134 / Basics of Environmental Science
Pollution is only one concern arising from our use of metals; the other centres on fears of their depletion.
Such fears were being expressed in the 1960s, but were stated more forcefully in the 1972 study The Limits
to Growth (MEADOWS ET AL., 1972), which predicted the imminent exhaustion of most of the mineral
resources on which we depend. The fear was based on a misunderstanding of the way the amount of a
reserve is determined. The concept is economic, not physical. Figures for the reserves of any particular
mineral are prepared by the mining industry primarily for its own use. They refer to the amount of the
substance that has been identified and that can be profitably extracted under present conditions. They say
nothing whatever about the total amount the world possesses, and changing circumstances may bring about
an increase or decrease in the amount of reserves. In an apparent paradox, should consumption increase
reserves may also increase to meet the demand; it was for this reason that between 1950 and 1970 global
reserves of bauxite (aluminium ore) increased by 279 per cent, copper by 179 per cent, chromite (chromium
ore) by 675 per cent, and tin by 10 per cent (ALLABY, 1995, pp 176–178). Historically, mineral consumption
has always increased faster than the rate of population growth. World population doubled between 1950 and
1990, for example, but during the same period production of aluminium, copper, lead, nickel, tin, and zinc
increased eightfold. It is now estimated that when allowance is made for anticipated population growth and
economic development, mineral reserves are adequate for the next century and the environmental problems
associated with their exploitation can be contained (HODGES, 1995).
Nor did the fears of exhaustion take sufficient account of the extent to which technological change
renders resources obsolete. Ceramics, made from clays and sand, are now starting to replace metals
for a number of uses that require tolerance of very high temperatures. Glass fibres, essentially made
from silica (i.e. sand) are replacing copper cables. Orbiting satellites handle communications that
were formerly transmitted by submarine cable. Electronic devices now form the basis of industrial
switchgear, formerly based on mercury. Such changes, and there are many, are introduced not because
of actual or anticipated shortages of the original material, but because they are superior.
The environmental implications of mining and mineral processing are well known. They can be minimized,
although the restoration of mined land is sometimes difficult. In years to come, however, environmental
pressures may ease. Technological advances now promise to reduce our dependence on some metals by
substituting superior materials that are extremely plentiful and can be processed with much less risk of
environmental harm, and by developing new, cheaper, and less disruptive extractive methods.
End of chapter summary
Without water we would die and so we may think of fresh water as the most fundamental of all the
resources on which we depend. Water moves between the ocean and land, but we can manipulate the
hydrologic cycle where the amount of fresh water is insufficient for our needs.
We also need soil. It is important to understand how soil forms and that it goes through a life cycle,
much like a living organism. There are young, mature, old, and even senile soils. The age of a soil is
directly relevant to the use that can be made of it. Fears over tropical deforestation, for example,
arise partly from the realization that many tropical soils are very ancient and that this makes them
inherently infertile, so alternative forms of land use may fail in the long term. Soil can be lost
through erosion. The mechanisms involved in this process are well known, as are the management
techniques by which they can be avoided.
Water and soil to grow food and fibre are resources essential for all animals. In addition to these, humans
need industrial resources. These comprise so-called fossil fuels, rocks for building, and minerals from
which metals and a range of chemical compounds are obtained. Obtaining these materials from the
ground and their subsequent processing create environmental problems that must be addressed. It is
usually better to prevent them by advance planning than to remedy them later.