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A Treeline Story

Filed under: — Ray Bradley @ 17 November 2009

Some of the highest growing trees in the world are also the oldest—bristlecone pines (Pinus longaeva) from the Great Basin in the western United States (eastern California, Nevada and Utah). The oldest example is more than 4800 years old. Because of their longevity and growth at high elevations (where the growth of trees is generally known to be limited by temperature) bristlecone pines have been of particular interest to dendroclimatologists (paleoclimatologists who study tree rings to reconstruct past climate). Numerous ecological studies carried out at treeline sites all over the world show that temperature imposes a critical limitation on the ability of trees to produce new tissue; mean daily temperatures of 8-9°C are required, so recent warming will have particular benefits for those trees that have managed to eke out an existence for so long, living “on the edge”.

An interesting characteristic of the western bristlecone pines is that their recent growth has markedly increased—ring widths have been higher than in previous decades. Previous studies have debated to what extent this “fact” is real, or just an artifact of the way tree-ring data are analyzed. Because the growth of trees is radial, as trees get older and the diameter of a tree increases, annual ring widths decline in thickness. This is the normal “growth function” that is commonly removed from measurements before further analysis is carried out. The trick is to do this carefully so that as much climate information is retained while the growth function is discarded, and dendroclimatologists know how to do this quite well. However, sometimes the “standardization” procedure can introduce spurious results. This led some to regard the apparent growth increase in bristlecone pines to be a meaningless result of the data processing. In a new article in the Proceedings of the U.S. National Academy of Sciences (PNAS) Matthew Salzer (Laboratory of Tree Ring Research, University of Arizona) and colleagues examine this issue head on. They studied hundreds of trees from treeline sites in the Great Basin, aligned all the samples according to date, and simply averaged the results (Figure 1). Given that these trees are all long-lived, the complicating factor of growth function (which is strongest for the early growth of a tree) was not significant for assessing the most recent growth. Their results show that mean ring width in the last 50 years has been greater than in any previous 50 year period over the last 3700 years. You have to go all the way back to ~1900-1300 B.C. to find mean ring widths approaching recent values. Furthermore, the recent increase in ring widths is seen in trees at the upper forest border at sites hundreds of km away (even when the treelines there were at lower elevations)—but not in trees below the upper forest border. Below the zone closest to treeline, wide rings are formed in cool, wet years, and narrow rings in warm, dry years, and trees from this lower zone do not show the 20th century growth surge.

It is thus clear that the bristlecone pines from the highest regions, close to their growth limit, are showing a very strong response to recent warming, and indicating just how unusual it has been in the context of the last few millennia. Previous explanations have focused on possible CO2 fertilization effects (increasing water use efficiency) but there is no obvious reason why such factors would have affected only trees within approximately 150m of local treeline in different locations. Rather, the high elevation trees, close to the limit of growth, have responded positively to the recent increase in temperature just as ecological studies would have predicted.

One final note: bristlecone pines often have an unusual growth form known as “strip bark morphology” in which annual growth layers are restricted to only parts of a tree’s circumference. Some studies have suggested that such trees be avoided for paleoclimatic purposes, a point repeated in a recent National Academy of Sciences report (Surface temperature reconstructions for the last 2,000 years. NRC, 2006). However Salzer et al’s study shows that there is no significant difference in their results when the data are divided into two classes—strip bark and non-strip-bark cases –when the raw unstandardized data are compared. So that particular issue has apparently had people barking up the wrong tree…

Figure 1: Median ring-widths (non-overlapping 50-year means) of upper forest border Pinus longaeva from 3 sites in western North America, plotted on first year of interval (from Salzer et al, PNAS, 2009)


144 Responses to “A Treeline Story”

  1. 101
    monty says:

    #60 anony mouse
    It’s a staple at RC to proclaim that “people thought the earth is flat”.
    NO ONE EVER THOUGHT THE EARTH IS FLAT. It’s a joke invented by Washington Irving in a fanciful account of a conference in 1491 at the University of Salamanca to investigate Columbus” claim that he could reach China by sailing west. The faculty told him he had rigged the numbers to make the earth smaller and China larger (which he had) and he and his crew would die of thirst if he tried. But if anyone suggested that they would fall off the end of the earth, they would have laughed themselves to death.

