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 Mount Pinatubo erupted in the Philippines in 1991, for example, the resulting ash cloud lowered the planet’s temperature by 0.6° Celsius (1.1° Fahrenheit) for at least two years.

The team behind the Chinese dynasty research surmises that volcanic aerosols triggered drought and ruined crops, leading to catastrophic social unrest across China’s agricultural economy. This causality is hard to prove conclusively, but the results suggests just how powerful an effect aerosols may have had on climate and civilization in the past — and today.