Population today. We all know the story since January 2020. The COVID-19 pandemic has been an historically large public health event, officially contributing to more than 5 million recorded fatalities worldwide, with over 220k people dying with COVID-19 in the past month alone. Taking a wider lens, the world has seen nearly 20 million more deaths than would normally have occurred since January last year, so-called “excess deaths” (not getting into their measurement today). This suggests that the ongoing pandemic is already around the 4th most deadly single event in modern history. Indeed, COVID-19 is the single most deadly event in US history, with more than ¾ of a million deaths so far (and “excess deaths” nearing 1 million).

Thankfully, it looks like the worst is now behind us. The number of daily fatalities peaked in early 2021. Broader vaccination, combined with further medical advances, is likely to result in further declines over 2022 (absent a significant, more-deadly mutation) as it slowly becomes endemic. Over half of the world’s population has received at least one dose of a vaccine, and at the current pace of rollout, the world will have administered nearly 9 billion doses by the end of 2021, and around 14 billion (~1.9 doses for every person) by the middle of 2022.

With most of the developed world vaccinated, and ample vaccine supply (company targets suggest ~20bn doses will be manufactured in 2022 alone), the main obstacles to better coverage across low-income countries remain logistical barriers and the developed world’s willingness to share. Vaccines continue to work very well, despite the emergence of the more contagious Delta variant. And although efficacy against catching COVID has fallen over time, booster shots have been remarkably effective. Cross-country evidence suggests that the Western vaccines remain more than 90% effective against severe illness. And an Israeli study suggests that a third dose delivers a further ~93% reduction in severe illness. Highly effective antiviral treatments are now coming too. For example, Pfizer’s pill is said to reduce the chance of serious illness by a further 89%. Authorities in the US have now approved vaccines for children aged 5-11. With children accounting for a large share of recent infections (the virus will clearly find those not protected), this should further reduce contagion. While there is room for optimism, in the near term, there is a risk that the Northern winter could see another large wave of infection, further stressing health systems, and slowing the services recovery. However, vaccination should ensure that fatalities remain well below previous peaks.

Germany (which has one of the lowest vaccination rates in Western Europe) is already seeing higher case numbers than during its peak last winter, its highest ever rate last Thursday (50k cases). And in the US, the improvement in cases has begun to stall, with the seasonal spike between Halloween and Christmas last year suggesting that higher cases may soon arrive. Notably, the US also has one of the lowest vaccination rates in the OECD, with ~58% of the total population fully vaccinated vs. a weighted average of 64% among OECD countries. Encouragingly however, the countries with very high vaccination rates have generally maintained very good control, with low fatalities per capita:

Overall, if we’re thinking of the global population of 7.8 billion and where it’s going, thus far, it’s safe to conclude COVID hasn’t touched it, so I base any further analysis on 2019 data which is un-covid’d.

A baby bust and COVID

Deaths aside, a surprising feature of COVID to many was the decline in births, as opposed to more, felt most interestingly in China which has not recovered from a reversal of its one child policy and there are now financial incentives to having more children, further complicated as marriage falls out of fashion. The findings are not surprising to many demographers, who have noted similar declines after catastrophic events such as the 2008 financial crisis and the 1918 influenza pandemic. But they are still noteworthy. The uncertainty associated with a global pandemic and its impacts on families’ economic circumstances are the most likely reasons for these trends. The long-term effects of people having fewer babies during the pandemic are a matter of speculation. The phenomenon could possibly lead to an economic boom like the roaring twenties after the 1918 influenza pandemic. Or it could lead to a two-tiered recovery in which some families who were hit hard by the COVID pandemic and its economic impacts might be less likely to have children, whereas others who were less affected or even benefitted might be more likely to do so. A third possibility is that the declines will amount to a blip in demographic terms, with little discernible effect on the population as a whole:

https://www.scientificamerican.com/article/the-pandemic-caused-a-baby-bust-not-a-boom/

