For years archaeologists and New Mexico tour guides talked about the mysterious, sudden “disappearance” of the Anasazi Indians, the people who built magnificent cliff dwellings in the Southwestern United States. That kind of talk irritated modern tribes such as the Hopi and Zuni no end; they knew the Anasazi never disappeared but were in fact their ancestors.

But the ancient people did suddenly abandon these ancient sites, and archaeologists now believe the trigger for this was climate change, specifically the Great Drought, from about 1276 to 1279. According to some recent research, the problem wasn’t so much because the people no longer had enough water for their crops; a relatively small expansion of their agricultural territory would have provided enough food. But the sudden climate change, these researchers theorize, led to a disruption in their beliefs and a loss of faith in their political structure. The people did not disappear, but their way of life collapsed as they scattered, forming much smaller and less formal village units.

In other words, it should come as no surprise that profound climate shifts profoundly affect civilizations. The more recent Little Ice Age is believed to have driven the Vikings from Greenland and to have been among the factors in the death toll from the Black Plague, the start of the Thirty Years’ War and even the westward expansion in the United States.