Food prices have doubled in little more than a year, provoking riots in many countries, including Haiti, Indonesia and Bangladesh. In Britain, one calculation suggests that supermarket food prices have risen by 15% in a year, adding £800 to a family’s annual shopping bill.

The United Nations talks of a “silent tsunami” that threatens 100m of the world’s poorest people with starvation. Gordon Brown held an emergency summit on what he described as a world food crisis that was killing 25,000 people a day from hunger-related diseases, that number growing for the first time in 40 years.

Food prices, he said, were the highest since 1945 because supply was lagging behind demand. And as prices have soared, so the finger of blame is being pointed. There is the rise of China and the fact that increasing wealth is producing a nation of meat-eaters, with every 1kg of beef requiring 6kg of grain to produce.

There is the switch to biofuels, which is taking valuable farm acreage and using it for energy rather than food production. There is climate change, which has produced a run of bad harvests, including Australia’s severest drought in living memory.

And there are the financial speculators who, since the credit crisis broke in the summer, have been pouring money into commodities, driving prices higher.

Could it be, however, there is a more straightforward explanation: that the world is running out of the ability to feed itself. Are there too many people and too little food?

It is more than 200 years since Thomas Malthus gave us his grim formula: “Population, when unchecked, increases in a geometrical ratio. Subsistence increases only in an arithmetical ratio. A slight acquaintance with numbers will show the immensity of the first power in comparison of the second.”

If population indeed increased geometrically – 1, 2, 4, 8, 16, 32 – while food production could only rise arithmetically as new acreage was brought into production – 1, 2, 3, 4, 5 – starvation would stalk the land, poverty would be endemic and, in the end, population growth would be constrained by food availability.

It did not happen. When Malthus wrote at the end of the 18th century, agricultural methods had barely changed in centuries. The industrial revolution, new techniques of food production and the opening up of world trade prevented the Malthusian nightmare. Between 1801 and 1901, Britain’s population grew from 10.5m to more than 38m.

But fears of a Malthusian nightmare on a global scale did not go away. Forty years ago Paul Ehrlich wrote The Population Bomb, which predicted that “population explosion” – he was the first to use the term – would lead to disaster for mankind.

Hundreds of millions would die as a result of starvation in the 1970s and 1980s, he predicted, and nothing could be done about it.

The world’s death rate was about to increase substantially because of a lack of food. Even America faced a future of declining population and falling lifespans. People in the poor countries would fare much worse.

Ehrlich appeared to be on to something. The early 1970s saw a sharp rise in food and other commodity prices, similar to the current surge.

The Club of Rome, a group of thinkers, warned that the world was running out of many commodities and that people’s expectations of rising living standards would have to be curbed. Its report, Limits to Growth, published in 1972, became a huge talking point.

But Ehrlich was wrong and so was the Club of Rome. Like Malthus, they failed to anticipate important changes. The “green revolution” in agriculture boosted production significantly, particularly in poor countries like India.

What about now? Can the world cope with a population rising from 6.5 billion to 9 billion by 2050? When 1.3 billion Chinese switch from rice to meat, does the rest of the world starve?

Some things are now certain. For years the European Union encouraged farmers to restrain their production to prevent surpluses building up. Set-aside subsidies have been an important part of the common agricultural policy. Farmers have been paid not to produce.

Last September, however, EU ministers agreed on a zero set-aside rate for 2007-8, to boost grain production by 10m tons. Set-aside no longer looks appropriate.

A big shift is inevitable on biofuels. A policy that ticked all the boxes – on the environment, reducing energy dependence on oil from fickle states and apparently limitless – looks like last year’s model. Brown, after his food summit, said Britain had to be more “selective” in its support for biofuels and would be pushing for change at EU level.

It has taken time for policy-makers to wake up to the danger of food shortages. Nearly a year ago, in May 2007, a UN report warned about the rush into biofuels. The challenge is to persuade America, reeling under high petrol prices and growing ever-larger acreages of biofuel crops, to change policy.

Another big shift, according to Paul Collier, author of The Bottom Billion, about the world’s poorest, has to be in the agricultural policies of developing countries.

For too long international agencies and western governments provided aid to peasant farmers in poor countries, believing it the best way to help them. What they need is something on a much larger scale, a new green revolution, Collier argues.

“The most realistic way is to replicate the Brazilian model of large, technologically sophisticated agro companies that supply the world market,” he says. “Large swathes of Africa could be used far more productively if properly managed by large companies. To contain the rise in food prices we need more globalisation, not less.”

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