The problem has nothing to do with one particular parameter of the possible, for example sea rise.  When all forms of ecosystems are now subject to irreversible damage, it's the totality of the effects which must be considered.  Who cares if the sea rises 1 or 3 or 5 meters if the basic foodstuffs are damaged by this civilization, if the destruction of genetic diversity leaves us hanging by our primordial toes, if the destruction of coral reefs is a symptom that even a higher sea has nothing to harvest, then it doesn't matter where you live.

"Life shrinks or expands in proportion to one's courage." - Anaïs Nin