  2. 102
    Sekerob says:

    Hank, 19 November 2009 at 2:12 PM

    Albedo… reminds me of this odd study by I think the university of bristol or something that claimed that the change of land use has been cause of a substantial part of the warming and the inclusion of the ‘we should slow down the deforestation’ comment in there… duh. I thought that agricultural land increased Albedo. Aside deforestation, interrupting the water vapor cycle at that, I’m more worried about the millions of square km of additional snow cover missing during summer period and the effects it has on the underlying permafrost. Coal plant sooth part of the cause?

  3. 103
    Phil Scadden says:

    #101 Hmm. “No one “, “ever”. China perhaps before 1000CE. Ancient Egypt, Babylon and other Mesopotamian cultures. Hunter/gatherer culturers in many parts of the world? On other hand I agree that it was not the world view of Europe at time of Columbus.

  4. 104
    SecularAnimist says:

    Andrew Hobbs wrote: “I too have read lots in that time and I can’t seem to find anything, anything at all, that would make me less convinced.”

    John H wrote: “You had to have been shletered by some means from the plethera of material produced by the dozen or so major skpetics and their troops.”

    The plethora of material produced by the dozen or so major “skeptics” and their troops is powerfully convincing, alright — it has powerfully convinced me that the dozen or so major so-called “skeptics” are brazenly, deliberately dishonest frauds and/or ill-informed, arrogant cranks, who neither understand nor care to understand the basic science, and their “troops” are gullible dupes who think a “skeptic” is someone who unquestioningly believes whatever Rush Limbaugh says.

  5. 105
    Phil Scadden says:

    Dave McKenzie. Alternative hypotheses are welcome – wouldnt we be relieved if it was suddenly discovered that AGW was wrong? However, alternative hypotheses are few on ground and they are only welcome if they make physical sense and match empirical observation better than current theory. AGW wins big time here. There is vast amounts of MISinformation, fraud and downright lies on various blogs – try sticking to the published science for fact. At very least, read IPCC WG1, SPM (Summary for policy makers). This outlines the science in easy to understand way. You delve then into the WG1 chapters for more detail, and from there to the science papers themselves.

    If you still think that blog science has points to make over the published papers, then RC would be very happy to discuss these with you I am sure.

  6. 106
    JE says:

    Is it possible to determine how much of the increased tree ring width in recent times is attributable to a more readily available supply of carbon dioxide? Is there any evidence that the width of the tree rings is increasing (perhaps in proportion to the increase of atmospheric CO2). Interested in whether this is significant and if so, how the observations are altered, if necessary, to accommodate for the increase in CO2.

  7. 107
    dhogaza says:

    @ Donald Oats: Haven’t read Pilmer, but web-sites, blogs and source articles where I can and time allows. Tried to cover the full spectrum of views in order to establish my own.

    Do you do this with all areas of science, or do you just study anti-science sites on the subject of climate science?

    For instance, if you want to understand physics, do you seek “balance” by reading perpetual motion crank sites?

    Do you seek “balance” on biology by reading Answers In Genesis? Or do you “balance” geology by studying the writings of those who claim the earth is 6,000 years old?

    If not, why not? What is it about climate science that requires “balancing” knowledge with outright lies? That’s what these people are doing. They’re lying to you. Why pay them attention?

    As for Galeleo, that’s just an example. The point I was trying to make is that just because the current wisdom supports a certain hypothesis about how a system works, then someone else comes along with an alternative hypothesis, that person isn’t necessarily dumb, stupid, ignorant, uncaring, etc.

