Leading article: The challenge ahead... how to feed the world over the coming century

Crowds in Haiti this week tried to storm the presidential palace. In Egypt, posters of President Hosni Mubarak were torn down by protesters. Last week, demonstrators in the Ivory Coast erected barricades in the city of Abidjan. There have been reports of violent protests in Cameroon, Bolivia, Senegal, Uzbekistan and Indonesia. Yet this is not merely another snapshot of our chaotic and troubled planet. There is a common factor behind all of these outbreaks of discontent: food.

Staples such as rice, wheat and maize have risen 40 per cent globally since the middle of last year. Grain stocks have fallen to alarmingly low levels. We are feeling the effects here in the UK in the form of rising inflation, but the pressure is much greater in poor countries, which spend a far larger proportion of their national income buying food.

Of course, farmers in developing nations will be benefiting from higher prices. But, overall, the trend is malign. According to the World Bank, higher food costs could drag an extra 100 million people below the subsistence line, rolling back the modest progress of recent years in enhancing prosperity in the world's most deprived countries.

So what lies behind higher food prices? One of the forces is a shortage of supply. Last year's flooding in Indonesia and Bangladesh, drought in Australia and cold weather in China and Vietnam have hammered crop yields. The sky-high price of diesel and petrol-based fertilisers has also constrained production. Another force is spiralling demand. Meat and dairy consumption is growing in booming economies such as China and India. In Asia, land formerly used for crops is being given over for the raising of cattle. And grain is increasingly being used for animal feed rather than food. Finally, there is the growth of the biofuel industry, which has seen farm land turned over for fuel production.

This all serves to demonstrate the complexity of the challenges of population growth, rising prosperity and climate change. To an extent, the market will shift to meet demand. World cereal production is projected to increase 2.6 per cent this year to a record 2.16 billion tons, according to a new United Nations report. But few analysts expect demand to ease off in the long term. And pressures on supply will surely only increase as the climate grows warmer. A less hospitable world will mean more expensive food.

The question is how to maximise supply in such conditions. Protectionism and the banning of exports are not the answer. In an integrated and global economy, the idea of agricultural autarky is a non-starter. Subsidies too are misguided. Consider the distortions and misery caused by George Bush's biofuel price guarantees for US farmers. In fact, the best way to encourage agricultural production in Africa, Asia and South America, where the food price crisis is at its most acute, is to abolish European and US subsidies to domestic grain farmers and to finalise the world free trade deal conceived in Doha seven years ago. And a moratorium should be called on the headlong rush from the developed nations to produce biofuels.

But in the immediate term, some form of serious international co-operation is necessary. Gordon Brown is right to propose that the World Bank, the International Monetary Fund and the UN work together to mitigate the social effects of this spike in world food prices. More support to food-importing countries and an increase in humanitarian aid is clearly needed.

Yet it is important to stress that this is not a passing problem. We seem destined to live in a hungrier world. A great challenge for our political leaders over the coming century will be to ensure that all those mouths can be fed.