Why has no-one questioned the validity of tree-ring data as a proxy for Temperature?

Question

On http://deepclimate.org/2009/10/07/let-the-backpedalling-begin/#comment-622 there is a defense of Mann's Hockey Stick graph from 'climate blogger Steve McIntyre’s scurrilous accusations of “cherrypicking”.' 
One correspondent, Michael Smith asks the question "What remains unexplained is why/how there can be a hockey stick in tree growth when there is no corresponding hockey stick in the local temperature measurements. That’s right — the LOCAL temperature record does not show a hockey stick. So we are supposed to think these trees are responding to some sort of global average temperature and not to local temperatures? Try thinking about that one for a while." 
That is a brilliant spanner thrown in the works of Mann et al's methodology. 
I have thought about it and there is only one explanation that explains the apparently contradictory observations: The trees are not responding to temperature at all; they are responding directly to the higher CO2 concentration: CO2 acts like plant food to make trees grow faster at the same temperature. Think about that for a while - it means using tree-ring growth as a proxy for temperature is fatally flawed, because the correlation is only valid while CO2 concentration is stable. As soon as CO2 levels increase, so do the width of tree-rings. It is therefore a proxy for CO2 levels. Researchers are cunningly demonstrating by tree ring data that CO2 concentration as measured by tree rings has a high correlation with CO2 concentrations as measured by analysis of ice core samples!!!
This makes all of Mann's Hockey Stick analysis irrelevant not because of cherry picking or inadequate statistical methods, but by a causal flaw in his base assumptions.
Deep Climate's own defence of Mann's methodology is pathetic: "Generally speaking, growth of northern tree species is known to be correlated with summer temperature." Instead of "Generally speaking", he should have said "All else the same", or "At constant CO2 concentrations."
Why have no climate Scientists asked this very basic question? I have only under-graduate degree-level qualification in Chemistry and Physics, but presumably these guys have doctorates? Does having a doctorate in climate change bar you from thinking outside the bounds of your own speciality?
Where is the common sense? During the period the tree rings in the Russian series were growing, the tree-line was retreating southwards, a strong indication of falling temperatures, yet the series was used as "Proof" of warming.

Portland-Joe · Accepted Answer

It looks like you are confusing the problems with the Sheep Mountain series and the Yamil series. Michael Smith was referring to the Yamil series when he complained about the presence of a recent temperature rise and the lack of a temperature rise in the local temperature. Phil Jones explained the reason for this in an interview with the BBC: http://news.bbc.co.uk/2/hi/science/nature/8511670.stm
80% down the interview under the question:
'In the e-mails you refer to a "trick" which your critics say suggests you conspired to trick the public? You also mentioned "hiding the decline" (in temperatures). Why did you say these things?'
Phil Jones responded:
'This "divergence" is well known in the tree-ring literature and "trick" did not refer to any intention to deceive - but rather "a convenient way of achieving something", in this case joining the earlier valid part of the tree-ring record with the recent, more reliable instrumental record.'

In other words, they hid the fact that the tree ring data did not match global temperature readings, and were dumped in favor of the global temperature readings for the 2001 IPCC TAR.

At least unitl 2007 when they "came clean":
"an issue which was later directly discussed in the 2007 IPCC AR4 Report." - Phil Jones in above link

As for the Sheep Mountain trees, they did show a hockey stick, but local temperature readings did not. For that reason, those trees were not considered to be reliable for temperature readings by the paleoclimatologists who created the data set. http://europa.agu.org/?uri=/journals/gb/92GB02533.xml&view=article
These were heavily weighted in M Mann's 2001 hockey stick. This cherry picking example was the result of a fortran program that M Mann used that created hockey sticks more than 99 times out of 100 when given red noise (random data sets) by selectively picking and weighting the data that conformed to a hockey stick shape. However, when McIntyre ran M Mann's cherry picking program without the Sheep Mountain trees, the hockey stick became a broom handle. The cherry picking charge is the result of a graph in M Mann's data as sent to McIntyre labeled "censored" that exactly matched the broom handle graph created by removing the Sheep Mountain trees. http://www.geo.utexas.edu/courses/387h/PAPERS/conf05mckitrick.pdf

The elimination of the beginning of Gaspé cedar ring width series (1400 CE to 1450 CE)
http://www.springerlink.com/content/g0n4x076260152q8/
from M Mann's data set deleted the hockey stick by showing the Little Ice Age. Note, that the authors of the series did not consider the data to be reliable until 1600, because paleoclimatologists do not consider series with less then 4 trees significant. Previous to 1600 CE, the data is not contiguous, but the first ring dates to 1404 CE. M Mann used the data to run back to 1400 CE by applying extrapolation techniques to cover the missing data. The data removed to delete the hockey stick shape consisted of 0 trees (1400 - 1404 CE), 1 tree (1404 - 1427 CE) and 2 trees (1427 - 1450 CE). http://multi-science.metapress.com/content/w152x48065n16q43/

The complaints of cherry picking addressed in your deepclimate.org link were irrelevant straw man attacks, and never addressed the issues involved with tree ring data, or the concerns that skeptics have with the hockey stick.