    Galileo is a horrible example, as it really had nothing to do with science at all. If anything, climate scientists are in the position of Galileo vs. the Church. The Church claimed we should ignore observation when it contradicts the Bible, and if you get special permission from the Pope to very carefully put forward data in opposition to the Bible, don’t put the Pope’s words and beliefs in the mouth of a character whose name can be translated as “simpleton”. Doing so led to Galileo being hauled up in front of the Inquisition.

    Today, we have an anti-science backlash which in essence says we should ignore observation/science when it contradicts certain political beliefs. Ignoring this dogmatic insistence risks your being hauled in front of Inhofe’s Inquisitional Senate Committee where you’ll be accused of scientific fraud on national TV.

    I’m well versed with models and computer simulations as such are aware of the pros and cons of such approaches. GCM’s are a couple of orders of magnitude more complex that anything I’ve ever dealt with, but the basics are still the same.

    There are different kinds of models and simulations so how do we know for certain that your experience is with models that are essentially the same as GCMs? Describe models you’re well-versed with, please.

    I know about the physics side of thing with CO2, but my understanding is that that only contributes a certain percentage of the projected warming (can’t recall the figure off the top of my head), the rest comes from hypothesized positive feedbacks.

    Why do you say they’re “hypothesized”? Why, for instance, is the statement that water vapor is a GHG a “hypothesis” rather than an observed fact? Why, for instance, is the statement that absolute water vapor will rise with temperature if there’s sufficient liquid water around to evaporate a “hypothesis” rather than part of established physics?

    I also think hard about appropriately accounting for and expressing uncertainty in estimated quantities. Things like error bars on quantities that are clearly estimates seem to be in short supply in much of the literature I’ve read to date.

    Yeah, right. This explains why climate sensitivity is nailed down to being roughly 2 to 4 C per doubling of CO2. It’s precise to so many digits because climate science is unaware of notions like “error bars” and “uncertainty”…

  8. 108
    D MacKenzie says:

    @ Phil Scadden: read big chunks of IPCC AR4, and that’s what got me really going down my current track. Bit ironic really. ;-)

  9. 109
    mike coombes says:

    Re 101: “NO ONE EVER THOUGHT THE EARTH IS FLAT.”

    The fact that the earth was a sphere had to be discovered. Educated people knew of the discovery. JB Russell’s paper goes over the details “Inventing the flat earth: Columbus and modern historians”

    However most people were not so educated. Even some educated people, up to the 1800′s, found this to be in conflict with their religious views and worked mightily to disprove the theory. The most famous was Parallax, see http://www.sacred-texts.com/earth/za/.

    Similarly just because most educated people believe the Earth is 4.6 billion years old does not mean that is what everyone believes.

  10. 110
    Phil Scadden says:

    D MacKenzie – okay what did you read in IPCC AR4 that made you more skeptical?

  11. 111
    dhogaza says:

    Read big chunks of IPCC AR4, and that’s what got me really going down my current track. Bit ironic really. ;-)

    Great, D MacKenzie. So now you’ll have no problem telling us precisely where you think climate science has it wrong. If you’re right, you’ll find us easy enough to convince.

  12. 112
    Hank Roberts says:

    > JE says: 19 November 2009 at 5:0 PM
    > Is it possible to determine how much of the increased
    > tree ring width in recent times is attributable to a more
    > readily available supply of carbon dioxide?

    That’s where the timberline comes in handy. CO2 is a well mixed gas and the CO2 will change in the same proportion everywhere on the mountain. So they look for the place where a slight increase in temperature will allow trees to grow noticeably better, right at the timberline.

  13. 113
    MarkB says:

    D. Mackenzie writes:

    “Things like error bars on quantities that are clearly estimates seem to be in short supply in much of the literature I’ve read to date.”

