2.7 Environmental Carrying Capacity
Discussions in the preceding paragraphs emphasised
that in an operational sense environmental sustainability refers to restricting
resource use and waste generation within the carrying capacity of the local
and global ecosystem. Meyers (1993) defined carrying capacity as "A function
of such factors as food and energy supplies, ecosystem services (viz., providing
freshwater, recycling nutrients, etc.), human capital, peoples lifestyles,
social institutions, political structures, cultural constraints, among many
other factors that interact with each other". Such a definition hardly helps
in devising an operational strategy for carrying capacity based development
planning. A more focussed definition of carrying capacity has been given by
the USEPA (1974) as "The capacity of natural and human environment to accommodate
or absorb changes without experiencing conditions of instability and attendant
degradation". Catton (1987) stressed that carrying capacity must be seen as
the ability to produce outputs from a limited resource base (input) while
at the same time maintaining the desired quality level in the resource base.
According to Khanna (1989) 'the carrying capacity comprises resources which
support production activities and, in turn, produce residuals that are assimilated
by the ecosystem, albeit to a finite extent'. Following the Hicksian definition
of income, Catton (1987) defined carrying capacity from an environmental stand
point as 'the maximum number of users, and their associated demands, which
an environment can permanently support'. Carey (1993) called it sustainable
carrying capacity which, according to him, can be achieved if human needs
can be defined and met in ways which do not impair (and perhaps improve) the
quality of life for future generations of all species. Perhaps the simplest
yet meaningful definition has been suggested by Westman (1985), 'Carrying
capacity is the level of resource use that can be supported by the natural
ecosystem without adverse ecological effect.'
In fact definitions of carrying capacity abound, - the above being representative
samples of many available definition. As a reconciliatory effort the author
puts forward the following definition.
Environmental carrying capacity is the level of human activity that can
be supported by a particular ecosystem without reducing the environment's
long-term ability to support the same level of human activity at the same
quality and quantity.
Supporting a human activity, of course, includes two components, supplying
necessary resources (raw materials) over the long term and assimilating the
wastes generated by human activity without any loss of ability to treat similar
quantity and quality of wastes in future. In other words recalling the definition
of environmentally sustainable development as 'the development without growth
beyond environmental carrying capacity' (Goodland 1994), we can reframe the
sentence meaning 'development is sustainable if it is within the carrying
capacity of local and global ecosystem'. Elements of regional carrying capacity
supporting the above definition are presented in Figure 2.4.
Recalling again the input-output rule for environmental sustainability, it
may be emphasised that the output rule deals with assimilative capacity and
input rule relates to the regenerative capacity for renewable natural resources
and to the rate of possible substitution for non-renewable natural resources.
While carrying capacity concept all along puts emphasis on no net loss of
'source and sink functions' of the ecosystem, in reality it is difficult to
determine conclusively the level of stress or shock at which permanent reduction
in ecosystem capability will commence.
In order to operationalise sustainable development through carrying capacity
based planning, it may be prudent to view carrying capacity as a function
of a number of variables, viz.; -
* the region in question, e.g. a watershed, the world;
*the type of resource in question, e.g., water, energy, whatever resource
would limit the growth;
* what is being 'carried', e.g., human population, noxious gas emissions;
* whether the resource is renewable or non-renewable and whether the resource
is assumed to be constant or not;
* whether what is being 'carried' is constant or not;
* value judgements, e.g., ideal/optimum capacity versus maximum/ minimum capacity
(Therivel et al. 1992).
The principal considerations for determination of an ecosystem carrying capacity
include the following.
1. Capability of the ecosystem to provide natural resources on perpetual basis.
2. Interrelationship between these resources.
3. Technology that in the form of process inputs changes these resources into
useful commodities.
4. Waste generated by the process, which is returned to the nature. The environment
receives these wastes and renders them, through natural processes, harmless
or even productive for the ecosystem.
The above considerations lead to an operational definition of carrying capacity.
Regional carrying capacity can now be defined as the level of human activity,
which a region can sustain at acceptable quality of life levels in perpetuity.
Carrying capacity determination, however, remains as problematic as ever.
Any reasonable estimate of carrying capacity will require, at the least, a
base line determination of availability of natural resources and computation
of assimilative capacity of the ecosystem within the defined spatial domain.
Further complications arise as both supportive capacity and assimilative capacity
of any ecosystem change with time and hence all baseline calculations, even
if they become possible, will require temporal adjustments which, at the present
level of knowledge of ecosystem dynamics is not possible to achieve. Moreover
carrying capacity is often affected by external factors such as enhancement
of supportive capacity through technological intervention. Drawing analogy
from Boulding's 'Spaceship Earth' theory it may be observed that the planet
can accommodate more people with low resource requirements than those people
with high resource requirements. Breaking down from the biosphere to a local
ecosystem carrying capacity thus becomes a function of affluence and technology
(Goodland and Sadler 1996). Notwithstanding the inherent difficulties in estimating
environmental carrying capacity the usefulness of carrying capacity concepts
in project evaluation can not be over emphasised as the concept forces a greater
consideration of the variables and constraints which determine the consequence
of development projects. Carrying capacity based planning processes have been
discussed in detail by various authors, viz., Khanna (1989a), Khanna (1989b)
Catton (1987), Saxena (1996), Carey (1993) etc.