"Climate in the North Pacific and North American sectors has experienced interdecadal shifts during the 20th century. A network of recently developed tree-ring chronologies for Southern and Baja California extends the instrumental record, and reveals decadal-scale variability back to AD 1661.
"The Pacific Decadal Oscillation (PDO) is closely matched by the dominant mode of tree-ring variability, which provides a preliminary view of multi-annual climate fluctuations spanning the past four centuries. The reconstructed PDO index features a prominent bidecadal oscillation, whose amplitude weakened in the late 1700s to mid-1800s.
"A comparison with proxy records of ENSO suggests that the greatest decadal-scale oscillations in Pacific climate between 1706 and 1977 occurred around 1750, 1905, and 1947."
"Reconstructed PDO since 1660.
Correlation between instrumental (dashed) and reconstructed PDO is 0.64 from 1925 to 1991.
"During warm periods, the eastern North Pacific is warmer than usual, and the central North Pacific
is cooler (viceversa during cool periods). Warm and cool PDO phases are qualitatively similar to warm
and cool ENSO events, but different because of slower temporal dynamics and stronger midlatitudinal responses."