Trees Make Bad Thermometers

OK, I would have assumed that the title for this post was obvious to all:  There are a lot of reasons that trees don’t make very good thermometers.  Now, that is not a criticism of climate archaeologists who use tree rings to infer the historical temperature record.  Sometimes, we have to work with what we have.  Historians are the first to admit that coins are not the best way to deduce history, but sometimes coins are all we have.

But when historians rely on imperfect evidence, there generally is an understanding that the historical record created from this evidence is tentative and subject to error.  Unfortunately, some climate scientists have lost this perspective when it comes to tree-ring analyses, such as Mann’s hockey stick.  They tend to bury the fact that:

“There are reasons to believe that tree ring data may not capture long-term climate changes (100+ years) because tree size, root/shoot ratio, genetic adaptation to climate, and forest density can all shift in response to prolonged climate changes, among other reasons.” Furthermore, Loehle notes “Most seriously, typical reconstructions assume that tree ring width responds linearly to temperature, but trees can respond in an inverse parabolic manner to temperature, with ring width rising with temperature to some optimal level, and then decreasing with further temperature increases.” Other problems include tree responses to precipitation changes, variations in atmospheric pollution levels, diseases, pest outbreaks, and the obvious problem of enrichment that comes along with ever higher levels of atmospheric carbon dioxide. Trees are not simple thermometers!

When the tree-ring folks like Mann first did their analyses, they calibrated tree ring growth over recent decades with the recent historical temperature record, and then projected this calibration backwards on history.  But, as noted in the quote above, there is a lot of evidence that these calibration factors may not be linear over time.  And in fact, the few people that have gone back and resampled Mann’s trees have found that their growth diverges substantially from predicted values – in other words, the relationship between tree ring growth and temperature is not constant. 

Now, this does not make Mann and his peers bad scientists.  They were trying their best to reconstruct history, they tried one methodology, but then evidence mounted that this methodology is flawed.  What makes them potentially bad scientists is their reaction to the negative evidence.  Once evidence of the divergence problem was raised, scientists have simply ceased resampling trees.  Their focus hs become defending their original approach, rather than improving it based on new information.

Often, new approaches require new people, as in this case:

Loehle gathered as many non-tree ring reconstructions as possible for places throughout the world (Figure 1). There are dozens of very interesting ways to peer into the climatic past of a location, and Loehle included borehore temperature measurements, pollen remains, Mg/Ca ratios, oxygen isotope data from deep cores or from stalagmites, diatoms deposited on lake bottoms, reconstructed sea surface temperatures, and so on. Basically, he grabbed everything available, so long as it did not rely on trees.

And he got this plot for a temperature reconstruction:


Only time will tell if this approach holds up better than tree rings, but it does better match the annecdotal history we have, including a Medieval warm period where Greenland was, you  know, green and a little ice age in the 17th century.  Like Mann, Loehle’s first version had some statistical and procedural errors.  Unlike Mann, Loehle reworked the whole analysis when these errors were pointed out.

  • RW

    Claiming that Greenland was, you know, green is about as strong an argument as saying that the Democratic People’s Republic of Korea is, you know, democratic. According to the relevant Icelandic Saga, In the summer Eirik went to live in the land which he had discovered, and which he called Greenland, “Because,” said he, “men will desire much the more to go there if the land has a good name.”

  • dearieme

    That cold spell in the late 1600s was very marked in Scotland: “King William’s ill years”.

  • BillBodell


    Icelandic Sagas aside, are you stating that there is no historical evidence that Greenland was “greener” in the MWP and that a thriving community existed there until the MWP ended?

  • RW

    I am stating merely that an argument about climate based on the name of Greenland is fantastically weak. The name of the place is the only ‘anecdotal’ evidence offered in this post for a warm climate 1000 years ago.

  • Very interesting look at Mann et al’s devious approach to science, W.

    The ancient vegetation that is being uncovered by glacier retreat appears to indicate an earlier era where Greenland was much more “green” than now.

    The evidence for a MWP and LIA are weak only to true-believing members of the climate orthodoxy.

