Thermodynamics is the science of the nature of relationships between heat and other forms of energy and their conversion, flow direction, and availability for work (e.g. Zemansky, 1997).
The first and second laws of thermodynamics are of most importance to sustainability.19,20 The
first law is commonly referred to as the law of conservation of energy and provides that while
19 The third law of thermodynamics provides that as a temperature of absolute zero (-273°C) is
approached, the extraction of energy from a system or its environment becomes increasingly more difficult.
20 Georgescu-Rogen’s (1977a, 1979) statements on material entropy have been popularly termed the
‘fourth law of thermodynamics’. He proposed (1979, p.1039) that in a closed system, such as the biosphere, “material entropy must ultimately reach a maximum”. In other words, the quality of matter decreases as waste products become scattered and unusable. The notion of material entropy has,
energy may be transformed during processes, it can be neither created nor destroyed.21 The second law is commonly referred to as the ‘entropy law’ (Georgescu-Roegen, 1971). Rephrased for interpretation by non-physicists, it can be formulated as, “[a] substance will always come to a unique equilibrium with its environment. The path it takes over time to reach this equilibrium is reproducible, depending only on the applied constraints and its initial condition” (Fisk, 2011). This law implies that if a system is in a low entropy (ordered) state, it will tend to move toward a state of maximum entropy (disorder). In addition, processes are irreversible in the sense that an injection of energy that is greater than the amount of energy liberated by the process in the first place, is required. An important corollary of this law is that open systems may only establish, and sustain, a state of low entropy (non-equilibrium) by creating flows of negative energy to the environment via the dissipation of energy and matter (Prigogine, 1967; Glansdorff and Prigogine, 1971; Prigogine, 1977; Schneider and Kay, 1992). Economic and environmental systems, which are among the class of systems often referred to as ‘dissipative structures’ (Schrödinger, 1944) and exist at a state far from thermodynamic equilibrium, hence depend on large amounts of high-quality energy supplied from outside the respective systems.
The law of conservation of mass or the so-called Mass Balance Principle (Ayres and Kneese, 1969) is often viewed as an outcome of the first law of thermodynamics. Strictly speaking, however, the first law only applies to the conservative nature of energy transformations. Regardless, the principle is important in helping convey the idea that, barring accumulation in the production process, all materials extracted from the environment for use in economic activities must ultimately be balanced by the returned of materials to the environment in the
form of residuals and unwanted materials (Ayres and Kneese, 1969; Kneese et al. 1970).
Informed by the first and second laws of thermodynamics and the Mass Balance Principle, the economy is seen as an open system embedded within the global biophysical system (e.g. Gilliland (1977)). Since the world only has a finite mass, growth in the physical size of the economy must come at the expense of the environment. In a physical sense, the size of the economy also cannot exceed the capacity of the biosphere to produce material and energy
21 As explained by authors such Faber et al. (1987), Binswanger (1993) and Ruth (1993), three types of
systems are recognised under thermodynamic analyses: (1) an isolated system involving neither energy nor matter exchange across a system boundary; (2) a closed system under which only energy may cross a system boundary; and (3) an open system under which both matter and energy may cross a system boundary. The first law implies that energy net transfer of energy across a system boundary as either heat or work, is equivalent to the net change in the internal energy of the system.
resources, or assimilate residuals. The economic system is further viewed by economists such as Ekins (1994), Reid (1995) and Wetzel (1995) as operating essentially via the transformation of inputs of low entropy materials and energy (e.g. fossil fuels, minerals) into outputs of degraded, high entropy materials/energy (e.g. gaseous emissions, waste heat). Note that the second law also implies that complete economic recycling of wastes and residuals is impractical, at least not without significant inputs of high quality energy to the recycling
processes (Georgescu-Roegen, 1971, 1976; Daly, 1987; Bianciardi et al., 1996). The system is
further constrained in that processes within the environment (including the biogeochemical cycles) that act to absorb high entropy matter/energy expelled by the economy and regenerate useful resources are themselves dependent on ongoing inputs of low entropy matter/energy from outside of those systems.
