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Sustainable Agriculture, Food Security, Corn Ethanol: Quantitative Study Problems
Sustainable Agriculture, Food Security, Corn Ethanol: Quantitative Study Problems
Sustainable Agriculture, Food Security, Corn Ethanol: Quantitative Study Problems
Sustainable Agriculture, Food Security, Corn Ethanol: Quantitative Study Problems
Sustainable Agriculture, Food Security, Corn Ethanol: Quantitative Study Problems
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Sustainable Agriculture, Food Security, Corn Ethanol: Quantitative Study Problems

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The problems below are a selection of real world problems developed for the teaching of sustainability/conservation related College classes. The exercises are designed to foster quantitative …

The problems below are a selection of real world problems developed for the teaching of sustainability/conservation related College classes. The exercises are designed to foster quantitative competence (numeracy) as well as critical thinking and systems thinking. They are basic but realistic and all data used are taken from the published scientific literature and from public online databases maintained by official organizations such as FAO and EIA.

No advanced Mathematics is required, yet these problems are challenging for most students. Many students need help to overcome a certain math anxiety or even phobia. These exercises must be accompanied by intensive discussion, assistance, and feedback. Students who complete these assignments successfully experience the power of even basic quantitative methods. They learn that informed citizens do not have to rely solely upon the advice of experts – with reasonable effort they can gather and interpret information and come up with approximate answers to important, non-trivial real world questions.

