186 M. Giampietro, K. Mayumi sector needed to deliver the required energy carriers – the energy consumption (or metabolism) of the energy sector; and (ii) Net Energy to Society – used for the production and consumption of “non-energy goods and services” - the energy con- sumption (or metabolism) of the rest of the society. In spite of an unavoidable level of arbitrariness in the calculation of EROI, this scheme indicates clearly the tremendous advantage of fossil energy over alternative energy sources (for more see Giampietro, 2007a). In relation to the costs of produc- tion of energy carriers, oil has not to be produced, it is already there. Moreover, in the previous century it was pretty easy to get: the EROI of oil used to be 100 MJ per MJ invested, according to the calculations of Cleveland et al. (1984). For this reason, in the community of energy analysts there is an absolute consensus about the fact, that the major discontinuity associated with the industrial revolution in all major trends of human development (population, energy consumption per capita, technological progress) experienced in the XXth century was generated by the ex- treme high quality of fossil energy as primary energy source (for an overview of this point see Giampietro, 2007a). This means that to avoid another major disconti- nuity in existing trends of economic growth (this time in the wrong direction), it is crucial that when looking for future alternative primary energy sources, to replace fossil energy, humans should obtain the same performance, in terms of useful work delivered to the economy per unit of primary energy consumed. As explained earlier a very high EROI means that the conversion of oil into an adequate supply of energy carriers (e.g. gasoline) and their distribution absorbs only a negligible fraction of the total energy consumption of a society. This small over- head makes it possible that a large fraction of the total energy consumptions goes to cover the needs of society, with very little of it absorbed by the internal loop “energy for energy”. Moreover, due to the high spatial density of the energy flows in oil fields and coal mines the requirement of land to obtain a large supply of fossil energy carriers is negligible. Finally, waste disposal has never been considered as a major environmental issue, until acid rain deposition and global warming forced world economies to realize that there is also a sink side – beside the supply side - in the biophysical process of energy metabolism of whole societies. As a matter of fact, so far, the major burden of the waste disposal of fossil energy has been paid by the environment, without major slash-back on human economies. Compare this situation with that of a nuclear energy in which uranium has to be mined, enriched in high tech plants, converted into electricity in other high tech plants, radioactive wastes have to be processed and then kept away (for millennia!) both from the hands of terrorists and from ecological processes. The narrative of the EROI is easy to get across: the quality of a given mix of energy sources can be assessed by summing together the amount of all energy in- vestments required to operate the energy sector of a society and then by comparing this aggregate requirement to the amount of energy carriers delivered to society. By using this narrative it is easy to visualize the difference that a “low quality energy source” can make on the profile of energy consumption of a society. This is illustrated in the two graphs given in Fig. 8.4 (from Giampietro et al., 2007). The upper part of the figure – Fig. 8.4a – provides a standard break-down of the 8 Complex Systems Thinking and Renewable Energy Systems 187 profile of different energy consumptions over the different sectors of a developed economy. Total Energy Throughput (TET) is split into the Household sector (Final Consumption) and the economic sectors producing added value (Paid Work sector – PW). The economic sector PW is split into: Services and Government, Productive Sectors such as Building, Manufacturing, Agriculture (minus the energy sector) and the Energy Sector (ES). The example adopts an average consumption per capita of 300 GJ/year and an EROI > 10/1. This entails that only less than 10% of TET goes into the energy sector. Let’s assume now that we want to power the same society with a “low quality primary energy source”. For example, let’s imagine a system of production of energy carriers with an overall output/input energy ratio of 1.33/1. The lower part of – Fig. 8.4b (right side) – shows that for 1 MJ of net energy carrier supplied to society this energy system has to generate 4 MJ of energy carriers. As mentioned earlier, the huge problem with primary energy sources alternative to oil is that they have to be produced, and they have to be produced using energy carriers. That is, a process of production of primary energy sources must use energy carriers which have to be converted into end uses. This fact entails a double energetic cost (to make the carriers that will be used then within the internal loop to produce the primary energy required to make the energy carriers). That is, this internal loop translates into an extreme fragility in the overall performance of the system. Any negative