New paleo study "leaves" me skeptical of the claim

Leaf in autumn. Image: Wikipedia

From Baylor University, a suggestion that leaves are a better paleo-proxy than tree-rings:

New Baylor Research Shows Using Leaves’ Characteristics Improves Accuracy Measuring Past Climates

NSF-funded study shows high promise for new method to estimate temperature, precipitation for ancient ecosystems

A study led by Baylor University and Wesleyan University geologists shows that a new method that uses different size and shape traits of leaves to reconstruct past climates over the last 120 million years is more accurate than other current methods.

The study appeared in the April issue of the journal New Phytologist and was funded by the National Science Foundation.

“Paleobotanists have long used models based on leaf size and shape to reconstruct ancient climates,” said Dr. Daniel Peppe, assistant professor of geology at Baylor, College of Arts and Sciences, who is an expert in paleomagnetism, paleobotany and paleoclimatology. “However most of these models use just a single variable or variables that are not directly linked to climate, which obviously limits the models’ predictive power. For that reason, they models often underestimate ancient temperatures.”

Baylor geology researchers, along with 26 other co-authors from universities around the world, collected thousands of leaves from many different species of plants from 92 climatically-different and plant-diverse locations on every continent except Africa and Antarctica. Multiple linear regression models for mean annual temperature and mean annual precipitation were developed and then applied to nine well-studied fossil floras.

The results showed:

• Leaves in cold climates typically have larger, more numerous teeth, and are more dissected. Leaves in wet climates are larger and have fewer, smaller teeth.

• Leaf habit (deciduous vs. evergreen), local water availability and phylogenetic history all affect the relationships between climate and leaf size and shape.

• The researchers’ multivariate mean annual temperature and mean annual precipitation models offer strong improvements in accuracy and precision over single variable approaches. For example, the mean annual temperature estimates for most of North American fossil floras were considerably warmer and wetter and in better agreement with independent paleoclimate evidence. This suggests that these new models offer the potential to provide climate estimates that will help scientists better understand ancient climates.

“Our study demonstrates that the inclusion of additional leaf traits that are functionally linked to climate improves paleoclimate reconstructions,” Peppe said. “This will help us to better reconstruct past climates and ecosystems, which will allow us to study how ecosystems respond to climate change and variations in climate on local, regional and global scales.”

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Since they have not included the actual paper with the Baylor press release, and didn’t even give a title for the paper, I have not been able to figure out which paper it is in the April edition of New Phytology here. Maybe some readers with more time than I can figure it out and leave a comment.

Three things make me just as skeptical of this claim as of tree rings being a good proxy for past temperature:

  1. Liebigs Law, which I cover in detail here: A look at treemometers and tree ring growth
  2. The revelation  that leaves seem to maintain a constant temperature: Surprise: Leaves Maintain Temperature, new findings may put dendroclimatology as metric of past temperature into question
  3. How do you calibrate such a thing? If using modern leaf response as a baseline, how do they know the response millions of years ago was the same?

I’m sure we’ll learn more in discussion.

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89 thoughts on “New paleo study "leaves" me skeptical of the claim

  1. All leaves from 900AD to 1400AD are automatically “adjusted” to a coller temperature since we know they are deniers.

  2. There’s also the variation in stomata in leaves to consider, but that relates directly to CO2 availability. More CO2 = smaller/fewer stomata, and hence reduced water transpiration/loss/use = higher productivity.

  3. I think I’ll stick to old bones and chicken blood to divine past temperatures …
    I swear sometimes it seems witch doctors have better scientific methods …

  4. Another big problem is dating the leaves from disparate species and regions. Carbon 14 dating has a limited resolution. You’d time smear any serious signal resolution. At least tree rings have accurate temporal resolution, even if that’s the only thing you know is accurate.

  5. I’m skeptical how one dates leaves? If we are talking eras and paleo-earth layer zones, what is the point? Resolution seems impossibly poor.
    This one isn’t it, but it is free:
    http://onlinelibrary.wiley.com/doi/10.1111/j.1469-8137.2011.03725.x/pdf
    I assume this is it:
    Sensitivity of leaf size and shape to climate: global patterns and paleoclimatic applications (pages 724–739)
    paywall: http://onlinelibrary.wiley.com/doi/10.1111/j.1469-8137.2010.03615.x/pdf

  6. Latitude at 1:33 pm: “and they are calibrating these leaf temperatures against what…”
    Mannian treemometers, of course.

  7. I take back what I said earlier as this study and method is looking at much longer time periods than I realized where C14 dating would be completely appropriate.

