H.T. Odum left an extraordinarily broad theoretical and methodological framework, but not a closed or completed one. Questions remained about the mathematics of emergy networks, the treatment of feedback and co-products, the interpretation of emergy indices, the calculation and standardization of unit emergy values, the global emergy baseline, and the relationship of emergy to other approaches to environmental accounting. Following Odum’s death in 2002, researchers around the world increasingly assumed responsibility for addressing these questions.
The Emergy Synthesis conferences became particularly important in this transition. What had begun during Odum’s lifetime as an international forum for emergy research continued as a place where unresolved theoretical and methodological problems could be presented and debated. In some respects, the conferences extended internationally the intellectual process that had characterized the Systems Seminars at the University of Florida. Ideas could be presented before they were finished, questioned by others, recalculated, revised, and presented again. The proceedings therefore document not only applications of emergy, but the continuing development of the methodology itself.
One important line of research concerned emergy algebra and complex networks. H.T. Odum and Dennis Collins had begun exploring how transformities should be calculated in systems containing feedback, multiple pathways, and cycling. Other researchers continued this work, developing and comparing pathway, eigenvalue, matrix, and other mathematical approaches. These studies addressed a fundamental problem: accounting rules that were relatively straightforward along a linear transformation chain became considerably more difficult when pathways branched, rejoined, recycled, or formed feedback loops. The mathematical treatment of emergy networks consequently became an important area of continuing research.
Other work focused increasingly on what could be learned from an emergy evaluation after the accounting itself had been completed. Measures of environmental loading, carrying capacity, natural capital, and sustainability were developed and refined to examine relationships between human activities and the environmental systems supporting them. National evaluations also began to move beyond single-year snapshots toward time series that could reveal changes in resource use, trade, environmental loading, and economic organization. Emergy accounting was thus increasingly used not only to compare systems, but to investigate how they changed through time.
Some research pushed the theoretical boundaries considerably farther. Corrado Giannantoni undertook a sustained effort to develop a mathematical formulation of the Maximum Empower Principle and to examine the mathematical foundations of emergy algebra. His work led him to question whether mathematical approaches developed principally for conservative physical systems were sufficient for describing the generative processes characteristic of living and self-organizing systems. Over a series of Emergy Synthesis conferences he developed ideas concerning generative processes, transformity, ordinality, and what he eventually termed the Maximum Ordinality Principle. Although this work was not widely incorporated into routine emergy practice, it represented one of the most ambitious attempts to provide a formal mathematical foundation for emergy and Maximum Empower. For a fuller account of Giannantoni’s work and its implications for emergy theory, click here.
The international research community also became increasingly institutionalized. Discussions at the Emergy Synthesis conferences led to formation of the International Society for the Advancement of Emergy Research (ISAER). Formation of a society was proposed at the third Emergy Synthesis conference in 2004, approved in principle at the fourth conference in 2006, and ISAER was incorporated in 2007. The Society provided continuity for the conferences while supporting communication, education, standards, databases, and collaboration among researchers. Responsibility for maintaining and extending the field was becoming increasingly distributed across an international community.
[Interactive map of institutions contributing to the development of emergy research]
The growing research community also created a need for greater standardization and reproducibility. As hundreds of emergy evaluations accumulated, questions arose over which unit emergy values should be used, how calculations should be documented, how values based on different global baselines should be compared, and how accounting rules should be applied consistently. The Emergy Society’s Standards Committee and its databases were developed in response to these needs. The objective was not simply to compile values, but to preserve their sources and calculations so they could be examined, compared, corrected, and revised.
A major step toward standardization was the development of the National Environmental Accounting Database (NEAD). Initial work at the University of Florida established standardized procedures and assembled comparable emergy accounts for more than 130 nations. After 2008, continued development of the database was taken over by Gengyuan Liu’s research group at Beijing Normal University. The most recent version provides standardized annual accounts for 222 countries and territories over the period 2001–2020, allowing changes in resource use, trade, environmental loading, and economic performance to be examined through time.
An important extension of the standardization effort came through research funded by the U.S. Environmental Protection Agency to develop emergy conversion factors suitable for use in Life Cycle Assessment. Work initiated by Christopher De Vilbiss and M.T. Brown developed Emergy Characterization Factors (ECFs) for a large range of environmental flows and materials, including more than one hundred mineral resources. After further development and an extended federal review process, the work was published by EPA as a publicly available Unit Emergy Value and Emergy Characterization Factor library. The project represented both an effort to standardize emergy conversion factors and an attempt to incorporate donor-side measures of environmental contribution into the widely used framework of Life Cycle Assessment.
