Guest “” by David Middleton
The Paleocene Eocene Thermal Maximum (PETM) was a geologically brief spike in temperatures, during the warmest climatic episode of the Cenozoic Era.
We are often told that the warmth of the Early Paleogene was driven by CO2; and that the cool-down from the Late Paleogene, into the Neogene and Quaternary Periods was driven by a draw-down of atmospheric CO2; however there is scant evidence for this hypothesis[1][2]. Despite the paucity of geological evidence, the notion of a CO2-driven climate has apparently become a paradigm.
This paradigm didn’t exist in the 1970’s.
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 methods of estimating past CO2 levels have improved, the Early Paleogene is still poorly understood, with estimates ranging from 300 to 3,500 ppm.
The recent publication by The Cenozoic CO2 Proxy Integration Project (CenCO2PIP) Consortium failed to significantly reduce Paleogene uncertainty despite claims to the contrary.
Why geologists are supposed to avoid paradigms
When I was studying geology, way back when The Ice Age Cometh in the 1970’s, we were taught to avoid getting hooked on paradigms or “ruling theories”. Geology, as a science, has very few unique solutions. This is why we were were taught to embrace Chamberlin’s Method of Multiple Working Hypotheses. I have to assume that either this is no longer the case or that homage must be paid to the current paradigm in order to get published. The CenCO2PIP Consortium embraced it BIG TIME.
The consortium’s members did not collect new data; rather, they came together to sort through published studies to assess their reliability, based on evolving knowledge. They excluded some that that they found outdated or incomplete in the light of new findings, and recalibrated others to account for the latest analytical techniques. Then they calculated a new 66-million-year curve of CO2 versus temperatures based on all the evidence so far, coming to a consensus on what they call “earth system sensitivity.” By this measure, they say, a doubling of CO2 is predicted to warm the planet a whopping 5 to 8 degrees C.
Paradigms and ruling theories drive scientists to looking for specific answers. And they tend to only see what they “shine a light on.” The current paradigm is that CO2 has driven climate change over the Phanerozoic Eon (the past ~540 MY).
- The Paleocene-Eocene was, on average, 4–15 °C warmer than today.
- Atmospheric CO2 was very likely in the 450-600 ppm range.
- Modern climate models would require 4,500 ppm CO2 to simulate the Paleocene-Eocene temperature range.
Therefore the equilibrium climate sensitivity must be 5-8 °C per doubling of atmospheric CO2, rather than the observation-supported 2.3 °C per doubling (a transient climate response of only 1.2-1.6 °C).
It never seems to occur to them that something completely different drove climate change over geologic time.
“And now for something completely different…”
Earth’s Orbit Mysteriously Altered by Chance Encounter Million of Years Ago
SPACE 19 February 2024
A grazing encounter between the Solar System and a passing star could once have changed Earth’s orbit enough to wreak havoc on the climate, new research has found.
Around 56 million years ago, at the boundary between the Paleocene and Eocene, Earth’s temperature warmed by up to 8 °C (14.4 °F).
This has always been a bit of a puzzle – but planetary scientist Nathan Kaib of the Planetary Science Institute and astrophysicist Sean Raymond of the Laboratory of Astrophysics of Bordeaux suggest a chance encounter may have been the culprit.
Their simulations show that a star passing by the Solar System could have introduced enough disruption to planetary orbits to nudge Earth slightly off course.
“One reason this is important is because the geologic record shows that changes in the Earth’s orbital eccentricity accompany fluctuations in the Earth’s climate,” Kaib says.
“If we want to best search for the causes of ancient climate anomalies, it is important to have an idea of what Earth’s orbit looked like during those episodes.”
[…]
Kaib and Raymond wanted to know if a passing star could have a similar effect, even from a significant distance. Their work focused on a single known event. Some 2.8 million years ago, a Sun-like star called HD 7977 passed the Solar System, potentially so closely that it flew inside the Oort Cloud.
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HD 7977 is one star, and the only flyby we can confidently identify. But scientists have estimated that a star passes by within 50,000 astronomical units every million years or so, and within 10,000 astronomical units every 20 million years or so.
