One of the most common misconceptions about polar seas is that if ice shelves or icebergs melt, the sea level will rise. This is actually not true - why?
1) Water expands when it freezes making it less dense than the water from which it freezes. In fact, its volume is a little over 9% greater (or density ~ 9% lower) than in the liquid state.
2) Therefore both ice shelves and icebergs float on the sea surface.
3) As they float, they displace the same volume of water that they contain.
4) So if they were to melt, the sea level would stay exactly the same.
Just because melting ice shelves and icebergs have no effect on sea level doesn’t mean that there isn’t actually a problem. If global warming causes large areas of Antarctic ice-shelf to break off and melt, the sea level won’t be affected; but what could happen is ice and snow covering the continent will no longer have anything holding it in place. If this slides into the ocean and melts, then the sea level will rise. It has been estimated that if the Antarctic ice sheet melted, it would raise sea levels by around 65 to 70 metres! So global warming could have catastrophic effects!