Problem with this is that if you got this much land sunk by geological rearrangements, you'd be seeing shallow seas become land without having a bunch of additional water from somewhere. What you've got there is way beyond melting the world's ice. Maybe instead of, or in addition to, nuclear war, the Large Hadron Collider can accidentally tear a hole through spacetime to the Plane of Water, causing massive rainstorms that deposit new water and flood the world.