[Note: My first post in which I had written commentary mysteriously lost all of its content, posting nothing but white space. This is some sort of internal wordpress error, but has never happened before. I have some elements restored below, but my original commentary is lost. -Anthony]
I’ve written before about the difficulties associated with extracting a valid temperature signal due to all of the confounding variable in Liebigs law of the minimum, which I describe in detail here: A look at treemometers and tree ring growth
Now a new confounding variable has been introduced that does not bode well for tree ring studies such as Mann et al.
A new paper by Brienen et al in the journal Global Biogeochemical Cycles suggests that there may be a whole new set of biases in tree ring studies.
Tree ring analysis allows reconstructing historical growth rates over long periods. Several studies have reported an increasing trend in ring widths, often attributed to growth stimulation by increasing atmospheric CO2 concentration. However, these trends may also have been caused by sampling biases. Here we describe two biases and evaluate their magnitude. (1) The slow–grower survivorship bias is caused by differences in tree longevity of fast- and slow-growing trees within a population. If fast-growing trees live shorter, they are underrepresented in the ancient portion of the tree ring data set. As a result, reconstructed growth rates in the distant past are biased toward slower growth. (2) The big–tree selection bias is caused by sampling only the biggest trees in a population. As a result, slow-growing small trees are underrepresented in recent times as they did not reach the minimum sample diameter. We constructed stochastic models to simulate growth trajectories based on a hypothetical species with lifetime constant growth rates and on observed tree ring data from the tropical tree Cedrela odorata. Tree growth rates used as input in our models were kept constant over time. By mimicking a standard tree ring sampling approach and selecting only big living trees, we show that both biases lead to apparent increases in historical growth rates. Increases for the slow-grower survivorship bias were relatively small and depended strongly on assumptions about tree mortality. The big-tree selection bias resulted in strong historical increases, with a doubling in growth rates over recent decades. A literature review suggests that historical growth increases reported in many tree ring studies may have been partially due to the big-tree sampling bias. We call for great caution in the interpretation of historical growth trends from tree ring analyses and recommend that such studies include individuals of all sizes.
Presumably, this new source of bias applies just as much to tree ring studies where the increase in growth is ascribed to temperature.
==================================================================
Here is the abstract from GLOBAL BIOGEOCHEMICAL CYCLES, VOL. 26, GB1025, 13 PP., 2012 doi:10.1029/2011GB004143
Detecting evidence for CO2 fertilization from tree ring studies: The potential role of sampling biases
Key Points
- Observed increases in tree ring widths may be caused by sampling biases
- Standard sampling methods lead to spurious trends in historical growth rates
- Reported increases in ring width may often not be due to CO2 fertilization
Roel J. W. Brienen
School of Geography, University of Leeds, Leeds, UK
Programa de Manejo de Bosques de la Amazonía Boliviana, Riberalta, Bolivia
Emanuel Gloor
School of Geography, University of Leeds, Leeds, UK
Pieter A. Zuidema
Programa de Manejo de Bosques de la Amazonía Boliviana, Riberalta, Bolivia
Ecology and Biodiversity, Institute of Environmental Biology, Faculty of Science, Utrecht University, Utrecht, Netherlands
Forest Ecology and Forest Management, Centre for Ecosystem Studies, Wageningen, Netherlands
Tree ring analysis allows reconstructing historical growth rates over long periods. Several studies have reported an increasing trend in ring widths, often attributed to growth stimulation by increasing atmospheric CO2 concentration. However, these trends may also have been caused by sampling biases. Here we describe two biases and evaluate their magnitude. (1) The slow–grower survivorship bias is caused by differences in tree longevity of fast- and slow-growing trees within a population. If fast-growing trees live shorter, they are underrepresented in the ancient portion of the tree ring data set. As a result, reconstructed growth rates in the distant past are biased toward slower growth. (2) The big–tree selection bias is caused by sampling only the biggest trees in a population. As a result, slow-growing small trees are underrepresented in recent times as they did not reach the minimum sample diameter. We constructed stochastic models to simulate growth trajectories based on a hypothetical species with lifetime constant growth rates and on observed tree ring data from the tropical tree Cedrela odorata. Tree growth rates used as input in our models were kept constant over time. By mimicking a standard tree ring sampling approach and selecting only big living trees, we show that both biases lead to apparent increases in historical growth rates. Increases for the slow-grower survivorship bias were relatively small and depended strongly on assumptions about tree mortality. The big-tree selection bias resulted in strong historical increases, with a doubling in growth rates over recent decades. A literature review suggests that historical growth increases reported in many tree ring studies may have been partially due to the big-tree sampling bias. We call for great caution in the interpretation of historical growth trends from tree ring analyses and recommend that such studies include individuals of all sizes.
Where is the treemometers talk about hide the decline. WordPress?
Oooookay. Am I going nuts here,Anthony? I see a title,tags,posted in,etc,but NO story. Oy.Do I need more caffiene or watt?
All that is showing right now:
Another reason trees don’t make good treemometers – new tree ring data bias discovered
Posted on March 20, 2012 by Anthony Watts
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Did you forget your content?
cheers,
gary
…and it’s worse than we thought.
