TED.com talk Like all predictions of the future the precis nature of the scenario will be different and the timing may be out. BUT ...............

with global warming as fact (debate the cause not the observation - please) there will be a squeeze, if not called a crisis. And almost (I hope) in my lifetime.
We have wars over water supply, which is directly about food production. The usable geography of a given food production is moving away from the equator. New Scientist reports findings: yields will reduce too.

The talker above talks in calories not tonnage and Africa is thus a net importer of calories. China is a net exporter, compare that to the BBC R4 Extra programme from a journalist who lived through the excesses of Mao and didn't see the full extent of starvation until after. (30 Million deaths - 5% of population).
They learned, will we?