Here is what will happen:
1) 90% of the world's species will disappear.
2) Shanghai, Lower Manhattan, and many other low-lying places will have to spend gigantic sums to keep the rising waters out. Low-lying islands will disappear.
3) A giant hurricane will cause the sandbank that is Nantucket (Martha's Vineyard is quite another matter, as Crevecoeur was the first to note) to disappear under the waves.
4) Well, I'm sure you stopped reading at #3, didn't you? You don't like this kind of prediction, do you? No, I didn't think so. So I'll keep the rest to myself. For now.