This is for entertainment only. Given the week we’ve had, I thought it might be interesting to gauge some opinion about dendroclimatology. While we can certainly argue the merits of “who said what” etc. the question on my mind is what do people think of the technique of using tree rings for determining past climatic history?
Readers, please invite others at non skeptical blogs to participate, use the “share this” link. I’ll extend a blanket invitation to anyone to participate, no matter what your view might be.
Since this is a highly polarized issue, I’ll note that the poll code is setup (by WordPress.com) to minimize the possibility of vote stuffing and encourage one vote per person. You’ll know you’ve hit that security feature if certain messages are displayed.
Here’s the poll question:
Of course I should add that no online poll is scientific, it is only an interesting and entertaining exercise in gauging the opinion of people who visit here.
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The question “Are trees an accurate enough recorder of air temperature to accurately determine past temperatures?”, is reasonable, but a better question I think would have been “Are trees an accurate enough recorder of air temperature to justify re-writing climatic history and discarding or ignoring hundreds of peer-reviewed papers that confirm the MWP and the LIA?”
I return to the quantitative point. Even if tree growth is influenced by temps, it is not linearly influenced by every degree of fluctuation. A difference between, say, 19, 20 or 21 degrees doesn’t make much of a difference in growth. Only extreme temperatures can be reflected in smaller ring widths. Say – temps below 15 or above 23. (All numbers are hypothetical).
So there is no way tree rings could be translated into temp differences at a resolution of 1/10 of degree, or even one whole degree.
Tree rings might tell which years were warmer (or had better growing conditions), qualitatively, but no by how much it was warmer quantitatively.
I think the tree rings are good indicators of how well that particular tree was growing in the given year. But why it was or was not growing is not so clear cut and sounds like so much guessing to me.
Like most polls people can take, there is rarely a response choice that reflects my opinion. Here’s mine:
Yes and no. Tree-ring data acts as a proxy. A proxy is a stand in, not the real thing. Sometimes the proxy might represent me (e.g. if I’m Temperature), other times it might represent someone else (e.g. my colleague Rainfall).
I voted in the unsure column–I do think that tree rings have some value, but only when there are a lot of trees involved and other factors can be controlled for, or they are used to support other data.
Having said that, my mother has 2 maple trees in her yard; they were about the same size when they were planted at the same time about 10 years ago. The appearance of the soil and presence of some bits of pottery and other artifacts have led us to speculate that one was planted on the site of an old outhouse. Guess which one is twice the diameter of the other now.
After reading the thread, particularly the post by Willis Eschenbach, I voted no. Before reading, I was unsure.
jacob; totally agree. There may be some temp relationship but the supposed small signal and the collosal error involved make it incredibly suspect to us engineers… I believe one of Steve McIntyre’s biggest criticisms of the reconstructions is the incorrect (or misleading) presentation of error. I’d love to see his analysis of the error limits (has he presented that before in graphical form?).
I think your post makes a lot of sense, Mr. Eschenbach. I would question this though:
“A perfect temperature for that kind of tree will lead to wider rings.”
It seems to me that perfect temperatures for a tree, if sustained, would lead to more trees growing near that tree, which means more competition for sunlight and other resources. So perfect temperatures might cause wider rings at first, but I would expect them to eventually get thinner again.
Whilst it is certainly possible that temperature will be demonstrated in the width of tree rings (given a large enough sample), there are other very important factors that affect them.
One, mentioned often here from experience, is sunlight. So if there are fewer clouds, there may be wider rings, regardless of temperature. Having said that, clouds affect the temperature too (more than CO2), so there could be a correlation, I have no idea if high and low clouds, which apparently have different effects on temperature, would affect a tree ring, however. Do we know? I suspect not.
Water is another mentioned here by many. Given plenty of water, a tree may grow very well in a hot year, whereas another would grow poorly given too little water. I have no idea what other combinations would cause. That is a subject in itself, I guess.
Finally, we have the start of the show, CO2. Now, CO2 is literally food for plants. Whereas we get our carbon (carbohydrates and protein, aka ‘food’) from plant and other animals (according to taste and availability), plants get all of their carbon from the air in the form of CO2. This is, therefore, what they ‘eat’. If they have an abundance of CO2, they do very well. In fact, doubling CO2 will cause an increase in growth of 40% given no other resource is lacking. If any other resource is lacking (for example in hot, arid countries), that increase could be as much as 100%. Quite a boost, you’d have to admit.
As an aside, if I wanted to ascertain that (not whether or not, mind you) CO2 levels were correlated with temperature, and I could also claim that tree ring widths were an accurate record of temperature, I’d be on to a winner. If CO2 levels are high, trees will grow more, therefore rings will be wider. So I’ve proved that there is a correlation between CO2 and temperature! It really is CO2 causing Al Gore Warming, as long as no-one points out my circular reasoning, of course….
^^^^
Sorry, CO2 should be the ‘star of the show’, although ‘start of the show’ works too, funnily enough!
^^^^^
Ha, ha! ‘Rings’ ‘circular reasoning’
missed that!
It’s a disappointing result.
Trees ain’t thermometers folks.
I would say no, simply. (better answers above)
Certainly the claims of robustness coming from the Hockey Team in defence of their graphs don’t make any sense whatsoever. Allowing one tree such influence over the final result seems an incredibly bad application of statistics to me. And I’m no statistician! Or scientist!
Peer review, my foot.
