Guest “I couldn’t make this kind of slate up if I tried” by David Middleton
H / T to Robert Bissett …
Decline in greenhouse gas caused global cooling 34 million years ago, study results
August 6, 2021, 6:00 a.m. / BY Abigail Eisenstadt
[…]
An article published in the journal Nature Geoscience confirms that a decrease in carbon dioxide about 34 million years ago caused the earth to enter a phase of global cooling known as the ice house state.
[…]
In the past, scientists have not been sure why the Eocene-Oligocene transition occurred. For a while they thought it was due to a change in the currents of the Antarctic Ocean. But this theory was gradually falling out of favor.
“The question was always what is driving this change,” said Naafs.
Using climate modeling, the researchers found that only a drop in carbon dioxide in the geologically short span of 300,000 years could have caused such a large drop in temperature.
[…]
Smithsonian Magazine
This is from the paper:
Two main mechanisms have been suggested as driving forces for this transition from greenhouse to ice house: (1) changes in the gates of the Southern Ocean leading to the thermal isolation of Antarctica and the onset of the Antarctic circumpolar current7,8; and (2) a decline in atmospheric pCO2, which is driving the cooling and building of continental ice sheets9–11. Various mechanisms have been used to explain this pCO2 decrease, including a shift from shelf to basin carbonate fractionation12, which promotes deepening of the calcite compensation depth13, possibly associated with increased weathering and / or a disruption of organic carbon fluxes14. Another hypothesis identifies the intensification of silicate weathering in connection with 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 should I start?
- Models cannot confirm anything.
- We know pretty well that the “thermal isolation of Antarctica and the onset of the Antarctic circumpolar current” occurred about 34 million years ago.
- We know pretty well that the abrupt cooling at the Eocene-Oligocene border coincided with the “thermal isolation of Antarctica and the onset of the Antarctic circumpolar current”.
- Estimates of atmospheric CO2 from the Paleocene-Eocene vary widely depending on the investigation method.
This is from my college meteorology textbook:
FORECAST THE FUTURE. We can now try to decide whether we are now in an interglacial period, in which further ice ages will follow, or whether the world has finally emerged from the Cenozoic Ice Age. According to Milankovitch’s theory, radiation fluctuations of the type shown in Fig. 16-18 must persist, and therefore future glacial stages will continue. According to the theory just described, polar latitudes will be cold as long as the north and south poles maintain their current thermally isolated positions; and as the Arctic Ocean oscillates between ice-free and ice-capped states, the glacial and interglacial climates will continue.
Whichever theory one subscribes to, we can ultimately expect the fluctuations of the past to continue for millions of years.
Donn, William L. Meteorology. 4th edition. McGraw-Hill 1975. pp. 463-464
The Antarctic ice sheet likely began to form before the sudden drop in temperature supposedly caused by a drop in atmospheric CO2 … This suggests that the onset of cooling likely preceded the onset of CO2 withdrawal.
Figure 1. High latitude SST (° C) from Benthic Foram δ18O (Zachos, et al., 2001) Click to enlarge (older is pointing down).
This is from my historical geology textbook:
The suggestion that changing levels of carbon dioxide in the atmosphere could be an important factor in climate change dates back to 1861 when it was proposed by British physicist John Tyndall.
[…]
Unfortunately, we cannot accurately estimate past changes in CO2 levels in the atmosphere or in the oceans, nor is there a solid quantitative basis for estimating the extent of the decrease in carbon dioxide levels necessary to cause icing. In addition, the whole concept of an atmospheric greenhouse effect is controversial as the speed of equilibrium between the ocean and the atmosphere is uncertain.
Dott, Robert H. & Roger L. Batten. Evolution of the earth. McGraw-Hill, Inc. Second Edition 1976. p. 441.
Although great strides have been made in estimating past changes in CO2 levels since 1976, this is still not accurate enough to conclude that CO2 was an important climatic factor during the Phanerozoic.