Our population

One of the big lessons from the demographic history of countries is that population explosions are temporary. For many countries the demographic transition has already ended, and as the global fertility rate has now halved (yes, read below), we know that the world as a whole is approaching the end of rapid population growth. Am not a fan of the UN, but they’ve done a good job in this respect and the UN Population Division has a lot of helpful visualisations here:

https://population.un.org/wpp/

Interestingly, the global population grew only very slowly up to 1700 – only 0.04% per year. In the many millennia up to that point in history very high mortality of kids counteracted high fertility. The world was in the first stage of the demographic transition. Once health improved and mortality declined things changed quickly, particularly over the course of the 20th century. Over the last 100 years global population more than quadrupled. As we see in the chart below, the rise of the global population got steeper and steeper and you have just lived through the steepest increase of that curve. This also means that your existence is a tiny part of the reason why that curve is so steep.

The 7-fold increase of the world population over the course of two centuries amplified humanity’s impact on the natural environment. To provide space, food, and resources for a large world population in a way that is sustainable into the distant future is without question one of the large, serious challenges for our generation. We should not make the mistake of underestimating the task ahead of us. Yes, I expect new generations to contribute, but for now it is upon us to provide for them. Population growth is still fast: every year 140 million are born and 58 million die, or thereabouts, maybe more in the last 2 years due to COVID but not much – the difference is the number of people that we add to the world population in a year: 82 million.

Where do we go from here?

In red below you see the annual population growth rate (that is, the percentage change in population per year) of the global population. It peaked around half a century ago. Peak population growth was reached in 1968 with an annual growth of 2.1%. Since then, the increase of the world population has slowed and today grows by just over 1% per year. This slowdown of population growth was not only predictable, but predicted. Just as expected by demographers, the world as a whole is experiencing the closing of a massive demographic transition.

This chart also shows how the United Nations envision the slow ending of the global demographic transition. As population growth continues to decline, the curve representing the world population is getting less and less steep. By the end of the century – when global population growth will have fallen to 0.1% according to the UN’s projection – the world will be very close to the end of the demographic transition. It is hard to know the population dynamics beyond 2100; it will depend upon the fertility rate and fertility is first falling with development – and then rising with development. The question will be whether it will rise above an average 2 children per woman.

In summary, as the world enters the last phase of the demographic transition, this means we will not repeat the past. The global population has quadrupled over the course of the 20th century, but it will not double anymore over the course of this century.

The world population will reach a size, which compared to humanity’s history, will be extraordinary; if the UN projections are accurate (they actually here have a good track record), the world population will have increased more than 10-fold over the span of 250 years.

We are on the way to a new balance. The big global demographic transition that the world entered more than two centuries ago is then coming to an end: this new equilibrium is different from the one in the past when it was the very high mortality that kept population growth in check. In the new balance it will be low fertility keeps population changes small.

As we see here, there is a significant fall in the population growth rate, particularly in the second half of the 21st century. Although the world population is still rising at the end of the century, it’s doing so very slowly. We would therefore expect growth to come to an end very soon after 2100. In this projection the world population will be around 10.88 billion in 2100 and we would therefore expect ‘peak population’ to occur early in the 22nd century, at not much more than 10.88 billion.

The world is reaching ‘peak child’

Following decades of very fast population growth, there is often concern that population growth is out-of-control: that an end to growth is not in sight. But we know this is not the case as population growth is slowing and will come to an end. How do we know? The moment in demographic history when the number of children in the world stops increasing is not far away. It is the moment that Hans Rosling famously called ‘peak child’ and it is pre-emptive of the moment in history when the population stops increasing:

https://onefiniteplanet.org/2019/05/25/peak-child/

Since 1950, the total number of children younger than 15 years of age increased rapidly, from 0.87 billion children to 1.98 billion today. The solid green and red lines in the visualisation below indicate the total number of children in the world. As we can see, we are not far away from the largest cohort of children that there will likely ever be. The world is approaching what the late Hans Rosling called “the age of peak child”. The blue line shows the total world population – rising life expectancy and falling fertility rates mean that the world population of adults will increase while the number of children is stagnating.

