However, the pendulum driven by the airflow is not an oscillator (assuming the swing of the pendulum doesn't change the coupling of the paddle to the airflow); it's a noise source, with the high and low frequency components filtered out by the pendulum. (realclimate.org)
In order to use tree rings as a temperature signal successfully, this low frequency component must be removed. (deepclimate.org)
If you run a cumulative sum based on the 20th century mean, you'll find that the result no longer resembles HADCRUT3 or GISTEMP at all in its low frequency components. (wattsupwiththat.com)