Besides asking whether today's agricultural production could sustain ten billion vegetarians, one should ask whether it would match the wants of ten billion eating what they could afford. Earlier, I cited Parikh's (1993a[Par3a]) projection often billion in 2050. He also estimated the farm production necessary to match their wants. Of his projections of wants from income growth, he wrote, ``They imply nations of obese gluttons." So he projected demand by a method respecting some calorie constraint. For ten billion people, his projected need for crops comes to 4,432 cal and 101 g of protein/day/ca. In other words, Parikh projected that the incomes of the ten billion would raise their demand for calories from crops about one-third above the total production from today's agriculture, which I tallied in Table A-1 in Appendix A. The demand of the ten billion for protein, on the other hand, would be more or less the present total production (Parikh, 1993a[Par3a]).
Earlier, Sanderson (1988[San88]) also carefully projected population and income growth, region by region. He estimated the corresponding growth in per capita consumption from a relation he found between income and original calories, i.e., calories in plants eaten directly plus the calories fed to animals and not recovered in milk, meat, etc. From nation to nation, he projected that original calories would climb to about 10,000/day/ca as annual income rose to 5,000 1976 dollars and leveled off. Sanderson's projected per capita demand of greater than 10,000 cal/day by 2075 AD. exceeds Parikh's projection twofold. Sanderson's projection would require greater than three times the 3,122 cal/day I calculated for present production and ten billion people.
A European projection of diets decreased cereals and oils, increased potatoes and fruit, and kept pork steady but increased other animal products. Although it left the caloric content steady near 3,400/day, more animal products would mean more of what Sanderson called original calories (Rabbinge et al., 1992[R92]). Under the rubric ``end use analysis," Bender analyzed reducing original calories in diets (Bender, 1993[Ben93]).
Finally, Seckler (1993[Sec93]) spied a subtle slowing of grain consumption. The consumption of cereal and oilseeds annually rose 4.3% from 1960-1973, but since 1977 it has risen linearly and more slowly. Seckler concluded, ``At the global level the demand for both food and feed grains will grow at rather slow and decreasing rates over the future corresponding with population growth; and not with economic growth .... Malthus is very much alive, but the complex of factors that created the green revolution succeeded in buying us enough time to get over the hump of population growth, and we are now comfortably on the downward slope."
The disparity among projections need not confuse us. In a few words, the disparity tells us that a vegetarian diet for ten billion could be furnished by present agricultural production but that production totaling 10,000 cal for ten billion obviously would exceed the capability of present agriculture on present cropland.