Global warming is making both places more important to global shipping and trade. 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.

Former national security adviser Robert O’Brien said in a Sunday interview that Denmark should let the U.S. “buy” Greenland if it cannot defend the self-governing country, noting the territory