What was done
Scientists frequently utilize tree-ring width and density data as proxies to reconstruct histories of climate (temperature and/or precipitation) at various locations around the globe when instrumental data are unavailable.  In this study, the authors applied two statistical procedures - wavelet transform analysis and Morlet complex wavelet analysis - to two data sets (a set of tree-ring width measurements from the Santa Catarina State of Brazil and the sunspot number time series) in an attempt to determine the influence of the solar parameter (sun spot number) on climate (tree-ring width) over the period 1837-1996.

What was learned
The complex Morlet wavelet analysis revealed the existence of an 11-year cycle in the tree-ring width data.  Not surprisingly, an 11-year cycle was also found in the sun spot data.  When comparing both data sets via cross-wavelet spectral analysis, the authors report that "a good correspondence is observed," which correspondence is strongest during the time of most intense solar activity, i.e., 1940-1970.

What it means
Once again, the influence of the sun on earth's climate leading up to and throughout the initial stage of the Modern Warm Period is demonstrated.