The paper by Shi et al (2013) is fairly convincing as to at least the last 1,000 years in the Northern Hemisphere. I am actually surprised that paper has not been discussed here since it aims at dealing with many of the criticisms of paleoclimate research. They use 45 annual proxies which are all greater than 1,000 years in length and all have a “demonstrated” temperature relationship based on the initial authors interpretations.
Robert correctly observed that Shi et al was well within the multiproxy specialization of Climate Audit and warranted coverage here. However, now that I’ve examined it, I can report that it is reliant on the same Graybill bristlecone chronologies that were used in Mann et al 1998-99. While critics of Climate Audit have taken exception to my labeling the dependence of paleoclimatologists on bristlecone chronologies as an “addiction”, until paleoclimatologists cease the repeated use of this problematic data in supposedly “independent” reconstructions, I think that the term remains justified.
While Robert reported that all these series had a “demonstrated” temperature relationship according to the initial authors’ interpretation, this is categorically untrue for Graybill’s bristlecone chronologies, where the original authors said that the bristlecone growth pulse was not due to temperature and sought an explanation in CO2 fertilization. (The preferred CA view is that the pulse is due to mechanical deformation arising from high incidence of strip barking in the 19th century, but that is a separate story.) As a matter of fact, by and large, the bristlecone chronologies failed even Mann’s pick-two test.
Shi et al also show a nodendro reconstruction. This has a much lesser semi-stick. This mainly uses a subset of Kaufman et al 2009 data. In a forthcoming post, I’ll show that even this weak result is questionable due to their use of contaminated data and upside-down data (not Tiljander, something different.)
Shi et al stated that they “started” with the 79 (Northern Hemisphere) proxies from the Mann et al 2008 proxy network, from which they discarded 60 series as “poor-quality data with coarse resolution”:
We started our proxy data collection using the large data set of climate records compiled by Mann et al. (2008), who collected 79 proxy records spanning 1000 yr to reconstruct NH temperatures. Of these series, 60 were not retained for this study, as they did not meet our very restrictive standards: e. g. some poor-quality data with a coarse resolution.
One very obvious quality control standard would be to implement the 2006 NAS panel recommendation that stripbark (bristlecone) chronologies be “avoided” in temperature reconstructions – a measure that surely ought to have recommended itself to the others, if only because so many prior studies have depended on Graybill bristlecones.
However, 10 of the 19 series carried forward from Mann et al 2008 were Graybill stripbark bristlecone chronologies (highlighted in yellow below):
Shi et al 2013 also appear to incorrectly believe that Graybill bristlecone chronologies have a “significant statistical relationship with the local instrumental temperature”:
Consequently, only 19 of these 79 proxy series were in common with both the present and the Mann et al. (2008) reconstructions. We also collected 26 other records, resulting in a total of 45 series used for our temperature reconstruction (Table 2). All references for the 45 proxies come from 21 studies (see Table 2). Here, every series was required to exceed a 90% confidence level with either one of the 2 closest instrumental temperature grid points over the calibration interval to ensure that it had a significant statistical relationship with the local instrumental temperature signal.
However, only a couple of these 19 series pass Mann’s pick-two test. It appears that Shi et al did not themselves verify this local correlation (since their Table 1 shows “ND” under the explained variance column) and relied on a presumed prior calculation in Mann et al 2008 establishing this supposed “significant statistical relationship”. However, Mann et al did not require such a relationship for inclusion in their overall network (which is a grab-bag), but only for inclusion in their CPS reconstruction. Mannian EIV methodology does not use this criterion – or even require that proxies be in the applicable hemisphere. Thus, Shi et al cannot assume that the inclusion of a proxy in the Mann et al 2008 network means that it has a “significant statistical relationship with the local instrumental temperature”: they seem to have misunderstood Mann et al 2008 procedures, something that is easy enough to do even for those for whom English is their first language.
But regardless of the reasoning of Shi et al for inclusion of these proxies in their network, the net result is that 10 of the 45 proxies in their network are Graybill bristlecone chronologies.
Many of their other proxies are familiar to the point of being sterotyped.
They use an older supersticked Yamal chronology (Briffa 2008). Plus Briffa chronologies from Taimyr and Tornetrask, a troika that is used in numerous multiproxy reconstructions and hardly new material.
Their running text is curiously silent (and even contradictory)on their use of Briffa chronologies (though they are listed in their Table 1). For example, they say of Tornetrask:
Briffa et al.’s (1992) and Grudd’s (2008) Fennoscandian treering sampling areas are the same (Torneträsk, Northern Sweden), but the Grudd (2008) record was updated from AD 501 to 2004 using new samples from 35 relatively young trees. This new Torneträsk treering maximum latewood density (MXD) record includes samples from a total of 100 trees and covers the period AD 441-2004. Therefore, we used the most up-to-date data from Grudd (2008).
Despite this, they used the Briffa’s Tornetrask chronology (under the alias “Fennoscandia”). This series was also used in Mann et al 2008.
They also use two Taimyr versions – one from Naurzbaev and one from Briffa. In their running text, they say:
Naurzbaev and Vaganov (2000) and Naurzbaev et al. (2002) both studied tree-rings in eastern Taimyr; the newer data by Naurzbaev et al. (2002) were used here
But, once again, they additionally used the Briffa et al 2008 Taimyr series (“Avam-Taimyr”). The Naurzbaev version that they used was also used in Mann et al 2008, where it was incorrectly attributed to Naurzbaev and Vaganov 2000. The Briffa 2000 Taymir version was also used in Mann et al 2008, though Shi et al can be forgiven for missing this: the “Tornetrask” series used in Mann et al 2008 was actually a composite of Briffa’s Tornetrask, Yamal and Taymir chronologies.
In fact, 27 of 45 (not 19 of 45) series are used in Mann et al 2008: 20 (not 19) ITRDB series, the three Briffa RCS chronologies, the Naurzbaev Taimyr version, the D’Arrigo Mongolia series, the Tan et al 2003 speleothem and Donard Lake varves.
Many of the series were also used in Kaufman et al 2009: all four ice core series; the five lake sediment series; the three Briffa tree ring chronologies and the D’Arrigo Gulf of Alaska tree ring chronology. The other series all appear to have been derived from Ljungqvist collections.
In tomorrow’s post, I’ll look at the lake sediment data, which we’ve been considering from time to time. Of particular interest are two series from Baffin Island. In connection with the recent interest in Miller et al on Baffin Island, I’ve re-examined the full Holocene information on Baffin Island lake sediments: there is convincing evidence that Shi et al used these series upside down (as have the many other users of these series) – an error that we previously observed in the PAGES2K use of Hvitavatn, Iceland sediments.
Shi et al 2013 applied several different methods to their dataset, all resulting in HS-shapes. At the end of the day, any reconstruction is a linear combination of the underlying proxies i.e. after much huffing and puffing, a vector of weights is calculated. One of the huge disadvantages of more “sophisticated” methods is that you can end up with series having negative weights i.e. being used upside down. On the other hand, you do want to downweight nearby series: e.g. multiple bristlecone series. However, this precaution doesn’t appear to have been observed in Shi et al.
But the main problem is the longstanding one: if you take a small subpopulation of hockeystick shaped bristlecones and mix them with a population of “proxies” that are indistinguishable from white noise/red noise and apply typical multiproxy recipes, you will get back a HS-shaped reconstruction. When you remove the bristlecones and the Briffa chronologies, is there still a HS reconstruction? I’ll start by examining the no-dendro chronology tomorrow.