, M., Vajda, V., Pole, M., and Holdgate, G., 2019, “Moderate levels of Eocene pCO2 indicated by Southern Hemisphere fossil plant stomata”: Geology, v. 47, p. 914–918, https://doi.org/10.1130/G46274.1

Tripati, A.K., C.D. Roberts, and R.A. Eagle. 2009.  “Coupling of CO2 and Ice Sheet Stability Over Major Climate Transitions of the Last 20 Million Years”.  Science, Vol. 326, pp. 1394 1397, 4 December 2009.  DOI: 10.1126/science.1178296

Zachos, J. C., Pagani, M., Sloan, L. C., Thomas, E. & Billups, K. “Trends, rhythms, and aberrations in global climate 65 Ma to present”. Science 292, 686–-693 (2001).

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August 9, 2021