The number of farms and farmers has decreased significantly in most developed countries including the US (farming.htm). The ability of a country to potentially export food should be indicated by the ratio of food produced to population. I have summarized UN production data for 2002 for wheat, rice, maize/corn, and soybeans and then divided by the populations in foods2002.htm. The last column indicates that Argentina has the highest ratio and would be the most likely to export. China is just above the world average ratio. Actual historical export data for wheat, rice, and maize/corn (exports.htm) show that Argentina is a major exporter of wheat and maize/corn. China exports less than 10% of its production even though it is the largest producer. In fact, many of the largest producers export very little because they also have very large populations. In the export tables, I have divided percent exports by percent population growth to estimate how many years each country is likely to be able to export each food assuming zero net immigration. Only Argentina, Australia, Canada, and the USA have much long-term potential to export these foods. When the percentage world exports are divided by the world population growth rate of 1.27%/year between 2000 and 2001, one obtains estimates that international trade will consume the wheat exports in 13 years, the rice exports in 3 years, and the corn exports in 10 years.
Adults use 1700 to 3000 nutritional calories (chemical kilocalories) per day or about 2350 calories per day on average. Adolescent boys, very active men under thirty-five, and lactating women consume about 3000 calories per day while children one to six years require 1100 to 1600 calories per day. In the following, I assume two-thirds of the total calories for humans come from wheat, rice, corn/maize, and soybeans or from animals fed them. World production of these primary foods was 1,931,665,546 metric tons in 2002. A metric ton is 1000 kilograms or 1 million grams. Each gram of these primary foods produces about 3 calories/gram. Thus, the world supply of these foods could feed about
3(1.93 x 10^9)(1.00 x 10^6)/(2350)(365)
= (5.79 x 10^15)/(0.86 x 10^6) = 6.7 x 10^9 = 6.7 billion humans
if these foods were the only source of calories. However, if these foods provide only two-thirds of the total calories, then the maximum human population might be about 10 billion if no other animals were fed these foods. The current human population is 6.2 billion and is increasing at about 1.27 percent per year. Such calculations indicate that the UN estimate of 9.3 billion humans in 2050 is at or near the limit of our food supply. Of course, food is never uniformly distributed, so the starvation we are seeing today will become very wide spread before 2050 unless all countries rapidly approach zero population growth (an average of two children per female or less).