One warm winter does not a climate make. The NAM is positive at the moment as is SAM and the polar fronts contract to higher latitudes.
See here for an explanation – http://www.dpi.vic.gov.au/agriculture/about-agriculture/newsletters-and-updates/newsletters/milking-the-weather/june-2011/sam
It seems associated with solar UV variability.
http://www.nature.com/ngeo/journal/v4/n11/full/ngeo1282.html
http://www.nipccreport.org/articles/2011/nov/2nov2011a3.html
http://www.ncas.ac.uk/index.php?option=com_content&view=article&id=890:solar-forcing-of-winter-climate-variability-in-the-northern-hemisphere&catid=53:current-news&Itemid=299
Which probably has decadal to centennial and longer variability. Here is an example of Hale cycle variability over the 20th Century.
http://www-ssc.igpp.ucla.edu/personnel/russell/papers/731/731index.htm
http://www-ssc.igpp.ucla.edu/personnel/russell/papers/731/fig1.gif
http://iopscience.iop.org/1748-9326/5/2/024001/fulltext/
The shift in atmospheric mass associated with sea level pressure changes at the poles must be linked to currents – in particular the Californian and Peruvian Currents – and therefore upwelling in the eastern Pacific. Although with lags and complex feedbacks – I don’t know how that could ever be proved. But it remains the only extant theory for the PDO.
I doubt if we know what the causes of recent warming were – if the satellite data is so unreliable that the implied albedo changes causing most of the warming are moot. Where is the future? It seems more likely to be more negative SAM and NAM on trend, negative PDO and declining solar activity. This must lead to cooler NH winters and cooler temps. generally.
Robert I Ellison
Chief Hydrologist