Standardization, however, did not mean that the underlying values became fixed. Unit emergy values and Emergy Characterization Factors depend upon the global emergy baseline and upon the methods used to quantify the processes generating environmental flows. The baseline itself therefore continued to be examined and revised as data and understanding improved. These reassessments illustrate an important characteristic of the developing field: values that had become widely used could still be reconsidered when their underlying assumptions or calculations warranted revision.
Most recently, the Biosphere Dynamic Empower (BDE) approach provides a different basis for evaluating the renewable processes driving the biosphere. Rather than treating the renewable emergy basis solely as the sum of independent global inputs, BDE evaluates the dynamic work generated through their coupled interaction within the biosphere. Adoption of this approach changes the global baseline and consequently requires recalculation of the Emergy Characterization Factors derived from it. This work is presented in M.T. Brown’s Emergy: The Coupling of Human and Natural Systems, forthcoming from University Press of Florida
The development of emergy since Odum’s death has therefore involved both continuity and revision. Maximum Empower, hierarchy, self-organization, transformity, and environmental accounting remain central to the framework, but their mathematical representation, quantitative values, databases, and applications continue to be examined. At the same time, responsibility for that development has shifted from a relatively concentrated group centered at the University of Florida to researchers and institutions distributed around the world.
Emergy and Systems Ecology therefore remain developing bodies of thought rather than completed methodologies. Their history has been characterized by repeated movement between theory and application: diagrams raised questions; measurements and calculations tested relationships; applications exposed shortcomings; and those shortcomings stimulated new theoretical and methodological development. The international research community that emerged from Odum’s work continues that process today.
Milestones and Key References
2002 onward — Emergy development after Odum
Following Odum’s death, emergy theory and methods continued to develop. Researchers extended emergy algebra and methods for analyzing networks with feedback and cycling, while other work developed new indices and approaches for evaluating national economies, resource use, environmental loading, and sustainability.
Representative key references
- Collins, D., and H.T. Odum. Calculating Transformities with an Eigenvalue Method. (1st Emergy Conference)
- Odum, H.T., and D. Collins. Transformities from Ecosystem Energy Webs with the Eigenvalue Method. (2ndEmergy Conference)
- Campbell, D.E., S. Brandt-Williams, and T. Cai. Current Technical Problems in Emergy Analysis.
- Brown, M.T., M.J. Cohen, and S. Sweeney. Predicting national sustainability: The convergence of energetic, economic and environmental realities
2000s — Giannantoni and a new mathematical interpretation of emergy
Corrado Giannantoni developed a distinctive mathematical interpretation of emergy, extending its theoretical foundations through concepts of ordinality and generative processes. His work represented one of the more fundamental attempts to extend the mathematical foundations of emergy after Odum.
For a fuller account of Giannantoni’s work and its implications for emergy theory, [click here].
2004–2007 — Formation of ISAER
The international research community created a formal organization to continue the conferences and support research, education, standards, databases, and communication. A society was proposed at Emergy Synthesis 3 in 2004, approved at Emergy Synthesis 4 in 2006, and incorporated as ISAER in 2007.
Key reference
2006 onward — Standardized National Environmental Accounting
Creation of a global emergy database established common data sources, conversions, UEVs, tables, and indices for national emergy synthesis. This work developed into NEAD and enabled increasingly consistent comparisons among countries and through time.
Key reference
National Environmental Accounting Database V2.0
2010s–present — UEVs, ECFs, and Life Cycle Assessment
EPA-funded research initiated by De Vilbiss and Brown developed Emergy Characterization Factors for environmental flows and materials and explored their incorporation into Life Cycle Assessment. After further development and federal review, EPA published the UEV/ECF library in 2024.
Key references
De Vilbiss, C., and M.T. Brown. 2015. The Emergy Characterization Factor Library for Characterizing Environmental Support in Life Cycle Assessment: Final Technical Report to the USEPA.
2020s — Biosphere Dynamic Empower
Biosphere Dynamic Empower provides a revised approach to evaluating the coupled renewable processes supporting the biosphere and provides the basis for recalculating Emergy Characterization Factors. It represents the most recent stage in the continuing reassessment of the quantitative foundations of emergy accounting.
Key reference
Brown, M.T. Emergy: The Coupling of Human and Natural Systems. University Press of Florida, forthcoming.