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New Tree Ring Study Ignores The Effect Of CO2

January 14, 2016

By Paul Homewood  




Andrew Montford has a post up on the latest tree-ring based temperature reconstruction of summer temperatures in the northern hemisphere. It attempts to show that current temperatures are unprecedented in the last millennium.

Steve McIntyre is already poring over the statistics, but there is one issue raised by several commenters. That is the question of what effect increased levels of CO2 in the atmosphere have had on the tree rings.

It is well established that CO2 has a significant effect on plant growth, and accepted that tree ring studies can be skewed as a result.

It was therefore astonishing to find this comment from one of the study’s authors, the UEA’s Tim Osborn, on Bishop Hill:


5. CO2 fertilisation effects.

We don’t identify or remove such effects. The empirical evidence for sustained effects (i.e. over decades) on trees in cool, moist locations over long periods of time is scarce.

Jan 14, 2016 at 5:36 PM


This one comment tells us so much about the lack of integrity in climate science nowadays. Just because there is a lack of empirical evidence does not mean the whole issue can be trundled off onto the sidelines.

Now maybe CO2 will make little or no difference. But if it cannot be properly accounted for, the whole study (or at least the 20th part of it) becomes worthless. Indeed it simply confirms what we already knew, the fact that the climate went very cold in the 19thC, and that since then temperatures have somewhat recovered.


There are 23 authors listed for the study, all I gather tree ring experts. Surely one should have had the integrity to stand up and point out the elephant in the room?

We often talk about the corruption of money in climate science, but I sense another factor in play here. This is the belief that they are all doing something so wonderfully important.

When saving the planet is the objective, why let a few inconvenient facts get in the way?

  1. Ian Magness permalink
    January 14, 2016 9:07 pm

    I have never understood how tree ring growth is supposed to be an accurate proxy for temperature. It’s much more complicated than that and, to take a prime example, water supply to the roots is very important. To state the bleedin’ obvious, a drought will stop growth, while a wet summer is perfect. Neither will imply a particular temperature. Then, what about soil fertility, parasites, insects, tree diseases and, of course CO2. Most of these cannot possibly be deduced in any way by tree rings. Surely this renders any supposed temperature/tree ring link meaningless and unusable?

    • AZ1971 permalink
      January 15, 2016 2:30 pm

      Up vote times ten thousand. So absolutely true, and requires no collegiate degree. All it requires is common sense and a basic understanding of the food for plants: CO2 and H2O. Temperatures are meaningless because trees (and plants) respond to hours of sunlight, not temperature specifically. This is why green-up in northern regions begins well before optimal growing conditions and why leaves turn color and fall off in autumn, Really, how can these so-called experts be taken seriously?

  2. Don Keiller permalink
    January 14, 2016 9:14 pm

    As a plant physiologist I am very aware of the effects of enhanced CO2 on plant growth.
    What is more raised CO2 is more effective in promoting the growth of plants under environmental stress- there are numerous studies to show this. Exactly the conditions that you find the trees used in this study.
    Tim Osborn’s comment either demonstrates ignorance, or deliberate deception.
    Take your pick.

  3. January 14, 2016 9:42 pm

    Dendrochronology is a useful tool for certain situations. However, it was vastly misused in the Univ. of East Anglia “climategate” scandal. First of all, the cored trees from the Yamal Peninsula were a data base of some 250. However, ca. 25 were “cherry-picked” for the pleasing data they gave. Sorry, that is not science. Another “study” was based on THREE trees from that data base. Secondly, CO2 is not something which can be discerned from a study of tree rings–there is just too much “noise”. Here is what they ARE useful for: dating tree ages; dating structures, such as the Mesa Verde Cliff Dwellings, by overlapping cores forwards to the present; showing trends of moisture and drought by the greater or lesser width of each growth year ring; showing temperature trends when corroborated by another piece of knowledge, as colder or hotter weather will also show greater/lesser growth in individual rings. It is now, with some factual data from the tree rings coupled with knowledge of the climate, that the fantastic tone is due to closer growth rings and thus denser wood from the Little Ice Age. Except for aging a tree or a structure, the other situations show trends and not specifics. I don’t for a minute think that the Motley CRU of UEA did not fully understand that using that method would allow them to attach whatever meaning to the “data” they needed/wished.