Paleocene-Eocene CO2 estimates range from 400-800 ppm to 2,000-3,000 ppm. The drawdown that supposedly caused the geologically sudden cooling at the beginning of the Oligocene cannot even be properly quantified.
Figure 2a. Marine pCO2 (Foram Bor δ11B, Alkenon δ13C), atmospheric CO2 from plant crevices (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 to Figure 3a.
Changes in atmospheric CO2 cannot be clearly identified with PETM, EECO, MECO or MMCO. be associated [1], [2]; however, a model now suddenly connects it to the one great Cenozoic climate shift, which has been well explained by plate tectonics and oceanic circulation changes. You can’t mean that seriously.
But climate models that can’t do anything else right, especially the late Pleistocene to the early Holocene, suddenly nail the Cenozoic Ice Age …
The models also failed to keep pace with records of past climates. With the new model from NCAR, for example, scientists have simulated the coldest point of the most recent ice age 20,000 years ago. Extensive paleoclimatic records suggest the earth has cooled nearly 6 ° C compared to pre-industrial times, but the model fed on low ice age CO2 showed temperatures almost double what suggesting that it was far too sensitive to the ups and downs of CO2. “That is clearly beyond the reach of geological data,” says Jessica Tierney, paleoclimatologist at the University of Arizona and co-author of the paper that appeared in the Geophysical Research Letters. “It’s totally out there.”
Science! (as in “she blinded me”)
They “solved” the “Holocene temperature puzzle” by simply applying a downward adjustment of the early Holocene temperatures. Unfortunately for them it remained unsolved.
Figure 3. “Something funny happened on the way to the Anthropocene.”
For their solution to the “Holocene Temperature Riddle” to be valid, much of the melting of the Laurentid ice sheet and the subsequent neoglaciation would have taken place with very little temperature changes. Fortunately, Kaufman et al., 2020 did not delete the CPS version of their reconstruction.
Figure 4. CPS with historical climatic periods and neoglaciation (Grosjean et al., 2007), Early Holocene ice expansion map (Dyke et al., 2003) and alpine tree height (Bohleber et al., 2021). PAGES 12K: The Ice Age Goeth
References
Bohleber, P., Schwikowski, M., Stocker-Waldhuber, M. et al. New evidence of glaciers for ice-free peaks in the life of the Tyrolean man from the ice. Science representatives 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, AS, 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 Studies. 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. Science data 7, 201 (2020). https://doi.org/10.1038/s41597-020-0530-7
Lauretano, V., Kennedy-Asser, AT, Korasidis, VA et al. Eocene to Oligocene terrestrial cooling of the southern hemisphere due to sinking pCO2pCO2. Nat. Geosci. (2021). https://doi.org/10.1038/s41561-021-00788-z
Pagani, Mark, Michael Arthur & Katherine Freeman. (1999). “Miocene Development of Atmospheric Carbon Dioxide”. Paleoceanography. 14. 273-292. 10.1029 / 1999PA900006.
Pearson, PN and Palmer, MR: Atmospheric Carbon Dioxide Concentrations Over the Last 60 Million Years, Nature, 406, 695–699, https://doi.org/10.1038/35021000, 2000.
Royer, et al., 2001. Paleobotanical evidence for near-modern concentrations of atmospheric CO2 during part of the Tertiary. Science June 22, 2001: 2310-2313. DOI: 10.112
Steinthorsdottir, M., Vajda, V., Pole, M., and Holdgate, G., 2019, “Moderate level of Eocene pCO2 selected by Southern Hemisphere fossil plant stomata”: Geology, v. 47, p. 914-918, https://doi.org/10.1130/G46274.1
Tripati, AK, CD Roberts, and RA Eagle. 2009. “Coupling of CO2 and ice sheet stability over important climatic transitions of the last 20 million years”. Wissenschaft, Vol. 326, S. 1394 1397, December 4, 2009. DOI: 10.1126 / science.1178296
Zachos, JC, Pagani, M., Sloan, LC, Thomas, E. & Billups, K. “Trends, Rhythms, and Aberrations in Global Climate 65 Ma to present”. Science 292: 686-693 (2001).
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