Global Population Projections Research Articles

Research Note: Intergenerational Transmission Is Not Sufficient for Positive Long-Term Population Growth.

All leading long-term global population projections agree on continuing fertility decline, resulting in a rate of population size growth that will continue to decline toward zero and would eventually turn negative. However, scholarly and popular arguments have suggested that because fertility transmits intergenerationally (i.e., higher fertility parents tend to have higher fertility children) and is heterogeneous within a population, long-term population growth must eventually be positive, as high-fertility groups come to dominate the population. In this research note, we show that intergenerational transmission of fertility is not sufficient for positive long-term population growth, for empirical and theoretical reasons. First, because transmission is imperfect, the combination of transmission rates and fertility rates may be quantitatively insufficient for long-term population growth: higher fertility parents may nevertheless produce too few children who retain higher fertility preferences. Second, today even higher fertility subpopulations show declining fertility rates, which may eventually fall below replacement (and in some populations already are). Therefore, although different models of fertility transmission across generations reach different conclusions, depopulation is likely under any model if, in the future, even higher fertility subpopulations prefer and achieve below-replacement fertility. These results highlight the plausibility of long-term global depopulation and the importance of understanding the possible consequences of depopulation.

Spatiotemporal dynamics of global population and heat exposure (2020–2100): based on improved SSP-consistent population projections

To address future environmental change and consequent social vulnerability, a better understanding of future population (FPOP) dynamics is critical. In this regard, notable progress has been made in producing FPOP projections that are consistent with the Shared Socioeconomic Pathways (SSPs) at low resolutions for the globe and high resolutions for specific regions. Building on existing endeavors, here we contribute a new set of 1 km SSP-consistent global population projections (FPOP in short for the dataset) under a machine learning framework. Our approach incorporates a recently available SSP-consistent global built-up land dataset under the Coupled Model Intercomparison Project 6, with the aim to address the misestimation of future built-up land dynamics underlying existing datasets of future global population projections. We show that the overall accuracy of our FPOP outperforms five existing datasets at multiple scales and especially in densely-populated areas (e.g. cities and towns). Followingly, FPOP-based assessments of future global population dynamics suggest a similar trend by population density and a spatial Matthew effect of regional population centralization. Furthermore, FPOP-based estimates of global heat exposure are around 300 billion person-days in 2020 under four SSP-Representative Concentration Pathway (RCPs), which by 2100 could increase to as low as 516 billion person-days under SSP5-RCP4.5 and as high as 1626 billion person-days under SSP3-RCP8.5—with Asia and Africa contributing 64%–68% and 21%–25%, respectively. While our results shed lights on proactive policy interventions for addressing future global heat hazard, FPOP will enable future-oriented assessments of a wide range of environmental hazards, e.g. hurricanes, droughts, and flooding.

Opportunities for an African greenhouse gas observation system

Global population projections foresee the biggest increase to occur in Africa with most of the available uncultivated land to ensure food security remaining on the continent. Simultaneously, greenhouse gas emissions are expected to rise due to ongoing land use change, industrialisation, and transport amongst other reasons with Africa becoming a major emitter of greenhouse gases globally. However, distinct knowledge on greenhouse gas emissions sources and sinks as well as their variability remains largely unknown caused by its vast size and diversity and an according lack of observations across the continent. Thus, an environmental research infrastructure—as being setup in other regions—is more needed than ever. Here, we present the results of a design study that developed a blueprint for establishing such an environmental research infrastructure in Africa. The blueprint comprises an inventory of already existing observations, the spatial disaggregation of locations that will enable to reduce the uncertainty in climate forcing’s in Africa and globally as well as an overall estimated cost for such an endeavour of about 550 M€ over the next 30 years. We further highlight the importance of the development of an e-infrastructure, the necessity for capacity development and the inclusion of all stakeholders to ensure African ownership.

Agriculture leaders identify critical issues facing crop production

AbstractBased on global population projections, the need for sustainable food production is paramount and the work of crop and soil science industries is foundational to the health and vitality of the world's population now and to come. Expert knowledge can inform how to maintain healthy, effective, efficient, and profitable standards in an industry that is obligated to be sustained. The current study used the Delphi Technique and the constant comparative method to gain consensus from a panel of crop and soil sciences experts and practitioners about the most critical issues currently facing industries related to crop and soil sciences. Results highlighted eight main categories (alphabetically ordered) pertaining to: (1) chemical usage, (2) climate and environmental factors, (3) current and future workforce training, (4) economic sustainability, (5) public understanding of production practices, (6) research and collaboration, (7) seed and food quality control, and (8) soil health and water usage. Expert insight into these areas can offer necessary foresight as practitioners and researchers alike prepare for the future of the discipline. Implications of the findings are discussed and applied to the current state of the field.

