Global Agriculture as an Energy Transfer System and the Energy Yield of World Agriculture 1961-2013

摘要

The global agricultural system is an energy transfer system converting solar radiation to stored chemical energy in the biosphere through photosynthesis and animal metabolism. Stored energy in the agricultural system is principally in the form of carbohydrates, proteins, fats, and oils that humanity appropriates for food, fiber, and fuel. The total annual production of global agriculture was tabulated using data from the Food and Agriculture Organization from 1961 to 2013. Annual agricultural production for each agricultural item (T y~-1) was converted to energy yield (RJ y~-1 ) utilizing published proximate analyses (% moisture, % protein, % carbohydrate, % fat/lipid, and % ash). Global agricultural energy yield grew linearly over the 1961-2002 interval. From 2002 onward, global agricultural energy yield also grew linearly, but at a rate 2 times the 1961-2002 rate. Overall, agricultural energy yield more than tripled from 1961 to 2013. Unsurprisingly, energy output of global crops dominated, averaging 85.5 ± 0.4% of total energy output. Livestock and poultry production averaged 13.6 ± 0.4% of annual agricultural energy output, while world fisheries and aquaculture averaged 0.8 ± 0.1% of global energy output. From 1961 to 2013, the feeding potential of global agricultural energy yield exceeded the human metabolic energy requirement by an average multiple of 2.1 ± 0.18. Thus, agricultural production is more than sufficient to feed "The Global Mouth" into the future, and feeding world population is not a production problem per se. Instead, the inability of global agriculture to meet worldwide food requirements results from systemic energy losses associated with significant global food waste, diversion of food energy as feed to livestock and poultry, and appropriation of primary agricultural output for biofuels synthesis.