There seems to be some confusion in the Twittersphere about one aspect of the relationship between hurricanes and global warming: the role of El Ninos. To loosely paraphrase one meme: “If hotter global temperatures mean more intense and frequent Atlantic hurricanes, then why don’t we get these strong storms during El Nino years?”
The problem with this line of thinking is that the historical evidence shows that El Ninos ultimately slow or possibly even stop hurricanes from forming; they don’t cause them.
It turns out that when there’s an El Nino in the Pacific, that means that there’s more wind shear—wind blowing in different directions or speeds at various altitudes—even in what would seem to be the faraway Atlantic Ocean. This increased wind shear then makes it harder for tropical storms and hurricanes to form.
A story in Bloomberg News’ by Brian K. Sullivan vividly described wind shear as “Kryptonite for hurricanes.” Sullivan explained further, saying that “As powerful as they are, tropical cyclones have delicate structures. Shear can tear them apart. A budding storm can’t get started and an established storm can’t get strong.”
But the San Jose Mercury News probably summed up the phenomenon best, in its headline: “How did Irma happen? Blame El Nino’s absence.”