Environmental Engineering Reference
In-Depth Information
Chapter
2
Energy and Earth
Earth is one of the smaller of the nine planets forming the solar system. Each planet is
distinct in terms of its physical geography. The different distances of the planets from the
sun, their different sizes and composition ensure that each world is unique. They all
depend for virtually all their energy upon the nearest star, which we call the sun. A basic
understanding of what energy is, how it moves and how it can be transformed is required.
In this chapter we examine the nature of energy and how it is emitted by the sun.
Variations in sun - Earth relations create changes in the pattern and distribution of energy
at the top of our atmosphere. Finally we study the mechanisms that carry this energy to
all parts of Earth's global system. No further reference will be made to the other planets
but similar physical laws operate there.
THE PLANETARY SETTING
Imagine Earth from 300,000 km into space. An isolated sphere; predominantly blue,
patched with brown and green and wreathed in white. A world of water, dotted with land,
partly clothed in swirling cloud. This is a view of the global system. Into this system
pours the input of solar energy; from it come reflected and reradiated energy, which are
its outputs. From our privileged vantage point we could measure, with suitable
equipment, the inputs to and outputs from Earth. We could therefore draw up a simple
model of the globe as an energy system (Figure 2.1) showing the inputs and outputs, but
that would give us no idea of what happens inside. It would be a picture of the globe as a
black box
system. It would be the simplest view of the system we could obtain, but it
would tell us nothing about the internal components or subsystems, or about the
relationships between them. We would see only what enters and leaves the globe.
Let us start by looking at those energy flows we
can
examine. Without doubt, the main
input of energy to the global system comes from the sun. Compared with the solar
contribution, all other inputs are negligible. Small
