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New Paper: PDO Controls North American Temperatures Via Changes In Cloud Cover

The Hockey Schtick

A paper published today in Atmospheric Research describes a mechanism by which changes in the natural Pacific Decadal Oscillation [PDO] affect air temperatures and water vapor, which subsequently affects cloudiness over North America [planetary albedo], and therefore land surface temperatures. As noted by Dr. Roy Spencer in his book,

The most obvious way for warming to be caused naturally is for small, natural fluctuations in the circulation patterns of the atmosphere and ocean to result in a 1% or 2% decrease in global cloud cover. Clouds are the Earth’s sunshade, and if cloud cover changes for any reason, you have global warming — or global cooling.”

According to the authors, “The TCM [thermodynamic model] generates a kind of atmospheric bridge by which the SST [sea surface temperature] produces a T7A [change in air temperature], the consequent condensation of water vapour anomaly and the corresponding εA [cloudiness] over the continent, affecting the planetary albedo and therefore the LST [land surface temperature].”

Fig. 1. PDO index for the summers (average of June, July and August) based on the CAF for SST over the North Pacific region during a period of 105 years, from 1900 to 2004 ( The global warming signal has been removed from the data. The upward bars indicate years with positive index, and the downward bars indicate years with negative index.