Population - A global challenge for the twenty-first century

Resumed from: Pages 126-148 in Hans van Ginkel, Brendan Barrett, Julius Court, and Jerry Velasquez, eds., Human Development and the Environment. Challenges for the United Nations in the New Millennium. New York: United Nations University Press.


Since population deals with birth and death, sex and marriage, with gender roles, with intergenerational relations and interregional migration, it tend to be touching upon foundations of culture, religion, and national identity.　The history of global population growth shown that the rapid increases in life expectancy were mostly due to falling child mortality rates. This factor combined with fertility rates that remained high led to soaring population growth rates in the many parts.

Trends in fertility and mortality resulted in different patterns of population growth in different parts of the world. The dominant feature of the global demographic landscape has been contrast between "the well off populations" in NDCs and the poorer populations in the LDCs. As an example in Africa the population pyramid is typical of a rapidly growing population, showing larger and larger cohorts at the bottom in the young age group. Contrary in Western Europe, which the pyramid is narrower at the bottom, due to the very low levels of fertility since the 1970s. At the same time, declining mortality rates have increased the size of older age cohorts. The narrowing of population pyramid at the bottom and widening at the top is called "population ageing".

The conventional theory of demographic transition predict that as living standards rise and health conditions improve, first mortality rate decline and then, somewhat later, fertility rates decline. There are two different ways to explain demographic transition. First, "Homeostasis argument" stresses that societies tend to seek equilibrium between birth and death. The other view assumes that modernization of society acts as a joint driving force for declining mortality and fertility. The biggest difference between the demographic transition processes in MDCs and LDCs has been the speed of mortality decline, which in MDCs its come about over the course of two centuries as a result of reduced variability in the food supply, better housing, improved sanitation, and progress in preventive and curative medicine. Three preconditions for a lasting fertility decline suggest tree parallel strategies to foster the transition from high to low fertility:

1. Emphasize universal basic education to bring fertility increasingly into the realm of conscious choice,
2. Pursue changes in socio-economic variables,
3. Invest in reproductive health and the availability of family planning services.

A synergism between the various factors, the national family planning programs, combined with socio-economic development and empowerment of women, result in fertility decline.

For population projection, assumptions about future variance in the distributions of the three components have traditionally been based on time series analysis or ex-post analysis of projection errors. For the IIASA Projection chose an approach that is more intensively based on expert judgment. The procedure fits normal distributions to the three values (high, central and low). Results were derived through a set of 4.000 simulations that randomly combined fertility, mortality and migration path from the tree normal distributions from 13 world regions. Three near certainties emerge from the range of scenarios and the probabilistic projections in the coming decades are:

1. World population will increase substantially from its current level (even in the extreme lowest growth scenario). A further doubling of world population has become unlikely.
2. The distributions of world populations will continue to shit towards LDCs.
3. The world population will continue to the age.

Human beings exploit natural resources through their consumption of good and services. Pollution, including emissions of CO2 and other greenhouse gases and services, resulting from production of good and services gives rise to residuals. Climate change and population growth is among a select group of issue that will have global implications for generations to come. The impact of population independent of possible feedback effect on other relevant variable called the direct effects of populations growth on the environment. Referring to ambiguities and dispute regarding the nature of indirect effect, also should be the focus of attentions. An encapsulation of research arrived at particularly strong conclusions:

1. The relationship between population and per capita income is ambiguous. Two opposing view, one that demographic growth mire population in poverty and the second that the demographic growth stimulate improvement in technology and organizations.
2. Population growth increases the share of productions accounted for by agriculture and the proportion of the land base devote to food productions. In this sense, demographic increase has the effect of concentrating output into a heavily polluting sector.
3. Most deforestation in mid latitude tropical forest occurs in a limited number of hot spot and can be traced ultimately to expansion of agriculture. Largely because of the link to agriculture, it has long been recognize that rapid population growth is correlated with rapid lost of Forest cover.
   

In addition to direct and indirect effect, there is a family of impact which might be called induced effect: changes in the ways social institutions cope with ecological stress, including changes in the institutions themselves, as a result of shifts in demographic regimes. Nevertheless, the kinds of population policies most in favor are probably "win-win" from the point of view of climate change.