On their way to the next UN food summit, delegates should take an introductory lesson in global land use by peering out of their aeroplane window. Others can take the same lesson on Google Earth. Set the camera to 35,000 feet, wiggle your mouse to get the image moving at a few hundred miles per hour and spend a few hours watching as you cross continents. The first surprise is how long it takes you to encounter a city or town of any size. More surprising is how hundreds of miles can go by without so much as a sniff of a cropped field.

The soaring cost of food over the past year and accompanying riots in some countries has raised the ghost of Thomas Malthus, the 19th-century reverend-cum-economist who advocated birth control to prevent an incipient global food famine. Never mind Peak Oil, a growing number of environmentalists are saying, we are close to approaching Peak Food: the moment that global food production peaks before mankind slumps into a long, slow agonising death by famine. According to this thesis, the Earth is already straining every sinew to feed us, but even this level of food production cannot be sustained as the soil degrades from the effects of overfarming, and the Earth warms, turning swaths of productive land into desert.

This thesis does not stand up to examination. Have a look at this statistic: the total landmass cultivated for arable crops in 2006, according Food and Agriculture Organisation of the United Nations (FAO), was 1.402 billion hectares - or 14 million sq km. In other words, all the world's cereals and vegetables are grown on an area equivalent to the USA and half of Canada. A further 34 million sq km - equivalent to the rest of North America, South America and two thirds of Australia - is given over to grazing, much of it extensive, unimproved grassland. The rest of the world - equivalent to the whole of Europe, Asia, Africa, Indonesia plus a third of Australia - is not used for food production in any way.

Some of this land, of course, is desert, mountain or rainforest, which either cannot be used for agriculture at all or would require irrigation, engineering or clearance. But a vast amount of it could quite easily be converted into agriculture, but has until now not been needed. Take Russia, which, apart from its northern fringe of tundra, spans the temperate belt. Just 7 per cent of Russia is turned over to arable crops, and another 5 per cent to grazing.

Moreover, the quantity of agricultural land in Russia is shrinking: 23 million hectares of arable land - equivalent to the whole of Britain - have been abandoned since the end of communism.

For Russia, read the world: the background to rising food prices is the shrinkage of global agriculture over the past decade and a half.

Globally, less food is being produced on even less land than was the case in the early 1990s. Take the US, which according to the FAO was producing 1,210kg of cereals per person per year between 1990 and 1992 and 1,104 kg between 2001 and 2003. Or Canada, at one time the “world's bread basket”, where cereal production fell from 1,905 kg per person per year in 1990-92 to 1,384 kg in 2001-03.

The reason for the fall in cereal production over 15 years has not been soil degradation or climate change: while crops yields are not increasing as fast as they were doing in the 1960s, they have still risen by 1-2 per cent per annum over the past 15 years. Rather, the decrease in production has been a straightforward response to overproduction.

Remember the grain mountains of the 1980s? They resulted in a collapse in prices that in turn persuaded grain producers to contract their operation. Now that prices are rising again the opposite has happened: the FAO estimates that this year's wheat harvest will rise by 13 per cent as a result of extra planting, putting downward pressure on prices next year.

That, of course, will come too late to stop food riots and hunger among the world's poor. But contrary to the Marxist view, this year's spike in food prices is not “market failure”. The main reason that the price of rice on international markets has surged by 141 per cent since January is the attempt of rice-producing countries to control inflation in their own economies by banning or restricting exports.

Hardly surprisingly, net rice importers have suffered as a result of the collapse in rice available on international markets. Moreover, the restrictions worsen the situation by deterring rice producers from increasing production because they are unable to benefit from high export prices.

A little belatedly, the EU did at least suspend its set-aside scheme last September, meaning that European farmers will not be forced to leave 10 per cent of their land fallow. But still, quotas and subsidies distort the marketplace. According to the Washington-based think-tank the International Food Policy Research Institute, 30 per cent of food inflation is down to biofuel subsidies, which divert land from food production: 80 million hectares worldwide have been turned over to the crops. There may be a case for governments to invest in converting the by-products of food crops - the straw and chaff - into biomass, but to pay farmers to switch from food production is a highly irresponsible policy at a time of rising food prices.

Biofuel subsidies have added to the mix of quotas, subsidies and price controls that have been perverting agricultural markets for decades, giving us glut and now shortage. The very worst thing that could happen now is for the world to shut down global trade in food in the name of protecting food security. It is societies dependent on local food who are only one bad harvest away from starvation. World markets, if only they are allowed to operate efficiently, will make sure that the world's vast additional capacity for food production can be realised.

Ross Clark is the author of How to Label a Goat: the Silly Rules and Regulations that are Strangling Britain

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