The Unstoppable Dirty Dozen
Posted by Jeff Id on November 8, 2009
Science is good fun. Lately we’ve been working with an unnamed paleoclimatologist who goes by the handle of Delayed.Oscillator. He’s been good enough to answer some questions on dendroclimatology temperature reconstructions. Recently I’ve made comments about the Yamal series data and Briffa’s corrections about not allowing for trees to grow faster as they age. Briffa uses an exponential decay for his corrections to Yamal tree growth which looks like this:
The data is divided by the red line in top pane in the above plots. It has been my contention that since the red line drops well below the rest of the data it amplifies the older data creating an artificial uptick at the end of the reconstruciton. DO has made the following statement at his blog:
Let me be as clear as I can be, there is no sign that I can detect that it is old trees that increase their growth at Yamal (even if identified, this phenomenon would require some hypothesis as to the cause), At Yamal, a portion of the old trees are those that were growing together during a period of climate warming. If you examine the raw ring width, there are a few fossil series that have rapid increases toward the end. If Jeff’s hypothesis were correct, we’d expect these to be the oldest, right? In fact, the seven subfossil samples I identified as having rapidly increasing growth in their later years, six had a wide range of ages from 90 to 180 years (this comes with the caveat that we don’t know the exact pith age).
Now DO beat me to an analysis suggested by Steve Fitzpatrick to separate the recent old trees from the historic old trees and verify whether the U shape in pane 1 above (the average of all old trees) is a result of recent climate or is a standard shape in older trees. There are plenty of explanations as to why trees can grow faster in older age that we can be certain DO is aware of so the parenthetic portion is a bit grumpy of him. In DO’s conclusion his plot looked like this:
This plot represents all trees with a last measured ring width dated before 1950. My own contention was trees greater than 200 years could show the increased growth though so it wasn’t enough to show what happens. We need to see the old trees separate from the record as Steve Mosher pointed out. So here’s a plot of the pre-1950 trees similar to that shown by DO.
There are only 19 trees to work with but here they are with an Esperesque spline fit.
You can see the curve in the top pane has almost the exact same shape as DO. Not bad really. In the bottom pane there is no apparent upslope in pre 1900 Yamal area trees with ages greater than 250 years. Now when this is compared to 250 year old trees with last RW after 1950 the plot looks like this.
The trees (first pane) show a clear upslope in later years. On the surface DO seems to be correct on this point. The trees ending before 1950 look like this.
Figure 5 just left more questions for me. Many of the trees seem to reach a minimum at 200 years of age and peak upward trickling back down before ending their lives. Is it possible that the difference between the post 1950 Yamal data is that they haven’t slowed down in their last 20 years before dying yet? Would that make the downslope at the end of pane 1 Figure 3. I don’t think it’s unreasonable because you can see the mid life minimums in L13371, PO9281 L21081 L11631, L00861,L01181, L01041, L13181 even though they have different climatological conditions. They started growing faster after about 200 years and then trickled off at the end. I’m still not certain that most trees don’t show an uptick as they age keep in mind that this data is the extent of my experience.
The last graph P09281(last graph above) starts increasing after 200 years and then drops off and dies. It getting warmer from 1100 to 1150 according to the last graph but not according to L09301 (third one down on the right) which was dying at that timeframe or L12641 which in 1100 AD was before its pre-200 year mimimum and still dropping (these graphs are uncorrected though so perhaps reasonable growth standardization corrections can turn it into warming).
Next is the same kind of plot for some of the Post 1950 trees. These trees haven’t shown their end of life dropoff cause most if not all were alive at the time of sampling.
There are a lot of trees which show increases in growth post 1900 but there are also quite a few which show less growth post 1900. Really lousy thermometers these. From Figure 4 pane 1 we would expect a steadily warming climate for the last 200 years (that’s the average) and that’s pretty well what we see in pane 3 of Figure 4.
So then I decided to calculate least squares slope fit’s to the ring widths since 1920 instead of by tree age. Since the slopes are from trees over 250 years that end post 1950, the EXP correction from Briffa or the spline corrections would have a negligible effect on slope. In a huge surprise, there are a lot of negative slopes in these trees during the greatest warming in the Yamal area. Remember these are 250 year old trees from 1920-1996 so it’s 174 years and older in pane 1 of Figure 4. – Look at pane 1 of the figure and you’ll see why negative slopes after 174 years are a surprise.
 0.09525731 -1.67765546 0.08194925 -1.57939710 1.56477900 -1.08070478
 0.10164856 -1.66012718 0.01617010 0.79523364 0.29315124 -4.15916120
 -0.15019269 -4.84568356 -0.31551278 0.02163996 -1.24181240 -1.88490060
 0.10123042 0.38330849 -0.05190331 2.60531409
There are 11 negative slopes of 22 series! That was unexpected! What’s more the average slope is -.572 (negative!) with a standard deviation of 1.66 – Not exactly precision agreement. Now 1920 was picked at random with consideration of when we started producing lots of CO2 around then. Be careful and don’t overconclude form these slopes – with this noise level different years will give different results. IMO the main conclusion from this is that the slope is not strongly positive – no indication of warming!!!! and not clearly defined! Since there is no evidence that trees are thermometers, rather than conclude anything about warming lets say tree growth is apparently not unprecedentedly large in recent years. Below is a histogram of the slopes. How’s that for a bell curve!
