Changing populations

Global population growth: the pattern behind the trend

The world's population has grown very quickly over the last two centuries, and it is still growing, but the headline figure hides the pattern that actually earns marks. Growth is not even in space and not even in time. Most of the growth happening now is in low-income countries, especially in sub-Saharan Africa and parts of South Asia, while many high-income countries are growing very slowly or not at all. So when a question asks about patterns and trends in global population growth, say where growth is fastest, where it has slowed and where populations are falling, and give the reason for each.

Where people live is uneven as well. Population distribution is how people are spread over an area and population density is how many people there are in each square kilometre, calculated as population / area in km2 and measured in people per km2. The world's people are crowded onto a small share of the land surface, on coastal plains, river valleys and cities, while deserts, ice sheets and high mountains are almost empty. Growth makes this concentration worse rather than better, because most of the extra people are born in the countries and the cities where people already live.

Three patterns are worth knowing separately. Rapid growth happens where the death rate has fallen but the birth rate is still high, so natural increase is large. Slowing growth happens where the birth rate has started to fall as girls stay in school longer, more women work and contraception is more widely used. Stable or declining populations happen where the birth rate has fallen below the death rate and people live a long time, so the population ages instead of growing; in a few countries, such as parts of eastern Europe, emigration adds to the decline.

Birth rate, death rate, fertility rate and natural increase

A population changes in only two ways: people are born and die, and people arrive and leave. The birth rate is the number of live births per 1,000 people per year, the death rate is the number of deaths per 1,000 people per year, and the fertility rate is the average number of children born to each woman. Keep those three apart: the birth rate counts births in a whole population in one year, while the fertility rate counts children per woman and is not affected by how many women of childbearing age the country happens to have.

Natural increase is the birth rate minus the death rate, and it is positive when there are more births than deaths. Because both rates are per 1,000, dividing the answer by 10 turns it into a percentage. A country with a birth rate of 34 and a death rate of 11 has a natural increase of 34 - 11 = 23 per 1,000, which is 2.3 per cent a year. That does not sound like much until you compound it: a population growing at 2.3 per cent a year doubles in about 30 years.

The two rates move at different times, and that gap is the engine of population growth. Better food, clean water, sanitation and vaccination cut the death rate first, and quickly. The birth rate falls later, because parents only have fewer children once they are confident that those children will survive, and once women have education and choices about work and family size. In the years between the two, births far outnumber deaths and the population grows fast. A fall in the birth rate is also a fall in the fertility rate, so the two are linked: fewer children per woman eventually means fewer births per 1,000 people.

Migration is the other half of the story. Immigration is arrival in a country, emigration is departure, and net migration is immigration minus emigration. Total population change is natural increase + net migration, and the two can pull in opposite directions, which is how a country with a high birth rate can still lose population, and how a country with a low birth rate can still grow.

• Birth rate = live births per 1,000 people per year. Death rate = deaths per 1,000 people per year.
• Fertility rate = average number of children per woman. It is not the same as the birth rate.
• Natural increase = birth rate - death rate. Divide by 10 to turn it into a percentage.
• Net migration = immigration - emigration. Total change = natural increase + net migration.
• Death rates fall before birth rates do, and the gap between them produces rapid growth.

The demographic transition model (DTM)

The demographic transition model shows how the birth rate and the death rate of a country change as it develops, and what that does to the total population. It has five stages, and in each stage the two lines are doing something different.

In Stage 1 (high fluctuating) the birth rate and the death rate are both high and both jump around with disease and poor harvests, so the population is small and barely grows. In Stage 2 (early expanding) the death rate falls sharply with better food, water and medicine while the birth rate stays high, so natural increase is large and the population grows quickly. In Stage 3 (late expanding) the birth rate starts to fall as education, contraception and urban living spread, so growth slows. In Stage 4 (low fluctuating) both rates are low and roughly equal, so the population is stable and larger than it was. In Stage 5 (decline) the birth rate falls below the death rate, so natural increase is negative and the population shrinks and ages.

