Emissions Scenarios - IPCC

112 Scenario Driving Forces
productivity (per capita economic output) would balance
shortfalls from possible reductions in the labor force (Disney,
1996) . However, lowered fertility and mortality rates will also
cause the elderly dependency ratio to increase, which might
lead to a trend of lower savings, characteristic of elderly
cohorts, which have a reduced incentive to save. In terms of
public savings, without institutional reforms aging could
eventually lead to severe strains on social security and health
care programs supported by governments and thus to reduced
goventmental savings (US Council of Economic Advisors,
1997) .
Interestingly, a case has been made that aging may have
significant impacts on future CO2 emissions. The suggested
mechanism for this relates to household formation rate
(MacKellar et al., 1995). An aging population has a greater
proportion of people in older age groups. Assuming agespecific
household foimation rates remain constant over time,
as more people enter the older age cohorts the overall
household formation rates will increase. This increase will be
accompanied by a decline in the number of people per
household (a process already observed in industrialized
countries) and is related to reduced fertility rates. As small
households consume significantly more energy per person than
large households (Ironmonger et al., 1995), the various effects
suggest COj emissions will increase with increased aging
(MacKellar et al., 1995). Important uncertainties of this effect
remain, not least because household formation rates of aging
populations are not well understood.
3.2.4.2. Urbanization
Urbanization is also a strongly anticipated demographic trend.
Since 1970, most urban growth has taken place in developing
countries. It is caused by both intemal increases of the existing
urban population and rural-to-urban migration (UN, 1997b).
Urbanization, though, is not a rigorously modeled phenomenon
within the projections. Essentially, future urban and rural
growth and decline rates are simply assumed and applied to the
projected population levels. Thus, the projections contain no
explicit feedback mechanism from urbanization to population
growth, even though urbanization is an important factor in
fertility rate changes (urban populations generally have lower
fertility rates than rural populations). Instead, urbanization
rates are considered implicitiy within the projections of future
fertility. It is estimated that by 2010 more than half of the
world's population will live in urban areas (UN, 1996).
Urbanization will lead to a rapid expansion of infrastructure
and especially transportation uses (Wexler, 1996). In addition,
urban households in developing countries use significantiy
more fossil fuels, as opposed to biofuels, than do rural
households. However, the choice of fuel is predominantly an
income effect rather than a function of locale (see Murthy et
ai, 1997), even within urban settings. Hence, urbanization
exerts its influence on emissions primarily via higher urban
incomes compared to rural ones. Generally, opportunities for
higher income are considered an important driver of rural-tourban
migration, and so contribute to rising urbanization rates
(HABITAT, 1996). Urbanization is obviously an important
factor for future GHG emissions.
3.2.5. Relationships
3.2.5.1. Introduction
Within the caveats in Section 3.1, a number of demographic
studies show that population change does exert a strong firstorder
scaling effect on CO^ emissions models (O'Neill, 1996;
Gaffin and O'Neill, 1997; O'Neill et al., 2000; Wexler, 1996).
These studies support the notion that population growth and
the policies that affect it are key factors for future emissions.
Balanced against this, however, are other studies that take a
more skeptical view (Kolsrud and Torrey, 1992; Birdsall, 1994;
Preston, 1996). A full review of model results that address this
question is given in O'Neill (1996) and Gaffin and O'Neill
(1997) and is not be reproduced here because of space
limitations (for a review see Gaffin, 1998). In essence, the
controversy is one of the relationships between population
growth and economic development, as well as other salient
factors that influence emissions. These relationships were first
discussed within the context of IPCC emissions scenarios by
Alcamo et al. (1995) and are discussed in more detail in the
following sections.
3.2.5.2. The Effect of Economic Growth on Population
Growth
Figure 3-7 shows the long-established negative coirelation
between fertility rates and per capita income. Clearly, richer
countries uniformly have a relatively low fertility rate. Poorer
countries, on average, have a higher fertility rate. Lower
fertility, however, does exist in some poor countries or regions,
which illustrates the importance of social and institutional
structures.
Barro (1997) reports a statistically significant cortelation
between per capita GDP growth and the variables life
expectancy and fertility in his analysis of post-1960 growth
performance of 100 countries. Other things being equal,
growth rates correlate positively (higher) with increasing life
expectancy and negatively (lower) widi high fertility, which
confiims the view that the affluent live longer and have fewer
children.
Figure 3-7, a snapshot of many counûies passing through the
"demographic fertility transition" can be explained from both
economic and socio-demographic points of view (Easterlin,
1978). Economically, Figure 3-7 can be interpreted as a
reflection of the substitution that families make - away from
having children and toward consuming more goods and
services. With greater wealth, both goods and services become
increasingly available as part of the families' "basket of
choices" for consumption and, accordingly, they shift away