The PAGES (2017) North American network consists entirely of tree rings. Climate Audit readers will recall the unique role of North American stripbark bristlecone chronologies in Mann et al 1998 and Mann et al 2008 (and in the majority of IPCC multiproxy reconstructions). In today’s post, I’ll parse the PAGES2K North American tree ring networks in both PAGES (2013) and PAGES (2017) from two aspects:

even though PAGES (2013) was held out as the product of superb quality control, more than 80% of the North American tree ring proxies of PAGES (2013) were rejected in 2017, replaced by an almost exactly equal number of tree ring series, the majority of which date back to the early 1990s and which would have been available not just to PAGES (2013), but Mann et al 2008 and even Mann et al 1998;

the one constant in these large networks are the stripbark bristlecone/foxtail chronologies criticized at Climate Audit since its inception. All 20(!) stripbark chronologies isolated by Mann’s CENSORED directory re-appear not only in Mann et al (2008), but in PAGES (2013). In effect, the paleoclimate community, in apparent solidarity with Mann, ostentatiously flouted the 2006 NAS Panel recommendation to “avoid” stripbark chronologies in temperature reconstructions. In both PAGES (2013) and PAGES (2017), despite ferocious data mining, just as in Mann et al 1998, there is no Hockey Stick shape without the series in Mann’s CENSORED directory.

PAGES2K references: PAGES (2013) 2013 article and PAGES (2017) url; (Supplementary Information).

Background: Stripbark Bristlecones and Mann’s CENSORED Directory

In our 2005 articles, Ross and I pointed out that the Mann’s hockey stick is merely an alter ego for Graybill’s stripbark bristlecone chronologies and that the contribution from all other proxies was nothing more than whitish noise. We noted that Graybill himself had attributed the marked increase in late 19th and 20th century bristlecone growth to CO2 fertilization, not temperature – a theory which was arguably a harbinger of the massive and widespread world greening, especially in dry areas, over the 30 years since Graybill et al (1985).

In a CA blogpost here, I further illustrated the unique contribution of bristlecones by segregating the additive contribution to the MBH98 reconstruction of bristlecones (red) and other proxy classes (e.g. ice cores, non-bristlecone North American tree rings, South American proxies, etc. in blue, green, yellow ). This clearly showed that (1) the distinctive MBH98 Hockey Stick shape arose entirely from bristlecones and that (2) all other proxy classes contributed nothing more than whitish noise – with their combined contribution diminishing in accordance with the Central Limit Theorem of statistics.

Mann had, of course, done a principal components analysis of his North American tree ring network without stripbark bristlecones – an analysis not reported in his articles, but which could be established through reverse engineering of his now notorious CENSORED directory – see CA post here. ) These non-descript PCs further illustrate the non-HSness of the Mann et al 1998 North American tree ring network without strip bark bristlecones.

Figure 2. Plot of five principal components in MBH98 CENSORED directory i.e. without Graybill stripbark chronologies, mainly from bristlecones, but a couple of limber pines.

The 2006 NAS panel stated that stripbark chronologies (i.e. the Graybill bristlecone chronologies) should be “avoided” in temperature reconstructions. Although Mann et al 2008 stated that it was compliant with NAS recommendations, Mann flouted this most essential recommendation by including all 20 stripbark series isolated from the CENSORED analysis.

Because of persistent criticism over the impact of these flawed proxies, Mann et al (2008) made the grandiose assertion that he could get a hockey stick without tree rings (and thus, a fortiori, without stripbark bristlecones) – a claim credulously promoted by Gavin Schmidt at Real Climate. However, it was almost immediately pointed out at Climate Audit (here) that Mann’s non-bristlecone hockey stick critically depended on a Finnish lake sediment “proxy”, the modern portion of which (its blade) had been contaminated by modern agriculture and road construction and which had been used upside-down to its interpretation as a temperature proxy in pre-modern times. Mann was aware of the contamination of lake sediments, but argued that his use of contaminated (and upside down) data was legitimate because he could get a HS without them – in a calculation which used stripbark bristlecones. When challenged to show results without either stripbark bristlecones or upside-down mud, Mann (and Gavin Schmidt) stuck their fingers in their ears, with the larger climate community obtusely refusing to understand a criticism that was obvious to any analyst not subservient to the cause.

