by Dr Roger Pielke, Sr.
With the McShane and Wyler paper examining and questioning the method, this look at the proxy data and its problems seems like a relevant issue to review.
Comment On Tree Ring Proxy Data and Thermometer Type Surface Temperature Anomalies And Trends
There was an interesting conclusion in a New York Times article on the relationship between tree ring proxy temperature trend analyses and thermometer type measures of temperature anomalies and trends. The article is
British Panel Clears Scientists by Justin Gillis published on July 7, 2010
The relevant text is on page 2 it is written
“But they were dogged by a problem: Since around 1960, for mysterious reasons, trees have stopped responding to temperature increases in the same way they apparently did in previous centuries. If plotted on a chart, tree rings from 1960 forward appear to show declining temperatures, something that scientists know from thermometer readings is not accurate.”
There are, however, problems with this conclusion. Since the thermometers are not coincident in location with the tree ring data (in the same local area), it would not be surprising that they are different. Indeed, this is yet another example that implies unresolved biases and uncertainties in the surface temperature thermometer type data as we discussed in several of our papers (see and see), as the thermometers are measuring elsewhere then where the proxy tree data is obtained. This obvious issue has been ignored in the assessment of this so-called divergence between the two methods to evaluate temperature anomalies and trends.
It is possible, of course, that the trees are responding differently due to the biogeochemical effect of added carbon dioxide and/or nitrogen deposition. Nonetheless, to accept the thermometer record as the more robust measurement of spatial representative temperatures is premature.
I have discussed this issue further in the posts
Comments On The Tree Ring Proxy and Thermometer Surface Temperature Trend Data
December 2007 Session ‘The “Divergence Problem’ In Northern Forests
I regret I did’nt build my house using timber. I could have read the temperature straight of the walls!
Many temp sensors are now in urban areas or on airports and there is a strange habit of cutting down trees to build houses and I haven’t seen many trees on or around the runway at Heathrow my “local” airport.
I may be, from ignorance of the research literature, be asking a silly question, but I’ll ask it nonetheless.
‘Why is tree growth linked to annual temperature??’
To me, there are numerous factors at play:
1. Temperature in the growing season
2. Sunlight.
3. Rainfall, both amount and distribution through the growing season.
4. Pests.
5. Soil nutrients.
6. Competitor plants nearby.
This year, we conducted a little experiment with tomato plants. My mother bought 4, but only three would fit in the special tomato grow bag, so we put one in the front garden. The effects are striking: after 3 months with the same sunlight and same temperature, the one in the front garden is about 2 feet high, whilst those in the special nutrient bag are 5 foot high.
I would also ask you to consider the effect on growth of a few hard winters, which both reduce temperatures but may also wipe out pests. Has work been done to correlate summer growth with cold winters and what results are there? Since it is clear that, in the case of some trees like apple, crop yields are best with a hard winter, a mild spring and a warm but watery summer……is that true also for main tree growth?
I am sure that all would agree that there is a great difference between annual temperature and seasonal temperature and it might be useful to readers to hear what the position is in research circles on that issue……
James Bull
Heathrow is frequently the warmest place in the country. According to the coordinates the temperature sensor is at the end of the runway near the perimeter fences. Are you able to confirm this visually?
tonyb
I think I can get a grant into looking into mushroom growth rings , it can all be carried out in the dark, you only need 3 mushroom heads to study them” no shortage”
I once had a look at Ostrov Dikson temperatures (quite close to both Yamal and the Polar Ural sites) to see if there really was any divergence. I downloaded the June-July-August temperatures from GISS for the station Ostrov Dikson and averaged with a 3-year period to remove some of the noise: http://i45.tinypic.com/2ns6jk6.jpg
Made me think that the divergence problem is really a problem with the temperature record, not the proxies…
It’s the precipitation, stupid.
The problem with tree ring data is that temperature is not the only thing that affects tree growth because rain and soil (mostly rain) and genetics, also affect growth. Another big problem is that tree growth is non-linear (a bell curve) and not matched to temperature. There is a “sweet spot” in temperature where growth is highest and everything less or more than that will show less growth. For example if temperature increase were infinite, tree growth would not be. Tree growth is constrained by genetics and other environmental factors. So, of course, tree growth will not follow temperature, and therefore tree rings samples are a very poor proxy for temperature. Thus Michael Mann’s “hockey stick’ is founded on unreliable data and is therefore mostly useless except to show how NOT to do science.
Ryan Welch says:
August 23, 2010 at 11:13 am
The problem with tree ring data is that temperature is not the only thing that affects tree growth because rain and soil (mostly rain) and genetics, also affect growth.
Ryan, I agree. Perhaps a “multi-species” approach is best when seeking to reconstruct the historical climate pattern of any region through the use of tree ring data.
The “tree and thermometer divergence problem” is improperly named. It should be named the “Tree and Hansen/Jones temperature record divergence problem.” Since we have repeated estimates that up to half of the warming in the thermometer record is due to land use changes, we do not know if there is a real tree and temperature divergence.
If we were to assume that the tree ring data is a somewhat valid measure of temperature, then we be able to use the tree ring data as a measure of how the HADCRUT and GISS temperature records diverge from real temperatures.
I wonder which way Dr. Briffa would care to argue this idea? 🙂
Quite relevant comments in general. Single trees are terrible proxies, as there are likely hundreds of variables impacting the growth. However the idea of using masses of tree samples is that local variables are averaged out. I would call this ‘cross-sampling’, which is common method in scientific signal processing, to strenghten phenomena and average noise away.
But actually what then tends to happen with tree samples is that northern and southern extream condition areas begin to dominate that signal. This is because changes or signal is more visible there than in more stable equatorial or lower latitudes. This is exactly why Mann’s work does not have much value. Samples were selected wither by nature or the team and cross-sampling criteria does not fulfill sceintific requirements for global temperature. It is surpricing, that this type of cornerstone criteria can be supressed in science
Tree rings are valueble source anyway, please check check some very high quality work done with Scandinavic trees, that actually leads just to opposite conclucions when compared to Mr. Mann:
http://lustiag.pp.fi/
Maybe most interesting
http://lustiag.pp.fi/treerings_and_climate-part1.pdf
pages 17 and 18
or
http://lustiag.pp.fi/viljavaranto_mt.pdf
Also Mann’s team has even revearsed some sedimentation data observed and published reversed data to match it better to their model, which is actually a clear scientific fraud.