Replies

dendrochronology

The study of growth rings in trees for the purpose of analyzing past climate conditions or determining the dates of past events.

Because trees grow more slowly in periods of drought or other environmental stress than they do under more favorable conditions, the size of the rings they produce varies.

Analyzing the pattern of a tree's rings provides information about the environmental changes that took place during the period in which it was growing.

Matching the pattern in trees whose age is known to the pattern in wood found at an archaeological site can establish the age at which the wood was cut and thus the approximate date of the site.

By comparing living trees with old lumber and finding overlapping ring patterns, scientists have established chronological records for some species that go back as far as 9,000 years.

Good response. Tree-rings are a good indication of environmental stress such as drought conditions when moisture is a limiting factor. They are less predictive of temperature unless that alone is the limiting factor.

Dendrochronology was developed using pines (conifers) in the southwest US where moisture generally is limiting factor. Further, most of tree growth and thus tree ring density (or thickness) occurs in the springtime. A wet winter will provide a thick ring, but a hot dry summer may not be reflected in the growth ring as most growing has already occurred. This is the point that Dr. Tim Ball has made in response to support of this study (Summary; Trees don’t represent temperature and half a year doesn’t represent an annual record. ).

The over 200 comments to the article at the "Watts Up With That?" blog express deep skepticism that tree rings are a good proxy for temperature for the reasons mentioned above (moisture is usually the most limiting factor and may be too localized or regional to draw worldwide conclusions).

On the other hand this study was conducted in Finland and the author posits that only temperature was a factor based on the late arrival of the growing season at that high latitude.

So the bottom line, in my opinion, is that the study may provide evidence of cooling in the vicinity of the study area, but to extrapolate it over the globe is way too overly simplistic.