Archives par mot-clé : Tree rings

Tree Rings & Michael Mann’s Hockey Stick

by P. Homewood, June 14, 2020 in NotalotofPeopleKnowThat


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.

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.

  •