Reproduced, with permission, from:
U.S. Office of Technology Assessment (OTA). 1991. Changing by degrees: Steps to reduce greenhouse gases. Washington, D.C.: Government Printing Office.
Food production involves activities up to and including harvest---cultivation, manufacture and application of fertilizers and pesticides, irrigation, and other practices (see figure 8-1). In 1985, the world's production of plant crops exceeded 3 billion metric tons, 60 percent of which was grains; meat, fish, and dairy products amounted to an additional 0.75 billion metric tons (114, 133). In developed countries, agriculture represents about 3 percent of the gross domestic product (GDP) output, whereas in some developing countries it contributes as much as 48 percent of GDP (109).
World food production has increased rapidly during the last 40 years, although per-capita production leveled off in the mid-1980s (114, 133). For example, grain yields per hectare more than doubled between 1950 and 1984 (12). To achieve this, existing agricultural lands and marine fisheries have been exploited more intensively, with heavy dependence on fossil fuel, commercial fertilizers and pesticides, and water---worldwide fertilizer use increased ninefold, irrigated acreage tripled, and farm tractor fleets quadrupled. Worldwide consumption of nitrogen fertilizers increased by 60 percent from 1975-76 to 1985-86 alone, to about 70 million metric tons of nitrogen (111). Water use for agriculture also has grown rapidly; more water is consumed in global agriculture than in all other applications combined (2, 62).[1]
Agriculture also has expanded (and continues to expand) into previously uncultivated areas that are only marginally suited for farming or ranching, including many mountainous and tropical forest areas. Varied environmental stresses such as water pollution, soil erosion, downstream flooding, and loss of biodiversity have come with this expansion.
A substantial portion of world crops is fed to animals. Nearly 50 percent of world coarse grain (ie., barley, corn, oats, rye, sorghum) production, and over two thirds in the United States, as well as over 30 percent of the world's fisheries catch, is used for animal feed (89, 115). Livestock populations have increased rapidly since 1950 and exceeded 4 billion in 1988[2], with India having the largest share (152). About one-third were cattle, and 8 percent of these were in the United States. Chicken populations are also quite large, totaling about 9.7 billion worldwide and about 1.3 billion in the United States alone (152).
Post-harvest activities take food, once harvested or killed, through a varying series of steps (ie., transportation, processing, packaging, marketing, storage, and cooking) (see figure 8-1). In industrialized countries such as the United States, most of the fossil fuel-related and CFC emissions associated with the food system result from post-harvest activities. Cooking accounts for a relatively small portion of post-harvest emissions in industrialized countries. In developing countries, however, cooking (mostly with coal or biomass) is probably the most important post-harvest source of emissions.
2 Includes cattle, sheep, goats, pigs, horses, buffaloes, and camels.
SOURCE: Office of Technology Assessment, 1991.
