"We just have had a really kind-of amazing string of just plain bad luck with weather. And it just keeps accumulating recently."

Experts say it will take at least two years of good harvests to build enough stocks to buffer prices.

In the meantime, the agreement the G20 agriculture ministers reached calls for "appropriate regulation and supervision" of commodity markets. It makes some suggestions, but provides few details. And it leaves the issue to the G20 finance ministers to work out what regulations are appropriate. A G20-appointed commission is expected to deliver its recommendations in the fall.