Global demographic trends and future carbon emissions

Abstract

Substantial changes in population size, age structure, and urbanization are expected in many parts of the world this century. Although such changes can affect energy use and greenhouse gas emissions, emissions scenario analyses have either left them out or treated them in a fragmentary or overly simplified manner. We carry out a comprehensive assessment of the implications of demographic change for global emissions of carbon dioxide. Using an energy-economic growth model that accounts for a range of demographic dynamics, we show that slowing population growth could provide 16-29% of the emissions reductions suggested to be necessary by 2050 to avoid dangerous climate change. We also find that aging and urbanization can substantially influence emissions in particular world regions.

Fig. 1.

Labor income per capita across household age, relative to the national mean (A), and household expenditure shares on four categories of goods (B) in the initial year of the simulations. Results are shown for national data used to characterize model regions. In the PET model, labor income data are used in the specification of exogenous labor supply, and expenditure shares are used in the calibration of household consumption preference parameters (in both cases, for household types defined by age, size, and urban/rural residence; SI Text).

Fig. 2.

Projected global totals (solid lines) and regional differences (colored bands) for population size. Individual colored bands indicate the contribution of each region to the difference between global scenarios.

Fig. 3.

Effect of population compositional change on emissions for the world (A and B) and by region (C and D; B2 scenario, 2100) in both absolute and relative terms. Effects shown are from changes in composition by age of the household head (age), household size (size), urbanization (urban/rural), and all three combined (combined effect). Bars show effects in the reference scenario, and uncertainty intervals show the range across all population scenarios.

Fig. 4.

Projected global totals (lines) and regional differences (colored bands) for CO₂ emissions. Individual colored bands indicate the contribution of each region to the difference between global scenarios. Solid lines shows emissions in the baseline scenario, and dashed lines show emissions in variants with alternative demographic assumptions. Both types of scenarios include the effects of changes in population composition by household age, size, and urban/rural status. Economic and technological assumptions are based on the IPCC A2 (A) and B2 (B) scenarios.