What causes riots? That’s not a question you would expect to have a simple answer.

But today, Marco Lagi and buddies at the New England Complex Systems Institute in Cambridge, say they’ve found a single factor that seems to trigger riots around the world.

This single factor is the price of food. Lagi and co say that when it rises above a certain threshold, social unrest sweeps the planet.

The evidence comes from two sources. The first is data gathered by the United Nations that plots the price of food against time, the so-called food price index of the Food and Agriculture Organisation of the UN. The second is the date of riots around the world, whatever their cause. Both these sources are plotted on the same graph above.

This clearly seems to show that when the food price index rises above a certain threshold, the result is trouble around the world.

This isn’t rocket science. It stands to reason that people become desperate when food is unobtainable. It’s often said that any society is three square meals from anarchy.

But what’s interesting about this analysis is that Lagi and co say that high food prices don’t necessarily trigger riots themselves, they simply create the conditions […]