Environmental Engineering Reference
In-Depth Information
Figure 7.4
Rising levels of atmospheric CO
2
at Mauna Loa, Hawaii. The smooth curve represents annual
average values; the zig-zag curve indicates seasonal fluctuations. The peaks in the zig-zag curve represent the
winter values and the troughs represent the summer values
Source:
After Bolin
et al.
(1986)
between several major reservoirs (see Figure 7.2).
The atmosphere, for example, contains more
than 750 billion tonnes of carbon at any given
time, while 2,000 billion tonnes are stored on
land, and close to 40,000 billion tonnes are
contained in the oceans (Gribbin 1978). Living
terrestrial organic matter is estimated to contain
between 450 and 600 billion tonnes, somewhat
less than that stored in the atmosphere (Moore
and Bolin 1986). World fossil fuel reserves also
constitute an important carbon reservoir of some
5,000 billion tonnes (McCarthy
et al.
1986). They
contain carbon which has not been active in the
cycle for millions of years, but is now being
reintroduced as a result of the growing demand
for energy in modern society being met by the
mining and burning of fossil fuels. It is being
reactivated in the form of CO
2
, which is being
released into the atmospheric reservoir in
quantities sufficient to disrupt the natural flow
of carbon in the environment. The greatest
natural flow (or flux) is between the atmosphere
and terrestrial biota and between the atmosphere
and the oceans (Watson
et al.
1990). Although
these fluxes vary from time to time, they have
no long-term impact on the greenhouse effect
because they are an integral part of the earth/
atmosphere system. In contrast, inputs to the
atmosphere from fossil fuel consumption,
although smaller than the natural flows, involve
carbon which has not participated in the system
for millions of years. When it is reintroduced,
the system cannot cope immediately, and
becomes unbalanced. The natural sinks are
unable to absorb the new CO
2
as rapidly as it is
being produced. The excess remains in the
atmosphere, to intensify the greenhouse effect,
and thus contribute to global warming.
The burning of fossil fuels adds more than 5
billion tonnes of CO
2
to the atmosphere every
year (Keepin
et al.
1986), with more than 90 per
cent originating in North and Central America,
Asia, Europe and the republics of the former
USSR (see Figure 7.3). Fossil fuel use remains
the primary source of anthropogenic CO
2
but
augmenting that is the destruction of natural
