Actually, the food available per person has increased each year until the mid 80's, but has been declining for the last ten years. Natural disasters are unpredictable, usually not included in projections, but could become more frequent if the forecasted effects of global warming materialize. The ability to control environmental degradation is becoming increasingly difficult. The impact of problems with allocating scarce water are just now beginning to be appreciated. Grain Harvest Projections World farmland planted in grain increased until 1980 and then started to decline because of environmental factors such as soil erosion, waterlogging and salting of irrigated land, air pollution, and water shortages.
Urban sprawl reduces farmland at the rate of one acre for each five births.
The loss of farmland has been compensated for by increasing the yield per acre by the development of disease and drought resistant grains which respond well to fertilizers. However, there are growing indications that efforts to increase crop yields have peaked. Available crop varieties have approached the agronomic limits of response to fertilizer and its use has declined for five consecutive years. Large dams built to irrigate arid desert lands are trapping 25 to 75 percent of the sediments normally carried downstream to become farmland seasonal nutrient replenishment. The trapped sediment also significantly reduce the dams irrigation water storage capacity.