The remarkable cold lingered in Europe for weeks. Lakes, rivers, and the sea froze over, and the soil solidified a meter deep. The cold cracked open trees, crushed the life out of livestock huddling in stables, and made travel a treacherous undertaking. It was the coldest winter in the past 500 years, and one of the coldest moments in a larger global phenomenon known as the Little Ice Age. Likely causes include volcanic activity, oceanic currents, and/or reforestation due to Black-Death-induced population decline. It is nearly certain, however, that it has something to do with the unusually low number of sunspots that appeared at that time, a phenomenon referred to as the Maunder minimum.
We now know that such solar minima correlate quite closely with colder-than-normal temperatures on Earth, but science has yet to ascertain exactly why. Solar maximums, on the other hand, have historically had little noteworthy impact on the Earth apart from extra-splendid auroral displays. But thanks to our modern, electrified, interconnected society these previously innocuous events could cause catastrophic economic and social damage in the coming decades.