The trees do respond to temperature, but they also respond to other things as well:
 - Atmospheric CO2
 - Precipitation
 - Sunlight
 - root crowding
 - fire
 - disease
 - soil fungi
 - volcanic ash
 - accidents
They also tend to respond to temperature extremes more than average temperatures.

Tree ring data is considered to be second class by many paleoclimatologists, and many prefer other means to analyze temperature. Here is a paper that incorporates all known studies at the time EXCEPT tree ring data:
(Full) http://multi-science.metapress.com/content/dxk28g4662481342/
(Summary) http://www.co2science.org/articles/V11/N5/C1.php

Ottawa Mike · Answer

Did you know that Michael Mann is not even an expert in tree ring chronology?

Edit:  Oh, here is his CV, where is dendochronolgy?  http://www.meteo.psu.edu/~mann/Mann/cv/cv_pdf.pdf

And here is what people say about that:

"14.  Then there is the palaeo data - Keith Briffa's speciality (and Michael Mann's) most notably the tree ring proxies for historical temperature reconstructions.  How was dendrochronology ever permitted to escape from university Archaeology Departments?  By some ambitious dendrochronologist seeking to expand his sources of funding, in all likelihood!  Wooden thermometers!  What sane person would give the concept the time of day?  But it got funded at the CRU, didn't it, and in a big way, too? "

http://www.publications.parliament.uk/pa/cm200910/cmselect/cmsctech/memo/climatedata/uc1302.htm

Noah H · Answer

The flaw in this critique is that the tree ring study isn't only about temperature.  It's about 'climate'. It's also about soil and the critters that live in the soil...slime mold ferinstance!  Trees can't thrive without slime mold, a huge variety of critters that break down soil nutrients so that trees can convert food to growth.  These critters are climate sensitive.  It's about the number of birds and the kind of birds. It's about pollen and bugs, both crawling and flying.  A 'tree' doesn't tell you much, but a 'forest of trees' exists within an overall climate.  It's about rain fall and the lengths of summers and winters.  It's about bugs and prevailing winds...the list goes on.   Coupling the health of forests with what we know from ice core and sea floor samples as to atmospheric CO2, evidence of volcanic outbursts and simply digging holes in the soil to reveal decade by decade the state of a forest's floor a general pattern of climate can be established.  The idea that some guy cut down a tree and checked it's rings sounds like something you'd hear from one of those right wing radio dummies.  Science is complex and the scientific method is relentless in tracking down the truth.  I'm sure the person that asked this 'question' means well, but it seems he's more interested in making HIS case, rather than answer the question as to how much CO2 can we continue to flood into our paper thin atmosphere with before a seriously robust and permanent greenhouse effect endangers the soon to be nine billion human beings and the overall environment of this tiny world we live on.

Anonymous · Answer

I don't know about temperatures, but they are a very accurate history of drought and rainfall. The Joshua pine here in California dates back 3000 years and has been used to calibrate inaccuracies in Radioactive/carbon dating. Weather changes caused by Pompeii and Krakatoa volcanic eruptions are clearly evident in the rings.

Anonymous · Answer

It comes down to the fundamental habit of the alarmists. Choose the data that support your claims and can generate the most fear to hype. (Whether or not they actually mean anything.) Ignore things that contradict your hype. 

(Manatees dying off at an extremely rapid rate in Florida would be front pages everywhere if it actually supported the idea of "global warming." That it supports the opposite conclusion, it's a story that is being ignored everywhere except where the dead ones are washing up on shore.)

That's why the reporting is going on as it does.. about tree rings or anything else.

Dana1981 · Answer

Because the world's climate scientists are idiots, and you and some random blogger are smarter than all of them.  That's what you wanted to hear, right?

There's an entire field of study on this subject.  It's called dendrochronology.  
The smart and less embarrassing way to phrase this question, by the way, would have been "has anyone questioned..." rather than "why hasn't anyone questioned...".  Don't assume that just because you're unaware of something, it doesn't exist.  This is one of the most common errors committed by deniers.  They assume that because they don't understand basic climate science concepts, nobody does.

And Ottawa, Mann never claimed to be a tree ring expert.  He simply used the work of dendrochronology experts like Keith Briffa as some of the many temperature proxies in his reconstructions.

*edit* I did answer the question.  The answer is "thousands of climate scientists have, Einstein".  Ask a stupid question....

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Why has no-one questioned the validity of tree-ring data as a proxy for Temperature?

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