This is an extraordinary moment in global history. In the past, as aforementioned and as we all know child mortality was super high, and only two children per woman reached adulthood – if more had survived the population size would have not been stable. This also means that the extended family with many children, that we often associate with the past, was only a reality for glimpse in time. Only the few generations during the population boom lived in families with many children – before and after two children are the norm. The future will resemble our past, except that children are not dying, but are never born in the first place. Food for thought, and there’s enough of that, pun intended.

Between 1950 and today it was mostly a widening of the entire pyramid that was responsible for the increase of the world population. What is responsible for the increase of the world population from now on is not a widening of the base, but a fill up of the population above the base. Not children will be added to the world population, but people in working age and old age. At a country level “peak child” is followed by a time in which the country benefits from a “demographic dividend”. The demographic structure of a country is reshaped so that the proportion of people in working age rises and that of the dependent young generation falls. The demographic dividend can result in a rise of productive contributions and a growing economy. Now there is reason to expect that the world as a whole benefits from a “demographic dividend”.

The big demographic transition that the world entered more than a century ago is coming to an end: global population growth peaked half a century ago, the number of babies is reaching its peak, and the age profile of the women in the world is changing so that ‘population momentum’ is slowly losing its momentum. This is not to say that feeding and supporting a still rising world population will be easy, but we are certainly on the way to a new balance where it’s not high mortality keeping population growth in check, but low fertility rates.

The past and future of the global age structure

In 1950 there were 2.5 billion people on the planet. Now in 2021, there are 7.8 billion. By the end of the century the UN expects a global population of 11.2 billion. This visualisation of the population pyramid makes it possible to understand this enormous global transformation.

Population pyramids visualise the demographic structure of a population. The width represents the size of the population of a given age; women on the right and men to the left. The bottom layer represents the number of newborns and above it you find the numbers of older cohorts. Represented in this way the population structure of societies with high mortality rates resembled a pyramid – this is how this famous type of visualisation got its name. In the darkest blue you see the pyramid that represents the structure of the world population in 1950. Two factors are responsible for the pyramid shape in 1950: An increasing number of births broadened the base layer of the population pyramid and a continuously high risk of death throughout life is evident by the pyramid narrowing towards the top. There were many newborns relative to the number of people at older ages. The narrowing of the pyramid just above the base is testimony to the fact that more than 1-in-5 children born in 1950 died before they reached the age of five.

Through shades of blue and green the same visualisation shows the population structure over the last decades up to 2018. You see that in each subsequent decade the population pyramid was fatter than before – in each decade more people of all ages were added to the world population. If you look at the green pyramid for 2018 you see that the narrowing above the base is much less strong than back in 1950; the child mortality rate fell from 1-in-5 in 1950 to fewer than 1-in-20 today.

In comparing 1950 and 2018 we see that the number of children born has increased – 97 million in 1950 to 143 million today – and that the mortality of children decreased at the same time. If you now compare the base of the pyramid in 2018 with the projection for 2100 you see that the coming decades will not resemble the past: According to the projections there will be fewer kids born at the end of this century than today. The base of the future population structure is narrower.

We are at a turning point in global population history. Between 1950 and today, it was a widening of the entire pyramid – an increase of the number of children – that was responsible for the increase of the world population. From now on is not a widening of the base, but a ‘fill up’ of the population above the base: the number of children will barely increase and then start to decline, but the number of people of working age and old age will increase very substantially. As global health is improving and mortality is falling, the people alive today are expected to live longer than any generation before us. At a country level “peak child” is often followed by a time in which the country benefits from a “demographic dividend” when the proportion of the dependent young generation falls and the share of the population in working age increases.

