Natural variation: Warm North Atlantic Ocean promotes extreme winters in U.S. and Europe

The extreme cold weather observed across Europe and the east coast of the U.S. in recent winters could be partly down to natural, long-term variations in sea surface temperatures, according to a new study. Researchers have shown that a phenomenon known as the Atlantic Multidecadal Oscillation (AMO) -- a natural pattern of variation in North Atlantic sea surface temperatures that switches between a positive and negative phase every 60-70 years -- can affect an atmospheric circulation pattern, known as the North Atlantic Oscillation (NAO), that influences the temperature and precipitation over the Northern Hemisphere in winter.

http://www.sciencedaily.com/releases/2014/04/140401210414.htm