Abstract

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.

Highlights

  • While future trends in the number and composition of humans on this planet has been a topic of scientific enquiry and discussion for centuries and at least since Thomas Malthus entered the field of structured quantitative analysis, the first modern global population projection, which explicitly considered the age and sex structure of the population, was carried out by Frank Notestein of the Princeton Office of Population Research in 1945 (Notestein 1945)

  • 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 Institute for Applied Systems Analysis (IIASA)

  • One of the purposes was to produce population projections as part of the Special Report on Emissions Scenarios (SRES) (Nakicenovic et al 2000) that underlie the global emission scenarios used by the Intergovernmental Panel for Climate Change (IPCC)

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Summary

INTRODUCTION

While future trends in the number and composition of humans on this planet has been a topic of scientific enquiry and discussion for centuries and at least since Thomas Malthus entered the field of structured quantitative analysis, the first modern global population projection, which explicitly considered the age and sex structure of the population (the so-called cohortcomponent method), was carried out by Frank Notestein of the Princeton Office of Population Research in 1945 (Notestein 1945). One of the purposes was to produce population projections as part of the Special Report on Emissions Scenarios (SRES) (Nakicenovic et al 2000) that underlie the global emission scenarios used by the Intergovernmental Panel for Climate Change (IPCC) This was followed by three rounds of probabilistic projections at the level of 13 regions (which were all published in the pages of Nature: Lutz et al 1997, 2001, 2008b). IIASA developed (in collaboration with Eurostat and the UK Office of National Statistics) a new approach for evaluating substantive arguments about alternative assumptions on possible future trends based on large numbers of questionnaires ascertaining the evaluation of alternative arguments by experts This is currently being translated (together with Oxford University) into a new set of science-based population projections for all countries in the world by age, sex and level of education for publication in 2012. We present the results for the specified regions and countries in tabular and graphical form

DIMENSIONS CONSIDERED IN POPULATION PROJECTIONS
TREATMENT OF UNCERTAINTY
THE PROSPECT OF WORLD POPULATION STABILIZATION OR DECLINE AFTER PEAK
PROPOSAL FOR USE OF POPULATION PROJECTIONS IN FOOD SECURITY ASSESSMENTS
DESCRIPTION OF RESULTS
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