Environmentalists and scientists often refer to the two different ends of the environmental problem as sources and sinks. Thus the environmental limits to economic growth manifests themselves as either: (1) shortages in the “source” or “taps” of raw materials/natural resources, and thus a problem of depletion, or (2) as a lack of sufficient “sinks”, to absorb wastes from industrial pollution, which “overflow” and cause harm to the environment. The original 1972 Limits of Growth study emphasized the problem of sources in the form of shortages of raw materials, such as fossil fuel, basic minerals, topsoil, fresh water, and forests. Today the focus of environmental concern gas shifted more to sinks, as represented by climate change, ocean acidification, and production of toxics. Nevertheless, the problem of depletion of resources used to production remains critical, as can be seen in discussions of such issues: declining freshwater resources, peak (crude) oil, loss of soil fertility, and shortages of crucial materials like zinc, copper, and phosphorus.
In conventional environmental analysis the issue of a shortage or depletion of natural resources has often been seen through lens as principally a problem of overpopulation. Thomas Malthus raised the issue in the late eighteenth century of what he saw as inevitable shortages of food in relation to population growth. This was later transformed twentieth-century environmental theorists into an argument that current or future shortages of natural resources resulted from a population explosion overshooting the carrying capacity of the earth.
The following analysis will address the environmental problem from to source or tap end, and its relation to population growth. No systematic attempt will be made to address the sink problem.
However, the tap and the sink are connected because the greater use of resources to produce goods resulted in greater flows of pollutants into the “sink” during extraction, processing, transportation, manufacturing, use, and disposal.
In approaching the source or tap problem, we have to recognize there is a finite planetary quantity of each nonrenewable resource that can be recovered economically. In theory, it is possible to calculate when the world will run out of a particular resource, given knowledge of the amount of resources that exists, technology, costs, and likely demand-though the various factors are often so uncertain as to make firm predictions difficult. However, the amount that can be extracted economically increases when the price of a particular resource increases or new technology is developed-it then becomes economically feasible to exploit deposits that are harder to reach or of less purity and more costly to obtain.
An easier question to answer is whether we are using a given resource in a sustainable manner. For renewable resources, such as water, soil, fish, forests, this means that use cannot exceed the rate of generation of the resource. For nonrenewable resources, as with fossil groundwater, fossil fuels, and high-grade minerals, this means the rate of use can be no greater than the rate at which renewable resources (used sustainably) can be substituted for these nonrenewable resources-that is, the sustainable use of nonrenewable resources is dependent on investment in renewable resources that can replace them. For pollutants the sustainable rate of emission is determined by the degree that they can be absorbed harmless in the environment.
There are some examples of renewable resources being sustainably substituted for nonrenewable ones, but most have had limited impact. For some resources that are part of modern life-such as many of the metals-there are no foreseeable renewable substitutes. These need to be used at relatively slow rates and recycled as efficiently as possible. And nonrenewable resources are required to manufacture equipment for “renewable” energy such as wind and solar power. By far the largest example of renewable resources being substituted for nonrenewables is the use of agricultural products such as corn, soybeans, sugarcane, and palm oil to produce ethanol and biodiesel to replace gasoline and diesel fuels. But the limited energy gain for most biofuels, the use of nonrenewable resources to produce these “renewable” resources, and the detrimental effects on people and the environment are so great as to make large-scale production and use of biofuels unsustainable.
Source: DIGEST January 2014