Archives par mot-clé : Tree rings

unclassified

Do European tree ring analyses indicate unusual recent hydroclimate?

by F. Bosse  & N. Lewis, Feb 23, 2023 in WUWT

Not really.

A recent paper (M. B. Freund et al 2023, MBF23 thereafter) in “Nature communication earth and environment” investigates the variability of the summer drought events since 1600. It uses the method of “stable isotope analyses C13/O18” to extend the “Standardised Precipitation-Evapotranspiration Index (SPEI) from 1950 to now back to 1600.

The paper describes and uses a multi proxy network over large parts of Europe (see Fig. 1 of MBF23) to reconstruct the history of summer droughts for a longer historic period. It finds interesting results about the dependency of those events on volcanos and solar forcing. It’s a worthwhile read and we were interested in whether the headline title is justified and likewise this claim in the Abstract:

“We show that the recent European summer drought (2015–2018) is highly unusual in a multi-century context…”

Thanks to the authors the used SPEI reconstruction annual data are available, so we were able to perform calculations to check these assertions.

An apparent first “confirmation” of the headline title of the paper appears in Figure 3a in MBH23:

Fig.1: A reproduction of Fig. 3a of MBH23. Annual European mean SPEI-data in blue/red, the low pass filter output is shown in black.

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climate-debate

Tree Rings & Michael Mann’s Hockey Stick

by P. Homewood, June 14, 2020 in NotalotofPeopleKnowThat

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Somehow what starts as a perfectly sensible review morphs into Michael Mann and his discredited hockey stick!

But, as the review itself admits, tree rings tell you more about rainfall than temperature, Indeed, in a much better review in Newsweek, we read how the book reveals in detail the effect that a long period of drought had on the declining Roman Empire in the 4thC.

In fact Mann’s Hockey Stick was hopelessly flawed in many ways. (I would recommend Andrew Montford’s book, “The Hockey Stick Illusion”, for anyone interested.

For a start, the Hockey Stick was based on shonky statistics, which were guaranteed to produce a hockey stick curve regardless of the data fed into it. This was because of the way Mann used Principal Component analysis. In simple terms, Mann’s statistics blew out of all proportion any data which showed a hockey stick effect and ignored all other data.

Secondly, as far as tree rings were concerned, it was heavily dependent on bristlecone pines. It has long been known that the marked increase in bristlecone growth in the 19th and 20thC is due to CO2 fertilization, not temperature. When bristlecones are taken out of Mann’s analysis. the hockey stick disappears.

Thirdly, when tree ring and other proxy data diverged from rising temperature data in the late 20thC, Mann ignored the proxies and spliced the temperature data onto his graph.

There are also a whole host of other major flaws in the Hockey Stick, not related to tree rings.

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climate-debate

Concord and discord among Northern Hemisphere paleotemperature reconstructions from tree rings

by Scott St. George Jan Esper, December 19, 2018 in WUWT

Highlights

  • Tree rings are the backbone of most last millennium temperature reconstructions.

  • Maximum density is a superior temperature proxy than ring-width but is less available.

  • The newest tree-ring reconstructions agree better with instrumental temperatures.

  • They also fit the memory structure of instrumental temperatures more closely.

  • It is imperative to develop new, long and up-to-date maximum density chronologies.

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