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In times of economic crisis and increasing food insecurity coupled with continued rapid population growth in the poor countries, as well as the prospect of dramatic consequences of climate change around the globe, the future looks rather bleak to many people. Hence the title of this editorial may sound oddly optimistic. But there is very good news hidden in the statistics of recent education trends around the world which imply significant future improvements in human capital and, as a consequence, likely improvements in global health and material well-being. In what follows I shall try to summarize what new statistical and demographic models applied to the long-term trends of population imply for our common future. Demographic trends can be forecast into the longer-term future with lower uncertainty than many other social and economic trends, but they are less predictable than most geobiophysical trends. The reason lies in the length of the human lifespan of currently around 70 years on the global average. If we know how many 10-year-old girls are alive today, we have a very good basis for projecting how many 60-year-old women will be alive 50 years from now. On the global level the only uncertainty lies in unexpected future changes in mortality. For national and regional projections, uncertainties about future migration matter. The same is true for projecting certain stable properties of people: knowing how many 30-year-old men have been to college today is a good basis for projecting how many 60-year-old men will have a college education in 2040. In doing so we also must consider the fact that generally more highly educated people have lower mortality rates. Whereas the ‘stocks’ are inert and rather easy to project, the projection uncertainties come from assumptions on the ‘flows’. For population projections it is the uncertainty about future trends in the birth rates that has the greatest effect on long-term population size. In the case of human capital projections, the future transition rates from lower to higher educational status are the main source of uncertainty. Fig. 1 shows the evolution of the world population for ages 15 years and above by level of educational attainment since 1970 and projected to 2050. It shows that the past decades have seen great progress in education. Whereas over the past 40 years the number of people without education or only primary education has remained roughly constant, those with secondary or higher education have increased almost fourfold. And, since throughout the world—and particularly in developing countries—the young have much higher levels of education than the old, further significant increases in the average education of the adult population is virtually preprogrammed. Even if school enrolment rates do not further increase, such improvements in average adult education would take place as a consequence of the past education expansion. But countries with high population growth will have to make very significant efforts not to see enrolment rates decline as increasingly larger cohorts enter school age. Recently, enrolment rates in some African countries have actually declined which, as the following discussion will show, is probably the worst thing that can happen to a country’s future. The world’s growing human capital: world population aged 15 years and above by level of educational attainment in 1970–2050, according to the mildly optimistic global education trend scenario (source, KC et al. (2008)) These data are based on new projections and reconstructions of populations by age, sex and four levels of educational attainment that were recently produced by using the demographic method of multistate populations (Lutz et al., 2007; KC et al., 2008), which is essentially based on Markov chain models with different fertility and mortality rates for people with different educational status. These new data on human capital since 1970 for 120 countries have also recently been used to resolve an old statistical puzzle concerning the importance of human capital for economic growth. Although at the individual level it has been established beyond any doubt that more years of schooling on average bring higher income, the analysis of country level panel data so far has not resulted in consistently positive and significant coefficients for human capital. This is due to the fact that they only considered the entire adult population aged 25 years and older as one age group and therefore rapid improvements in education of the young adult population—an important driver of economic growth—did not produce enough statistical signals in this very broad age group, which also includes elderly, poorly educated people. On the basis of the new data by 5-year age groups, Lutz, Crespo Cuaresma and Sanderson (2008) could conclusively show that indeed educational attainment is the key driver of economic growth. Moreover, their results indicate that universal primary education is not enough, and only when combined with broadly based secondary education will the poorest countries be able to come out of their poverty traps. Not surprisingly, the results also show that, for industrialized countries, tertiary education matters most. As to the positive implications of education on longevity and health, the literature has been less ambiguous and, almost universally, more highly educated people have better health and live longer. In Europe the differences in life expectancies at birth between the highest and lowest education groups are 5–10 years depending on the country. Hence, again, the good news is that the population with secondary and tertiary education is likely to double over the coming four decades (increasing by a factor of 7 compared with 1970) whereas a further doubling of world population is highly unlikely (Lutz et al., 1997). But education and population growth are not independent: the higher the education of women, the lower the fertility rate. These educational differentials, which are due to lower desired family size (a move from ‘quantity’ to ‘quality’) as well as better access to family planning, are particularly pronounced in countries in the early phases of demographic transition. In Ethiopia women without education have on average six children, whereas those with at least junior secondary education have only two. Hence, it is fair to say that progress in female education together with access to family planning services are the key determinants of future population growth in the less developed countries. Cohen (2008) has recently argued that universal secondary education should be a policy priority for many reasons but in particular for limiting world population growth to a more sustainable level. KC et al. (2008) have illustrated this numerically by showing that, when assuming otherwise identical education-specific fertility rates, the difference between the most optimistic and most pessimistic education scenarios for Africa is that of a population size of 1.8 billion compared with 2.4 billion by 2050. For the world as a whole, the difference due to education is about 1 billion by 2050. The further we go into the future, the