In the weeks prior to Climategate, I used increasingly harsher terms for the addiction of the paleoclimate community to the data-snooped stripbark chronologies, describing them as “heroin for paleoclimatologists”, with Briffa’s spurious Yamal chronology as “cocaine” (e.g. here here), occasioning much pearl-clutching within the hockey stick “community”.

PAGES 2013

To the accompaniment of claims of quality control, PAGES (2013) dramatically culled the population of the Mann et al 2008 North American tree ring network.

The predecessor network used 790 North American tree ring chronologies: 696 individually identified series plus 94 Schweingruber density (MXD) series that contributed to 37 gridded MXD series. (The fudging of these 37 gridded series is an interesting and under-appreciated chapter in hide the decline, in which Mann chopped off post-1960 declining values and replaced them with instrumental data – see here.)

The new PAGES (2013) network was reduced to 146 series, i.e. 81% (644 series) of the Mann et al (2008) was discarded as presumably not meeting PAGES (2013) quality control criteria. Approximately 45% (66) of these series were reported in PAGES (2013) as having a positive relationship to temperature according to their criterion, with 55% (80) having a negative relationship.

Despite the 81% cull, every (all 20) Graybill stripbark chronology of the MBH98 CENSORED directory (each of which had been subsequently used in Mann et al 2008) was used once again in the PAGES 2013 North American network. In this new network, just like Mann et al 1998, the non-stripbark series – even when opportunistically oriented after the fact according to PAGES (2013) procedure – do not have a Hockey Stick shape. The next diagram compares network averages of scaled chronologies (left- stripbark; right – all other chronologies after orientation), also showing network counts in lower panels. Scale in top panel is identical for both series, but there are far more series in right diagrams.

Figure 3. Top left: average of the 20 stripbark bristlecone chronologies common to Mann et al 1998 and PAGES (2013), standardized to standard deviation units; top right – same for the other 126 tree ring chronologies in the PAGES 2013 tree ring network. Bottom: left – count of number of sites included in the stripbark network (maximum of 20); right – same for other 126 chronologies. Note that scale in bottom panel differs between two sides. PAGES(2013) truncated series to 1200-1987 (with many further truncated to 1500-1980). For this diagram, original chronologies from NOAA archive were used.

The simple average of the PAGES 2013 stripbark chronologies has a shape very similar to the distinctive MBH98 Hockey Stick shape (the MBH98 shape is somewhat more pronounced due to extra weighting of more extreme blades in its PC calculation.) The combination is precisely identical to the pattern which I had observed in the MBH98 networks years ago: Graybill stripbark chronologies contribute the Hockey Stick; the vast majority are nothing more than whitish/reddish noise and have no overall climate signal whatever.

PAGES (2013) determined orientation of each series ex post through temperature correlation in the 20th century – a practice that I’ve criticized from my beginning in this field. My position has been that, if, for example, high-altitude or high-latitude black spruce are believed to be temperature proxies, then you have to use all sites in a consistent ex ante orientation, rather than opportunistically flipping series ex post simply because they go down. While the network is subject to this criticism, there is so much noise in the data in the network shown in the right panel that there is no HS even

Notice that the amplitude of fluctuations of the much larger network on the right (126 versus 20 series) is considerably less than the smaller network on left: this is a trivial result of the Central Limit Theorem of statistics: the standard deviation of an average of noise decreases as the dataset gets larger.

