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 energyeconomic 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.climate change | energy | integrated assessment | population | households S tatistical analyses of historical data suggest that population growth has been one driver of emissions growth over the past several decades (1-3) and that urbanization (2), aging (3), and changes in household size (2) can also affect energy use and emissions. Demographers expect major changes in these dimensions of populations over the coming decades (4). Global population could grow by more than 3 billion by mid-century, with most of that difference accounted for by growing urban populations. Aging will occur in most regions, a result of declines in both fertility and mortality, and is expected to be particularly rapid in regions like China that have recently experienced sharp falls in fertility. The number of people per household is also declining as populations age and living arrangements shift away from multigeneration households toward nuclear families.Despite these expectations, explicit analysis of the effect of demographic change on future emissions has been extremely limited (5). Early exploratory analyses considered only population size or total numbers of households (6, 7) and used simple multiplicative models (8) that did not account for important relationships between population and economic and technological factors. Furthermore, these early models used little or no regional disaggregation, an important consideration given that, with some exceptions including the United States, population growth tends to be highest where per capita emissions are lowest.More recently, a large emissions scenario literature (9) has developed that informs a wide range of climate change analysis and related policy discussions. Model sophistication and scope has increased substantially over time. Scenarios typically span timescales of decades to centuries, include emissions of multiple gases and aerosols from a range of sectors, including land use, and consider a wide range of emissions drivers (10-12). They have been used to study possible emissions in the absence of mitigation policy as well as the costs and other consequences of emissions reduction strategies. Although nearly all scenarios include assumptions about future population growth, none has explicitly investig...

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