Michael Mann won’t be happy about this.
A new paper now in open review in the journal Climate of the Past suggests that “modern sample bias “has “seriously compromised” tree-ring temperature reconstructions, producing an “artificial positive signal [e.g. ‘hockey stick’] in the final chronology.”
Basically, older trees grow slower, and that mimics the temperature signal paleo researchers like Mann look for. Unless you correct for this issue, you end up with a false temperature signal, like a hockey stick in modern times. Separating a valid temperature signal from the natural growth pattern of the tree becomes a larger challenge with this correction.
Here is a relevant excerpt:
Much of the work in dendrochronology, and dendroclimatology in particular, relies on accurate, unbiased reconstructions of tree growth long into the past. As a result, a great deal of effort has been put into trying to isolate important trends and identify potential 5 biases. However, one major bias called “modern sample bias”, first identified by Melvin (2004), is still largely neglected in applied studies, despite its potential impact on all regional curve standardization chronologies (Brienen et al., 2012a).
Dendrochronologists observed that the older a tree was, the slower it tended to grow, even after controlling for age- and time-driven effects. The result is an artificial downward signal in the regional curve (as the older ages are only represented by the slower growing trees) and a similar artificial positive signal in the final chronology (as earlier years are only represented by the slow growing trees), an effect termed modern sample bias. When this biased chronology is used in climate reconstruction it then implies a relatively unsuitable historic climate. Obviously, the detection of long term 15 trends in tree growth, as might be caused by a changing climate or carbon fertilization, is also seriously compromised (Brienen et al., 2012b). More generally, modern sample bias can be viewed as a form of “differing-contemporaneous-growth-rate bias”, where changes in the magnitude of growth of the tree ring series included in the chronology over time (or age, in the case of the regional curve) skew the final curve, especially 20 near the ends of the chronology where series are rapidly added and removed (Briffa and Melvin, 2011).
A likelihood perspective on tree-ring standardization: eliminating modern sample bias
J. Cecile, C. Pagnutti, and M. Anand
University of Guelph, School of Environmental Sciences, Guelph, Canada
Abstract
It has recently been suggested that non-random sampling and differences in mortality between trees of different growth rates is responsible for a widespread, systematic bias in dendrochronological reconstructions of tree growth known as modern sample bias. This poses a serious challenge for climate reconstruction and the detection of long-term changes in growth. Explicit use of growth models based on regional curve standardization allow us to investigate the effects on growth due to age (the regional curve), year (the standardized chronology or forcing) and a new effect, the productivity of each tree. Including a term for the productivity of each tree accounts for the underlying cause of modern sample bias, allowing for more reliable reconstruction of low-frequency variability in tree growth.
This class of models describes a new standardization technique, fixed effects standardization, that contains both classical regional curve standardization and flat detrending. Signal-free standardization accounts for unbalanced experimental design and fits the same growth model as classical least-squares or maximum likelihood regression techniques. As a result, we can use powerful and transparent tools such as R2 and Akaike’s Information Criteria to assess the quality of tree ring standardization, allowing for objective decisions between competing techniques.
Analyzing 1200 randomly selected published chronologies, we find that regional curve standardization is improved by adding an effect for individual tree productivity in 99% of cases, reflecting widespread differing-contemporaneous-growth rate bias. Furthermore, modern sample bias produced a significant negative bias in estimated tree growth by time in 70.5% of chronologies and a significant positive bias in 29.5% of chronologies. This effect is largely concentrated in the last 300 yr of growth data, posing serious questions about the homogeneity of modern and ancient chronologies using traditional standardization techniques.
The full paper is here: http://www.clim-past-discuss.net/9/4499/2013/cpd-9-4499-2013.pdf
h/t to The Hockey Schtick
Trees are calibrated against other proxy data that is also wrong else they wouldn’t agree. This isn’t rocket science.