    • January 14, 2016 9:46 pm

      Sorry, I left out the “fantastic tone” of what: the Stradivarius violins, violas, cellos and various other stringed instruments.

  4. January 14, 2016 10:41 pm

    Thanks, Andrew, Paul. But how sad!
    “The empirical evidence for sustained effects (i.e. over decades) on trees in cool, moist locations over long periods of time is scarce.”
    Yes, but the empirical evidence for sustained effects of CO2 on global climate is even scarcer.
    It is the empirical evidence for the corruption of climate science that is mounting.

  5. January 15, 2016 12:14 am

    Reblogged this on Climate Collections.

  6. John F. Hultquist permalink
    January 15, 2016 1:46 am

    Tree-ring dating of artifacts and events (dendrochronology) is a great technique for many sorts of studies.
    “Treemometers” are a manifestation of the Texas sharpshooter fallacy.

  7. John F. Hultquist permalink
    January 15, 2016 2:03 am

    If there are readers that have not seen Steve McIntyre’s “Ohio State Presentation” here is the link:

    This is a talk Steve gave on May 16, 2008. We got a broadband connection (DSL) in September of that year and I found this paper almost first thing, and then WUWT, Jeff Id (Condon) of ‘the Air Vent’, Joanne Nova, and more.
    At least give the short version of the Ohio State Presentation a read.

  8. NeilC permalink
    January 15, 2016 8:28 am

    Reduced photon activity below a specific level (quantity & wavelength), irrespective of the temperature, photosynthesis can’t occur. No photosynthesis, no metabolism, no growth.

    Low levels of CO2, water, and essential nutrients in the ground reduces or halts the metabolic process, irrespective of temperature. No metabolism, no growth.

    Tree ring growth is not a good proxy for temperature reconstruction.

  9. January 15, 2016 10:09 am

    Sadly, the BBC, Guardian and Independent will have already published this as further firm evidence from “scientists” of the approaching doomsday. As noted in the article, “When you are saving the planet, why let a few inconvenient facts get in the way”.

    Climate science is joining political science, social science and nutritional science in the world of “self-proven junk science”.

  10. January 15, 2016 12:32 pm

    Here’s a technical discussion of why tree rings are worthless as a proxy for temperature. Of course the author is an academic so he has to tip-toe around the issue, but you see, the discussion is twelve parts long.

    • January 15, 2016 8:48 pm

      I appreciate the link but I didn’t “tip-toe” around anything. I said full-on what I meant and explained the technical problems in great detail. I also called out PNAS for their atrocious review. I realize that many academics do in fact “tip toe” when it comes to criticisms of science/scientists, and many more just avoid it altogether, but I really don’t play that game. I’ve criticized many studies of various kinds on my blog (mostly on topics involving forests/trees/climate). I’ve also published two peer-reviewed comments in high impact journals (GRL and Ecological Applications) and believe me, it is an enormous headache to do that. It takes a LOT of work and persistence. Plus you make enemies. That’s why people don’t generally do it.

      Furthermore, your statement is wrong. Tree rings are not “worthless as a proxy for temperature” and I never said such a thing. Rather, certain types of analytical procedures, commonly applied to certain tree ring variables, are unreliable in returning what they claim to return, such that for example, tree ring density is much less problematic than are tree ring widths. Big difference in meaning.

  11. Don B permalink
    January 15, 2016 3:15 pm

    “When saving the planet is the objective, why let a few inconvenient facts get in the way.”

    Noble Cause Corruption

  12. January 15, 2016 4:53 pm

    I’m currently stuck behind the great firewall of China and it doesn’t like wordpress. I patched together a work around. I’m posting an abstract to a significant field study concerning the effects of increasing atmospheric CO2 on the growth rates of Western Juniper over 100 years. I can’t post the link because of limitations in time and circumstance. I’ll be back in February if you need the whole paper and can’t find it let me know.

