Environmental Economics and Demography

Overview

Use the same welfare framework for environment and demography. For the environment, ask: what is the externality, who bears it, what is the efficient level of pollution or resource use, and which instrument reaches it cheapest? For demography, ask: what drives births, deaths and migration, what age structure results, and what does that structure imply for dependency, saving and labour supply? Both fields reward careful measurement: environmental valuation without a method is assertion, and population analysis without rates, ratios and life tables is anecdote. Keep the distinction between levels and rates central: a falling birth rate can coexist with a rising number of births if the population base is large, just as falling emission intensity can coexist with rising total emissions if output grows faster.

Environment as a public good

The environment provides multiple services: it supplies resources such as timber, water, minerals and fisheries; it absorbs and assimilates waste; it provides life-support functions such as climate regulation, nutrient cycling and biodiversity; and it offers amenity and cultural values such as recreation and aesthetic enjoyment. Many of these services are public goods or common pool resources. Clean air is non-excludable and non-rival over relevant ranges, so no private market will supply it efficiently and free riding undermines voluntary provision. Fisheries, groundwater and grazing land are non-excludable but rival, so open access leads to over-exploitation: each user ignores the depletion cost imposed on others, the stock falls, and the resource can collapse even though all users would prefer restraint. This is the tragedy of the commons, and its solutions are property rights, quotas, taxes or community management rules that align individual incentives with collective sustainability.

Environmental market failure has several sources beyond public goods and commons problems. Externalities arise when production or consumption imposes costs, such as air and water pollution, or benefits, such as carbon sequestration by forests, on third parties without price signals. Missing markets mean future generations, who will bear long-run environmental costs, cannot bid in current markets, creating an intergenerational externality that discounting and sustainability criteria must address. Information failures mean polluters and consumers may not know damages or alternatives, justifying disclosure and labelling. Non-convexities and thresholds complicate policy: ecosystems can flip abruptly once a tipping point is crossed, so marginal analysis that assumes smooth responses can mislead near thresholds, and precautionary approaches gain force. The efficient level of pollution is generally not zero: abatement has rising marginal costs, damage has marginal costs, and efficiency equates marginal abatement cost with marginal damage, accepting some pollution where eliminating the last unit costs more than the damage it prevents. This efficiency logic must be paired with equity: pollution burdens fall disproportionately on low-income communities, and cost-benefit analysis that values all damages equally can hide that distribution.

Market failure, Coase theorem, valuation

The Coase theorem states that if property rights are well defined and transaction costs are negligible, private bargaining will achieve an efficient outcome regardless of who initially holds the rights, though the distribution of gains depends on that assignment. A polluter who holds the right to pollute will accept payment to reduce pollution up to the point where compensation equals forgone profit, while victims who hold the right to clean air will pay for abatement up to their damage avoided, and both routes converge on the efficient level where marginal profit from polluting equals marginal damage. The theorem is powerful as a benchmark and limited as a policy guide: transaction costs are rarely negligible when many polluters and victims are involved, information is asymmetric, free riding undermines victim coalitions, and wealth effects and fairness concerns affect which assignment is acceptable. Where bargaining fails, policy instruments include Pigouvian taxes equal to marginal damage, tradable permits that cap total pollution at least cost, standards that limit emissions per source, subsidies for abatement or clean technology, and liability rules that make polluters pay damages after harm occurs. Taxes give price certainty but uncertain quantities; permits give quantity certainty but uncertain prices; standards give quantity certainty per source but at higher cost when abatement costs differ. Cost-benefit analysis for environmental projects must value non-market effects, because ignoring them implicitly values them at zero. Revealed preference methods infer values from observed behaviour: hedonic pricing uses housing price differences to value air quality or noise, travel cost method uses trip costs to value recreation sites, and averting behaviour uses defensive expenditures to value risk reduction. Stated preference methods ask directly: contingent valuation surveys elicit willingness to pay for a hypothetical environmental change, and choice experiments present trade-offs among attributes to estimate values. Revealed methods are grounded in real choices but capture only use values and require strong assumptions; stated methods can capture non-use values such as existence value, the value of knowing a species survives even without using it, but suffer from hypothetical bias and strategic answering. Benefit transfer applies values estimated in one context to another with adjustments, a practical shortcut that must be used cautiously.

Theories of population

Malthus argued that population grows geometrically while food supply grows arithmetically, so population pressure would eventually be checked by famine, disease and war, the positive checks, unless prevented by moral restraint, the preventive check of delayed marriage and abstinence. The theory correctly identified the tension between population and resources but underestimated technological progress in agriculture, the demographic transition to lower fertility, and the role of contraception and education. Neo-Malthusian views revive resource concerns for environmental limits, while critics note that population growth can stimulate innovation, specialisation and scale economies, the Boserup argument that population pressure induces agricultural intensification and technological change. Demographic transition theory describes the historical pattern: high birth and death rates in pre-industrial societies give way first to falling death rates as nutrition, sanitation and medicine improve, producing rapid population growth, then to falling birth rates as urbanisation, education, female employment and contraception spread, slowing growth and eventually stabilising population at low birth and death rates.

The theory of demographic transition has stages, but timing and speed vary with culture, policy and development, and some societies experience stalled transitions or fertility below replacement level, raising ageing concerns. Optimum population theory asks what population size maximises welfare, balancing larger markets and specialisation against resource pressure and congestion, but welfare depends on distribution and technology as well as numbers, so no single optimum is robust. The demographic dividend hypothesis links transition to growth: when fertility falls, the working-age share rises relative to dependents, raising saving, labour supply and human capital investment per child, provided jobs and education absorb the larger workforce; without employment and skills, the dividend becomes a burden of youth unemployment. Population policy therefore spans family planning access, female education, child health, social security that reduces reliance on children for old-age support, and urban and employment policies that convert demographic structure into productive capacity. Coercive population policies raise ethical and effectiveness concerns and are inferior to voluntary, rights-based approaches that expand choices, especially for women.

