What Ras says is true its because when water freezes the molecules of water form an open structure rather than the tight structure of liquid water. The theory works fine for ice in the sea, BUT, what about the glaciers that are on land?
So taking that all into account the water levels WILL rise as the atmosphere warms up.
As for the comments about Global warming being a completely natural and reversible process, may I humbly suggest you check out what happened on Venus
Edit - Knew I'd covered this ground before!
http://www.cableforum.co.uk/board/sh...8&postcount=51