Climate: IPCC AR6 - riddled with errors and biases

 From Judith Curry.

The report referred to can be found here.

JC's comment follows.

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CLINTEL’s critical evaluation of the IPCC AR6

Posted on May 13, 2023 by curryja | 22 Comments

by Judith Curry

Clintel has published a new report entitled “The Frozen Climate Views of the IPCC: Analysis of the AR6.”

“The new Report provides an independent assessment of the most important parts of AR6. We document biases and errors in almost every chapter we reviewed. In some cases, of course, one can quibble endlessly about our criticism and how relevant it is for the overall ‘climate narrative’ of the IPCC. In some cases, though, we document such blatant cherry picking by the IPCC, that even ardent supporters of the IPCC should feel embarrassed.”

Climate Intelligence (CLINTEL) is an independent foundation that operates in the fields of climate change and climate policy. CLINTEL was founded in 2019 by emeritus professor of geophysics Guus Berkhout and science journalist Marcel Crok.

The CLINTEL Report is edited by Marcel Crok and Andy May, with contributions from Javier Vinos, Ross McKitrick, Ole Humlum, Nicola Scafetta, and Fritz Vahrenholt.

The Chapter topics are:

No confidence that the present is warmer than the mid-Holocene

The resurrection of the Hockey Stick

Measuring global surface temperature

Controversial Snow Trends

Accelerated sea level rise: not so fast

Why does the IPCC downplay the Sun?

Misty climate sensitivity

AR6: more confidence that models are unreliable

Extreme scenarios

A miraculous sea level jump in 2020

Hiding the good news on hurricanes and floods

Extreme views on disasters

Say goodbye to climate hell, welcome climate heaven

The key issue is this: the IPCC focuses on “dangerous anthropogenic climate change,” which leads to ignoring natural climate change, focusing on extreme emissions scenarios, and cherry picking the time periods and the literature to make climate change appear “dangerous.”

“The IPCC ignored crucial peer-reviewed literature showing that normalised disaster losses have decreased since 1990 and that human mortality due to extreme weather has decreased by more than 95% since 1920. The IPCC, by cherry picking from the literature, drew the opposite conclusions, claiming increases in damage and mortality due to anthropogenic climate change.”

With regards to IPCC AR6’s error ridden assessment of extreme weather events, see also this analysis by Roger Pielke Jr that demonstrated egregious errors in incorrectly reporting the conclusions from papers that were actually cited by the IPCC.

With regards to ignoring natural climate variability, Chapters 1 (mid-Holocene), 2 (Hockey Stick) and 6 (the sun) are excellent.

I’ve looked at the AR6 WGI Report fairly thoroughly, focusing mainly on specific material that was relevant for my new book Climate Uncertainty and Risk. I am familiar with nearly all of the issues raised in the CLINTEL Report, but the material in Chapters 2 (Hockey Stick) and 4 (snow trends) was new to me. The next section focuses on the Hockey Stick.

Zombie Hockey Stick

Shortly after publication of AR6 WGI, I spotted some comments in twitter regarding the resurrection of the Hockey Stick. After wondering “what fresh new Hockey Stick hell is this?”, I didn’t investigate further.

Well the Clintel Report did the work for me. Subtitle for Chapter 2:

“A big surprise in the new IPCC report is the publication of a brand new hockey stick. The IPCC once again has to cherry pick and massage proxy data in order to fabricate it. Studies that show larger natural climate variations are ignored.”

Excerpts from the Chapter:

<begin quotes>

The PAGES 2k group is specialised in climate reconstructions and back in 2013 was comprised of the majority of all active paleoclimatologists. The PAGES 2k Consortium (2013) published a reconstruction in which parts of the first millennium were occasionally as warm as present-day

In 2019, PAGES 2k published a new version of the temperature development of the past 2000 years (PAGES 2k Consortium, 2019)11. Surprisingly, it differed greatly from the predecessor version. Even though the database had only mildly changed, the pre-industrial part was now suddenly nearly flat again. The hockey stick was reborn.

