Interesting part of the movie

yesterday I was watching movie call inconvenient truth, there was a part that very surprising. If Green lands massive ice sheet were to melt, something that could occur over the very long term, they could raise the sea level by 23 feet 7 meters. I never knew it, I never thought that could happened. I thought when the ice froze the sea level decrease because they use water from the sea, and when the ice melt the sea level will be at the same level that when they didn't freeze.