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166 GÁBOR PIRISI In the last decades, the stress regarding global problems has slightly shifted: we are not so much scared of running out of energy resources as of the conseguences of their use. The global climate crisis has taken center stage. One may regretfully but safely declare that it was primarily caused by human activity. Chief among them is the burning of fossil fuels, followed by human agriculture with some of its direct and indirect effects. In comparison, the problem of overpopulation has been somewhat neglected (rightly, for certain reasons, as will be seen), although it must not be forgotten that the demand for energy resources is fed by the immense growth of the global population. (The chapter by Melinda Mihály and Dorottya Mendly discusses the problems of food.) The growth of the global population The size of the population of any area is fundamentally determined by two factors: natural growth and net migration (the balance between immigrants and emigrants). Since — in an optimal case — the latter is zero for the Earth as an entity, the only decisive element of changes in the global population is natural growth (of course, migration is an extremely important factor for individual regions or countries). Natural growth has two components: number of live births and number of deaths. The difference between the two is the growth rate (or, for that matter, decrease). Both births and deaths are calculated per unit of population, usually 1,000 persons, rarely in percent. Both indexes depend on modifications in diverse components, both natural and social, political and economic. Though these rates may sometimes change in the short term in response to disasters or drastic shocks which hit society, they normally alter slowly, typically over decades. In purely mathematical terms, the birth rate is determined by two factors: the fertility rate (the number of children per woman in the reproductive period of her life) - which actually indicates the “willingness of women to have children” or the “probability of having children” — and the number of women of reproductive age within the whole population. In demographic terms, the former is more important, as it predicts future processes. It may occur that a country currently experiences positive natural growth (more children were born in a period of higher fertility rate, many of whom are now of reproductive age), but when the fertility rate drops below a certain number (usually 2.1 in developed countries), population growth will soon be negative. Globally, the maximum fertility rate is in excess of six (fig. 1): there are four countries in the world in which the average woman gives birth to over six children (!). There are more than 50 countries above the figure 3.0, which indicates fast growth. The global average is around 2.3. The average in Europe is already below 1.5, along with some 30 countries. The most significant negative anomaly is represented by South Korea, where the fertility rate does not reach 1.0. The figure clearly shows that there is a close correlation between natural growth and fertility in the interval between zero and five. The fertility rate of the countries which experience natural decrease is not much lower than that of countries with slight growth; in their case, the lower birth rate is due to an aging population. It can also be observed that above a certain limit, high fertility is not necessarily accompanied by the further acceleration of population growth, first of all because of infant mortality.
