Emergy

The term 'Emergy' was originally coined by David M. Scienceman in collaboration with the late Howard T. Odum. H.T.Odum used 'emergy' to mean both ''sequestered'' energy and ''emergent property of energy use''. However Scienceman also used the term 'emergy' to refer to the concept of ''energy memory'', a concept which motivated Scienceman and B.M. El-Youssef (1993) to propose the addition of a new dimension to physics, [P] for "past". Some researchers maintain that it can be expressed as a scientific unit which is called the "emjoule", a contraction of "''em''ergy joule".

Historical development

As a word, 'emergy' is a simple contraction of the term "'em'bodied en'ergy'". The need for the new word of "emergy" arose apparently because of an important difference in the way the two related disciplines of systems ecology and energy analysis were using the term "embodied energy". As H.T.Odum (1984, p.189) observed "There is more than one type of embodied energy". Various authors have struggled to clarify their usage, and ambiguity seems to continue in the literature to this day.

Prior to 1986, both systems ecologists and energy analysts used "embodied energy" to refer to the sum over time of all energy of one type required to generate a flow of energy (H.T.Odum and E.C.Odum 1983, p. 13). Energy embodied in water was also defined in this way as the energy required directly and indirectly to generate the flow in processes of the biosphere or a typical desalination plant for example (Wang et al. 1980, p. 201).

However unlike energy analysts, systems ecologists were, and continue to be also interested in the relationship of structure and function of ecological systems (E.P. Odum 1962), together with the biophysical properties that afford plants the ability to accumulate and transform radient energy into a structural form useable by other organisms (E.N. Transeau 1926). Scienceman (1987, p.260) observed this difference noting that the systems ecologist H.T. Odum had introduced an additional factor into the definition of embodied energy:

The term "embodied energy" was therefore also used by systems ecologists to describe the energy that had been used in, and accumulated into structure-development (Odum 1970, p.62) and which could be fed back into the system to draw in more energy (J.R. Richardson 1988, p. 18). This structural-cybernetic aspect of ecosystem research (Patten 1959, Patten and E.P.Odum 1981) was apparently not included in the energy-analytic definition of "embodied energy".

However the fact that both systems ecologists and energy analysts used the same term but with different levels of content seems to have led to considerable confusion.