  8. As everyone know, the leaves at the bottom of a tree are usually different in size and thickness that those from the top of the tree. How do they know they have a bottom or top leaf fossil?

  9. All that and with Decimal Degree Precision!
    So why they didn’t put the leaves in various true greenhouses with different temperatures they should show something different…

  10. So how do you acount for changes in trace gas levels (including CO2) light levels (yes, oddly enough plants depend on sunlight, a bit like ourselves) and other variables, such as rainfall, air pollution (or didn’t they have volcanoes and forest fires back then?) mineral changes, animal and insect population changes (yep, they eat leaves) and deseases.
    But hey, lets use these ever so accurate measurements to base the spending of countless trillions of dollars on, after all that’s what we are doing with tree rings. Not that using that money to acutally clothe, feed, medically care for and educate folk might actually be a better idea (duh!).
    As interesting as these studies are, should public money really be funding them? Haven’t we got more serious things to do with our limited academic funds?

  11. The claimed reason for not updating tree ring proxies to cover modern times is that it is too hard.
    What will be the excuse for not collecting leaf samples to update the proxies?

  12. Isn’t there a problem here? Nine ‘well studied fossil flora’ may not adequately represent flora of the past at all. This might be the equivalent of self chosen responders to surveys.

  13. Oh for crying out loud. As they get more desperate, they start grasping for ever more subjective ways to validate their hypothesis.

  14. I read the summary of Peppe’s paper and when I came to this … “This work also illustrates the need for better understanding of the impact of phylogeny and leaf habit on leaf–climate relationships.” … I became aware of what was at the root of the initial study.
    They want more money to continue looking at the remnants of old vegetation.
    If I was the financier, I’d just say “Endex!”
    (Those with a background in any disciplined service will understand that!)

  15. For example tree A1 is in a wet environment tree A2 is in a dry environment. The trees are the same species but have different leaf characteristics.
    How are they going to separate out climate effects and simple genetic differences?

  16. Have the paleo-community considered constructing a temperature history from fossilized straw?
    (Though, I am sure that even the least clairvoyant among us can guess the shape that such a temperature chronology would possess.)

  17. Not only will they have to figure out climate impacts on leaf growth, they will also have to sort out climate variables that affect fossilization.
    My hypothesis is that cooler weather/climate makes preservation more likely. Therefore the sample of fossilized leaves will have to be recongnized as being biased toward one climate extreme and somehow corrected.

  18. The word model is frightening me . A climate model based on past paleo-records of leaves ? It is sounding to me like indian hocus-pocus . Do these researchers , who are most probably paid by governmental donations , make their basic materials available for other scientists or will they also block FOI – requests as usual with alarmists ?

  19. I think leaves from deciduous trees would make much better proxies than trunks. A tree grows it’s leaves in relation to that spring/summer climate.
    Their biggest problems will be figuring out which year the leaf fossil is from and of course calibration. But it looks promising.

  20. Leif Svalgaard says:
    April 18, 2011 at 1:41 pm
    How do you calibrate such a thing? If using modern leaf response as a baseline, how do they know the response millions of years ago was the same?
    Dana Royer has some good research on this:
    http://droyer.web.wesleyan.edu/research.htm
    Personally, I think the method is sound and has a lot of promise.

    I thought you might, sir. What’s in a name, eh? 😉

  21. This study sounds pretty reasonable. The typical morphology of angiosperm leaves is an indication of typical climate. Some species ( e.g. almost any Australian Acacia) even have different leaf forms dependent on weather (not climate).

  22. crosspatch says:
    April 18, 2011 at 2:10 pm
    Oh for crying out loud. As they get more desperate, they start grasping for ever more subjective ways to validate their hypothesis.

    Exactly. It’s all boiling down to model validation. Model this, model that, if the model says so, etc., etc. Oops!!! The MODEL was wrong, have to recalibrate! Let’s see: While we do that, let’s just add another decade to the predfiction date to buy us some time, and watch the cash roll in, because in our grant application, we mentioned “temperature”.
    How collossally transparent and tiresome, all at the same time.

  23. Some variables:
    ° Temperature
    ° Rainfall
    ° Nutrients (including CO2 [ ])
    ° Genetics
    ° Drought
    I’ll stop listing at 5.
    John von Neumann, the great, late physicist and meteorologist has two quotes that put the paper in best context:
    “With four parameters I can fit an elephant, and with five I can make him wiggle his trunk”.
    “There’s no sense in being precise when you don’t even know what you’re talking about.

  24. So what we get are “precise,” “accurate” “improvements” on “measurements” of the past temperatures and rainfall; but of course the “measurements” are really estimates. And these improvements of accuracy in estimations of the past are actually in mean annual averages. All of this improvement of accuracy is as over against past estimates, which were less accurate.
    And the best thing is you get “high promise” and a “new model.”

