Seems to me removing the Aswan high dam would be a hell of a lot easier, but what do I know?
Climate Control
If the Mediterranean Sea continues to increase in salinity, shifting climatic patterns throughout the world may cause high-latitude areas in Canada to glaciate within the next century. The Mediterranean is starved of freshwater by human activities: most of the annual flow of the Nile River is now used for irrigation and no longer enters the sea. The sea surface evaporation losses are also increasing as the surface warms due to rising CO2 concentrations in the atmosphere. Consequently, the Mediterranean hydrologic deficit is steadily increasing. The deficit is the difference between the larger amount of water lost by evaporation and the smaller amount received from rainfall and river inputs. The difference is made up by a two-way exchange of water with the Atlantic at Gibraltar. Barring a significant change in regional atmospheric circulation, these two human modifications of the environment will cause the salinity of the Mediterranean to increase for some time as fossil fuels are consumed.
The higher salinity will lead to a larger volume of the Mediterranean outflow at Gibraltar, which will modify high-latitude oceanic-atmospheric circulation and, in effect, initiate new glaciation. This hypothesis arises from a recent study of climate conditions and inferred circulation changes that probably triggered the last glaciation [Johnson, 1997] . The hypothesis will be tested in coming decades. If it is validated by the onset of ice-sheet growth in Canada and cooling in northern Europe, a partial dam at the Strait of Gibraltar could be constructed to limit the outflow and reverse the climate deterioration, thus holding off the next ice age.
And
are the highlights of the calculated problem.If all the Nile flow entered the Mediterranean, the hydrologic deficit would be approximately 31,000 m3 s-1, estimated from Mediterranean outflow and inflow volumes and salinities at Gibraltar [Bryden and Kinder, 1991; Price et al., 1993] , river discharges, and an assumed steady state. A larger hydrologic deficit due to the loss of Nile River discharge is the main difference between today and 120,000 years B.P. in the chain of factors in Figure 2.
Ninety percent of the 2700 m3 s-1 average Nile flow is now diverted for irrigation and lost by evaporation. Most of the diversion has been accomplished in modern times and has increased the Mediterranean hydrologic deficit by about 8%, with half of this increase due to the Aswan High Dam. This dam was completed in 1968 and is a major source of Egyptian power [Gasser and El-Gamal, 1994] . It impounds the annual Nile flood water from the monsoons in Lake Nasser for power production and irrigation, thus preventing the floods from reaching the Mediterranean. The planned additional diversion of 300 m3 s-1 from Lake Nasser at Abu Simbel will bring the deficit increase up to 9%. The mixing time for an ideally mixed Mediterranean Sea (that is, the time needed to attain 63% of a new higher steady-state salinity after an abrupt reduction in fresh water input) is about 100 years. Consequently, most of the effect on northern North Atlantic circulation caused by the 9% increase in the deficit will be realized by the end of the next century as the salinity rises and the Mediterranean outflow increases.
The solution is to
To minimize the eventual increase in Mediterranean salinity to a few parts per mil caused by the more restricted exchange with the Atlantic, the present counterflow entrainment of salt from the outflow into the inflow could be greatly reduced by confining the outflow to a narrow opening, possibly 1 km wide or less, with most of the inflow consisting of shallow water entering at a distance. A detailed hydrodynamic model of the flow field would be required to determine the width of the opening needed to maintain the specified flow restriction when the ultimate Mediterranean salinity and density is attained. Such a model is one of many research tasks needed in the planning of the dam.
Which will in theory
The cost of the dam would be minor compared to the benefits of a mild climate in northern Europe and Asia and the prevention of widespread new ice sheets in Canada. However, the cost and the magnitude of the task and the associated uncertainties would probably generate controversy that might delay a decision to build the dam until the threatened climate deterioration becomes a reality in Canada and Europe. Would the dam construction then be too late ? Probably not, because the redirection of warm North Atlantic Drift into the Nordic Seas would duplicate the strong meridional North Atlantic circulation of 8000 years ago, when the outflow was smaller, the Labrador Sea was cold, and deglaciation was rapidly removing the Laurentide Ice Sheet. However, until the dam is completed and more warmer North Atlantic Drift water is again allowed to enter the Nordic Seas, cold climatic fluctuations in Europe are likely to become increasingly severe.
If a decision to build the dam is delayed, a more worrisome concern is the scarcity of petroleum supplies that will probably develop in the next century. This could lead to political or military conflicts that would increase the difficulty of organizing the broad international effort needed to carry out the project. The sooner the decision is made, the easier it will be to plan and complete the dam. The Aswan High Dam's effect on Mediterranean salinity will trigger glaciation much more quickly than would CO2 warming alone, thus providing a compelling motive to build the remedial dam, and quickly, while petroleum supplies are still plentiful and society is stable.
I still say removing Aswan would be a lot easier/cheaper, and if that is not an option diverting deep saline waters into the Quatarra Depression through a tunnel connected to a pipeline into the deep basin would act to help in three ways, it would restore humidity to air over the northern Sahara, it would generate hydroelectric power, and it would remove a good volume of the deep saline water they are so concerned about thereby restoring the saline balance of the deep basin area's of the Med Sea. Given that the Quatarra depression hydroelectric project would produce substantial electricity it would even ameliorate the loss of the Aswan high dam and could make its removal or at least reduction in the volume of Lake Nasser a more economic alternative for Egypt.