    …which leads me to believe you haven’t read much of the scientific literature including “big chunks of IPCC AR4″. You might be interested in this concise review article on the lines of evidence leading to estimates of climate sensitivity. You can follow the various studies it summarizes. It’s pretty hard to miss the error bars.

    http://www.iac.ethz.ch/people/knuttir/papers/knutti08natgeo.pdf

    Feedbacks aren’t merely “hypothesized”. Some are observed as well.

    http://www.agu.org/pubs/crossref/2008/2008GL035333.shtml

  14. 114
    Monty says:

    re #’s 103-&-109 Flat Earth
    It may be true that only educated people knew that the earth is a sphere but the poor couldn’t have cared less, living very hardscrabble lives. As far as dates go, Erastostenes in 300BC calculated the circumference of the earth within 2%.

  15. 115
    Peter T says:

    Jon at 29

    re Hastings – I recall reading that Britain is rising at the north end and sinking at the south. Bit like a see-saw with a large weight (a mile or so of ice) taken off one end. So the sea level would be higher (actually land lower) 1000 years ago.

    Another possible explanation is that the salt marshes which fringed the coast have gone due to human activity – leaving a wider margin of firm ground.

  16. 116
    KLR says:

    Could someone point me to a study analyzing the early 80s downturn in GHG emissions and corresponding registered CO2 etc. levels – which, to my not so keen eye, look not to have noticed the concurrent change at all. This is puzzling, and alarming. I wouldn’t be surprised if someone has attempted to put it forth as evidence that anthropic sources have nothing to do with CO2 levels, too.

    A recommendation for a book covering the subject would be welcome as well. I’ve snooped around a bit for info but to no avail.

  17. 117
    Deech56 says:

    D MacKenzie: Dhogaza makes an important point that I think needs to be reinforced when he writes, “This explains why climate sensitivity is nailed down to being roughly 2 to 4 C per doubling of CO2.” If climate sensitivity with feedbacks is much less than 2°C/doubling, then we can breathe a sigh of relief, but if it is in the 2°-4.5° range we have real problems.

    I hope in your perusal of the literature, you’ve found John Cook’s excellent post describing Knutti & Hegerl’s review of the various climate sensitivity calculations. Yes, there is a range, but there are constraints. James Annan used another observation-based analysis to bolster the consensus 3°C value.

    If anyone tells you differently, they need to show pretty strong evidence.

  18. 118
    Dan M says:

    I hope that humans have enough foresight to plant bristlecone pines in a number of habitats in hope that some might survive long enough to provide a long history, for whatever intelligent creatures might want to know why the climate tanked in the previous five or ten thousand years.

  19. 119
    William T says:

    JE @106 – you should read the paper that this post points to – they explicitly test whether an effect such as increased CO2 could have caused the wider rings, but have to discard that hypothesis because the data very clearly doesn’t support it.

    There is a good reason why these tree ring chronologies all seem to come from very cold places and not just any old trees…

  20. 120
    William T says:

    #71 D.MacKenzie,

    “10 years I whole-heartedly agreed with AGW, now with the more I read, the less I’m convinced.”

    Maybe you should stop reading so much and get out a bit more. Visit the countryside or the mountains, ask the old locals a few questions…

  21. 121
    Ken says:

    A bit off topic, but it is highly likely Parallax knew the earth was round. He was just an artful scammer who knew where the fame and money lay. However, some of the people who took up his torch were almost certainly genuine believers in a flat earth. [/OT]

  22. 122
    Andrew Hobbs says:

    #95 John H
    Thanks Gavin, I couldn’t have put it more succinctly myself.

    It is a bit hard for immediate comment with the rest of you being so out of phase with the real world here, in Australia. :-}

    As for the original comment. I have probably read as many articles arguing against global warming as I have for it, and, indeed, I am sure that I have seen at least some of “the plethera (sic) of material produced by the dozen or so major skpetics (sic) and their troops.”

    However if I forget the myriad of articles with little substance, and only consider those published articles which have ‘original’ research results or ‘original’ re-analyses of published results, many have flaws which even I, as a non-statistician and non-climatologist, can see through. By the time one includes the papers where the flaws have been pointed out by professional statisticians and climatologists, and one can follow the arguments etc, there really isn’t much left. Certainly none come even close to suggesting I should rethink my position on AGW.