Such insights have had a wide influence within the sustainability literature (Ayres and Kneese, 1969; Georgescu-Roegen, 1971, 1977b; Victor, 1972; Daly, 1977, 1996, 2008; Perrings, 1987; Ayres, 1999; Odum and Odum, 2006). Daly (1992, p.16), for example, proposed a steady-state economy characterised by “constant stocks of people and artefacts, maintained at some desired, sufficient levels by low rates of maintenance ‘throughput’, that is, by the lowest feasible flows of matter and energy from the first stage of production (depletion of low entropy materials from the environment) to the last stage of consumption (pollution of the environment with high entropy wastes and exotic materials.” He further proposed the principle of appropriate ‘scale’ as one of the three core principles for an efficient, just and sustainable economics (Daly, 1992). Scale, in turn, is defined as physical volume of throughput via the flow of low-entropy raw materials from the environment and the return of high- entropy wastes. More recently, Pelletier (2010, p.1892) states that the principle of scale is legitimised when “[i]nformed by thermodynamic principles, which dictate the most basic
conditions necessary to ecological integrity across scales of organization”.22 Research on how
to conceptualise the scale of human activities is now widely recognised as a core agenda for
the discipline of ecological economics (Røpke, 2005; Rockström et al., 2009).
Importantly, thermodynamic principles have had a significant impact within the field of ecology. To a large extent this is attributable to the work of the Odum brothers beginning in
22 Although thermodynamic principles are frequently credited as a major source of inspiration and
thought on the physical conditions limiting the scale of human enterprise (Hammond, 2004), contributions to the scale debate have arisen out of more than thermodynamic principles alone. Paul
Ehrlich’s book The Population Bomb (1968), for example, focused particularly on population growth and
the 1950s (Odum, 1953).23 Key concepts from ecology are outlined separately in the next section.
Clearly thermodynamic considerations, along with the Mass Balance Principle, also underpin
the field of Industrial Ecology.24 As stated by Bringezu and Moriguichi (2002, p.79), the
paradigm vision for the field is “a sustainable industrial system characterized by minimized and consistent physical exchanges between human society and the environment, with internal material loops driven by renewable energy flow”. Material Flow Analysis (MFA), a methodology within Industrial Ecology, is concerned with the tracing of socio-economic materials and energy flows, and assessment of changes in relevant ecosystems related to these flows. The use of the Mass Balance Principle within MFA helps avoid overlooking important uses of resources and/or their release to the environment (Lifset and Gradel, 2002).
As also noted by Haberl et al. (2004), a key advantage of MFA is that it is able to link data and
models used to analyse socioeconomic systems (e.g. IO analysis and general equilibrium modelling) to data and models used for environmental systems (e.g. box-flow models). MFA is further recognised as a key tool for assessing the resource efficiency of economies, in particular providing valuable insights into analyses concerned with evaluating the rate of
decoupling of natural resources and environmental impacts (Fischer-Kowalski et al., 2011).
Decoupling, which has been defined simply as “breaking the link between ‘environmental
bads’ and ‘economic goods’” (OECD, 2001),25 is now one of the most frequently promoted
objectives of national and international agencies in relation to sustainability (refer to, in
particular, UNEP et al. (2011)).
23 See, in particular, the later work of H.T. Odum (1983). Thermodynamic concepts and consequences
are also discussed by Morowitz (1968), Brooks and Wiley (1988), Wicken (1985), and Zotin (1985), among others.
24 Industrial Ecology, which emerged during the 1990s (Ayres and Simonis, 1994; Erkman, 1997), is now
said to encapsulate sufficient tools, studies, publication, and resources to characterise itself as a discipline (Ehrenfeld, 2000, 2001). A central tenet of Industrial Ecology is that Nature is a model for
industrial ecological systems (Isenmann et al., 2008), that is, as put by Cleveland (1999, p.148), “to look
to the natural world for models of highly efficient use of resources, energy and byproducts”.
25 Decoupling has been further categorised as either ‘relative’ or ‘absolute’ (UNEP et al., 2011). Relative
decoupling occurs when the growth rate of an environmentally relevant parameter is lower than the growth rate of a relevant economic parameter. Under absolute decoupling, however, the environmentally relevant parameter declines, irrespective of the growth rate of the economic parameter. Thus, absolute decoupling can only occur when the growth rate of resource productivity exceeds the growth rate of the economy.