The new hockey stick was immediately incorporated into the AR6 report (IPCC, 2021). Among the lead authors of AR6 chapter 2 is Darrell S. Kaufman who is a co-author of the new hockey stick in the PAGES 2k Consortium (2019). This is probably not a coincidence.

Evidence suggests that a significant part of the original PAGES 2k researchers could not technically support the new hockey stick and seem to have left the group in dispute. Meanwhile, the dropouts published a competing temperature curve with significant pre-industrial temperature variability (Büntgen et al., 2020). On the basis of thoroughly verified tree rings, the specialists were able to prove that summer temperatures had already reached today’s levels several times in the pre-industrial past. However, the work of Ulf Büntgen and colleagues was not included in the IPCC report, although it was published well before the editorial deadline.

Like its predecessor, the new hockey stick by PAGES 2k 2019 is based on a large variety of proxy types and includes a large number of poorly documented tree ring data. In many cases, the tree rings‘ temperature sensitivity is uncertain. For example, both PAGES 2k Consortium (2013) and PAGES 2k Consortium (2019) used tree ring series from the French Maritime Alps, even though tree ring specialists had previously cautioned that they are too complex to be used as overall temperature proxies.

In contrast, Büntgen et al. (2020) were more selective, relied on one type of proxy (in this case tree rings) and validated every tree ring data set individually. Their temperature composite for the extra-tropical northern hemisphere differs greatly from the studies that use bulk tree ring input.

In some cases, PAGES 2k composites have erroneously included proxies that later turned out to reflect hydroclimate and not temperature. In other cases, outlier studies have been selected in which the proxies exhibit an anomalous evolution that cannot be reproduced in neighbouring sites (e.g. MWP data from Pyrenees and Alboran Sea in PA13). Outliers can have several reasons, e.g. a different local development, invalid or unstable temperature proxies, or sample contamination.

Steve McIntyre has studied the PAGES 2k proxy data base in great detail and summarized his criticism in a series of blog posts on his website Climate Audit. For example, the PAGES 2k Consortium (2019) integrated a tree ring chronology from northern Pakistan near Gilgit (“Asia_207”) which shows an extreme closing uptick. Incorporation of data series like this strongly promote the hockey stick geometry of the resulting temperature composite. McIntyre analysed the original tree ring data and found that the steep uptick in the Asia_207 chronology is the result of questionable data processing. When calculating the site chronology using the rcs function from Andy Bunn’s dplR package, the uptick surprisingly disappears. In fact, the series declines over the 20th century.

Conclusion: The resurrected hockey stick of AR6 shows how vulnerable the IPCC process is to scientific bias. Cherry picking, misuse of the peer review process, lack of transparency, and likely political interference have led to a gross misrepresentation of the pre-industrial temperature evolution.

<end quotes>

JC reflections

The CLINTEL Report provides a much needed critical evaluation and intellectual counterpoint to the IPCC AR6.

There is a lot of good material in the AR6 WG1 Report, but there is also a lot of cherry picking and flat out errors in the Report (the AR6 WG2 Report is just flat out bad). With any kind of serious review, or if the author teams have been sufficiently diverse, we would not see so many of these kinds of errors. Unfortunately, the IPCC defines “diversity” in terms of gender, race and developed versus underdeveloped countries; actual diversity of thought and perspective is dismissed in favor of promoting the politically mandated narrative from the UN.

The consensus disease that that was caught by the IPCC following publication of the First Assessment Report in 1990, combined with pressures from policy makers, is resulting in documents that don’t reflect the broad disagreement and uncertainties on these complex topics. The IPCC’s mandated narrative has become very stale. Worse yet, it is becoming increasingly irrelevant to policy making by continuing to focus on extreme emissions scenarios and the embarrassing cherry picking that is required to support the “climate crisis” narrative that is so beloved by UN officials.

In any event, UN-driven climate policy has moved well past any moorings in climate science, even the relatively alarming version reported by the IPCC. The insane policies and deadlines tied to greenhouse gas emissions are simply at odds with the reality of our understanding of climate change and the uncertainties, and with broader considerations of human well being.