@Greg at 3:04 am:
“There is a wilful attempt by many involved in dendroclimatology and particular dendrothermometry to confound all these terms in the hope that unscientific attempts to use trees as thermometers will get a free pass and be granted the hard-earned credibility of dendrochronology.”
Greg, add in that botanists use the same tree rings to determine precipitation. The botanists assume constant temps year-to-year, and the dendroclimatologists assume constant precipitation. Obviously, both can’t be right. The answer is that both are major factors in tree-ring growth, and that no one can look through a crystal ball into the past and tell which of the two factors contributed how much to any single tree ring.
This overall puts the entire “science” of dendroclimatology on very thin ice.
If you sit down and actually calculate the volume of new wood laid down per year, the surprise is that Old Trees do not grow more “slowly.” In fact they tend to add wood at increasing rates as long as they remain healthy. The reduction in ring thickness is because new wood is added to entire outer surface of the tree (trunk, branches and all) and that surface steadily increases with time. The ring pattern only appears to reflect slower growth over time.
Also, dendrochronology is perfectly serviceable as a dating tool regionally. It continues to work well for instance in the American southwest for dating construction work in Anasazi and other contemporary sites. What we don’t know and probably never will, are the precise environmental elements that create those regional patterns. Water availability almost certainly, but other things as well. Mann and his team don’t do dendrochronology but something more akin to “dendrophrenology.” They look at the bumps and slumps in growth and claim to interpret them. Lay off on dc and start picking on it’s misuse instead.
Addressing the overall issues in climate science, as time has gone on and we have learned about the details that are important for each and every kind of temperature reconstruction, we keep finding out that certain assumptions that we on the sidelines thought were “settled science” simply are not valid at all. There is and has always been a wrongness to the assumption that tree ring growth over the life of a tree is constant. That is the point of this paper.
People looking at reconstruction curves initially assume the details have all been dealt with. Yet every half year or so we find out differently. The details have NOT been considered properly.
This paper even castigates the reconstructionists for not having properly included this extra “term” (factor) in their formulas – the ones that go into producing the curves we see. If I understand them correctly, the authors point out that without this factor figured in the older growth will be seen as slower – and therefore COOLER. This, they seem to say, tilts the curve and long-term trend lines upward, giving the ARTIFICIAL appearance that recent times are hotter.
This is a BIG deal. Reconstructionists are not filed climatologists; they take others’ work and assume all the details have been worked out so that the field workers’ output is standardized to the final degree. All the reconstructionists do is sit at their computers and take the results and plug in the data as if it is 100% reliable. This paper argues that such is not the case.
Excellent!
The Divergence Problem.
This paper needs to be taken into context with the Divergence Problem. The recent tree-ring data ALREADY shows far too low of a trend since 1940. If added together, the two mean the tree-ring vs measured temps is even MORE diverging.
This is a BIG deal.
@Duster at 10:38 am
Yep. People need to stop confusing dendrochronology with dendroclimatology.
The former is, more or less, counting rings, regardless of width, in order to date artifacts and sites.
In order to “back-predict” temperatures, the latter makes the assumption that precipitation is constant, and that assumption is unsupportable, even if the scientific community hasn’t recognized the disconnect yet.
dp says:
August 16, 2013 at 10:32 am
“When used as a temperature proxy, a tree must be calibrated in just the same way that a thermometer is calibrated.
Trees are calibrated against other proxy data that is also wrong else they wouldn’t agree. This isn’t rocket science.”
You are correct, sir. I should have extended my comment to say that a tree’s environment is dynamic and that experimentation must be continued over the entire period that the tree is used as a proxy. Other problems remain. The most notable is comparing local environments from different regions.
A forest is dynamic. It is rarely like a stand of thousand year old Sequoias. It is no less dynamic than a beach on a barrier island on the east coast of the US, to borrow one of Willis’ examples.
Steve Garcia says:
August 16, 2013 at 10:47 am
Excellent little essay, Steve.
