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
I’m with Mosher on this one. With respect, some of the comments in this thread seem more scoffing (underinformed) than skeptical.
I have a friend with an advanced degree from MIT who is a CAGW believer. When I asked him why, he replied that a local professor showed simple back-of-napkin math in a public lecture that proved to him that the earth must warm drastically as CO2 levels rise. Sadly, having been so easily persuaded, he never dug any deeper.
In whatever direction, drawing and expressing oversimplified, underinformed conclusions only entrenches ignorance..
ATheoK says:
August 16, 2013 at 2:21 pm
I grew up in the largest National Forest (a managed forest) outside of the Pacific Northwest. It is in northwest Alabama. My father owned a sawmill and employed logging crews. I walked tracts of timber to see if they were suitable for purchase when I was twelve years old. This was before clear cutting had been imagined. We examined thousands of trees one at a time. North Alabama, north of Birmingham, is total hills. Walking through the forests is an up and down experience. South Alabama, south of Montgomery, is where the plantations were and it is flat.
Any praise that I gave your post is well deserved. Also, I am always happy to encounter someone who knows forests and what some creative people can do with forests and trees. Thanks for your stories, especially about the Luthier.
Mosher sed:
I believe it is more accurate to say the tree ring investigator is being dismissed, not the tree. The tree cannot help but be what it is but the investigator as often as not makes the tree what it is not. That being a stepping pad to fulfilling the CAGW agenda. Never misunderestimate the skeptic mind – we’ve learned what the climate hysteria advocates have not – It is harder for the CHA team to be more honest than accurate. That is to say, their numbers don’t add up. Briffa seems to be the only squeamish one of the bunch as revealed in the CG letters and post-CG statements.They have all lost credibility by being incredible as a group.
Borderline off-topic:
The discussion of growth variation reminds me of how tree rings work (or semi-work) for temperature reconstruction at all only because vegetation like trees typically grows significantly faster during warmer times (although also affected by carbon fertilization and non-temperature factors). Nominally such is just stating the obvious. However, CAGW-movement publications are able to report on a tree ring temperature reconstruction like the skewed hockey stick of Mann, then spin around to practically implying global warming has had no benefit or harmed the biosphere, with only a few noticing the internal contradiction (because many people don’t keep enough disparate pieces of info in the front of their mind simultaneously).
Here is a tree-ring paper which is a joy to read. It was published in Ecology vol.1 no.1 Jan 1920.
Evidence of Climatic Effects in the Annual Rings of Trees by A.E. Douglas.
http://ltrr.arizona.edu/sites/ltrr.arizona.edu/files/bibliodocs/Douglass%2C%20AE_Evidence%20of%20Climatic%20Effects%20in%20the%20Annual%20Rings%20of%20Trees_1920.pdf
The paper is also available here, but the above link is nicer and it is signed by the author.
http://www.jstor.org/stable/view/1929253
From Wikipedia: “Douglass founded the discipline of dendrochronology, which is a method of dating wood by analyzing the growth ring pattern. He started his discoveries in this field in 1894 when he was working at the Lowell Observatory. During this time he was an assistant to Percival Lowell and William Henry Pickering, but fell out with them, when his experiments made him doubt the existence of artificial “canals” on Mars and visible cusps on Venus.” Another skeptic doubts the dogma story.
He was looking for the solar cycle in the tree rings. He found it, but it was only a small effect.
For more history about Douglas and background for the above paper, see
http://www.treeringsociety.org/TRBTRR/TRRvol59_1_21-27.pdf
Ralfellis says: August 16, 2013 at 1:14 am
a. Tree experiences a very cold summer, with no growth. (a temperature signal?)
b. Tree experiences a very hot but too dry summer, with no growth. (a temperature signal?)
c. Tree experiences a cool but nicely moist summer, with good growth. (a temperature signal?)
d. Tree experiences a very hot and wet summer with good growing conditions but a rampant pest infestation, with no growth. (a temperature signal?)
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Steven Mosher says: August 16, 2013 at 9:12 am
When selecting a tree as a treemometer the scientist will try to
A) select a species that is particularly temperature sensitive.
B) select a stand of trees where the growth is temperature limited
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Well, they did not do very well at Yamal, then, did they? No two tree rings series from Yamal looked the same – some were up, some were down. What you are saying is that despite the careful selection process, you STILL cannot find a good reference tree-ring series. So at the end of the day, you toss a coin to decide which trees to accept. (“Let’s hear it for YAD 061 – the loudest cheer wins….”)