change in this loop does amplify in non-linear way. A small reduction of about 10% in the output/input ratio – e.g. from 1,33/1 to 1,20/1 implies that the net supply of 1 MJ delivered to society would require the production of 6 MJ of energy carriers rather than 4MJ (for more on this point see Giampietro and Ulgiati, 2005). Fig. 8.4a The pattern of metabolism across compartments of a developed society with a “high quality” primary energy source (EROI >10/1) 188 M. Giampietro, K. Mayumi Fig. 8.4b The pattern of metabolism across compartments of a developed society with a “low quality” primary energy source (EROI < 2/1) Let’s image now to power the same society illustrated in Fig. 8.4a (a developed society) using a “low quality primary energy source” (EROI = 1.33/1) and keeping the same amount of energy invested in the various sectors (beside the energy sector). The original level of energy consumption per capita for the three sectors described in Fig. 8.4a is 279 GJ/year, which is split into: (i) 90 GJ/year in Final Consumption (residential & private transportation); (ii) 63 GJ/year in Service and Government; and (iii) 126 GJ/year Building and Manufacturing and Agriculture. In this case, the energy sector – when powered by low quality energy sources – would have to consume for its own operations 837 GJ/year per capita. Then, when combining the energy consumed by the rest of society and the energy consumed by the energy sector the total energy consumption of the society would become 1,116 GJ/year per capita – an increase of almost 4 times of the original level! Obviously such a hypoth- esis is very unlikely. It would generate an immediate clash against environmental constraints, since the industrial and post-industrial metabolism of developed society at the level of 300 GJ/year per capita has already serious problems of ecological compatibility, when operated with fossil energy. However, the environmental impact would not be the only problem. There are also key internal factors that would make such an option impossible. Moving to a primary energy source with a much lower EROI than oil would generate a collapse of the functional and structural organi- zation of the economy. In fact the massive increase in the size of the metabolism of the energy sector would require a massive move of a large fraction of the work force and of the economic investments right now required in the other sectors of the economy. A huge amount of hours of labor and economic investment will have to be 8 Complex Systems Thinking and Renewable Energy Systems 189 moved away from the actual set of economic activities (manufacturing and service sector) toward the building and operation of a huge energy sector, which will mainly consume energy, material and capital for building and maintaining itself. 8.2.2 The Combination of Biophysical and Socio-Economic Constraints Determines a Minimum Pace for the Throughput to be Metabolized Due to the organization of metabolic systems across different hierarchical levels and scales, there are “emergent properties” of the whole that cannot be detected when considering energy transformation at the level of the individual converter. In socio-economic systems, these “emergent properties” may be discovered only when considering other dimensions of sustainability – e.g. the characteristics of social or economic processes determining viability constraints – which are forcing metabolic systems to operate only within a certain range of power values. To clarify this point let’s discuss an example based on an analysis of the possible use of feeds of different quality in a system of animal production. This example is based on the work of Zemmelink (1995). In the graph shown in Fig. 8.5 numerical values on the horizontal axis (e.g. A1, A2) represent an assessment of the quality of feed (based on nutrient and energy content per unit of mass). They reflect the given mix of possible feed types which are available in a given agro-ecosystem: (i) dedicated crops or very valuable by- products = high quality; (ii) tree leaves = medium quality; and (iii) rice straw = low quality. Therefore, moving on the horizontal axis implies changing the mix of possible feed types. “Very high quality feed” implies that only dedicated crops or very valuable by-products can be used; “very low quality feed” implies that also rice straw can be used in the mix. The points on the curve represent the size of the herd (e.g. S1, S2, on the vertical axis on the right). The diagonal line indicates the relation between levels of productivity (pace of the output) of animal products – i.e. beef – (e.g. P1 and P2 on the vertical axis on the left) and the “quality” of feed used as input for animal production (e.g. the point A1 and A2 on the horizontal axis). When using only animal feeds of a high quality one can get a high level of productivity (boost the output), but by doing so, one can only use a small fraction of the total primary productivity of a given agro-ecosystem. This analysis describes an expected relation between: (i) productivity in time (power level – on the vertical axis on the left); (ii) ecological efficiency (utilization of the available biomass – on the horizontal axis); (iii) stocks in the system (the size of the herd – on the vertical