During the past three years, MAGIC has critically examined prevailing narratives and proposed innovations in EU policy spheres involving one or more elements of the resource nexus: water, energy, food and the environment. To this end, MAGIC researchers have employed quantitative story-telling, a novel approach that involves a predominantly quantitative exploration of multiple narratives in a given policy domain. Rather than trying to compile evidence in support of a given narrative, or determine the ‘best course of action’, researchers explored whether or not the examined narratives were congruent with quantitative analytical checks. Previous issues of the Nexus Times have focused on the outcomes and policy relevance of this research. In this issue, we take a look behind the screen and show how these quantitative analytical checks are obtained in what we call the MAGIC ‘Nexus Structuring Space’.
In our first article, Mario Giampietro briefly explains the challenges involved in a quantitative analysis of the resource nexus and sets out how these challenges have been overcome in MAGIC’s Nexus Structuring Space. He does so by drawing an analogy with Harry Potter’s Marauder’s Map.
Ansel Renner and Juan Cadillo-Benalcazar then illustrate how the nexus structuring space has been used to characterize the current EU’s food system and to assess the changes that would be required to achieve self-sufficiency in food.
In our third article, Louisa Di Felice describes the energy sector as a multi-scale network to answer questions such as: which functions of the energy sector emit most greenhouse gases? What would happen to the nexus elements across scales if the energy sector were to be electrified?
Laura Pérez-Sánchez, Raúl Velasco-Fernandez, Michele Manfroni, Sandra Bukkens and Mario Giampietro’s article focuses on the key role of time use in MuSIASEM and explains how the use of labour is intricately linked with the natural resource nexus in the societal metabolic pattern.
Our last article, by Maddalena Ripa, focuses on a particularly ‘wicked’ case study in MAGIC, that of biofuels. It shows how the nexus structuring space and quantitative story-telling have been used to debunk the idea that biofuels represent a sustainable use of biomass to produce liquid fuels and a way out of a nexus policy impasse.
Dialogue Space > The Nexus Times > A Marauder’s Map to depict the resource nexus
In the saga of Harry Potter, the Marauder’s Map allows the magician to reveal the whereabouts of any person in space, covering all the levels (floors) of the castle, its secret passages, as well as the surrounding grounds. The term marauder (i.e., a plunderer1) neatly reflects the roving nature of the scientist involved in multi-scale transdisciplinary assessment. The resource nexus requires the scientist to identify relevant descriptive domains and reconcile top-down and bottom-up assessments, thereby providing meaning and coherence to the various sets of non-equivalent data required for informing policy across scales and dimensions. In this sense, the Nexus Structuring Space, developed in MAGIC, can be considered a sort of Marauder’s Map guiding the use of the MuSIASEM2 tool-kit for the analysis of the nexus. It allows the analyst to move quantitative assessments across levels and dimensions to check the feasibility, viability, desirability and openness of the metabolic pattern of a social-ecological system.
Figure 1 shows an overview of the functioning of the Nexus Structuring Space and its ability to identify, as in the Marauder’s Map, the sources of information that are relevant for different research questions. Starting from the left, we see the information available when looking through the macroscope. On the top left, we see the entanglement over the activity of the constituent components of the system (agriculture, energy and mining, manufacturing and construction, service and government, and the household sector). They are producing and consuming the inputs for/from each other. In MAGIC, we define a socio-economic system as “a metabolic network in which constituent components stabilize each other in an impredicative (self-referential) set of relations in presence of favorable boundary conditions” [1, 2]. A quantitative representation of the forced metabolic relations across the elements of the constituent components is obtained by characterizing these forced relations in an end-use matrix. Using the macroscope, the end-use matrix allows us to see: (i) who is using either energy, food, water; (ii) why; (iii) how much; and (iv) how. The end-use matrix thus allows the establishment of a bridge with demographic variables (i.e. the demographic structure) and characterizes the profile of distribution of the secondary inputs among the different constituent compartments. The resulting concept of Bio-Economic Pressure (Figure 1) indicates that economic development requires a significant fraction of internal resources to be allocated to final consumption and to the service sector.
