Since the dawn of civilization, humanity's level of development has been
inextricably linked to the use of energy. All animals consume food to provide
the energy needed for metabolism, movement and work, but ours is the only
species which uses external energy, other than food, to any significant extent.
The process began with the discovery of fire - a process in which the energy
contained within organic molecules (primarily in wood) could be converted into
heat. This provided the ability to cook food, and thus the ability to use a
much wider range of food items. Fire also provided heating which enabled humans
to survive in colder climates. The next breakthrough in harnessing energy came
with the use of animals such as the donkey as a means of transport and a beast
of burden, and oxen to till the soil. Fire was then used in the production of
improved tools made of bronze and iron, which transformed the way of life for
much of humanity. Machines, such as the wheel, were developed to permit more
efficient use of external energy. The pyramids are a monument to the devices
which must have been developed to provide mechanical advantage, although the
energy used was still primarily manpower. Further harnessing of energy was
achieved by the use of streams to turn a wheel, and, in due course, windmills.
Wood or charcoal was burnt to produce lime, which permitted the construction of
more elaborate buildings. Right up to the time of large-scale use of coal,
which led to the Industrial Revolution, humans had only been using renewable
energy, supplied by the sun.
Combustion of coal, followed by oil and natural gas, permitted a quantum leap
in transportation (and hence trade) and manufacture of a vast range of
products, all of which enabled human societies to become more complex, and, for
most people at least, to enjoy an enhanced quality of life. Our consumption of
energy continues to grow, despite major efforts at increasing efficiency.
Solar energy has thus permitted the development and civilization of the human
race but we must not forget that it also facilitates the growth and survival of
all forms of life and it drives the global circulation systems. Thus ocean
currents, climate, rainfall and all freshwater resources, are dependent on the
energy of the sun. Without the sun there would be no fresh water!
Thus for most of history, all activity, human and otherwise, was dependent on
energy in the form of solar radiation. This can be regarded as solar capital.
In relatively recent times humanity has learned to exploit the natural
resources of the earth to produce energy, but this is using a legacy which is
not being replaced. Coal, oil and natural gas are fossil fuels. For a few
centuries they are providing an enormously useful bonus, but the reserves are
being depleted and we can only rely on them for a few more generations. Fossil
fuels represent a major component of what can be regarded as earth capital.
This includes natural resources such as minerals and human resources. These two
forms of capital support and sustain all life and all economies on earth.
Thus energy is essential for all human activities,
and by harnessing external energy on a massive scale, humans have managed to
dominate the earth. Figure 1 indicates the range of human activities, driven by
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