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Social Metabolism and Accounting Approaches
Social Metabolism: A Biophysical Approach to the Economy
In recent years a consensus seems to have grown that regards sustainability as a problem of the interaction between society and nature (Haberl et al. 2004). The precise nature of this interaction is biophysical: It is the continuous throughput of materials and energy on which each socio-economic system depends and which constitutes its relation to the natural environment. Such an understanding of society as a socially organized and thermodynamically open system has been termed social (Fischer-Kowalski and Haberl 1993) or industrial metabolism.
The application of the biological concept of metabolism (Stoffwechsel) to social systems can be traced back to Marx who, influenced by Liebig and Moleschott, talks about the ―metabolism between man and nature as mediated by the labour process‖. Such a biophysical approach to the economy was not unusual at the turn of the 19th century but arguably did not form an integrated school of thought until recently (see Martinez-Alier 1987; Fischer-Kowalski 2002). This biological analogy grew from the observation that biological systems (organisms, but also higher level systems such as ecosystems) and socio-economic systems (human societies, economies, companies, households etc.) decisively depend on a continuous throughput of energy and materials in order to maintain their internal structure (Fischer-Kowalski and Haberl 1993).
Social Metabolism Accounting Methods
The social concept links material and energy flows to social organization, recognizing that the quantity of economic resource use, the material composition and the sources and sinks of the output flows are historically variable as a function of the socio-economic production and consumption system. When speaking of metabolism however, one must have adequate knowledge of the system that has to be reproduced. Only then is it possible to assess the material and energetic flows required for the maintenance of the system in question. Most likely the system is a society at a specific level of scale and might be described as an organized set comprising a cultural (symbolic) system and those material elements accorded preferential treatment by the cultural system (human population and material artefacts) (Fischer-Kowalski and Weisz 1999). The flows are accounted where society appropriates or releases materials from or to nature.
Today, social or industrial metabolism, along with standardized methods to account for its energy flow, material flow, and land use aspects, provides the basis for empirical analyses of the biophysical structure of economies and for developing strategies towards more sustainable production and consumption patterns. A number of operational tools have been developed to analyze the biophysical aspects of social metabolism, its associated driving forces and environmental pressures (Haas et al. 2005). Examples outlined below include material and energy flow analysis (MEFA, or MFA), input-output analysis (IOA) and life cycle analysis (LCA), but other instruments in the social metabolic toolkit include HANPP, EROI, and Virtual Water, as well as related concepts such as ecological footprinting and ecological rucksacks.
Material Flow Analysis (MFA)
Material flow accounting (MFA) is a specific environmental accounting approach, aiming at the quantification of social metabolism. MFA is applicable to various geographic and institutional scales. MFA at the national level (denoted as economy-wide MFA) is probably most advanced in terms of methodological standardization and indicator development. Economy-wide MFAs are consistent compilations of the annual overall material throughput of national economies, expressing all flows in tons per year. After the seminal work of Robert Ayres and Allen Kneese, MFA was ―reinvented‖ in the 1990s as a consequence of the growing importance of the notion of sustainable development. In recent years, methods for economy-wide material flow accounting have been harmonized and a large number of material flow studies for both industrial and developing countries have been published to date.
As MFA accounts for materials entering and leaving a system, the mass balance principle applies. Based on the conservation of mass principle it states that matter can neither be created nor destroyed. The mass balance principle can be formulated as: All material inputs into a system over a certain time period equal all outputs over the same period plus the stock increases minus the releases from stock. In principle net stock changes can be positive, indicating net accumulation, or negative, indicating stock depletion. In MFA, the mass balance principle is used to check the consistency of the accounts. It also provides one possibility to estimate the net additions to stock (NAS).
A flow is a variable that measures a quantity per time period, whereas a stock is a variable that measures a quantity per point in time. MFA is a pure flow concept. It measures the flows of material inputs, outputs and stock changes within the national economy in the unit of tonnes (= metric tonnes) per year. This means that in MFA stock changes are accounted for but not the quantity of the socio-economic stock itself. Although MFA is a flow concept, it is still important to define carefully what is regarded as a material stock of a national economy because additions to stocks and stock depletion are essential parts of the MFA framework. The definition of material stocks is also crucial in identifying which material flows should or should not be accounted for as inputs or outputs.
In MFA, three types of socio-economic material stocks are distinguished: artefacts, animal livestock, and humans. Artefacts are mainly man-made fixed assets as defined in the national accounts such as infrastructures, buildings, vehicles, and machinery as well as inventories of finished products.
Highly aggregated indicators are derived from MFA. These are: domestic extraction (DE), direct material input (DMI), domestic material consumption (DMC), physical trade balance (PTB), total material requirement (TMR), total material consumption (TMC), and net additions to stock (NAS). Overall, these indicators are intended to represent a proxy for aggregated environmental pressure comparable to aggregated energy use or aggregated land use. By relating these MFA indicators to macro-economic parameters (predominantly GDP) resource efficiency indicators can be derived which measure either material use per unit of GDP (resource intensity) or vice versa GDP per unit of materials used (resource productivity). For benchmarking national economies per capita values are commonly used (Haas et al. 2005).
Society’s material (and energy flows) within the M(E)FA framework. (Source: Haberl et al 2004)
Input-Output Analyses (IO)
Input-output economics is a body of theory created by Nobel Prize laureate Wassily Leontief in the late 1930s and was originally designed to analyse the interdependence of industries in an economy. Since the late 1960s, IO analysis was extended to allow for addressing economy-environment relationships, focusing predominantly on energy use and pollution. Within industrial ecology, IO analysis has been applied increasingly to LCA (see below) in past years. Limited work has been done concerning the application of IO analysis to economy-wide MFA.