    Detecting potential regional effects of increased
    atmospheric CO2 on growth rates of western juniper
    P A U L A . K N A P P , * P E T E R T . S O U L EÂ ² and H E N R I D. GR I S S I N O – M A Y E R ³
    *Department of Anthropology and Geography, Georgia State University Atlanta, GA 30303; ²Department of Geography and
    Planning, Appalachian State University, Boone, NC 28608; ³Department of Geography, The University of Tennessee, Knoxville,
    TN 37996, USA

    Evidence of an atmospheric CO2 fertilization effect on radial growth rates was
    uncovered by examining climate±growth relationships for seven western juniper
    tree-ring chronologies in central Oregon using multiple regression models.
    Consistent upward trends of the residuals from dendroclimatic models indicated
    a decreased ability for climate parameters to predict growth with time.
    Additionally, an assessment was made of whether enhanced growth was detectable
    under drought conditions, because a major bene®t of elevated atmospheric
    CO2 is the reduction of water stress. Mean ring indices were compared between
    ecologically comparable drought years, when atmospheric CO2 was lower (1896±
    1949), and more recent drought years that occurred under higher atmospheric CO2
    concentrations (1950±96/98). The results presented herein show that: (i) residuals
    from climate/growth models had a signi®cant positive trend at six of seven sites,
    suggesting the presence of a nonclimatic factor causing increased growth during
    recent decades; (ii) overall growth was 23% greater in the latter half of the 20th
    century; (iii) growth indices during matched drought and matched wet years were
    63% and 30% greater, respectively, in the later 20th century than the earlier 20th
    century; and (iv) harsher sites had greater responses during drought periods
    between early and late periods. While it is not possible to rule out other factors,
    these results are consistent with expectations for CO2 fertilization effects.
    Keywords: atmospheric CO2 enrichment, climate±growth responses, western juniper
    Received 8 February 2001; revised version received and accepted 20 June 2001

    The effects of elevated atmospheric CO2 on plant growth
    in natural environments are unclear. While many laboratory
    studies have documented the positive responses of
    plants to

  13. R2Dtoo permalink
    January 15, 2016 5:18 pm

    One knows that something is amiss when there are many authors. This is just another trougher effort designed to pad publication records for all. This is, plain and simple, “the team”. The limitations of dendrochronology have been known for years.

  14. January 15, 2016 9:32 pm

    If I could make a general comment: I appreciate that the post itself is toned down–it identifies a potential problem and more or less leaves it at that (although I disagree that Tim Osborne’s comment regarding lack of evidence on CO2 effects on growth is evidence of lack of integrity).

    And I agree, the inability to account, quantitatively, for possible CO2 fertilization effects is a very real problem that needs to be explicitly addressed. Indeed, CO2 fert is only one of several such non-climatic effects, which leaving aside the genetically determined growth rate variation, includes such things as N fert., changing tree competitive conditions with time, and changing activity of the vascular cambium (which produces the rings) around the tree bole. This difficulty does not make it impossible, and there have been studies attempting to tease out the CO2 fert effect from the climatic, but it does require very careful thought and analysis.

    What the online “climate skeptics” often fail to realize, and badly, is that this presentation of actual or potential technical issues is **all that is needed**. Some (not all!) people who are interested and knowledgeable of the subject will take notice of these, although this notice, or a response, may not be immediate. But as soon as you start into all the conspiracy and stupidity stuff, you lose a **whole bunch of people**–and the very ones with the ability to change how the science is conducted no less. I guarantee you this is true.

    • January 15, 2016 11:13 pm

      I am not sure how they can publish an paper claiming one thing, while ignoring the CO2 effect which, until satisfactorily accounted for, utterly underminds their findings.

      Perhaps you can explain how that is in any way “scientific”?

      • January 16, 2016 12:31 am

        As I stated above, I agree that this is a very real problem and is being too readily glossed over or ignored. I just saw a comment by Rob Wilson at the Montford blog, giving his justification for why they ruled out CO2 fert and I do NOT agree with Rob’s reasoning on that issue. This issue is related to that of the problems in RCS detrending and it would take me another blog post to explain it in detail. However, there was in fact a paper that appeared in PNAS this week, in which side-stepping this CO2 fert issue is *much* more serious than the Wilson etal paper–that paper appears to be seriously flawed and if I get time for a post, it’s going to be on that one. In fact, this paper by Wilson et al is a definite improvement on other works of its type–primarily because they use max latewood density as the response variable in many of the series analyzed, which is much less of a problem, as far as T estimates go, than is ring width.