  25. All these studies remind me of the “Stock Market Scam” (Paulos 1989)
    In the scam, you send a predictions to 32,000 people, half predicting higher the other half lower. For those 16,000 where you guessed right, you do it again. Then there are 8,000 who believe you were right 2 for 2,
    4,000 who think you were write 3 for 3,
    2,000 who think 4 for 4
    1,000 who think you are an amazing 5 for 5 and will believe anything you say.
    Only in this case, we have 32,000 hypotheses, of which at least 1,000 will be “proven” after 5 successive tests. If you want to allow for experimental error, far more will still survive.
    “The first principle is that you must not fool yourself—and you are the
    easiest person to fool.” – Richard Feynman
    http://www.entheology.org/library/winters/QUACK.TXT

  26. Lonnie E. Schubert says: April 18, 2011 at 1:42 pm
    I’m skeptical how one dates leaves?
    Like a panda … who Eats, shoots and leaves!

  27. Any tea leaves in this new improved highly promising model, by chance? I like tea leaves.

  28. jeez says:
    April 18, 2011 at 1:38 pm
    … Carbon 14 dating has a limited resolution. …

    In fact, C-14 is useless over spans of more than 20 to 50 kya. The leaf morphology approach was pioneered to investigate the environment that polar dinosaurs experienced over 100 mya. The initial investigations correlated leaf shape and size with latitude. One of the significant facts is that “toothy” leaves correlate with cooler climates. The leafs of temperate and cooler climate plants have glands on the points of the leaf serrations to help maintain water pressure in the stems and leafs and prevent wilting in colder weather. In the tropics atmospheric temperature does this without needing any special adaptations by the plants. During the Mesozoic we find dinosaurs within about 5 degrees IIRC of the pole, much closer than there is land at present. The leafs from these deposits resemble the cooler temperate rain forests in Canada and southern Alaska. It goes without saying that this was during a “warmhouse” period without polar ice caps.
    REPLY: see his later comment, saying the same thing – Anthony

  29. “Visions of sugar plums danced in their heads,” along with rich grants and an appointment or two to the NAS … if the result is “correct.”

  30. In perusing some of the more panicky, skeptical responses here, it seems pretty clear that some of us need to learn to read and watch that old knee-jerk response. It is also evident that a primer on alternative means of dating geological evidence would help some of us. Then there are “skeptical” responses that are strictly political when the persiflage is peeled away. While politics can insert itself into science, and scientists are often encouraged to be more “active” these days, there is simply no reason to presume that science, “paleoclimate” and politics are chained together at the ankles.
    For example, only in “climate science” will you see “paleoclimate” attached to studies for time periods in which there are historical records available. Geologists would laugh at the idea, while archaeologists (prehistorians anyway) would tend to smirk. “Paleo-” simply isn’t applied to periods with written records. The article, and leaf geometry studies in general, looki at much longer periods than “the team” is interested in. In fact, even 8,000 years ago the word “unprecedented,” as employed by the team, loses any significance. When you are stomping around 120 mya, the present looks like what it is – an Ice Age. So, please, leave off the hysteria; “model” and “climate” are not necessarily bad words. Leave it for warmists. We are in a cold climate period and have been for a (geologically) long time.

  31. You have to wonder whether conditions that create fossilised leaves bias results towards …well subsets of conditions under which leaves are fossilised.

  32. What is needed as with all these claims is validation.
    So give the researchers some leaves from trees where the temperature (and all other weather variables are known. Ensure that some leaves are from the top of the tree others from the bottom, some are from a tree at the top edge of the forest and others are from trees in the middle of the forest by a river etc etc. In other words standard validation testing technique. Then have them use their clever model to tell you what the weather conditions were in which the leaf grew. No ‘clever tricks’ just straightforward validation testing. Perhaps enhance the impact of the testing to include the loss of tenure for any results less than 50% correct – it would concentrate their minds before making claims that they have not tested themselves.
    This is relatively basic undergraduate level experiment design – perhaps these people have forgotten what that is?

  33. ZT says: “Have the paleo-community considered constructing a temperature history from fossilized straw?”
    I’m partial to global temperatures derived from ancient batpoop laminae in three caves in Kuala Lumpur. Paleospeleochiropterocoproclimatology.

  34. Ian W says:
    April 18, 2011 at 4:21 pm
    What is needed as with all these claims is validation.
    So give the researchers some leaves from trees where the temperature (and all other weather variables are known. […]
    This is relatively basic undergraduate level experiment design – perhaps these people have forgotten what that is?