Hey, *somebody* had to say it.
I think you got ahead of yourself and posted before givng us something to read.
REPLY: I think you got ahead of yourself and jumped to conclusions – Anthony
Sampling bias! This should help.
http://www.c3headlines.com/2012/03/the-infamous-hockey-stick-tree-scientists-michael-mann.html
http://hockeyschtick.blogspot.com/2012/03/another-death-blow-to-hockey-stick-new.html
by my count tree growth is effected by at least 4 variables: sunlight, temperature, water and soil/nutrients … since we have no historical data for sunlight, water or nutrients it is impposible to calculate historical temperature using tree growth rates … impossible … Why is this still being debated by anyone ?
in a previous thread, a poster worried that all science might be tarnished by the impacts of the bogosity that has overrun the field in the last 20 years.
Well, all science DESERVES to be tarnished for having let this nonsense go on this far. This has happened because the scientific “establishment”, such as it is, has allowed it to happen and left it up to a handful of outsiders to point out what is wrong. Until “science” starts taking serious steps to point out how compromised this entire warmista project has been, they will be rightly seen as nothing but another special interest group packed with rent-seeking apparatchik’s willing to say and do anything for money and status.
It’s worth noting that for all their self declared ‘vast knowledge ‘ there is not one amongst ‘the team’ who actual understand plant physiology well.
We been here before of course with statistics, were people with far more expertise in an area can show us how the ‘the Team’ can be totally out of its depth and its only the arrogance ,that seems to be part of being a ‘climate scientists ‘, that stops them admitting it and accepting advice form those outside their little club.
Anthony,
Try the “Lazarus” add-in for firefox. If you are doing your wordpress editing from firefox, you will be able to recover text from various text boxes even if you have navigated away. The length of time to save is configurable. You want the status bar visible to do this. To recover text, just right click the same text box and see your choices of what has been saved. Mine is set to save for 4 weeks.
Strangely enough, I just had to use it for this post since I wasn’t logged in to wordpress…
Will Mann et al review this peer-reviewed paper? He should be e-mailed a copy and asked for his comments.
If it’s too cold, trees have sluggish growth.
If it’s too hot, trees have sluggish growth.
That sort of sums it up, trees are not thermometer material
Wait for the push-back, nothing these days must be allowed to challenge or interfere with our carefully constructed and cultivated tree rings. The ready response team’s “bogus is as bogus does team”, will fix this even if they have to turn the tree ring data upside down!!
So many variables influence tree growth that one has to wonder if tree rings can be interpreted as proxies for anything. Nature is seldom as simple as some would like to think it is.
I think we’ll get the standard “The science is settled” statements and the authors can look forward to people going through their trash looking for their connection to Big Oil. I suppose though that they’ll just use the new methodology and make up a fake document to ‘prove’ the link.
Given the wide variety of influences on any growth of anything over time; it is simply a fools journey to do anything but the most generalizing about it. Add such confounding elements as variations in genetics and the variations of genetic responses to variations in stimulation… this is all simply a waste of time and time is money.
Not sure what impact it has… but in reference to the figure, an R2 value of 0.39 indicates little/no correlation between the trendline and the data.
Forget about tree rings, too many factors.
Use the changes in the geomagnetic field
http://www.vukcevic.talktalk.net/HmL.htm
My early career was a series of “discussions” with the PTB, at the time, that most of their sampling methods introduced so much error in their studies that they were worthless…(I was not all that popular, as you can imagine.) Once I started to produce reports that showed ways to save money by accurate and precise tests that were NOT biased by sampling error, it fixed a lot of problems. 🙂
That was in natural products so I can appreciate the difficulty inherent in dealing with anything that is hard to randomize when selecting samples. That does not, however, condone the practices of the GISS gang and their cohorts.
Well, darn, I like counting tree rings. I remember being astonished once when a wind storm toppled two douglas firs that were the same size on my property. They were next to each other. One had thirty rings, one had sixty. I still don’t know how that happens.
Note the article isn’t talking about temperature at all (or precipitation, etc.) — just CO2. Presumably this is because it can be pitched to counter arguments that CO2 is beneficial, and hence it qualifies as OK Sceance with the granters-that-be. Also note that it is modelling; no trees were actually harmed (cut or cored) to crank out this study.
Let’s be scupulous here, this study is based on models: “We constructed stochastic models to simulate growth trajectories based on a hypothetical species with lifetime constant growth rates and on observed tree ring data from the tropical tree Cedrela odorata.” If we criticize the climate models for their weaknesses, we need to do the same here. This model very well may point out a new bias but we need much more proof that in fact it makes a difference. One might hypothesize that slow-growing old trees of the same species in the same climatic zone respond to environmental factors in relatively the same ways. If so, the bias of fast-growing young trees may make no substantial difference.
Color me crazy but an interesting experiment would be to place a high resolution thermometer by a tree for about 20 years with a data recorder and then compare the derived vs actual temperatures?
Just saying….
I’m surprised we haven’t seen newspaper headlines: “Global warming causes trees to put on weight”?