This is now happening at a global scale. For every child younger than 15 there were 1.8 people in working-age (15 to 64) in 1950; today there are 2.5; and by the end of the century there will be 3.4. Richer countries have benefited from this transition in the last decades and are now facing the demographic problem of an increasingly larger share of retired people that are not contributing to the labour market. In the coming decades it will be the poorer countries that can benefit from this demographic dividend.

The change from 1950 to today and the projections to 2100 show a world population that is becoming healthier. When the top of the pyramid becomes wider and looks less like a pyramid and instead becomes more box-shaped, the population lives through younger ages with very low risk of death and dies at an old age. The demographic structure of a healthy population at the final stage of the demographic transition is the box shape that we see for the entire world for 2100:

 

More than 8 out of 10 people in the world are expected to live in Asia or Africa by 2100

The United Nations projects that world population growth will slow significantly over the course of the 21st century, coming close to its peak at 10.9 billion by 2100. But how is this growth distributed across the world? How does the world look in 2100 compared to today?

In this chart below we see the global population split by region. This shows historical data, but also projections to 2100 based on the UN’s medium growth scenario. The striking change between now and 2100 is the expected growth in the African population. Today, its population is around 1.3 billion; by 2100 it’s projected to more than triple to 4.3 billion.

Over the past 50 years Asia experienced rapid population growth. Today its population stands at around 4.6 billion. By 2050 it’s expected to rise to 5.3 billion, but then fall in the latter half of the century. Am not getting into the driving force behind these demographic changes but by 2100 Asia’s population is projected to fall almost back to levels we see today. Today Africa has just over 17% of the global population; by 2100 this is projected to rise to 40%. Asia will see a significant fall from almost 60% today to just over 40% in 2100. By the end of the century, more than 8 out of every 10 people in the world will live in Asia or Africa, as per the sub-heading, but it deserves another mention, right?

North, Central and South America, and Oceania, are projected to also see a rise in population this century – but this growth will be much more modest relative to growth in Africa. Europe is the only region where population is expected to fall – today its population stands at around 747 million; by 2100 this is projected to fall to 630 million.

These changes will bring new opportunities and challenges. Extreme poverty, for example, is expected become increasingly concentrated in Africa in the decades which follow. 

 

India will soon overtake China to become the most populous country in the world

China has been the world’s most populous country for a long time: back in 1750, it had a population of 225 million, around 28% of the world population. By 2016, China had a population larger than 1.4 billion. But China is soon to be overtaken by India. In the chart below we see historic and projected population by country, spanning from 10,000 BCE through to 2100. The projections – made by the UN’s Population Division – suggest that by 2027, India will surpass China to become the world’s most populous country.

Projections are always associated with a degree of uncertainty and this means the crossing point could be a few years earlier or later. But even within this degree of uncertainty, it’s expected that India will become the most populous country within the next decade. Rapidly declining fertility rates – from an average of 6 children down to 2.4 children per woman – in India means its population growth has fallen significantly over the last few decades. This means that while it will be the most populous country for the rest of the century, it’s expected to reach ‘peak population’ in the late 2050s at around 1.7 billion before slowly falling in the second half of the century.

Global population growth has slowed down markedly since the peak in the 1960s. 

At the global level population growth is determined by the number of births and deaths. To understand the likely trajectory for population growth we need to examine how births and deaths are changing – and, one level deeper, what is happening to those factors which in turn affect them. Increasing life expectancy and falling child mortality in every country are of course increasing population numbers. The countervailing trend are falling fertility rates – the trend of couples having fewer children is what brought rapid population growth to an end in many countries already, and what will bring an end to rapid population growth globally.

In aggregate, births, deaths, and migration are driving population growth. There we are also discussing the demographic transition as the central concept that explains why rapid population growth is a temporary phenomenon.

Births and deaths

The world population has grown rapidly, particularly over the past century: in 1900 there were fewer than 2 billion people on the planet; today there are 7.8 billion. The change in the world population is determined by two metrics: the number of babies born, and the number of people dying.

