We'd have to look at the various options for the easiest migration possible, i.e., planning ahead for people to go to the nearest appropriate area rather than letting it happen and later regretting it.
That's a mind-blower. This would involve cooperation (uh oh) between governments.
well, that would be a problem, but let's look at that.
In the Land Distribution thing, the big winners of gaining new land due to Global Warming would be Russia and Canada, both of whom have lots of land which isn't terribly useful because they are so cold. Even if they get warmer, they aren't goign to be terribly useful because you'll have very long days and very short nights in the summer and the converse in the winter.
But let's say a billion Indians want to relocate to Siberia because India is under water or too hot. They'd quickly outnumber the 160 million Russians, and pretty soon, Russia wouldn't be Russia anymore. It'd be India North.
Probably easier to knock off what we are currently doing before it becomes a problem.