I must disagree that climate change is the greatest threat to humankind. I would give it a distant second compared with those thousands of nukes set on a world ending hair trigger. With climate change we may have tens of decades before a goodly portion of human kind is killed off. With nukes it may only be a matter of minutes from right now before all of humankind is terminated.

Sure we tend to think of global warming first because we can already see the results as it progresses to its bitter end, while conversely we will never see the thermonuclear end coming at us.