Environmental Engineering Reference
In-Depth Information
It is an intriguing question, also, whether changes in global conditions could arise
owing to adjustments in the outputs independently of change in energy inputs. Any event
that significantly alters the reflectivity of Earth's surface might trigger such changes. An
increase in the extent of the oceans relative to land due, perhaps, to major earth
movements; increased snow cover as a result of mountain building; changes in vegetation
cover due to these events (or even human activity); or changes in the atmosphere brought
about by massive volcanic eruptions - all could lead to significant changes in the global
climate and hence in energy outputs. The implications for the world's climate are very
important.
What is certain is that marked variations in global energy outputs do occur in the long
term. Many of these variations are probably cyclical, related to changes in solar inputs
such as those resulting from differences in the tilt and orbit of Earth. It is also apparent
that such variations in output are critical if Earth is to adjust to alterations in the energy
inputs that are known to occur, and thereby maintain steady-state equilibrium. An
unanswered question is: to what extent can humans change these outputs and upset the
equilibrium?
THE LAWS OF THERMODYNAMICS
key concepts
The basic principles of energy are embodied in the laws of thermodynamics.
These were initially developed in 1843 by Prescott Joule, an English physicist,
to explain processes seen in steam engines. Since then it has been appreciated
that they have far wider significance, and they now represent basic precepts of
science. The first two laws of thermodynamics state that:
1 Energy can be transformed but not destroyed.
2 Heat can never pass spontaneously from a colder to a hotter body; a
temperature change can never occur spontaneously in a body at uniform
temperature.
The first law therefore defines the conservation of energy. The second law
leads to the principle that energy transfers are a result of inequalities in energy
distribution and that energy is always transferred from areas of high energy
status to areas of low energy status, that is, down the energy gradient.
The third law of thermodynamics is less easy to explain. In very general
terms, it says that systems tend towards equilibrium, that is, a random
distribution of energy over time.
ENERGY AND WORK
Transfer and conversion of energy are associated with the performance of work. The sun
performs work in heating Earth through its provision of radiant energy. A river uses
kinetic energy to perform the work of moving bed load. The weathering of rocks or the
decomposition of plant debris involves work carried out largely by chemical energy.
Indeed, it is the work done in these ways that characterizes the myriad processes
operating in the environment.
