Bishop Hill Reisinger and the divergence problem
Feb 22, 2010 Climate: CRU Climate: MWP Climate: other An interesting article from the New Zealand Herald, looking at the divergence problem. What particularly fascinated me was the explanation of the issue from Andy Reisinger, who some will remember as being a man who is very close to Rajendra Pachauri.
Reisinger is a climatologist, but not, if I remember correctly, a paleo guy. It's odd then to see him being the expert interviewed on the subject of the divergence problem. It might also explain the explanation he gives for this inconvenient effect:
Dr Andy Reisinger, a climate researcher at Victoria University who has followed the progress of proxy temperature reconstructions, said it could be that a lack of rain in recent decades had stunted tree growth in some high-altitude spots - or that when temperatures reached a certain point, trees began to react differently.
Whatever the cause, "the relationships [between tree-rings and temperature] that we've developed for the last 500-100 years may not apply in the last 50," he said.
Now correct me if I'm wrong, but I thought that paleoclimatologists picked trees that were sensitive to temperature rather than precipitation when they set about recreating temperatures of the past. If a drop in rainfall can cause a drop in growth now, then it could have caused a drop in the past. In other words, the paleo guys will have to admit that they know absolutely nothing about temperatures before the nineteenth century.
Reader Comments (79)
I believe that William Ockham would have a thought or two on this new theory. From wikipedia this line seems so spot on.
I can't believe you all missed the most "logical" explanation for this: the increase in carbon dioxide in the atmosphere is what is causing the trees to not show warming over the past 50 years. In short the lack of evidence of recent warming IS evidence of recent warming, and this lack of evidence is entirely consistent with what the models predict.
Give them a couple of more weeks and I am sure we were hear a variation of this argument.
This is incredible. They can prove all of us deniers wrong so simply with irrefutable proof. We are doomed. All they have to do is go out and drop any tree older than 50 years and show us where the growth of the rings suddenly changes due to this new effect on the trees. Once we have seen where the rings suddenly change with out own eyes the game is done and I won't be able to collect my oil cheque any more. It was fun while it lasted.
So i take it that none of the contributors to this thread have made any effort to check what the dendro reconstruction proponents have claimed about divergence? It's just a big game of Chinese whispers for most of you, I guess.
Divergence exists. I don't believe there is a good understanding of how widespread the effect is, but I am fairly sure some justifications have been made to claim that it is not a massive effect. It may be telling that an 'expert' is not able to present a convincing case, but that alone does not mean that it's game over. Yamal was discussed at length recently, and is maybe not done yet, but there is more work to do yet - and not just in terms of who can 'shout loudest' (I assume this is a family blog, substitute a cruder phrase at will)
Sean,
the skeptics are pointing out the problems those promoting the AGW theory are ahving with pesky little details like honesty and truth.
It is not our job to solve the promoter's problems.
and, by the way, being unable to prove one's theory with evidence that is
- reproducible
-sustainable under critical scrutiny
is, in fact, failure to prove.
The game is, in fact, over. The game, in fact, was never actually 'on'.
Other factors that seem to have been overlooked are the effects of cosmic radiation on tree growth, independently of temperature and/or precipitation: http://wattsupwiththat.com/2009/10/19/cosmic-rays-and-tree-growth-patterns-linked/ ,
and also that leaf temperatures are constant, regardless of ambient air temperature: http://dsc.discovery.com/news/2008/06/11/tree-leaf-temperature-02.html . Does that observation also apply to stem tissue temperatures?
Seems the dendro guys have a lot of homework to do in getting their act together before scaring us kiddies, any further.
Peter Dunford,
re: cloudiness - more clouds, less sun, less ring.
John Daly could have added
cloudiness - more clouds, more rain, more ring.
Sean
Any material divergence is adequate to destroy dendro as an accurate estimate of past temperatures, without further discussion; unless the tree rings are an unimpeachable measure of the observed temperature record, any extrapolation is without logical foundation. So the science is indeed settled, in so far as dendro cannot be used, and I don't see why people continue to engage with the dendro community. Ice core data, while potentially promising, is only available for certain latitudes (or altitudes) for obvious reasons, so cannot give useable information about the global temperatures at any point in time. This kicks away one of the three legs of the AGW stool, with the second being the observed temperature records, shown to be horribly compromised, and the third being the GCMs, which now have no credible base data, past or recent, against which to be calibrated. This leaves us in a position where, although we suspect the earth is warming, we do not know how fast, whether it is unprecedented, or to what extent the warming is anthropogenic either via CO2 or other GHGs. So all this money spent, and barely any science left to speak of. Oh dear.
