大气中的恶棍：大学英语精读第2册第5单元课文及翻译

大气中的恶棍：大学英语精读第

2

册第

5

单元课文及翻译

Unit5

There is one gas present in the air we breathe that is essential to life. Unfortunately,

one can have too much of a good thing and the growth in carbon dioxide threatens to

warm up our planet to a dangerous extent. Isaac Asimov introduces us to this villain in

the atmosphere, explaining how it works and what can be done about it.

The Villain in the Atmosphere

The villain in the atmosphere is carbon dioxide.

It

does

not

seem

to

be

a

villain.

It

is

not

very

poisonous

and

it

is

present

in

the

atmosphere in so small a quantity — only 0.034 percent — that it does us no harm.

What’s more, that small quantity of carbon dioxide in the air is essential to life. Plants

absorb carbon dioxide and convert it into their own tissue, which serve as the basic

food supply for all of animal life (including human beings, of course). In the process

they liberate oxygen, which is also necessary for all animal life.

But here is what this apparently harmless and certainly essential gas is doing to

us:

The sea level is rising very slowly from year to year. In all likelihood, it will continue

to rise and do so at a greater rate in the course of the next hundred years. Where there

are low

-

lying coastal areas (where a large fraction of the world’s population lives) the

water will advance steadily, forcing people to retreat inland.

Eventually

the

sea

will

reach

two

hundred

feet

above

its

present

level,

and

will

be

splashing against the windows along the twentieth floors of Manhattan’s skyscrapers.

Florida

will

disappear

beneath

the

waves,

as

will

much

of

the

British

Isles,

the

crowded Nile valley, and the low

-

lying areas of China, India, and Russia.

Not only will many cities be drowned, but much of the most productive farming areas

of the world will be lost. As the food supply drops, starvation will be widespread and

the structure of society may collapse under the pressure.

And

all

because

of

carbon

dioxide.

But

how

does

that

come

about?

What

is

the

connection?

It

begins

with

sunlight,

to

which

the

various

gases

of

the

atmosphere

(including

carbon dioxide) are transparent. Sunlight, striking the top of the atmosphere, travels

right

through

miles

of

it

to

warm

the

Earth’s

surface.

At

night,

the

Earth

cools

by

radiating heat into space in the form of infrared radiation.

However,

the

atmosphere

is

not

quite

as

transparent

to

infrared

radiation

as

it

is

to

visible light. Carbon dioxide in particular tends to block such radiation. Less heat is

lost at night, for that reason, than would be lost if carbon dioxide were not present in

the

atmosphere.

Without

the

small

quantity

of

that

gas

present,

the

Earth

would

be

distinctly cooler, perhaps uncomfortably cool.

We

can

be

thankful

that

carbon

dioxide

is

keeping

us

comfortably

warm,

but

the

concentration

of

carbon

dioxide

in

the

atmosphere

is

going

up

steadily

and

that

is

where the villainy comes in. In 1958, carbon dioxide made up only 0.0316 percent of

the atmosphere. Each year since, the concentration has crept upward and it now stands

at 0.0340 percent. It is estimated that by 2020 the concentration will be nearly twice

what it is now.

This

means

that

in

the

coming

decades,

Earth’s

average

temperature

will

go

up

slightly. As a result, the polar ice caps will begin to melt.

Something like 90 percent of the ice in the world is to be found in the huge Antarctica

ice cap, and another 8 percent is in the Greenland ice cap. If these ice caps begin to

melt, the sea level will rise, with the result that I have already described.

But why is the concentration of carbon dioxide in the atmosphere steadily rising? To

blame

are

two

factors.

First

of

all,

in

the

last

few

centuries,

first

coal,

then

oil

and

natural

gas,

have

been

burned

for

energy

at

a

rapidly

increasing

rate.

The

carbon

contained in these fuels, which has been safely buried underground for many millions

of years, is now being burned to carbon dioxide and poured into the atmosphere at a

rate of many tons per day.

To make matters worse, Earth’s forests have been disappearing, slowly at first, but in

the last couple of centuries quite rapidly. Right now it is disappearing at the rate of

sixty

-

four acres per minute.

Whatever replaces the forest — grassland or farms or scrub — produces plants that do

not consume carbon dioxide at an equal rate. Thus, not only is more carbon dioxide