As humankind entered the twenty-first century, approximately 50% (estimates of this kind are difficult to make and are subject to revision) of terrestrial net production and most aquatic net production remain for life support, goods, and services, and to support all organisms with which we share the Earth. In 2000, the estimated 6.1 billion people in the world each required about 1 million kcalyr-1 or a total of 6 x 1015 kcal of food energy needed to support the human biomass. The food estimated to be harvested worldwide is inadequate because of poor distribution, waste, and low protein quality. Only about 1% of food comes from the sea, and most of that is of animal origin (the small size and rapid turnover of phytoplankton preclude the accumulation of harvestable biomass). Because overfishing has become a worldwide phenomenon, obtaining more food from the sea seems out of the question. As a matter of fact, aquaculture is already responsible for much of the seafood and fish in today's markets.
The gap between rich and poor countries in food production has soared over the past half century, because some countries cannot afford the energy subsidies necessary to support high-yield genetic varieties. About 30% of all people live in a developed country, and this is defined as a country with a per capita gross national product (GNP) of more than US$ 8000. Likewise, developed countries have a low rate of population growth (1% per year or less). Sixty-five percent of the world's people live in underdeveloped countries, which have a per capita GNP of less than US$ 300, often less than US$ 100, and they also have a high population growth rate (more than 2% per year). Underdeveloped countries have a low food production per hectare since they cannot afford the energy subsidies necessary for high yields. These two masses of humanity are sharply divided.
Forests, grasslands, or organic farming are all models for natural, unsubsidized, solar-powered ecosystem or landscape including energy inputs (rain and sunlight), natural by-products (carbon dioxide and water runoff), yield (net primary production), and energy loss or respiration (entropy or heat loss from the system). In contrast, in a human-subsidized, solar-powered ecosystem or landscape, in addition to rain and solar energy inputs, large amounts of fossil fuels, fertilizers, and chemical pesticides enter as inputs. The frequent leakage of unnatural by-products from the system requires significant sums of money and energy resources to clean them up.
Cropland has increased about 15% worldwide during recent years, but in Europe, the United States, and Japan, the harvested area has decreased. Less-developed countries have increased their food supply as much by increasing the land area under cultivation as by increasing yields. If such a trend continues, more and more marginal land will be cultivated at increasing cost and the risk of environmental degradation.
For more than half the world's population, wood is the chief fuel used for cooking, heating, and light industry. In the poorest countries, wood is burned much faster than it can be grown, so forests are turned into shrublands and then into deserts. The shortage of firewood has been referred to as the 'other energy crisis', as oil is the energy crisis most talked about. For the African countires of Tanzania and Gambia the consumption of wood fuel per capita is about 1.5 tyr~ and 99% of the population uses wood as fuel. In North America and other regions with large standing stocks of vegetation, more people have become interested in using biomass, both from forest and agricultural lands, as fuel to supplement or replace dwindling supplies of petroleum, which is a nonrenewable resource.
Scientists at The Land Institute located near Salina, Kansas, for example, are devoting much thought and research to the feasibility of harvesting native perennial species on the prairie lands of the Midwest. Native prairies are multispecies ecosystems that replenish the fertility of the soils, have deeper roots to build the soil, and are better buffered against nature's vagaries. As such natural, unsubsidized systems and landscapes could be turned to 'agricultural ends', as scientists such as Wes Jackson believe, they would have great promise to prevail as time-sustainable agriculture.
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