Thursday
Feb032011
by 
Bishop Hill
Bishop Hill Briggs on tree rings
Feb 3, 2011 Climate: MWP Statistician to the stars, Matt Briggs, casts his gaze over the science of tree-ring temperature reconstructions and wonders whether, in a world of rapidly rising temperatures, tree ring growth could respond in a linear fashion.
Reader Comments (17)
Gotta love the comment at that column from Mike D:
That's a good read, from top to bottom! I also liked Mike D's excellent round-up and damning conclusion! :o)
I also liked:
'As a physicist, I would say “How do you know? Where is your evidence?”. The evidence would suggest that trees most likely have a very non-linear response, and therefore tree ring thermometer proxies should be treated as unreliable. I’ve seen better evidence supporting the existence of UFOs.'.
Excellent read. Well spotted Bishop.
This has been researched.
I understand that tree rings record the amount a tree grows each year. Bad years mean poor growth and narrow rings, good years the opposite. How can you tell if the poor growth in a bad year is caused by a heat wave and drought or a cold wet summer since the tree will not grow well in both cases? Without an explanation I will treat all methods of reconstructing temparature from tree rings with extreme caution.
The assumption of linear and non linear response to slow and rapid climate change appears to me to be too simple.
Trees are not simple linear devices that get a bit non linear if pushed. Trees have many genes in them that can 'switch on' and 'switch off' in response to many and varied stimuli. (Ask my missus, this is her field of expertise). The response of trees to any form of climate change is certainly highly unpredictable at this time.
For instance they could (hypothetical) switch on a gene that changes the shape and porosity of leaves in response to water or temperature stress. The side effect of that could well be reduced trunk growth and hence give a false impression of temperature response.
Trees - and lots of other life forms are not pure Darwinian. The ability to switch genes is closer to Lamarckian, or even that Russian guy whose name I forget right now.
There must be hundreds of forestry commission plantations etc. with known planting dates, there are certainly many tree crops with know planting dates, presumably this has been studied in the tree ring circus.
I live near a crop of cricket bat willows, 1200 trees all planted about 12 yrs ago in two days, probably genetic clones as they were planted as rods. There are many sizes of trunk from about 16" down to about 6". One of the reasons I think the tree ring circus is the greatest show on earth, good for entertainment value, not for much else.
I was wondering why all that extra CO2 didn't help...
As I commented on Mr Brigg's thread - I wonder if any of the "denrothermometrists" have ever done any gardening?
"denDrothermometrists"
Paul Dennis said…
Before I add anything further to the debate I should say that I’m an Isotope Geochemist and Head of the Stable Isotope and Noble Gas Laboratories in the School of Environmental Sciences at the University of East Anglia. I’ve also contributed to and published a large number of peer-reviewed scientific papers in the general field of palaoclimate studies.
I don’t say this because I think my views should carry any more weight. They shouldn’t. But they show there is a range and diversity of opinion amongst professionals working in this area.
What concerns me about the hide the decline debate is that the divergence between tree ring width and temperature in the latter half of the 20th century points to possibly both a strong non-linear response and threshold type behaviour.
There is nothing particularly different about conditions in the latter half of the 20th century and earlier periods. The temperatures, certainly in the 1960′s, are similar, nutrient inputs may have changed a little and water stress may have been different in some regions but not of a level that has not ben recorded in the past.
Given this and the observed divergence one can’t have any confidence that such a response has not occurred in the past and before the modern instrumental record starting in about 1880.
Paul Dennis was thought by many newspapers to be the potential ‘whistleblower’ of the climategate emails. He commented a few times at Simon Singh’s blog and his identity was confirmed at Bishop Hill
It strikes me as odd that the dendrologists and later the climate researchers have apparently never thought of conducting a long-term experiment, similar to the Experimental Earthwork Project at Overton Down in Wiltshire, which was set up in 1960 and is being re-visited by archaeologists since then:
http://www.thefreelibrary.com/The+Experimental+Earthworks+revisited.-a021221482
Some interesting data would have been available by now.
@James P
Good old Geoffrey Lean repeats the CO2 = pollution mantra in his latest DT blog. Plants may have another take on that...
A world of rapidly rising temperatures? Do these guys ever look at a global temperature chart like HadCRUT3 that shows no warming since 1998. Really, honestly.
as bender at CA would say, read the CA blog for info on tree selection.
IIRC they sample trees (live & dead) at tree line/edge of growth, because these trees are the most stressed by climate.
then they come up with novel interpretations that fooled some of the people ...etc.
The start for tree ring proxies is HC Fritts, "Tree Rings and Climate." It is the absolute "Bible." Read that and you will agree with me that tree rings cannot be a reliable proxy. Quite aprt from the fact that rainfall is often as large a determinant of width as temperature, there are other common factors, and often they interact non-linearly in space and in time.
The whole "science" is nonsense.