Unfortunately if the greenland & antarctic icecaps start melting we have bigger problems than the SF area. the greenland ice can raise sealevels by 7m (24.3ft) and the antarctic in total could cause another 75m(250ft) if melting totally. Most coastal areas would be in deep trouble.
Well, sure. Look at what that same 6 meter rise does to the Shanghai region for instance:
http://flood.firetree.net/?ll=37.9095,-122.0526&z=9&m=6
It's just that
1) this happens to be a thread about damming the Golden Gate, so I have offered the only reason I can imagine sane people considering to try it.
2) the payoff in terms of land saved versus miles that have to be dammed is unusually high in the Central California case. If you just take these flood maps and scroll around, you'll see that some regions of coastline suffer remarkably little damage (on a 6-7 meter scale rise; the picture keeps changing the higher the water goes of course) while others suffer dramatic flooding. But rarely can a large tract of land be saved by merely damming one small bottleneck.
So actually doing it might be within the means of local Californian finance and engineering, while larger entities are melting down in panic.
Scrolling down to the Los Angeles area, a 7 meter rise does remarkably little to most of that megacity's beachfront. But the map shows a huge tract of the Imperial Valley (down by the Mexican border) already submerged--the Salton Sea of course is already below sea level--the flood map can't distinguish low-lying land that is cut off from the ocean from terrain that would indeed be flooded. But at 7 meters, the ridges dividing the huge potential Imperial Sea from the Sea of Cortez are already getting mighty thin--the Sea of Cortez is already a fair number of miles north of its current shore, and meanwhile a large arm of it that doesn't exist OTL is reaching northwest, then arcing to the northeast, and threatening to pour water into the Imperial Valley by another route entirely.
So that would be another place for a strategic dam or rather two--unless perhaps someone decides to evacuate and see if letting the Sea of Cortez extend that far north doesn't do good things for the inland desert.
Which is an option that might get considered at several other such dramatic breakthrough sites--such as in the northern Sahara or in central Australia. These deserts might benefit from a part of them getting flooded.
So that makes situations like damming the Golden Gate all the rarer, since sometimes one would not want to stop the flooding even if one could.
...And add some of the fog that is often around, and its not recognizable indeed.
Um, yes. Again. I actually did say that.