What Factor Would Contribute to a Sharp Decline in Death Rate, Such as the One Shown in Stage 2?

• Journal List
• Philos Trans R Soc Lond B Biol Sci
• v.364(1532); 2009 Oct 27
• PMC2781829

Philos Trans R Soc Lond B Biol Sci. 2009 October 27; 364(1532): 2985–2990.

Homo population growth and the demographic transition

Abstract

The globe and near regions and countries are experiencing unprecedentedly rapid demographic change. The virtually obvious example of this modify is the huge expansion of human numbers: 4 billion take been added since 1950. Projections for the next one-half century expect a highly divergent world, with stagnation or potential decline in parts of the developed globe and continued rapid growth in the to the lowest degree developed regions. Other demographic processes are also undergoing extraordinary change: women's fertility has dropped rapidly and life expectancy has risen to new highs. By trends in fertility and mortality accept led to very young populations in high fertility countries in the developing globe and to increasingly older populations in the developed globe. Gimmicky societies are now at very different stages of their demographic transitions. This paper summarizes primal trends in population size, fertility and bloodshed, and historic period structures during these transitions. The focus is on the century from 1950 to 2050, which covers the period of most rapid global demographic transformation.

Keywords: population growth, demographic transition, fertility, bloodshed, age structure

1. Introduction

After centuries of very irksome and uneven growth, the world population reached one billion in 1800. The modern expansion of human numbers started then, rising at a wearisome but more steady footstep over the next 150 years to ii.5 billion in 1950. During the second half of the twentieth century, however, growth rates accelerated to historically unprecedented levels. As a upshot, world population more than doubled to 6.five billion in 2005 (United Nations 1962, 1973, 2007). This population expansion is expected to continue for several more decades before peaking near x billion later in the xx-showtime century. Around 2070, the world's population volition exist 10 times larger than in 1800.

The recent period of very rapid demographic modify in most countries around the world is characteristic of the central phases of a secular process chosen the demographic transition. Over the course of this transition, declines in nascency rates followed by declines in decease rates bring about an era of rapid population growth. This transition usually accompanies the development process that transforms an agricultural gild into an industrial one. Earlier the transition'south onset, population growth (which equals the difference between the nascence and death rate in the absenteeism of migration) is near zero every bit high death rates more or less offset the high nascency rates typical of agrarian societies before the industrial revolution. Population growth is again near zero later on the completion of the transition as birth and expiry rates both achieve low levels in the well-nigh adult societies. During the intervening transition period, rapid demographic change occurs, characterized by two distinct phases. During the beginning phase, the population growth rate rises as the expiry rate declines while the birth rate remains high. In the second phase, the growth rate declines (but remains positive) due to a decline in the birth rate. The entire transition typically takes more than a century to complete and ends with a much larger population size.

The plot of world population size over fourth dimension in effigy 1 (top solid line) shows the typical S-shaped pattern of estimated and projected population size over the course of the transition. Population growth accelerated for near of the twentieth century reaching the transition's midpoint in the 1980s and has recently begun to decelerate slightly. Today, nosotros are nevertheless on the steepest part of this growth curve with additions to globe population exceeding 75 million per year between 1971 and 2016.

Population size estimates, 1900–2005 and projections 2005–2050. High, medium and depression variants.

Contemporary societies are at very different stages of their demographic transitions. Key trends in population size, fertility and mortality during these transitions are summarized below. The focus is on the century from 1950 to 2050, roofing the period of most rapid global demographic change. The chief source of data is the United Nation'south 2006 world population assessment, which provides estimates for 1950–2005 and projections from 2005 to 2050 (Un 2007).

two. Future population trends

The projected rise in world population to ix.2 billion in 2050 represents an increase of ii.seven billion over the 2005 population of 6.5 billion. Nearly all of this time to come growth will occur in the 'S'—i.e. Africa, Asia (excluding Nippon, Australia and New Zealand), and Latin America—where population size is projected to increase from 5.iii to vii.9 billion betwixt 2005 and 2050 (table 1). In dissimilarity, in the 'North' (Europe, Northern America, Japan and Australia/New Zealand), population size is forecast to remain about stable, growing slightly from i.22 to 1.25 billion between 2005 and 2050. The divergence in trends between these two world regions reflects the later stage of the transition in the North compared with the Due south.

