A century or more ago when I was in my early teens at school, I recall going caving with my class on more than one occasion. England’s West Country is riddled with wonderful nooks and crannies if you can get over the early stages of claustrophobia. I remember not being too impressed with stalactites and stalagmites and such like. Luckily, others had more sense.
Via Anthropology.net, I learn of work that has been done on a stalagmite in Wanxiang Cave, China, that allows researchers to figure out the detailed climatic conditions back more than a thousand years at intervals of just 2.5 years. In particular, they can pick out the drought of the ninth century that seems to have contributed to the collapse both of the Tang Empire in China and of the Mayans in the Americas. The researchers have also found evidence of low rainfall at the times of the end of the Yuan and Ming dynasties.
In all cases it seems, the carrying capacities of their agricultural systems couldn’t handle the pressures caused by years of low rainfall, and the civilizations crashed.
We usually look at the histories of empires, their rise and fall, as a confluence of human emotions, power, technology, military advantage, economics. We often forget that climate is a truly global player that can cause history-changing effects simultaneously on both sides of the globe; effects that no human power has yet figured out how to tame.