The 1800s fell at the end of a relative cool snap that lasted around the world for almost 500 years. The prevailing theory today is that volcanic activity, including that from Tambora and other eruptions was at least one of the primary contributors. However, 1816 was not the only year in that time period that had weird weather in general.
The 2015 episode covers a volcano eruption in Sumbawa, Indonesia in 1816, that combined with several other factors to create an unusual -- and catastrophic -- series of weather events.
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