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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It is my understanding that tree rings when correlated with temperature records can provide a reasonable proxy for temperature beyond the range of where correlation is possible.
What Mann does is to correlation a limited subset of the data (bristle comb pine from the US SW) with temperature and then adjust the rest of the tree ring data to fit the correlation. The result of his approach is that in forcing a fit he makes all the data prior to the instrumental record (and especially the data that is not the limited set he correlated) do weird things – like erasing the MWP. What Briffa appears to be doing is similar.
This approach is apparently only acceptable in the world of dendrochronology (or dendroclimatology for those that like the alternative term). Why it is acceptable there appears to relate to what in science is called “confirmation bias”.
Climate science isn’t the first field where confirmation bias has been allowed to run amok. That does not however make it acceptable.
Now that major government policy that can (and likely will) devastate the economies of the western world is being adopted (based in large part on the perceptions generated by the results of Mann’s and Briffa’s work), it has become imperative that the science community insist upon better proof.
In a perfect world where science is buffered from politics this is what would occur. But alas, we live in a world where science has bee hijacked by politics, so get ready for a wild ride down the economic slide.
Might be a good idea for younger readers to learn Chinese or Hindi as that is where the world economy appears to be headed.
Original, tree rings were used solely for dating purposes and for that they are very useful. Their use for temperature measurement, proxy, came much later and has always been somewhat dubious.
As our biology friends have already pointed out tree growth is subject to many environmental parameters and separating them from one another is extremely difficult and cannot be done by the method that ‘the team’ has used.
Probably tree rings are probably better indicators of rain as others have stated, as sunlight on it’s own can bring about a plants demise. A drought can produce narrow tree rings which can happen at high or low temperatures.
Some years ago there was an incredible TV program called The Green Machine. One thing I remember from that was the sound of photosynthesis which appeared to be driven by sunlight. In which case I would say tree rings are an accurate indicator of sunlight and rain. That is NOT temperature and rain.
However, maybe there is a tree out there that grows in response to temperature alone. But to derive gloabl temperatures from that tree I would have thought you would then need to find the same kind of tree scattered evenly around the planet.
Another aspect of tree ring growth is what a trees growth profile would be over it’s lifetime. Do trees have the potential to have even growth rings throughout their lives?
I thought tree rings were used primarily as a means of dating historical artefacts, and have been a useful cross reference for carbon dating, and magnetic dating.
Vigorous, healthy tree growth in recent years (whether a proxy for temperature or not) is considered evidence of something disasterous coming our way.
A different “selection” of trees indicates that they’re not doing so well in recent years. This is considered “good news” (by some).
Are we in favor of tree growth, or opposed?
Watts up with that???
Best,
Frank
Probably too many probablys.
I should add that an atmospheric temperature signal will only be found in cold climates.
I have only to look out my window here in Western Australia to see plants grow like crazy in the winter because it rains. Come summer almost all plant growth will stop because it doesn’t rain.
Jacob (13:36:02) :
The attempt to created temperature “records” 2000 years back, with a resolution of one tenth of a degree is absolutely insane.
Yes, it is absolutely insane; however, the purported resolution is not one tenth of a degree, but worst… one hundredth of a degree, i.e. index of growth*0.01 °C. It’s not science. I have used the formula for calculating the change of temperature based on treerings growth, then compared with solar irradiance and the resulted correlation is amazingly high. Then I plotted the raw data, without making the conversion to temperature and compared the results with the solar irradiance databases…
The correlation didn’t disappear, but reinforced. What does it mean? That the treerings growth depends mostly on insolation; the last assertion coincides with what we know about plants physiology. Siberian Larch Trees, or Russian Pines, slow their growth when the insolation is higher than 50% of the total available, so the conversion of treering growth index to change of temperature will always give false results and flattened lines. There is no doubt about it.
