Environmental Engineering Reference
In-Depth Information
natural capital as well as interest, that is, we are not living sustainably. We
have exceeded the new carrying capacity.
Humans' impact on the biosphere is more than a function of mere num-
bers. Over three decades ago, Paul Ehrlich and John Holdren introduced the
I=PAT formula (Ehrlich & Holdren 1974). The environmental impact of a
population (I) is the product of the size of the population (P), its affluence
(A - a measure of consumption) and the technology required (T) to bring
material goods to the population. Because T is difficult to quantify, a simpler
way to consider total impact is that it is equivalent to the product of average
individual impact and the number of people in a population. So even if per
capita impact stayed the same, a doubling of the population would double
the total impact. While this formula is from an environmental perspective, it
also has implications for social scientists and economists. For instance,
assuming standards of living stay about the same, a doubling of the popula-
tion will require a doubling of infrastructure and services. Those genuinely
concerned about sustainability cannot ignore this multiplier effect.
We now discuss the other issues addressed in this topic and how popula-
tion affects them.
Water
A sustainable and secure society is one that meets its water needs without
destroying the ecosystems upon which it depends or the prospects of gener-
ations to come (Postel & Vickers 2004). Freshwater is, unfortunately, distrib-
uted unevenly between and within countries and many nations are already
water-stressed, that is, unable to meet their water needs in a sustainable way.
While over a billion people do not have ready access to potable water, this
figure may rise to as much as five billion in 25 years because of both global
warming and population growth. This is likely to trigger conflict across Asia
and Africa (McGuire 2002).
In Australia, tensions already exist between States over the waters of the
Murray-Darling Basin. Though (as Peter Cullen notes in Chapter 6), most
States have moved beyond simplistic water planning that focuses only on
extracting water for irrigation. They now understand that rivers must have
water left in them for ecological purposes. Extractions from the Murray-
Darling Basin were capped at 1994 levels in an effort to arrest the severe dete-
rioration in the river's health. But the cap was set too high, for even returning
a further 1500 GL to the river annually gives only a moderate chance of a
