Environmental Engineering Reference
In-Depth Information
the way out than it was on the way in. This radiation is therefore trapped within the Earth's
'greenhouse' (see Figure 5.1 ) .
Figure 5.1. The greenhouse effect.
As a student, I discovered firsthand the basic principle behind the greenhouse effect. At
the end of a long Saturday night, my friend Garry and I were thirsty for more beer, but
all the bars in town had closed. As we approached my flat, we passed a large warehouse
yard belonging to a brewery. We paused before its unguarded gates and gazed inside, like
hungry sheep into a lush meadow. I turned to Garry with an impish smile and he quickly
guessed what I was thinking. He was a year older and his greater wisdom showed in his
remark: “Steve, we could break in, but could we break back out again?”
Without the “greenhouse effect” our planet would have an average surface temperature
of -18 degrees Celsius, instead of its actual +15 degrees. Water would exist, as on Mars,
only in the form of ice. Indeed, the only place on Earth where life could exist would
be surrounding thermal vents or geysers. Evolution of life, therefore, could not have
progressed beyond very simple forms, such as bacteria, algae, and small crustaceans.
So, why is it that the greenhouse effect is usually spoken of as a problem? This comes
from the fact that when most people speak about the greenhouse effect, what they really
mean is the artificial greenhouse effect. The greenhouse gases (GHGs) - carbon dioxide
(CO 2 ), methane (CH 4 ), nitrous oxide (N 2 O) and ozone - are not pollutants in and of
themselves; in fact, they are a natural part of the Earth's life cycle. Plants, for example, live
by converting carbon dioxide into chemical energy - glucose - through photosynthesis.
Indeed water, the elixir of life on Earth, is, in the form of vapour, the most potent of all
GHGs.
Because of human activity, we have witnessed in the past 200 years a steady and
accelerating increase in the quantity of GHGs in the Earth's atmosphere. This is because
we have been burning fossil fuels to generate energy, cutting down forests for timber
and to make way for cities and farms, and because those farms are more intensive and
industrialized thaneverbefore.TheseGHGshavebecome pollutants because thequantities
emitted disturb the natural balance.
Scientists have been aware of atmospheric warming since at least the 1950s. However, it
wasn't until the late 1960s that human interference with the natural climatic order became a
subjectofpublicdebate.In1968theAmericanbiologistPaulEhrlichwrote The Population
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