Basic access to food is slipping out of reach for many people in developing countries.

The cost of the rice has risen by more than three-quarters in two months and the price of wheat has more than doubled in the same time.

The desperation in dozens of countries has turned deadly of late. In the past week alone there have been violent, food-related riots in Haiti, Indonesia, the Philippines and Cameroon.

For all the economists and consumers who hope high food prices are temporary, here’s one reason why they probably won’t be: Farm costs are skyrocketing, making permanently higher prices essential for farmers to keep expanding production.

Inflation is biting farmers world-wide. In New Zealand, farm wages are up as much as 20% this year, and the average price of a dairy cow has jumped to more than $1,900 – almost double last year’s average of about $1,000. In Thailand and Indonesia, farmers are complaining about sharp increases in the price of fertilizer and diesel fuel.

Two years ago the UN’s Food and Agriculture Organisation expected biofuels to help eradicate hunger and poverty for up to two billion people. Yesterday the UN secretary general, Ban Ki-moon raised real doubt over that policy amid signs that the world was facing its worst food crisis in a generation.

Since the FAO’s report in April 2006 tens of thousands of farmers have switched from food to fuel production to reduce US dependence on foreign oil. Spurred by generous subsidies and an EU commitment to increase the use of biofuels to counter climate change, at least 8m hectares (20m acres) of maize, wheat, soya and other crops which once provided animal feed and food have been taken out of production in the US.

Robert Zoellick, president of the World Bank, said this week that prices of all staple food had risen 80% in three years, and that 33 countries faced unrest because of the price rises.

A global rice shortage that has seen prices of one of the world’s most important staple foods increase by 50 per cent in the past two weeks alone is triggering an international crisis, with countries banning export and threatening serious punishment for hoarders.

With rice stocks at their lowest for 30 years, prices of the grain rose more than 10 per cent on Friday to record highs and are expected to soar further in the coming months. Already China, India, Egypt, Vietnam and Cambodia have imposed tariffs or export bans, as it has become clear that world production of rice this year will decline in real terms by 3.5 per cent.

Rice prices jumped 30 per cent to an all-time high on Thursday, raising fears of fresh outbreaks of social unrest across Asia where the grain is a staple food for more than 2.5bn people.

The increase came after Egypt, a leading exporter, imposed a formal ban on selling rice abroad to keep local prices down, and the Philippines announced plans for a major purchase of the grain in the international market to boost supplies. Global rice stocks are at their lowest since 1976.