While the final analysis above seems to hammer another nail in the CAGW dendro addiction illness, the paper seems to avoid or blindly assume what trees do because they look at the rings. Talk about not seeing the forest for the trees, now it’s they can’t see the tree for the rings.
As Gary Pearse mentions above, there is much in forestry that dendro-chronologists could learn from. Add to that what woodworkers and luthiers have learned over the centuries and perhaps much of this voodoo chronology thinking could be moderated.
When I look at tree rings, all too frequently as I actively cut wood for wood stove heat in the winter, I find myself wondering just what the rings can actually indicate. One signal that is quite clear here in central Virginia is the drought cycle that is likely influenced by ENSO.
Counting the years get very iffy, especially in the older trees. If one follows some of the odd rings around the tree, they seem to merge, diverge, wither away. Very puzzling, was the tree damaged on one side that year? I’ve not taken any of these curious ring cuts inside to put under the binocular microscope, to verify whether or not the rings really do merge, diverge, whatever. Just not interested in the chrono part that much. Wood inside. good, into the stove, aahhh.
In all of the wood working fields and perhaps especially in luthier work, it is well known that trees grow in response to local conditions. An ideal tonewood tree is evenly grown, flexed evenly by the winds and straight as a telephone pole.
Yes, a tree does grow thinner rings as the tree gets older. It’s not that the tree is tired and old. What happens is that the tree fills the ecological niche and attains it’s range of maximum leaf and root mass in it’s little competitive spot. This plateau of leaf mass and root systems are significant drivers towards thin even rings. Food, water, sunlight, fire are all major inputs that cause changes to tree mass. Did something drop a large pile of fertilizer on one tree’s root ball, then the root mass will develop complexity, leaf mass will increase and the tree will attain a brief growth spurt, perhaps indicated by micrometers in ring thickness. No fertilizer, less water, bug infestation, fire destroys leaf mass and injures the cambium layer and the tree makes a thin tree ring. As far as I know, the rings do not indicate the provider of abundance nor do they indicate meager sustenance, lack of water or physical damage, (remember, cambium is often damaged, not destroyed or seriously marred).
Luthiers love tonewood trees with thin rings. The deal is that trees have thick rings during their early life and as the tree gets older and more massive, the outer tree rings get thinner. Only the rings closest to the cambium layer are not as stiff or stable as heartwood.
Now stating as the tree gets older tree rings get thinner is an automatic blind spot in thinking about the tree. As a tree reaches it’s maximum available resource intake concurrently it achieves it’s maximum growth capability in building tree rings on an ever expanding column of wood. The newest ring may still have greater total volume than the previous year’s ring.
As I explained above, I’ve never put this wood under a microscope, measured mass on a Mettler scale (it’s what I have), measured thickness and density over decadal ring growth periods and charted this out. Still, I suspect that the tree manages to slightly increase the total wood mass through a larger cambium area every year, but the rings are thinner as the tree builds over larger wood acreage every year.
Again, back to the wood; there are issues that can occur in every tree. The overall term is ‘reaction wood’ as the tree’s cellulose product is in response to environment conditions. A common adverse growth condition in conifers is compression wood.
Compression wood forms when the tree is under stress from leaning, snow loads, excessive growth on one side, hard steady winds over long periods. What happens is that the growth of the tree is affected with eccentric growth rings. (adapted from “Understanding Wood, A Craftsman’s guide to wood technology”, R. Bruce Hoadley)
These are local effects from a range of conditions and like many other effects, they can be changed when conditions change. A leaning tree because the hillside slumped, straightens when the hill slumps again. Branches break off and snow loads or wind burdens shift. Every change changes the tree ring growth, often in ring thickness.
Local on the tree conditions affect tree rings within those conditions. Insects, twig or branch growth, deer rutting, carnivores sharpening claws and so on change tree ring widths. What is worse, Many of these conditions are extremely difficult to spot unless one happens upon the exact source or cause.