So the next thing was to look at uncorrected tree ring data for trees at least 250 Years old which have a last ring after 1950. These are probably 100% living trees but we don’t know.
This does not look like Figure 1. The EXP corrected version (Briffa’s style) results in the plot in Figure 9.
The exponential hockystickization correction of Figure 9 is just enough to push the blade into unprecedented territory but not by much. This doesn’t look like Figure 1 either. The spline corrected version of the data is Figure 4. Figure 4 looks a lot like the simple mean of Figure 8, this represents reasonable standardization of old trees across the time series. This is my #1 criticism of Yamal that the original version didn’t look like the mean, indicating the blade was created by the standardization.
Ok, so let’s get into some new stuff. The total dataset in the Yamal area includes the following groups:
Yamal, Live, Jah, Por, Yad, Khad, Russ035
The russ035 is from SteveM’s sensitivity test. You learn so much more playing with the data than you can reading about it. I discovered that in several cases the ‘new’ briffa sensitivity test has the same core ID’s as the old briffa data.
The total unique series names available is 302, Yamal itself had 252, Live -17, jah – 25, por-12, yad – 10, khad – 18 (Russ035 – 35 – SteveM’s not used by Briffa). In Briffa’s sensitivity test, there were 82 series which should have been unique to prove that Yamal is not sensitive to different datasets. However, the sum of the non-Yamal series = 17+25+12+10+18 = 82 series added to Yamal for sensitivity. However there are only 302 – 252 = 50 unique new series from the original Yamal. Thirty two series were used at least twice in the Briffa sensitivity test.
JAH141 – *
JAH162 – *
POR011 – *
POR031 – *
POR051 – *
POR081 – *
YAD041 – *
YAD061 – *
YAD071 – *
YAD081 – *
YAD121 – *
Stars are the original dozen. You need to be following along for this but if the dirty dozen are re-included in the sensitivity test to determine the effect of the dirty dozen? Is that a fair test?
Probably the main criticism of Yamal by some dendro’s was the low core count in recent years. If we don’t double up the trees and properly sort the data, what is the core count for all the data in the region and how does that compare to the original Yamal? Core counts are shown per year in table 1. All series include SteveM’s schweingruber set.
|Yamal||Briffa Series||All Series|
What does the full RCS style hockeysticization reconstruction look like now with all trees included and the original Briffa style corrections.
Core counts in 1996 have doubled now to an anemic 9 but the blade was cut from a Figure 1 peak amplitude of 2.75 (red line) down to 2.25. A good size jump downward from the new trees but it’s still an excellent quality hockey stick. If you cut off the last 6 years the plot doesn’t look the same but that’s not the point. RCS corrections to the tree ring widths rely completely on the homogeneous nature of the data. We are applying the same correction to all the data. Differences in homogeneity will result in unexpected results. Since RCS is an ad-hoc style correction, great care needs to be used to determine if the results make sense.
Briffa’s correction used for Yamal was an exponential decay. The exponential curve plot (Figure 10 pane 1) tapers off to a flat horizontal line becoming pretty horizontal after 100 years. To be clear, there isn’t much slope in the correction after that time. This means that for the average older trees in the recent 100 years, a correct standardization would reproduce results similar to the mean of the data. There just shouldn’t be a huge difference because there isn’t a huge slope correction. My contention is that there is a big difference created entirely by RCS reacting with the inhomogeneity and has resulted in coining the phrase hockeystickization.
I must mention that Roman M is the first to point out this effect on a CA thread. Roman does a lot of things first. Anyway, this is what the mean of the data looks like. In this form the oldest data is distorted but the recent data should be reasonably similar to Figure 10.
Now that looks a little different wouldn’t you say?!! This means that there is nothing unique or unusual about the 20th century tree rings. There is an upslope in the last few years of the plot represented by very few trees but the ring widths don’t exceed 1930.
– Briffa’s sensitivity test used the original Yamal data and got the original result!!
– RCS standardization is reacting poorly to the typical data and creating an artificial hockey stick on the end of the data!! – Homogeneity must be questioned.
– There is nothing unique or unprecedented in recent tree ring widths in Yamal area.
– Average slopes of living trees in Yamal area after 1920 for older trees are actually negative. I picked 1920 for industrialization, I did not try other years or pick the best one on purpose. Results are going to be dependent on the choice of start year.
– The standard deviation of the slope variance is huge, selection of different years will result in huge differences. – The data is noisy!!
– The math is creating most of the variance (hockeystick) in Yamal’s new version in recent years and must be thoroughly (and honestly) examined to accept any sort of corrections.
Somehow the pro’s don’t agree!
Now the next step will be to redo the whole sensitivity test by Briffa without the dirty dozen and see what we get! I’m tired though and these posts take a lot of work.
Does anyone want to bet what all the data looks like with the dirty dozen removed?