The old adage that “as goes silver, so go soybeans” is more than just a whimsical piece of American farming folk wisdom. That commodity prices tend to rise and fall in unison is a deadly serious economic phenomenon for consumers around the world as food costs increase sharply, in some countries at the fastest pace for decades.

Agricultural commodity prices are often volatile, in part due to weather fluctuations that affect crops. But what is unusual about recent price increases is that so many prices – everything from grains to ground nut oil – are rising simultaneously.