How many are born each year?

The stacked area chart shows the number of births by world region from 1950 to 2015.

In 2019, there were approximately 140 million births – 43 million more than back in 1950. 

How many die each year?

In 2019 around 55 million people died. The world population therefore increased by 84 million in that year (that is an increase of 1.14%). 

As the number of deaths approaches the number of births global population growth will come to an end. How do we expect this to change in the coming decades? What does this mean for population growth?

Population projections show that the yearly number of births will remain at around 140 million per year over the coming decades. It is then expected to slowly decline in the second half of the century. As the world population ages, the annual number of deaths is expected to continue to increase in the coming decades until it reaches a similar annual number as global births towards the end of the century. As the number of births is expected to slowly fall and the number of deaths to rise the global population growth rate will continue to fall. This is when the world population will stop to increase in the future. This view compares the number of annual births to the number of deaths:

The visualisation below shows the total fertility rate – the number of children per woman – by the level of development and includes the UN projections through 2099. The global average fertility rate was 5 children per woman until the end of the 1960s and has halved since then. Until 1950, the fertility rate in the ‘more developed regions’ had already declined to less than 3 children per woman. Then, in the 1960s the fertility rate in the ‘less developed regions’ started to fall and another decade later the fertility rate in the ‘least developed regions’ followed this decline:

As health is rapidly improving around the world, life expectancy is also increasing rapidly:

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Population growth comes to an end when fertility rates decline. In the past mortality rates were so high, that they kept population growth in check. This is not the case in the 21st century. Even with COVID. Remarkably, population growth is high where child mortality is high. This correlation is surprising to many: child mortality in fact is inversely correlated with population growth.

Where child mortality is high the population grows fast. A major reason for this correlation is that the fertility rate is high where child mortality is high:

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Where the fertility rate is high population growth is high.

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The United Nations projects that global population will reach 9.7 billion people in 2050, and population growth almost coming to an end at 10.8 billion in 2100.

Should we believe these projections?

One way to gauge the credibility of UN projections for the future is to look back at its track record of predictions in the past. Every few years the United Nations publishes its latest population statistics, covering historical and current estimates, and future projections. Each release of these statistics is called a revision, and allocated the year of publication (e.g. 1990 Revision). The latest revision in 2017 was the UN’s 25th publication.

In this chart we see comparison of various UN Revisions of world population, dating back to the 1968 publication. Shown as the solid line is the latest 2017 Revision, which one can consider to be the ‘actual’ population size up to 2015. Here we see that although each revision provided different projections, most turned out to be relatively close. For example, it’s estimated that the global population in 1990 was 5.34 billion. Most projections were close to this value: even the earliest revision in 1968 projected a 1990 population of 5.44 billion.

In 2010, it’s estimated the global population was seven billion; previous projections were in the range of 6.8 to 7.2 billion. In 2015, the global population was estimated to be 7.4 billion; the 1990 Revision overestimated with a projection of 7.7 billion whilst the 1998 Revision underestimated at 7.2 billion. Similar results are true for UN projections even earlier than the 1970s. Kielman (2001) looked at how UN projections from 1950 to 1995 matched with the actual population figures. Projections as far back as 1950 were remarkably close to the later estimates.

There are of course many factors which will influence the rate of population growth in the coming decades. Projections become increasingly uncertain (and tend to converge most) the further into the future they go. This means we’d expect higher uncertainty in projections for 2100 than those for 2050. Future projections will continue to be refined over time. Nonetheless, the surprising accuracy of historical projections should give us confidence that although imperfect, UN population projections have usually turned out to be very close to the truth:

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The UN projections are called ‘assessments’ and a new update is published in their World Population Prospects series every two years. The different variants of population projections by the UN. Shown here is the increase of the world population since 1750 combined with the latest projections of the UN Population Division. The UN publishes several variants of their population projections:

  • The Medium Variant is the projection that the UN researchers see as the most likely scenario. This is the source of the majority of projections shown here.
  • The High- and Low-Variants are based on the Medium Variant and simply assume that the total fertility rates in each country are 0.5 higher and 0.5 lower than the Medium variant by the end of this century in every country.
  • The Constant Fertility Scenario is an illustrative scenario that plays out how the world population would change if fertility rates remained constant. It is obviously not intended to be a realistic scenario.

