Global food prices have more than doubled over the last decade, increasing the burden on the world’s poorest to feed themselves. If this trend continues, spreading food unrest will likely lead to political instability. This is not just an agricultural problem, writes Lester Brown, author of “Full Planet, Empty Plates,” but one involving energy, water resources, transportation and health and family planning.

Producing enough grain to make it to the next harvest has challenged farmers ever since agriculture began. But now, the challenge is deepening as new trends--falling water tables, plateauing grain yields and rising temperatures--join soil erosion to make it difficult to expand production fast enough.

As a result, world grain carryover stocks have dropped from an average of 107 days of consumption a decade or so ago to 74 days in recent years.

World food prices have more than doubled over the last decade. Those who live in the United States, where 9% of income goes for food, are largely insulated from these price shifts.

But how do those who live on the lower rungs of the global economic ladder cope? They were already spending 50% to 70% of their income on food. Many were down to one meal a day already before the recent price rises.

Now millions of families routinely schedule one or more days each week when they will not eat at all. What happens with the next price surge?

Belt tightening has worked for some of the poorest people so far, but this cannot go much longer. Spreading food unrest will likely lead to political instability. We could see a breakdown of political systems. Some governments may fall.

As food supplies have tightened, a new geopolitics of food has emerged. In that brave new world, the global competition for land and water is intensifying and each country is fending for itself.

At the same time, we cannot claim that we are unaware of the trends that are undermining our food supply--and thus our civilization. We know what we need to do.

There was a time when, if we got into trouble on the food front, ministries of agriculture would offer farmers more financial incentives, like higher price supports, and conditions would soon return to normal.

But responding to the tightening of food supplies today is a far more complex undertaking. It involves the ministries of energy, water resources, transportation and health, among others.

Because of the looming specter of climate change that is threatening to disrupt agriculture, we may find that energy policies will have an even greater effect on future food security than agricultural policies do.

In short, avoiding a breakdown in the food system requires the mobilization of our entire society.

Environmentalists have talked for decades about saving the planet, but now the challenge is to save civilization itself.

This is about restructuring the world energy economy and doing it before climate change spirals out of control and before food shortages overwhelm our political system.

Editor’s note: This article is adapted from Full Planet, Empty Plates: The New Geopolitics of Food Scarcity (W.W. Norton) by Lester Brown.