No one can quite explain why 1709 became the year that Europe froze, but freeze it did:
In England they called the winter of 1709 the Great Frost. In France it entered legend as Le Grand Hiver, three months of deadly cold that ushered in a year of famine and food riots. In Scandinavia the Baltic froze so thoroughly that people could walk across the ice as late as April. In Switzerland hungry wolves crept into villages. Venetians skidded across their frozen lagoon, while off Italy’s west coast, sailors aboard English men-of-war died from the cold. “I believe the Frost was greater (if not more universal also) than any other within the Memory of Man,” wrote William Derham, one of England’s most meticulous meteorological observers. He was right. Three hundred years on, it holds the record as the coldest European winter of the past half-millennium.
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Why it was quite so cold is harder to explain. The Little Ice Age was at its climax and Europe was experiencing climatically turbulent times: the 1690s saw a string of cold summers and failed harvests, while the summer of 1707 was so hot people died from heat exhaustion. Overall, the climate was colder, with the sun’s output at its lowest for millennia. There were some spectacular volcanic eruptions in 1707 and 1708, including Mount Fuji in Japan and Santorini and Vesuvius in Europe. These would have sent dust high into the atmosphere, forming a veil over Europe. Such dust veils normally lead to cooler summers and sometimes warmer winters, but climatologists think that during this persistent cold phase, dust may have depressed both summer and winter temperatures.