It’s about this time of year that investors in reinsurance lie awake worrying about the Atlantic multidecadal oscillation. That is because June marks the start of the North Atlantic hurricane season, making the third quarter a crucial time of year for companies selling catastrophe protection. Impossible a task as it seems, there are hordes of meteorologists whose job it is to predict the severity of the coming season, observing everything from the ocean’s currents to its salinity levels.

The focus on forecasting has increased since the particularly extreme years of 2004 and 2005, which included hurricane Katrina. Indeed, there have been three times more big Atlantic hurricanes in the past 10 years, compared with the previous decade. Most climate experts reckon the Atlantic is still in a high activity phase, so it was a surprise when last year ended up being freakishly benign, with only five hurricanes and not one reaching the US coast. Reinsurance stocks were sold off this time last year in expectation of a bad season, but then rallied.