Yer Grace
Here is John Daly's comment on Cook et al. 1991, "Climatic Change in Tasmania Inferred from a 1089-Year Tree-Ring Chronology of Huon Pine"
http://www.john-daly.com/huonpine.htm
'Talking to the Trees in Tasmania'
I've spent quite a bit of time in the dendro literature, both in the general case and specifically on the divergence problem.
First, in the general case: It is widely recognized in the literature and texts that temperature is not the dominant factor in tree ring characterics (width, density) under many, if not most, conditions for that tree species. However, many dendros believe that temperature is a dominant factor near the cold extreme for that species, at the "tree line" -- the upper limit in either altitude or latitude for the species. IMO, it is certainly plausible to posit a significant effect of temperature variation near the cold extreme on tree ring characteristics; whether this effect can be teased out from other factors is a different issue.
(The linked article in this post does not make clear that the divergence issue has to do with these "tree-line" series.)
However, I have seen quite a few reconstructions where this limitation to tree lines is ignored. Notably, the "Gaspe Cedar" series important in the original "hockey stick" reconstruction (MBH98/99) does not appear to be anywhere near the tree line in either altitude or latitude.
Furthermore, even if temperature were a/the dominant factor during the calibration period, it might not be so outside that period. For example, the California bristlecone pine series that are the dominant series in MBH98/99 show very low growth during the Medieval period, which the reconstruction interprets as evidence for cool conditions. But we know that this was a very dry period in the Western US, what climatologists call a "megadrought". So even if recent tree rings from these trees were a good reflection of temperature (they aren't, but that's a separate story...), it doesn't mean you can infer back 1000 years (and this is without any divergence problem).
On the divergence issue, I've read several of the prominent papers on the issue, and not found anything more than a listing of speculative possibilities for the cause. And most of the papers ignore a couple of the 500-pound gorillas in the room: first, the possibility of loss of sensitivity to temperature once temperatures get out of the minimum range; and second, the possibility that the good correlations during the early part of the 20th century were spurious (many prospective data sets did not have these good correlations -- did the ones that were selected just have these by chance?). If either of these were true, that whole field of science would be fundamentally discredited.
In the Climategate e-mails, we do see concern "inside" that the first of these possibilities might be a serious issue that could keep the reconstructions from recognizing past warm conditions. But somehow this concern never makes the public pronouncements.
Trees throughout much of the northern hemisphere have experienced, like most of us, the coldest winter for many years. Their growth rings will reflect this. At the same time, the 'global temperature' satellite reading for January is the highest ever recorded. Is that suffiecient argument to demonstrate concusively that we have no idea at all how to determine accurate past temperature from tree rings, and that 'global temperature' is a meaningless concept?
"Shouldn't that be 'dendro guys' rather than 'paleo guys'? Ice-core temperature reconstructions seem to stand up quite well compared to other data (like glaciations)."
Yes, it's not paleoclimatology; it's dildoclimatology, and it's in the same league as phrenology, Lysenkoism, and phlogiston theory: Cargo cult science.
I have a new stock market predicting system that is in perfect alignment (and predictions) with the market from 1880 through 1960. After that is doesn't work well at all, and often predicts the exact opposite of what does happen.
So please read my nice glossy brochure, and send me your life saving for investment with my company. After all, my prediction is correct 2/3 of the time.
In fact, Tom Wigley himself describes the problems with proxy data in 12 Aug 96 email.
http://www.eastangliaemails.com/emails.php?eid=7&filename=839858862.txt
Of note:
(3) How useful are paleodata? I support the continued collection of
such data, but I am disturbed by how some people in the paleo community
try to oversell their product. A specific example is the ice core
isotope record, which correlates very poorly with temperature on the
annual to decadal timescale (and possibly also on the century
timescale)---question, how do we ever demonstrate the usefulness or
otherwise of ice core isotopes on this timescale?
