school energy&environment

Sustainability and resources

When can it be said that use of a natural resource is sustainable?
Generally we can say that a natural resource is used by man in a sustainable manner when, knowing its capacity to reproduce (consider fish as a natural resource) or to maintain a determined quality (for example the purity of the air we breathe) it is not exploited more than a determined threshold. When use of a resource exceeds the said threshold, it means that there will be a progressive and dangerous impoverishment, in terms of quantity (the global population of fish drops  to a limit below which the species is destined to disappear) or in terms of quality (the air is so polluted that it is bad to breathe and causes severe diseases among human beings).  If this “impoverishment” of the natural resource is definitive (disappearance of the species)  we say that an “irreversible” damage has been provoked, i.e. it is not possible to go back and bring the species back to life. Impoverishment, instead,  is considered “reversible” if it is possible to go back and recover the natural resource (polluted air can become breathable if polluting substances are no longer emitted).
Actually the concept of sustainability can only be applied to renewable natural resources that can be reproduced in times that belong to a “human scale” (for example, firewood). For non-renewable sources, such as fossil fuels, it is best to talk of  optimum exploitation. In other words we must try our best to use these in an efficient manner (making them last as long as possible) and in the meantime, find technologies that allow the exploitation of alternative sources in their place, which may even be characterized by a “renewable” nature (for example to replace the energy produced by fossil fuels in the future with solar energy, which is a renewable source).