lee
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The re-emergence of the Hockey Stick
"Curiously, this leading diagram of the Summary of Policy-Makers does not appear in the Report itself. (At least, I was unable to locate it in Chapter 2.) However, it is clearly the progeny of PAGES2K Consortium (Nature 2019) and Kaufman et al (2020), both of which I commented on briefly on Twitter (see here).
It’s hard to know where to begin.
The idea/definition of a temperature “proxy” is that it has some sort of linear or near-linear relationship to temperature with errors being white noise or low-order red noise. In other words, if you look at a panel of actual temperature “proxies”, you would expect to see series that look pretty similar and consistent.
But that’s not what you see with the data used by the IPCC. You’d never know this from the IPCC report or even from the cited articles, since authors of these one- and two-millennium temperature reconstructions scrupulously avoid plotting any of the underlying data. It’s hard for readers unfamiliar with the topic to fully appreciate the extreme inconsistency of underlying “proxy” data, given the faux precision of the IPCC diagram.
Many of the series discussed in this post, including nearly all of any HS-shaped series, have been previously discussed in Climate Audit blog posts (tag/pages2k) from 2, 5, 10 or even 15 years ago or in tweets from 2019 and 2020 (see here).
The PAGES2019 is not a “random” selection of proxies, but winnowed through ex post criteria. As Rosanne d’Arrigo explained to the NAS panel many years ago: if you want to make cherry pie, you first have to pick cherries.
The PAGES2019 dataset consists of 257 proxies, selected from the prior PAGES2017 dataset consisting of 692 proxies, which had previously been selected from thousands of proxy series accumulated by many authors over the years.
In order to give readers an overview of the underlying data – not the massaged final product, I’ve plotted three batches of 11 randomly selected series from each of PAGES2017, PAGES2019 and then PAGES2019 North American tree rings and then commented on each batch. (The samples were selected by R formula sample(1:K, 11) where K is the size of dataset being sampled.) In each case, there were usually series that I had already studied plus numerous non-descript series, which are notable and important to show precisely because the majority of proxies are non-descript and you need to see this to understand it.
This post will be a work in progress for a few days, as I have some sections on special issues that I will try to add as I have time.
A First Batch: PAGES2017 Proxies
As a first illustration, below is a random sample of 11 PAGES2017 series. The series carried forward to PAGES2019 are in blue. For reference, the IPCC curve is shown in red. As you can easily see, most of the series are non-descript and short. Only one series in this sample (Cape Ghir temperature alkenones) has a hockey stick shape, but it goes down.
It’s not as though PAGES2K made a composite from 257 series that are two millennia long, all or a majority having a HS shape. One series in this sample does look a lot like the IPCC stick and will be discussed at length below, but the others look very different.
Four of the series in the sample are very short – three of them are actually shorter than the instrumental record. These are all coral Sr or coral d18O series, which make up 25% of the PAGES2019 data set. The extremely short records illustrated above are typical, indeed almost universal, in this class of proxy. They do have a pronounced trend in the instrumental period. This contrasts with the lack of trend that one sees in the two long proxies in the middle column above – a tree ring series from Mt Read, Tasmania (also used in MBH98) and a 1983 ice core series by Fisher from Devon Ice Cap on Baffin Island (also available to 1990s vintage multiproxy studies).
The short coral series do not contribute information to the medieval and earlier periods which one is trying to compare to the modern period. So what is their function? Do they contribute anything other than painting a moustache on the non-descript longer series?
The tree ring series in this sample are rather short; the screening procedures have somewhat concentrated series with slight upticks. (The stripbark bristlecone chronologies that were so prominent in the Mann et al Hockey Stick continue to be used in PAGES2019 – as discussed below.) I discussed the series in the left column with large uptick (Asi_MUSPIG aka paki033) in a 2019 tweet thread here. I located the underlying ring width measurements at NOAA and re-calculated the tree ring “chronology” using standard methodology – see below. The high-frequency details match, showing that the underlying measurement data is apples-to-apples. No chronology from original authors is archived at NOAA: so how did PAGES2K manage to get such a hockey stick? I have no idea.
The most “interesting” series in this sample batch is the borehole temperature reconstruction that has such an uncanny resemblance to the eventual IPCC reconstruction. By coincidence (or not), I wrote about this borehole temperature reconstruction (from WAIS Divide, Antarctica) in February 2019, a few months before publication of PAGES 2019 – see here – scroll down – for a more thorough analysis.
TBC
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