Page 31 - Alternative Energy Systems in Building Design

8 GLOBAL WARMING: CLIMATIC AND ATMOSPHERIC CHANGES

Through the passage of millennia, these remains of organic carbonized material are
manifested in the form of solid coal or liquid crude oils, referred to as fossil fuels. Fossil
fuels, therefore, are considered to be sequestered forms of concentrated solar energy.
One of the most common sources of energy known to humans is the chemical com-
bination of carbon molecules with oxygen. At a certain kindling point (elevated temper-
ature), one atom of carbon (C) combines with two atoms of oxygen (O ), giving rise to
2
a carbon dioxide molecule (C + O = CO ). During this chemical combination, a certain
2
2
amount of heat energy is released. We normally refer to this as a burning process.
Carbon dioxide, in its normal state, is a gas that is heavier than air. Under certain
atmospheric pressures and temperatures, it liquefies. This liquid form of CO is used
2
in common fire extinguishers. Under normal temperature conditions, CO , when present
2
in the air, displaces oxygen and ceases the spread of fire by preventing oxygen present
in the air from reacting or combining with other forms of hydrocarbon-based material.
This is referred to as oxygen starvation.
When heated, CO molecules, owing to thermal agitation, distance themselves from
2
each other, rendering the gas lighter than air. Large quantities of CO result from burning
2
fossil fuels. When heated by the sun’s energy, CO rises to higher elevations and
2
surrounds the planet in a blanket of gas referred to as the inversion layer (Fig. 1.7).
When solar rays impinge on the earth, they are repelled from its surface and the
north and south polar ice caps. The reflection of solar energy back into the earth’s
outer stratosphere moderates global temperature to levels that promote the existence
of various life forms. Minor elevations in the earth’s climatic conditions, in turn, affect
the organic life and the reproductive cycles of all species.
As discussed earlier, global climatic temperature is moderated not only by the reflection
of solar rays but also by the heat-absorption capability of the earth’s oceans. Two-thirds
of the earth’s surface is covered by oceans, which absorb significant amounts of solar
energy. Owing to earth’s relative rotational tilt angle to the sun (23.5 degrees), the

Figure 1.7 CO 2 emissions of various countries in 1995. Courtesy of United Nations
Environmental Program/GRID-Arendal.