Luthiers and wood workers know that wood cut parallel to the tree’s height is strongest, especially when all of the wood grain is parallel. The best way to achieve this is to split the wood along the wood fibers. A luthier carving violin or cello tops from spruce or maple will pay a significant premium for well-cut tight grained wood. These same luthiers all too frequently spend hours carving the wood only to discover a pin-knot, bug-hole, hidden reaction wood or other flaw. As a side note, cello luthiers carve tops from wood that starts out 18 to 25mm in thickness down to 1-2mm thickness for a well sounding top.
Back to the dendrochronology folks out boring a tree’s poor sacroiliac with their tiny bits and corers believing that such small looks within a tree’s life will tell them everything about that life. If people whose livelihoods depend on wood cannot tell before carving an entire piece of wood just what is in every particle of that wood; I seriously doubt that small cores can do much more than hint with huge chances for error. Just because a researcher can measure the width of a tree ring in a core, doesn’t mean that that ring is consistently that width even within a few millimeters.
All trees are sensitive to temperature; but they’re far more sensitive to sunlight, water and nutrients. A small change in sunlight falling upon the tree causes major changes in tree biosphere. Consider the hard maple ‘Acer saccharum’ where sap is collected in late winter. The trigger is “…The flow of sap is triggered by a thaw following on a hard frost in the sunny days of late winter (February, March and April)…” Note that caveat of ‘sunny days’, the sap flows best on bright sunny days regardless of the temperatures. Please do not mistake ‘thaw’ for winter is over and birds are singing spring; it is literally the first warmish days concurrent with bright sun and can occur January through March. Collecting sap by hand means trudging through snow to the trees and trucks. Buckets left overnight can be ice capped, (still goes into the collecting tank). The sap season can also be spotty and not give a good run if the weather and sun don’t allow it. Spring still arrives, leaves flesh out and summer arrives. It isn’t just the warmth! We may think trees are stone cold, but the trees are still engaged in life.
Reblogged this on Public Secrets and commented:
This is potentially a huge blow to the Cult of Anthropocentric Global Warming. Tree-rings have been used as proxies, in lieu of having direct instrumental measurements of temperature change in ages past. They’ve been foundational to the assertion of a connection between CO2 levels and warming, and thus as evidence that Man has accelerated that warming. And if it turns out the tree-ring analysis was severely biased…. Well, Al Gore won’t be pleased at all.
ATheoK says:
August 16, 2013 at 11:40 am
Excellent little essay, ATheoK. Light is a huge variable in tree growth. Trees compete with one another for available light and put themselves through all sorts of compression to get to the light. The amount of available light for each tree changes dynamically as the competition proceeds. Also, most forests are on rather hilly ground. The effect of the hills, river gulches and such is to make the available light highly variable on the ground. Saplings ten feet apart can receive vastly different amounts of light. Pity the poor Luthier.
That still only gives a tiny window of a few years against the entire lifetime of the tree. All that one could be sure of is the conditions prevalent during the proxy study period; and that only if someone is there full time to record local variables.
The sequoia comment is interesting. I greatly enjoyed my stay at Sequoia National Park and hiked through several groves. I was astounded to see trees with deformities from local impacts; one tree lost a large piece of it’s top and most of it’s leaf mass (needles). Yup, they’ll sure know in another thousand years that the tree lost it’s top and tree rings are thin because of the loss in photosynthesis. Three other trees were burned, mostly on one side from a fire years before. A number of other trees were not, but they’re side by side; the difference is brush fires burn fast without much tree damage while accumulated fallen deadwood burns hot. A truly tall tree that was only five – six feet (almost two meters) thick fell and opened up a long sunlit glade…
Even amongst the sequoias, bristlecone pines and redwoods the forests are dynamic.
Steven Mosher says:
August 16, 2013 at 9:12 am …..
1. Take cores from tree rings going back to 1850
2. Use the instrument record from 1900 to present to calibrate
3. Predict the temperature from 1850 to 1900 using the calibration ( called verification)
4. compare your prediction against the actual.
