emergy

Emergy is a measure of the energy that has been consumed to produce a good or service, expressed in emergy units such as solar emjoules (seJ). Coined by systems ecologist Howard T. Odum in the 1980s, emergy represents the energy memory embedded in materials, products, and ecosystems by converting diverse inputs—solar energy, chemical fuels, labor, and manufactured energy—into a single common unit through transformity values.

Transformity is the emergy per unit of input energy, reflecting the quality or transformative effort required to produce a given energy form. The emergy of a system is obtained by listing all inputs within a defined boundary and converting each to emergy units using their transformities, then summing to yield the total emergy available in the product or service.

Emergy analysis yields indicators such as the Emergy Yield Ratio (EYR), the Environmental Loading Ratio (ELR), and the Emergy Sustainability Index (ESI), which compare the emergy available from a product with the emergy invested and the reliance on renewable versus nonrenewable resources. These tools are used to assess sustainability, resource use efficiency, and environmental impact in fields ranging from energy planning to ecological engineering and agriculture.

Emergy analysis has been applied to compare production systems, natural resources, and urban metabolism, and is often presented alongside life cycle assessment. It has faced criticisms for relying on subjective transformities, varying data quality, and limited acceptance in mainstream economics. Nonetheless, it remains a formal framework for analyzing the energy foundation of economic and ecological processes.