For input-output computations to deliver reliable results, an appropriate level of disaggregation by sectors or commodities is necessary. The most common IO approach is where the measurement to express the quantities of output of all sectors of the economy is money value (expressed in national currency and current prices). Such a table is called a monetary input-output table (MIOT).
Another approach is a purely physical model based on an input output table where the quantities of the output of all sectors are measured in one single unit of mass. Such a table is called a physical input-output table (PIOT). Also for a PIOT sectoral input must equal sectoral outputs, according to the mass balance principle (Weisz 2006).This approach involves the exhaustive physical coverage of the movement (origins and uses) of most environmentally relevant materials induced by an economic region (sometimes disaggregated to the level of elements or simple chemical compounds). The PIOT method traces how natural resources enter, are processed, and subsequently) as commodities, are moved around the economy, used, and finally returned to the natural environment in the form of residuals. It undertakes the detailed investigation of intersectoral physical flows of environmental resources inputs and commodity weights and residuals, and given this intersectoral specification and transactions matrix structure, has the ability to evaluate the cumulative environmental burden (total direct and indirect effect material requirements and pressures) of private consumption and other final demand for the products of different industries.
The third approach is a mixed unit model based on an input-output table where the output from the production sectors is measured in mass units and the output from the service sectors is measured in money value. In a mixed unit input-output table only total output, but not total input, can be computed, because total input would imply adding different units. It follows that no input output equation can be applied to a mixed unit input-output table (Weiz 2006).
Life-Cycle Assessment (LCA)
Life-cycle assessment (LCA) is an environmental management tool for identifying (and comparing) the whole life cycle, or cradle-to-grave, environmental impacts of the creation, marketing, transport and distribution, operation, and disposal of specific human artifacts. The approach considers direct and, ideally, related processes and hidden, nonmarket flows of raw materials and intermediate inputs, and waste and other material and energy outputs associated with the entire existence or ―product chain‖ or ―system‖. The LCA procedure often involves a comparison of a small number of substitutable products assumed to provide a similar consumption service.
Life Cycle Assessment is conducted to answer questions such as:
*How do two different manufacturing processes for the same product compare in terms of resource use and emissions?
*What is the benefit of changing technology (chemicals)?
*What are the relative contributions of the different stages in the life cycle of this product to total emissions?
*What is the environmental footprint of my product, service, and company?
*How can I decrease it? What matters the most?
*What is my Carbon contribution to Green house effect?
Life Cycle Assessment (LCA) evaluates the mass balance of inputs and outputs of systems and to organize and convert those inputs and outputs into environmental themes or categories relative to resource use, human health and ecological areas (http://www.science-environment-consulting.com/en/life-cycle-assessment.html).
Life Cycle Inventory (LCI)
The quantification of inputs and outputs of a system, i.e. material and energy flows (Ekvall and Finnveden 2001) is called Life Cycle Inventory (LCI) (http://www.science-environment-consulting.com/en/life-cycle-assessment.html). In the case of multi function processes an allocation problem arises in LCI: Concerning production processes with more than one product – this is: What share of the environmental burdens of the activity should be allocated to the product in question i.e. included in the LCI? The chosen solution to the allocation process can have a decisive impact on results of an LCI and a number of different solutions have been proposed including a standard procedure by the The International Organisation for Standardisation‘ (ISO 14041, 1998) (Ekvall and Finnveden 2001).
Life Cycle Impact Assessment (LCIA)
Life Cycle Impact Assessment (LCIA) converts inventoried flows into simpler indicators. In a Life Cycle Impact Assessment (LCIA), essentially two methods are followed: problem-oriented methods (mid points) and damage-oriented methods (end points). In the problem-oriented approaches, flows are classified into environmental themes to which they contribute. Themes covered in most Life Cycle Assessment (LCA) studies are: Greenhouse effect (or climate change), Natural resource depletion, Stratospheric ozone depletion, Acidification, Photochemical ozone creation, Eutrophication, Human toxicity and Aquatic toxicity. These methods aim at simplifying the complexity of hundreds of flows into a few environmental areas of interest. EDIP and CML 2000 methods are examples of problem-oriented methods. The damage-oriented methods also start by classifying a system‘s flows into various environmental themes, but model each environmental theme damage to human health, ecosystem health or damage to resources. For example, acidification - often related to acid rain may cause damage to ecosystems (e.g., in the Black Forest in Germany), but also to buildings or monuments. In essence, this method aims to answer the question: Why should we worry about climate change or ozone depletion? EcoIndicator 99 is an example of a damage-oriented method.
Impact assessment methods have been developed as tools to broaden the information and context of Life Cycle Inventory (LCI) data, which refer mainly to mass and energy. The fact that LCIA indicates that certain emissions are associated with certain environmental themes or impact categories does not imply that the studied product or system actually causes effects. It means however, that in the course of the life cycle, emissions are generated that contribute to a pool of similar emissions known to be associated with these environmental themes or impact categories. Used this way, Life Cycle Assessment is an appropriate tool for helping to determine to what extent a particular product, process or ingredients emissions may be associated with a particular impact category (http://www.science-environment-consulting.com/en/life-cycle-assessment.html).