This means that it’s entirely possible that a passing star has affected Earth’s climate in the past – and may even have played a role in the thermal maximum.
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The full text of their paper is available and worth reading.
5. HD 7977 and the Paleoclimate
It is clear that the stellar passages expected within the solar neighborhood significantly influence the orbital evolution of the Sun’s planets, and we now assess the effects of a specific encounter known to have occurred. Among past stellar encounters inferred from Gaia Data Release 3, HD 7977 stands out as potentially the closest recent known encounter. This 1.1 M⊙ star passed near the solar system ∼2.8 Myr ago at ∼27 km s−1 (Bailer-Jones 2022; Gaia Collaboration et al. 2023). Although this encounter’s median inferred impact parameter is ∼13,200 au, there is a large amount of uncertainty, with a 5% probability of passage within ∼3900 au. This range of impact parameter corresponds to over 1 order of magnitude variation in impulse gradient (which governs the level of planetary perturbation).
What happened ~about 2.8 million years ago (MYA)? The onset of Pleistocene Epoch (~2.58 MYA) and the coldest climate since the Late Paleozoic Ice Age (formerly Karoo Ice Age) 330-280 MYA.
While it’s clear that plate tectonics and the changing configurations of continents and ocean basins have been primary drivers of past climate change… It’s also quite possible that astrophysical phenomena related to our solar system’s peregrinations around the Milky Way galaxy have also been primary drivers of paleoclimate change. Our solar system’s crossings of the galaxy’s spiral arms have been linked to the major Phanerozoic ice ages (Shaviv & Veizer, 2004, Shaviv, Svenmarsk & Veizer, 2022) and the formation of continental cratons (Kirkland, et al., 2022). While we can effectively measure the Milankovitch Cycles and have correlated them to Pleistocene glacial-interglacial stages, phenomena like our solar system’s crossings of the galaxy’s spiral arms and interactions with rogue stars are much more difficult to nail down… It’s just easier to blame ExxonMobil for whatever the weather does.
References
Berner, R.A. and Z. Kothavala, 2001. “GEOCARB III: A Revised Model of Atmospheric CO2 over Phanerozoic Time”, American Journal of Science, v.301, pp.182-204, February 2001.
Dott, Robert H. & Roger L. Batten. Evolution of the Earth. McGraw-Hill, Inc. Second Edition 1976. p. 441.
Kaib, Nathan A. and Sean N. Raymond 2024 ApJL 962 L28DOI 10.3847/2041-8213/ad24fb
Kirkland, C.L., P.J. Sutton, T. Erickson, T.E. Johnson, M.I.H. Hartnady, H. Smithies, M. Prause; Did transit through the galactic spiral arms seed crust production on the early Earth?. Geology 2022;; 50 (11): 1312–1317. doi: https://doi.org/10.1130/G50513.1
[1] Middleton, David H. “A Clean Kill of the Carbon Dioxide-Driven Climate Change Hypothesis?” WUWT. 25 September 2019.
[2] Middleton, David H. “Middle Miocene Volcanism, Carbon Dioxide and Climate Change”. WUWT. 3 June 2019.
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
[Link] Royer, D. L., R. A. Berner, I. P. Montanez, N. J. Tabor and D. J. Beerling. “CO2 as a primary driver of Phanerozoic climate”. GSA Today, Vol. 14, No. 3. (2004), pp. 4-10
Shaviv, N., & Veizer, J. (2004). CO2 as a primary driver of Phanerozoic climate: Comment. GSA Today, 14, 18.
Shaviv, N. J., Svensmark, H., & Veizer, J. (2023). The phanerozoic climate. Annals of the new York Academy of Sciences, 1519, 7–19. https://doi.org/10.1111/nyas.14920
[Link] 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
The Cenozoic CO2 Proxy Integration Project (CenCO2PIP) Consortium*† ,Toward a Cenozoic history of atmospheric CO2.Science382,eadi5177(2023).DOI:10.1126/science.adi5177
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).