Long-term shortage of food and live animals

Improvements are unlikely. Our past success has brought us alarmingly close to the ecological ceiling. There is a growing sense in the scientific community that it will be difficult to restore the rapid rise in agricultural yields we saw between 1950 and 1984. In agriculturally advanced nations there just isn't much more that farmers can do.

Humanity already uses, destroys, or "co-opts" almost 40 percent of the potential output from terrestrial photosynthesis. Doubling the world's population will reduce us to fighting with insects over the last scraps of grass.