Monday 23 November 2009

CRU emails no 22 - tearing into tree rings

John Daly has a go at using tree rings to determine temperature. This is the best description of the problems with this technique that I have read so far.

From: "John L. Daly"
To: Chick Keller
Subject: Re: Hockey Sticks again
Date: Sat, 10 Feb 2001 21:47:57 +1100

Dear Chick & all

> the first is Keith Briffa's rather comprehensive treatment of getting
> climate variations from tree rings: Annual climate variability in
> the Holocene: "interpreting the message of ancient trees", Quaternary
> Science Reviews, 19 (2000) 87-105. It should deal with many of the
> questions people raise about using them to determine temperatures.

Take this from first principles.

A tree only grows on land. That excludes 70% of the earth covered by water. A tree does no grow on ice. A tree does not grow in a desert. A tree does not grow on grassland-savannahs. A tree does not grow in alpine areas. A tree does not grow in the tundra

We are left with perhaps 15% of the planet upon which forests grow/grew. That does not make any studies from tree rings global, or even hemispheric.

The width and density of tree rings is dependent upon the following variables which cannot be reliably separated from each other.

*sunlight - if the sun varies, the ring will vary. But not at night of course.
*cloudiness - more clouds, less sun, less ring.
*pests/disease - a caterpillar or locust plague will reduce photosynthesis
*access to sunlight - competition within a forest can disadvantage or advantage some trees.
*moisture/rainfall - a key variable. Trees do not prosper in a drought even if there's a heat wave.
*snow packing in spring around the base of the trees retards growth temperature - finally!

The tree ring is a composite of all these variables, not merely of temperature. Therefore on the 15% of the planet covered by trees, their rings do not and cannot accurately record temperature in isolation from the other environmental variables.

In my article on Greening Earth Society on the Hockey Stick, I point to other evidence which contradicts Mann's theory. The Idso's have produced more of that evidence, and a new article on Greening Earth has `unearthed' even more.

Mann's theory simply does not stack up. But that was not the key issue. Anyone can put up a dud theory from time to time. What is at issue is the uncritical zeal with which the industry siezed on the theory before its scientific value had been properly tested. In one go, they tossed aside dozens of studies which confirmed the existence of the MWE and LIA as global events, and all on the basis of tree rings - a proxy which has all the deficiencies I have stated above.

The worst thing I can say about any paper such as his is that it is `bad science'. Legal restraint prevents me going further. But in his case, only those restraints prevent me going *much* further.


John Daly

John L. Daly
`Still Waiting For Greenhouse'

1 comment:

Margo's Maid said...

There is some speculation the source of the leak may be closely involved in this email, BOAB, but I'm not going to add to it, cos if it's true then good for him.