Year without a summer

Year Without a Summer
1816 summer temperature anomaly compared to average temperatures from 1971–2000
Volcano	Mount Tambora
Date	April 10, 1815
Type	Ultra Plinian
Location	Lesser Sunda Islands, Dutch East Indies 8°15′S 118°0′E / 8.250°S 118.000°E / -8.250; 118.000
VEI	7
Impact	Caused a volcanic winter that dropped temperatures by 0.4 to 0.7 °C worldwide

The year 1816 is known as the Year Without a Summer (also the Poverty Year, the Summer that Never Was, Year There Was No Summer, and Eighteen Hundred and Froze to Death) because of severe climate abnormalities that caused average global temperatures to decrease by 0.4–0.7 °C (0.7–1.3 °F). This resulted in major food shortages across the Northern Hemisphere.

Evidence suggests that the anomaly was predominantly a volcanic winter event caused by the massive 1815 eruption of Mount Tambora in the Dutch East Indies (the largest eruption in at least 1,300 years after the extreme weather events of 535–536), perhaps plus the 1814 eruption of Mayon in the Philippines. The Earth had already been in a centuries-long period of global cooling that started in the 14th century. Known today as the Little Ice Age, it had already caused considerable agricultural distress in Europe. The Little Ice Age's existing cooling was aggravated by the eruption of Tambora, which occurred during its concluding decades.

The Year Without a Summer was an agricultural disaster. Historian John D. Post has called this "the last great subsistence crisis in the Western world". The unusual climatic aberrations of 1816 had the greatest effect on most of New England, Atlantic Canada, and parts of western Europe. Typically, the late spring and summer of central and northern New England and southeastern Canada are relatively stable: temperatures (average of both day and night) average between about 20 and 25 °C (68 and 77 °F) and rarely fall below 5 °C (41 °F).

In the spring and summer of 1816, a persistent "dry fog" was observed in parts of the eastern U.S. The fog reddened and dimmed the sunlight, such that sunspots were visible to the naked eye. Neither wind nor rainfall dispersed the "fog". It has been characterized as a "stratospheric sulfate aerosol veil".