  • Mann is very much a bad scientist. McIntyre and McKitrick’s takedown of his hockey stick should have made him hide his face in shame. It is not just that he used tree rings, it was that his statistical methods were so transparently bad.

    And then he had the gall to refuse to share his raw data and methodologies with other scientists.

    That makes him a bad scientist.

    And once his mistakes were pointed out, such as using the wrong coordinates for temperature sensing stations, he refused to correct them in later versions of his paper.

    That makes him a bad scientist.

    And now he proclaims that his bristlecone pines at Almagre are somehow magically tuned in to global climate, through “teleconnections.”

    That makes him a good candidate for a guest spot on “Coast-to-Coast AM,” not a good scientist.

    Hanson is a bad scientist for the same types of reasons: bad-faith data collection, bad methodologies, and an insistence on hoarding his data.

    Oh, and hurling ad-hominems at his detractors for not recognizing his superior intellect.

    That’s not good science. That’s politics. Mix the two at your peril.

  • davidcobb

    If you look on Mann’s wikipedia site you will see a picture of him holding a section of bristlecone pine. A close look at this section will show a large growth lobe, demonstrating that his “teleconnected” trees were not even robust to variations in the angle of sampling.

  • Adirian

    RW – here, too?

    Come now. Be effective. Who in here is claiming that Greenland’s name is the reason we think it was once warmer? There are several rather bad play-on-words, but nobody has claimed that, and you’re attacking a straw man.

    If you really want to convince anyone of anything – and the skeptic’s position is, in spite of all claims to the contrary, the default position, from which any responsible individual must start – you have to do better than that. < - You can find Greenland's temperature records here, incidentally, if you don't mind that it isn't in English. These are reconstructed from glacial ice cores in Greenland, which, I think you will find, are just a little bit more accurate than tree growth rings as a temperature reconstruction device.

  • RW

    Adirian: are you not able to read, or did you just not notice the paragraph in which Greenland’s name is touted as evidence for a mediaeval warm period?

  • vandervekken

    The comment about Greenland being, well, green, was tongue in cheek. Realists have a sense of humor, Religious Fanatics don’t.

  • RW

    What makes you think it was tongue-in-cheek?

  • TR


    That Erik chose Greenland as a name to attract settlers does not imply that it was the only reason for the name. I doubt that Erik would have tried to deceive his own people, including is wife and two sons, into making a dangerous journey to a vast frozen wasteland if he didn’t believe it was promising.

    The anecdotal evidence of the reason Erik called it Greenland is NOT evidence that it wasn’t farmable and capable of supporting a population.

    So, saying “Greenland was, you know, green” is not even close to making a ludicrous statement like “the Democratic People’s Republic of Korea is, you know, democratic.” Since we have pretty strong evidence that North Korea is, you know, a brutal dictatorship. But we don’t have any such evidence that Greenland was uninhabitable when Erik convinced his fellow countrymen to settle there. We do, however, have evidence that points to the opposite. Thus, it is reasonable to assume that the name Greenland may come, partly at least, from the habitability of the land at the time.

    Likewise, you needn’t fear for your life if you go to Monster Island — because the name is misleading…. it’s really a penninsula.

  • RW

    Certainly parts of Greenland were habitable when Eiríkur rauði first went there – as they are now, and as they have been throughout. The Inuit inhabitants never disappeared, just the Norse ones. But the rather more habitable island to the west was called Iceland and I’ve never seen that claimed as evidence of cold weather in 891AD. The point remains that if you want to believe that it was warmer 1000 years ago than it is today, the name of Greenland is a very very weak piece of evidence. The author gave no others.

  • dearieme

    “But the rather more habitable island to the west>>”: East!

  • RW

    Correct… oops. And it was in 874AD that Ingólfur Arnarson landed there, not 891AD.

  • TCO

    There were a lot of errors in Loehle’s work. And they were very easily shown. I think it was a very amateur effort and shows that E&E is not a serious journal. Even people sympathetic to skepticism were treating the thing s something needing serious revision before being published. Should have been a discussion paper. Not “published”…if you consider E&E publishing that is.

