Botkin Environmental Science Earth as Living Planet 8th txtbk

74 CHAPTER 4 The Human Population and the Environment
0.86 kg/person (1.9 lb/person) in 1960, and cereal
crops at 342 kg/person (754.1 lb/person) in 1977. 24
Before these peaks were reached, per capita production
of each resource had grown rapidly.
Since the rise of the modern environmental movement
in the second half of the 20th century, much attention
has focused on estimating the human carrying
capacity of Earth—the total number of people that our
planet could support indefinitely. This estimation has
typically involved three methods. One method, which
we have already discussed, is to simply extrapolate from
past growth, assuming that the population will follow
an S-shaped logistic growth curve and gradually level off
(Figure 4.6).
The second method can be referred to as the packingproblem
approach. This method simply considers how
many people might be packed onto Earth, not taking into
sufficient account the need for land and oceans to provide
food, water, energy, construction materials, the need
to maintain biological diversity, and the human need for
scenic beauty. This approach, which could also be called
the standing-room-only approach, has led to very high estimates
of the total number of people that might occupy
Earth—as many as 50 billion.
More recently, a philosophical movement has
developed at the other extreme. Known as deep ecology,
this third method makes sustaining the biosphere the
primary moral imperative. Its proponents argue that the
whole Earth is necessary to sustain life, and therefore
everything else must be sacrificed to the goal of sustaining
the biosphere. People are considered active agents of
destruction of the biosphere, and therefore the total number
of people should be greatly reduced. 25 Estimates based
on this rationale for the desirable number of people vary
greatly, from a few million up.
Between the packing-problem approach and the
deep-ecology approach are a number of options. It is possible
to set goals in between these extremes, but each of
these goals is a value judgment, again reminding us of one
of this book’s themes: science and values. What constitutes
a desirable quality of life is a value judgment. The perception
of what is desirable will depend in part on what we
are used to, and this varies greatly. For example, in the
United States, New Jersey has only a half acre (0.22 ha)
per person, while Wyoming, the most sparsely populated
of the lower 48 states, has 116 acres (47.2 ha) per person.
For comparison, New York City’s Manhattan Island has
71,000 people per square mile, which works out to an area
of about 20 20 feet per person. Manhattanites manage
to live comfortably by using not just the land area but
also the airspace to a considerable height. Still, it’s clear
that people used to living in Wyoming and people living
in New Jersey or in Manhattan skyscrapers are likely to
have very different views on what is a desirable population
density.
Moreover, what quality of life is possible depends not
just on the amount of space available but also on technology,
which in turn is affected by science. Scientific
understanding also tells us what is required to meet each
quality-of-life level. The options vary. If all the people
of the world were to live at the same level as those of
the United States, with our high resource use, then the
carrying capacity would be comparatively low. If all the
people of the world were to live at the level of those in
Bangladesh, with all of its risks as well as its poverty and
its heavy drain on biological diversity and scenic beauty,
the carrying capacity would be much higher.
In summary, the acceptable carrying capacity is not
simply a scientific issue; it is an issue combining science
and values, within which science plays two roles. First,
by leading to new knowledge, which in turn leads to new
technology, it makes possible both a greater impact per
individual on Earth’s resources and a higher density of human
beings. Second, scientific methods can be used to
forecast a probable carrying capacity once a goal for the
average quality of life, in terms of human values, is chosen.
In this second use, science can tell us the implications
of our value judgments, but it cannot provide those value
judgments.
4.8 Can We Achieve Zero
Population Growth?
We have surveyed several aspects of population dynamics.
The underlying question is: Can we achieve -
—a condition in which the human population,
on average, neither increases nor decreases? Much of
environmental concern has focused on how to lower the
human birth rate and decrease our population growth. As
with any long-lived animal population, our species could
take several possible approaches to achieving zero population
growth. Here are a few.
Age of First Childbearing
The simplest and one of the most effective means of
slowing population growth is to delay the age of first
childbearing. 26 As more women enter the workforce
and as education levels and standards of living rise, this
delay occurs naturally. Social pressures that lead to deferred
marriage and childbearing can also be effective
(Figure 4.11).