After 22 years of mostly cool temperatures, the North Pacific sea surface has been warm for the past 2 years. This raises the question of whether the warming trend in the North Pacific Ocean will continue for the next 20 years. The answer depends partly on whether the observed variability is an internal oscillation with its own time scale or whether it is externally driven.
We are addressing this issue because important predictions are at stake. Positive North Pacific sea-surface temperature (SST) anomalies tend to cause droughts in the southwestern and northeastern United States. Some scientists have assumed that a fundamental “regime shift” has now occurred with 20 years of warmer temperatures to come and California has been advised to prepare for a 20-year period of drought. The basis for assuming a 40-year periodicity is the century-long record of North Pacific SSTs [Mantua et al., 1997]. More recently, a longer, proxy-based data set [Chao et al., 2000] suggested that a) North Pacific SSTs oscillate in phase with a comparable spatial pattern in the South Pacific, and b) two periods of approximately 20 and 70 years exist.
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