• Strengths: it explains why LICs tend to have youthful, fast-growing populations and HICs ageing, slow-growing ones, and it gives you a ready-made structure for comparing two countries at different levels of development.
• Strengths: it links population change to development, which is exactly the relationship the syllabus asks you to understand.
• Limitation: it was based on the experience of western European countries during industrialisation, and it assumes every country will pass through the same stages in the same order.
• Limitation: it has no timescale, so it cannot tell you how long a country will spend in a stage, or whether it will ever reach Stage 4 or 5.
• Limitation: it ignores migration completely, yet migration can change a country's population far more than its birth and death rates.
• Limitation: some countries do not follow the model. A war, a famine or an epidemic such as HIV/AIDS can hold a country in Stage 2 for decades, and a government policy can force the birth rate down so quickly that the country appears to jump from Stage 2 to Stage 4.

Population pyramids and how structure changes

A population pyramid is a bar chart turned on its side. The vertical axis is age, usually in five-year bands from 0-4 at the bottom upwards. The horizontal axis is the size of the population in each band, either as a number or as a percentage of the total so that countries of different sizes can be compared. Males are shown on the left and females on the right, so the length of the bars tells you the balance between males and females.

Read it in three parts. The base shows the birth rate: a wide base means a high birth rate and a large young dependent population, and a narrow base means a low birth rate. The sides show how many people survive into middle age: sides that fall away steeply mean a high death rate and a shorter life expectancy, and sides that are nearly straight mean most people reach middle age. The top shows life expectancy, and it is usually longer on the female side because women live longer than men on average.

Two features catch examiners out. A bulge in the middle of a pyramid is a large group of people of the same age, caused by a baby boom or by a wave of migrants arriving when they were young adults; that bulge climbs up the pyramid as the group ages. A notch, or short bar, marks a group thinned by war, famine, disease or a sudden fall in the birth rate, and it climbs the pyramid in the same way.

Natural increase and net migration are what change a structure over time. Natural increase widens the base first, because a high birth rate adds children at the bottom, and those children move up the pyramid year by year, which is why a youthful structure stays youthful for a generation even after the birth rate falls. Net migration changes the structure differently, because migrants are usually young adults: immigration widens the middle of the pyramid and, if the migrants have children in the destination country, widens the base a few years later. Emigration thins the middle and the base of the country that loses them.

Youthful and ageing populations: causes, impacts and evaluation

A youthful population has a pyramid with a very wide base that narrows quickly, so a large share of the people are under 15, the working-age group is proportionally small and there are few elderly people. It is caused by a high birth rate combined with a death rate that has already fallen, which is Stage 2 or early Stage 3 of the DTM. The impacts are all about children: the government must build schools, train teachers, provide child health care and maternity services, and supply enough food and clean water. Then, fifteen years later, it must find work for the largest group of new adults the country has ever had.

An ageing population has the opposite pyramid: a narrow base because the birth rate is low, and long bars in the 60s and above because life expectancy is long. It is caused by a low birth rate together with better health care and medicine throughout life. The impacts move upwards with the population: pensions, health care, social care and long-term medicine must be paid for by a working-age group that is no longer growing, and there may not be enough workers to fill the jobs that are available. Many HICs respond by raising the retirement age, encouraging immigration of working-age adults, or both.

The pressure is often summarised by the dependency ratio: the number of dependents per 100 people of working age, worked out as (under 15 + 65 and over) / 15-64 x 100. Two countries can share the same dependency ratio and need completely different policies, because one ratio is built from children and the other from elderly people. That is why you should always say who the dependents are.

Evaluate both structures rather than calling one good and one bad. A youthful population is not automatically a problem: it is a large future workforce and a large market for goods and services, and countries that educate and employ it well, as several East Asian economies did, grow quickly as a result. Its cost is that schools, clinics and jobs must all be provided before the country has the tax revenue to pay for them, which is why a youthful structure can trap a country in low-income status. An ageing population is not automatically a problem either: it has an experienced workforce, lower spending on schools and often a growing care industry. Its cost is that a shrinking working-age group carries the pensions and health care of a growing elderly group, and that the money is committed for decades and cannot easily be moved to other priorities.

• Youthful: wide base, high birth rate, falling death rate. Impacts fall on schools, child health care, food, water and jobs.
• Ageing: narrow base, long life expectancy, low birth rate. Impacts fall on pensions, health care, social care and the size of the workforce.
• Evaluate: a large young population is an opportunity if the country can educate and employ it, and a burden if it cannot.
• Evaluate: an ageing population brings experience and a care industry, but the cost is carried by a working-age group that is not growing.