greater will be the long-term effect of near-term education efforts. The very-long-term future of population size will also crucially depend on the future fertility levels at the low end of today’s distribution. Currently, already more than half of the world population is below the so-called replacement level of two surviving children per woman (Wilson, 2004) and what will be the future level of human reproduction is still a very poorly understood question. Whereas the UK, France and the Nordic European countries have quite stable fertility levels only slightly below replacement, central, eastern and southern Europe have much lower levels. And East Asia has what has recently been labelled ‘ultra low fertility’ with fertility levels often around half of replacement. New data for Shanghai (with 20 million representing a bigger population than Sweden, Norway and Finland together) show a total fertility rate of only 0.6. Even after adjusting for possible distortions caused by the postponement of childbearing (the ‘tempo’ effect) this (now voluntarily) very low level is still hardly above a third of replacement. Will the long-term future of global reproduction follow the pattern of Scandinavia or that of Shanghai? We simply do not know yet and this topic has not been given enough research attention. It deserves a serious interdisciplinary research effort because of its significant long-term consequences. Another important uncertainty is the future of life expectancy. The current discussion is dominated by the conflict between two opposing schools of thinking: one argues that we shall not see much further increase in maximum life expectancy, whereas the other paints a picture of ever increasing life expectancy virtually without limit. Faced with such uncertainties about the future of longevity and post-demographic transition fertility levels, statisticians in their projections can only try to provide fair numerical representations of these uncertainties and illustrate the consequences in terms of distributions of possible outcomes. Fig. 2 (on its left-hand side) depicts the uncertainty distribution resulting from the stochastic projections of world population as published by the International Institute for Applied Systems Analysis (Lutz, Sanderson and Scherbov, 2008). They show an 80% range for the world population in 2100 going from a low 6.2 to a high 11.1 billion with the median lying at 8.4. These projections also confirm earlier results that there is an 80–85% chance that the world population will peak and start to decline during this century (Lutz et al., 2001). Total world population in billions (for the scenario labels, see the text; source, Lutz and Scherbov (2008)): probabilistic projections until 2100 (, 90% interval; , 60% interval; ■, 20% interval) and extensions to 2200 The right-hand side of Fig. 2 shows selected scenarios that extend the time horizon to the end of the 22nd century (Lutz and Scherbov, 2008). In the International Institute for Applied Systems Analysis probabilistic long-range projections, uncertainty ranges for fertility and mortality were defined only until 2080, so the additional lines start in 2080 at different points of the distribution and keep fertility and mortality constant at the indicated levels. Unlike the United Nations world population projections to 2300 (United Nations, 2004) where a long-term fertility rate of 1.85 is the lowest fertility level considered, Lutz and Scherbov (2008) presented a much broader range of scenarios with long-run fertility ranging from 1.0 to 2.5 combined with life expectancy trends that either reach a maximum (LEMAX in Fig. 2) at 90 or 120 years. Whereas most of the scenarios start from the median of the distribution in 2080, others depart from the upper and lower ends of the 95% interval in that year. These scenarios into the 22nd century must be viewed as hypothetical ‘if–then’ calculations. We simply know too little about the long-term trends to judge which are more likely. But we can conclude from these calculations that a world of (3–4) billion—which is sometimes stated as a sustainable global population size by prominent ecologists—can be reached not only through a Malthusian ‘positive check’ operating through increased mortality but also in the benign way through voluntarily low fertility. If global fertility after 2080 stayed roughly constant at the level of 1.7, then the world population size would decline to (4.9–5.8) billion in 2200 (and (2.4–3.5) billion in 2300) depending on the life expectancy chosen. A fertility of 1.7 is higher than has been observed in Europe over the past decades (Lutz et al., 2003). If we choose the current average European fertility of 1.5 as the long-term level, then the world population would decline to (3.5–4.4) billion in 2200 (and (1.1–1.7) billion in 2300). These exploratory scenarios teach us that a substantial long-term decline in world population size is entirely feasible and can happen at the same time with significant further improvements in health and life expectancy. Although under such scenarios the world population would clearly continue to age (actually under a total fertility rate of 1.7 the speed of ageing would be relatively slow), the future elderly can be expected to have a much better health status than today’s elderly, in particular because they will be better educated than today’s elderly and, almost universally, better educated people have lower levels of disability at any given age. This, finally, brings us back to the overriding importance of education. A global fertility level of 1.5–1.7 in 2080 is only likely to materialize if the world population will be about as educated as Europe is today. Given the strong causal effect that education has on health and wealth, such a well-educated world population of (2–6) billion is very likely to be better off than the average world citizen today. And most ecologists would see fewer people as a highly welcome relief of environmental pressures, although what matters more is per capita consumption. As to the expected negative consequences of unavoidable climate change, it seems plausible to assume that, with a large world population, more people will suffer than in a lower population density world. And, again, education is probably the single most important determinant of empowerment for coping with and adapting to the dangerous consequences of climate change. Whether or not this benign transition to a much smaller, better educated and therefore healthier and wealthier world population in the 22nd century can be achieved will largely depend on actions that are taken over the coming decades. In a number of African countries educational improvements and with them declines in fertility rates have stalled and child mortality increased. Meanwhile, international development policies seem to be in disarray and without clear orientation. The considerations that are summarized in this short note suggest very clearly that continued efforts for universal primary and secondary education around the world should become the overriding priority in international development and climate change adaptation policies.
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