Sergei Scherbov

The coming acceleration of global population ageing

The future paths of population ageing result from specific combinations of declining fertility and increasing life expectancies in different parts of the world. Here we measure the speed of population ageing by using conventional measures and new ones that take changes in longevity into account for the world as a whole and for 13 major regions. We report on future levels of indicators of ageing and the speed at which they change. We show how these depend on whether changes in life expectancy are taken into account. We also show that the speed of ageing is likely to increase over the coming decades and to decelerate in most regions by mid-century. All our measures indicate a continuous ageing of the world’s population throughout the century. The median age of the world’s population increases from 26.6 years in 2000 to 37.3 years in 2050 and then to 45.6 years in 2100, when it is not adjusted for longevity increase. When increases in life expectancy are taken into account, the adjusted median age rises from 26.6 in 2000 to 31.1 in 2050 and only to 32.9 in 2100, slightly less than what it was in the China region in 2005. There are large differences in the regional patterns of ageing. In North America, the median age adjusted for life expectancy change falls throughout almost the entire century, whereas the conventional median age increases significantly. Our assessment of trends in ageing is based on new probabilistic population forecasts. The probability that growth in the world’s population will end during this century is 88%, somewhat higher than previously assessed. After mid-century, lower rates of population growth are likely to coincide with slower rates of ageing.

The end of world population growth

There has been enormous concern about the consequences of human population growth for the environment and for social and economic development. But this growth is likely to come to an end in the foreseeable future. Improving on earlier methods of probabilistic forecasting, here we show that there is around an 85 per cent chance that the worlds population will stop growing before the end of the century. There is a 60 per cent probability that the worlds population will not exceed 10 billion people before 2100, and around a 15 per cent probability that the worlds population at the end of the century will be lower than it is today. For different regions, the date and size of the peak population will vary considerably.

Doubling of world population unlikely

Most national and international agencies producing population projections avoid addressing explicitly the issue of uncertainty. Typically, they provide either a single projection or a set of low, medium and high variants,, and only very rarely do they give these projections a probabilistic interpretation. Probabilistic population projections have been developed for specific industrialized countries, mostly the United States, and are based largely on time-series analysis. On a global level, time-series analysis is not applicable because there is a lack of appropriate data, and for conceptual reasons such as the structural discontinuity caused by the demographic transition. Here we report on a new probabilistic approach that makes use of expert opinion on trends in fertility, mortality and migration, and on the 90 per cent uncertainty range of those trends in different parts of the world. We have used simulation techniques to derive probability distributions of population sizes and age structures for 13 regions of the world up to the year 2100. Among other things, we find that there is a probability of two-thirds that the worlds population will not double in the twenty-first century.

The End of World Population Growth in the 21st Century: New Challenges for Human Capital Formation and Sustainable Development

The 20th century was the century of explosive population growth, resulting in unprecedented impacts; in contrast, the 21st century is likely to see the end of world population growth and become the century of population aging. We are currently at the crossroads of these demographic regimes. This book presents fresh evidence about our demographic future and provides a new framework for understanding the underlying unity in this diversity. It is an invaluable resource for those concerned with the implications of population change in the 21st century.

Average remaining lifetimes can increase as human populations age

Increases in median ages, the most commonly used measure of population ageing, are rapid in todays wealthier countries, and population ageing is widely considered to be a significant challenge to the well-being of citizens there. Conventional measures of age count years since birth; however, as lives lengthen, we need to think of age also in terms of years left until death or in proportion to the expanding lifespan. Here we propose a new measure of ageing: the median age of the population standardized for expected remaining years of life. We show, using historical data and forecasts for Germany, Japan and the United States, that although these populations will be growing older, as measured by their median ages, they will probably experience periods in which they grow younger, as measured by their standardized median ages. Furthermore, we provide forecasts for these countries of the old-age dependency ratio rescaled for increases in life expectancy at birth. These ratios are forecasted to change much less than their unscaled counterparts, and also exhibit periods when the population is effectively growing younger.

Demography. Remeasuring aging.