Tabular array ane.

Population estimates (1950–2005) and projections (2005–2050), by region. Adapted from Un (2007).

	population (billions)			% increase
	1950	2005	2050	1950–2005	2005–2050
Africa	0.22	0.92	2.00	311	117
Sub-Saharan	0.18	0.77	1.76	327	129
Asia	1.41	3.94	5.27	179	34
Latin America	0.17	0.56	0.77	233	38
Europe	0.55	0.73	0.66	33	−9
Northern America	0.17	0.33	0.45	94	34
South	i.72	v.30	7.95	208	50
North	0.81	ane.22	i.25	49	2
World	2.54	6.51	9.19	157	41

The global demographic transition began in the nineteenth century in the now economically adult parts of the globe (the North) with declines in death rates. Large reductions in nascency rates followed in the early part of the twentieth century. These transitions are at present more or less complete. But, as shown in table 1, trends for the two primary regions in the Due north are expected to diverge between 2005 and 2050: an increase from 0.33 to 0.45 billion in Northern America, and a decline from 0.73 to 0.66 billion in Europe. In fact, several countries in Europe (e.chiliad. Russia) and Eastern asia (e.g. Japan) face significant population declines as nativity rates take fallen beneath expiry rates.

The demographic transitions in Africa, Asia and Latin America started subsequently and are still underway. In 2005, Asia had a population of 3.94 billion, more than half of the globe total, and its population is expected to grow past 34 per cent to 5.27 billion by 2050. Africa, with 0.92 billion inhabitants in 2005, is likely to experience by far the most rapid relative expansion, more than than doubling to 2.0 billion by 2050. Latin America, with 0.56 billion in 2005, is the smallest of the regions of the South; its projected growth trend is like to that of Asia.

It may seem surprising that population growth continues at a rapid pace in sub-Saharan Africa, where the AIDS epidemic is most severe. This epidemic has indeed caused many deaths, merely population growth continues because the epidemic is no longer expanding and the nativity rate is expected to remain college than the elevated death rate in the future (UNAIDS 2007; Bongaarts et al. 2008). The epidemic'south demographic touch can be assessed by comparing the standard UN population projection (which includes the epidemic's effect) with a separate hypothetical projection in which AIDS mortality is excluded (Un 2007). In sub-Saharan Africa, the former projects a 2050 population of i.76 billion and the latter a population of 1.95 billion. The difference of 0.2 billion in 2050 betwixt these projections with and without the epidemic is due to deaths from AIDS as well as the absence of the descendents from people who died from AIDS. Co-ordinate to these projections, the population of sub-Saharan Africa will grow past ane billion between 2005 and 2050 despite the substantial impact of the AIDS epidemic. In fact, no land is expected to meet a decline in its population size betwixt 2005 and 2050 due to high AIDS mortality. Most populations in sub-Saharan Africa will more than double in size, several will triple and Niger is expected to quadruple by 2050 (United nations 2007).

Transitions in the developing earth have mostly produced more rapid population growth rates in mid-transition than historically observed in the North. In some developing countries (e.yard. Kenya and Uganda), peak growth rates approached four per cent per year in recent decades (implying a doubling of population size in two decades), levels that were very rarely observed in developed countries except with massive immigration. Two factors account for this very rapid expansion of population in these nonetheless largely traditional societies: the spread of medical technology (e.g. immunization, antibiotics) later World War II, which led to extremely rapid declines in decease rates, and a lag in declines in birth rates.

Population sizes for the 10 largest countries in 2005 and in 2050 are presented in table 2. In 2005, China (1.31 billion) and India (1.13 billion) were past far the largest countries, together accounting for near half the Due south'southward total. The top 10 include half-dozen Asian countries and simply one country each in Latin America and Africa. By 2050, the ranking is expected to have shifted substantially, with India'due south population exceeding People's republic of china'due south, and with Federal democratic republic of ethiopia and DR Congo ascension to the top 10, replacing Nihon and the Russian Federation.

Table two.

