The IPCC recently published something called the “Synthesis Report of the Sixth Assessment Report”. And there was a time around 1990 when the IPCC was a recognizable group of experts who put out relatively short scientific summaries that credibly represented the best available knowledge. But now, 30+ years later, as all government entities tend to, it has ballooned into a massive out-of-control bureaucracy consisting of many different and ever-expanding groups who never confer with each other, with thousands of agenda-driven academics attaching themselves to every available surface whether or not they have any qualifications, yet every emanation gets presented to the public as somehow representing the last word on the science despite most scientists now having no input into the IPCC process. All it takes is one clear example of the problem to show how rotten the process has become. And thanks to Roger Pielke Jr. we can give you such an example. It concerned the lack of evidence of changes in tropical cyclones and how the IPCC spun that into the claim that they are getting worse and greenhouse gases are to blame.
The story begins with a 2019 paper that asserted that the fraction of tropical cyclones exhibiting intense (Category 3 or higher winds) had trended upward in all regions globally. But an alert reader noticed an error in the math and the authors published a correction showing that in fact the trends were too small to be statistically significant (which is how those in the field say “distinguishable from random chance”) in all but two of the regions they examined. As Pielke Jr. notes, this was a massive correction.
The authors also used a nonstandard approach to the data which led to much confusion. Instead of looking at the overall categorization of entire hurricanes they looked at the individual (6 hour) data retrievals and asked how many of those were in the Category 3 or higher range. While there were about 4,000 hurricanes worldwide over 1979-2017, there were about 225,000 individual samplings, which they referred to as instances. A hurricane which was considered to be a Category 2 storm might still exhibit brief 6 hour intervals where the winds get up to Category 3 or 4 then fall back down. Hence a Category 4 instance is not the same as a Category 4 storm occurrence. The 2019 study had asserted that the proportion of intense storm instances as a fraction of all hurricane instances globally had risen over time. But in the correction they said no, not globally, just in a couple of places.
The IPCC Sixth Assessment Report discussed this issue in Chapter 11 of the Working Group I Report (which we previously quoted here). They relied on the flawed original results to claim that “a significant increase is found in the fractional proportion of global Category 3–5 TC instances (6-hourly intensity estimates during the lifetime of each TC) to all Category 1–5 in stances.” So that’s the first problem: they quoted the incorrect original results and made no mention of the later correction that retracted most of the original claim. Although elsewhere they noted, correctly, “There is low confidence in most reported long-term (multidecadal to centennial) trends in TC [Tropical Cyclone] frequency- or intensity-based metrics.”
Then it got worse. In the chapter 11 summary they said “It is likely that the global proportion of Category 3–5 tropical cyclone instances has increased over the past four decades.” burying the definition of “instances” in a footnote. Then in the Summary for Policymakers of the same report they rephrased this as “It is likely that the global proportion of major (Category 3–5) tropical cyclone occurrence has increased over the last four decades.” They switched the word “instance” for “occurrence”, making it sound like entire hurricanes were getting stronger.
Then the authors of the Synthesis Report grabbed hold of the inaccurate Summary from the report that used uncorrected findings, without noticing the switch in wording, and said “It is likely that the global proportion of major (Category 3–5) tropical cyclone occurrence has increased over the last four decades.” [The emphasis on likely was in the Summary but not Pielke’s quotation.] The IPCC in another report had pointed out that they can hardly attribute changes in TC frequency to greenhouse gases when they haven’t even detected such changes:
“The lack of confident climate change detection for most TC metrics continues to limit confidence in both future projections and in the attribution of past changes and TC events, since TC event attribution in most published studies is generally being inferred without support from a confident climate change detection of a long-term trend in TC activity.”
But having already botched the review of tropical cyclone data by conflating instances and occurrences, the new Synthesis went further and simply invented an attribution claim out of nowhere:
“Evidence of observed changes in extremes such as heatwaves, heavy precipitation, droughts, and tropical cyclones, and, in particular, their attribution to human influence, has strengthened since AR5.”
Pielke Jr. pulls his punches in his assessment of this mess, saying only “I come to the conclusion that the IPCC needs reform. Mistakes can creep into massive assessments, to be sure, but the failures I document below are absolutely unacceptable.”
So we’ll say what he was reluctant to. This blunder was a toxic mix of dishonesty and carelessness amplified by the fact that the IPCC is now dominated by activists with axes to grind. Unless they retract these errors, kick out the clowns responsible and notify world leaders of the correction, you are entirely justified in assuming that any and all parts of IPCC reports are likewise unreliable.