Material cycles
Our economy is built on the transformation of raw materials into goods and services. During this process matter is not created or destroyed but it can be changed from one form to another. For example, compounds change as different elements are combined and recombined in different ways. Unfortunately, much industrial activity results in unwanted and difficult-to-recover materials, which are then regarded as wastes (see Chapters 3 and 4).
Of increasing concern is the future availability of some raw materials, increased global competition for key materials and increases in raw materials prices, especially for finite resources.
The overriding objective is to minimise the exploitation of natural resources by re-using that which we have already extracted from the environment. However, this means we need to avoid contaminating one material with another, particularly if the contaminant is a harmful material.
Renewable and non-renewable resources
The definition of a renewable resource is a material whose stocks in the environment will be replenished within one or a few human generations.
Using up renewable resources can be looked upon as living off the earth’s natural ‘income’. Using non-renewable resources is living off the earth’s ‘capital’. Once a particular resource is used up, then we have to move on and exploit alternative stocks elsewhere.
Many natural resources, once thought of as inexhaustible, are now seen as being finite. For example, stocks of cod in the North Sea are now known to be on the verge of collapse. Too many immature fish are being removed from the sea every year, leaving insufficient numbers to breed and replenish the population.
The alternatives are to exploit the resource until the species dwindles to extinction or to drastically limit (or even ban) its exploitation until natural population levels recover sufficiently to be out of danger. One other complicating factor is the possibility that an increase in sea temperature due to climate change is also having a detrimental effect on cod stocks.
Another example of non-renewable living resources is the situation with several species of hardwood from tropical forests. Complex ecosystems like the rainforest take many decades or even hundreds of years to re-establish themselves. These, coupled with the rapid erosion of soils on newly logged areas and the exploitation of the available land for other purposes such as cattle ranching, makes successful regeneration very unlikely. However, they can be exploited in a managed way (see waste management).