TAMPA, Fla. (WFLA) — A new study led by NOAA sheds some light on a long-standing mystery about hurricane seasons in the North Atlantic. Why was there a downturn in hurricane activity in the 1970s and 80s?

Some scientists had surmised it may be due—believe it or not—to cleaner air. According to the new research, that is correct.

The graph below shows a 15-year rolling average of hurricanes in the Atlantic Basin. The cycles seem evident with a downturn in the 1970s and 1980s.

It was long thought that the up and down cycle had to do with a multidecadal internal natural oscillation, but now it appears more likely to be man-made through changes in North Atlantic air pollution.

Vecchi Et Al. 2021 shows cyclical nature in hurricane number over Atlantic with downturn in 1970s and 80s

From the mid 1900s onward through the 1970s, air pollution was on the rise in the US. That air pollution was blown from the US over the Atlantic Ocean and acted to reflect some of the sun’s rays back into space, cooling the oceans. Cooler water means less energy to feed storms.

Image: WFLA
Image: WFLA

But in the 1970s the Clean Air Act took effect and started to bring pollution numbers down. Since the 1980s we’ve seen about a 50% decrease in pollution over the Atlantic Ocean coming from the US and, according to the study, that is one key ingredient in the 33% increase tropical systems over the Atlantic since 1980.

The blue shading over the eastern US represents decreased pollution since 1980 and the red/ yellow over Asia reveals increased pollution.
The red/yellow shading over the Atlantic shows increased tropical activity due to less pollution since 1980. The blue/ green over the Western Pacific reveals less tropical activity due to increased pollution.

WFLA’s Chief Meteorologist and Climate Specialist Jeff Berardelli spoke to the lead author of the paper, Dr. Hiro Murakami, of NOAA’s Geophysical Fluid Dynamics Laboratory. He said over the past 40 years pollution has played a larger role than climate change in regulating hurricane seasons. But in the future, he says greenhouse warming will play the more dominant role.