axis on the right) in animal production. This emergent property of the whole determining the viability and desirability of different types of biomass depends on both: (i) the required level of productivity (determined by the socio-economic context) – the economic break-even point on the vertical axis on the left; and (ii) the characteristics of the agro-ecosystem (the set of biological conversions and the ecological context). This study confirms that the need of operating at a high level of productivity implies 190 M. Giampietro, K. Mayumi Fig. 8.5 Feed quality and net productivity of animal production reducing the ecological efficiency in using the available resources. That is, when the socio-economic constraints force to operate at a very high level of productivity, a large fraction of tree leaves and all available rice straw can no longer be considered as feed, but they will result just waste. This analysis provides a clear example of the need of contextualization for bio- physical analysis. That is, when looking only at biophysical variables we can only characterize whether or not a feed input of quality “A1” is an input of “adequate quality” for a system of production of beef operating at a rate of productivity P1. However, the ultimate decision on whether or not the level of productivity P1 is feasible and desirable for the owner of the beef feed-lot cannot be decided using only this biophysical analysis. The viability and desirability of the level of productivity P1 depends on the constraints faced on the interface beef feed-lot/rest of society. This evaluation of desirability has to be done considering a different dimension of analysis. In this case, the acceptability of P1 has to be checked using a socio- economic dimension (the position of the economic break-even point on the vertical axis on the left). This viability check has to do with the evaluation of the pace of generation of added value (linked with the level of productivity P1) required for the viability of the production system. In conclusion, the very same feed input of quality “A1” can be either: (1) per- fectly adequate for that system of animal production in a given social context (e.g. in a developing country); or (2) not acceptable, when moving the same biophysical 8 Complex Systems Thinking and Renewable Energy Systems 191 process from a developing country to a developed country. That is, a change in the socio-economic context can make level P1 no longer acceptable. When forced to operate at a higher level of productivity (e.g. P2) to remain economically viable, the owner of the feed-lot would find the feed input of quality “A1” no longer either vi- able or desirable. In biophysical terms, the feed input of quality “A1” would remain of an adequate quality for sustaining a given population of cows, but no longer of an “adequate quality” for sustaining, in economic terms, the threshold of productivity, required by the owner of the feed-lot to remain economically viable. The set of relations described in the graph of Fig. 8.5 is based on well known biological processes for which it is possible to perform an accurate analysis of the biological conversions associated with animal production. Yet, due to the complex- ity of the metabolic system operating across multiple scales, and due to the differ- ent dimensions of analysis which have to be considered, the concept of “quality of the energy input to the whole system” depends on: (1) the hierarchical level at which we decide to describe the system – e.g. the cow level versus the whole beef feed-lot level; and (2) the context within which the system is operating (in this case on the economic side of the animal production system). When considering also socio-economic interactions, there are emergent properties of the whole (the performance based on multiple criteria mentioned by Carnot), which can affect the viability or desirability of an energy input (the minimum admissible feed quality for achieving an economic break-even point). These emergent properties can af- fect the admissible pace of the metabolism of the whole, and therefore induce a biophysical constraint (the need of reaching a certain threshold of power level) within a particular conversion process (the transformation of feed into beef at the hierarchical level of the whole production system). This can imply that what is an effective energy input, when operating at a lower power level (in this example the mix of feed of quality “A1” in Uganda) is no longer a viable or desirable energy input when operating in the USA. That is, even when the biophysical parameters of the system remain completely unchanged – keeping the same cows, the same set of potential energy inputs for the feed, the same techniques of production – it is the coupling with the external context – beef feed-lot/rest of society – that will affect the biophysical definition of “quality” for what should be considered as a viable energy input. In conclusion the question: “are crop residues useful feed for a beef feed-lot?” cannot be answered without first checking the biophysical constraints on energy transformations which are determined by the set of expected characteristics of the whole metabolic system. These expected characteristics are determined by its inter- action with its context. The question about the viability and desirability of crop residues as alternative feed cannot be answered just by looking at one particu- lar dimension and one scale of analysis. According to the analysis presented in Fig. 8.5 crop residues may provide nutritional energy to cows, but their viability and desirability depends on the severity of the biophysical constraints determined by the socio-economic characteristics of the whole. Exactly the same answer can be given in relation to the possibility of using biomass for the metabolism of a socio-economic system. 