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Clintel Report: The disappearance of the Holocene Optimum

31 May 2023 | Science Notes

This week we begin a detailed look at the new report from Clintel.org, a Netherlands-based group whose World Climate Declaration against the Climate Emergency has garnered over 1500 signatures from scientists and experts the world over. Entitled The Frozen Climate Views of the IPCC, the report examines several prominent claims of the IPCC and points out where they are overstated, implausible or just plain wrong. In Chapter 1, Dr. Javier Vinós examines the claim of the IPCC that it is more likely than not that today’s temperatures are higher globally than at any time in the past 125,000 years. Which sounds remarkable, except that for the first 115,000 or so of those years the world was in an ice age glaciation, so the comparison is meaningless. It is only during the past 10,000 years that the world has been hospitably warm, and up until recently it was generally believed that the warmest part of the current interglacial was the Holocene Thermal Maximum (HTM) about 6,000 years ago. The IPCC wiped it out with their new, super-elongated hockey stick. But as Vinós shows, to get this result they had to use a new proxy reconstruction backed by umpteen tendentious assumptions. A look at the hard evidence left behind by glaciers and forests shows a very different picture.

Vinós begins by showing that the reconstruction used by the IPCC doesn’t actually show that the world is warmer than it was 6,000 years ago, because there is too much uncertainty to say for sure. But, he adds, their claim, such as it is, has the added problem that it is based on temperature proxies like tree rings which often do a poor job at recording local temperature changes. Also, proxy graphs can be changed dramatically with a few tweaks to the formula. He gives as an example the infamous case of the Marcott reconstruction from 2013 which showed a slow cooling over the past 10,000 years then a dramatic warming in the past century, as shown in this closeup of the past 2,000 years:

This was the version of the graph that got worldwide press coverage, but the one in Marcott’s PhD dissertation 2 years earlier looked very different:

There is a remarkable story of how the second graph was manipulated to get the uptick shown in the first graph, though Vinós doesn’t tell it (you can read it here: it’s another example of Steve McIntyre’s remarkable sleuthing. Suffice it to say the ending segment of the first graph is bogus and the authors quietly withdrew their conclusions when confronted with the evidence.) Instead Vinós focuses on the evidence the IPCC ignored which looks at the changes in glaciers and forest lines over the past 10,000 years.

When glaciers retreat and advance, or when tree lines migrate up and down mountains, they leave large indelible clues to what the climate must have been like in ages past. If fossil remains show that a forest once stood on what is today Arctic tundra, we can be certain that it was much warmer in the past than it is now. Vinós reviews published evidence from different teams of authors who have shown the mid-Holocene was characterized by large-scale glacier retreat and forest advances, putting it into conditions that appear to have been warmer than today. By ignoring this evidence and putting all their trust in a shiny new statistical proxy chart, the IPCC has waived away the HTM the way they did the Medieval Warm Period using Michael Mann’s infamous hockey stick graph. As the Clintel report shows, however, the past has a story of its own to tell.

4 comments on “Clintel Report: The disappearance of the Holocene Optimum”

  1. "If fossil remains show that a forest once stood on what is today Arctic tundra, we can be certain that it was much warmer in the past than it is now."
    Maybe since the Holocene, but this inference does not hold on longer time scales. The reason we find dinosaur fossils in the Arctic is because the Arctic used to be near the equator, and has since drifted north. You have to take plate tectonics into account on long time scales.

  2. @Thylacine True, for large enough timescales. However, (carbon and other-)dating here shows a much shorter timespan, in the order of (ten-)thousands of years. A scale at which continental drift is definitely measurable but won't affect local climate enough to turn a tundra into a forest. A new mountain range, disappearance of a sea, opening of a new channel between oceans, etc can do that, but not at this geologically short timescale (which is the point of the graphs and the article).

  3. Gore's Inconvenient Truth was an apt title, but not for the reasons he espoused, nor in relation to the 'truth' he revealed.....

  4. Graph A is a fraud.And that has been discussed a thousand times over at CDN et al, with clear evidence showing why.

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