[Abraham]

You seem to assume all change will be negative.

The NW Passage opening up would be a boon to trade between Europe and Asia. I'm sure there are other possible positive effects, like longer growing seasons over large amounts of the Earth's surface in Northern Canada and Russia.

The last time there was such an influx of fresh water into the North Atlantic was 30,000 years ago. It ushered in a mini-Ice Age into Europe, which was the golden age of the Neanderthals. We're now fresh out of Neanderthals, so having continental Europe covered in snow is not a good thing.

And if oceans continue to rise at the current rate, by the end of the century, Manhattan, Venice, Shanghai, Calcutta and numerous other cities will be under water.