There's no need to go as far as nuclear war. Climate change will manifest itself in political instability and mass migration (see Syria and Africa), and perhaps

There's no need to go as far as nuclear war. Climate change will manifest itself in political instability and mass migration (see Syria and Africa), and perhaps even more fundamentally, rampant desertification which is liable to lead to food shortages in poorer countries. But yes, it _is_ a global catastrophe and sadly few people seem to care enough to do something about it.