When it happens in the natural cycle that it reaches Roman warm temps it will simply be a return to what was... I guess building on the sea bed is a bad idea, but who knows when that'll be, not anytime soon...

And absolutely nothing we do will have any effect. 

 Might be an idea if they want to build on a sea bed to raise it at least 3m, the 2m higher it was when Ostia was still a port plus a metres grace eh...