  15. manicbeancounter permalink
    January 15, 2016 10:22 pm

    It is worth looking at the CO2 effects in another way. Does this latest study corroborate or undermine the idea that CO2 is having a significant impact on temperatures? That is does it support the idea that a doubling of CO2 levels will, even after a time lag, cause temperatures to rise by about 3C. Or does the data support something much lower – between 0C and 1C for a doubling of CO2? To substantiate the 3C climate sensitivity claim, the additional warming over and above any natural variation would have to be substantially more than that any natural variation. Even with lagged effects, one would expect a 40% rise in CO2 since 1780 to have produced 1C or more of warming by 2011, most of which should be since 1945. What is more, in the Northern Hemisphere, where average temperature variation has been larger than in the tropics or the Southern Hemisphere, the human-caused warming effect should be even more pronounced.
    Rather than eye-balling the graph above I have tried to replicate it by first averaging the data sets for each year, then calculating a 15 year centred moving on those annual averages. My graph is below.

    This is a close match to the N_TRENDS2015 graphic above, but some of the “spikes” in my graph are greater. For instance the C9th warming and the C15th cooling spikes are greater in my graph.
    What is most important is the marginal contribution from CO2 and other greenhouse gases. If that is large in nearly 1300 years of data, the highest will all be in recent years. Below are where the 15 year MAVs are above 0.82. It was only in the 1990s that average temperatures exceeded those in the 1160s.

    Year 15 YR MAV
    1161 0.830
    1162 0.844
    1163 0.838
    1993 0.823
    1995 0.842
    1996 0.902
    1997 0.917
    1998 0.940
    1999 0.978
    2000 1.049
    2001 1.103
    2002 1.106
    2003 1.183
    2004 1.369

  16. manicbeancounter permalink
    January 15, 2016 11:54 pm

    Continuing from the previous comment, to substantiate the human signal requires there is more to than looking at 1300 years of data. Within the last two hundred years does the proxy temperature data
    a) Give a reliable data set?
    b) Confirm a human-caused signal?
    c) Give a fair comparison with the data sets based on the thermometers?

    Reliable data set?
    One of the good features of Wilson et. al 2016 is that from 1710 to 1988 there are 53 data sets. Inevitably the further one goes back, the sparser the data going further, but there are still 23 data sets for the year 1000, 30 for 1200 and 42 for 1510.
    One point is the fall-off after 1988. In 1990 the count is 33, in 2000 24, in 2010 7 and 2011 just 3. A crude average of 2011 is 3.30, against 1.63 for 2010 and 1.79 for 2003 (the next highest). The spike at the end of the series seems to be reliant on very little data. Maybe not as notorious as the Yamal or Marcott proxies, but still proxy data after the year 2000 should not have been included.

  17. January 16, 2016 9:27 pm

    OK, I averaged all 54 data series from 1710 to 1998. The period for which they all have data. Then I plotted the results without any statistical nonsense. Here is the result. As can be seen temperatures have been rising steadily since the early 1800’s, long before CO2 was an issue.

    This is VERY STRONG evidence that CO2 is not the cause of the current warming!!

    • January 16, 2016 9:36 pm

      I even spy the 1940s peak!

      • January 16, 2016 9:52 pm

        I even spy the 1940s peak!
        yes, on that basis I’d say there is good evidence these rings are valid proxies.

        The problem comes when you try and apply statistical methods to “improve” the signal to noise ratio. All too often what really happens is that the noise get amplified, such as happens with “tree ring calibration”, better know in the other soft sciences as “selecting on the dependent variable”.

        At least the other disciplines have begun to realize that faulty math gives faulty conclusions. However, in the field of Climate Science such result are all too often seen as a positive, when in fact they are a false positive.

  18. January 17, 2016 5:33 pm

    I’ve re-analysed all 54 datasets for the period 1710-1998, the period where all sets have data. No statistical nonsense was applied. Calculating both the average and standard deviation, there is an interesting result!

    For the period 1710 to 1998, there is virtually no change in the 30 year average of the deviation. What this says loud and clear is that there is no evidence in this data for climate change being due to anything other than natural causes. There is no evidence that industrialization is affecting the variability of climate. Otherwise we should be seeing a statistically significant increase in the variance. But we don’t.

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