China has seen dynasties rise and fall over the last two millennia. Such are the vagaries of human history. But researchers at Trinity College, Dublin, and Zhejiang University, Hangzhou, recently suggested a surprising natural explanation: volcanoes. Of 68 dynastic collapses since 0 AD, they found that 62 were preceded by major volcanic eruptions around the world. Volcanoes throw tons of tiny particles known as aerosols skyward. These float in the atmosphere with sometimes huge effects: scattering sunlight, absorbing solar radiation, cooling the earth, and changing rainfall patterns. When Moun…

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