    Besides which the stage at which one or two contrary results can completely ‘disprove’ AGW is long past. Such a position may have been acceptable in the middle of last century. Now the hypothesis of AGW and its ramifications have been so well studied, it explains so many phenomena that are happening today, and it fits so well with well established, fundamental physical principles it would take much more to overturn it than a few contrary results that may have been misreported, misinterpreted etc.

  23. 123
    Tony Rogers says:

    Mike,

    Re #84. Thanks for your answer. I did understand that the data was from Graybill and Idso’s study and I did get the point about the standardisation. I was just struck by the difference in trends between the strip-bark and whole-bark over the period shown in the graph (S4).

    When you say “Before that, the whole bark trees have wider rings because the whole bark trees are younger” is that because really old trees eventually all become strip-bark? Are there any/many old whole-bark trees or young strip-bark trees? (Reminds me of “there are no old, bold pilots…”) Thanks.

  24. 124
    Rod B says:

    William T (120), the old Ted Turner proof of AGW, eh?

  25. 125
    DrCarbon says:

    #123 – Tony. It is harder (but not impossible) to find whole bark trees at the highest elevation. The mean segment length given in the S4 figure caption (1,052 years for strip-bark and 279 years for whole-bark) indicates that the whole bark trees are younger and therefore faster growers. The lack of trend in the young whole bark trees from figure S4 is interesting. There is no guarantee that Graybill and Idso sampled their strip-barks and whole barks at the same elevation. And the Salzer paper makes it clear how important very short elevation differences are that to modern trends! Compare the trends in the whole barks from figure S4 to figure 3 and see what you think.

  26. 126
    Tony Rogers says:

    Re #125 – DrCarbon. I would say that the whole-barks in figure S4 and figure 3 are fairly similar over the period shown for the Graybill data; about .4mm to .8mm +/- quite a lot using my Mk 1 eyeball. The strip-bark differences between the two are greater, Graybill’s showing a much larger trend.

    Maybe it depends which strip-barks you choose or how much bark they lost? Salzer has shown that trees below the upper forest border don’t show the thickening trend so I wonder what the location/situation of Graybill’s strip-barks were and why they show such a marked trend?

    Assuming Graybill’s strip-bark data was correct and show a very high ring witdth trend whilst Salzer’s strip-barks (on average) were no different to whole-barks, doesn’t that mean you have to very careful about which strip-barks you use and test to check that they are not anomolous in comparison with whole-barks? I would probably conclude that it may not be wise to use Graybill’s strip-barks in a reconstruction rather than conclude that all strip-barks are as good as whole-barks.

  27. 127

    D MacKenzie (#100): the feedbacks are more than “hypothesized”. The starting point for understanding the contribution of CO2 to climate was paleoclimate studies that attempted to explain movement in and out of ice ages, when it turned out that energy variation arising from adjustments in the earth’s orbit and axial tilt were insufficient to explain the magnitude of the resulting temperature shifts. We know that any initial trigger for warming will increase humidity, because relative humidity tends not to vary, and water vapour is a greenhouse gas. We know that if there is less ice on the planet, its albedo decreases, increasing absorption of incoming radiation. We also know that if the oceans warm, their capacity for holding CO2 decreases. All of these things are well studied in paleoclimate research, going back to the 19th century. You also can’t explain venus without an interplay between factors like runaway water-vapour driven initial greenhouse warming, followed by subsequent absence of chemical processes requiring liquid water to scrub CO2 out of the atmosphere. You can find all this on this site, or at Spencer Weart’s Discovery of Global Warming pages (or find his book with the same title). You can also find Raypierre’s The Climate Book if you’re quick: it will disappear from the web once published.

    This stuff is extremely well studied through both paleoclimate research and planetary climate research. The myth that this is some new, flaky area of science made up by pot smoking hippies to de-industrialise the world is an image created by the denial camp because they have no plausible competing hypothesis let alone theory. They don’t particularly care even if they contradict themselves, as long as they keep the uninformed public confused. If you read the denial sites uncritically, you will certainly get confused, because that’s the goal. Read them critically and you will quickly realise that there is no plausible alternative theory out there (if there were, we’d all be happy, because disaster is not something one likes to predict, particularly when the political will to avert it doesn’t exist).

