Causes
It is now generally thought that the aberrations occurred because of the 1815 (April 5–15) volcanic Mount Tambora eruption on the island of Sumbawa, Indonesia (then part of the Dutch East Indies, but under British rule during Napoleon's occupation of the Netherlands), described by Thomas Stamford Raffles. The eruption had a Volcanic Explosivity Index ranking of 7, a super-colossal event that ejected immense amounts of volcanic ash into the upper atmosphere. It was the world's largest eruption since the Hatepe eruption over 1,630 years earlier in AD 180. That the 1815 eruption occurred during the middle of the Dalton Minimum (a period of unusually low solar activity) may also be significant.
Other large volcanic eruptions (with VEI at least 4) during the same time frame are:
- 1812, La Soufrière on Saint Vincent in the Caribbean
- 1812, Awu in the Sangihe Islands, Indonesia
- 1813, Suwanosejima in the Ryukyu Islands, Japan
- 1814, Mayon in the Philippines
These other eruptions had already built up a substantial amount of atmospheric dust. As is common following a massive volcanic eruption, temperatures fell worldwide because less sunlight passed through the atmosphere.
Read more about this topic: Year Without A Summer