The apparent spike in 2002 non-stripbark ring widths (right) has a neat explanation. For some reason, ring widths in 2002 were exceptionally low. Examined in detail (and I looked at the underlying rwl measurement data), many trees at these sites (fewer in number in 2002 than a decade earlier) had negligible, even zero, growth in 2002. Because so many such series had been assigned negative orientation in PAGES 2013, these very low ring width values resulted in very “high” values in the composite.

There are other peculiarities in the PAGES 2013 network. Regardless of the length of the chronologies available to them, they were truncated into two separate subsets: a short subset truncated to 1500-1980 and a “long” subset truncated to 1200-1987. One dataset was archived as original chronology; the other standardized to SD units. Some series were included in both datasets; other series, which on their face qualified for both datasets, were not, for no obvious reason.

The only representation of the North American tree ring reconstruction in the PAGES (2013) article was the color bar (middle panel below) – a style, which either despite or because of its lower information content, has become popular among climate activists. It turns out to be a representation of a 30-year averaged series (bottom panel) which was archived in the Supplementary Information. The 30-year version appears to have been derived from the 10-year average version associated with it in the Supplementary Information.

Figure 4. PAGES (2013) North American reconstruction from tree ring network: middle panel – excerpt from figure in original article; bottom panel – plot of data from SI showing 30-year version of PAGES2K North American tree ring network; top panel – plot of data from SI which, for other regions shows annual data, but for North American tree rings, shows 10-year data.

PAGES (2017)

In PAGES (2013), as noted above), the NOAMER tree ring network contained both positive- and negative-oriented chronologies, the sign being assigned ex post based on the correlation of the chronology with temperature. PAGES (2017), in the supposed cause of “more stringent criteria”, introduced the restriction that the tree ring proxies (in all networks) be restricted to proxies which had a significant positive correlation to temperature:

more stringent criteria resulted in the exclusion of some records. .. In most regions, some records were excluded because they did not meet the stricter standards for the minimum length or temporal resolution (criteria detailed above), or because of ambiguities related to the temperature sensitivity of the proxy, or because they have been superseded by higher-quality records from the same site… To be included in the current database, tree-ring data were required to correlate positively (P<0.05) with local or regional temperature (averaged over the entire year or over the growing season). Trees whose growth increases with temperature (e.g., direct effect of temperature on physiological processes and photosynthetic rates) are more likely to produce a reliable expression of past temperature variability compared to trees that respond inversely to temperature, for which the proximal control on growth is moisture stress (e.g., evapotranspiration demand)

They reported that the new positive orientation criterion resulted in the exclusion of 124 tree ring series from. the PAGES (2013) network:

Of the 641 records that together comprise the previously published PAGES2k datasets, 177 are now excluded, of which 124 are tree-ring-width series that are inversely related to temperature.

Relative to a supposed worldwide total of 124 series excluded through negative correlation, no fewer than 123(!) series can be identified in the North American tree ring network. Previously, I’d noticed 3 such exclusions in the South American network. In a quick check, there were zero in the Asia network. PAGES (2017) did not explain (or even observe) the unique impact of this criterion on the North American network, but it’s an interesting question. Only 23 North American tree ring series were carried forward from PAGES (2013) to PAGES (2017). The devastation of the PAGES 2013 network itemization can be seen in the excerpt of the Supplementary Information shown below:

As usual, there is an additional irony and puzzle when the screening is examined in detail: of the 123 NOAMER tree ring series excluded due to their “negative” relation to temperature, 29(!) had been assigned a positive sign in PAGES (2013). This apparent inconsistency was not explained (or even reported) by the PAGES (2017) authors.

There are 126 “new” tree ring series in the PAGES 2017 North American tree ring network, but the majority of these series date back to the mid-1990s and even the early 1980s, as shown in the chart at left. Many of the numerous series from the early 1980s and 1990s are from the Schweingruber collection from which the Briffa reconstruction (with its notorious decline) was calculated. These series had presumably been previously considered in Mann et al 1998, Mann et al 2008 and PAGES (2013), but, for some reason, qualified in PAGES 2017 for the first time.

