Relevant

9 Sep 2010: Much was made last winter of the huge snowfalls in the Washington D.C. area and elsewhere. But, were they really due to "Global Warming" or anthropogenic climate change? Various analyses have shown that may not be the case (though many toss in a statement at the end leaving open the door to that potential).

From Columbia University we understand that it was converging weather patterns. "The extraordinarily cold, snowy weather that hit parts of the U.S. East Coast and Europe was the result of a collision of two periodic weather patterns in the Atlantic and Pacific Oceans." El Nino brought wet weather to the southeastern U.S. while the North Atlantic Oscillation delivered "frigid air from the arctic" to the East Coast and across northwest Europe. This was published in the journal Geophysical Research Letters (GRL): "Northern Hemisphere winter snow anomalies: ENSO, NAO and the winter of 2009/10".

NOAA agrees: their "Climate Scene Investigators" wanted to know "if humans could be to blame." They conclude that it's not likely, and that "there is not evidence -- no human 'fingerprints' -- to implicate our involvement in the snowstorms." Their conclusion appears to be that natural phenomena are much more likely to be responsible (NAO and ENSO are again named). And such conditions have existed before. One example is the cold European winters in the 1940s (the World War II era). NOAA's ClimateWatch Magazine has a several page spread on the subject.

Read more:

http://www.ldeo.columbia.edu/res/div/ocp/drought/snow.shtml

http://www.climatewatch.noaa.gov/2010/articles/forensic-meteorology-solves-the-mystery-of-record-snows