Bristlecone Pines and Siberian Larch Pines respond also to temperature in the same way. Their growth slows when temperature is above 23 °C. There is no way to know if the narrowing of the treerings growth was due to low or to high temperatures. The claim on associating the treerings growth with the environmental temperature is simply fraudulent.
More fraudulent is the fact that some dendroclimatologists have chosen C3 plants (pines) for their assessments when they perfectly know the treerings growth will give its maximum value at 23 °C, and lesser or minimum values at temperatures both below and above 23 °C. It would be fair if they would have chosen C4 trees from mid, tropical and equatorial latitudes, which respond proportionally to increases of insolation.
On the other hand, the growth of any tree depends on the healthy state of its leaves, which is where 95 % of photosynthesis occurs. However, if an army of ants decide to cut leaves of a group of trees in a given region, those trees will offer an extremely low growth even when the insolation index is 1, or if the temperature and humidity are optimal for the tree grows splendidly.
Conclusion, treerings are absolutely useless as proxies for assessing environmental temperatures.
The only thing tree ring widths tell you is whether conditions were favorable for a particular tree at a particular time. This might mean warm and/or wet weather, but what factors matter/mattered when and where and for which trees is…impossible. Dendroclimatology is, as far as I am concerned, a waste of time given the difficulties inherent which out weigh the dating advantages IMAO.
air temperature has little infuence on tree growt. if there is enough rain and lots off sunshine but colder temps then the tree will have a good year.
I’ve only ever considered tree rings to be useful in determining the trees age.
Wouldn’t hang my hat on the accuracy of any temperature data that may be implied by them.
Ian
Canberra
Whether or not a given tree species grow in a certain area can be a temperature indicator, so the ‘tree line’ or limit seems to be a reasonable indicator of climate. Certainly no palm trees in Antarctica.
I think its clear that ring width is a function of many factors, temp being only one, and for that reason width should be discounted as a temperature proxy. I would suggest that a better means of analysing cores is to look at isotopic ratios, much as is done with speleo core data. Determining carbon isotope ratios of course is easy, of course, and I’m no expert, what possibly could be used here?
For sure not enough precision.
Tree rings are a possible source of temperature history.
Trees rings are a possible source of precipitation history.
Trees rings can possibly tell us about surrounding vegetation, particularly taller trees.
The trick is to figure out which of many factors the tree is trying to tell us about.
In the papers I’ve read, I didn’t see any reasonable methods being applied to try and separate out the various factors.
It would be interesting to take the various tree ring datasets and use CPS or other methods, but trying to extract a precipitation history. That should be as valid (or invalid) as trying to extract a temperature history.
==============================
All of the above comments also apply to sediment varves, such as used by Mann to determine the annual hurricane count back several hundred years. Of course the multiple factors affecting sediment varve thickness aren’t all the same as for tree rings, but the challenge is the same — to determine which of many different possible driving agents are the ones affecting varve thickness in different levels of the core. Just like with tree rings, we have no assurance that the reason for different thicknesses in one time frame is the same as in another time frame.
As one wag put it “Torture the data sufficiently and one can get any answer. “
How are these “other” hockey stick graphs addressed in this post at Real Climate.
http://www.realclimate.org/index.php/archives/2009/09/hey-ya-mal/
Eh. What poll? Where’s the poll? And what’s the question?
Like global warming it isn’t showing up here.
Or am I looking in the wrong place?
Kindest Regards
REPLY: Try turn on photos for your browser or use a different browser.- A
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…
From what I can see, studying tree rings requires even MORE random sampling than other proxies for the simple and obvious fact that each tree’s growth will depend mightily on rainfall, light, location (valleys and mountain shadows, other trees, underground water, etc.)
Trees are notoriously different between themselves, even identically aged trees next to each other in a forest.
I could see using trees for general, averaged climate as long as you gather and use data from a fairly large number of trees over a fairly large area. Anything else, any other use, any lesser method of gathering “data” will be meaningless. Or maybe, will be wishful thinking.