PAGES (2017) retained (only) 23 series from PAGES (2013). The number retained from Mann et al 2008 via PAGES2K was only 10, the majority of which were classic stripbark bristlecone chronologies, including Graybill chronologies from Timber Gap Upper, Flower Lake, Cirque Peak, Pearl Peak, Mount Washington, San Francisco Peaks,and, of course, Sheep Mountain. The PAGES (2017) network added two “classic” stripbark chronologies, which had not been used in PAGES (2013), but which had been a staple of many multiproxy studies: Graumlich’s Boreal Plateau and Upper Wright Lakes stripbark foxtail chronologies from the early 1990s, previously used in Esper et al 2002, Briffa and Osborn 2006, Hegerl et al 2007 and others. (Discussed on numerous occasions at CA, including here here).

It also added a composite (Salzer et al 2013) which updated three Graybill sites: Pearl Peak, Mount Washington, Sheep Mountain), each of which is thus included in both versions. The PAGES2017 version of the Salzer composite continues to 2009 – three years later than the series in the original publication or in archived ring width data. The provenance of this extra data was not reported. The extension is shown at right (green for 1980-1990; red for 1991-2009). The stripbark bristlecone data reached its peak in the late 1970s, exactly when Mann terminated his bristlecone-based reconstruction. Since then, bristlecone widths at these three sites have gone down despite increasing temperatures over the past 40 years, though they remain at historically elevated levels. In our 2005 criticism of Mann et al 1998, we had speculated that bristlecone ring widths would not continue to increase with higher temperatures and, indeed, they have not done so.

The stripbark chronologies, though reduced somewhat in number from the PAGES 2013 network, continue to play a unique role in the North American tree ring chronology. The diagram below compares the stripbark series in PAGES (2017) to non-stripbark chronologies in the same style as Figure 3 above. Despite industrial-scale ex post screening, in the non-bristlecone network (140 series – right panel), there is only a very slight increase at the start of the 20th century increase, no increase in the second half of the 20th century, with a possible reversion towards the mean in the sparser recent data. This pattern seems just as likely, or more likely, to be nothing more than what can be expected from ex post screening of reddish noise, and obviously does not capture the expected temperature “signal”. Nor do the bristlecones perform much better.

Figure 5. In same style as Figure 3, but for PAGES (2017). The stripbark network consists of the seven series from the CENSORED directory carried forward into PAGES 2017 plus two stripbark foxtail chronologies (Graumlich) re-introduced in PAGES (2013).

In passing, I noticed some frustrating technical misinformation that I might as well document. Although we’ve already seen that the PAGES 2017 technical spreadsheets explain exclusion of North American tree ring networks as due to “negative” correlation to temperature, elsewhere PAGES (2017) stated that many exclusions were due to other technical reasons: use of a reconstruction rather than a chronology (measurement data) in the earlier PAGES 2013 network, including reconstructions that made use of principal components – a topic not unfamiliar to readers of Climate Audit:

Unlike [3 – PAGES 2013], in the present version, tree-ring records include only ring-width or density measurements rather than the reconstructions derived from them. Therefore, many of the North American dendroclimatological records used in [3] are no longer employed. Also, in the North American component of [3], unlike the current version, tree-ring data were screened and incorporated into the North American temperature reconstructions as the leading principal components of the tree-ring chronologies utilized. The rationale, methodological detail, and associated reconstruction performance metrics for that usage are described in the supplemental information in [3] (cf. section 4a).

While this explanation seems superficially plausible, none(!) of the 146 records in the PAGES (2013) North American tree ring network were (temperature) reconstructions, let alone reconstructions calculated with the use of principal components. Every series in the PAGES (2013) North American network was either an ITRDB chronology truncated to 1500-1980 or an ITRDB chronology standardized to SD units (after truncation to 1200-1987).