    The whole thing is kind of illuminating. The skeptics want to find flaws in other people’s work but won’t even do the normal standard of good work themselves. This makes me less and less likely to think much of their arguments. Heck, look t McIntyre running off to conferences and writing his talks the night before he gives them. It’s just shoddy. I think McIntyre doesn’t get published (hasn’t for over 2 years) because he is lazy and sloppy and disorganized.

    Put a little Minto and Zelazny up their asses, kay-yote!

  • Chris Schoneveld

    I must admit that RW makes the climate skeptic blog entertaining and lively, especially since he is able to comment on any posted subject. He singlehandedly dominates Climate-Skeptic. Begs the question, is this guy doing any substantial work apart from blogging? Where does he get the time for all this and does he really think that the time he spends on this blog is productive? I am retired and intellectually often bored, so reading blogs and occasionally commenting on them is sort of fun but an active and serious scientist(?) should not lower himself the way RW does, especially since the latter dares to question McIntyre’s credentials as a scientist. Maybe not surprising after all considering his tiring display of superiority in most of his comments.

  • Paul M

    TCO’s critiscism of Loehle’s work is fairly typical of the AGW children. Loehle was willing to submit his work to a full public anlysis on CA and responded positively to many of the comments, suggestions and corrections. Indeed he made amendments to his work on the basis of this thorough analysis. Many of the snipes from the likes of TCO were nitpicking rather than presenting any fundamental challenge.

    When Mann and his claque publish all their data and when all the code for the climate models is published so that it can be tested, then perhaps we can listen to TCO and the other arm waivers.

    RW presents a silly argument about Greenland. It is a perfect example of arguing about something that is irrelevant rather than engage. The historical record rather than defective treemometers tells us clearly about the MWP and the Viking colonisation of Greenland. By the way, is Iceland covered in ice?

    Ah well , off to Tesco’s.


  • TCO

    A. I’m not an AGW child. You just think I am because I don’t wack off to the party line. I’m actually more conservative than you are, you fucking OBL dick sucker.

    B. Loehle did respond to criticism of his paper. I’m in agreement, you little moron you. My POINT, you blind vidiot, is that his initial paper was a discussion paper with major flaws not only in execution but in design, in the “issue tree analysis” itself. Anyone who has done good work knew that Loehle had done a slack job. This indicts “publishing on E&E”. Only AFTER significant revision did people like Bender think it was EVEN publishable. I mean heck, the most basic thing is thta his paper is essentially a variation of Moberg’s work, but Loehle doesn’t even have the science smarts to consider this and give a good analysis of similarity and differences to that work.

    C. Loehle and McIntyre are WEAK.

  • TCO

    And at least Loehle had discussion paper. McIntyre just has usufruct-filled meanders for the last 2.5 years, in a non-permanent and self-edited (after the fact and without notification) format.

  • Paul M

    TCO – you need to get out more. I’m curious. What does OBL mean? Btw I suggest you read the latest New Scientist about the valuie of published and peer reviewed work. Just because Mann et al are published and peer reviewed does not stop their papers being defective.

    My name is Paul Maynard. I assume TCO means The Complete Arsehole – whoops can’t spell either.

  • Paul M


    The Complete Onanist

    In fact a prize to the best answer to what TCO means.



  • PhilA

    Gee, TCO really doesn’t like Loehle does he?

    However I am curious when we’ll see him apply the same standards of criticism to Mann’s papers and the journals they appeared in. Given said papers are riddled with even greater errors than Loehle’s and haven’t had these errors (even the most basic like tabular data putting measurements on the wrong continents!) corrected in later versions.

    Or is the real issue that Loehle got – and continues to get – the “wrong” answer, so different rules can be applied? Ah…

  • TCO

    repeated for the gazillionth time:

    A. Mike Mann’s sins don’t absolve others. Poor methods are bad practice regardless of who else practiced them or even regardless if your answer is “right”. Wegman addressed this well.

    B. I have previously commented negatively on Mann, many many times (but point A stands regardless of if I have or how much I have).


    You all need to get OVER the attitude of allowing faults for your side or ignoring valid points of the other side. Don’t be a lightweight trying to buttress your biases. Try to invalidate them. Come up with critical analyses. Come up with tests that show something. Be a curious thinker.