Refugees bring very little across borders, but they cling to their stories. These days they mostly want to talk about the weather. The refugees I work with often say the same thing: It got hot. Then hotter. Then the jobs dried up and eventually the food did too. Add in political, racial or religious tensions, or a natural disaster that was the final straw. It all led to the same conclusion: There is no future here. And these are from the “lucky ones” who made it out. Today there are millions of climate refugees — people who have fled their...