Flood by Stephen Baxter

Forget the 10m rise in sea levels predicted by proponents of global warming. What if the waters kept rising until every piece of land on the planet was submerged. Baxter's terrifying novel postulates vast sub surface aquifers busting through and flooding the planet's surface over a few short decades.

The back story to this novel relates the experience of a group of former hostages who somehow live long enough to experience all the stages of this extinction level event. The real story though is Baxter's description of the collapse of humanity in the face of overwhelming natural forces. I found it genuinely scary and it brought home to me how precariously balanced out existence really is.  At first I was disappointed in the portrayal of the surviving members of humanity fighting over ever diminishing scraps of land rather than investing serious efforts into a transition to a water bound world but to be honest this is probably a correct prediction of our response.