The Future of International Migration: Developing Expert-Based Assumptions for Global Population Projections

The Future of International Migration: Developing Expert-Based Assumptions for Global Population Projections

Managing an Ageing Population: Challenging Oral Epidemiology.

Global population projections indicate that the proportion of older people is increasing and will continue to do so for the foreseeable future. Many countries are already experiencing the challenges of managing an ageing population, including increased pension contributions from workers, rises to national retirement ages, and spiralling healthcare costs. In oral health terms, in addition to simply an ageing population, epidemiological studies have demonstrated significant changes in the oral health of older adults in recent years. As the numbers of edentulous older adults has declined, there has been a significant increase in the number of partially dentate elderly. Changing attitudes, improved access to dental care and more effective preventative programmes have meant that large numbers of patients are now retaining natural teeth into old age. However, as older patients retain natural teeth for longer, the dental profession is charged with controlling chronic dental diseases in an increasingly challenging oral environment.

Fertility, mortality, migration, and population scenarios for 195 countries and territories from 2017 to 2100: a forecasting analysis for the Global Burden of Disease Study

SummaryBackgroundUnderstanding potential patterns in future population levels is crucial for anticipating and planning for changing age structures, resource and health-care needs, and environmental and economic landscapes. Future fertility patterns are a key input to estimation of future population size, but they are surrounded by substantial uncertainty and diverging methodologies of estimation and forecasting, leading to important differences in global population projections. Changing population size and age structure might have profound economic, social, and geopolitical impacts in many countries. In this study, we developed novel methods for forecasting mortality, fertility, migration, and population. We also assessed potential economic and geopolitical effects of future demographic shifts.MethodsWe modelled future population in reference and alternative scenarios as a function of fertility, migration, and mortality rates. We developed statistical models for completed cohort fertility at age 50 years (CCF50). Completed cohort fertility is much more stable over time than the period measure of the total fertility rate (TFR). We modelled CCF50 as a time-series random walk function of educational attainment and contraceptive met need. Age-specific fertility rates were modelled as a function of CCF50 and covariates. We modelled age-specific mortality to 2100 using underlying mortality, a risk factor scalar, and an autoregressive integrated moving average (ARIMA) model. Net migration was modelled as a function of the Socio-demographic Index, crude population growth rate, and deaths from war and natural disasters; and use of an ARIMA model. The model framework was used to develop a reference scenario and alternative scenarios based on the pace of change in educational attainment and contraceptive met need. We estimated the size of gross domestic product for each country and territory in the reference scenario. Forecast uncertainty intervals (UIs) incorporated uncertainty propagated from past data inputs, model estimation, and forecast data distributions.FindingsThe global TFR in the reference scenario was forecasted to be 1·66 (95% UI 1·33–2·08) in 2100. In the reference scenario, the global population was projected to peak in 2064 at 9·73 billion (8·84–10·9) people and decline to 8·79 billion (6·83–11·8) in 2100. The reference projections for the five largest countries in 2100 were India (1·09 billion [0·72–1·71], Nigeria (791 million [594–1056]), China (732 million [456–1499]), the USA (336 million [248–456]), and Pakistan (248 million [151–427]). Findings also suggest a shifting age structure in many parts of the world, with 2·37 billion (1·91–2·87) individuals older than 65 years and 1·70 billion (1·11–2·81) individuals younger than 20 years, forecasted globally in 2100. By 2050, 151 countries were forecasted to have a TFR lower than the replacement level (TFR <2·1), and 183 were forecasted to have a TFR lower than replacement by 2100. 23 countries in the reference scenario, including Japan, Thailand, and Spain, were forecasted to have population declines greater than 50% from 2017 to 2100; China's population was forecasted to decline by 48·0% (−6·1 to 68·4). China was forecasted to become the largest economy by 2035 but in the reference scenario, the USA was forecasted to once again become the largest economy in 2098. Our alternative scenarios suggest that meeting the Sustainable Development Goals targets for education and contraceptive met need would result in a global population of 6·29 billion (4·82–8·73) in 2100 and a population of 6·88 billion (5·27–9·51) when assuming 99th percentile rates of change in these drivers.InterpretationOur findings suggest that continued trends in female educational attainment and access to contraception will hasten declines in fertility and slow population growth. A sustained TFR lower than the replacement level in many countries, including China and India, would have economic, social, environmental, and geopolitical consequences. Policy options to adapt to continued low fertility, while sustaining and enhancing female reproductive health, will be crucial in the years to come.FundingBill & Melinda Gates Foundation.

The potential impacts of 21st century climatic and population changes on human exposure to the virus vector mosquito Aedes aegypti.

