There is no "extra" water. Since (at normal earth temperatures) water can be in the form of a solid, a liquid, or a gas the changes in the ocean depth just indicate that the balance among the three forms has changed. Less ice and/or lower atmospheric concentration of water vapor equals more liquid water in the system and higher shorelines. Add in the (very) occasional contribution of water from a Comet strike and plate tectonics with concurrent rises and falls in land levels, and there you have it. Earth history in a nutshell.
Now if you want an explanation of why some people think that climate change is new, that's more complicated since then we'd have to discuss socialist religion and the public school system.
Nice general dodge. Where'd all the extra water come from?
Ok...let's try again. You are familiar Archimedes principle, I assume. Fill the bathtub with water - get in - the water rises - where did the extra water come from? - get out - the water level falls - where did the extra water go?
Second experiment - take a big cooler, pour water in so there's about a half inch of water in it, put a little pile of sand in one end, make a little sand city, in the other end, put a big block of ice (the kind where the entire container for your fridge's ice maker freezes into one big art deco ice blob), close the lid and let your cooler sit for the day and then check it - the ice melts and the little sand beach city is partly underwater - where'd the extra water come from?
Earth goes through warm and cold phases. Cold phases, water concentrates at the caps as ice and water levels in the oceans fall. Warm phases, the ice melts and the ocean levels rise. Also, the surface of the Earth moves. Sections rise and fall. This will "move" the coastlines. There's no extra water.