We drive, they starve. The mass diversion of the North American grain harvest into ethanol plants for fuel is reaching its political and moral limits.

	A demonstrator eats grass in front of a U.N. peacekeeping soldier during a protest against the high cost of living in Port-au-Prince

"The reality is that people are dying already," said Jacques Diouf, of the UN's Food and Agriculture Organization (FAO). "Naturally people won't be sitting dying of starvation, they will react," he said.

The UN says it takes 232kg of corn to fill a 50-litre car tank with ethanol. That is enough to feed a child for a year. Last week, the UN predicted "massacres" unless the biofuel policy is halted.

We are all part of this drama whether we fill up with petrol or ethanol. The substitution effect across global markets makes the two morally identical.

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.

Argentina, Canada, and Eastern Europe are joining the race.

The EU has targeted a 5.75pc biofuel share by 2010, though that may change. Europe's farm ministers are to debate a measure this week ensuring "absolute priority" for food output.

"The world food situation is very serious: we have seen riots in Egypt, Cameroon, Haiti and Burkina Faso," said Mr Diouf. "There is a risk that this unrest will spread in countries where 50pc to 60pc of income goes to food," he said.

Haiti's government fell over the weekend following rice and bean riots. Five died.

The global food bill has risen 57pc in the last year. Soaring freight rates make it worse. The cost of food "on the table" has jumped by 74pc in poor countries that rely on imports, according to the FAO.

Roughly 100m people are tipping over the survival line. The import ratio for grains is: Eritrea (88pc), Sierra Leone (85pc), Niger (81pc), Liberia (75pc), Botswana (72pc), Haiti (67pc), and Bangladesh (65pc).

This Malthusian crunch has been building for a long time. We are adding 73m mouths a year. The global population will grow from 6.5bn to 9.5bn before peaking near mid-century.

Asia's bourgeoisie is switching to an animal-based diet. If they follow the Japanese, protein-intake will rise by nine times. It takes 8.3 grams of corn feed to produce a 1g of beef, or 3.1g for pork.

China's meat demand has risen to 50kg per capita from 20kg in 1980, but this has been gradual. The FAO insists that this dietary shift is "not the cause of the sudden food price spike that began in 2005".

Hedge funds played their part in the violent rise in spot prices early this year. To that extent they can be held responsible for the death of African and Asian children. Tougher margin rules on the commodity exchanges might have stopped the racket. Capitalism must police itself, or be policed.

Even so, the funds closed their killer "long" trades in early March, causing a brief 20pc mini-crash in grains. The speculators are now neutral on the COMEX casino in New York.