Environmental Engineering Reference
In-Depth Information
THE RESPONSE OF THE ENVIRONMENT
individual environments to encompass the entire
system.
In material terms the earth/atmosphere is a
closed system, since it receives no matter (other
than the occasional meteorite) from beyond its
boundaries. The closed nature of the system is of
considerable significance, since it means that the
total amount of matter in the system is fixed.
Existing resources are finite; once they are used
up they cannot be replaced. Some elements—for
example, water, carbon, nitrogen, sulphur—can
be used more than once because of the existence
of efficient natural recycling processes which
clean, repair or reconstitute them. Even they are
no longer immune to disruption, however. Global
warming is in large part a reflection of the
inability of the carbon cycle to cope with the
additional carbon dioxide introduced into the
system by human activities.
The recycling processes and all of the other
sub-systems are powered by the flow of energy
through the system. In energy terms the earth/
atmosphere system is an open system, receiving
energy from the sun and returning it to space
after use. When the flow is even and the rates of
input and output of energy are equal, the system
TO HUMAN INTERFERENCE
The impact of society on the environment
depends not only on the nature of society, but
also on the nature of the environment. Although
it is common to refer to 'the' environment, there
are in fact many environments, and therefore
many possible responses to human interference.
Individually, these environments vary in scale and
complexity, but they are intimately linked, and
in combination constitute the whole earth/
atmosphere system (see Figure 1.2). Like all
systems, the earth/atmosphere system consists of
a series of inter-related components or
subsystems, (see Figure 1.3) ranging in scale from
microscopic to continental, and working together
for the benefit of all. Human interference has
progressively disrupted this beneficial
relationship. In the past, disruption was mainly
at the sub-system level—contamination of a river
basin or pollution of an urban environment, for
example—but the integrated nature of the
system, coupled with the growing scale of
interference caused the impact to extend beyond
Figure 1.2
Schematic diagram of the earth/atmosphere system