Looking through the mesoscope, we can identify other sources of information that permit an analysis of the level of openness of the system determined by trade (see Figure 1). Here, we have to change the categories of accounting and use another metric (metric #2) to assess the flow of commodities. Through the lens of the mesoscope we study how much of the production of internal inputs in the various constituent components of the system is due to local processes or to imports. After having clarified this point, we look at the system through the virtualscope to characterize what exactly is required in terms of end-uses and environmental pressures to produce the local secondary inputs inside the system and what is required in terms of end-uses and environmental pressures to produce the imported commodities (right hand side of Figure 1).
To identify the sources of useful information for this assessment we have to move to yet another set of descriptive domains, which are illustrated in Figure 2. Starting from the left of Figure 2, and using as inputs the overall required supply of commodities observed through the mesoscope and measured in metric #2, we can associate the set of commodities locally consumed to a set of production processes required for their production. At this point, we need to look through the microscope to visualize, at the local scale, the profile of inputs and outputs associated with each of the local processes. These inputs and outputs can go: (i) inside and outside the technosphere (secondary flows that are relevant for the socio-economic process); and (ii) inside and outside of the biosphere (primary flows that are relevant for the compatibility with ecological processes). When observing local processes with the microscope we can geo-localize these processes and check whether the environmental pressures associated with the primary flows exchanged with the biosphere – both on the supply and sink side – are compatible with local ecological funds and therefore assess the resulting environmental impacts.
In conclusion, when dealing with the analysis of the nexus, depending on the research question, we can use a logical map —the Nexus Structuring Space — to guide our search for and use of data from among the available sources of information. The Nexus Structuring Space shows the role of the various available grammars in MuSIASEM (specified sets of expected relations over metabolic processes) and helps the analyst to identify the type of data that is relevant to generate the desired types of result.
More information on the toolkit and its applications is available in MAGIC Deliverable 4.4.
2 MuSIASEM: Multi-Scale Integrated Analysis of Societal and Ecosystem Metabolism
 Giampietro, M., Renner, A., 2020. The Generation of Meaning and Preservation of Identity in Complex Adaptive Systems: The LIPHE4 Criteria, in: Braha, D., et al (Eds.), Unifying Themes in Complex Systems X: Proceedings of the Tenth International Conference on Complex Systems. Springer (Series: Springer Proceedings in Complexity), Cham, Switzerland
 Renner, A., Giampietro, M., Louie, A.H., 2020. Cyborgization of modern social-economic systems: Accounting for changes in metabolic identity, in: Braha, D., et al (Eds.), Unifying Themes in Complex Systems X: Proceedings of the Tenth International Conference on Complex Systems. Springer (Series: Springer Proceedings in Complexity), Cham, Switzerland
Dialogue Space > The Nexus Times > Applying the nexus structuring space to characterize the EU food system
Applying the nexus structuring space to characterize the EU food system
In the MAGIC project, an evaluative framework called quantitative story-telling (QST) was developed as a capable way of generating robust inputs on the science-policy interface. This article demonstrates the potential of that approach to characterize a flexible information space capable of supplying the structured quantitative data demanded by QST exercises. In this article, we focus on examples taken from an analysis of European Union (EU) agriculture.
In diagnostic mode, our analysis evaluated the current metabolic profile of the agriculture sectors of 29 European countries (the EU-27 plus the United Kingdom and Norway). In anticipation mode, our analysis then evaluated the possibility of a dramatic agricultural internalization for each of those 29 countries—what would be needed for near-complete self-sufficiency in foodstuffs, a crude look at downscaling planetary boundaries to the national level under the assumption that current imports become undependable. Across both analytical modes, a semantic interface referred to as the nexus structuring space was developed in which four lenses across four different descriptive domains were used. Fig. 1 summarizes the four lenses used.
When adopting a macroscope lens (symbol A in Fig. 1), multi-metric data concerning the absolute and relative sizes of the various societal sectors (the household sector, the manufacturing sector, the agriculture sector, etc.), as well as their respective metabolic characteristics, was generated. In our analysis, the macroscope gathered information on the end-uses of various foodstuffs and related those end-uses to more general societal consumption patterns. The mesoscope lens describes the dependence of the country under study on other social-economic systems. This dependence is evaluated in terms of how much of each agricultural commodity consumed is of local origin and how much is imported. In Fig. 1, two descriptive domains are identified for the mesoscope—symbol B describes the external dependency in terms of primary/secondary products while symbol C describes the external dependence in terms of live animals required to maintain animal production systems. The mesoscope thereby provides rich information relevant for discussions of food security and vulnerabilities to external factors. The microscope lens (symbol D in Fig. 1) describes the pressure exerted by local agricultural activities on the local ecosystem, differentiating between elements under human control (for example, fertilizers, human activity/labor, blue water) from those that are not (for example, green water, aquifers, soil). Finally, the virtualscope lens describes the characteristics of the “virtual” production processes that are required for the production of imported goods. The virtualscope is not visualized in Fig. 1 since, in practice, its characterization depends on the set of assumptions made. For example, the virtualscope can be understood from the anticipatory perspective of saving local biophysical resources (what would be needed for local self-sufficiency) or from the diagnostic perspective of pressure exerted on external social-ecological systems (outsourcing).