There are other well known proxy data issues that need careful thought...
(a) Sedimentary records---dating. Are 14C-dated records of any value at
all (unless wiggle matched)?
(b) Seasonal specificity---how useful is a proxy record that tells us
about a single season (or only part of the year)?
(c) Climate variance explained by the proxy variable--close to zero for
ice core isotopes, up to 50% for tree rings, somewhere in between for
most other indicators. How valuable are such partially explained records
in helping explain the past?
Back in 96, Fred Pearce wrote an article, and asked Briffa for a review. I have no idea if the article ever got published. It is contained in this e-mail, and is tto long to copy here.
http://www.eastangliaemails.com/emails.php?eid=14&filename=845217169.txt
The description of divers recovering logs from near frozen lakes is telling. You don't have a choice of tree type, or age of tree, etc. You have a sample you might not even know the type of tree it is from.
At college in the mid 80s, we were given a dendro paper too read and comment on, one of the authors was Brubacker. As I remember it, I think it was dating volcanic eruptions in the Cascade range.
General consensus in the class was that so many numerical transformations and adjustments had been carried out on the data set, that we couldn't see how anything apart from adjustments remained.
That was mid 80s, and I've had precious little contact with dendro anything since then.
Given what we are seeing with temperature record "adjustment".
Is the dendro "record" "adjusted" to hell as well?
Oh, should have said, ash clouds and gasses reduced ring width - yet another variable into the mix.
Has anyone mentioned nitrogen availability in peaty waterlogged soils?
@Tom, Feb 22, :- "David Chappell, Entrails of Pigs=PoE's? Hebrew acronym humor? Would you be clear please?"
Nowt Hebrew... David amusingly picked up on my hypothetical Chair of "Climatic Re-creation from Examining the Entrails of Goats"... Realised that the acronym from that was CREEG and suggested that should "pig" be substituted for "goat" we'd get CREEP. :-)
However, there are religious objections to involving pigs, so I think we'd better leave it be.
Witness the IPCC AR4 dancing around the dendro problems
First: In certain situations, this process may restrict the extent to which a chronology portrays the evidence of long time scale changes in the underlying variability of climate that affected the growth of the trees; in effect *providing a high-pass filtered version of past climate*.
i.e., - higher temperatures may get chopped off, from a tree-ring reconstruction
Second: However, this is generally not the case for chronologies used in the reconstructions illustrated in Figure 6.10. Virtually all of these used chronologies or tree ring climate reconstructions produced using methods that *preserve multi-decadal and centennial time scale variability*.
i.e., - the current proxies (Mann and others) do not have a high-pass filtering effect. They track well with instrumental series
Third: Several analyses of ring width and ring density chronologies, with otherwise well-established sensitivity to temperature, have shown that they *do not emulate the general warming trend* evident in instrumental temperature records *over recent decades*,
i.e., they are not tracking the heights. Just like a a high-pass filtering effect. But...this is *not* a high-pass filter effect, this is (gasp) a 'divergence problem'!
Fourth: Briffa et al. (2001) specifically excluded the post-1960 data in their calibration against instrumental records, to avoid biasing the estimation ...implicitly assuming that the ‘divergence’ was a *uniquely recent phenomenon*,
i.e., special rules apply for the present. Ah, the science of it all.
Fifth: Others, however, argue for a breakdown in the assumed linear tree growth response to continued warming, invoking a possible threshold exceedance beyond which moisture stress now limits further growth (D'Arrigo).
i.e., the trees reconstructions may be a high-pass filter after all. And therefore fail to track higher temperatures (!!)
Sixth: If true, this would imply a similar limit on the potential to reconstruct possible warm periods in earlier times at such sites.
i.e., a direct contradition, atleast in spirit, with the second statement above.
Conclusion: They broke their own hockey stick.
Either they admit that there may a high-pass filtering effect, and therefore admit that temperatures could have been higher in the medieval warm period. Or they claim that there are 'divergence' issues and give up on dendro-climatic reconstructions, for the moment.
These guys want their tree-rings for its 'interannual' resolution but want to paper over its 'divergences'. What a joke, a costly one at that!
