Pan-basin warming now overshadows robust Pacific Decadal Oscillation

Abstract The Pacific Decadal Oscillation (PDO) has served as a key index linking basin-scale climate variability to marine ecosystem changes in the North Pacific. However, recent apparent breakdowns of PDO–ecosystem correlations have raised concerns about the stability of the mode and its continued relevance in a warming climate. Here we show that basin-wide warming now overwhelms PDO-related sea surface temperature (SST) variability, although neither the PDO’s spatial pattern nor its strength have changed. We introduce the pan-basin pattern as a complementary index to describe the non-stationary SST baseline of the North Pacific. Regional SSTs increasingly reflect the superposition of these two signals, providing an explanation for weakened or inverted PDO–ecosystem correlations. Future use of the PDO index in management will require discerning the effects of internal dynamics from those of absolute changes in SST as extreme and no-analogue ocean conditions driven by interacting natural variability and anthropogenic warming become more common.