Ten largest countries by population size in 1995 (estimate) and 2050 (medium projection). Adjusted from Un (2007).

rank	1995		2050
	state	population size (millions)	country	projected population (millions)
1	China	1313	Republic of india	165
ii	India	1134	China	140
3	United States	300	Usa	40
iv	Indonesia	226	Indonesia	29
5	Brazil	187	Pakistan	29
6	Pakistan	158	Nigeria	28
7	People's republic of bangladesh	153	Brazil	25
8	Russian Federation	144	Bangladesh	25
nine	Nigeria	141	D.R. Congo	18
10	Nippon	128	Ethiopia	18

To simplify the presentation of results, all projections discussed in this written report are taken from the medium variant of the UN projections (United nations 2007). The Un has a good record of making relatively authentic projections (National Research Quango 2000), simply the hereafter is of course uncertain and actual population trends over the side by side one-half century volition likely diverge to some extent from current projections. The Un makes an effort to capture this uncertainty by publishing divide high and low projections. For the globe, the high and low variants achieve seven.8 and 10.8 billion, respectively, in 2050, indicating a rather wide range of possible outcomes (come across dashed lines in figure 1).

iii. Drivers of population growth: fertility and mortality

The globe'due south population increases every year because the global birth rate exceeds the expiry rate. For instance, in 2000–2005 population size increased at a charge per unit of one.17 per cent per yr, which equals the divergence between a birth rate of ii.03 per cent and a expiry rate of 0.86 per cent. At the country level, population growth is too afflicted by migration, just for the regional aggregates of population used in this assay, migration is usually a minor factor, and it volition therefore non be discussed in detail.

The annual birth and death rates of populations are in turn primarily determined by levels of fertility and mortality experienced by individuals. The most widely used fertility indicator is the full fertility rate (TFR), which equals the number of births a adult female would take past the finish of her reproductive years if she experienced the historic period-specific fertility rates prevailing in a given year. Mortality is often measured past the life expectancy (LE) at birth, which equals the average number of years a newborn would live if subjected to historic period-specific mortality rates observed in a given yr.

(a) Fertility

The UN'due south past estimates and future projections of fertility levels past region for the period 1950–2050 are presented in figure 2. In the 1950s, the TFR in the South was high and most stable at around six births per woman on boilerplate. This high level of fertility reflects a virtually absence of birth control, a condition that has prevailed for centuries before the middle of the twentieth century. In the late 1960s, a rapid decline in fertility started nearly simultaneously in Asia and Latin America. In contrast, Africa has experienced only express reproductive change. As a result of these divergent past trends, fertility levels in 2000–2005 differed widely among regions from equally high as v births per woman (bpw) in Africa, to 2.5 bpw in Asia and Latin America. Boilerplate fertility in the North was already low in the early 1950s and has since declined to 2.0 bpw in Northern America and to 1.4 bpw in Europe.

Trends in the total fertility rate past region.

The pass up in the average fertility in the South from 6 to 3 bpw over the by half century has been very rapid by historical standards. This reproductive revolution is mainly due to ii factors. Beginning, desired family size of parents has declined every bit the cost of children rose and kid survival increased. Second, regime intervention played a primal role. In China this took the class of a coercive and unpopular i-child policy, but well-nigh other countries implemented voluntary family planning programmes. The aim of these programmes is to provide information about and admission to contraceptives at subsidized prices so that women who want to limit their childbearing tin can more readily do so.

Un projections for the South assume that the TFR will eventually reach and and then autumn slightly below the so-called 'replacement' level in all regions. Replacement fertility is only above 2 bpw and it represents the level at which each generation just replaces the previous one, thus leading to zero population growth (in the absence of bloodshed change and migration). Below-replacement fertility produces, in the long run, population decline. As is evident from effigy 2, the TFRs in Asia and Latin America are expected to reach the replacement level around 2020. Africa is assumed to be on a much slower trajectory towards replacement fertility considering of its lower level of socio-economic development. High fertility therefore remains a cardinal crusade of future population growth in this region. In dissimilarity, the already low fertility of the North is expected to remain below replacement and is no longer driving population growth.

(b) Mortality and life expectancy

Bloodshed levels have too inverse chop-chop over the past several decades (figure 3). The S experienced infrequent improvements in LE from an boilerplate of 41 years in 1950–1955 to 64 years in 2000–2005. Past the early on 2000, Latin America reached mortality levels similar to those prevailing in the Northward in the 1970s, and Asia was merely a few years behind. Africa experienced the highest mortality and improvements in LE stalled in the 1990s due to the AIDS epidemic. As a issue, Africa's LE, at 52 years in 2000–2005, was still substantially below that of Asia (68) and Latin America (72). Every bit expected, Europe and Northern America already achieved relatively depression levels of mortality past 1950, simply they have nevertheless seen significant further improvements since then. Europe'south LE (74) is now lower than North America's (78) because of a rise in mortality in Eastern Europe after the break-up of the Soviet Marriage.

