To imagine the kind of future a hotter, dryer climate may bring, and the geopolitical challenges it will create, look no farther than two parts of the world that Donald Trump wants America to control: Greenland and the Panama Canal.

Threat Status is closely tracking whether Mr. Trump will follow through on his threat or is simply trying to compel policy outcomes before his inauguration. Consider, for instance, that German automakers could duck tariffs by making more automobiles in the U.