The human ecology of climate change - Climate Change: Biological and Human Aspects - page 375

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1950 1970 1990 2010 2030 2050 2070 2090

Year

Fig. 7.5 Thelast150yearsofthe3000yearsrepresentedinFigure7.4(a).ThisdetailstheEarth'spopulationoflate

20thcenturyto2010andalsoforecasts(inhigh,mediumandlowscenarios)thefutureupto2100(UN
PopulationDivisionoftheDepartmentofEconomicandSocialAfairs,2010).

from super-exponential growth to a more logistic rate of growth, when the population
stabilised.
Figure 7.4a helps explain a good part of the reason why human impact on the global
commons (the atmosphere and oceans) has been most marked in recent decades, rather
than in pre-industrial times.
From the perspective of the Ehrlich-Holdren equation, the post-Industrial Revolu-
tion escalation in human population and industrially born wealth has had a profound
effect on likely environmental impact. Indeed, future population growth and wealth
will be drivers of future greenhouse gas emissions.

7.1.3 Futurepopulation

The UN forecast for the future of the Earth's population is based on three scenarios:
high, medium and low. These are shown at the right-hand end of Figure 7.4a, which
covers 3000 years, but are seen more clearly when the Earth's population for the last
decades of the 20th century are plotted together with the UN forecast for the 21st
century from 2010 onwards (see Figure 7.5).
With increased individual wealth a range of factors come into play that affect likely
future population growth. These include increased control over personal reproduction
(with late 20th-century biomedicine), lower childhood mortality (so increasing future
parental security), increased aspirations for offspring and, from this last, increased
cost of raising offspring to realise such aspirations. Each of these factors serves to
lower the need and/or desirability for offspring and so lower the rate of population
growth. However, past population growth still impacts on the present and the future
because typically a birth in one decade will see a contribution to the population
for a number of decades (through the individual's lifespan and own reproductive
contribution).