FYI, here is an email I have just sent to the NPR ombudsperson:
Dear Sir or Madam:
As a longtime environmentalist and fan of NPR, who does retain a scientific world view on controversial subjects like the widespread but increasingly religious belief in C02 induced “global warming” I have been appalled by the lack of objectivity apparent in almost all NPR shows that claim to treat this subject in an objective fashion. I’m sure that we can all agree that were the alarmist prognostications of the IPCC valid, then extreme measures would indeed be appropriate. The trouble is, they just aren’t. In fact, it should by now be evident to any reasonably objective person who has bothered to follow the real scientific debate on this topic, that the “consensus science” on which the public statements of Mr. Gore, Dr. Mann, Dr. Briffa, and other global warming advocates are based, is currently in the advanced stages of a complete melt down. This is particularly true now, given the manner in which Dr. Stephen McIntyre has recently revealed the dependence of Dr. Briffa’s new substitute “hockey stick” on tree ring data that is little less than bogus. If you don’t believe me, please visit wwww.wattsupwiththat.com and consider the recent relevant posts and discussion comments.
NPR staffers can’t even seem to get very basic facts, like the current state of arctic sea ice, correct in their news stories. It is quite untrue to categorically assert, as a gerundive fact, that “with arctic sea ice disappearing” anything else should be postulated. Arctic sea ice is NOT disappearing, notwithstanding the drumbeat of today’s mass media, including NPR. Here, for your information, is AMSR-E’s data on arctic sea ice for the past seven years: http://www.ijis.iarc.uaf.edu/en/home/seaice_extent.htm
Please note that we are the *third year* of a strong, apparently cyclic rebound, in arctic sea ice extent. The strength of the pattern over three years is particularly evident in this third season. This trend is consistent with the known reality that, for the last 8-10 years, there has not been ANY increase in global temperatures; if anything, there has been a slight decline, and many informed scientists expect this decline to continue for the next twenty years or more, at least.
The facts are diverging from global warming rhetoric. Its your job to notice that.
Given the extent of the denial and hysteria that mark the current state of discussion on global climate predictions, it is safe to predict at least one thing: whether the recent 8-10 year flatlining of the IPCC’s projected increases in global warming (and consequent divergence between the alleged cause and its predicted effects) continues, or merely represents a temporary divergence between theory and reality, the theory of CO2 induced global warming (which has always been based on the incorrect assumption that climate modellers actually understand the energy dynamics of earth’s system well enough to distinguish a real cause from a hypothetical one), seems destined one day to be a textbook example of the “extraordinary popular delusions” about which Charles Mackay first wrote in 1841.
First, Anthony, thanks for an interesting question. It is actually two questions, viz:
1. Does temperature leave a signal in the width of the tree rings?
2. Can we reconstruct the signal from the width of the tree rings?
The answer to the first question is definitely yes. A perfect temperature for that kind of tree will lead to wider rings.
The answer to the second question, however, is generally no.
Tree rings are not good thermometers. Trees grow poorly when it is too cold. But they also grow poorly when it is too hot. There is no way to tell which is which. A hot year is indistinguishable from a cold year.
This makes it theoretically impossible to extract the original signal. If a tree ring with a width of 2.7 mm could either represent 60°F or 80°F, we simply cannot reconstruct the original signal from the tree ring widths.
But wait, there’s more, as the pitchman says on TV … it gets worse!
Narrow rings can also occur because it is too dry, too windy, too much frost, late spring, waterlogged soil, and a host of other things.
Goldilocks in the story had three temperatures — too hot, too cold, and just right.
With trees, wide rings definitely mean “just right”. The timing of the frosts and the water when needed and the sunlight and the temperature and the nutrients and the clouds and the wind all conspired to make a good year for that tree. Things were just right. Not one thing was lacking.
But unlike Goldilocks, tree rings cannot tell too hot from too cold. Both of them make narrow rings. So does a lack of water. So does the wind blowing from the wrong quarter, and a host of other environmental factors.