So, when you see St. McIntyre slamming Mann because of verification statistics you see the Stronger argument against the result. The weaker argument just dismisses all tree rings.
The weaker argument says “we cant know”. the weaker argument is anti science.
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Absolutely incorrect.
First of all, which iteration of the instrument record would you recommend for calibration? For instance, not to pick on GISS, but, because it’s handy …. http://suyts.wordpress.com/2013/08/14/gisss-first-30-years-of-our-temp-record/
So, which one would you use for calibration? If you used the older iteration of our temps, and they give us another version which alter the historic temps, as we continually do at all levels (GISS only bringing us a final product), then we know that the calibration would necessarily be in error because the temps used to calibrate are now different. So, in that sense, it is entirely based upon strong science and argument that it can’t possibly be done.
Every tree ring study, or any and all paleo studies using past instrument records to calibrate are in error today because the past instrument records have changed. You can use GHCN, NOAA, GISS, HadCrut …. any and all and you absolutely do know that the calibration period has been altered since the time of the study. They are not correct and cannot be correct because of the continuous history revisionism.
But, more to the point, we also absolutely do know that dendro studies are nothing but numerology. Photosynthesis, necessary for tree growth is done through the leaf or pine needles. We know that various preceding years will directly effect the growth of the subsequent years. Meaning that each year retains a signal from the prior years irrespective of what occurred in the year being addressed. Bristle pine, for instance, can retain their needles for up to 60 years. And, probably longer. But, we don’t know, and can’t know how much each year contributes to the year being addressed as it would be different for each and every tree.
I love the contributions Steve Mc has made to climate science and our knowledge. But, in these instances, the elegant statistics used, clouds and confuses the discussion. And, it lends a form of legitimacy to the lunatics making proclamations about our temps using tree rings, because it allows for the possibility that one can, and puts forth an argument that it was just their maths that was wrong. It isn’t their maths!! It is their lack of understand base and fundamental science! And this paper once again establishes that the lunatics don’t have a clue as to what they’re doing.
It isn’t a strong argument to prove the moon isn’t made of cheese with statistics. It’s a waste of time and muddles the discussion.
Again, for clarity, I am not dismissing Steve Mc’s contribution. He can rightfully take credit as being one of the driving forces in the skeptical movement. He demonstrated alarmist fallibility and by my reckoning, humanity owes him a debt. But, we’ve moved on from that point and now we’re at the point of establishing that alarmists have zero credibility because their assumptions are not based on science.
Who knew that trees are physically limited in their growth capacity and that as they age they grow slower? Well, just about any 4th grader out there….. well except for the poor children being taught today. God knows what they’re teaching them now.
I love numbers. Numbers are great! But, they carry no meaning if they are not properly derived. It is numerology. Elegant and sophisticated, but numerology nonetheless.
ATheoK says:
August 16, 2013 at 12:06 pm
Good point. I heartily agree.
James Sexton:
With respect to global temperature data against which treemometers are calibrated, at August 16, 2013 at 12:42 pm
http://wattsupwiththat.com/2013/08/16/oh-mann-paper-demonstrates-that-tree-ring-proxy-temperature-data-is-seriously-compromised/#comment-1392486
you say
Yup! I have been trying to explain that to anybody who would listen for years;
e.g. see http://www.publications.parliament.uk/pa/cm200910/cmselect/cmsctech/memo/climatedata/uc0102.htm
Richard
{ @izen says:
August 16, 2013 at 8:21 am
However lumber companies use the temperature history of a stand of trees to estimate the amount of wood they can extract. There are other factors of course, but at least to a first approximation just the temperature record is a good correlate with tree growth. }
I call B.S. they use precipitation data.
I googled it. You can try.
richardscourtney and James Sexton:
I will add my name to those two and state that there are to many problems with Dedrochronology to be able to derive any useful temperature records. There are to many problems with the surface temperature records to accurately claim what changes have been experienced even during the time thermometers have been in use.
