Hurricanes and tropical storms increasing in the North Atlantic, study finds

A study recently published by an atmospheric scientist at the Massachusetts Institute of Technology found that while the frequency of hurricanes has held pretty steadily globally, numbers are rising in the North Atlantic.

"We're still puzzling about why that's so. It's not necessarily because of global warming although that might have something to do with it," Professor Kerry Emanuel told Island Morning host Laura Chapin. 

"It's a great mystery for science detectives like me. It's definitely something we want to try to understand."

Emanuel used climate modelling to reconstruct the history of hurricanes all the way back to 1851. 

He said he thought the early observational reports — from sea and land — might have under-reported the number of hurricanes in the mid-19th century.

"As we go back in time, there are fewer and fewer actual observations. For example, no satellites before about 1970, no airplanes before about the mid-1940s taking observations over the Atlantic," said  Emanuel. 

"So as one goes back in time, the shipping becomes more sparse, land observations become more sparse, and that affects the quality of the record. And so I was looking for a way to check that historical record to see how good it really was."

Kerry was surprised to find through his re-analysis that those early observations were actually quite accurate. 

Ongoing work

His study also picked up on a hurricane drought that occurred around the 1980s. 

"We got suspicious that this might actually have been a manmade drought, not due to greenhouse gases, but due to aerosols which are a product of fossil fuel combustion," he said. 

"We know that aerosols ramped up very quickly over the North Atlantic and Western Europe and Africa during the 1950s through 1970s and then because of clean air acts, they ramped down just as fast in the '80s and '90s."

This reduced the monsoons in the Sahara Desert, which led to big increases in dust outbreaks from Africa, according to Emanuel. 

"It was primarily the dust that cooled the Atlantic and therefore reduced hurricane activity," he said.

Moving forward, Emanuel said he intends to continue working to discover why North Atlantic hurricanes and tropical storms appear to be increasing. 

He plans to look at the changes in ocean currents and dust conditions in the Sahara.

"Maybe there's a long term trend in that and if that's the case, that might explain it. But then we have the problem why would there be a long term trend in African dust?"