Implications for the next decade of different views of the Pacific Decadal Oscillation

The Pacific Decadal Oscillation (PDO) is often defined in terms of SST cross-correlations from an area in the central North Pacific extratropics. This view leads to a SST pattern with a fan-like teleconnection to the tropics and subtropics erroneously described as "ENSO-like." The time series for this area has decade-to-decade swings in polarity some prefer to call the "Interdecadal Pacific Oscillation" but most often the PDO. The common presumption is that the pattern and time series represent a single mode of variability, although there is no basis for this and the most simple dynamical considerations suggest otherwise.

An alternative analysis, which presumes very little, leads to the conclusion that practically all of the central North Pacific SST variability associated with the tropics and subtropics can be explained by ENSO and a coherent global signal operating on much longer than interdecadal time scales and representing a global climate shift. The remaining variability, which is most reasonably associated with internal ocean-atmosphere processes in the extratropics, has a modest amount of very non-systematic interdecadal power. The results of the alternative analysis are highly insensitive to changes in record lengths, data sets, averaging periods, seasons, etc. and are completely consistent with expected signatures of global warming.

Predictions of a return to a period of cold winters and more frequent droughts for North America and more active Atlantic/Gulf hurricane seasons dependent on an expected basin-wide swing of the PDO are not likely to verify in the context of the alternate analysis.