“In keeping with the new trend, hedge funds and investment banks have started buying up farms worldwide. Morgan Stanley, for example, already owns several thousands of hectares of agricultural land in Ukraine. An agriculture fund operated by Blackrock, a New York investment group, acquired more than 1,100 hectares (2,717 acres) in Britain's Norfolk County. Others are combing the world, from Russia to South America, for investment opportunities. In Argentina, prices for the most productive fields have increased by 80 percent in recent years.

The British hedge fund Emergent Asset Management is currently collecting €1 billion ($1.55 billion) to buy up African farmland south of the Sahara Desert.

"Hedge fund managers may not be good farmers," says Paul Christie, Emergent's marketing chief, "but with the right partners they can be good farm managers."

In rough terms, 1,000 hectares covers about four square miles.

After oil and minerals, food offers the next big market boom. Water supplies are involved too, of course, but in many places governments have scrambled to maintain publicly owned control of them. The water supply in the Great Lakes, shared by Canada and the US, is not to be used for commercial exploitation. Whether, and for how long, that prohibition holds up under severe climate change, no one can say.