Comments on: Bunn et al. [2005] – 20th century tree growth in the Sierra Nevadas

By: Hans Erren

Hans Erren — Sat, 10 Nov 2007 21:54:42 +0000

There is a host of literature around on dendro-archeology. Holland just got a first professor who is also a prized poet. Check for prof. Esther Jansma, professor of dendrochronology and paleo-ecology of the Quarternary at
Utrecht university.

By: BobFJ

BobFJ — Tue, 17 Jul 2007 05:30:21 +0000

This has been an interesting read, but I suggest a simpler engineering approach: It is obvious that the Dendros are still developing their methods, and cannot yet agree on much. (and the CO2 church will defend anything that can be "scientifically" refuted) Consequently, although very interesting, it is probably futile to argue about the conflicting details in the dendro industry. On the other hand, MBH99 has a simple GLARING ISSUE in that the proxy data is discontinued in 1980. The problem is, that if it is OK to use tree-ring data to infer millenial past temperatures, then it should also be OK to take it for the full period under review. Unfortunately, MBH99 prefers, to "illegally" stop short and create an impression of ballistically upward trend stopping with the totally different/irrelevant instrumental global average high spike back in 1998. However, if the red data is removed from the graph, the remaining blue proxy data is clearly showing an unresolved substantial down-trend over 3 decades versus a larger up-trend on T. (That is without considering any CO2 response etc, which would seem to make the contradiction even worse) OK...what does later proxy data suggest...Briffa 2000 managed to take it to the full period of review, and there is a 50 year mean downtrend from 1950....Oh dear! I remember a paper by Jan Esper from about 2000 in which he is clearly distressed by sustained opposing trends between "recent" growth rates and T, but it seems to have been removed from his massive list of publications Has anyone seen anything to contradict an apparent major divergence of 5 decades or more? Why has the IPCC dropped MBH99 in the 4AR 2007? Should policy makers and media be carefully advised?

By: Steve Sadlov

Steve Sadlov — Tue, 01 May 2007 16:23:53 +0000

RE: #85 – Once again, we arrive at cherry pie.

By: Steve McIntyre

Steve McIntyre — Tue, 01 May 2007 12:52:55 +0000

#84. There obviously is no such equation relating ring widths to underlying conditions. There is a tremendous variation between sites and a natural temptation for dendrochronologists to ex post pick chronologies that fit their world view. Unfortunately this habit is deeply ingrained in dendros and even as thoughtful a dendro as Rob Wilson challenges what seems to be an elementary point.

By: MC

MC — Tue, 01 May 2007 10:10:53 +0000

I needed to comment somewhere after reading various websites and papers on dendrochronology, PCA analysis and the like and its impacts
on climate predictions. I read the Mann paper and a few others from the realclimate site and links. Interesting.
I’m a physicist and mathematician and my major objection to the use of proxy data is that there is a lot of statistical analysis without
understanding the relationship between tree growth, species of tree, water, temperature, Co2 etc. Where can I find the equations
showing how a tree ring is formed in a certain atmospheric concentration of Co2 and water at a given temperature?
PCA analysis is a good tool if you already know the form of the underlying relationships. otherwise immediately you are assuming a
linear relationship between variables and more importantly this isn’t being stated as an assumption (i.e. rule no 1 in scientific
method). I understand it requires lots of work to get the underlying functions
but it seems that some biologists (is this the proper word for dendros) are using the
tools without understanding them and then standing back and saying ‘but look there’s a correlation’.
That’s misrepresenting the truth and the method. Science isn’t tough to do but you have to do it properly.

By: Armand MacMurray

Armand MacMurray — Tue, 03 Apr 2007 01:10:05 +0000

Re: #81
Thanks for the link, bender — looks very interesting! You’re no shrinking violet.
This statement in the intro caught my eye:

First, there are nonclimatic influences
on tree-ring records, including tree biology, size, age and
the effects of localized forest dynamics [Cook and
Kairiukstis, 1990]. Successful elimination of these influen-
ces is now routinely achieved via careful site selection,
sampling, data analysis and a posteriori tests to ensure that
the tree-ring record is dominated by the single climate
variable of interest.

I’ll look on my own, of course, but any link to exactly *how* these influences are routinely eliminated would be welcome.

By: John Baltutis

John Baltutis — Tue, 03 Apr 2007 00:10:26 +0000

Re: #80 What's your take on this from 5.3. Implications for Statistical Paleoclimatology?

…in a majority of the tree-ring width chronologies studied here, the decadal variability was not skillfully resolved at or above the 90% level of significance by either modeling approach. This suggests that much of the decadal-scale variability evident in the tree-ring width data may not be directly related to decadal-scale climate variations.

Mine is that there isn't a relationship between their studied tree-ring width data and decadal-scale climate variations and both modeling approaches were found wanting.

By: bender

bender — Mon, 02 Apr 2007 21:30:16 +0000

The link to the Evans et al (2006) paper didn’t take. Here it is:
http://rainbow.ldeo.columbia.edu/~alexeyk/Papers/Evans_etal2006.pdf

By: bender

bender — Mon, 02 Apr 2007 20:34:02 +0000

Re #55

Reichert et al.: A FORWARD MODELING APPROACH TO PALEOCLIMATIC INTERPRETATION OF TREE-RING DATA

is now published as: Evans, M. N., B. K. Reichert, A. Kaplan, K. J. Anchukaitis, E. A. Vaganov, M. K. Hughes, and M. A. Cane, A forward modeling approach to paleoclimatic interpretation of tree-ring data, J. Geophys. Res., 111, G03008, doi:10.1029/2006JG000166, 1-13, 2006 This, from the intro:

Two major uncertainties lie in the statistical development, analysis and interpretation of tree-ring data for paleoclimate studies. First, there are nonclimatic influences on tree-ring records, including tree biology, size, age and the effects of localized forest dynamics [Cook and Kairiukstis, 1990].

Perhaps of more concern is that tree ring data reflect a nonlinear response to multivariate climate forcings.

Read the whole paper for context. This shows the dendros are working on the problem.

By: Dane

Dane — Tue, 03 Oct 2006 20:45:38 +0000

My 2 cents worth. I went to my undergraduate geologic field camp in the southern White mountains, Cerro Gordo peak and adjacent areas. Very dry thats for sure. I am wondering if possibly human influence in the valley bottoms might have an indirect effect on the trees growing at altitude? Before say 1890, the Owens valley (just west of the area in question) had a significant river running through it, which filled Owens Lake. After the late 1890′s to early 1900′s (correct me if my timing is slightly off, its been many years)the water from that river was diverted to the Los Angeles basin. What once had been a lake dozens of feet deep year round is noting more than a giant dust bowl today, this is the area just south and east of Lone Pine Calif. But the point and effect have travelled all the way north into Mono Lake near Mammoth. Water that once naturally moved through the valley is now mostly transfered to the LA/So Cal area.

So, the question is, will that effect growth rates in the trees at altitude that are used for the studies mentioned in this blog? I don’t know, but it seems like it might have some effect. Seems like it might slightly change the valleys climate/air moisture content, and in such a dry place, doesn’t every drop of water count in plant/tree survival? Would this possibly bias the studies in some way?