Pro-natalist and anti-natalist policies

Governments try to change the birth rate because it decides how many workers, taxpayers and consumers the country will have in twenty years. A pro-natalist policy aims to raise the birth rate, and an anti-natalist policy aims to lower it. Both work through the same levers: money, time, information and the law.

Pro-natalist techniques include cash bonuses or payments for each child, tax allowances that grow with family size, subsidised or free childcare, longer paid parental leave, priority access to housing or school places, and publicity campaigns encouraging larger families. France has used a package of cash benefits, tax allowances for larger families and subsidised childcare for decades. Singapore offers a baby bonus, subsidised childcare and priority school places. Countries that once restricted births have reversed their policies, and China's move from its one-child policy to a two-child and then a three-child policy is a clear example of that reversal.

Anti-natalist techniques include free or subsidised contraception, family planning clinics and advice, sex education in schools, raising the legal age of marriage, financial incentives or penalties linked to family size, and, at the extreme, limits on the number of children a couple may have. China's one-child policy, introduced at the end of the 1970s and relaxed from 2016, is the best-known example, and it was enforced with fines and pressure on employers as well as through information campaigns.

Evaluate them honestly. Pro-natalist policies are expensive, and they usually have a small and slow effect, because birth rates fall for reasons that money alone does not change: women's education and careers, the cost of housing, and the expectation of a certain standard of living for each child. Where they do work, the effect is often a short-lived rise in births followed by a fall back. Anti-natalist policies can cut the birth rate much faster, but they create new problems: a population that ages quickly with too few young workers, an imbalance between the number of boys and girls where families prefer sons, and, where the policy is enforced harshly, real hardship and lost trust in the government. The strongest answers judge which policy suits which country and why, and point out that both kinds of policy take at least a generation to show their full effect.

International migration: types, causes, impacts and management

The syllabus names three types of migrant and you must be able to tell them apart. An economic migrant moves to another country to find work or a better income, and the choice is voluntary. A refugee has been forced to leave their country because of war, persecution or disaster and is protected under international law, so they cannot safely return. An asylum seeker has fled for the same reasons and has applied for protection in the destination country but is still waiting for a decision. The difference between a refugee and an asylum seeker is therefore about the stage of the claim, not about how serious the danger was.

Causes of migration are sorted into push and pull factors. Push factors drive people away from the origin country: unemployment, low wages, poor services, drought and crop failure, conflict and persecution, and a lack of opportunity for young people. Pull factors attract them to the destination: jobs, higher wages, better schools and hospitals, safety, family and community already there, and a familiar language. Most migrations have several causes at once, and the honest answer weighs them rather than listing them.

Impacts on the migrant: higher wages, new skills and the ability to send money home, set against leaving family behind, the cost and danger of the journey, language barriers, qualifications that are not recognised, and the risk of being exploited in low-paid or informal work. Impacts on the country of origin: money sent home, called remittances, which families spend on food, housing, school fees and medicine; less pressure on jobs and land; but also a loss of skilled workers such as doctors, nurses and engineers, known as a brain drain, families split across countries, and more households headed by women. Impacts on the destination country: a supply of workers for jobs that are hard to fill, tax revenue, cultural diversity and new businesses; but also pressure on housing, schools, health services and transport, competition for low-paid work, and sometimes tension between communities.

Managing international migration uses several kinds of strategy. Border controls, visas, work permits, quotas and points-based systems decide who may enter and for how long. Asylum systems, refugee camps, resettlement schemes and safe legal routes process people who are fleeing. Integration policies, such as language classes, help with housing and a path to citizenship, help newcomers settle. International agreements and co-operation between origin and destination countries try to make the process orderly. And longer-term strategies try to reduce the need to leave in the first place, through trade, investment, aid and development in origin countries.

Evaluate those strategies. Strict controls can reduce the number of people entering legally, but they often push migration onto dangerous routes and into informal work where migrants have no protection, and they can be expensive to enforce. Safe legal routes and integration programmes cost money and can be politically difficult, yet they make migration more orderly and help migrants contribute sooner, which matters to ageing HICs that need workers. Sustainable management means meeting the needs of the migrants, the origin country and the destination country without storing up problems for the future: workers arrive through legal routes with their rights protected, remittances are not the only thing the origin country depends on, and the destination country plans the housing, services and jobs that the new arrivals will need.