Environmental Engineering Reference
In-Depth Information
yls) found in fluids used in electric equipment; and radioactive substances deriving
from nuclear accidents, nuclear tests, and radioactive leakages.
The Earth's atmosphere is almost fully transparent to incident solar radiation. A
fraction of this radiation is reflected to space, but most of it hits the planet surface,
mainly as visible light, where it is absorbed and reemitted as thermal radiation.
However, the atmosphere contains a small amount of gases, mainly carbon dioxide
(CO
2
), that are not transparent to thermal radiation and that act as a blanket, warm-
ing the whole atmosphere and the surface of the Earth in the same way as a farm
greenhouse remains sufficiently warm in winter to allow the growth of out-of-sea-
son vegetables and flowers (
Figure 8.1
)
.
In 1896 Svente Arrhenius suggested that anthropogenic CO
2
emissions result
in warming of the Earth, but this concept remained an academic issue until the
mid-20th century.
The origin of this blanket is the burning or oxidation of organic matter, and it
has remained approximately constant for the last few thousand years. However,
since the beginning of the industrial age at the end of the 18th century, the burning
of increased amounts of fossil fuels has resulted in the steady rise in the amount of
CO
2
in the atmosphere.
As a consequence of the action of the so-called greenhouse gas effect, the planet
emits less heat into space. The existence of the atmosphere and of the greenhouse
gases allows life on the planet. They act as stabilizers against sudden changes in
temperature between night and day. Without them it is estimated that the average
temperature on the Earth's surface would be 15-20°C below zero. Whereas the
Moon and Mars do not have an atmosphere and suffer from large differences in
temperature, Venus has a very thick “cover” of carbon dioxide, keeping its temper-
ature permanently high.