Projections of hereafter LEs by the UN assume connected improvements over time in all regions. The North is expected to reach 82 years in 2050 despite the increasing difficulty in achieving increments as countries achieve always college levels of LE. Asia and Latin America are expected to go on to shut the gap with the North, and Africa volition continue to lag, in function because the continent remains affected past the AIDS epidemic.

Information technology should exist noted that the assumptions made by the UN about future trends in fertility and mortality are not based on a firm theoretical footing. Instead, the Un relies on empirical regularities in past trends in countries that have completed their transitions, more often than not in the North, where fertility declined to approximately the replacement level, and increases in LE became smaller over time. This is a plausible approach that unfortunately leaves room for potential inaccuracies in projection results.

4. Changing population age composition

Over the course of the demographic transition, declines in fertility and mortality crusade important changes in a population'due south age composition. In full general, countries in the early stages of the transition have a younger historic period structure than countries in the after stages.

Figure iv presents the distribution of the 2005 population in iv broad age groups: 0–fourteen, 15–24, 25–64 and 65+ by region. Most of the regions in the South—Africa, Latin America, South asia and West Asia—have very young historic period structures with most one-half of the population under historic period 25 (62% in Africa). The exception is East Asia (mostly Red china) where this proportion is 37 per cent. In the Due north, the population under 25 is however smaller: 35 per cent in North America and just 30 per cent in Europe. The reverse pattern is observed for the proportion 65+, which is much higher in the North than in the South, ranging from as loftier as fifteen per cent in Europe to equally depression as just 3 per cent in Africa.

Distribution of population by historic period, by region, 2005.

(a) The age-dependency ratio

A changing age distribution has significant social and economical consequences, e.g. for the allocation of education, healthcare and social security resources to the young and old. Assessments of this touch on often rely on the so-called historic period-dependency ratio (DR) that summarizes key changes in the historic period structure. The DR at a given point in time equals the ratio of population aged below fifteen and over 65 to the population of historic period 15–64. This ratio aims to measure how many 'dependents' there are for each person in the 'productive' age group. Patently, not every person below fifteen and over 65 is a dependent and non every person between ages 15 and 65 is productive. Despite its crudeness, this indicator is widely used to document broad trends in the historic period limerick.

Over the grade of a demographic transition, the DR shows a characteristic pattern of change. Figure 5 presents this blueprint as observed in the South from 1950 to 2005 and projected from 2005 to 2050. Early in the transition, the DR typically first rises slightly as improvements in survival chances of children raise the number of immature people. Next, the DR falls sharply as declines in fertility reduce the proportion of the population under age 15. This turn down has important economic consequences because it creates a so-called 'demographic dividend', which boosts economic growth by increasing the size of the labour force relative to dependents and by stimulating savings (Birdsall et al. 2001). Finally, at the end of the transition, the DR increases again equally the proportion of the population over historic period 65 rises. Figure 5 also plots the DR of the North from 1950–2050. From 1950 to 2010 information technology showed a slight decline, only after 2010 information technology rises steeply every bit very low fertility and increasing longevity increases the proportion 65+. This ageing of the Due north poses serious challenges to support systems for the elderly (OECD 1998, 2001).

Dependency ratio estimates, 1950–2005.

(b) Population momentum

At the end of the demographic transition natural population growth reaches aught once three conditions are met:

1. Fertility levels-off at the replacement level of about ii.1 bpw (more than precisely, the net reproduction charge per unit should be 1). If fertility remains above replacement, population growth continues.

2. Mortality stops failing. In practice, this is not probable to happen because improvements in medical technology and healthcare as well as changes in lifestyles, etc. volition probably ensure connected increases in LE.

