Unpopular, sad and inconvenient truth is that without shrinking human population we won't survive the climate apocalypse. So migration may not be the solution.
What I'm saying is that we already triggered the genocide by human activities of the past 100+ years - we reached the point of no return so a lot of people will die due to the effects of climate change.
Relocate populations? We won't even handle a few hundred thousand refugees of wars we've started, and you're talking about global migration.