What was done
The authors derived a composite Glacier Expansion Index (GEI) for Alaska based on "dendrochronologically-derived calendar dates from forests overrun by advancing ice and age estimates of moraines using tree-rings and lichens" for three climatically-distinct regions -- the Arctic Brooks Range, the southern transitional interior straddled by the Wrangell and St. Elias mountain ranges, and the Kenai, Chugach and St. Elias coastal ranges -- after which they compared this history of glacial activity with "the ¹⁴C record preserved in tree rings corrected for marine and terrestrial reservoir effects as a proxy for solar variability" and with the history of the Pacific Decadal Oscillation (PDO) derived by Cook (2002).

What was learned
Wiles et al. report that "Alaska shows ice expansions approximately every 200 years, compatible with a solar mode of variability," specifically, the de Vries 208-year solar cycle; and by merging this cycle with the cyclical behavior of the PDO, they obtain a dual-parameter forcing function that is even better correlated with the Alaskan composite GEI, with major glacial advances clearly associated with the Sporer, Maunder and Dalton solar minima.

What it means
In introducing the rational for their study, Wiles et al. say that "increased understanding of solar variability and its climatic impacts is critical for separating anthropogenic from natural forcing and for predicting anticipated temperature change for future centuries."  In this regard, it is most interesting that they make no mention of possible CO2-induced global warming in discussing their results, presumably because there is no need to do so.  Alaskan glacial activity, which, in their words, "has been shown to be primarily a record of summer temperature change (Barclay et al., 1999)," appears to be sufficiently well described within the context of solar and PDO variability alone.

References
Barclay, D.J., Wiles, G.C. and Calkin, P.E.  1999.  A 1119-year tree-ring-width chronology from western Prince William Sound, southern Alaska.  The Holocene 9: 79-84.

Cook, E.R.  2002.  Reconstructions of Pacific decadal variability from long tree-ring records.  EOS: Transactions, American Geophysical Union 83: S133.