Let it happen. First world countries will experience a construction boom as housing, businesses and infrastructure has to relocate, previously inaccessible mining sites and mineral resources will open up, boosting the economy of countries with the resources to extract them. Newly Arable land will open up in the northern hemisphere, which will offset farmland lost in the southern hemisphere, creating a situation where northern nations will have unprecedented influence over starving nations south of the equator.
The developing world will suffer as lands are submerged or become desert, displacing some of the largest, but poorest populations around the world.
There will probably be a rush to collect whatever resources remain on affected lands before being lost forever. This may help some of the developing world relocate, but those who have nothing to offer in trade for sanctuary will find life very tough, if they even survive at all.
I'm fortunate enough to live in the developed world