Earth is running out of room.

• Author: Brown, Lester R.

THE WORLD is entering a new era, one in which it is far more difficult to expand food output. Many knew that this time would come eventually; that, at some point, the limits of the Earth's natural systems, cumulative effects of environmental degradation on cropland productivity, and shrinking backlog of yield-raising technologies would slow the record increase in food production of recent decades. Because no one knew exactly when or how this would happen, food prospects were debated widely. Now, several constraints are emerging simultaneously to slow that growth.

After nearly four decades of unprecedented expansion in both land-based and oceanic food supplies, the world is experiencing a massive loss of momentum. Between 1950 and 1984, grain production expanded 2.6-fold, outstripping population growth by a wide margin and raising the grain harvested per person by 40%. Growth in the fish catch was even more spectacular--a 4.6-fold increase between 1950 and 1989, thereby doubling seafood consumption per person. Together, these developments reduced hunger and malnutrition throughout the world, offering hope that these biblical scourges would be eliminated one day.

In recent years, these trends suddenly have been reversed. After expanding at three percent a year from 1950 to 1984, the growth in grain production has slowed abruptly, rising at scarcely one percent annually from 1984 until 1993. As a result, grain production per person fell 12% during this time.

With fish catch, it is not merely a slowing of growth, but a limit imposed by nature. From a high of 100,000,000 tons, believed to be close to the maximum oceanic fisheries can sustain, the catch has fluctuated between 96,000,000 and 98,000,000 tons. As a result, the 1993 per capita seafood catch was nine percent below that of 1988. Marine biologists at the United Nations Food and Agriculture Organization report that the 17 major oceanic fisheries are being fished at or beyond capacity and that nine are in a state of decline.

Rangelands, a major source of animal protein, also are under excessive pressure, being grazed at or beyond capacity on every continent. This means that rangeland production of beef and mutton may not increase much, if at all, in the future. Here, too, availability per person will decline indefinitely as population expands.

With both fisheries and rangelands being pressed to the limits of their carrying capacity, future growth in food demand can be satisfied only by expanding output from croplands. The increase in demand for food that was satisfied by three food systems must now be satisfied by one.

Until recently, grain output projections for the most part were simple extrapolations of trends. The past was a reliable guide to the future. However, in a world of limits, this is changing. In projecting food supply trends now, at least six new constraints must be taken into account:

* The backlog of unused agricultural technology is shrinking, leaving the more progressive farmers fewer agronomic options for expanding food output.

* Growing human demands are pressing against the limits of fisheries to supply seafood and rangelands to supply beef, mutton, and milk.

* Demands for water are nearing limits of the hydrological cycle to supply irrigation water in key food-growing regions.

* In many countries, the use of additional fertilizer on currently available crop varieties has little or no effect on yields.

* Nations that already are densely populated risk losing cropland when they begin to industrialize at a rate that exceeds the rise in land productivity, initiating a long-term decline in...