Was climate change responsible for the Mongol hordes?

First scientists told us that a “distinct drying” during the third century might have encouraged the fall of the Roman Empire, prompting critics to decry the idea as the “latest global warming scare tactic.” Now the journal Science is highlighting similar speculations that wet and warm conditions in the central Asian steppe in the 13th century help explain the exceptionally rapid expansion of the imfamously cruel Mongols under Genghis Khan.

Mongol horsemen relied on domesticated animals; Amy Hessl, one of the scientists involved in the research, explained to LiveScience in July that a single Mongol fighter required 10 horses, plus livestock that could keep up with the horde and provide food. Wetter conditions in the steppe would have encouraged grass and other plants to grow, providing plentiful grazing opportunities for all sorts of animals. When the climate became colder and dryer in the middle of the 13th century, the Mongol Empire splintered, and its rulers moved their capital away from the steppe to modern-day Beijing.

It is, in fact, because scientists deduced that plantlife flourished and then failed in Mongolia during this period that they can make these connections. Both the Mongol and the Roman hypotheses rely on the information researchers such as Hessl gathered from tree rings. Wider rings indicate more favorable growing conditions. Thinner ones indicate leaner times. Matching up tree rings with historical dates produces fascinating correlations.

Of course, in neither the Mongol nor the Roman case were humans responsible for changing climate conditions; people just reacted to them. But scientists behind both studies have not been able to resist drawing parallels to the climate change happening now. This is tricky, since, among other things, explanations for historical events are so often varied — if not obscure — making it hard to draw clear lessons. Maybe something else entirely mostly or entirely explains the Mongols’ rise.

But as research into how climate interacted with human civilizations in the past improves, it is fair to make a simple but profound point that often unmentioned in the squabbling over anthropogenic global warming: Changing climate can affect the way human societies function. As the world warms, many will probably have to adapt their infrastructure, adjust their way of life or move. Some might end up better off, as the Mongols seem to have been for a time. Many might be worse off, as were those Genghis Khan subjugated, or, perhaps, the Mongols who didn’t move to Beijing when life got harder on the steppe. Humans now have more ability to adapt than at any time in the past. But that ability is not unlimited.