192 M. Giampietro, K. Mayumi 8.2.3 Economic Growth Entails a Major Biophysical Constraint on the Pace of the Net Supply of Energy Carriers (per hour and per ha) in the Energy Sector Let’s image that, in order to reduce the level of unemployment in rural areas of devel- oped countries, a politician would suggest to abandon the mechanization of agricul- ture and to go back to pre-industrial agricultural techniques requiring the tilling and the harvesting of crops by hand. By implementing this strategy it would be possible to generate millions and millions of job opportunities overnight! Hopefully, such a suggestion would be immediately dismissed by political opponents as a stupid idea. Everybody knows that during the industrial revolution the mechanization of agricul- ture made it possible to move out from rural areas a large fraction of the work force. This move had the effect to invest human labor into economic sectors able to generate added value at a pace higher than the agricultural sector. This is why, no developed country has more than 5% of its work force in agriculture and the richest countries have less than 2% of their work force in agriculture (Giampietro, 1997a). As a matter of fact, changes in the structure and the function of socio-economic systems can be studied using the metaphor of societal metabolism. The concept of societal metabolism has been applied in the field of industrial ecology (Ayres and Simonis, 1994; Duchin, 1998; Martinez-Alier, 1987), in particular in the field of matter and energy flow analysis (Adriaanse et al., 1997; Fischer-Kowalski, 1998; Matthews et al., 2000). By adopting the concept of societal metabolism it is pos- sible to show that the various characteristics of the different sectors (or compart- ments) of a socio-economic systems must be related to each other, as if they were different organs of a human body. In particular it is possible to establish a mech- anism of accounting within which the relative size and the relative performance of the various sectors in their metabolism of different energy and material flows must result congruent with the overall size and metabolism of the whole. These two authors have developed a methodological approach – Multi-Scale Integrated Analysis of Societal and Ecosystem Metabolism (MuSIASEM) – originally pre- sented in several publications as MSIASM – e.g. Giampietro, 1997b, 2000, 2001; Giampietro and Mayumi, 2000a,b; Giampietro et al., 1997a, 2001; Giampietro and Ramos-Martin, 2005; Giampietro et al., 2006c, 2007; Ramos-Martin et al., 2007; Giampietro, 2007a – which can be used to perform such a congruence check. That is, the MuSIASEM approach can be used to check the congruence between: (i) the characteristics of the flows to be metabolized as required by the whole soci- ety; and (ii) the characteristics of the supply of the metabolized flows, as generated by individual specialized compartments. An overview of the possible application of this method to the analysis of the quality of energy sources is presented in Giampietro, 2007a; Giampietro et al. 2007. Just to provide an example of the mech- anism used to perform this congruence check, we provide in Fig. 8.6 an analysis of the energetic metabolism of a developed society (e.g. Italy) in relation to the profile of use of human activity over 1 year. Very briefly, when considering the system “Italy” at the hierarchical level of the whole society – considered as a black box (on the right of the figure) – we can 8 Complex Systems Thinking and Renewable Energy Systems 193 Fig. 8.6 Minimum threshold of energy throughput per hour of labor in the energy sector of a developed country say that 57.7 millions of Italians represented a total of 503.7 Giga hours (1 Giga = 10 9 ) of human activity in the year 1999. In the same year they consumed 7 Exa Joules (1 Exa = 10 18 ) of commercial energy. This implies that at the level of the whole society, as average, each Italian has consumed 14 MJ/hour (1 Mega = 10 6 ) of commercial energy. Let’s imagine now to open the black box and to move to an analysis of the in- dividual sectors making up the Italian economy (moving to the left of the figure). In this way, we discover that the total of human activity available for running a society has to be invested in a profile of different tasks and activities which have to cover both: (i) the step of production of goods and services; and (ii) the step of consumption of goods and services. For example, more than 60% of the Italian population is not economically active – e.g. retired, elderly, children, students. The fraction of human activity associated with this part of the population is therefore not used in the process of