Volcanic winter
A volcanic winter is the reduction in temperature caused by volcanic ash and droplets of sulfuric acid obscuring the sun, usually after a volcanic eruption (hence the name). The explosion of Krakatoa in 1883 precipitated just such a condition; the next four years were unusually cold, and the winter of 1888 was the first time it was warm enough to snow; snowfalls that year broke all records worldwide.
The eruption of Mount Tambora in 1815 occasioned mid-summer frosts in New York State in the "Year Without a Summer" of 1816. A paper written by Ben Franklin in 1783 blamed the unusually cool summer of that year on volcanic dust coming from Iceland.
A comparable episode happened earlier in the 6th century; see climate changes of 535-536.
See Also
de:Vulkanischer Winter