Among the necessities for human life — indeed, all life — food obviously occupies a central place. In recent decades advances in agriculture and in the ability to distribute food around the world seemed to promise an end to the age-old scourge of famine.

But lately, threats have grown to the affordability and even availability of food. Staples such as grains have been hit especially hard. Some traditional food exporting countries are limiting or barring exports.

The United Nations says wheat prices have gone up by 130 percent worldwide, and soy prices by 87 percent, in the last year. Food now represents up to 80 percent of consumer spending in developing countries. The UN and the World Bank have joined humanitarian organizations in warning the crisis will only get worse.

Protests have escalated around the world in recent weeks over scarce food supplies and soaring prices. Haiti’s prime minister lost his job as a result; demonstrations have also hit Italy, the Philippines, Thailand, Indonesia, Egypt, Cameroon, Ivory Coast and other nations.

Here at home, though food costs are a much smaller part of household spending than in developing countries, and prices haven’t risen as fast as elsewhere, eggs still cost 25 percent more than last year, while milk and other dairy products have gone up by 13 percent. People driven to the edge by the economic crisis must increasingly rely on food stamps and on food banks that themselves face steeply rising costs.

Choices by transnational corporations and the governments they control are strong factors in this crisis. Global warming, which the Bush administration refuses to combat, has contributed to drought and other weather-related problems around the world. The Iraq war has raised oil prices, making shipping food supplies more expensive. Policies of industrialized countries to subsidize agribusiness and food exports have undermined agriculture in developing countries, depriving them of the ability to grow food sufficient for their populations.

And a very clear factor is the diversion of huge swathes of land to grow grain for biofuels, cutting food supplies and encouraging deforestation.

These policies need to be changed. Security means food security, too.