production of goods and services (but it is used in the phase of consumption). Furthermore the active population works only for 20% of its available time (in Italy the work load per year is 1,780 hours). This implies that out of the total of 503.7 Giga hours of human activity available to the Italian society in 1999, only 36.3 Giga hours (8% of the total!), were used to work in the economic sectors producing goods and services. In that year, almost 14 hours of human activity have been invested in consuming per each hour invested in producing! Let’s now see how this profile of distribution of time use affect the availability of working hours to be allocated in the mandatory task of producing the required amount of energy carriers in the energy sector. This requires looking at what happened within the tiny 8% of 194 M. Giampietro, K. Mayumi the total human activity invested in the productive sector. Out of these 36.3 Giga hours, 60% has been invested in the Service and Government sector. The industrial sector and the agricultural sector have absorbed another 38%, leaving to the energy sector less than one percent (<1%) of the already tiny 8% of the total. This is a well known characteristic of modern developed societies, which are very complex. This complexity translates into a huge variety of goods and services produced and consumed, which, in turn, requires a huge variety of different activities across the different sectors associated with different jobs descriptions and different typologies of expertise (Tainter, 1988). In conclusion, in Italy in 1999, only 0.0006 of the total (not even 1/1000th!) of the total human activity has been used for supplying the energy carriers associated with the consumption of 7 Exa Joules of primary energy consumed in that country that year. This means that by dividing the total consumption of the “black box Italy” by the hours of work delivered in the energy sector, the performance of the energy sector in relation to the throughput of energy delivered to society per hour of labor in the energy sector has been of 23,000 MJ/hour. It should be noted that if rather than considering Italy had we considered USA the consumption per capita would have been much higher (333 GJ/person year or 38 MJ/hour in 2005). After adjusting for a different population structure (50% of the population in the work force) assuming 2,000 hours/year of work load and only 0.007 of the work force – about 1 million workers* – in the sector supplying fossil energy carriers, the resulting throughput of energy delivered to society per hour of labor in the energy sector is 47,000 MJ/hour. [* this excludes almost 1 million workers in gas stations and trucks needed for transporting liquid fuels, which are not included in the calculation since they are required for the distribution of fuels independently from the energy source used to produce them]. 8.3 Using the MuSIASEM Approach to Check the Viability of Alternative Energy Sources: An Application to Biofuels 8.3.1 The “Heart Transplant” Metaphor to Check the Feasibility and Desirability of Alternative Energy Sources To visualize the type of integrated analysis based on the MuSIASEM approach for linking the characteristics of the energy sector to the characteristics of the whole society, we propose the metaphor of a heart transplant, illustrated in Fig. 8.7 (more details in Giampietro and Ulgiati, 2005; Giampietro et al., 2006c). Let’s imagine that the actual energy sector based on fossil energy as primary energy source, is the heart, which, at this very moment, is keeping alive a given person (e.g. a given society). Let’s imagine now that we want to replace this heart with an alternative heart (e.g. an energy sector powered by biofuels from agricultural production). Let’s imagine that we want to perform this transplant because someone claims that the alternative 8 Complex Systems Thinking and Renewable Energy Systems 195 Fig. 8.7 The metaphor of the heart transplant heart is much better (e.g. it makes it possible to have “zero emission” of GHGs from the energy sector and a total renewability of the supply of energy carriers). Still, it would be wise, before starting the operation of transplant, to check whether or not such a substitution is: (i) feasible; and (ii) desirable. To do such a check it is necessary to compare the performance of the actual heart with the performance that we can expect from the alternative heart we want to implant. This comparison can be obtained by checking the congruence between: (A) the pace of the required flow of energy carriers determined by the characteristics of the whole society; and (B) the pace of the net supply of energy carriers which can be achieved by the “alternative energy sector” we want to implant. The application of this approach is presented in the next section, which compares the performance of the actual energy sector powered by fossil energy with the performance of an energy sector powered by biofuels. For the sake of simplicity we will focus only on two biophysical constraints on the pace of the flow of energy carriers: (i) “the requirement of hours of labor in the energy sector to generate the required supply” versus “the availability of hours of labor which can be allocated in the energy sector by a given society”; (ii) “the requirement of hectares of land in the energy sector to generate the required supply” versus “the availability of hectares of land which can be allocated to the energy sector by society”. With this choice, we ignore additional issues, which are very relevant when checking the viability of biofuels as alternative energy sources. These additional issues should include: water demand, soil erosion, preservation of natural habitat for biodiversity. [...]