And your explanation also completely demolishes the pseudo-science of dendrochronology – because your test wood sample for dating was most certainly not selected by your criteria. In fact, you will most probably have no idea where the sample came from. So how can you compare it to the ‘select’ reference trees?
And so we must turn again to the defenders of dendrochronology, like Greg, who are desperately separating it from dendrothermometry. Just what do you think the dendrochronologists are measuring?? Do you think there is a date embedded into each tree ring?
No, they are measuring the width of tree-rings, and the changes in the width of successive rings to build up a graphic of good and poor growth. And what causes those tree-ring changes, eh? Ah, yes, temperature and moisture – as well as nutrients, pests, tree age, and canopy cover. So please do tell me, how the test sample of wood (which came from a balmy glade in southern France) can compare with the reference sample that came from a select micro-climate in California or the wetlands of Southern Ireland? Just what is the link between the two? None. And so how can you compare them?
Oh, and I forgot to say that the test sample had a five-year pest infestation, which resulted in 5 years of no growth in the middle of the sample (which looks like 5 years of cold or dry weather). Now how do you match the test and reference samples? Ah, yes, I know – you find 5 successive years of no growth in the reference sample, which equates to 687 BC. But then the archaeologist complains that the boat was built in the 17th century…..
Voodoo science.
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“A likelihood perspective on tree-ring standardization: eliminating modern sample bias”
This is a very interesting paper. The conclusion is that it is possible for a biased climate ‘researcher’ to cherry pick data dendro chronological data to push one’s own climate change agenda.
Mann cherry picked inaccurate dendro chronological data, hide that cherry picked data from other researchers, hide the faulty application of a mathematical algorithm that was used to enable the cherry picked inaccurate data dendro chronological data to create the ‘hockey’ stick. An indicate that Mann’s paper is incorrect scientifically and appears to be the work of an advocate is the hockey stick is not supported by other proxy data, is not supported by previous analysis by prominent scientists, not supported by the historical record written by people at time (which note climate facts such as the Medieval warm period was a warm period or the Little Ice Age was a cold period) and is not supported by agriculture practices at the time (such as which Northern regions could or could not grow grapes for wine production and famines due to crop failures during the cold times, such as the Little Ice Age.).
To eliminate sampling bias from ‘modern’ climate research, there needs to be a test to determine if the research is done by a scientist rather than an advocate who is trying to create propaganda. There needs to be another paper written on the problem of climate advocates posing as climate scientists. There needs to be a paper written on the climate advocates blocking so called ‘skeptical’ papers in climate research publications. There needs to be a paper written that explains how and why Mann’s hockey stick graph was used by the IPCC to push an agenda.
http://wattsupwiththat.files.wordpress.com/2013/08/clip_image0061.jpg
http://wattsupwiththat.com/2013/08/16/historic-variations-in-temperature-number-four-the-hockey-stick/
Greenland ice temperature, last 11,000 years determined from ice core analysis, Richard Alley’s paper.
http://www.climate4you.com/images/GISP2%20TemperatureSince10700%20BP%20with%20CO2%20from%20EPICA%20DomeC.gif
Isn’t the fact that the paper is published a reason for celebration? It shows that the stranglehold the AGW crowd had on the peer review system is weakening.
ralfellis says:
August 17, 2013 at 3:34 am
What a bracing argument. Woke me from my dogmatic slumber. Maybe dendrochronology is not sound after all.
Two comments regarding reading the tree rings
1) All plants have an optimum temp growing range, too cold = slow growth – too warm = slow growth. How do you differentiate between small tree rings due to being too cold and being to hot
2) global temps (ave) vary only slightly from year to year (.02 c or less). However, local temps can very immensely from year to year. For example, the temp difference in north texas during 2011 was approx 2.0c or more warmer than 2013. However, when reviewing the tree ring reconstructions, you almost never see a temp variation from year to year greater than .3c
Not to harp on the famous bristlecone pines, but my recollection is they did not pick up the north american heat wave of the 1930’s. But hey climate scientists note that would be cherrypicking.
Well, that was disappointing. I waited for 4 minutes for him to give me something convincing that the hockey stick is legit and that temperature reconstructions like it are just as legit, but all I got was “Mann’s hockey stick is legit because other people did the same thing and got similar results.”
Juice says:
“…all I got was ‘Mann’s hockey stick is legit because other people did the same thing and got similar results’.”
But Nature was forced to print a Correction to Mann’s Hokey Stick chart. If others got the same results, then they were wrong, too.