Fertility, morbidity and mortality

Fertility measures childbearing. The crude birth rate divides births in a period by mid-period population, but it is affected by age structure, so age-specific fertility rates, births to women in each age group divided by women in that group, are more precise. The total fertility rate sums age-specific rates and gives the average number of children a woman would bear if she experienced current rates throughout her reproductive life; it is the standard summary of fertility levels and is unaffected by current age structure. Replacement level fertility, around two children per woman in low-mortality settings, is the level at which each generation exactly replaces itself absent migration, higher where mortality is high. Fertility determinants include age at marriage, contraceptive use, female education and employment, child survival, urbanisation, cultural norms, and the economic costs and benefits of children, including old-age support and labour contributions in agrarian settings. The proximate determinants framework organises these into marriage, contraception, postpartum infecundability and abortion, through which all social factors must operate to affect fertility.

Mortality measures death. The crude death rate divides deaths by population but is age-structure sensitive, so age-specific death rates and standardised rates are preferred for comparisons. Infant mortality rate, deaths under age one per thousand live births, and under-five mortality are sensitive indicators of health systems, nutrition and sanitation. Maternal mortality reflects obstetric care and female status. Life expectancy at birth summarises the mortality schedule into the average years a newborn would live if current age-specific rates persisted; it is not a forecast for any individual cohort but a period summary. Morbidity measures illness rather than death: incidence counts new cases in a period, prevalence counts existing cases at a point, and disability-adjusted life years combine years lost to premature death with years lived with disability to compare disease burdens. The epidemiological transition describes the shift from infectious diseases and high child mortality toward chronic, non-communicable diseases and ageing-related conditions as development proceeds, changing health system priorities from sanitation and immunisation toward chronic care and risk factor management.

Age structure and demographic dividend

Age structure is the distribution of a population across age groups, displayed in a population pyramid with young ages at the base and old ages at the top. Expansive pyramids with wide bases indicate high fertility and rapid growth; constrictive pyramids with narrow bases indicate low fertility and slow or negative growth; stationary pyramids indicate roughly equal cohorts. The dependency ratio divides dependents, children plus elderly, by the working-age population, and its components matter separately: a high child dependency ratio burdens education and health systems, while a high old-age dependency ratio burdens pensions and elderly care. The support ratio, the inverse, shows workers per dependent. Age structure is shaped by past fertility, mortality and migration, so it carries momentum: even if fertility falls to replacement immediately, population continues to grow for decades because large young cohorts enter reproductive ages, a phenomenon called population momentum.

The demographic dividend occurs when the working-age share rises and dependency falls, creating a window for faster growth if the economy provides education, jobs and saving mechanisms. The first dividend is mechanical: more workers per dependent raise output per capita even at constant productivity. The second dividend is behavioural: fewer children and longer life expectancy encourage saving for retirement and investment in each child education, raising capital per worker and human capital over time. Realising the dividend requires policies that are often harder than the demography itself: quality schooling, vocational training, labour market flexibility, female labour force participation, financial inclusion for saving, and urban infrastructure for a growing workforce. Failure converts the window into youth unemployment, informal work and social frustration. At the other end, ageing societies face rising old-age dependency, pressure on pay-as-you-go pensions where current workers fund current retirees, health care costs, and potential labour shortages, addressed by later retirement, higher productivity, immigration, funded pensions and technology, each with distributional consequences. Ageing is not a crisis by itself; it is a predictable structural shift whose costs depend on institutions and productivity.

Life table and migration

A life table is a demographic accounting device that follows a hypothetical cohort through ages under current mortality rates. Starting from a radix, conventionally one hundred thousand births, it applies age-specific probabilities of dying to compute survivors to each age, deaths in each interval, person-years lived, and life expectancy at each age. The table distinguishes period life tables, based on mortality in a single period, from cohort life tables, based on actual experience of a birth cohort over its lifetime. Life tables underpin insurance pricing, pension calculations, and population projections, because they convert mortality rates into survival probabilities that can be applied to any population. Stationary population is the theoretical population implied by a life table with constant births: its age structure is proportional to person-years lived, and its growth rate is zero. The stable population model generalises this to constant fertility and mortality with a constant growth rate, giving an age structure determined by vital rates regardless of initial structure, a powerful result for projecting populations with limited data.

Migration is movement across a boundary with change of residence, classified as internal within a country or international across countries, voluntary or forced, permanent or temporary, and rural to urban, urban to rural, or between urban areas. Ravenstein laws observe regularities: most migrants move short distances, migration proceeds step by step toward larger centres, rural to urban flows dominate, women dominate short-distance migration in many contexts, and migration increases with economic development and transport improvements. Push factors at origin include unemployment, low wages, land pressure, conflict and environmental stress; pull factors at destination include jobs, wages, services and networks. The Harris-Todaro model explains rural to urban migration despite urban unemployment: migrants compare expected urban wages, the wage multiplied by probability of employment, with rural wages, so migration continues while expected urban income exceeds rural income, and urban unemployment can persist in equilibrium. Lee intervening obstacles model adds distance, cost, information and personal factors that mediate push and pull. Migration affects both origin, through remittances, brain drain or brain gain, and labour supply, and destination, through labour markets, housing, services and diversity, and its net effect depends on who migrates, their skills, and integration policies.

Environmental policy instruments

Demographic transition stages

Fertility and mortality measures