I don’t want to alarm anybody, but maybe it’s time for Americans to start stockpiling food.

No, this is not a drill.

You’ve seen the TV footage of food riots in parts of the developing world. Yes, they’re a long way away from the U.S. But most foodstuffs operate in a global market. When the cost of wheat soars in Asia, it will do the same here.

Many parts of America, long considered the breadbasket of the world, are now confronting a once unthinkable phenomenon: food rationing. Major retailers in New York, in areas of New England, and on the West Coast are limiting purchases of flour, rice, and cooking oil as demand outstrips supply. There are also anecdotal reports that some consumers are hoarding grain stocks.

At a Costco Warehouse in Mountain View, Calif., yesterday, shoppers grew frustrated and occasionally uttered expletives as they searched in vain for the large sacks of rice they usually buy.

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.