2+2=4 is easy. Take two apples. Add two more apples to it. How many do you have? Twice the value of two. That is four. Tada. :P

Anyway, Dawnseeker is correct with the ice argument. Generally speaking, 90% of ice in the ocean is already submerged underwater, we only see the top 10%. Water also expands when it freezes (though I can't remember by what statistic increase), so if all ocean-bound ice were to melt, consider that most of it is already in the water, and that it would actually shrink the amount of space it occupies. And I doubt the ice above water could compensate for the size loss caused by the submerged ice melting.

Another fun trivia is the argument of how it's dangerous to let the ice caps melt because only 3% of the water on Earth is fresh water, and glaciers hold 67% of that fresh water. But, considering we actually never use water from the ice caps, and our water sources come from the hydrologic cycle, it's really an irrelevant argument. It can get some people in a hype, though.