Source:
Quotes from
pages 25 and 26
of a 33-page PDF
"MYTH #3:
MANN HOCKEY STICK “CONFIRMED”
In the past 10 years, ClimateGate apologists have propagated the myth that the Mann Hockey Stick has been “verified” or “confirmed” by multiple independent studies, most notably the PAGES2K multi-proxy networks (2013, 2017 and 2019), and that the original controversy is therefore entirely moot.
This is untrue.
We discussed the reliance on the Yamal series in the introduction.
Going further, there has been no scientific progress in this field since ClimateGate. Instead, during the past 10 years, climate academics have doubled down on the defective techniques exposed in ClimateGate emails:
• PAGES2K and similar studies remain primarily dependent on problematic and inconsistent tree ring data, many of which go down in the last half of the 20th century.
In order to extract a Hockey Stick shape from inconsistent tree ring data, climate academics, including PAGES2K, have resorted to ad hoc methods (ex post screening, ex post orientation) which are condemned by mainstream statisticians and in statistical literature, but which enhance the hockey stickness of the resulting reconstruction.
The ex post screening and manipulation even extends to data used in seemingly technical reports
• Use of tree ring widths as a temperature proxy is made even more problematic by the impact of the extraordinary worldwide “greening” during past 30 years, primarily attributed by specialists to carbon dioxide fertilization, on ring widths – an effect which is not disentangled in PAGES2K.
• The controversial strip-bark bristlecone series, relied upon by Mann et al 1998, continue to be used in PAGES2K reports, even though the 2006 NAS panel recommended that such data be “avoided” in temperature reconstructions.
• In their zeal to obtain a hockey stick, PAGES2K authors, like Mann et al 2008, have introduced sediment series without taking care to ensure a physical link, leading to a series of embarrassing gaffes arising from series contaminated by construction run-off and even used upside down.
Ex Post Screening/Orientation of Inconsistent Tree Ring Data
Even before Climategate emails, there had been considerable controversy over Mann-style reconstructions using tree ring data.
As early as 2006, Valerie Masson-Delmotte, an eminent scientist and now the chair of IPCC Working Group 1, told us privately that she found persuasive our critique of multi-proxy temperature reconstructions, primarily relying on tree ring data, and that, in her opinion, the only way forward for the field was the development of new and better proxies – a process that, in her opinion, could easily take 20 years.
Although 14 of the 20 years have now passed, the PAGES2K multiproxy reconstructions continue to predominantly rely on tree ring data.
Tree ring chronologies made up 83% of the PAGES2K (2013 network used in IPCC AR5 (PAGES 2017 – 60%).
If there were a consistent “signal” in tree ring site “chronologies” (ring width time series), the “signal” could be easily recovered by simple averaging.
But that’s not what was done in PAGES2K, which has thrashed about frenetically in the impossible task of extracting temperature estimates from inconsistent tree ring data."