The mass diversion of the North American grain harvest into ethanol plants for fuel is reaching its political and moral limits.
"The reality is that people are dying already," said Jacques Diouf, of the UN's Food and Agriculture Organization (FAO).
Mr Diouf says world grain stocks have fallen to a quarter-century low of 5m tonnes, rations for eight to 12 weeks. America - the world's food superpower - will divert 18pc of its grain output for ethanol this year, chiefly to break dependency on oil imports. It has a 45pc biofuel target for corn by 2015.
Brazil has the world's biggest reserves of "potential arable land" with 483m hectares (it currently cultivates 67m), and Colombia has 62m - both offering biannual harvests.
The catch is obvious. "The idea that you cut down rainforest to actually grow biofuels seems profoundly stupid," said Professor John Beddington, Britain's chief scientific adviser.