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Rob L says:
Too bad that it is treemometers, they will always have questionable validity.
That said as with ice-cores we see the 1000 year warming-cooling cycle that produced the Minoan, Roman, Medieval and now Modern warming, on this graph it appears to have an amplitude of about 0.5-0.7 deg (1-1.5 deg C peak to trough from linear trend). That this cycle coincides with modern warming (which started before significant CO2 rise) is very powerful evidence against “strong” CAGW. Gisp2 cores have similar amplitude, though the long term cooling trend is steeper at about 0.7deg/millenium.
Would be nice to see an expanded vertical axis and a few grid lines to get a better view of the temperature variation, that graph they produced is near useless without a vertical reference.
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Tim Ball says:
Apart from the fact that trees rings don’t, for the most part, reflect temperature, this study is even more problematic because it only looks at summer temperatures. All the actual records show that it is winter temperatures that change the most.
For example, summer temperatures were about the same at the nadir of the Little Ice Age around 1680, but winters were much colder, Since then summer temperatures have remained about the same and winter temperatures have increased creating an increase in annual average.
Summary; Trees don’t represent temperature and half a year doesn’t represent an annual record.
There have been similar studies of petrified trees from millions of years ago. As I recall all they showed was a distinct solar cycle. But that is not surprising because that was the original reasonable application of tree ring studies by Douglass.
A. E. Douglass was an astronomer whose main interest was dendroclimatology, particularly the relationship between midlatitude precipitation patterns, especially drought cycles.
http://ltrr.arizona.edu/sites/ltrr.arizona.edu/files/bibliodocs/Douglass, AE_Evidence of Climatic Effects in the Annual Rings of Trees_1920.pdf
I used his work because I found a similar 22 year drought cycle in a spectral analysis of approximately 200 years of precipitation data for York Factory on Hudson Bay that appeared correlated with sunspot activity. It was an alien idea even then (1982) as my doctoral committee initially rejected that portion of the work. I risked failure but insisted on its inclusion, which, to their credit, they approved.
Theodor Landscheidt later developed the relationship between solar activity and midlatitude droughts.
http://www.john-daly.com/solar/US-drought.htm