What was done
The authors compiled a transect of six tree ring-width chronologies from stands of mountain hemlock growing near the treeline that extends from southern Oregon to the Kenai Peninsula, Alaska, analyzing the data in such a way as to "directly relate changes in radial growth to annual variations in the North Pacific ocean-atmosphere system."  The period covered by their study spanned nearly 400 years, stretching from 1599 to 1983.

What was learned
It was determined that "much of the pre-instrumental record in the Pacific Northwest region of North America is characterized by alternating regimes of relatively warmer and cooler SST [sea surface temperature] in the North Pacific, punctuated by abrupt shifts in the mean background state," which were found to be "relatively common occurrences."  The authors concluded, for example, that "regime shifts in the North Pacific have occurred 11 times since 1650" and that "another regime-scale shift in the North Pacific is almost certainly imminent."

What it means
The significance of these findings resides in the fact that the abrupt 1976-77 shift in this Pacific Decadal Oscillation, as it is generally called, is what is responsible for the vast majority of the past half-century's warming in Alaska, which climate alarmists wrongly hype as evidence of gradual CO2-induced global warming.  Take away what occurred in that single year, for example, and Alaska is no different from the rest of the world, with most of its temperature stations showing either no subsequent warming or an actual cooling trend.

Clearly, when properly understood, Alaska is far from being a valid "poster child" for the IPCC crowd and their prescription for planetary health.  The region's temperature history does not provide evidence of obvious human intervention, since it's been doing what it's done over the past half-century for nigh unto 400 years ... and probably a whole lot longer.