Willis Eschenbach takes the prize. Thanks for the clarity. It’s a false mapping from temperature to tree rings because many “input variables” (temp, water, sunlight, wind, insect stress, browsing animals, soil conditions) all map to the same “output” of ring-width. That “multiplexing” means you can’t extract the temp signal from the aggregate (confounding) factors unless you do huge sample sets and rigorous methods and independently corroborate, as a physical process, ring width goes with temp. But here the statistical rigor is absent and in any case it seems, per Willis Eschenbach’s comment, that ring width is inherently ambiguous for temperature: low temp and high temp both map the same way.
Bottom line, dendroclimatology = junk science. Whoever gave Mann and Briffa their degrees, never mind their funding, should be run out of town.
Understand, the temperature signal *IS* in the tree-ring data, but in order to extract it you would need solid proxy’s for precipitation, solar radiation, etc… all down the line for all the other factors in order to extract what you want.
Real scientific investigation would be finding a method of doing just that, not taking the ring data at face-value.
John Cooper (15:24:20) :
What Wade (13:08:38) : said was exactly right.
Two years ago I planted about ten Dawn Redwood tree seedlings all within 100 feet of each other.. Some of them have done really well and others are puny. Whether it’s the soil, the sun, neighboring trees sapping their nutrients, I don’t know. Location, Location, Location…
To follow onto your post, a co-worker and I each purchased a forest pansy redbud three years ago from the same nursery on the same day. His was slightly better than mine visually. He lives only several miles away in the same general climate. He visited the house this summer and ask where ours was. I said you’re standing beside it. He said, “no, I mean the one from three years ago. This one is much older”. Seems I planted mine in a location where a blue spruce had been excavated, and the nutrients have cause it to now be twice the size of my co-workers tree. All in three years.
I have to admit, I have never seen a forest pansy redbud (slow growing tree) grow this fast. The greatest growth was this summer, when our temps averaged -1.5C. The point is that nutrients play a huge role in tree growth spurts, and the negative temp aspect had nothing to do with it. In fact, when you think about it, nutrients, water, and photosynthesis (it’s always about the sun) are the three most important players in a tree’s life. Not temp. It almost seems like a no-brainer.
It seems almost gratuitous to mention that water stress, for example; either too much or too little, provokes, in a plant, the production of abscisic acid. This is a growth regulator (hormone, if you like) that suppresses growth. This retardation persists long after the environmental stress is mitigated. A plant can sit and sulk for the entire season after a brief but intense period of drought or water-logging.
Also, how come there’s no allusion to spring and summer wood? Surely, they could tell me not just how warm it was in the year but in the two growing seasons; pines and larches usually have very distinctively colored rings.
Anybody lacking an incremental borer ( the tool of choice for sampling without killing) and disinclined to the wanton felling of someone else’s trees can do their own subjective assessment of the variability of individual tree responses to the slings and arrows of forest life by strolling through a juvenile plantation of conifers and noting the length of this season’s leaders and comparing the internodes between branch whorls of previous years.
I’m pretty sure I voted ‘No’ but Anthony appears to have sneakily switched the order of the questions.
I think tree rings are valuable. There is information in there. We just can’t get ahead of ourselves. At some point we may be able to analyse the woody material that make up each ring to the point where we can gain additional insight and de-confound the data of interest. We are not to the point yet where it is anything other than a rough tool.
I do not see how tree ring records can be used to deduce anything over a time period longer than a fair fraction of the life-span of the tree species involved.
There must inevitably be a high pass filter effect.
This science is probably just as valid as the one where they measure the bumps on your head. I forget what they called it, and NO, I am not going to look it up on google. I hate google.
[Phrenology. The maps look much the same, come to think of it. ~ Evan]
I vote that someone here or anywhere write a paper that can be published showing how tree rings are not/cannot be indicators of temperature.
Please! Somebody do more than write a post. Publish a Paper about this matter if you are so convinced that trees cannot be used for establishing past temperatures. Otherwise, this is all conjecture. (And please spare all of us the conspiracy theories about peer-reviewed science).
For more than a decade, like othe commenters here, I have been planting tree seedlings. My trees along a railway plant corridor show diverse growth, some flourish, some do not. Like the climate system, tree development is not simple.
I have to say I am not sure.
The Yamal series, for example, seems reasonably on the mark–except for that one single tree!
Do I trust MBH? Heck, no.
I wouldn’t want to write of the entire methodology as completely worthless. Which it may be. Or not.
After all . . . I don’t much trust the GHCN final Surface Temperature results, but that does not mean that I don’t believe thermometers can be used to measure temperature . . .
End of story. Tree rings tell you something (unreliably) about the conditions the tree has experienced. Nothing else. And certainly nothing about Hemispherical temperatures. Enough already, move on.
I work with bonsai trees, which are interesting because the balance must be very precise for the tree to grow well. Not mentioned very much so far is disease. I don’t have any formal training, but it is evident from the bonsai that fungal growth is directly related to climate. Warm, wet weather seems to encourage fungal growth in our trees, while dry, cold weather retards fungal growth. The fungus is also somewhat cyclical… the tree is more infected in early spring if the weather is wet and warm, so growth is slow. If the weather dries out, or there is a cold snap, the tree rebounds and growth becomes stronger. If the wet conditions persist, the needles or leaves will be smaller, less effective, and cell collapse will continue. Such a weakened tree will be even weaker in the fall. Some trees are more resistant than others. A tree weakened by several seasons of warm, wet weather, insect infestation, etc would show quite retarded growth, it seems to me. These are just observations, though, and could be quite different for polar trees.