Continued world population growth is inevitable.
The means of controlling it require extensive efforts to influence
birth rates, with all the consequent problems of addressing the
underlying reasons for large family size. One reason for increasing
that effort is to break the vicious circle of population growth and
poverty. The influence of population growth on resource
availability and environmental quality contributes to the poverty
process. At the global level, more people mean a higher consumption
of energy, and hence more atmospheric pollution, unless means are
found by which to lower per capita consumption of materials
and energy without impairing standards of living. More people mean
a greater demand for cultivable and residential land, and hence
less forest and wetlands, contributing to further pollution and
losses of biodiversity.
One way of assessing the ultimate limits of
population growth is to look at the carrying capacity of
natural resources and land. Simply put, the carrying capacity of a
given area is the maximum number of people that can be sustained by
the resources on that land. The carrying capacity of a region is
categorically not the desirable level of population, unless
the level of well-being at which the population is sustained is
itself desirable. Usually, however, carrying capacity is defined as
relating to the maximum sustainable population at the minimum
standard of living necessary for survival. For example, it is
possible to compute the maximum food output (measured in calories,
say) of a given area of land. Suppose this is represented by Q.
Then Q can be divided by the minimum number of calories required
for human survival of one individual. Call this M. Carrying
capacity is then measured as:
Carrying Capacity = Q/M
The most extensive analysis of the carrying
capacity of the world was carried out by the Food and Agriculture
Organization (FAO) of the United Nations. The fao approach involved
looking at the potential food production of each of 117 countries.
Obviously, potential food production depends on the level of
technology applied to agriculture. fao categorized these as:
-
low-level: corresponding to no fertilizers, pesticides or
herbicides, with traditional crop varieties and no long-term
conservation measures;
-
intermediate-level: corresponding to use of basic fertilizers and
biocides, use of some improved crop varieties and some basic
conservation measures;
-
high-level: corresponding to full use of fertilizers and biocides,
use of improved crop varieties, conservation measures and the best
crop mixes.
On the basis of these different technological
scenarios it was then possible to estimate the potential calorie
output for each level of technology (Q in the equation). By
dividing this by the per capita calorie intakes recommended
by fao and the World Health Organization for each country (M in the
equation), a sustainable population can be estimated. These
estimates were made for 1975 and the year 2000 Table 1 shows the
results in a convenient form.
Table
1
Input
|
Africa
|
SW
Asia
|
S
America
|
C
America
|
SE
Asia
|
Average
|
Low
|
1.6
|
0.7
|
3.5
|
1.4
|
1.3
|
1.6
|
Intermediate
|
5.8
|
0.9
|
13.3
|
2.6
|
2.3
|
4.2
|
High
|
16.5
|
1.2
|
31.5
|
6.0
|
3.3
|
9.3
|
It shows the ratio of potential sustainable
population in 2000 to the expected population in 2000 for various
regions of the world, and at the three different levels of
technology. For example, for the developing world as a whole, if
all cultivable land was devoted to food crops, at the lowest level
of technology those lands could support 1.6 times the number of
people expected in the year 2000. In South-West Asia the actual
expected population will exceed the carrying capacity at both low
and intermediate technology levels. As the technological
assumptions improve, so, dramatically, does the carrying capacity
of the regions.
Box 1 appears to suggest a fairly optimistic
picture. Certainly, it highlights the role which technological
improvement can play in vastly increasing carrying capacity.
However, it is important to understand why the picture is far from
an optimistic one. There are several problems:
- carrying
capacity relates to the maximum number of people that can be
sustained with the given resource, not to the desirable level;
- the
carrying capacity figures relate to a minimum calorie intake, so
that even for a single person the approach makes no allowance for
increasing nutritional levels;
- the time
horizon of 2000 does not permit much change to take place in levels
of applied technology, so that at least the high- technology input
scenario is of limited relevance to what will actually be the
case;
- the
approach assumes that all cultivable land will come under
food production or livestock pasture, which is a clear exaggeration
of what is feasible. Allowing for non-food crops, the ratio of 1.6
in Box 7.2 becomes 1.07 - i.e. at low technology the carrying
capacity of the developing countries is only 7 per cent more than
the actual population.
In fact the situation may be worse even than
this. The FAO study was concerned with carrying capacity in terms
of food, but other resource scarcities begin to exert an
influence before cultivable land. A notable example is the
availability of fuelwood.
A study of the Sahelian and Sudanian zones of
West Africa computed the carrying capacity of various zones
according to the limits set by crops, livestock and fuelwood. The
results indicate that the carrying capacity of natural forest cover
- the main source of fuelwood - is very much lower than that of
crops using traditional technologies. Moreover, in five of the six
regions fuelwood carrying capacity is already exceeded, compared to
two regions where food and livestock carrying capacity is exceeded.
The general picture on world zone carrying capacities may therefore
understate the problem of resource carrying capacity generally.
What matters is which resource scarcity "bites" first.
Carrying capacity calculations are helpful up to
a point. They can be used to indicate the broad-scale seriousness
of a problem, but there are considerable dangers in deriving too
many conclusions from them. The main drawbacks are as
follows:
- at the
country or small-region level, carrying capacity can be readily
increased by trade. If we calculated the carrying capacity of, say,
South Korea, it would show up adversely. Yet by trading on the
basis of its comparative advantage in technology and industry,
Korea can import food and so sustain a larger population;
- as
population grows, so there is a "forcing" effect on technology. It
may, for example, lead to changes in the way in which agriculture
is practised. Population growth generally explains the transition
from shifting cultivation with long fallow periods, to short fallow
farming and cropping rotations with organic manuring, to modern
intensive monocultures based on high-yield crops, irrigation,
fertilizers and chemicals. Carrying capacity tends to be a "static"
concept, and thus cannot capture these dynamic, interactive
effects.
Despite these drawbacks, a casual glance at the
level of population - resource imbalance and the rate of
agricultural growth suggests that the greater the pressure on
natural resources, the slower agricultural growth becomes. This
relationship for four groups of countries in Sub- Saharan Africa is
shown in Table 2
Table 2
Country
group
|
Agriculural
growth (%p.a.)
|
1
|
1.1
|
2
|
2.2
|
3
|
3.5
|
4
|
1.5
|
Group 1 relates to countries where actual
population exceeded the sustainable population in 1982; Group 2
relates to countries where this will occur in 2000; group 3 to
countries where it will happen in 2030; and group 4 to the
remaining countries - i.e. those whose carrying capacities will not
be exceeded by 2030. In all cases the measure of carrying capacity
is that of the fao. The data suggest that the closer a country is
to its carrying capacity, the slower is its agricultural growth
rate. In turn this suggests that the relationship between
population growth and food output might reduce to the balance
between two forces working in opposite directions: the role of
population pressure in inducing technological inducement to higher
productivity, and its role in wider resource degradation that
reduces agricultural growth.