The standard way to attempt to get around this problem is by simply interpreting narrow rings as representing cooler years. Inevitably, this pushes the calculated “temperature” downwards. It falsely represents the past peak temperatures as being lower than they actually were. Any event that slows tree growth, including too hot a temperature, is calculated as though it were a cooler temperature. You can see what that might do to e.g. the Medieval Warm Period.
So there are two huge problems with extracting the temperature signal from the tree rings:
1. A narrow ring can mean either too hot or too cold.
2. No one single factor (e.g. moisture, temperature, hours of sunshine) can cause a wide ring. All of them have to be right to get a wide ring. But a variation in any single factor can cause a narrow ring.
Problem #1 means that even in the best of cases, with all other factors being equal, our resulting reconstruction will be inaccurate and also biased downwards.
Problem #2 means in the real world, our resulting reconstruction will more inaccurate and will be biased even further downwards.
So my vote on the poll is no, at present the temperature signal can not be reconstructed through tree ring width.
My best to all,
w.
Thanks Anthony.
I am always annoyed when I read in some media “that a majority of people believe in AGW” and feel that one single climatologist always trumps 100,000 uninformed people…
I still trust the Hudson’s Bay Temperature records much more than I would trust dendro. Very close to 400 years of sub-artic temperature records that amount to millions of data points. Compared to that, the dendro stuff is very weak. No wonder there was such a concerted effort to marginalize the guy who was documenting that record. The Hudson’s Bay Company was probably in cahoots with big oil anyway, ……. 8^]
Some nice words here about dendrochronology being a better tool than dendroclimatology. I think that is true but there are limits. The same variations in growth of individual trees discussed here has the potential to make some wood samples simply unmatchable to a master chronology. Local climates and microclimates have similar effects.
There is however a natural human temptation to produce a match rather than no-match and a less than rigorous match is sometimes quoted as ‘the best available match’. But what is not always recognised or even mentioned when such dates are quoted is the very real possibility that the date produced might be wrong. Keenan has written about this.
Sometimes dendro dates are ‘supported’ by similar radiocarbon dates. However the master dendro sequences have been put together with the assistance of radiocarbon dating and radiocarbon dating is calibrated by information from the dendro sequences. I am not a scientist nor a historian but to me this means that the dates produced have a degree, perhaps a large degree, of uncertainty.
Years AD are not generally a problem because there is usually plenty of other evidence about dates so dendro dates are often simply used to refine an already reasonably well known date. But in years BC, particularly in pre-Classical times, there may be no available belt to go with the braces. There are therefore a lot of issues about chronology at this time and every reason for scepticism about the certainty of the scientific dates that are available.
All this is further confounded by the refusal of some dendrochronologists to publish or otherwise make available their data…
OT : I used to live in State College, PA (yes, home of M. Mann). On Mount Nittany there are two Hemlock trees, side by side, that are thousands, yes thousands, of years old growing in the middle of a small stream. They are extremely big and healthy and a sight to behold. If you ever get to that area, do visit them. It does require a bit of a hike, but knowing that you are touching something that is still alive and is that old is a very humbling experience, much like visiting a Stonehenge.
No, I do not believe our present science can determine past temperature using treerings.
Sorry. OT and not entertaining.
Britons creating ‘more emissions’ http://news.bbc.co.uk/1/hi/sci/tech/8283909.stm
Greenhouse gas emissions created by Britons are probably twice as bad as figures suggest, says the government’s new chief energy scientist Professor David MacKay.
“Other countries make stuff for us so we have naughty, naughty China and India out of control with rising emissions but it’s because they are making our stuff for us now,” he said…
…”This not only means that the true scale of required emissions reductions in the Western world will be much higher but that the impact on economic growth and living standards there will also be more severe than so far believed.”
I wonder what support this viewpoint will have amongst those people that have seen their jobs go to China?