In diagnostic mode, the macroscope revealed substantial heterogeneity in the dietary profile of the EU countries, due mainly to a mix of cultural and environmental factors. In Portugal, for example, 21% of food consumed derives from animal products (in energy terms, fat products and marine/aquatic products not included). That same figure is 31% for Sweden. Similarly, 27% of the food consumed in Austria derives from grains, roots and tubers (in energy terms, again). On the other hand, grains, roots and tubers represent a full 46% of food consumed in Romania. The mesoscope suggests that when products are considered in terms of primary product equivalent, most of the countries assessed (20 out of 29) exceeded a 50% self-sufficiency level concerning plant products. That number of countries reduces by approximately half when analyzing animal products. When assessing animal feed (again, primary product equivalent), nearly all countries stand at less than 30% self-sufficiency. In anticipation mode, evaluating the possibility of a near-complete (90%) internalization of foodstuff imports by 2050—considering also population, diet and yield projections—the microscope and virtualscope lenses revealed that countries such as the Netherlands and Belgium would need to increase their agricultural area by 14x and 8x, respectively. In terms of NPK fertilizer usage, those same two countries would expect to increase application rates by approximately 90%. It should be stressed that these figures include in their consideration import for re-export, but also that the obverse (e.g. the elimination of high throughput agribusiness) would imply dramatic economic transformation in some countries.
The results obtained in our application of the nexus structuring space to agriculture in the EU illustrate—across a wide set of biophysical indicators—that the import of low added value agricultural products is an essential lifeline for the EU's contemporary agribusiness model. Our examples prove highly relevant when considering aspects such as the expected dramatic increase in global food demand by 2050 (putting strain on imports), the major agricultural demands being placed on EU agriculture by the European Green Deal, ongoing revision efforts related to the Common Agricultural Policy (CAP) and the uncomfortable fact that the CAP’s nine primary objectives currently imply several mutually antagonistic actions. The objective of "increasing competitiveness", for example, may likely lead to increased biophysical stress, which is antagonistic to the objective of "preserving landscapes and biodiversity". Our approach facilitates the integration of diverse perspectives by researchers and the development of policy-relevant indicators capable of informing the discussion between what is wanted and what can be done. More information can be found in Cadillo-Benalcazar et al. (2020) and Renner et al. (forthcoming).
Cadillo-Benalcazar JJ, Renner A, Giampietro M (2020) A multiscale integrated analysis of the factors characterizing the sustainability of food systems in Europe. J Environ Manage in press: https://doi.org/10.1016/j.jenvman.2020.110944
Renner A, Cadillo-Benalcazar JJ, Benini L, Giampietro M (forthcoming) Environmental pressure of the European agricultural system: An exercise in biophysical anticipation. Ecosyst Serv.
Dialogue Space > The Nexus Times > Modelling energy systems as multi-scale systems
One of the main goals of the MAGIC project has been that of modelling the interactions between energy, food and water, taking a perspective that is grounded in complexity. Most systems in the world can be broken down into components: cities are made of neighbourhoods; molecules are made of atoms; societies are made of people. Nexus interactions span through systems across different scales, with each scale affecting one another. For example, a coal power plant may affect its local embedding environment by polluting a nearby water source, while also generating global greenhouse gas emissions which, in turn, alter its local environment.
Our approach to modelling nexus interactions has been to focus on this multi-scale perspective, by using different information to describe nexus patterns at different scales of analysis. These types of information cannot be reduced to a single metric, and each description may be more or less useful depending on the goal of the analysis. This is why in MAGIC we do not rely on single indicators, such as efficiency or energy intensity, to measure the performance of the energy system.