... valuation Science 210 , 12 19 12 24 Costanza, R and Herendeen, R 19 84 Embodied energy and economic value in the United States Economy: 19 63, 19 67 and 19 72 Resources and Energy 6, 12 9 16 3 Cottrell, W.F 19 55 Energy and Society: The Relation between Energy, Social Change, and Economic Development McGraw-Hill, New York Debeir, J.-C., Deleage, J.-P., and Hemery, D 19 91 In the Servitude of Power: Energy and Civilization... Science 311 , 506–508  210 M Giampietro, K Mayumi Fischer-Kowalski, M 19 98 Societal Metabolism: The intellectual history of material flow analysis part I, 18 60 19 70 Journal of Industrial Ecology 2 (1) , 61 78 Fluck, R.C 19 81 Net Energy Sequestered in agricultural labor Transactions of the American Society of Agricultural Engineers 24, 14 49 14 55 Fluck, R.C 19 92 Energy of Human Labor In: R.C Fluck (Editor) Energy. .. energy sources, energy carriers and end uses By doing so, energy analysis can explain pretty well the link between energy and economic growth (Ayres et al., 2003; Ayres and Warr, 2005; Cleveland et al., 19 84, 2000; Costanza and Herendeen, 19 84; Gever et al., 19 91 ; Hall et al., 19 86; Jorgenson, 19 88; Kaufmann, 19 92 ) This literature is extremely 208 M Giampietro, K Mayumi clear and effective in making the... C.A.S., and Kaufmann, R 19 84 Energy and the U.S Economy: A Biophysical Perspective Science 225(4665), 890 – 897 Cleveland, C.J., Hall, C.A.S., and Herendeen, R.A 2006 Letters – energy returns on ethanol production Science 312 , 17 46 Cleveland, C.J., Kaufmann, R., and Stern, S.I 2000 Aggregation and the role of energy in the economy Ecological Economics 32, 3 01 317 Costanza, R 19 80 Embodied energy and economic... 19 00 19 98 Energy 28(3), 2 19 –273 Ayres, R.U and Simonis, U.E 19 94 Industrial Metabolism: Restructuring for Sustainable Development United Nations University Press, New York Ayres, R.U and Warr, B 2005 Accounting for growth: The role of physical work Structural Change and Economic Dynamics 16 (2), 18 1–2 09 Batty, J.C., Hamad, S.N., and Keller, J., 19 75 Energy inputs to irrigation Journal of Irrigation and. .. favorable of the two assessments NET technical coefficients for biofuel over the whole process TOTAL ETHANOL ENERGY → 66 .1 GJ/ha → 21. 5 GJ/liter CARRIERS OUTPUT TOTAL FOSSIL ENERGY → 61. 2 GJ/ha → 19 .9 GJ/liter CARRIERS INPUT OUTPUT/INPUT IN ENERGY → 1. 1 /1 → 1. 1 /1 CARRIERS NET SUPPLY = 9% of the supply of ethanol – 11 liters of gross ethanol → 1 liter net supply The Net Supply of energy carriers (biofuel)... and Drainage Div ASCE 10 1(IR4), 293 –307 Brody, S 19 45 Bioenergetics and Growth Reinhold Publ Co New York, pp 10 23 Carnot, S 18 24 Reflexions sur la puissance motrice du feu sur les machines propres a developper cette puissance Bachelier, libraire Paris Cleveland, C.J 19 92 Energy quality and energy surplus in the extraction of fossil fuels in the U.S Ecological Economics 6, 13 9 16 2 Cleveland, C.J., Costanza,... labor → 12 hours/ha/year → 4 hours /1, 000 liters land → 3,076 liters/ha → 0.32 ha /1, 000 liters fossil energy → 29. 3 GJ/ha → 9. 5 GJ /1, 000 liters STEP 2 – Fermentation/Distillation of Ethanol – GROSS TECHNICAL COEFFICIENTS INPUT labor → 14 .76 hours/ha/year → 4.8 hours /1, 000 liters land → negligible → negligible fossil energy → 31. 9 GJ/ha → 10 .4 GJ /1, 000 liters The assessment of labor demand for the phase... be assessed considering the overall EROI Other scientists claim that it is just a matter of using common sense – e.g work of Cottrell ( 19 55); Smil ( 19 83, 19 91 , 20 01, 2003) and Pimentel and Pimentel ( 19 79) – to conclude that food is more valuable of fossil fuel for any type of society There are others that propose elaborated approaches to account for the differences in quality between energy sources, energy. .. Georgescu-Roegen, N 19 75 Energy and economic myths Southern Economic Journal 41, 347–3 81 Gever, J., Kaufmann, R., Skole, D., and V¨ r¨ smarty, C 19 91 Beyond Oil: The Threat to Food and oo Fuel in the Coming Decades University Press of Colorado, Niwot Giampietro, M 19 97 a Socioeconomic pressure, demographic pressure, environmental loading and technological changes in agriculture Agriculture, Ecosystems and Environment . ecology (Ayres and Simonis, 19 94; Duchin, 19 98; Martinez-Alier, 19 87), in particular in the field of matter and energy flow analysis (Adriaanse et al., 19 97; Fischer-Kowalski, 19 98; Matthews et. process. TOTAL ETHANOL ENERGY CARRIERS OUTPUT → 66 .1 GJ/ha → 21. 5 GJ/liter TOTALFOSSILENERGY CARRIERS INPUT → 61. 2 GJ/ha 19 .9 GJ/liter OUTPUT/INPUT IN ENERGY CARRIERS → 1. 1 /1 → 1. 1 /1 NET SUPPLY = 9% of the. which analysts should associate an energetic and economic costs and not a positive return (Giampietro et al., 19 97b). 8 Complex Systems Thinking and Renewable Energy Systems 19 9 8.3.2.3 Benchmark