At the national level, macroeconomics is often grasped in terms of monetary flows, but is also studied by ecological economics through the analysis of material flows. This is called the study of social metabolism.
For example, it is calculated that a resident of the European Union currently consumes an average of 15.5 tons of material per year.
By comparing the energy and material content of countries' imports and exports, it is possible to measure the environmental footprints corresponding to the living standards of its inhabitants. Thus, EU countries import three times more natural resources and energy than they export.
Soil, water, raw materials, CO2 emissions, etc. expressed in relation to meeting the needs of its inhabitants (food, mobility, shelter). Therefore, it is increasingly welcomed by regions outside its borders.
Considering the generally applicable trade conditions for energy and natural resources, there is an alternative way of studying international trade. This has led some authors to talk about ecologically uneven change.
Such biophysical analyzes can also be performed at the sectoral level. Extending studies, eco-energy studies conducted in the 1970s compare the amount of energy produced and consumed by corn planting and agriculture more broadly in the United States in the 20th century.
The increase in agricultural productivity observed since the end of the Second World War is due to the increased use of fossil fuels for agricultural machinery, fertilizer production, irrigation, etc. they show that they were obtained there thanks to.
This allows Americans to confirm that they mainly consume oil. It calculates the "energy return rate" of agricultural activities.
These studies have shown that energy efficiencies decrease over a long period of time. More and more kilocalories from fossil fuels must be consumed to produce the kilocalories found in food, which some authors have interpreted.
Thanks to these approaches in terms of energy and material metabolism, we can also examine production areas and industrial areas or focus on a production sector. One of the best-known studies concerns orange juice consumed in Germany.
Material and Energy Circulation in Ecosystems
Ecosystems are dynamic and evolving systems through which an energy flow, usually from the sun, passes. Some of the energy from solar radiation is stored by chlorophyll plants, which produce living matter from mineral matter and thus store solar energy in a chemical form.
The net primary production of an ecosystem measures the mass of living tissue produced by plants over a given period of time. This primary biomass can then be used for other species.
It is the first link in the food chain of an ecosystem. That's because plants are the only living beings that convert solar energy directly into chemical form (which is why ecologists call them "producers").
Animals (herbivores and carnivores) then simply transform them. Materials, and thus the amount of energy provided to produce their own matter.
After their death, the tissues of all organisms are converted by decomposers into mineral elements or new living organisms. (micro-organisms, fungi, etc.) The cycle, or rather the numerous cycles in an ecosystem, is gradually closing.
However, if chemical elements, the basic building blocks of organisms, do not change in nature, the same is not true for energy. In the case of transforming the latter, the first principle of thermodynamics is a conservation of energy quantity. But its second principle, known as the entropy principle, stipulates that there is a qualitative distribution of energy.
As it transforms, it becomes less and less concentrated. It loses its productive usefulness until it is unable to produce movement or work. The energy is irreversibly degraded during its conversion and is eventually dissipated in the form of heat released, for example, by the sweat of an animal or by a combustion engine.
This entropic property of energy is found in food chains. Ecologists thus calculated that green plants store an average of 1% of the solar energy received on Earth, herbivores store about 10% of the energy found in the plants they eat, and their predators 10%.
The small amount of energy available to living things at the end of the food chain explains why it cannot be made up of an infinite number of links. This suggests that ecologists make productivity and energy efficiency calculations when studying ecosystems. This eco-energy analysis, which was very developed in the 1970s, fed energy efficiency.
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