By itself, a 6 foot increase in sea-level would affect hundreds of millions of people. I believe that is on the high-end of predictions for 2100 if we continue

By itself, a 6 foot increase in sea-level would affect hundreds of millions of people. I believe that is on the high-end of predictions for 2100 if we continue to fail to take serious action, so yes, it may not be that bad. But it's just one example. We can also look at the more modest predictions of a 2 to 3 foot sea-level increase. That would still throw the lives of dozens of millions of people into complete chaos. Not to mention the disruption to the economic systems in these coastal areas, and those that flow through those areas. And this isn't even discussing the actual temperature increases, agricultural issues, floods / droughts, and so on.