North American Tree Ring Chronologies in PAGES Arctic Network

The PAGES2K (2013) Arctic network contained four North American tree ring series, while the PAGES (2017) Arctic tree ring network contained three North American tree ring series.

Three of the PAGES (2013) records were regional chronologies from D’Arrigo 2006: Central NWT, Seward and Yukon. The fourth was Wilson’s Gulf of Alaska/Coastal Alaska temperature reconstruction – the only temperature reconstruction in PAGES 2013 from North American tree rings, which, for good measure, was used in a duplicate copy the North American network.

As long-time Climate Audit readers are aware, Jacoby and D’Arrigo withheld supplementary information for almost 10 years. The eventual archive, published shortly before Jacoby’s death, remains incomplete and frustrating. In 2016, I wrote a very detailed examination (Cherry Picking By D’Arrigo) of the Central NWT regional chronology of D’Arrigo 2006 (and now PAGES 2013), as it represented many of the worst practices of the paleoclimate community. It annoys me to re-read the article. The Central NWT chronology built on the earlier Jacoby chronologies at Coppermine River and Hornby Cabin, which were used in Mann et al 1998.

The PAGES (2017) Arctic network contained three North American tree ring chronologies. It replaced Wilson’s Gulf of Alaska temperature reconstruction with a Gulf of Alaska temperature reconstruction (Wiles et al 2014) with more elevated closing values. I discussed these two datasets quite critically in a 2016 post entitled Picking Cherries in the Gulf of Alaska. These comments carry forward to the similar replacement in PAGES 2017. Ironically, although PAGES 2017 purported to replace reconstructions with original chronologies, in the only PAGES 2013 North American tree ring series which was a reconstruction (Wilson’s Gulf of Alaska), it replaced it with a series which was also a reconstruction.

As the present post is already long, I’ll visit this topic on another occasion.

Conclusions

ex post screening based on recent proxy trends necessarily biases the resulting data towards a Hockey Stick shape – a criticism made over and over here and at other “ske;ptic” blogs, but not understood by Michael (“I am not a statistician”) Mann and the IPCC paleoclimate “community”;

the PAGES 2017 North American tree ring network has been severely screened ex post from a much larger candidate population: over the years, approximately 983 different North American tree ring chronologies have been used in MBH98, Mann et al 2008, PAGES 2013 or PAGES 2017. I.e. only ~15% of the underlying population was selected ex post – a procedure which, even with random data, would impart Hockey Stick-ness to any resulting composite

despite this severe ex post screening (in both PAGES 2013 and PAGES 2017), the composite of all data other than stripbark bristlecones had no noticeable Hockey Stick-ness and does not resemble a temperature proxy.

PAGES 2013 and PAGES 2017 perpetuate the use of Graybill stripbark chronologies – despite the recommendation of the 2006 NAS Panel that these problematic series be “avoided” in future reconstructions. PAGES 2013 (like Mann et al 2008) used all 20(!) stripbark chronologies, the effect of which had been analysed in Mann’s CENSORED directory. PAGES 2017 continued the use of the most HS stripbark chronologies (Sheep Mt etc) both in the original Graybill version and in a more recent composite (Salzer et al 2014), while adding two stripbark chronologies used in Esper et al 2002 and other IPCC multiproxy studies.

In the past, I charged Mannian paleoclimatologists as being addicted to Graybill stripbark bristlecone chronologies – which I labeled as “heroin for paleoclimatologists” (also describing Briffa’s former Yamal chronology as “cocaine for paleoclimatologists”. Unfortunately, rather than confronting their addiction, Gavin Schmidt and others responded with haughty pearl-clutching indignation, while, behind the scenes, the PAGES consortium doubled down by perpetuating use of these problematic proxies into PAGES 2013 and PAGES 2017.

On this day in 2009, a few weeks before Climategate, I suggested appropriate theme music by Eric Clapton and Velvet Underground. Still apt nine years later.



