World agriculture today faces pressure from many sources. On the production side, the amount of unused arable land worldwide has dwindled. Overworked soils are becoming eroded and degraded, and overpumped aquifers are being depleted. Meanwhile, as the global population grows and increasing biofuel production converts grain into fuel for cars, demand for food continues to climb. In Chapters 2 and 9 of Plan B 4.0, Lester Brown discusses these challenges.