text: if the density of ice is half that of water, why would melting icebergs cause an increase in sea levels?   melting icebergs can only change the sea level in a very small amount, almost insignificant but not zero. this is because sea ice is much fresher than sea water. when the ice melts the resultant melt water is slightly less dense than the original sea water, so the melt water still 'stands' a little higher than the local sea level. the amount of extra height depends on the salinity difference between ice and ocean, and corresponds to about 2% of the thickness of the original ice floe.    there is a calculus for this: "for 30 million square kilometers of ice (global maximum extent) and average thickness of 2 meters (the arctic ice is about 3 meters, the antarctic is about 1), the corresponding change in global sea level would be:  2(meters) * 0.02 (salinity effect) * 0.10 (fraction of ocean covered by ice), or 4 mm.  not a large figure, but not zero either." http://www.radix.net/~bobg/faqs/sealevel.faq.html  what can really change the sea level is the ice that is not floating, the ice sheets in the antarctic that are grounded on land.   ---addition--- reading the answers above, just remember archimedes principle to understand why an ice that melts in a glass of water doesn't change the water level. in the case of the icebergs the result is slightly different because the iceberg doesn't have the same components as the sea water (salinity)