    Here’s a little experiment for you to try: search for “DNA not double helix molecule”. You’ll find at least one person pushing that particular barrow. Why does he not get regular column space in The Australian? The Watson-Crick discovery of the double helix structure of DNA has roughly the same amount of history behind it as the discovery of the greenhouse effect. Why, you have to ask yourself, does a conservative newspaper give massive publicity to one bunch of dissenters against mainstream science, and completely ignore another? I have some ideas, but I’ll leave this as an exercise for the reader.

  28. 128
    CB says:

    A few comments on the tree questions:

    Regarding damage to the trees caused by sampling – as others said above only small cores are removed from living trees and the holes heal within a year or two. Trees are well adapted to survive damage that naturally occurs and pines are particularly adept producing resins that seal off the wounded area prior to covering it with new tissue. Tree stems function as mechanical support and consist largely of dead tissue. Additionally, this study made use of a large number of samples that came from dead wood.

    Regarding the strip bark form of growth – full-barked trees of any species must grow larger every year. This is the nature of the growth form, as older tissue becomes non-functional new cells must be produced and added to the core every year. One can see that for an organism capable of living thousands of years this mandate to become larger becomes a liability – the larger you become the more gravity is your enemy. The larger you become the more living tissue must be supported by providing an ever increasing volume of food and water.

    Among other long-lived species like giant sequoia that don’t have strip-bark growth form death by falling over is extremely common. These trees commonly deal with the height-growth problem by dying back at the top once they reach about 250′, but they still increase in circumference every year.

    The strip bark growth form allows trees like the bristlecone to maintain a relatively fixed amount of live tissue that needs to be supported. The trees don’t become taller every year and suffer increasing risk of toppling over. The oldest trees typically grow only along one or two linear axises and maintain relatively fixed live crown, bark, and root ratios.

    Because of this growth adaptation the usual geometric growth problem that afflicts a full-barked tree that is adding circumference every year (and necessitating mathematical treatment by standardization to remove this geometric growth trend from ringwidth series) is minimized or eliminated.

    Val LaMarche used the raw bristlecone pine ringwidths to make climatic inferences in a 1974 paper: LaMarche, Jr., V.C. 1974. Paleoclimatic inferences from long tree-ring records. Science 183: 1043-1048.

    Regarding the contribution of increasing CO2 to growth: The authors make the point that trees growing at lower elevations (with similar CO2 concentrations) do not show increased growth over the past century – despite the fact that trees growing at lower altitudes respond strongly (positively) to moisture availability and thus might be expected to benefit from increases in CO2 concentrations by increasing their water use efficiency, and thus their growth rates. For this reason the authors assign the most likely cause of the increasing growth at upper treeline to warming and rule out CO2 as an important factor.

  29. 129
    D MacKenzie says:

    When I said “hypothesized” I was meaning it in a general sense about how people believe a system was working, didn’t mean to imply that there might be no data supporting such a view.

  30. 130
    CB says:

    One additional note:

    Although I haven’t seen it mentioned in comments here the break in the time series graph at about ~2,000BC is related to frost damage to trees at these sites around 2,030BC. The damaged ring presents a site of physical weakness that is attacked by the weathering process and over thousands of years wood from this time period fractures and decays leading to a discontinuity in a majority of samples – and thus low sample depth and inability to properly estimate the curve value.

  31. 131
    Bill DeJager says:

    Re: #17, Pinus longaeva is generally found at elevations of over 3000 m., including sites in California such as the ones mentioned outside of Bishop. The highest mountains in the geographic range of this species get up to about 4300 m. (the White Mountains near Bishop) but most mountain ranges where these trees grow top out at more like 3500 m.,leaving little range for upward expansion. Natural expansion northward (via planting of seeds by birds) would be possible with a much slower warming process, but at the likely speed of warming this migration will need to be artificially assisted.

