The Pacific Decadal Oscillation (PDO)

The Pacific Decadal Oscillation (PDO) was defined by fisheries scientist Steven Hare in the mid-1990’s, based on observations of Pacific fisheries cycles. The PDO index is calculated from sea surface temperatures and sea level pressures. An overview of the PDO is given by Nathan Mantua (Joint Institute for the Study of the Atmosphere and Oceans, University of Washington)

[http://www.atmos.washington.edu/~mantua/REPORTS/PDO/PDO_egec.htm].

The PDO goes through warm and cool phases of the cycle with phases typically lasting about 30 years. The causes of the oscillation are currently unknown. A good source of information on the PDO ishttp://jisao.washington.edu/pdo/.

The following figure is from that web site and shows the monthly PDO index from 1900 to September 2008.

PDO Index 1900 – September 2008

The recent phases of the PDO can be seen in the above figure, with a cool phase starting around 1945 and switching to a warm phase in 1977. It appears that 2008 may be the start of the next cool phase. According to the above-mentioned PDO web site:

“Major changes in northeast Pacific marine ecosystems have been correlated with phase changes in the PDO; warm eras have seen enhanced coastal ocean biological productivity in Alaska and inhibited productivity off the west coast of the contiguous United States, while cold PDO eras have seen the opposite north-south pattern of marine ecosystem productivity.”

 [http://www.iphc.washington.edu/Staff/hare/html/papers/ei/ei.pdf] state: “It is now widely accepted that a climatic regime shift transpired in the North Pacific Ocean in the winter of 1976–77. This regime shift has had far reaching consequences for the large marine ecosystems of the North Pacific. Despite the strength and scope of the changes initiated by the shift, it was 10–15 years before it was fully recognized. Subsequent research has suggested that this event was not unique in the historical record but merely the latest in a succession of climatic regime shifts.”

The following figure is from a NOAA study of the impact of the PDO variability on the California Current ecosystem and shows the approximately 60-year cycle of the PDO and the corresponding northern Pacific Ocean temperature regimes 

[www.nwr.noaa.gov/Salmon-Hydropower/Columbia-Snake-Basin/upload/Briefings_3_08.ppt]

The following figure is from the NASA Earth Observatory, April 2008. It shows the sea surface temperature anomaly in the Pacific Ocean from April 14–21, 2008 as measured by satellite. The anomaly compares the recent temperatures with an average from 1985–1997. Places where the Pacific was cooler than normal are blue, places where temperatures were average are white, and places where the ocean was warmer than normal are red.

[http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=18012 ]. The NASA article states: “while the La Niña was weakening, the Pacific Decadal Oscillation—a larger-scale, slower-cycling ocean pattern—had shifted to its cool phase.

… The shift in the PDO can have significant implications for global climate, affecting Pacific and Atlantic hurricane activity, droughts and flooding around the Pacific basin, the productivity of marine ecosystems, and global land temperature patterns.”

Sea Surface Temperature Anomaly April 14-21, 2008 Compared to 1985 – 1997 Average

Addressing the Washington Policymakers in Seattle, WA, Dr. Don Easterbrook (Dept. of Geology, Western Washington University) said that “shifting of the Pacific Decadal Oscillation (PDO) from its warm mode to its cool mode virtually assures global cooling for the next 25-30 years and means that the global warming of the past 30 years is over.”

[http://icecap.us/images/uploads/WashingtonPolicymakersaddress.pdf]  

The following table summarizes North American climate anomalies associated with PDO (from [http://www.atmos.washington.edu/~mantua/REPORTS/PDO/PDO_egec.htm]).