Environmental Engineering Reference
In-Depth Information
the desirability and implications of proposed activities for managing the
carbon cycle.
A DAM ACROSS THE STRAIT OF GIBRALTAR
The possibility that global climate change could result in abrupt shifts in
global ocean circulation patterns is generally recognized.
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More specifi-
cally, R. J. Johnson has hypothesized that, as a result of human reduction of
freshwater flow into the Mediterranean Sea, increased salinity in that water
body could lead to a higher volume of outflow from the Mediterranean
Basin at Gibraltar.
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This, in turn, could modify high-latitude oceanic-
atmospheric circulation patterns in such a way as to cause extensive glacia-
tion in Canada and cooling in northern Europe. As mitigation, Johnson
proposes a partial dam across the Strait of Gibraltar, which would limit the
outflow and reverse the climate deterioration. The dam would be a huge
construction project designed to limit the Mediterranean flow through the
Strait to some 20 percent of what it is now; it would likely take decades to
construct and require about 1.27 cubic kilometers of material.The proposal
has been strongly criticized and defended.
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Several points about this proposal are of interest.The first is that the shift
in salinity in the Mediterranean is primarily a result of human diversion of
water from the Nile: some 90 percent of the Nile's 2,700-square-meter-
per-second flow is now diverted for agriculture or lost through evapora-
tion. Significantly, much of this is due to the Aswan High Dam, so the
(potential, and unanticipated) effects of shifts in the salinity of the Mediter-
ranean—such as increased Canadian glaciation—are attributable, at least in
part, to a single hydrologic construction project.The implications of failing
to take a systems view of major engineering projects when they are first
proposed, as industrial ecology would require, are apparent. This case also
illustrates that Earth Systems Engineering is not something completely
new—although understanding such projects in a systemic, rather than ad
hoc, way has yet to occur.
The need for new ways to evaluate such systems—the use of indus-
trial ecology principles, among others—is apparent from the scale and
nature of the perturbation and impacts arising from such complex cou-
pled human/natural systems. In this case, for example, the potential
causal connections run from a historical pattern of increasing human
