امور جمعیتی در اقتصاد محیط زیست

It is an axiom of ecological economics that resource depletion and environmental pollution depend on the number of people and how many goods‐and‐services each consumes, modified by the technological efficiency of production. The paper reviews some studies quantifying the contribution of human numbers to environmental impact. It warns against playing this factor off against that of high consumption in rich countries. It asks whether from the environmental point of view complacency about either present or predicted population size is warranted. The answer depends both on fertility and mortality assumptions and on constraints such as resource and food availability. The concept of cultural carrying capacity would aid societies in determining their optimal population when account is taken not only of subsistence, but of quality of life. A population-control toolkit for both rich and poor societies is sketched, and some controversial, ‘coercive’ policy possibilities analysed.

Ecological economics seeks ways to lower environmental impact to sustainable rates of resource consumption and pollution, necessitating analysis of the factors contributing to the impact. For this it has for four decades applied the formula I = PAT: amounts of natural-resource consumption and pollution (Impact) are a function of number of people (Population), how many goods-and-services the average person consumes (Affluence), and the amount of natural-resource input or pollution per unit of goods-and-services (Technology as efficiency).1 I = PAT is more accurately written I = f(P,A,T) to indicate that a change in any of the three right-side factor affects the other two (Alcott, 2010). For instance higher population, ceteris paribus, means lower affluence ( Boserup, 1981 and Cohen, 1995). Higher affluence lowers mortality and can both raise and lower fertility (Lin, 2010, pp. 260-261).2 By increasing resource scarcity, higher P × A increases pressure for greater resource efficiency (lower T) ( Boserup, 1981 and Simon, 1996).3 Lowering T – raising efficiency, e.g. in cars or steel production – in turn enables more goods-and-services to be produced (higher A, the rebound effect) (Alcott, 2005). Due to this interdependence, autonomous reduction of any right-side factor does not necessarily result in lower impact.4 Concerning population reduction, the lesson is that after its first-order effect of freeing up resources, it enables higher affluence. Should a community decrease in numbers whilst the supply of resources remains the same, the smaller number of people can then use the resources for further economic activity; in this case this rebound effect raises present affluence (hopefully reducing poverty) but does not affect impact. Lower P is thus not a sufficient condition for lower I. It is not even a necessary condition, because if A and T decrease sufficiently, I could decrease even with rising P. There are two main reasons why population size is nevertheless relevant for ecological economics. (1) Any particular environmental problem – e.g. overdrawn groundwater or toxic emissions into groundwater – is easier to solve when there are fewer groundwater consumers. To lower impact the required adjustments in affluence (greater frugality) and technology (greater efficiency) would be physically and psychologically less burdensome; the costs of the benefits of lower impact would be lower. (2) Even if no impact reduction results from population reduction, it raises affluence, and if accompanied by policies for less economic disparity helps alleviate poverty — another goal of ecological economics.

Six main conclusions of this paper are: (1) Using the I = f(P,A,T) formula, both population and affluence contribute to the size of impact. Instead of playing these two factors off against each other, research is better directed at measuring their relative contributions with regard to specific impacts. (2) If it is the case that at desirable levels of affluence (A) and realistic increases in resource efficiency (T) the present population is not sustainable, it is unwise to complacently ignore population size and/or rely on its natural peaking in several decades. Limits to food production, the precautionary principle and declining death rates all argue against complacency. (3) Whatever the net effect on impact of lower or stable population, it substantially eases the task of alleviating poverty. (4) There is a method with which individual countries can approach decisions on optimal population size (‘cultural carrying capacity’): After determining sustainable and desirable levels of impact and the desirable level of affluence – including the welfare of future humans and other species – a realistic level of technological efficiency increase in the use of resources can be estimated. Using P = I/AT the number of people compatible with these assumptions can then be derived. (5) When population stabilisation or reduction policies are debated, it should be remembered that they pertain to rich as well as poor societies, and that all policies ‘coerce’ us, even ‘soft’ financial (dis-)incentives. (6) Societies should confront the debate between procreative rights and procreative responsibilities to decide whether reproductive behaviour falls within the realm of activities legitimately controlled by democratic majority. Ecological economics is well-equipped for many specific tasks: 1. measuring the relative contributions to I of P, A and T analytically, using biophysical units; 2. comparing the cost-effectiveness of the marginal impact-reduction investment, again in terms of P, A and T; 3. rejecting high estimates of maximum human population, often based on ‘huge feedlot’ standards, whether on grounds of ecology or present utility; 4. defining sustainable agriculture and measuring its yields per hectare, as well as sustainable fuel use; 5. computing realistic estimates of national cultural carrying capacity so that society can formulate population-size goals; 6. identifying and re-evaluating pro-natalist subsidies; 7. recognising that humans compete with other species for space and resources; 8. answering ethical questions surrounding policies for population constraint within the frameworks of inter-generational justice and the dangers of open-access commons; and 9. applying the principle of multi-disciplinarity by explicitly discussing legal and rights issues. Whilst any given policy to reduce population, affluence, toxicity, or inefficiency can unfortunately be compensated by expansion in other human-ecological realms, negotiating political paths to sustainability requires clear decisions on desirable population goals. To close with a concrete issue, consider some questions raised by EU efforts for a biological corridor from Orkney to the Black Sea, or American efforts for one from Guatemala through the Darien Gap. Do the EU and the Americas have a moral obligation to use these entire areas agriculturally in order to feed undernourished humans? Are these corridors harder, or easier, to establish if human population grows? Finite resources imply that population must eventually stabilise. Our only choice is to control it consciously, humanely and democratically or to wait for real limits to do it for us. The intent of this paper has been to make room within ecological economics for fresh discussion of our sheer numbers.