The ecologist Howard Odum analyzes energy
The ecologist Howard Odum analyzes energy and materials with a system that traces their flows within and between society and the environment. It is important to differentiate between two aspects of Odum’s contribution. The first is his development of a biophysically based, systems-oriented model of the relationship between society and the environment. Here, Odum’s early contributions helped lay the foundation for the biophysical analysis of energy and material flows, an area of research that forms part of the intellectual backbone of ecological economics. The insight from this part of Odum’s work is illustrated by the fact that ideas he emphasized— energy and material flows, feedbacks, hierarchies, thresholds, and time lags—are key concepts of the analysis of sustainability in a variety of disciplines.
The second aspect of Odum’s work, which we are concerned with here, is a specific empirical issue: the identification, measurement, and aggregation of energy and material inputs to the economy, and their use in the construction of indicators of sustainability. Odum measures, values, and aggregates energy of different types by their transformities. Transformities are calculated as the amount of one type of energy required to produce a heat equivalent of another type of energy. To account for the difference in quality of thermal equivalents among different energies, all energy costs are measured in solar emjoules, the quantity of solar energy used to produce another type of energy. Fuels and materials with higher transformities require larger amounts of sunlight to
produce and therefore are considered more economically useful.
Several aspects of the emergy methodology reduce its usefulness as a method for aggregating energy and/or material flows. First, like enthalpy and exergy, emergy is one-dimensional because energy sources are evaluated based on the quantity of embodied solar energy and crustal heat. However, is the usefulness of a fuel as an input to production related to its transformity? Probably not. Users value coal based on it heat content, sulfur content, cost of transportation, and other factors that form the complex set of attributes that determine its usefulness relative to other fuels. It is difficult to imagine how this set of attributes is in general related to, much less determined by, the amount of solar energy required to produce coal. Second, the emergy methodology is inconsistent with its own basic tenant, namely that quality varies with embodied energy or emergy. Coal deposits that we currently extract were laid down over many geological periods that span half a billion years. Coals thus have vastly different embodied emergy, but only a single transformity for coal is normally used. Third, the emergy methodology depends on plausible but arbitrary choices of conversion technologies (e. g., boiler efficiencies) that assume users choose one fuel relative to another and other fuels based principally on their relative conversion efficiencies in a particular application. Finally, the emergy methodology relies on long series of calculations with data that vary in quality. However, little attention is paid to the sensitivity of the results to data quality and uncertainty, leaving the reader with little or no sense of the precision or reliability of the emergy calculations.