By Andy May
As my regular readers know, I have been writing about the Holocene, specifically the Holocene climate, for over ten years. My colleagues, Javier Vinós and Renee Hannon, have also written extensively on the subject. This fills the void left by the IPCC, ignoring the Holocene, a fact made clear in my last two articles, This And This. Here I want to review a very comprehensive and informative Rate the article about what the authors, Darrell S. Kaufman and Ellie Broadman, call the “Holocene Global Temperature Conundrum.” The article was published in Nature February 15, just over a week ago. A reader who identified himself as “Mike G” was aware of it, and he was kind enough to send me a pdf of the article.
Kaufman and Broadman define the Holocene temperature conundrum this way:
“A landmark reconstruction of the GMST shows the highest temperature in the mid-Holocene, when the GMST reached about 0.8 °C higher than pre-industrial times. In contrast, the initial transient climate model showed that the GMST was about -0.5 °C colder during the mid-Holocene than during the pre-industrial period. [aka Little Ice Age] temperature, followed by further heating. This discrepancy between late Holocene global cooling trends inferred from proxy evidence versus warming trends simulated by climate models is known as the ‘Holocene temperature conundrum’. ”
(Kaufman & Broadman, 2023)
Therefore, the proxy evidence we have has suggested that the global mean surface temperature (GMST) in the early Holocene was about 0 ,8°C, but IPCC/CMIP6/PMIP4 climate models suggest that the early Holocene was colder, from 0.3 to 0.5°C compared to the Little Ice Age.
After scrutinizing the evidence for temperature changes during the Holocene, Kaufman and Broadman concluded that the global mean surface temperature (GMST) used to higher during the Holocene Climate Optimal and global cooling then takes place in the next period commonly known as the Neoglacial. Figure 1 is from my previous post, it provides a reasonable regional temperature reconstruction for the Arctic, Northern Hemisphere, Tropics, Southern Hemisphere and Antarctica.
As Figure 1 makes clear, it is difficult to accurately and faithfully represent temperature changes during the Holocene with the “global average”. At the beginning of the Holocene, different slices of latitude went in different directions, and the cooling of the New Ice Age did not really take place globally, but mainly in the Northern Hemisphere. However, Kaufman and Broadman conclude:
“The GMST probably peaked around the end of the first half of the Holocene, at about 6.5 ka [4500BC], supported by extensive proxy data and supported by theory and models. Delegated evidence reported in several studies indicates that the GMST was about 0.5 °C higher during this millennial scale period than during the period 1850–1900, with most warming occurring in mid to high latitudes in the Northern Hemisphere.”
(Kaufman & Broadman, 2023)
Thus, the data runs against the models. When I was a computer modeler, this was the end of it, sorry man, you screwed it up. But we live in a different world today. The authors go on to say:
“In terms of modeling, none of the 16 latest generation global climate models entered the recent competition. CMIP6-PMIP4, the 6-ka experiment simulated GMST beyond their pre-industrial controls. The GMST at 6 ka in these models is 0.3 °C cooler on average than pre-industrial times (Figure 1b), opposing the global HTM.”
(Kaufman & Broadman, 2023)
They provide a graph of the CMIP6 modeled temperature difference between the Holocene Climate Optimal (HCO) and the Little Ice Age (LIA). That’s our Figure 2.
The map of the climate model resulting in Figure 2 is dangerous enough, but the graph on the right shows that the latitudes in the middle of the Northern Hemisphere are almost the same in the HCO and the LIA! We know that can’t be true. Numerous historical, authorized, and archaeological records from around the world show that LIA was the coldest and most miserable time in human history in the Northern Hemisphere.
Kaufman and Broadman conclude:
“If our preferred interpretation [the HCO was warmer than the LIA] is correct and recent global warming is driven by global cooling trends over several centuries, this points to the need to improve our understanding of gaseous agents and responses. natural climates, along with their representation in climate models. The very large latitude and seasonal changes in sunshine caused by orbital forcing are most likely responsible for the climate feedbacks during the second half of the Holocene.”
(Kaufman & Broadman, 2023)
All I had to say was “listen! listen!” Climate models clearly don’t model natural climate change accurately, especially not orbital forcing.If you can’t model natural climate change, you If you can’t model the Holocene correctly, you don’t understand climate change.
Kaufman, D., & Broadman, E. (2023, February 15). Revisiting the Holocene global temperature conundrum. Nature, 614, 425-435. Taken from https://doi.org/10.1038/s41586-022-05536-w
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