A transect of climate sensitive tree ring-width chronologies from coastal western North America provides a useful proxy index of North Pacific ocean-atmosphere variability since 1600 A.D. Here we use this high-resolution record to identify intervals of an enhanced interdecadal climate signal in the North Pacific, and to assess the timing and magnitude of abrupt shifts in this system. In the context of this record, the step-like climate shift that occurred in 1976--1977 is not a unique event, with similar events having occurred frequently during the past 400 years. Furthermore, most of the pre-instrumental portion of this record is characterized by pronounced interdecadal variability, while the secular portion is more strongly interannual in nature. If the 1976--1977 event marks a return to this mode of variability there may be significant consequences for natural resources management in the North Pacific Sector. ¿ 2001 American Geophysical Union