Historians have always known it. The weather can play a role in the rise and fall of civilisations and empires. Until now, their focus has mainly been on the role of weather in their decline (for example, the effects of drought on Mayan city states) but new data suggests that the weather has a role to play in the rise of political structures too.

Dendochronologist (tree-ring researcher), Dr Amy Hessl of West Virgina University and  Professor Neil Pederson of Columbia University’s session at this month’s American Geophysical Union conference, looked at tree ring data which suggests that a very long  period of wet and warm weather from 1208-1231 helped Genghis Khan and his horde to conquer half of Eurasia and build the world’s biggest contiguous land empire.

Until recently, it was thought that periods of drought and survival instincts drove Mongol hordes to invade neighbouring territories. However, it seems more likely that good weather,  good grazing and a well fed herd provided the optimum environmental conditions for Genghis to build an empire. This week’s  Economist article ‘A horde of data‘ is clear, “no one thinks that the Great Khan himself had nothing to do with it’. But his strategic genius might have been naught if the climate had provided him only with broken down nags.”

In the second half of the 20th century, Mongolia warmed by 2 degrees centigrade. Knowing more about their past climate may help Mongolians understand how to handle climate change today and so the multidisciplinary project on the energetics and ecology of the Mongol Empire continues, with collaborators from history, archaeology, paleoecology and now ecosystem modeling on board. Data analysis is key to their work and the intention is to  analyse earlier data relating to the first millennium AD  to find out more about the impact climate had on earlier Mongolian tribes too.

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