Flood by Stephen Baxter. About the entire world being flooded, in 40 years. No, not just a large-scale sea rise of, say, ten metres. Literally the entire surface of the Earth is flooded. The last scene of the book has the characters watching the peak of Everest go under.
I don't know what's more insulting; the vague assertions by the author that this is possible because of massive water reservoirs beneath the ocean floor that might be there (despite the fact the sea level rise accelerates exponentially, because everyone knows that when you pierce a pressurised container, the contents dribble out at first, then gradually leak out faster and faster /sarcasm), the fact it takes a mere 40 years to happen, the way that every character who's trying to save humanity is treated as a villain, while the Luddite bastards who sabotage these attempts are somehow treated as the good guys.
The child of one of the main characters is such a precocious little twat I was begging for him to die in some horrible way before the end (it doesn't happen). He somehow ends up in an American nuclear submarine, and has a chance to see the submerged ruins of London. He isn't interested. All the little bastard wants to do is swim. I have never been so overwhelmed with hatred towards a character before.
It is the only book I've gladly thrown in a charity bag. It is utter cack, and I urge you not to read it.