By Joseph D’Aleo, CCM

Back in 1977, the Pacific Ocean underwent a major transformation that was called the Great Pacific Climate Shift. Suddenly warm water replaced cold water that had dominated for most of the prior three decades near the west coast of North America and along the equatorial eastern Pacific. In 1997, researchers at the University of Washington in a paper in the Bulletin of the American Meteorological Society reported they had discovered a multidecadal oscillation in Pacific sea surface temperature and pressure while trying to explain decadal changes in salmon fishery production. They called it the Pacific Decadal Oscillation. They noted that major shift that had taken place in 1977 was a change in the PDO from what they termed the cold phase to the warm phase.

In the warm mode with warm water favored in the eastern tropical Pacific, El Ninos were favored over La Ninas and indeed since 1977 there have been more frequent and stronger El Ninos that have helped contribute to global warming.

Starting in the late 1990s a shift to the cool mode began but it was halted in the early 2000s. This year with the help of a developing relatively strong La Nina, the cool mode is again increasing.

Current sea surface Temperature anomalies (blue colder than normal, yellows and red warmer)

Annual mean PDO from 1950 to 2007

If that change to the cold PDO is this time a lasting one (and given past intervals of warm and cold which typically averaged 20 to 30 years, it certainly appears very possible), we may be entering a new era with more La Ninas and a very different climate, especially if the sun goes into its usual 200 year deep sleep as more and more solar scientists are beginning to believe will happen. Read the likely outcome of such a Pacific ocean change here.