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:
- Liebigs Law, which I cover in detail here: A look at treemometers and tree ring growth
- 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
- 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.
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.
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?
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 ?
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
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.
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…
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 !
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
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 !
“this new method …
is more accuratesucks less than other current methods”Fixed that for ’em!
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
[Snip. You know why. ~dbs, mod.]
Surely it’s a good point and worthy of discussion. How can someone comment on a paper without reading it?
[snip]