This one’s an exercise in scalability.
If glaciers in Antarctica and Greenland continue melting at current rates, the world is looking at a sea-level rise that will put many major cities below sea level. See here for some of the possible scenarios.
Reducing (or even removing) greenhouse gases from the atmosphere may mitigate the damage, but even so we’re looking at serious consequences over the next century, paid out in blood and treasure.
There might be something we can actually do about all that extra water though.
Mental image: Picture industrial scale desalination plants, located at the coast of Antarctica, gulping in vast quantities of sea water. Vast pipes would carry the resulting purified water deep inland, to where (even in worst case scenarios) it would still be cold enough to remain frozen. Artificial snow machines, on an enormous scale, would turn the water into snow, and deposit it into brand new glaciers, locking it away.