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| Fig. 1: The total land areas of various interesting metrics as an illustration of the underlying scales of the land requirements. [1,6] (Source: E. Courtney) |
The Industrial Revolution sparked large-scale global demand for energy, particularly hydrocarbons such as oil and coal. However, despite the current plenitude of these fuels, their inherently limited quantities has ignited scientific and economic interest in establishing renewable source of energy on scales sufficient to power modern civilization. Biofuels are a particularly enticing option, due in large part to the existing ability of plants to convert sunlight into chemical energy and the existing agricultural techniques already developed to grow crops on large scales. However, there exists an enduring question - namely, the ability of Earth's arable land to both feed and fuel a population of multiple billions.
The world population reached 8 billion (8×109) people in late 2022; while recommended daily diets for adult humans range from 2000 to 3000 food calories per day, this report will use 1000 food calories per person day as a minimum baseline to estimate the minimum number of calories required to maintain survival of this population. [1] Thus, a minimum daily supply of 8×1012 calories is required to feed the world; therefore, at 4,184 joules per food calorie, the world must produce at least 1.2×1019 joules per year to support a population of 8 billion people. For comparison, the BP Statistical Review of World Energy in 2022 reported that well over 4.5×1020 joules of energy were produced from oil, natural gas, and coal in 2021 - thus, if biofuels are to entirely replace fossil fuels, significantly more land must be used for biofuels than for food. [2]
In 2020, the National Agricultural Statistics Service that the average yearly yield per acre of corn in the USA was 172.3 bushels per acre, at about 2,380 food calories per kilogram - assuming that humans can extract 65% of the calories from field corn as a ruminant animal like a cow. [3,4]
| Energy Yield | = | 172.3 bu ac-1 × 56 lbs bu-1 × 2380 kcal lb-1 × 4184 J kcal-1 × 247 ac km-2 |
| = | 2.37 × 1013 J km-2 |
Thus, a population of 8 billion people could be sustained at 1000 food calories per day if roughly 506,000 square km of arable land were dedicated to growing field corn. However, the Food and Agriculture Organization (FAO) of the UN reported in 2001 that 1,506 million hectares of arable land was used as farmland in 1997-1999, representing 36% of the world's total arable land - from this, one concludes the world has almost 4.2 billion hectares (4.2×107 million km2) of potentially arable land (crop and pasture). Therefore, while less than 1.5% of the world's arable land would be absolutely required to sustain a population of 8 billion people - less than 3% at a healthier diet of 2000 food calories per day - actual usage was over one-third of the world's arable land to feed the population of what was then 6 billion people. The discrepancy between the theoretically minimum amount of land required for food, and the actual land area used, is due to modern standards of living and market demand for land-intensive foods such as red meat..
With the complete conversion of fiber and starch, 1 bushel of corn can produce 3.08 gallons of ethanol. [5] At roughly 80 million joules per gallon, assuming a fuel efficiency of 35% (comparable to the efficiency of gasoline in most modern combustion engines), the world's fossil fuel consumption requires 5.2×1012 bushels of corn to be converted to ethanol per year, requiring 1.4×108 km2 of farmland, requiring over 9×107 km2 more farmland than is currently on Earth, an area of farmland larger than the total land areas of Asia and Africa combined.
The world's current population could theoretically survive on less than 3% of the world's arable land - less than a tenth of the land area actually used for agriculture today. However, while biofuels may ameliorate fuel shortages or provide a means of energy storage, corn- based ethanol cannot entirely fulfill the energy demands currently satisfied by fossil fuels. As shown in Figure 1, without considering the land area used to feed the world, a total replacement of fossil fuels by corn ethanol will require more than three times the total arable land on earth to be dedicated to growing corn for ethanol.
© Elijah Courtney. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] P. H. Gleick , "Basic Water Requirements for Human Activities: Meeting Basic Needs," Water Int. 21, 83 (1996).
[2] "BP Statistical Review of World Energy2022," British Petroleum, June 2022.
[3] "Crop Production," U.S. Department of Agriculture, November 2022.
[4] G. Lardy, "Feeding Corn to Beef Cattle," North Dakota State University Extension, AS1238, May 2018.
[5] R. H. Mumm et al., "Land Usage Attributed to Corn Ethanol Production in the United States: Sensitivity to Technological Advances in Corn Grain Yield, Ethanol Conversion, and Co-Product Utilization," Biotechnol. Biofuels 7, 61, (2014).
[6] J. Bruinsma, Ed., World Agriculture: Towards 2015/2030, an FAO Perspective, 1st Ed. (Routledge, 2003).