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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
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Marks says:
Appears Real Climate and Michael Mann began their spin a day ago on this story:
http://www.realclimate.org/index.php/archives/2012/07/tree-rings-and-climate-some-recent-developments/#more-12427
I agree completely with that statement. As a student (a long time ago) I studied tree rings in the southwest US. There is a direct relation between tree-ring thickness and moisture and a more indirect relation between tree rings and temperature. First, most tree ring growth occurs in the spring and is a function of winter moisture. An El Niño winter generally is moist and cool which contributes to thicker tree rings as soil moisture is more likely to be retained for vegetation use. A La Niña winter is more likely to be drier and warmer leading to thinner tree ring growth. So indirectly, we can conclude that winter temperatures are likely warmer with a La Niña event.
However, summer precipitation and temperature, at least in the southwest US, are not driven by either seasonal climate event. In the summer, precipitation comes from tropical moisture from either or both the Gulf of Mexico and the far eastern Pacific Ocean. The occurrence and duration is dependent on the position of the continental high pressure dome which circulates moisture from these two areas clockwise over the southwest. If the location is over NM or west Texas, moisture will not flow northward. Further east over the central US, moisture will stream into the area in the pattern commonly known as the summer monsoon. A connection between La Niña/El Niño events and the high pressure area location has not been defined to my knowledge. In any event, summer temperatures and precipitation are not a markedly important factor in tree ring growth so conclusions as to historic summer temperature and climate based on tree rings are tenuous at best.