But there are also a number of other institutions that are preparing their own projections of the world population. Global population projections are also published by the US Census, the Population Reference Bureau (PRB), and by the closely related Austrian research centres IIASA and the Wittgenstein Centre. The World Bank also published projections for some time but has stopped doing so in the mid-90s.

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The WC-IIASA projections

There are a range of projections for future population growth. These differ based on two key factors: the change in fertility rate and life expectancy over time. All future projections of global population are uncertain. Much of the uncertainty comes from the fact that we do not know how the drivers of population growth will change. The key driver of population change in the 21st century is not mortality, but fertility, as we have seen earlier. And fertility rates are determined by a number of factors that change rapidly with development. If the world develops faster we can expect a smaller world population. Investments the world will make in those systems that determine mortality and fertility – most importantly in education. The WC-IIASA projections are a set of influential projections, published by IIASA and the Wittgenstein Centre, and are helpful to gauge how much smaller the world population will be if the world develops faster.

Their key difference to the UN projections are that they are scenarios – they tell us what happens tomorrow depending on what we do today. But there are other differences too.

Differences between the UN and WC-IIASA projections

The WC-IIASA projections differ from the work of the United Nations in a number of fundamental ways. The UN projections are taking into account the empirical data on each country’s demography and are building projections based on this quantitative information. In contrast to this the WC-IIASA projections are also taking into account the qualitative assessments of 550 demographers from around the world which the WC-IIASA researchers have surveyed to gather their ideas on how the population change in different parts of the world will play out. They then combine the country specific expertise of these researchers with similar quantitative information that the UN and others rely on as well. The work by WC-IIASA is highly respected among demographers and key publications by the researchers are regularly published in Nature which obviously I’d like.

The WC-IIASA projections are taking into account the demographic structure of the educational attainment of the population. While other projections are only structuring the demographic data by sex and age-group, the WC-IIASA data is additionally breaking down the population data by the level of highest educational attainment of different parts of the population. This information on educational attainment is then used for both the output of the model – so that population projections for each country of the world by highest educational attainment are available (also seen in Our World in Data). And crucially the information on education is also used as an input into the model, so that the impact of different future scenarios for education on both mortality and fertility can be modelled explicitly.

The level of highest educational attainment is categorised in a system that aims to capture the structure of populations across the different country-specific educational systems. These categorisations are based on the the International Standard Classification of Education (ISCED), which was designed by the UNESCO to make education statistics comparable across countries. WC-IIASA breaks down the educational structure into the following 6 categories and the table summarizes how the six categories are defined, how they correspond to ISCED 1997, and the main allocation rules the researchers used. For children younger than 15 years old no educational attainment information is available as most of them are still in the process of education.

Categories of educational attainment used by IIASA-WC and how they correspond to the ISCED levels:

Edu attainment iiasa wc

The four scenarios for global education by WC-IIASA

Projections of the global population take into account how the fertility rate will change in each country over the coming decades. The WC-IIASA projections are particularly helpful for the discussion here as they are the only projections that break down the demographic projections by the educational level of the populations and then model how different educational scenarios would affect the fertility rate in countries across the world. This then allows comparisons of how education matters for the size and distribution of the future population of the planet.

The researchers developed 4 different basic scenarios and a larger number of combinations based on these scenarios:

Constant Enrollment Numbers (CEN): This is the researcher’s most pessimistic scenario. Here it is assumed that no more schools are being opened in any place in the world so that the absolute number of people reaching a particular educational level is frozen at the current number. This means that enrolment rates are declining when the population size increases. In practice the WC-IIASA researchers almost always consider CER as the most pessimistic scenario and only rarely discuss CEN.

