If you pumped all of the Mediterranean into the rest of the world oceans, that would raise sea level about 7.4 meters. (The volume of the Mediterranean is about 3,750,000 km^3, the surface area of the rest of the world oceans is about 507,500,000 km^2.)

I think a few existing coastal cities might object...

Yes we do!

I live on a small island that's just above sea level and of course the main city and other towns are on the coast. We'd lose about 50% of the land here.

Sorry, I was unclear. By "this", I just meant the dam across the strait of Gibraltar. That would allow the Mediterranean sea to be kept at its current level. I was not referring to the plan to drain the whole Mediterranean.

Alternatively, you could pump the water to land for desalination and agriculture.

Where do you think the water goes after being consumed by humans or plants?

If we're talking about fantasy-scale ecological modifications, there's no reason to ever turn off the pumps, is there?

I was thinking the same. We'd need only the dam of Gibraltar for that and let enough water in to compensate evaporation. The article includes a warning about long term increases of salinity and the need to pump salty water from the deep layers of the Mediterranean to the Atlantic.

How would sea creatures get in and out?

I don't think many, if any, cross it as it is. Not as a necessity in their life cycle anyway.

The strait is really narrow, with really strong currents and a huge change in salinity.

Not fun.

I didn't think about this. A quick search and I found one population of tuna that live in the Atlantic and breeds in the Mediterranean http://www.treehugger.com/clean-technology/unraveling-the-se...

Probably they're not the only sea creatures that cross Gibraltar so this is a concern. Non a minor objection, but one among the many that would be raised. Think also about the political and military implications of a bridge from Africa to Europe.

Fish catapults?

That seems like a minor objection.

What do you mean?