America confronts a long list of critical problems and they all require urgent attention. But among them, two issues stand out: catastrophic climate change and nuclear war are unique in the threat they pose to the very survival of human civilization. The enormity and imminence of these twin existential threats cannot be overstated… As climate change progresses over the coming decades, large areas of the planet will be unable to support their human population. As a result, there will likely be forced migrations on a scale unknown in human history… – CNN