Coast Lines under water?

As previously noted, subtle changes have already occurred, even if they're not yet noticeable to most people. See the 2007 AR4 and research released since. Most of the concern is about the future: Once certain changes begin, they likely won't stop for a very long time, and in some cases they greatly accelerate. Disintegration of the ice sheets being a good example. Changes are unlikely to remain linear, so sea level will probably rise in fits and starts in the next few decades and beyond.