The way we have broken down the energy system across different scales has not been in purely material forms – e.g., breaking down power plants into their components. Instead, we have focused on the distinction between function and structure of the energy system, taking inspiration from biology. For the case of energy, this means considering the different functions played by energy technologies – e.g., providing heating, or fuels, or baseload electricity.
Figure 1 shows an example of this, mapping Spain’s energy sector as a multi-scale network. The main node, “Energy sector”, is split into a fuels and an electricity component (since Spain does not have a heating sector). Electricity and fuels are then split hierarchically into further sub-sectors. Additional functional layers could be added depending on the goal of the analysis. Electricity, for example, could be split into baseload, peak and intermittent electricity. Each node in the network represents a processor, i.e., each node is associated with a set of nexus inputs and outputs (water, GHG emissions, labour, land, etc.). Further information on how elements of the energy systems can be described as processors can be found in Di Felice et al. (2019) (see the link to the open-access article at the bottom of this page). While intermediate levels in the network are functional, at the lowest level these functional layers are mapped onto their structures, i.e. the technologies fulfilling different purposes.
Here, the network in Figure 1 shows a distinction between blue and red nodes. Blue nodes are local ones. They are the processes taking place within the geographic boundaries of Spain. This includes most power plants and most refineries. Red nodes, instead, are those connected to Spain’s energy system, but which take place elsewhere (what we refer to as externalised processes). These include the extraction processes tied to Spain’s direct and indirect imports, for example. Mapping the energy sector across these different functional layers, associating each node with a set of nexus inputs and outputs, and making the distinction between local and externalised processes allows us to tap into questions that are relevant to the multi-level governance of sustainability, including:
Which functions of the energy sector emit most greenhouse gases? How can these functions be reduced or substituted?
What would happen to nexus elements across different scales, if the energy sector were to be gradually electrified?
How would the pattern of local and global environmental effects shift, if Spain decided to produce all of its energy locally?
We are currently working on this application, providing a multi-scale network description of the energy sector of the EU as a whole, and relating it to pressing policy questions. Follow us on twitter at @MAGIC_NEXUS to find out when the article is out!
Di Felice, L. J., Ripa, M., & Giampietro, M. (2019). An alternative to market-oriented energy models: Nexus patterns across hierarchical levels. Energy Policy, 126, 431-443. https://doi.org/10.1016/j.enpol.2018.11.002
Dialogue Space > The Nexus Times > The role of human activity in the nexus structuring space
The role of human activity in the nexus structuring space
Laura Pérez-Sánchez, Raúl Velasco-Fernández, Michele Manfroni, Sandra Bukkens & Mario Giampietro
Current discussions on sustainability tend to focus principally on the shortage of natural resources and environmental degradation: water and material footprints, peak oil, greenhouse gas emissions, destruction of habitats, etc. Society is mostly pictured as a black box and its environment as a factor limiting its expansion. Constraints operating inside the society are often overlooked. Human activity or time use is one such constraint. A shortage of human time in one or more critical elements of society constrains the trajectory of economic growth, in a way like other biophysical production factors do, such as water, energy, and land. Whereas the limits to primary resource supply and sink capacity are difficult to assess, the human time yearly available both at the national and at the global level has a well-defined limit: population size × hours in a year. MuSIASEM is unique in that it analyzes sustainability from a metabolic perspective including internal societal constraints. Indeed, MuSIASEM expresses resource flows not only per unit of land but also per unit of time use (e.g. electricity per hour of human activity in the transport sector). The adopted metabolic perspective thus allows us to address the entanglement over the diverse factors (demographic, cultural, socio-economic, technical and biophysical) that affect the option space of desirable (compatibility with culture and values), viable (compatible with technology, infrastructure, and institutions) and feasible (compatible with nature’s capacity to contribute to people) profiles of human time allocation.
