You seem to be ignoring human nature. Those few hundred million people are not going to simply accept their fate and go quietly into the night, these climate

You seem to be ignoring human nature. Those few hundred million people are not going to simply accept their fate and go quietly into the night, these climate refugees are going to migrate, and do whatever is required to survive. The social unrest caused by this will be a powder keg that could and most likely will explode into a major conflict. Humans are the exact same savage beasts we were 70000 years ago. We havent evolved, our knowledge has. Institutions keep us in check and without them... scary stuff. Stuff like the Walking Dead is pretty tame comoared to history. During the dow fall of the Aztec empire, they sacrificed(heavily disputed) between 4000 and 84000 people in just 4 days.