Last week, the nation focused its attention on the 10-year anniversary of Hurricane Katrina, the most destructive hurricane in U.S. history. As bad as the storm was, though, it wasn’t the worst storm that could have possibly hit New Orleans. That’s true of many, many other places, too. And now, in a new study in Nature Climate Change, Princeton’s Ning Lin and MIT’s Kerry Emanuel demonstrate that when it comes to three global cities in particular — Tampa, Fla., Cairns, Australia, and Dubai, United Arab Emirates — there could come a storm that is much worse than anything in recent memory (or in any memory).

Granted, these theoretical storms are also highly unlikely to occur — in some cases, they are 1-in-10,000-year events, or even rarer. The researchers refer to these possible storms as “gray swans,” riffing on the concept of a “black swan” event, an unpredictable catastrophe, or highly impactful event. A “gray swan,” by contrast, can indeed be predicted, even if it is extremely rare. FULL REPORT