    What makes you think that the claim is not validated? See their Figure 2. Did you even read the paper?

  35. “Ray says:
    April 18, 2011 at 1:56 pm
    As everyone know, the leaves at the bottom of a tree are usually different in size and thickness that those from the top of the tree. How do they know they have a bottom or top leaf fossil?”
    And those juvenile leaves from Eucalyptus and Corymbia species in Australia are often much larger than adult leaves. Others have extremely variable shaped and sized leaves and have scientific names which include …variifolia.

  36. “”””” For example, the mean annual temperature estimates for most of North American fossil floras were considerably warmer and wetter and in better agreement with independent paleoclimate evidence. “””””
    Recommendation to Baylor researchers:-
    Be safe stick with “”””” independent paleoclimate evidence . “”””””
    It’s independent, and better too.

  37. Another suggestion for Baylor researchers:-
    Would you recommend using tree leaf size, and number of points as a Temperature proxy to control the operation of a Nuclear reactor; if not; Why not ??

  38. Duster and Anthony,
    Thanks for jumping in for me Anthony, but even in my take back I screwed up and Duster is right to call me on my error.

  39. @jorgekafkazar
    Paleospeleochiropterocoproclimatology.
    What a magnificent word!
    Maybe a shorter version could find popular usage:
    Coproclimatology.
    Reminds me of a UN panel for some reason…

  40. Anthony,
    Scientist forget that EVERYDAY is different. NEVER the same due to the planet moving away and slowing down year from year. Tilting changes and the atmosphere WAS different back millions of years ago. Centrifugal force was faster meaning that the atmosphere was less dense than today. Oceans compensated by having more salt to change the density to be heavier. Following the salt trail trough time is a very interesting trek.

  41. I am disappointed with many of the immature attacks here thrown at the cited paper. Most attackers probably didn’t read the paper and are not qualified to judge it. It appears that we have pre-conceived notions and ideological biases, exactly what some warmists are guilty of. Lets stick to the science and cool the insults. I will be reading the link to Dana Royer’s work given by Leif as it sounds quite interesting. Are some of you afraid that this research will support Mann? I personally just want the truth.

  42. Major civiliazation collapse and barbarian invasions as one region’s climate tanked and neighboring regions soared are anchoring events.
    A strange phenomenon is that Climate Change often preceeds economic and agricultural collapses, as nature rubs salt in self-inflicted wounds.

  43. A lot of research has been done on leaf stomata which totally invalidates the ice core data, a good place to start is the work by Dr. Friederike Wagner of Utrecht University I could post a whole string of references, there are also some very good papers analyzing the shortcommings of ice core results which are well worth looking up.

  44. As many others have pointed out, the simple fact that trees vary on the same tree and between individual trees makes this as ‘scientific’ as reading tea leaves.
    In the wonderful world of over-simplification:
    “Leaves in cold climates typically have larger, more numerous teeth, and are more dissected. Leaves in wet climates are larger and have fewer, smaller teeth.”
    How about the huge leaves of devil’s club in a cold wet climate?
    There is clearly way too much money and way too many researchers if this kind of garbage is supposed to be a worthwhile project.
    And if we cut all this funding, the world would be a much better place.

  45. Duster says:
    April 18, 2011 at 3:57 pm
    In perusing some of the more panicky, skeptical responses here, it seems pretty clear that some of us need to learn to read and watch that old knee-jerk response. It is also evident that a primer on alternative means of dating geological evidence would help some of us. Then there are “skeptical” responses that are strictly political when the persiflage is peeled away. . .
    The article, and leaf geometry studies in general, look at much longer periods than “the team” is interested in. In fact, even 8,000 years ago the word “unprecedented,” as employed by the team, loses any significance. When you are stomping around 120 mya, the present looks like what it is – an Ice Age. So, please, leave off the hysteria; “model” and “climate” are not necessarily bad words. Leave it for warmists. We are in a cold climate period and have been for a (geologically) long time.