    Re: #130, cross-dating of discontinuous tree ring records to continuous ones is routinely done to enable accurate dating of such records. This is basic dendrochronology.

  32. 132
    CB says:

    Dear Bill,

    I was just pointing out the reason for the gap in the figure – low sample depth because of a physical problem with the majority of samples. Of course the earlier portion is cross-dated using the few continuous specimens and material from lower elevation sites that don’t experience severe frost damage.

  33. 133
    Paul Gosling says:

    I have only just had time to read the paper in full and have not read all of the comments here, so someone might have answered this. If the trees at the lower sites are responding negatively to increased temperatures and are located as little as 150m below to trees at the upper sites which are responding positively to temperature, this suggests to me that only a small increase in temperature (less than 1.5 C) above the present will result in the upper trees first becoming unresponsive to temperature and then flipping and responding negatively to increased temperature, like the lower trees. Given this , these trees seem unlikely to show evidence of higher temperatures that may have existed in the past, indeed higher temperatures in the past will look like lower temperatures, so how useful really are these trees as temperature proxies?

  34. 134
    CB says:

    A good question Paul. I didn’t see that the authors addressed this in the main paper and I haven’t read through the supplemental material, but here is a quick answer.

    Treeline has fluctuated over time at these and all similar sites. There is an abundance of remnant material above current treeline and many of the samples used came from this pool. All samples were mapped with a GPS and it is possible to map the target zone as it fluctuated through time. The presence of latewood frost rings in a sample is also a pretty clear indication that the tree was growing within this zone.

    While it is true that individual trees can live over 5,000 years and thus would have experienced changes in their surrounding environment over such a span, typical samples are from trees that were a few thousand years of age and lived out their span within one or other of the response zones.

    I believe the authors are working on modeling the tree-line fluctuations and their relationships to temperature and would expect to see more from them on this subject.

  35. 135
    Hank Roberts says:

    Paul, I think you’re mixed up there.
    Think about the time series of events.

    Look at the long slow cooling since the last ice age
    (from many different proxies)

    http://www.globalwarmingart.com/wiki/File:Holocene_Temperature_Variations_Rev_png

    Look at the change of the Bristlecone treeline over time — it’s been moving downhill until the very recent past:
    http://www.jstor.org/pss/1550214
    Those remnant trees above current treeline go back many thousands of years.

    Look at the sudden temperature jump (the line rises to “2004″ at the right edge of that picture)

  36. 136
    Paul Gosling says:

    Hank

    It looks to me as if the presence of so many large trees above the current tree line is confirmation that this location was much warmer in the past and therefore the trees at the current tree line are highly likely to have had a negative response to temperature in the past. It’s a hell of a job to try and disentangle when the current tree line trees flipped from negative to positive temperature response, I guess using ‘fossil’ wood from above the current tree line, but still, rather them than me.

  37. 137
    Neil Craig says:

    Following the money trail:

    Can anybody name 2 scientists who aren’t paid directly or indirectly by government (that includes Friends of the Earth) or charities/foundations specificly committed to alarmism who have said catastrophic warming is real. That excludes statements along the lines of “most of the 20thC warming (0.6C) may be anthropogenic” but genuine catastrophism.

  38. 138
    Jim Bouldin says:

    Paul, the short answer is they are still highly useful, notwithstanding the fact that you have hit directly on a very important point. You’re touching on one of the possible causes of divergence (there are other, non-environmental, possible causes as well; see Esper and Frank, 2009). This is one of the difficulties of using any biological proxy–it’s always constrained to function best only within a certain range of environmental forcings (temp in this case), and if you go beyond that range, its responsiveness WILL decrease, as you note. In this case, it even flips from + to – response.

