The core problem with climate changes is not sea level rise or bio-diversity; it is food supply.
We are just barely able to feed the current six-and-a-half billion people on the planet, thanks to the Green Revolution and a shift to very energy-intensive agriculture. At 2 degrees hotter, many hundreds of millions are at risk but, with global cooperation and a switch away from meat production (let people eat the grain, not cows), they wouldn't have to starve. At 5 degrees hotter, there are no good options left.
What makes this a political and potentially a strategic issue is the fact that the misery will not be equally shared. As rainfall patterns shift, some countries lose most of their best crop-lands while others come through the change unharmed or even gain new food-growing areas in the sub-Arctic. There is a bitter irony here, for the list of beneficiaries includes most of the countries that industrialised early and caused the problem to grow to its current size.
There is also huge scope for conflict, including armed conflict, because nobody will sit quietly and watch their children starve when any alternatives remain, including violent ones. Some of those watching their children starve will have the resources and technology to threaten those who still have food (but just enough food).
The only way to avoid this future, if it can be avoided, is to get greenhouse gas emissions down drastically in the next ten to fifteen years. But making the deal that would mandate and enforce those deep cuts in emissions, especially the part of the deal that brings the 'new' industrialising countries into the effort, is ferociously difficult politically, and there is no guarantee that it will happen in time. If it doesn't, the next few generations are in for a wild ride.
