Environmental Engineering Reference
In-Depth Information
1
Environmental Problems,
Their Causes, and Sustainability
50 times, the folded paper would almost reach the
sun, 149 million kilometers (93 million miles) away!
Between 1950 and 2005, world population in-
creased from 2.5 billion to 6.5 billion. Unless death
rates rise sharply, somewhere between 8 billion and
10 billion people will live on the earth by the end of
this century (Figure 1-1).
We live in a world of haves and have-nots. Despite
an 8-fold increase in economic growth between 1950
and 2005,
almost one of every two workers in the world
tries to survive on an income of less than U.S.$2 per day.
Such poverty affects environmental quality because to
survive many of the poor must deplete and degrade
local forests, grasslands, soil, and wildlife.
Biologists estimate that human activities are caus-
ing premature extinction of the earth's species at an
exponential rate of 0.1% to 1% per year—an irre-
versible loss of the earth's great variety of life forms,
or
biodiversity.
In various parts of the world, forests,
grasslands, wetlands, coral reefs, and topsoil from
croplands continue to disappear or become degraded
as the human ecological footprint spreads exponen-
tially across the globe.
There is growing concern that exponential growth
in human activities such as burning fossil fuels and
clearing forests will change the earth's climate during
this century. This could ruin some areas for farming,
shift water supplies, alter and reduce biodiversity, and
disrupt economies in vari-
ous parts of the world.
Great news.
We have
solutions to these prob-
lems that we could imple-
ment within a few
decades, as you will learn
in this topic.
CASE STUDY
Living in an Exponential Age
Two ancient kings enjoyed playing chess, with the
winner claiming a prize from the loser. After one
match, the winning king asked the losing king to pay
him by placing one grain of wheat on the first square
of the chessboard, two grains on the second square,
four on the third, and so on, with the number dou-
bling on each square until all 64 were filled.
The losing king, thinking he was getting off easy,
agreed with delight. It was the biggest mistake he ever
made. He bankrupted his kingdom because the num-
ber of grains of wheat he had promised was probably
more than all the wheat that has ever been harvested!
This fictional story illustrates the concept of
exponential growth,
in which a quantity increases at
a constant rate per unit of time, such as 2% per year.
Exponential growth is deceptive. It starts off slowly,
but after only a few doublings, it grows to enormous
numbers because each doubling is more than the total
of all earlier growth.
Here is another example. Fold a piece of paper
in half to double its thickness. If you could continue
doubling the thickness of the paper 42 times, the stack
would reach from the earth to the moon, 386,400 kilo-
meters (240,000 miles) away. If you could double it
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11
10
9
?
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7
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Figure 1-1
The
J-
shaped curve
of past exponential world popu-
lation growth, with projections to
2100. Exponential growth starts
off slowly, but as time passes the
curve becomes increasingly
steep. Unless death rates rise,
the current world population of
6.5 billion people is projected to
reach 8-10 billion people some-
time this century. (This figure is
not to scale.) (Data from the
5
4
3
2
Black Death—the Plague
1
0
2-5 million
years
8000
6000
4000
2000
2000
2100
Time
B.C.
A.D.