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  • 1. 1 | T. Menninger, Quantitative Exercises in Sustainability Education and Energy Literacy, © 2013Quantitative Practice Problems in Sustainability Educationand Energy LiteracyToni Menninger, toni.menninger at gmail dot comhttp://www.slideshare.net/amenning/presentationsThe problems below are a selection of real world problems developed for the teaching ofsustainability/conservation related College classes. The exercises are designed to fosterquantitative competence (numeracy) as well as critical thinking and systems thinking. They arebasic but realistic and all data used are taken from the published scientific literature and frompublic online databases maintained by official organizations such as FAO and EIA.No advanced Mathematics is required, yet these problems are challenging for most students.Many students need help to overcome a certain math anxiety or even phobia. These exercisesmust be accompanied by intensive discussion, assistance, and feedback. Students whocomplete these exercises successfully experience the power of even basic quantitativemethods. They learn that informed citizens do not have to rely solely upon the advice ofexperts – with reasonable effort they can gather and interpret information and come up withapproximate answers to important, non-trivial real world questions.I am putting the exercises below in the public domain for educational purposes. Feel free to usethem or adapt them for your own instruction. Feel free to contact the author with questions orcomments or to request an instructor version. Any feedback is welcome!
  • 2. 2 | T. Menninger, Quantitative Exercises in Sustainability Education and Energy Literacy, © 2013Agricultural Productivity and Food Security in a World of 7 billionIn this exercise, you will explore the sustainability of the global food system. Read the instructionscarefully, follow the order of the exercise and be sure to understand what is asked. All informationrequired to complete the assignment is found in the instructions – you do not need to look up any data. Itis helpful to use a spreadsheet. Enter the data into your spreadsheet and label each. Note the exact units.Perform the calculations step by step, label each result, and keep track of all units. Check your results!Double check all your conversions and think about whether each result appears plausible and consistentwith what you know from other sources. Remember that the year has 365 days. All units are metric.Hint: Google can help you with conversions.1T [metric tonne] =1,000 kg, 1 Ha [hectare] = 10,000 m2and 1 km2=1,000,000 m2= 100 Ha.1. Grain ProductionThe Food and Agriculture Organization of the United Nations (FAO) maintains an extensivedatabase (faostat.fao.org) reporting data about growing area, production and yields fornumerous crops for each country and region. In 2010, the global cereal harvest (mainly rice,wheat, and maize) was 2.43 billion metric tonnes grown on 6.8 million km2of cropland and theaverage yield of cereal crops was 3.6 T/Ha. The caloric content of grain is about 3,200 kcal/kg.It depends of course on the variety and other factors such as moisture content. The world’sarable land area is about 13.8 million km2; this does not include pasture land. Assume that ahuman on average needs about 2,700 kcal per day and the number of people is 7 billion. In thisanalysis, we only take into account the calorific (energy) content of grain. Of course, a healthydiet must be balanced and diverse.a) How much grain (in kg per year) can feed a person?b) How much cropland, in m2, can feed one person?c) How much grain (in T per year) can feed the world?d) What percentage of the 2010 harvest does that represent?e) How much cropland, in km2, is required to grow enough grain to feed the world?f) What percentage of the world’s arable land area does that represent?g) Interpret your results. Is there enough food for everybody? Is food security threatened byinsufficient agricultural productivity?
  • 3. 3 | T. Menninger, Quantitative Exercises in Sustainability Education and Energy Literacy, © 20132. Meat ProductionFAO also reports data on each country’s average diet. The American diet includes an average of124 kg of meat per year (the global average is 40 kg). Note that the calorific content of meat isabout half that of grain (depending on the fat and moisture content). FAO assumes that onaverage about 3kg of grain is needed as feed for each kg of meat produced.a) How much feed grain (in kg per year) is needed to support the average American meat diet?b) How much feed grain (in T per year) would be needed if the entire world adopted theAmerican diet?c) What percentage of the 2010 harvest does that represent?d) How much cropland, in km2, is required to grow this amount of feed grain?e) What percentage of the world’s arable land area does that represent?f) What do your results imply? Is a meat-based diet a sustainable option for feeding the world?What are the likely consequences when developing countries like China increase their meatconsumption? What, in your view, does this mean for citizens of developed countries?Additional Background Data (not needed for completing the exercise)Average diet accordingto FAOTotal foodkcal/dayAnimal productskcal/dayMeat supplykcal/dayMeat supplykg/yearUS 3750 1030 450 124World average 2800 481 218 40Least developedcountries2160 146 59 11.3The US diet according to FAO data contains 3750 kcal per person per day and is composed of22% cereals excl. beer, 17% sugar and sweeteners, 18% vegetable oils, 12% meat, 10% milk excl. butter,4% alcoholic beverages, 3% fruits excl. wine, 3% animal fats, 3% starchy roots.For comparison Mexico: 44% cereals excl. beer, 15% sugar and sweeteners, 8% vegetable oils, 9% meat,5% milk excl. butter, 4% fruits excl. wine, 4% pulses, 2% animal fats.Sources and further reading FAOSTAT: faostat.fao.org UNEP: World Food Supply, http://www.grida.no/publications/rr/food-crisis/page/3562.aspx Pimentel and Pimentel (2003). Sustainability of meat-based and plant-based diets and theenvironment. www.ajcn.org/content/78/3/660S.full
  • 4. 4 | T. Menninger, Quantitative Exercises in Sustainability Education and Energy Literacy, © 20133. US Corn EthanolYou earlier examined the efficiency of using grain to feed either people or livestock. Grain isalso used to “feed” cars. The federal government has been supporting and subsidizing theproduction of corn ethanol for fuel. The Energy Independence and Security Act of 2007 includesa mandate to produce an increasing amount, currently 13 billion gallons per year, of ethanol,mostly from corn, which is then blended with conventional gasoline. The process involvesfermentation and distillation and yields about 400 liters of ethanol per ton of corn. The energycontent of ethanol is 33% lower than conventional gasoline – 1.5 L of ethanol is needed tosubstitute 1 L of gasoline. A typical US passenger car consumes about 550 gallons of gasolineper year (source). 1 gallon = 3.78 L.In the US, the average corn (maize) yield in 2010 was 9.6 T/Ha (notice that this is much higherthan the world average). This year’s harvest will be much lower because of the record droughtthroughout the Midwest but we will use the higher number for this exercise.a) How much corn (in T) is needed to make enough ethanol to run the average car for a year?b) How many people could be fed by that corn (use the result from 1.a assignment 3)?c) How many square meters of US cropland can “feed” a car? Compare this to 1.b assignment 3!d) The US motor vehicle fleet in 2011 consumed 507 billion liters (134 billion gallons) ofgasoline (source: EIA). How much corn (in T) would need to be grown to substitute 100% of thisfuel with corn ethanol?e) How much cropland, in km2, would that require? Compare to the total US arable land area,1.6 million km2.f) Interpret your results. Is corn ethanol production a sustainable option?4. Agricultural Conversion of Solar EnergyAgriculture is a process of capturing, via photosynthesis, and storing solar energy in a formuseful to humans. We can therefore analyze agricultural productivity in energetic terms: howefficient are crops in capturing and storing solar radiation?Average insolation (the amount of solar energy reaching the surface of the earth) in the UnitedStates is about 200 W/m2. This amounts to 1750 kWh per year per square meter (rememberthat W [Watt] is a unit of power, that is energy flow over time; kWh [kilowatt-hour] is a unit ofphysical energy; the year has 8,760 hours). Assume that the caloric content of corn is about3,200 kcal/kg. Ethanol energy content is 6.5 kWh/L and 1 kcal = 0.001163 kWh.
  • 5. 5 | T. Menninger, Quantitative Exercises in Sustainability Education and Energy Literacy, © 2013a) Estimate the energy output of growing corn in kWh/m2.b) What percentage of the total solar energy reaching a cornfield does that represent?c) How much ethanol, in L/Ha, can a US cornfield be expected to yield?d) Estimate the energy output of corn ethanol production in kWh/m2.e) What percentage of the solar energy does that represent? In other words, we are analyzingthe conversion efficiency of converting solar energy into ethanol.f) What energy output could be expected, in kWh/year/m2, from photovoltaic panels with aconversion efficiency of 12%? Compare to your results in a) and d). Which method of capturingsolar energy is more efficient, and by what factor?5. In a one page essay, summarize your main findings. Which of them surprised you? Which ofthem would you want to share with a policy maker? Being an informed citizen but not ascientific expert, how confident are you of the validity of your conclusions? Have you learnedanything about “systems thinking”?Sources and further readings EIA: Biofuels in the U.S. Transportation Sector,http://www.eia.gov/oiaf/analysispaper/biomass.html Baker and Zahniser (2006): Ethanol Reshapes the Corn Market, Amber Waves USDA: Bioenergy, http://www.ers.usda.gov/topics/farm-economy/bioenergy/background.aspx National Geographic: Biofuels, http://ngm.nationalgeographic.com/2007/10/biofuels/biofuels-text George Monbiot: Hunger Games BBC: US biofuel production should be suspended, UN says Tom Murphy: Do the Math, http://physics.ucsd.edu/do-the-math/ (Solar potential, Food energy)

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