    Well-said, and an important corrective. Anthony often posts articles about papers that offer interesting, even important, contributions to science and have no necessary or obvious connection to the Realist (‘Skeptic’) versus Alarmist climate wars.
    Understandably, readers here have their antennae out for any hint of Warmist BS, but as Duster says, just using the terms ‘model’ or ‘climate’ should not trigger an alert. Little did I know that leaf morphology is an accepted area of study in paleo- studies, and an important tool in understanding ancient environments. It’s great to learn new things. That’s why this is an award-winning science blog, not just an anti-CAGW blog, though it does of course play an important role in disinfecting that canker.
    /Mr Lynn

  46. I am, so far, scratching my head… You could draw some broad based general conclusions about the micro climate around the tree (or trees), but you have to make so many assumptions its hard for me to understand there could be any “accuracy”; no more than tree rings anyway
    If you happen to study an area that humans occupied you might decide the climate is temperate and warm, when in reality the humans occupied the most comfortable (temperate and warm) micro-climate available to them (near the coast, in a valley, by a lake). That doesn’t mean most of the area further away isn’t colder, or dryer… So how do you draw a conclusion on the climate? Other than the tree grew nearby and that tree likes this type of climate?
    Well, its interesting, but I really would like to find a more direct physical proxy for temperature and a separate one for “wetness” – like a chemical reaction, then use a biological proxy like leaf shape.

  47. I had heard about at least one study similar to this some time back. It seemed in that particular study of leaves, at that time yet to be reviewed, “solved” the problem of the (alleged) disconnect between the temperature during parts of the Miocene and the carbon dioxide levels.

  48. This is an interesting approach, though still very much in the early stages of development. It won’t develop chronologies, but could reasonably characterize local and regional climate regimes. It needs a much larger database of samples since Europe, Africa, and most of Asia are unsampled. I’m a little concerned how they related leaf characteristics to modern temperatures (a model with 1km gridding) and I’d want to know more about phenotypic plasticity among the dozens of species they examine.

  49. reconstruct past climates over the last 120 million years is more accurate than other current methods.
    Ummm perhaps going back 10,000 might make sense but going back further millions of yeas back into history i think the problem that the trees evolve and we have no idea of the evolutionary paths that modern trees took.
    There is no reason to think that leave shapes and sizes followed the same climate patterns as modern trees do now.
    For all we know a 10 million year old fossilized leaf pattern is the shape and size it is because it had adopted to a peristaltic moss that long ago went extinct…and we end up with a climate 10 million years ago that is several degrees off because of it.

  50. I’m certainly skeptical and withholding judgment at this point, but it is very interesting that they say: (i) current methods (read existing tree-ring reconstructions, among others) don’t cut it, and (ii) analysis of tree leaves shows a warmer past, consistent with other evidence (and inconsistent with the hockey stick).
    It sounds like these researchers are open to the possibility that the past was warmer and that the hockey stick is unreliable. Are the tree leave proxies going to hold up under additional scrutiny? I don’t know. But it is good to see a different line of research, in the peer reviewed literature, using a different proxy, that comes to a different result than the Team got. Before completely trashing this study, let’s at least recognize it as, at a minimum, one more welcome stake in the hockey stick coffin.

  51. Zeke the Sneak says: April 18, 2011 at 3:39 pm
    “Any tea leaves in this new improved highly promising model, by chance?”
    Nope, Coca leaves maybe, or perhaps Khat leaves. Coca does seem more likely though, sort of matches the timing of the start of the big lie and the mindset of the believers.

  52. http://northernwoodlands.org/discoveries/tree_leaves_regulate_their_own_temperature/
    Tree Leaves Regulate Their Own Temperature
    “Seventy degrees? Well that’s just about the perfect temperature, isn’t it?
    It turns out we’re not alone in our admiration of the 70-degree mark. According to scientists at the University of Pennsylvania, trees around the world strive to maintain a near-constant temperature of 70 degrees in their leaves. This finding contradicts conventional wisdom that assumed leaf temperature mirrored that of the ambient air around it.”
    Turns out that 70 F is also the most common average temperature for the earth for the past 600 million years. As compared to 55 F today.
    http://www.geocraft.com/WVFossils/Carboniferous_climate.html
    So if the earth has been 15F warmer on average for most of its history, and both trees and humans like it warmer, who is to say that most of the other life on earth won’t like it warmer as well? It seems a stretch for the IPCC and others to forecast global disaster at a 2C temperature rise. Heck, it goes up and down at least 10C where I live every day.

  53. ““solved” the problem of the (alleged) disconnect between the temperature during parts of the Miocene and the carbon dioxide levels.”
    Temperature has been at 22C for most of the past 600 million years, regardless of CO2 levels. The disconnect is between reality and the followers of the church of algore.
    http://www.geocraft.com/WVFossils/CO2_Temp_O2.html
    the question for humans going forward is do we really want to see the northern hemisphere under a couple of miles of ice, which is the most likely future based on historical records. Or would we instead like to return to the 22C that is more normal for the planet? If CO2 does indeed affect warm the planet, then rather than destroy the future, we could well be saving it. We should make sure before spending our future tilting at windmills.

  54. Andrew30 says: Nope, Coca leaves maybe, or perhaps Khat leaves.
    Well, what’s a little stimulant/dopamine reuptake blocker when you are a hardworking “researcher,” “collecting leaves” from almost every continent? It is a big job, after all.