Any human society simultaneously generates and requires human time for its reproduction. The demographic structure of society and the prevailing social practices define a forced dynamic equilibrium between supply and demand of time. Natural population growth does not necessarily solve a problem of shortage of time, as it does not only lead to a larger supply of human activity but also an increased requirement of working time (e.g. for child care, education, health care etc.). Post-industrial countries can (temporarily) overcome economic stagnation caused by shortage of working time through the use of technology and energy—boosting labor productivity, through immigration of adult workers—notably seasonal and temporary workers— and through the externalization of the requirement of working time in the form of imported goods and services. Indeed, the contemporary mode of socio-economic development has entailed a massive movement of workers away from the agricultural and industrial sectors to the service and government sector. This was made possible during the industrial revolution, which saw the mechanization of the primary and secondary sectors thus freeing up labor time for the service sector and, importantly, leisure time for the consumption of goods and services [1–4]. The post-industrialization process (globalization) has consolidated this trend through the use of embodied working time in the form of imported goods and services (notably in agriculture, mining, manufacturing, and waste treatment) and (seasonal/temporary) foreign migrant workers (notably for low-skilled occupations in the sectors of agriculture, mining, construction, transport and the private sector—house cleaning). Note that imported working time in the form of imported goods and services often concerns labor with lower salaries and less social protection.
Many of the applications of the Nexus Structuring Space in MAGIC have addressed the externalization of human labor. But probably the most striking ones are the comparison of the metabolic pattern of China with that of the EU and the USA  and the assessment of the virtual hours of labor embodied in imports in the EU . These applications concern the use of the macroscope (internal end-use matrix), mesoscope (trade) and the virtual scope (embodied labor in imported goods and services). For instance, the overall amount of work required to produce the goods and services consumed by an average US, EU and Chinese citizen is respectively: 1430, 1230 and 985 hours per capita per year . As for the actual hours of paid work allocated to the economy of these countries, we found that the USA and EU allocate, respectively, 790 and 730 hours per capita per year, whereas China allocates 1300 hours per capita per year (see Figure 1). China is the only country of these three presenting a positive work balance: a part of the available work hours of its internal work force goes into exports. The USA and the EU, on the other hand, almost double the internally available hours of labor to produce the goods and services they consume, thanks to embodied labor in imported goods and services. For instance, in 2011 the EU used 500 hours of embodied work per capita per year in its imports that are equivalent to more than 120 million annual work units (virtual workers; assuming a work load per unit/virtual worker of 1700 hours/year). Similar results were found for the USA. The large import of hours of embodied work in the EU is possible only because of the small size of its population compared to the world population. Given the fixed time budget at the global level, the reproduction of EU (and US) consumption levels that emerging economies such as China and India are striving for is simply implausible, given the limited size of the ‘fund’ of human activity. This raises important ethical issues and questions the EU’s commitment to the Sustainable Development Goals.
The characterization of human activity patterns currently observed through the macroscope refers only to the allocation of human activity inside the paid work sector. In the future we plan to extend this analysis by characterizing the metabolic pattern associated with social practices outside the formal economy (e.g. residential/household sector). Social practices outside of the paid work sector represent the equivalent of the microscopic view of the technological process of production inside the paid work sector.
These applications show the relevance of the MuSIASEM framework in informing sustainability discussions with regard to the viability and desirability concerns. A detailed theoretical exposition on the profile of time allocation as an emergent property of the metabolic pattern of society is forthcoming .
 G.K. Zipf, National unity and disunity: The Nation as a Bio-social Organism, Principia Press Inc., Bloomington, 1941.
 V. Smil, Making the Modern World : Materials and Dematerialization., Wiley, 2013.
 C.M. Cipolla, The Economic History of World Population, Pelican Books, 1962.
 M. Giampietro, K. Mayumi, A.H. Sorman, The Metabolic pattern of societies: where economists fall short, Routledge, London, 2012.
 R. Velasco-Fernández, L. Pérez-Sánchez, M. Giampietro, A becoming China and the assisted maturity of the EU: assessing the factors determining their energy metabolic patterns, Energy Strateg. Rev. in press (2020).
 L. Pérez-Sánchez, R. Velasco-Fernández, M. Giampietro, The international division of labor and embodied working time in trade for the US, the EU and China, Ecol. Econ. (2020).
 M. Manfroni, R. Velasco-Fernández, M. Giampietro, The profile of allocation of human time and societal organization: the internal constraint to perpetual economic growth, Unpubl. Manuscr. (2020).
Dialogue Space > The Nexus Times > The biofuel promise: examining sustainability and policy expectations around liquid biofuels
The biofuel promise: examining sustainability and policy expectations around liquid biofuels
Biofuels represent a ‘wicked problem’ (i.e. a problem characterized by a diversity of conflicting values at stake and associated with high uncertainties) and have triggered sharply contested views in the policy arena. The heterogeneous methods used to measure compliance of biofuels with sustainability criteria, as well as the changing regulatory frameworks and moving targets have created a substantial confusion.
