In 1815, Mt. Tambora in Indonesia erupted. The eruption spewed ash and sulfur dioxide into the stratosphere.
The sulfur dioxide reflected the sun’s rays, which caused a massive cooling event across the globe the following year.
Two feet of snow fell in Vermont on June 11, 1816, and flurries were reported as far south as the Washington D.C. area.
On top of that, food prices skyrocketed over the course of the year due to massive crop losses across the globe.
Europe had a really cool summer that year.
It didn’t help that 1816 was in the middle of the Dalton Minimum and at the end of the ‘Little Ice Age,’ when temperatures were one degree Celsius colder than today due to low sunspot activity.