  55. “Are some of you afraid that this research will support Mann? I personally just want the truth.”
    The case is worse than i thought…so the leaves will say it is Co2 plus will show the last 100 years of temperature up to 0.1 degree precision?

  56. This seems like a long shot to me, and if more accurate than other paleo-proxies, than that just shows how poor the others really are!
    One example that springs to mind is the tree Totara (Podocarpus totara), this is a tree unique to NZ and evolved in a much warmer climate, hence it grows faster than current when grown in an artificial climate. However, it also seems well enough adapted to grow as far south as Christchurch and further south, only it grows very slowly. To me this would suggest that it either changes it grow rate to suit the climate (as per tree ring studies) or it has not yet adapted, as the adaption process is very slow and as the climate in NZ has only been cooler for the last few thousand years, it has not yet had time to catch up – and there is the issue – do leaves adapt immediately to the climate on a annual timescale, or do the leaves change on an evolutionary basis over hundreds or thousands of years, and if so, than it will be an adaption to an average climate over time, or will only occur if stable for prolonged enough periods – hence I would seriously question the validity of such a tax payer funded jolly

  57. Mike Bromley says:
    April 18, 2011 at 3:05 pm
    crosspatch says:
    April 18, 2011 at 2:10 pm
    Oh for crying out loud. As they get more desperate, they start grasping for ever more subjective ways to validate their hypothesis.
    Exactly. It’s all boiling down to model validation. Model this, model that, if the model says so, etc., etc. Oops!!! The MODEL was wrong, have to recalibrate! Let’s see: While we do that, let’s just add another decade to the predfiction date to buy us some time, and watch the cash roll in, because in our grant application, we mentioned “temperature”.
    How collossally transparent and tiresome, all at the same time.

    Why stop at leaf morphology and tree rings?
    Why not stop all scientific research. One can never be sure of anything.
    Scientists have no idea about what they are doing and are constantly wasting our money. Let us invest in a sure thing – the ignorance of the general public.

  58. Tree rings and leaves are both organic and suffer the same inputs so neither is more reliable than the other.

  59. Anthony Says:
    Three things make me just as skeptical of this claim as of tree rings being a good proxy for past temperature:
    1. Liebigs Law, which I cover in detail here: A look at treemometers and tree ring growth
    2. The revelation that leaves seem to maintain a constant temperature: Surprise: Leaves Maintain Temperature, new findings may put dendroclimatology as metric of past temperature into question
    3. How do you calibrate such a thing? If using modern leaf response as a baseline, how do they know the response millions of years ago was the same?
    I’m sure we’ll learn more in discussion.

    All three of third points seem wrong to me.
    Liebig’s law doesn’t apply here, because the researchers are looking at multiple variable morphological analysis. All morphological variables do not respond in the same way to environmental variables that determine leaf morphology. In that way the impact of different combinations of environmental variables can be determined.
    The variables in tree rings are latewood density and ring width. These are combined with position in the range of the trees in an attempt to tease out the role of different environmental variables.
    Since we know that all climates don’t have a constant temperature, in order to keep a constant temperature during growth, the morphology of leaves has to change. The same may be said of humidity. Since the interior of leaves has to have liquid water, the morphology of leaves in a dry climate has to be different from the morphology of leaves in a wet climate.
    The third point is similarly misguided. Photosynthesis is based on physics and chemistry which is unchanging, and evolution optimizes the formation of plants over time to grow in different environments. The paper itself answers the question of how plant evolution has worked to optimize the features of plants to survive in different environments and provides the calibration.
    It seems to me that your skepticism is driven more by a desire to have the science shown to be wrong, than by an understanding of the underlying science, but I could be biased as well. At any rate, the experts in paleobotany, who study this stuff 24/365 are the ones who will sort it out over time. The number of experts, and the number of graphs, and the number of cititations make the paper quite impressive.