    One of the key points of this, and many, TR reconstructions, is the spatial aspect. The comparison of their Sheep Mtn chronology, with the two treeline chrons in eastern Nevada, as shown in their Fig 4b, shows a broadly concordant spatio-temporal pattern–that’s important. One could argue that this would not be the case if any of the 3 sites had become unresponsive to temperature over the past 600 years. However, the 3 sites are not perfectly correlated over that time (e.g. the 1700s aren’t as “tight” as the other centuries are), so maybe climate-change induced divergence is the cause of that. But that could also be explained by say, differences in the spatial patterns of weather systems/air masses at different points in time, not changing tree sensitivity. Such different possibilities could be tested by intensifying the spatial sampling and looking at the spatio-temporal concordance between sites.

    Also, I’d add that I’ve extended their figure 4b back about 500 to 1000 years further, depending on site sample size, with some quick analyses, and the concordance still holds over the last 1000 to 1500 years.

    The other thing to keep in mind is that their elevational transect in the Whites was not all from one place–the lower elev chrons were 1 to several km away from the treeline chron at Sheep Mtn. There could thus have been topographic factors, esp slope aspect, at work in addition to the elevational gradient. Maybe they accounted for that though–I’ll have to check again.

    But I like your thinking. It’s legitimate–and productive–skeptical scientific thought, unlike the garbage that is offered up as such by various elements.

    Esper and Frank, 2009. Divergence pitfalls in tree ring research. Climatic Change 94:261-66.

  39. 139
    Jim Bouldin says:

    p.s.

    I would hasten to add, amidst the roar of those screaming about “data secrecy” problems, that I was able to extend their treeline chronologies back in time–and do a host of other possible analyses–because….

    …they freely offered up ALL of their relevant data files, from all 3 sites, so that anyone could use them.

    I bet you won’t hear about that from Steve McIntyre.

  40. 140
    Jim Bouldin says:

    Can anybody name 2 scientists who aren’t paid directly or indirectly by government (that includes Friends of the Earth) or charities/foundations specificly committed to alarmism who have said catastrophic warming is real. That excludes statements along the lines of “most of the 20thC warming (0.6C) may be anthropogenic” but genuine catastrophism.

    Define catastrophic. Scientists don’t generally talk in such terms. Look to the press and politicians for that.

    If you’re denying that catastrophic warming is possible if we don’t change course, that’s plainly foolish. As for the government funding, it’s ubiquitous and does NOT come with strings attached as to what the result needs to be.

  41. 141
    Jim Bouldin says:

    “Can anybody name 2 scientists who aren’t paid directly or indirectly by government (that includes Friends of the Earth) or charities/foundations specificly committed to alarmism who have said catastrophic warming is real. That excludes statements along the lines of “most of the 20thC warming (0.6C) may be anthropogenic” but genuine catastrophism.”

    Define catastrophic. Scientists don’t generally talk in such terms. Look to the press and politicians for that.

    If you’re denying that catastrophic warming is possible if we don’t change course, that’s plainly foolish. As for the government funding, it’s ubiquitous and does NOT come with strings attached as to what the result needs to be.

  42. 142
    Neil Craig says:

    Catastrophic warming would be warming whose effects were likely to be catastrophic. Certainly above the 2 degree increase of the MWP or even the probably 4 of the Climate optimum, neither of which melted Greenland. Obviously only such warming would justify cutting the use of fire by 50%, 80% etc.

  43. 143
    Robert Way says:

    Comment No. 142,
    Your Statement is incorrect as the MWP was not 2 degrees warmer than the current climate. It was in fact on par with the early parts of the 20th century at its warmest (Viau et al. 2006).

  44. 144
    Dan Lufkin says:

    I notice that paragraph 2 of the intro above contains the infamous word trick, and in the context of analyzing dendro data. Viz:

    Because the growth of trees is radial, as trees get older and the diameter of a tree increases, annual ring widths decline in thickness. This is the normal “growth function” that is commonly removed from measurements before further analysis is carried out. The trick is to do this carefully so that as much climate information is retained while the growth function is discarded, and dendroclimatologists know how to do this quite well.

    The date is 17 Nov. This looks like the key to what Phil Jones was talking about in the unfortunate e-mail.


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