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.