Page 27 - Alternative Energy Systems in Building Design

4 GLOBAL WARMING: CLIMATIC AND ATMOSPHERIC CHANGES

Figure 1.3 Global atmospheric concentration of CO 2 . Courtesy of United Nations
Environmental Program/GRID-Arendal.

ORBITAL VARIATIONS
Orbital variation patterns of the earth’s movement around the sun result in solar energy
absorption variability because small variations in the earth’s orbit lead to much more
considerable changes in the distribution and abundance of sunlight reaching the earth’s
surface. Such orbital variations are a consequence of basic physics owing to the mutual
interactions of the earth, its moon, and the other planets. These variations are considered
the driving factors underlying the glacial and interglacial cycles of the last ice age.
Some of the most notable climatic variations observed, such as the repeated advance
and retreat of the desert, have been the result of these orbital variations.

VOLCANISM

Large volcanic activities that occur several times per century also have had a signifi-
cant effect on climate, causing cooling for periods of a few years. For instance, the
1991 eruption of the Mount Pinatubo in the Philippines affected the global climate
substantially. The huge eruptions that have taken place a few times every hundred
million years can be verified based on the magmatic variations in rocks and have
reshaped the climate for millions of years. It has been speculated that the dust emitted
into the atmosphere from large volcanic eruptions in the past has been responsible for
cooling owing to the fact that the dust particles have partially blocked transmission of
the sun’s rays to the earth’s surface. However, recent studies of and measurements
taken from volcanic eruptions indicate that most of the dust thrown in the atmosphere
returns to the earth’s surface within 6 months.