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In the early summer of 1783, Laki erupted, releasing vast rivers of lava. The explosive volcano also ejected a massive amount of volcanic ash and sulfur dioxide into the air — the eruption was so violent that the ash and sulfur dioxide were injected into the stratosphere, some 8 miles up. This cloud was then swept around the world by the stratospheric winds. The result was a significant decrease in the amount of sunlight reaching the Earth’s surface for several years.
That reduction in sunlight brought about bitter cold weather across the northern hemisphere. The winter of 1784 was the coldest ever seen in New England and in Europe.