The mosquito Aedes (Ae). aegypti transmits the viruses that cause dengue and chikungunya, two globally-important vector-borne diseases. We investigate how choosing alternate emissions and/or socioeconomic pathways may modulate future human exposure to Ae. aegypti. Occurrence patterns for Ae. aegypti for 2061-2080 are mapped globally using empirically downscaled air temperature and precipitation projections from the Community Earth System Model, for the Representative Concentration Pathway (RCP) 4.5 and 8.5 scenarios. Population growth is quantified using gridded global population projections consistent with two Shared Socioeconomic Pathways (SSPs), SSP3 and SSP5. Change scenarios are compared to a 1950-2000 reference period. A global land area of 56.9 M km2 is climatically suitable for Ae. aegypti during the reference period, and is projected to increase by 8% (RCP4.5) to 13% (RCP8.5) by 2061-2080. The annual average number of people exposed globally to Ae. aegypti for the reference period is 3794 M, a value projected to statistically significantly increase by 298-460 M (8-12%) by 2061-2080 if only climate change is considered, and by 4805-5084 M (127-134%) for SSP3 and 2232-2483 M (59-65%) for SSP5 considering both climate and population change (lower and upper values of each range represent RCP4.5 and RCP8.5 respectively). Thus, taking the lower-emissions RCP4.5 pathway instead of RCP8.5 may mitigate future human exposure to Ae. aegypti globally, but the effect of population growth on exposure will likely be larger. Regionally, Australia, Europe and North America are projected to have the largest percentage increases in human exposure to Ae. aegypti considering only climate change.

Re-Examining the Fertility Assumptions for Pacific Asia in the UN's 2010 World Population Prospects

Pacific Asia is currently home to some of the lowest fertility rates – and hence the fastest aging populations – in the world. This Barnett Paper presents a systematic overview of both the reasons for this low fertility, and why it is unlikely to increase markedly in the near future. As well as a comprehensive review of scholarly opinion, the paper examines the uniquely low fertility ideals in the region; the results of a global survey of population experts on the future of Asian fertility; the assumptions of local statistical offices and the theoretical background of ‘feedback’ effects. Furthermore, the paper includes an extended discussion on the prospects for immediate fertility increase in China. This Barnett Paper systematically challenges the assumptions presented by the United Nations in their most recent global population projections which are based upon statistical models, suggesting that any assumption of fertility increase is profoundly Eurocentric and ignores the unique demographic experience of Pacific Asia over the past four decades. As such, the theoretical contribution of the text is to challenge the universality of a two-child norm as an endpoint to fertility transition. This is then considered in the context of other countries in South and South-East Asia who are in the midst of rapid fertility decline. The main policy conclusion of the paper, meanwhile, is that any assumption of an immediate increase in fertility could be extremely counter-productive in terms of leading to complacency among policymakers. Indeed, the paper argues that radical family policy interventions as well as huge cultural shifts in work-life balance and gender roles will be the only way to challenge such low fertility.

Dimensions of global population projections: what do we know about future population trends and structures?

The total size of the world population is likely to increase from its current 7 billion to 8–10 billion by 2050. This uncertainty is because of unknown future fertility and mortality trends in different parts of the world. But the young age structure of the population and the fact that in much of Africa and Western Asia, fertility is still very high makes an increase by at least one more billion almost certain. Virtually, all the increase will happen in the developing world. For the second half of the century, population stabilization and the onset of a decline are likely. In addition to the future size of the population, its distribution by age, sex, level of educational attainment and place of residence are of specific importance for studying future food security. The paper provides a detailed discussion of different relevant dimensions in population projections and an evaluation of the methods and assumptions used in current global population projections and in particular those produced by the United Nations and by IIASA.

Uncertainties in the Composition of World Population in the Twenty‐First Century

Past interest in long‐range global population projections has been almost exclusively centered on future population size and, to some extent, on changes in the age structure. Uncertainties concerning future demographic dynamics are typically dealt with by preparing multiple projections, distinguished by differing fertility trajectories ranging from high to low. The usual assumption, that the constituting units of the global population— countries and regions—all follow the same variant projection (such as high or low), masks another potential uncertainty of future population dynamics: uncertainty in the composition of the global total by the relative sizes of its constituting units. Using a set of long‐range population projections covering the period 2000–2100, this note explores plausible ranges of this uncertainty with reference to six constituting units of the global population.

