Emergy. An innovative concept for ecological engineering

Where do the natural resources we consume come from? Whether fossil or renewable, liquid, gaseous or solid, they are all the fruit of a succession of natural mechanisms. These are based on solar radiation, the gravitational attraction of the sun and moon, and heat from the earth's core. It is therefore possible to use an energy unit to characterize the natural "cost" of producing any resource or service provided by the environment. By extension, since every object manufactured by man is the result of the exploitation of natural resources, we can say that everything that exists on Earth can be characterized by this quantity, which we call emergy ("energy memory").

It's a quantity that accounts for the intrinsic value of a resource or product, as opposed to the use value generally used to characterize an object through its utility. The point of emergy is to highlight the fact that nothing on Earth is free, and that we have every interest in not wasting too quickly what nature takes millions of years to produce. Emergie also visualizes the successive transformations of different forms of energy, illustrating the fact that generating 1 kWh of electricity requires more resources than generating 1 kWh of heat; in other words, that not all forms of energy are equivalent.

The emergent approach thus enables us to situate a human activity in relation to its level of exploitation of natural resources, and thus to consider it in relation to its environment. In contrast to the usual tools of environmental accounting (carbon footprint, ecological footprint, life-cycle analysis), with which the analyst will be oriented towards a search for the reduction of negative impacts, emergent assessment directs the decision towards a search for synergies with the natural and human environment. This tool, developed almost 40 years ago, also has the advantage of being applicable to all human activities, thus providing complementary indicators, particularly in the economic dimension.

This article provides an introduction to the concept of emergy, as well as to the environmental accounting method derived from it, and illustrates its areas of application. Emergetic assessment still deserves to be refined and deepened, as it is an important key to sustainable development: a constructive vision for reconciling the human species with its environment.