  60. One great proxy of climate past are the leaf fossiles in the Spitsbergen… Aren’t we lucky the ahmosphere did not boil into the space and turn earth into venus2 😉

  61. Having read the abstract only (am getting tired of having to register at every publication online …), perhaps those who have read the article can say something about the methods used, e.g. where did these leaves come from, stratigraphically.
    I’m asking this because of two concepts which must play a role in their methods, but which weren’t mentioned in the abstract.
    One is ‘taphonomy’ – which addresses why stuff found in the ground ended up there, and from where it originally came. It is very important in environmental archaeology.
    The other is something botanists must know and address: ‘environmental plasticity’.
    It isn’t just weather/climate which has an influence on leaf size …
    Oh – and perhaps it’s worth mentioning that very young trees (up to about 5/6 years old) tend to have leaves much larger in size than old trees of the same species …

  62. “We applied our multivariate models to 10, well-studied, latest Cretaceous to Eocene fossil floras (Table 1). We emphasize that the climate estimates presented here are provi-sional until the potential confounding effects already discussed (especially phylogeny and leaf habit) are more fully accounted for. Nonetheless, we feel an initial application of this new approach is warranted and demonstrates its promise.”
    Sites and their age in My:
    Fox Hills 66.5
    Williston Basin I 65.5–64.0
    Williston Basin II 64.0–63.0
    Williston Basin III 61.0–58.5
    Palacio de los Loros 61.7
    Cerrejon 58
    Hubble Bubble 55.8
    Laguna del Hunco 51.9
    Republic 49.4
    Bonanza 47.3
    And about the recent leaves analyzed:
    All leaf images used in this study are available from Dryad (http://dx.
    doi.org/10.5061/dryad.8101) and the personal websites of DJP and DLR.

  63. Leif Svalgaard says:
    April 18, 2011 at 4:38 pm
    Ian W says:
    April 18, 2011 at 4:21 pm
    What is needed as with all these claims is validation.
    So give the researchers some leaves from trees where the temperature (and all other weather variables are known. […]
    This is relatively basic undergraduate level experiment design – perhaps these people have forgotten what that is?
    What makes you think that the claim is not validated? See their Figure 2. Did you even read the paper?

    Show me where they can show that summers are 35 deg C and dry while winters were wetter and as low as minus 3 deg C – the kind of temperatures and differences that are being argued that made the MWP more or less warm than today. I am sure (as Dana Royer’s research makes plain) that the size and shape of leaves found as fossils in certain geographic localities varies after a period of time dependent on temperature and water availability and possibly also on CO2 availability. but showing that the climate at a particular position geographically tends to favor certain sub-species with a particular leaf shape is a not the same as being able to say what the actual atmospheric temperatures were.

  64. Ian W says:
    April 19, 2011 at 10:07 am
    This is relatively basic undergraduate level experiment design – perhaps these people have forgotten what that is? […]
    Show me where they can show that summers are 35 deg C and dry while winters were wetter and as low as minus 3 deg C

    Did you read their paper carefully? What specifically [page and line numbers] do you object to or think is poor science?

  65. Well I don’t have any problem with Botanists looking at tree leaf fossils, and looking for apparent patterns of variation.
    But when it comes to global climate we are making critical decisions based on changes of hundredths of a deg C; and that out of a data range, the extends from about -90 deg C to about +60 deg C total range possible on any northern summer day. And due to a clever argument by Galileo Galilei (Italian Physicist), we can say with certainty, that on any continuous path between the two points having the two extremes of Temperature, can be found some point(s) having any and every possible Temperature value between those extremes. And there are an infinite number of such possible continuous paths, and points.
    So no, I really don’t care how interesting this Botany paper is; I’m just not into leaves (but I’m glad some others are). But it’s a far cry from some leafy patterns, and major global economic disruption based on how many points are on the fossilized leaf of some ancient tree. I like reliable Thermometers please, if we are going to talk about Temperatures; and if we want to know hundredths of a degree C, then I want good thermometers; not some flimsy non-linear resistor, and certainly not an old leaf.
    I’m sure that there are a lot of other variables that determine how many points there are on some tree leaf, or the fossil of a tree leaf. I’d like to see a breakdown of say just the top ten tree leaf point count adjusting variables, including Temperature (where/when), which properly apportions the number of points etc, to the various and sundry variable that determine that.
    Is Temperature 37% of the count; of maybe 75%; perhaps rainfall, is only 12% of the count. Well give us a breakdown of all the leading variables (well only the top ten.)
    We laugh about the Yamal, hockey tree; how often do you run across a fossil leaf ?

  66. There doesn’t seem to much that is new in this. That leaf shape is related to climate has been known for about a century, and it was put on quantitative paleoclimatic basis by Wolfe back in the sixties.
    Using multivariate techniques isn’t new either, that’s what Wolfe did with CLAMP (Climate Leaf Analysis Multivariate Program) twenty years ago.
    At most what these people have done is to develop a new, and (hopefully) better software for relating fossil leaf-shapes to climate. The rest is just press-release hype.
    Here is a good review paper on the subject:
    http://www2.brandonu.ca/academic/environmental/images/CFS_258_095-108_Greenwood_wm.pdf