Approaches and Experiences in Projecting Mortality Patterns for the Oldest-Old

In 1998 the United Nations Population Division extended the age format of its estimates and projections of population dynamics for all countries and areas of the world from 80 years and above to 100 years and above. The paper is based on experiences made during the implementation of relevant mortality projection methodologies and their application in two rounds of global population projections. The paper first briefly addresses the need for the explicit inclusion of very old population segments into the regular UN estimates and projections. It is argued that since population aging is an important issue for both developed and developing countries, the need for more information regarding the elderly, and the oldest-old in particular, is significant. The paper then documents the methods that have been evaluated and implemented, namely, the relational mortality standard proposed by Himes, Preston, and Condran, the Coale-Kisker extrapolation method for extending empirical age patterns of mortality to very high ages, and the Carter-Lee projection method for projecting model patterns of mortality to very high levels of life expectancy at birth. The methods are critically reviewed, and possible improvements to the methods are discussed. The paper concludes with a discussion of different views regarding the future evolution of mortality at older ages, their regional variability, and the necessity to improve the coverage and quality of data collected in this area.

A Guide to Global Population Projections

Interdisciplinary studies that draw on long-term global population projections often make limited use of projection results due at least in part to the historically opaque nature of the projection process. The authors present a guide to such projections aimed at researchers and educators who would benefit from putting them to greater use. Drawing on new practices and new thinking on uncertainty methodology and the likely future courses of fertility and life expectancy the authors discuss who makes projections and how and the key assumptions upon which they are based. They also compare methodology and recent results from prominent institutions and provide a guide to other sources of demographic information pointers to projection results and an entry point to key literature in the field. (authors)

The World's Changing Human Capital Stock: Multi‐State Population Projections by Educational Attainment

This research note presents the first global population projections by educational attainment using methods of multi‐state population projection. The educational composition of the population by age and sex and educational fertility differentials are estimated for 13 world regions, and alternative scenarios are presented to the year 2030. One of these scenarios assumes constant educational transition rates and the other assumes that all regions reach Northern American levels of enrollment rates by 2030. The strong momentum or, as the case may be, inertia in the transformation of the educational composition of a population, seen in the results, arises because education is mostly acquired at a young age. The sex bias in the educational composition, especially evident in some developing countries, is unlikely to disappear soon. China has made remarkable progress in improving educational enrollment and as a consequence by 2030 is expected to have more educated people of working age than Europe and Northern America together.

Implications of Future Fertility Trends for Contraceptive Practice

If the estimated contraceptive prevalence and total fertility rates for 1984 are approximately correct then it is clear that a dramatic change in reproductive behavior has taken place in most of the developing world over the past 2 decades. Aggregate total fertility has dropped from 6.0 in the early 1960s to about 4.0 at present; contraceptive prevalence increased from 9 to 43% over the same period. East Asia experienced the most rapid change which was almost entirely due to an extrordinary decline in Chinas fertility transition. Latin America and most of South Asia have also made major progress into the fertility transition. Only in Sub-Saharan Africa is there no significant trend in reproductive behavior. The most recent long-range global and regional population projections made by the UN assume that fertility will decline in all major regions of the developing world. Reducing fertility further according to the trends incorporated in the UN medium projections will require that contraceptive prevalence in the developing world be increased from 43% at present to 68% in 2025. While this will hardly be a simple task the momentum built over the past 2 decades suggests that this is an obtainable goal. This future trajectory of prevalence implies very rapid growth in the numbers practising contraception from about 256 million at present to 736 million in 2025 because both the prevalence level and the number of married women of reproductive age are increasing. During this period (1984-2025) the largest increases in contraceptive prevalence will be required in Africa (12 to 59%) while East Asia needs only a 5% point increase. Corresponding prjections of the number of women practicing contraception by region are also presented. The contraceptive methods used are likely to continue to be the modern clinical ones such as sterilization the IUD pill and injectables. As a consequence a rapid expansion of family planning services provided by both the public and private sectors will be required over the next several decades. (summaries in ENG FRE SPA)

A Review of the Population Sector in The Limits to Growth

A technical exposition and review is presented of the demographic sector of the computer model that was the basis of the book The Limits to Growth by Donella H. Meadows et al. The model summarizes in the form of over a hundred mathematical equations the basic causal relationships between the major variables believed to be 1) the determinents of growing industrialization 2) rapid population growth 3) widespread malnutrition 4) depletion of nonrenewable resources and 5) increasing environmental pollution. The author states that the significance of the present model probably lies not in the projections it makes but in the fact that it is the first attempt to construct a complete population model. All variables and causal relationships that the Meadows team considered important as determinants of population change are allowed to interact simultaneously in 1 model. The author makes certain recommendations. He suggests that the model would be more realistic if there was disaggregation to a regional or subregional level where population behavior is more homogeneous. The testing of the model should be extended possibly in smaller populations where extensive reliable data are available. An effort should be made to specify certain of the quantitative relationships especially the sensitive ones in more detail and with more data. The model would probably benefit from an expansion into subsubmodels in a number of places depending on what it is used for. The population model is recognized as a new and challenging attempt to come to grips with the complex dynamic and nonlinear nature of demographic processes but much work remains to be done if it is to be used for anything other than crude global population projections.