1/1 - eCommons@Cornell - Cornell University
1/1 - eCommons@Cornell - Cornell University
1/1 - eCommons@Cornell - Cornell University
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a given species that can be supported<br />
indefinitely by the local environment.<br />
K is defined by limiting factors—limited<br />
amounts of space, limited<br />
amounts of food and water, competition<br />
from other species and other<br />
threats.<br />
You may remember the ominous<br />
graphic representation of carrying<br />
capacity from your introductory biology<br />
course (see illustration). The<br />
number of individuals erupts as the<br />
species exploits an area's supply of<br />
food and space, reproducing unchecked.<br />
As resources run out, the<br />
population first plateaus, then plummets<br />
sickeningly as individuals die,<br />
eventually stabilizing at a number<br />
just below the almighty K.<br />
Where does Pimentel put us on<br />
the graph of Earth's human population?<br />
"Right now, while we still have<br />
relatively abundant fossil fuel energy,<br />
I would say that we're getting near<br />
the inflection—the point where the<br />
sharp rise in population begins to<br />
flatten off."<br />
Sharp rise, indeed. Almost 5.6<br />
billion people now live on the planet.<br />
The population is projected to reach<br />
nearly 8.4 billion by the year 2025<br />
and 15 billion by 2100. Every day the<br />
total rises by a quarter-million. The<br />
relative abundance of young people<br />
in their reproductive prime gives the<br />
world population explosion surprising<br />
momentum. "Even if we adopt a<br />
zero population growth strategy tomorrow—a<br />
little over two children<br />
per couple—the world population<br />
will nearly double by 2060," explains<br />
Pimentel. "It wouldn't stop growing<br />
for about 60 years."<br />
According to the <strong>Cornell</strong> team,<br />
the primary limiting factors that define<br />
the Earth's carrying capacity for<br />
humans are fertile land, fresh water,<br />
fossil fuel energy and a diversity of<br />
helpful natural organisms. All are<br />
essential in the production of food,<br />
and worldwide stocks of all four are<br />
being consumed faster than they can<br />
be replaced.<br />
More than 25 million acres of<br />
arable and pasture land, the source<br />
of 98 percent of the world's food, are<br />
critically degraded and abandoned<br />
each year. An additional 12.5 million<br />
acres of new fertile land must be put<br />
into production to feed the 92 million<br />
new mouths added each year to<br />
RESEARCH<br />
the world population. One and a quarter<br />
acres of good crop land are needed<br />
to provide a diverse, nutritious diet<br />
of plant and animal products for one<br />
person. The current world average<br />
of crop land per capita is just over<br />
two-thirds of an acre.<br />
Fresh water supplies are being<br />
overdrawn from surface and groundwater<br />
sources. The primary consumer:<br />
agriculture, which absorbs,<br />
without possibility of recovery, 87<br />
percent of the fresh water used each<br />
year in the world. "It takes 1,400<br />
pounds of water to produce one<br />
pound of food," says Pimentel.<br />
Fossil energy from oil, gas and<br />
coal may be the first limiting resource<br />
to disappear. Essential for industrial<br />
production, fuel, construction, heating<br />
and cooling, packaging, delivery<br />
of clean water and fertilizer manufacture—about<br />
319 quads (that's<br />
10,000,000,000,000,000 BTUs in airconditionerese)<br />
of fossil fuel are used<br />
worldwide each year (one-fourth of<br />
which is burned in the United States).<br />
The <strong>Cornell</strong> team cites research<br />
suggesting that world supplies of oil<br />
and gas should last about 35 years at<br />
current pumping rates, coal and uranium<br />
stocks about 100 years.<br />
The easiest natural resource to<br />
overlook is provided by the living<br />
organisms that share the planet with<br />
us. "Humans have no technologies<br />
that can substitute for the services<br />
provided by wild biota," says<br />
Pimentel. "There are about half a<br />
million species of animals, plants, and<br />
microbes that provide essential functions<br />
for humans in the United<br />
States." Large-scale food production<br />
would be impossible without pollinators,<br />
decomposers, scavengers and<br />
waste recyclers. Biodiversity also<br />
ensures a future gene bank for<br />
tomorrow's forestry and agriculture.<br />
Researchers estimate that 150 species<br />
are lost daily due to human activity.<br />
(See "Biodiversity: What's in it<br />
for Us?" November 1993, <strong>Cornell</strong><br />
Magazine.,)<br />
In order to arrive at their optimum<br />
population figures, Pimentel<br />
and his colleagues make the optimistic<br />
assumption that humanity will<br />
make maximum use of Earth's finite<br />
resources. Even if humans make a<br />
transition to renewable energy<br />
sources, stop polluting and degrad-<br />
CORNELL MAGAZINE<br />
18<br />
ing their environment and accept a<br />
standard of living equal to one-half of<br />
that enjoyed by Americans today, the<br />
numbers stay the same.<br />
Getting there will be painful,<br />
Pimentel admits, but achievable.<br />
Population reduction will require a<br />
growing proportion of elderly to be<br />
supported by a shrinking number of<br />
younger, more productive humans.<br />
"It will create economic and social<br />
stress when we have to make these<br />
changes," he acknowledges. "But<br />
our alternative is far worse economic<br />
and social stress." If global human<br />
fertility can be reduced from the<br />
current rate of 3.3 children per female<br />
to 1 to 1.5 children per female,<br />
Pimentel estimates that the population<br />
can be reduced to carrying capacity<br />
in 100 to 150 years.<br />
Population control presents ethical<br />
problems. "You have to take your<br />
choice," explains Pimentel. "People<br />
say that they should have the freedom<br />
to reproduce. I'm sympathetic<br />
to that view. But you're going to either<br />
lose some of that freedom, or<br />
your children and your grandchildren<br />
will lose some of their freedoms—<br />
freedom from starvation, freedom<br />
from disease."<br />
Pimentel wonders about critics<br />
(rumored to include high-voltage media<br />
commentator Rush Limbaugh)<br />
who claim that technology will allow<br />
humanity to keep pace with a steep<br />
population curve. "Look at fishery<br />
production. We built bigger ships,<br />
larger nets, and now the fish populations<br />
of the oceans, lakes and rivers<br />
are lower than they've been since<br />
1970. Look at the Colorado River. As<br />
it flows south, California, Arizona,<br />
and Colorado take a big piece out of<br />
it to support their populations. By the<br />
time that river reaches Mexico, it's<br />
dry. What technology do we have<br />
available, short of manipulating the<br />
climate, that can double the flow of<br />
the Colorado River?"<br />
And how does Pimentel respond<br />
to those who say that the endless,<br />
painful cycle of population booms and<br />
busts is nature's way? "I think that<br />
we're too intelligent to let nature<br />
control our numbers," he says, ultimately<br />
the optimist. "I think that we<br />
can do a more effective job of limiting<br />
our numbers than nature can."<br />
—HillelJ. Hoffmann '85