Pacific Decadal Oscillation (PDO)

What is it? Short answer -- Just one variable in the Earth's climate change equation.

For the past century at least, global temperatures have tended to mirror the 20-to 30-year warmings and coolings of the north-central Pacific Ocean. We don’t know just why, but the pattern of the last century is clear: the earth warmed from about 1915 to1940, while the PDO was also warming (1925 to 46). The earth cooled from 1940 to 1975, while the PDO was cooling (1946 to 1977). The strong global warming from 1976 to 1998 was accompanied by a strong and almost-constant warming of the north-central Pacific. Ancient tree rings in Baja California and Mexico show there have been 11 such PDO shifts since 1650, averaging 23 years on length.

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The "Pacific Decadal Oscillation" (PDO) is a long-lived El Niño-like pattern of Pacific climate variability. While the two climate oscillations have similar spatial climate fingerprints, they have very different behavior in time. Fisheries scientist Steven Hare coined the term "Pacific Decadal Oscillation" (PDO) in 1996 while researching connections between Alaska salmon production cycles and Pacific climate (his dissertation topic with advisor Robert Francis). Two main characteristics distinguish PDO from El Niño/Southern Oscillation (ENSO): first, 20th century PDO "events" persisted for 20-to-30 years, while typical ENSO events persisted for 6 to 18 months; second, the climatic fingerprints of the PDO are most visible in the North Pacific/North American sector, while secondary signatures exist in the tropics - the opposite is true for ENSO. Several independent studies find evidence for just two full PDO cycles in the past century: "cool" PDO regimes prevailed from 1890-1924 and again from 1947-1976, while "warm" PDO regimes dominated from 1925-1946 and from 1977 through (at least) the mid-1990's. Shoshiro Minobe has shown that 20th century PDO fluctuations were most energetic in two general periodicities, one from 15-to-25 years, and the other from 50-to-70 years.

There is a tracked Pacific Decadal Oscillation (PDO) Index defined as the leading principal component of North Pacific monthly sea surface temperature variability (poleward of 20N for the 1900-93 period). Digital values of the PDO index are available from Nate Mantua's anonymous ftp directory.

Coincidence?

The PDO Index switched negative at about the same time the sun's geomagnetic averaged planetary index(AP) dropped off in October 2005 and has stayed more or less negative since then. Is it just a coincidence that the PDO Index went negative about the same time as the sun's geomagnetic averaged planetary index dropped. Curious.


The folks that track the PDO Index are located here.

Is the Atlantic multidecadal oscillation (AMO) the next to shift? And what about the ... ?? Settled science my ass.