Some of the most alarming science surrounding climate change is the discovery that it may not happen incrementally — as a steadily rising line on a graph — but in a series of lurches as various “tipping points” are passed. And now comes a new concern: These tipping points can form a cascade, with each one triggering others, creating an irreversible shift to a hotter world. A new study suggests that changes to ocean circulation could be the driver of such a cascade.