Discussions

I have been thinking a lot about rising sea-levels and what kind of impact an extra 15cm of water will have on our planet.  
 
while I'm aware that the recent UN figures of 15 cm is hardly a giant change sea-level I am having a hard time reconciling what I would consider minimal change in sea-level with the rest of the reports "increased confidence" in dire predictions for coastal areas.  
 
So i sat and thought and thought some more, then I think I found an answer. now I'm a layman but i suddenly remembered a couple of things about the oceans on our planet.  
 
1. they are freaking huge! i mean big isn't a good enough word. physicalgeography.net gives a figure of 361132000 sq. kilometres(139397000 sq. miles) that's big  
 
2. they are not static. the water in the ocean is sloshed around on the face of the earth by the gravitational pull of the moon. Tides are the common term. now in some places tides are measured in feet. in some places tides are measured in meters it seems to depend on the moon the earth and the local topography as to which type of tides you will get on a given day in a given year.  
 
so I was wondering when we talk about this paltry 15 cm of water what do we mean, how will it affect tides. the 15cms of water works out to (by my rough calculations to be)148940000000 litres when spread over the face of the earths oceans. is this 15cm average a much more dangerous figure than first blush would tell us? 'm not sure but before everyone starts tossing this 15cm around as a reasonable and ineffective amount I'd like to have someone who can explain what effect an additional 1.4 trillion? (i think) litres of saltwater sloshing around is gonna do to the coastlines of the world.  
 
I also worry about the reduced salinity in the oceans as all of that freshwater ice melts into the seas and what effect that will have on the plankton which all ocean life depends on.  
 
now I just fiddled my way through those calculations so I may be wrong with some decimal points and such. And i am not an expert on tidal forces so any informed corrections would be appreciated.