The Pacific decadal oscillation and long‐term climate prediction

Abstract

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.

VARIATION IN THE RELATIONSHIP BETWEEN SNOWMELT RUNOFF IN OREGON AND ENSO AND PDO1

“…While ENSO changes phase interannually, PDO conditions persist in the same phase for 10 to 30 years, with excursions into the opposite phase for at most two to three years (Mantua et al, 1997). Finally, while ENSO is a reasonably well studied and widely accepted phenomenon with a prediction lead time of several months, the origin and teleconnections of decadal oscillations in the Pacific are disputed (Gu and Philander, 1997;Mantua et al, 1997;Zhang et al, 1997;Barnett et al, 1999;Hunt and Tsonis, 2000;Barlow et al, 2001). Nonetheless, PDO appears to influence Pacific Northwest climate and streamflow as much as ENSO (McCabe and Dettinger, 2002).…”

Decadal changes in global ocean chlorophyll

“…The PDO entered positive phase in 1977 [ Mantua et al , 1997]. There is recent evidence of reversed phase, beginning near the launch of SeaWiFS (mid‐1997) [ Hunt and Tsonis , 2000] or perhaps more recently [ Schmidt and Webb , 2001].…”