evidence: A monstrous change indeed — and one that we’ve known about for decades. The possibility that climate change could flip and, in just a matter of years, plunge part of the world into a new ice age is something that has occasionally made its way into the media. Yet the world has done very little about it. Massive amounts of greenhouse gases are still being pumped into the atmosphere. The climate is getting warmer and weirder. [...] Calvin’s article is filled with frightening details, including evidence that natural global warming in millenia past triggered ice ages in exactly the same way he was warning us about. Of course, those previous warm spells were not accelerated by human activity. Calvin also suggested that the flip-flop would not be gradual; once under way, it could wreak its havoc in just a few years. [...] Re-entering the Paris climate agreement is nice, and was a necessary first step. But it’s not going to do much to prevent a new ice age — or the unimaginable human suffering that would come with it.