Sean,
Take a big picture look from a skeptic's point of view. The onus is on them to prove their theory right. The divergence itself can easilly be used to disprove these reconstructions as presented (unless and until they finally mange to account for it). Yes, they should work on it longer but to a skeptic's view they have already proven to be biased by presenting only the results which are based on this assumption WHILE OMITTING the much less favorable (yet more obvious) alternative assumptions.
This will make it less likely for us to trust their "justification" when they get around to submitting it... and this should not surprise you if you take a neutral point of view. This issue is getting allot of scrutiny right now and all you hear is that the problem is "known" (not "solved"). Don't you think it's weird that they don't publish results based on other assumptions? That they don't evaluate how their particular unproven assumption affects the results? Doesn't that seem biased to you?
I'd be more inclined to believe that your average skeptic has read into these journals and looked at the methods more than your average AGW supporter. That's often the reason they are skeptics in the first place.
Pogo, Thank you for the update. Since I have been dealing with the PNS-AGW folks, I have been called a Poe, from time to time. Not that there is anything wrong with that... It was new to me when I first heard the term used last November. Google, "Poe's Law". It is a label with a lot of twist.
What I find funny is that the EPA has decades of experience with divergence and emissions parameters. The senior staff at the agency know as much more about evaluating parameters as anyone in the world. If I tried to say anything like this to underreport emissions, my employer would be subject to millions in fines and I would be rightly clapped in irons. However, when it is the agency doing the bad science, it is somehow Ok.
Bishop,
But it didn't, did it? After all the question of whether there was divergence in the past is so blatantly obvious that surely someone has looked into it before now?
You must be referring to those 'sceptics' who run around convinced that the MWP was global and warmer than now, on the basis of no evidence at all.
Gaga they may be, but it seems a tad ageist to bring their advanced years into it, and to call them 'paleo' seems particularly harsh.
Frank
The Cook argument is that since the southern sites don't show the divergence, the divergence in the northern sites must be anthropogenic, although he can't explain the reasons.
Unfortunately Cook's southern sites use foxtails. That's why they have a non-climatic growth pulse in the twentieth century. So in essence you would have a divergence in the low latitude sites if the sites hadn't been cherrypicked.
This leaves the explanation for the northern divergence looking rather thin.
Frank,
your link still does not provide any basis for assuming that tree ring data is a reliable "temperature" proxy outside of its 1880 to 1960 calibration range.
I put "temperature" in quotes, as we have still to see if there is a correlation with un "adjusted" temperatures.
Bishop,
"Unfortunately Cook's southern sites use foxtails. That's why they have a non-climatic growth pulse in the twentieth century. "
You're rather glossing over some details (in that your argument here is completely missing). I suspect you are trying to get me to buy your book :-) It is irrelevant anyhow because...
"This leaves the explanation for the northern divergence looking rather thin."
...the main issue is not the reasons for the divergence, but whether it happened in the past. Not 'could have' happened, but did happen. I could have won the lottery last week, but I didn't.
Cook's result provides some evidence that this didn't happen before, at least back as far as the MWP. Not conclusive (as the more comprehensive review of the literature on this which is also at the link I gave states), but this is more evidence than the 'it happened before' side has.
Not only that but the question of whether the current temperature is unprecedented (yet) is not very relevant to the question of whether the current trend is man made anyhow. Whether we have already surpassed previous temperatures is all these tree proxies are used to establish, to 1700 years ago, and to 1300 years ago they're not even necessary for that much.
We certainly haven't reached the mediterranean or higher temperatures during this interglacial that were required for rubification (reddening) of palaeosols in East Anglia.
http://www.telegraph.co.uk/earth/earthnews/7309688/Met-Office-to-look-again-at-global-warming-records.html
Met Office to look again at global warming records: "Vicky Pope, Head of Climate Change Advice, at the Met Office, said the new global temperature analyses would not change the trend of global warming. "
So we're paying for 3 years work that WILL confirm the bad results we already paid for *sigh*
the worst thing Phil Jones Mum ever did was send him to that Universityof Lancaster, where stupid boys just copy down what the lecturer says. She should have sent him to Oxford, where eachweekhis tutor would have given him a big reading list and an essay question. The question, however it was couched, was always the same: Tell me why this lot are talking balls. Proper education encourages scepticism, half-education develops devotees of bullshit.