Constant Enrollment Rates (CER): This is another pessimistic scenario. While in the CEN scenario the absolute number of enrolled students stagnates, the assumption in the CER scenario is that the rate of enrollment stagnates. In this scenario the most recently observed rates of educational enrollment are frozen at their current rate and no further improvement in enrollment is assumed.
This will still result in further improvements of adult education because in many countries the younger cohorts are better educated than the older ones. But in the longer run this scenario also implies stagnation.

Fast Track (FT): This scenario is the most optimistic one and here it is assumed that countries follow the most rapid education expansion achieved in recent history which is that of South Korea.

Global Education Trend (GET): This is the middle scenario and here the researchers assume that countries will follow the average path of educational expansion that other countries already further advanced in this process have experienced. In this scenario the researchers project the medium future trajectory based on the experience of all countries over the past 40 years. The researchers write: “The GET scenario is moderately optimistic, and can be considered as the most likely.”

The size and structure of the world population under different educational scenarios

Now we can see how the size of the total world population and the educational achievements of this population will evolve under these four scenarios. In this visualisation below one see that how fast education will become available in the short term will matter very substantially for the size of the world population in the longer-term – even for the evolution of world population over the next 5 decades. By 2060 the world population is projected to reach 9.8 billion under the Constant Enrolment Rates (CER) scenario, which is pessimistic about improvements in global education. If one assumes optimistic progress in global education, as in the Fast Track (FT) scenario, then global population is projected to increase to only 8.9 billion. A difference of almost one billion – as early as 2060 – may therefore be solely driven by differences in progress on global education.

This finding – alternative education scenarios alone make a difference of one billion for the global population over such a short time-frame – is discussed in Science so this makes all the top journals.

While the differences between the educational scenarios are slow to materialise and only show up after some decades, they are then very substantial and matter hugely for the size of the future world population. Whether or not the world is making fast progress in making education available to more children faster will matter for the size of the global population in just a few decades:

 

World population projections by education scenarios iiasa wc

Global demand for education: the population of school-age children

And the size of the cohort of school children in turn, will of course matter how easy or hard it is to make education available for all. Let’s see how different possible scenarios in educational improvements matter for ‘peak child’ and the size of the population in school age. For this one can only rely on scenarios of the WC-IIASA researchers which differ only in the assumptions on educational attainment. The visualisation below shows the three projections of the size of the population of school-age-children until the end of this century.

According to the projection of the pessimistic Constant Enrolment Scenario the population younger than 15 will evolve similarly to the Medium Variant projection of the UN: the number of children will continue to increase slowly and reach a plateau in the mid-21st century before the population will decline to a size similar to today’s population of under-15-year-olds.

The medium projection of WC-IIASA – the projections they see as most likely – substantially differs from the UN’s Medium projection: In the most likely scenario – Global Education Trends (GET), which the WC-IIASA researchers see as a continuation of the recent educational trends – the size of the population younger than 15 will soon start to fall and at the end of the century the population of under-15-year-olds will be one-third smaller than today! According to this middle-of-the-road scenario by WC-IIASA the world is very close to ‘child peak’.

Even faster will be the decline in the Fast Track scenario. If the world can achieve such a rapid expansion of education, then the size of the population of under-15-year-olds is projected to fall and decline to just one billion in 2100 (almost the same level as 1950).

What this comparison of scenarios shows us is that the size of the global population younger than 15 – the upper bound for the global demand for education – will very much depend on how rapidly access to education can be extended.

