Emergy is an expression of all the energy and material resources used in the work processes that generate a product or service, calculated in units of one form of energy. In the early 1970’s, Howard T. Odum recognized that traditional methods of measuring energy did not account for the “quality” of different forms of energy (e.g., sunlight, versus fossil fuels or electricity). As a systems scientist with expertise in many fields, including biogeochemistry, ecology, meteorology, and open systems thermodynamics, Odum reasoned that a measure of a product’s quality could be obtained from evaluating the total energy and matter directly and indirectly required to make it. Odum and his colleagues began using sunlight as the base to evaluate all other forms of energy, reasoning that, all other forms are nothing more than concentrated sunlight. As the concept matured, evaluations were conducted on many processes of the biosphere (ecological and technological) calculating the energy required to transform energy and materials from one form into another. David Scienceman, an Australian colleague of Odum’s, coined the term emergy. Odum believed that emergy was a universal measure of the work of nature and society made on a common basis and therefore a measure of the environmental support to any process in the biosphere. The ratio of the total emergy input to the available energy of the product was named transformity. Since all energy transformations of the geo-biosphere can be arranged in an ordered series to form an energy hierarchy reinforced and stabilized by web-like and feedback interactions, transformities can be used as indicators of hierarchical position and role of a component in the thermodynamic hierarchy of the whole system.
Mark Brown (Lead Author);Sergio Ulgiati (Contributing Author);Cutler J. Cleveland (Topic Editor) "Emergy". In: Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). [First published in the Encyclopedia of Earth November 18, 2008; Last revised Date November 18, 2008; Retrieved May 20, 2013 <http://www.eoearth.org/article/Emergy>