Food security: What crops will feed the world if we run out of farmland?
In The Future, Will We All Be Forced To Eat Yams?
The citizen’s guide to the future.
June 12 2012 6:30 AM

I Think, Therefore I Yam

When farmland is scarce, will we all eat roots and tubers?

A farmer holds up a bunch of cassava roots, dug up from his farm in Oshogbo, in Osun State on August 26, 2010.
A farmer holds up a bunch of cassava roots, dug up from his farm in Osogbo, in Osun State on Aug. 26, 2010.

Photograph by Pius Utomi Ekpei/AFP/Getty Images.

Since Thomas Malthus, alarmists have been pointing out that the world has a finite amount of arable land, whereas its human population keeps growing. Common sense would seem to dictate that eventually there won’t be enough farmland to feed everyone, and catastrophic famine will ensue.

Will Oremus Will Oremus

Will Oremus is Slate's senior technology writer. Email him at or follow him on Twitter.

The incredible pace of technological innovation has staved off that eventuality for hundreds of years, seemingly making fools of Malthus and intellectual successors like Paul R. Ehrlich, who in his 1968 book The Population Bomb predicted mass starvation in the 1970s and 1980s. Instead, the green revolution brought high-yielding crop varieties, fertilizers, and pesticides to hungry countries such as Mexico and India, leading to a doubling of food production between 1950 and 2010 with only a 10 percent increase in the amount of farmland. And in the past decade, global population growth has slowed, a deeply encouraging sign (and one that neither Malthus nor Ehrlich envisioned).

Yet the world’s food future may be shakier than ever. It’s not because of the absolute number of people or even the amount of available farmland, but because of what those people eat and how that farmland is used. In short, there’s enough land to feed the world—but not enough to feed the world Big Macs. Absent another productivity revolution, the 21st century might raise a new question for farmers: If beef provides the smallest amount of calories per acre of land required to raise it, what crops provide the most?


Today about 1 billion people “eat like Westerners,” in the words of University of California-Berkeley resource economist David Zilberman. That means, basically, that they wolf down historically unprecedented quantities of meat and dairy—getting up to half their calories from animals rather than plants. Meat consumption appears to be reaching a plateau in the United States and Europe, but it’s only now taking off in many poorer parts of the world. Zilberman believes that 40 years from now there may be 3 billion or 4 billion people who eat like Westerners. And that’s a problem, because every pound of edible beef takes some 20 pounds of grain to produce. Give a man a 12-ounce porterhouse and you feed him for a day; give him a pound of grain and you can feed a dozen other people for a day, too. (Raising meat also requires five to 10 times as much water as growing grains, using up a resource that may prove even scarcer than land.)  

In a 2009 study, the Food and Agriculture Organization estimated that production would have to rise 70 percent by 2050 to meet the world’s needs. But Zilberman and others believe that the continued rise of the global middle class could result in a number much higher than that. By his lights, even if we were to develop all of the world’s remaining arable land—much of it in Brazil and other Latin American countries—we’d have to wring twice as much productivity from every acre of land under cultivation. While that’s not impossible, it won’t be easy. Water is one obstacle, as is the increasing proportion of grain that’s being used for biofuels rather than food. A third problem, less talked about, is that intensive farming practices appear to be degrading the world’s topsoil, raising the possibility that usable farmland will actually become scarcer in future decades. Climate change could exacerbate the problem, as droughts turn what today is arable land into desert. (Taking off on the concept of “peak oil,” agriculture alarmists have labeled this specter “peak soil.”)

If that happens, people may have little choice but to eat less meat. What would they eat instead? Vegetables are crucial to nutrition, but they aren’t the most potent energy sources. Grains are better, but people already eat plenty of them, and they’re not at the top of the list in terms of the amount of nutrition they provide per unit of land. That honor goes to roots and tubers like garlic, sunchokes, and sweet potatoes.

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