In MAGIC, biofuels have been framed both as a technological innovation—referring to the sustainable use of biomass to produce energy (mostly fuels)—and as a promise, providing a way out of the nexus policy impasse.
First, biofuels are framed as innovations potentially offering win-win solutions to the double problem of reducing the consumption of fossil fuels (to improve energy security and/or mitigate climate change) and supporting economic growth (and all the activities dependent on liquid fuels that cannot run on electricity). Over the last twenty years, several assessment methods have been employed to investigate biofuels from a sustainability viewpoint, such as energy analyses, life cycle assessment, carbon and water footprints (Azadi et al., 2017). These approaches, however, are usually based on just one or a limited set of indicators (e.g. GHG emissions and energy efficiency) that can be reduced to a single index (UNEP, 2017). Even when a larger set of indicators are provided, the protocol of analysis dislocates these indicators from any specific context (Bridge, 2001; Levidow, 2013). For example, questions of uneven spatial distribution in terms of where biomass has come from, which regions have borne the negative impacts, which ones benefited, and alternative techniques of production are not typically included in ‘sustainability assessment’. As a result of the lack of a more holistic picture and despite a large amount of studies, controversy has historically surrounded the assessment of the sustainability of biofuels and uncertainty has been growing in relation to their possible benefits and risks.
In MAGIC, we developed an analytical framework to characterize and contextualize in quantitative terms the performance of biofuel systems (see Ripa et al. 2020). This framework derives from the integration of three scientific fields—energetics (Ostwald, 1907), relational analysis (Rosen, 2005), and the flow-fund model of Georgescu-Roegen (Georgescu-Roege, 1975)—and helps to tame the confusion about the performance of biofuels. Figure 1 presents the four relevant perspectives on biofuels of the proposed framework:
The social factors determining their requirement on the demand side—why do we want to produce biofuels?
The internal technical and economic constraints affecting their mode of production on the supply side—how can we produce biofuels?
The external biophysical constraints limiting their production—what are the material limits imposed by the availability of natural resources?
The level of openness of the biofuel system referring to imports being specifically used to overcome local limits (thus externalizing the requirement of natural resources and technical production factors).
The framework aims to check the quality of energy strategies in terms of desirability, viability and feasibility by comparing the technical characteristics of the energy supply system against the specific characteristics of the social-ecological systems expected to use them (Figure 2). Therefore, this analytical framework enhances the diversity of the quantitative information used in the process of decision-making. Rather than looking for the ‘best course of action’ or ‘optimal solution’ in relation to technical processes described “in general” and out of context, our approach allows a special tailoring of the definition of both the purpose of the analysis and the resulting characterization of performance.
The second framing used in MAGIC is that of biofuels as a promise. In this case, what matters is the idea of biofuels as an environmentally-friendly and renewable way of producing fuels. The EU has consistently supported biofuels, despite controversies, criticisms and even discontinuities in political support. Hence, in this analysis we examined why some ‘solutions’ persist, even when they have persistently failed once materialized.
Our results show that, in spite of scientific criticisms regarding the viability of biofuels, the European Commission has maintained its support for their development through a continuous adjustment of expectations (i.e. why producing biofuels) - energy security, reduction of GHG emissions, employment in agriculture, improvement of fuel quality, contribution to the circular economy and avoidance of sunk costs to investors - and targets in the various policies regarding biofuels (Cadillo-Benalcazar et al. 2020). Our analysis challenges the plausibility of biofuels’ policies and concludes that, depending on their specific legitimate perspectives, social actors may first identify a convenient target to set (or preserve) and then select a fitting justification (from among the many possible ones) to support that target. Therefore, achieving biofuel targets has become a justification in itself (Cadillo-Benalcazar et al. 2020).
Ripa, M., Cadillo-Benalcazar, J.J., Giampietro, M., 2020. Cutting through the biofuel confusion: an analytical framework to check the feasibility, viability and desirability of biofuels. Energy Strategy. Under Review.
Rosen, R., 2005. Life itself: a comprehensive inquiry into the nature, origin, and fabrication of life. Columbia University Press, New York.
UNEP, 2017. Assessing Biofuels. Towards Sustainable Production and Use of Resources.