Adjusting aging forecasts to incorporate increases in longevity and health can provide better tools for policy-makers. Population aging is an international concern, in part because of consequences of coming age-structure changes, e.g., growth in the number of elderly, decline in the number of youth, and accompanying economic and social costs (1–4). These expectations are based on conventional measures of aging that link expected phenotypes to fixed chronological ages. But as life expectancies increase and people remain healthy longer, measures based solely on fixed chronological ages can be misleading. Recently, we published aging forecasts for all countries based on new measures that account for changes in longevity (5–8). Here, we add new forecasts based on disability status. Both types of forecasts exhibit a slower pace of aging compared with the conventional ones.

Expert-based probabilistic population projections

Most users of population projections are interested in one likely path of future population trends based on the best existing knowledge. Whether it is called the medium variant, central scenario, or median of an uncertainty distribution, this projected path will be taken as a forecast on which further considerations can be based. For many users such a best guess will suffice. It can be taken as an exogenous input into their own models for school planning, social security considerations, energy outlook, and the like. For this reason a medium projection is an indispensable component of any set of published projections intended for practical use.

An expert-based framework for probabilistic national population projections: the example of Austria.

The traditional way of dealing with uncertainty in population projections through high and low variants is unsatisfactory because it remains unclear what range of uncertainty these alternative paths are assumed to cover. But probabilistic approaches have not yet found their way into official population projections. This paper proposes an expert-based probabilistic approach that seems to meet important criteria for successful application to national and international projections: 1) it provides significant advantages to current practice, 2) it presents an evolution of current practice rather than a discontinuity, 3) it is scientifically sound, and 4) it is applicable to all countries.In a recent Nature article (Lutz et al., 1997) this method was applied to 13 world regions. This paper discusses the applicability to national projections by directly taking the alternative assumptions defined by the Austrian Statistical Office. Sensitivity analyses that resolve some methodological questions about the approach are also presented.

Marriage and Fertility in Russia of Women Born between 1900 and 1960: A Cohort Analysis

In this paper we present a demographic analysisof the marital and fertility careers of Russianwomen, born between 1900 and 1960 and based onindividual retrospective life histories,collected in the most recent (five percent)microcensus of the Russian Federation from1994. It extends an earlier analysis of womenborn between 1910 and 1935. Although politicalevents often had profound effects on themarital life course, none of the observedcrises in Russia has succeeded in exerting adecisive influence on the fertility transition.The fertility decline started late, but takinginto account infant and child mortality thatcontinued to be very high until the fifties,all generations born since 1920 had a completedfertility near or below replacementlevel.

Measuring the Speed of Aging across Population Subgroups

People in different subgroups age at different rates. Surveys containing biomarkers can be used to assess these subgroup differences. We illustrate this using hand-grip strength to produce an easily interpretable, physical-based measure that allows us to compare characteristic-based ages across educational subgroups in the United States. Hand-grip strength has been shown to be a good predictor of future mortality and morbidity, and therefore a useful indicator of population aging. Data from the Health and Retirement Survey (HRS) were used. Two education subgroups were distinguished, those with less than a high school diploma and those with more education. Regressions on hand-grip strength were run for each sex and race using age and education, their interactions and other covariates as independent variables. Ages of identical mean hand-grip strength across education groups were compared for people in the age range 60 to 80. The hand-grip strength of 65 year old white males with less education was the equivalent to that of 69.6 (68.2, 70.9) year old white men with more education, indicating that the more educated men had aged more slowly. This is a constant characteristic age, as defined in the Sanderson and Scherbov article “The characteristics approach to the measurement of population aging” published 2013 in Population and Development Review. Sixty-five year old white females with less education had the same average hand-grip strength as 69.4 (68.2, 70.7) year old white women with more education. African-American women at ages 60 and 65 with more education also aged more slowly than their less educated counterparts. African American men with more education aged at about the same rate as those with less education. This paper expands the toolkit of those interested in population aging by showing how survey data can be used to measure the differential extent of aging across subpopulations.