AS CLIMATE-CHANGE negotiators from nearly 200 countries meet this week in South Africa, Carter Roberts, the World Wildlife Fund’s president, argues that the leading environmental challenge of this century won’t be global warming. It will be feeding people.

The WWF reckons that about 70 percent of the world’s land either is used to produce food or is unsuitable for that. Global population is heading from 7 billion toward a possible 10 billion by 2100. Per capita consumption rises as countries develop. Some vacant land may not be all that fertile.