What is it about Vladimir Putin and Donald Trump? Theories that the Russian has some dirt on his American counterpart lack hard evidence. But (as American spies have repeatedly concluded) Mr Putin clearly prefers Mr Trump as president, and Mr Trump never aims his trademark insults at Mr Putin. Lexington has a simpler theory of what binds the two men.

And while climate change is a gradual danger, climate-watchers also fear tipping points: the collapse of Greenland’s ice-sheet (making sea levels rise) or of the Atlantic Meridional Overturning Circulation (making Europe far colder and drier) could happen suddenly. Researchers are trying to work out how close such events may be—and how to prepare for the consequences of them.