A larger increase in the educational attainment in the short-run will mean that the size of cohorts that need investments in the long-run will be much smaller: The difference between no further improvements in the educational enrolment (CER scenario) and a continuation of the successful last decades will mean that the global population of under-15-year-olds will be half a billion smaller at the end of the century. An acceleration to the Fast Track (FT) scenario would mean that this global figure is again smaller by yet another 200 million children. Here you go:

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Projections of the total population – UN vs IIASA-WC

Thus far we have looked at the total figures for the global population. What we have not yet taken into account is how the size of the population will evolve in different regions and countries of the world. The Medium Variant of the UN projections for all world regions until the end of this century is shown in this chart. Changes to the population size of the Americas, Oceania, and Europe are very small compared to the large expected changes in Asia and Africa. The UN expects the population of Africa to increase 3.3-fold – from 1.3 billion in 2021 to 4.28 billion by the end of the century. The population of Africa then will be as large as the population of Asia today, and the rate of this increase in the coming decades will also be very similar to the rate of population growth in Asia over the last few decades (Asia’s population increased from 1.4 billion in 1950 to 4.6 billion today). For Asia, the UN projects an increase only until the mid-21st century when population is projected to plateau around 5.3 billion. In the second half of the 21st century, the demographers foresee a decline of the Asian population to less than 5 billion by 2100. This visualisation shows in contrast the projections of the WC-IIASA researchers. Again the projected changes in the Americas, Oceania, and Europe are modest compared to changes in Africa and Asia:

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For Asia, this medium scenario by WC-IIASA projects an evolution that is very similar to the UN projection: The population will increase until the mid-21st century when the population plateaus (on a slightly lower level than in the UN projections) and then falls to well below 5 billion until the year 2100. The big difference is Africa: While the UN projects that the population of Africa will increase 3.5-fold, the WC-IIASA researchers expect only a doubling. The demographers expect the African population to stay well below 3 billion, with population growth almost coming to a halt at the end of this century.

The projections by education scenario can be seen here now:

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Fertility rate – UN vs IIASA-WC

As we have seen above, the crucial variable for how the world population will evolve is the total fertility rate: the number of children per woman. Let’s see how this crucial variable is projected to evolve.

There is some uncertainty about the level of the fertility rate today in some countries with poorer coverage of demographic statistics. This discrepancy in estimates today is also obvious in the comparison of the UN and WC-IIASA, where the UN mostly assumes that fertility rates today are higher than those assumed by WC-IIASA. For the development over the next century however the changes over time are more fundamental. So let’s see what the projections of the UN and WC-IIASA entail.

Fertility rate: UN

The UN series shows that until 1966 women around the world had more than 5 children on average. Since then the fertility rate has halved and is now just below 2.5 children per woman. The UN projects that the fertility rate will further decline to 2.1 in 2070 and by the end of the century the fertility rate will fall below 2. A global fertility rate of 1.93 then would imply a decline of the global population over the long run. In Africa the fertility rate only fell below 5 in 2005 – four decades later than the global average. For the 21st century the UN Medium Variant projects a slow decline of the fertility rate in Africa to 2.1 children per woman until the end of the century:


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Fertility rate: WC-IIASA

In their medium scenario – SSP2 with the GET assumptions on global education – the researchers project a much faster decline of the fertility rate than the UN. As early as the 2050s, the fertility rate will fall below 2 and by the end of the century will be 1.68 children per woman. Africa too will reach a fertility rate below 2 by the 2070s under the medium assumptions.

Interestingly the projections for the total fertility rate under the pessimistic Constant Enrolment Rates (CER) scenario are again very similar to the UN Medium projection. Under this scenario the WC-IIASA researchers project a global fertility rate just below 2 and a fertility rate for Africa just above 2. The pessimistic scenario of WC-IIASA is similar to the UN Medium projection, and all of the more optimistic WC-IIASA scenarios imply lower fertility rates. In these optimistic scenarios, the global population is therefore significantly smaller at the end of the century, with smaller cohorts of school-age children throughout this period.

In past decades UN demographers have been consistently too pessimistic in their projections of the global fertility rates I think as per this:

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Prof. Justin Stebbing

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