Jeff Masters has an impressively detailed post laying out the argument that 2010, with its record setting snowstorms, droughts, heatwaves, flooding, hurricanes, etc, had the most extreme weather since 1816, the year without a summer.
Looking back through the 1800s, which was a very cool period, I can’t find any years that had more exceptional global extremes in weather than 2010, until I reach 1816. That was the year of the devastating “Year Without a Summer”–caused by the massive climate-altering 1815 eruption of Indonesia’s Mt. Tambora, the largest volcanic eruption since at least 536 A.D. It is quite possible that 2010 was the most extreme weather year globally since 1816.
— Masters (2010): 2010 – 2011: Earth’s most extreme weather since 1816? on Weather Underground.
Notes
NOAA’s Historical Hurricane Tracks map is an excellent interactive webpage, and data source.