My apologies for the windy epistle. It is also interesting to understand how forest trees adapt and grow within a forest to achieve a mature forest. While that sounds great, it isn’t the best for wildlife in general. Deer and other ungulates are primarily grazers and broken country serves them best. From open glades through meadows, young forests and old growths, all support different creatures differently.
Theo: I don’t recall where you are physically located, but here in America we have forests on flat, hilly and mountainous land. The forests in Alabama, Louisiana, Florida and parts of Mississippi are on quite level ground, old sea floor.
There is a hike on a local Boy Scout campground; it is about five to seven miles from hilltop to hilltop and over the course of a week the patrol visits as many hilltops in six days as they can. The name of the hike is something like “Seven Scenic Peaks”.
Well Virginia does have some peaks, but most of these hike hilltops were hills, just tall ones. When the hike was originally set up many years ago, the area had been logged and when one reached a hilltop there was a good view. Nowadays, one gets to see trees, tall mature trees, in all directions and I’m not going to try and climb one, seven or more hiking miles from doctoring.
Ever hear of a rich luthier?
Even the incredible ‘Antonio Stradivari’ (Stradivarius) is reputed to have searched firewood piles for possible tonewoods. Antonio personally selected his tonewoods and then air dries those woods for years.
A comparison of tree ring widths of Stradivari instruments shows that many of his instruments, including the most famous, have wider tree ring widths than currently favored by luthiers; master grade tone wood today often boast ring widths of 30-40 rings per inch while one study has the violin masters making instruments with woods from 5-25 rings per inch.
While the study results versus ‘consensus’ are opposite to some degree there are a number of luthiers who are seriously testing their tonewood densities and constructing their instruments accordingly.
Tapping instrument wood listening to the tone tap is a very old method for judging how good a tone wood is. Perhaps what the masters tapped for was stiffness along with tone.
Thank you for your kind praise,
Another Theo.
Ah, the rings of truth.
“But, we’ve moved on from that point and now we’re at the point of establishing that alarmists have zero credibility because their assumptions are not based on science. “
Well Said!
You put a tree ring in,
You take a lake core out,
You put your garbage in,
And you shake it all about,
You make the Hockey Stickey
and your cash cow comes around
That’s what it’s all about.
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I’ve commented before how the temperature record for my little spot on the globe has been changed (“adjusted” if you prefer) between 2007 and 2012.
Which instrument record would you use for #2? The “raw” data or the “corrected” data?
richardscourtney says:
August 16, 2013 at 1:14 pm
James Sexton:
I love numbers. Numbers are great! But, they carry no meaning if they are not properly derived. It is numerology. Elegant and sophisticated, but numerology nonetheless.
Yup! I have been trying to explain that to anybody who would listen for years;
e.g. see http://www.publications.parliament.uk/pa/cm200910/cmselect/cmsctech/memo/climatedata/uc0102.htm
Richard
================================================
I know Richard, and you’ve done a great job at articulating this thought. What I don’t get is why it is so hard for other people to recognize this? The temp records are a huge circle of self-affirmation. As you’ve pointed out, they don’t really agree. But, in some views they can generally agree, but, that’s only after revisions.
They revise to maintain the general agreement, and claim validity because the various data sets generally agree. How stupid is that? But, we can’t get even many of the skeptics to acknowledge this basic fact and flaw in the climate thinking.
All of the models, all of the sensitivity calculations, all of the studies regarding historical temps are in error. They calibrate against air and imagination!
http://wattsupwiththat.com/2013/08/16/oh-mann-paper-demonstrates-that-tree-ring-proxy-temperature-data-is-seriously-compromised/#comment-1392645
A PS for Steve Mosher
Not only is natural “Climate” Chaos, the records have become “chaos”. The records are where “Man-made” has entered in.
When I first got interested in AGW about ten years ago, the first thing I did was get out my old college botany book. After my study, I rejected the dendro story for the reason outlined here, as well as others.
I have to wonder if any of the dendro folks have even a nodding acquaintance with biology.