Effects of population and affluence on CO2 emissions

Abstract

We developed a stochastic version of the Impact = Population x Affluence x Technology (IPAT) model to estimate the effects of population, affluence, and technology on national CO2 emissions. Our results suggest that, for population, there are diseconomies of scale for the largest nations that are not consistent with the assumption of direct proportionality (log-linear effects) common to most previous research. In contrast, the effects of affluence on CO2 emissions appear to reach a maximum at about $10,000 in per- capita gross domestic product and to decline at higher levels of affluence. These results confirm the general value of the IPAT model as a starting point for understanding the anthropogenic driving forces of global change and suggest that population and economic growth anticipated over the next decade will exacerbate greenhouse gas emissions.

Figure 1

Effects of population on CO₂ emissions. Solid line indicates the effect of population size relative to the geometric mean of population across nations (12.3 million). Population effects calculated at the geometric mean of gross domestic product ($1476). Data points are plotted using identification numbers from Table 1. Countries are plotted at the point corresponding to the expected population effect multiplied by the residual displayed in Table 1.

Figure 2

Effects of affluence on CO₂ emissions. Solid line indicates the effect of gross domestic product per capita relative to the geometric mean of gdp across nations ($1476). Affluence effects calculated at the geometric mean of population (12.3 million). Data points are plotted using identification numbers from Table 1. Countries are plotted at the point corresponding to the expected gdp effect multiplied by the residual displayed in Table 1.