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Has The PDO Flipped To A Warming Phase?

20.07.2015 13:03 Age: 2 yrs

The Pacific Decadal Oscillation Index has been positive for the last year. This may mean that the PDO has shifted from a long-term cooling phase into a warming phase although a leading NOAA scientist cautions it will be several years before we know for sure. This shift could have significant implications for the so called pause in global warming

Click to enlarge. A graph showing NOAA's Pacific Decadal Oscillation Index. Red bars correspond to a positive index and blue bars to a negative index. Courtesy: NOAA

Click to enlarge. This slide from a NOAA press conference shows why NOAA believes the PDO has shifted into a warm phase. Courtesy: NOAA

Click to enlarge. A table showing NOAA PDO Index values since December 2013. They were consistently positive for the year from July 2014 to June 2015. Courtesy: NOAA

The Pacific Decadal Oscillation (PDO) may have moved into a warming phase during the last year, according to the National Oceanic and Atmospheric Administration (NOAA) of the US.

The PDO is a long term pattern of heat exchange between the ocean and the atmosphere that is centred over the mid-latitudes of the Pacific basin and is linked to a cycle in sea surface temperature (SST) variations.

The PDO plays an important role in the overall transfer of heat between the world's ocean and the atmosphere. NOAA suggests that the Pacific may have moved to a phase where the Pacific Ocean surrenders more heat to the atmosphere than it absorbs.

Extreme phases of the PDO are classified as being either warm or cool, as defined by SST anomalies in the north east and tropical Pacific Ocean. The PDO had been in a negative or cooling phase for a number of years prior to 2014 but several factors suggest this may have changed:

  • The monthly PDO Index maintained by NOAA has been consistently positive for the year to end-June 2015 (see table right);
  • Waters in the tropical Pacific, off the west coast of North America, and north eastern Pacific waters off Alaska, have all been warmer than normal;
  • Waters east of Japan have been colder than normal;
  • Sea surface temperatures (SSTs) in the North Pacific Basin hit record highs during 2014.

Blip or flip?

Pause to end?


NOAA State Of The Climate 2014 report published as a supplement to the Bulletin of the American Meteorological Society July issue here.

NOAA press conference here.

NOAA website here.

See also

Our report Warming Pacific Drives Global Temperatures here.