Dramatic increases in food prices over the last few years have severely impacted vulnerable populations worldwide, triggering riots in more than 30 different countries. Many factors have been proposed as causes for the price increases, from adverse weather to meat consumption in China, from increases in oil prices to exchange rates. In a recent paper [1,2], we tested these factors one by one, and constructed a model that explains what is behind the odd behavior of food prices. The results show there are just two main causes: increasing corn-to-ethanol conversion in the United States and excessive ﬁnancial speculation.
Marco Lagi, Alexander S. Gard-Murray and Yaneer Bar-Yam "Impact of ethanol conversion and speculation on Mexico corn imports", New England Complex Systems Institute, http://necsi.edu/research/social/foodprices/mexico/ (May 2012)