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Atlantropa, Herman Sörgel's proposal to turn vast swathes of the Mediterranean Sea into livable dry land by installing five hydroelectric dams (the main one across the Strait of Gibraltar), is an awful idea for a great MANY reasons. Ignoring all the pesky social and political problems with the concept, what's the worst possible environmental outcome of a successful Atlantropa project?

Many articles mention that the project would raise the sea level around the world with understandably disastrous consequences, but Popular Mechanics implies an even worse scenario:

The reduced weight of water over the volcanic Mediterranean sea floor would probably lead to violent eruptions and earthquakes. (Popular Mechanics March 1977, "Power from the sea: Fact or Fancy" p 193)

I can easily imagine such geologic upheaval causing tsunamis and worldwide atmospheric effects, not unlike the 1883 eruption of Krakatoa. Others have claimed it would cause a European ice age. I expect there's a myriad other factors I haven't run into yet.

What's the worst plausible outcome of a successful attempt to create Atlantropa, with regard to global physical/environmental disasters (not social or political), both short-term and over the next decades? If it matters, assume it's implemented in the late 1940s without any environmental impact oversight whatsoever.

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The Atlantropa project envisioned damming the Gibraltar in order to lower the Med by 200 meters. Anything more than 20 meters would transform the Bosphorus into a gigantic waterfall, cutting off (in clockwise order) Bulgaria, Romania, Russia, and Georgia from the Mediterranean. The immediate and devastating effect would be a war between the proponents of the scheme and Russia.

The scheme would be very short lived.

Geologically speaking, not much will happen. The Med is 1500 meters deep on the average, wiping off 200 of those meters is not really that important. The water volume of the Med is tiny compared to the ocean, so the increase in sea levels elsewhere will be modest.

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  • $\begingroup$ My question is about environmental, not political, effects. (And the Atlantropa project also includes a wall across the Dardanelles--not a solution, but it would cause different problems.) $\endgroup$ – BESW Feb 8 '17 at 8:28
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    $\begingroup$ @BESW: The wall across the Dardanelles is useless (and silly). The Black Sea has excedent of water; that water must go somewhere, such as over the Russian and Ukrainian plains. Bad idea. And damming the Gibraltar would lower the Med faster than it can be replenished from the Black Sea; the Marmara would drain on its own. $\endgroup$ – AlexP Feb 8 '17 at 8:34
  • $\begingroup$ So you discount the idea that it would cause a European ice age, or PM's claim that it would raise sea levels by three feet? $\endgroup$ – BESW Feb 8 '17 at 8:37
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    $\begingroup$ @BESW: Lowering the Med by 200 meters would not make the Med much smaller. Most land reclaimed would be on the nice civilised northern shores. There would still be a sea between Europe and Africa. The Nile valley would cut a deep canyon just about immediately (because the Nile now flows on top of a soft sediment deposit in an ancient canyon); Russia will have the help of Egypt in dealing with the idiots who started the scheme, making it even more short-lived. $\endgroup$ – AlexP Feb 8 '17 at 8:42
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This would be an incredibly BAD idea. The environmental and economic changes would be incredibly negative. We can actually see the results of a much smaller sea drying up when we take a look at what happened to the Aral Sea during the 70s, 80s & 90s

Draining the Mediterranean - far from simply creating vast new areas of land for people to colonize - would actually create massive new deserts. In addition it would devastate coastal economies right around the entire sea.

The entire coastline would shift by dozens if not hundreds of miles.

It would also have the effect in current geopolitical circumstances of making it far easier for refugees to get to Europe.

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    $\begingroup$ Can you please edit in more details about the environmental problems this would cause, like Popular Mechanics' claim that it would cause volcanic activity, or its effects on the Gulf Stream? I'm not interested in the sociopolitical fallout. $\endgroup$ – BESW Feb 8 '17 at 8:32
  • $\begingroup$ The costaline would shift, but not by very much. There is a nice map at the Wikipedia article. $\endgroup$ – AlexP Feb 8 '17 at 8:35
  • $\begingroup$ Do you discount the idea that it would cause a European ice age, or PM's claim that it would raise sea levels by three feet? $\endgroup$ – BESW Feb 8 '17 at 8:38
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    $\begingroup$ Hmm - I do not agree with it creating a European Ice Age or with it creating an increase in volcanic activity - but the other claims - that it would lift sea levels by 3 feet - That actually seems plausible. This would cause pretty significant environmental impact outside the Med - there are countries that are under pressure now from the rather modest sea level rise we have been experiencing (EG Tuvalu). It also seems plausible that there COULD be a minor increase in seismic activity $\endgroup$ – kiltannen Feb 8 '17 at 8:47
  • $\begingroup$ Please expand your answer with details about these significant and incredibly negative environmental changes. I'm asking for the global worst-case scenario, not broad "it'd be bad." I kinda got that. Tuvalu is a great example. $\endgroup$ – BESW Feb 8 '17 at 8:52
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On top of what other answers are suggesting, I am sure that removing 200 meters of water over the entire surface of the Mediterranean sea (2.51 million square meter, counting to 500 million cubic meter, roughly 500*10^9 kg) will sensibly alter the momentum of inertia of the planet and will consequently affect its rotation, slightly changing the duration of the day and the rotation axis.

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