  67. Perhaps some clarification is in order here. There is no doubt that this method is sound in principle. If you know a bit about botany it is easy enough to predict the climate in any area approximately based on leaf shape and size. However temperature is not the only significant variable, moisture and wind also have an influence.
    Also, this is not a year-to-year or even century-to-century technique. Leaf shapes are actually remarkarkably conservative from an evolutionary point of view.
    If you compare for example leaves grown in Washington DC today and, say, 15,000 years ago you would certainly notice a large difference and could probably estimate the respective climates fairly well, but not because the trees have changed the shape of their leaves, rather it is the trees that move north and south with climate, so 15,000 years ago it would have been a very different set of tree species in the Washington area.
    However there is something slightly ominous about that press release:
    “the mean annual temperature estimates for most of North American fossil floras were considerably warmer and wetter and in better agreement with independent paleoclimate evidence”
    It has always been a problem that climates in the past apparently weren’t nearly as hot as they should have been according to the amount of CO2 and the orthodox climate sensitivity, so there has been a marked tendency in recent years to try and find proxies that can be made to yield higher temperatures than the traditional ones. This may be the latest try.

  68. What a lot of unmitigated tosh most of the responses to this paper are! Those of you who assume it’s “bad” science because it utilises models, please explain how you do science *without* models! Are you claiming it’s sufficient to have a theory that *cannot* be tested. Of course trees evolve over time… slowly. But they do so within limits. For example, Fagus (beech) remain staunchly cool-temperate plants. You won’t find them in a sub-tropical climate unless put there by humans.
    Why assume that the researchers are unaware of confounding variables when you can read the paper and the authors’ discussion of them? Grrrr…

  69. Pompous Git says:
    April 19, 2011 at 1:04 pm
    What a lot of unmitigated tosh most of the responses to this paper are! […]
    Why assume that the researchers are unaware of confounding variables when you can read the paper and the authors’ discussion of them? Grrrr…

    Agree !

  70. Leif Svalgaard says:
    April 19, 2011 at 1:07 pm
    Pompous Git says:
    April 19, 2011 at 1:04 pm
    What a lot of unmitigated tosh most of the responses to this paper are! […]
    Why assume that the researchers are unaware of confounding variables when you can read the paper and the authors’ discussion of them? Grrrr…
    Agree !

    The initial post was written without having read the paper. That set the tone of the discussion. Of course once the facts are pointed out, either the detractors ignore them, or wheel out the argument that the scientists are just fooling the public in order to get grant money.
    REPLY: Mr. Adler. The TONE was set by the non-inclusion of the paper in the press release. Something that I’ve griped about for a long time. If the academics want to put our PR without providing the paper, then they will have to accept the TONE that follows.
    Take your comments elsewhere if you want to complain about the TONE without the paper. Or argue to these universities to include the paper, but don’t you dare blame me for not having read the paper when they don’t include it in the first place. I’d go broke having to subscribe to journals. – Anthony

  71. eadler says:
    April 20, 2011 at 1:09 am
    The initial post was written without having read the paper. That set the tone of the discussion. […]
    REPLY: Take your comments elsewhere if you want to complain about the TONE without the paper. Or argue to these universities to include the paper, but don’t you dare blame me for not having read the paper when they don’t include it in the first place.

    Agree !

  72. “this new method … is more accurate sucks less than other current methods”
    Fixed that for ’em!

  73. Anthony Watts said,
    REPLY: Mr. Adler. The TONE was set by the non-inclusion of the paper in the press release. Something that I’ve griped about for a long time. If the academics want to put our PR without providing the paper, then they will have to accept the TONE that follows.
    Take your comments elsewhere if you want to complain about the TONE without the paper. Or argue to these universities to include the paper, but don’t you dare blame me for not having read the paper when they don’t include it in the first place. I’d go broke having to subscribe to journals. – Anthony

    The paper could actually be found easily on the Internet by Googling some of the authors and the title. You chose not to look for it and commented anyway.
    REPLY: And that still doesn’t excuse the sloppy amateurish press release where they
    1. Didn’t even bother to mention the name of the paper (almost unheard of in science PR)
    2. Got the month it was published in the journal wrong (and yes I DID look, and it is noted in my post where I said: I have not been able to figure out which paper it is in the April edition of New Phytology here.)
    3. Didn’t bother to provide the paper that was apparently free access
    But you’ll defend such sloppiness by the Authors/PR office/University since it suits your points, and you then make it “my problem”, instead of placing the blame where it correctly lies, with the University.
    You have no scruples Mr. Adler. As I said, take your comments elsewhere. That’s a permanent invitation to leave.
    – Anthony

  74. Surely it’s a good point and worthy of discussion. How can someone comment on a paper without reading it?

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