Abstract

In terms of energy, the Earth is an open system: it constantly receives energy from solar radiation and emits the same amount of energy in the form of more degraded radiation; the displacement of the equilibrium point between these two flows due to the growth of greenhouse gases, increases the average temperature of the Earth and causes climate change. On the other hand, in relation to matter, the Earth is a closed system, apart from the sporadic fall of some meteor. Nature has the ability to regenerate the organic materials of living beings but not with many other materials.

Today, the volume of materials involved in human activities is 12.5 tons per person per year (1.5 to 4 times more in rich countries): 25% of the total comes from biomass (including food), 15% are fossil fuels, 10% are metal ores, 42% are other minerals (mainly for construction) and 8% are recycled. On the other hand, obtaining and transporting materials worldwide requires more than 40% of the energy of the human system, a value that is growing with the use of increasingly rare, scarce and dispersed materials. The overexploitation of resources coupled with the increasing use of non-renewable energy resources (fossil fuels and uranium), with the consequent energy and climate crisis and the deterioration of the environment, leads both to a change in the energy model and to rethinking the practices today dominant of continuous economic growth and the linear economy based on extract-use-throw.

The purpose of this communication is, after presenting the figures on the global metabolism of materials, to reflect on some of the new attitudes and actions that will need to be adopted within the framework of sustainable development. By way of example, the following are cited: 1) Moderate, reduce, eliminate the use of materials where possible; 2) Extend the life of goods and material infrastructures; 3) Reuse, recover, recycle materials; 4) Return as much as possible biologically based materials, more recyclable; 5) Avoid, as far as possible, technologies based on rare or scarce materials; 6) Avoid the dispersion of materials in the environment (atmosphere, water, soil); 7) Encourage the use of local materials in order to minimize transport and its energy impact; 8) Take care of the quality and good health of basic resources: air, water and fertile soil.