I should tell you that there is a fairly strong temperature signal in the tree-ring density series, but that a non-temperature trend is also apparent post-1950 that gets bigger and deteriorates the temperature relationship. This makes calibration somewhat harder (hence I've been working on them for 2 years...!), but you also have to make the assumption that this non-temperature signal is something anthropogenic and didn't occur in the past.
Understanding The Precautionary Principle
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