3. The historic period structure has adjusted to the mail service-transitional levels of fertility and mortality.

The adjustment of the age construction at the end of the transition takes many decades to complete. A cardinal implication of this slow aligning process is that population growth continues for many years after replacement fertility is reached if, every bit is often the instance, the population is still relatively young when fertility reaches the replacement level. The tendency of population size to increment afterwards a two-child family size has been reached is referred to as population momentum; it is the event of a young population age construction ('immature' is defined relative to the age construction in the current life table) (Bongaarts & Bulatao 1999).

The population momentum inherent in the age construction of a detail population at a given signal in time tin can be estimated with a hypothetical population projection in which future fertility is set instantly to the replacement level, bloodshed is held constant and migration is gear up to nada. Since such a variant is not directly available from UN projections, it will not exist presented here. However, the UN does provide 'instant replacement' projections in which bloodshed and migration trends are the aforementioned as in the standard project. This project gives an approximation of the combined effect on future growth of population momentum and declining bloodshed in the South because the role of migration is small-scale. The difference between this hypothetical projection and the standard medium UN projection is a measure of the affect of high fertility on future population growth.

Results of these two projections are presented in figure half dozen, which compares the per cent growth between 2005 and 2050 for regions in the Southward. The blackness bars requite the growth in the standard (medium variant) projection and the grey bars give the growth in the 'instant replacement' projection. Three results are noteworthy. First, the 2 projections differ almost in Africa (+117% versus +50%) which is as expected because fertility is still very high in this region. 2d, in all regions of the S exterior Red china, populations would be expected to ascent by fifty per cent (62% in West Asia) if fertility were set to replacement in 2005. This implies that momentum and declining mortality are responsible for virtually half of the projected future population growth in Africa and for the big majority of growth in Latin America, and South and West Asia. Third, in East Asia and in Latin America the replacement project exceeds the medium UN projection. This finding is explained by the fact that fertility in these regions is assumed to average below the replacement level over the next half century.

Pct increase in population 2005–2050, by region, alternative projections. Black confined announce medium Un projection; grey bars denote instant replacement projection (hypothetical).

v. Conclusion

The world and near countries are going through a period of unprecedentedly rapid demographic change. The most obvious case of this change is the huge expansion of man numbers: 4 billion have been added since 1950. Other demographic processes are too experiencing extraordinary change: women are having fewer births and LEs accept risen to new highs. By trends in fertility and/or mortality take led to very young populations in loftier fertility countries in the South and to increasingly older populations in the North. Nonetheless other important demographic changes which were non reviewed here include rapid urbanization, international migration, and changes in family unit and household structure.

Global population growth will go along for decades, reaching around 9.ii billion in 2050 and peaking still higher later in the century. The demographic drivers of this growth are high fertility in parts of the South, besides as declining bloodshed and momentum. This large expansion in human numbers and of the accompanying changes in the age structure will have multiple consequences for society, the economy and the surround as discussed in the subsequent capacity in this outcome.

Footnotes

References

• Birdsall N., Kelley A., Sinding South.2001Population matters: demographic change, economic growth and poverty in the developing world Oxford, Britain: Oxford University Press [Google Scholar]
• Bongaarts J., Bulatao R.1999Completing the demographic transition. Popul. Dev. Rev. 25, 515–529 (doi:10.1111/j.1728-4457.1999.00515.x) [Google Scholar]
• Bongaarts J., Buettner J., Heilig Yard., Pelletier F.2008Has the AIDS epidemic peaked? Popul. Dev. Rev. 34, 199–224 (doi:10.1111/j.1728-4457.2008.00217.10) [Google Scholar]
• National Research Council 2000Across half dozen billion: forecasting the earth'due south population (eds Bongaarts J., Bulatao R.). Washington, DC: National Academy Press [Google Scholar]
• OECD 1998Maintaining prosperity in an ageing guild Paris: OECD Publications [Google Scholar]
• OECD 2001The financial implications of ageing: projections of historic period-related spending. OECD Economic Outlook 69, 145–167 [Google Scholar]
• UNAIDS 2007AIDS Epidemic Update Geneva: UNAIDS [Google Scholar]
• United nations 1962Demographic yearbook New York, NY: Un [Google Scholar]
• United Nations 1973The determinants and consequences of population trends New York, NY: Department of Economic and Social Affairs, Population Studies fifty, United Nations [Google Scholar]
• United Nations 2007World population prospects: the 2006 revision New York, NY: Un Population Division [Google Scholar]

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Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2781829/

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