Behind the Forecast: Less air pollution leading to more hurricanes?

LOUISVILLE, Ky. (WAVE) - Scientists monitor air pollution closely, especially when it comes to weather and climate impacts. A recent study shows that air pollution reduction may have an unexpected negative weather impact.

The results of a National Oceanic and Atmospheric Administration (NOAA) study, published in early May, showed that the reduction of some air pollution in parts of North America and Europe led to an increase in tropical cyclones in the North Atlantic and a drop in those cyclones in the Southern Hemisphere.

Between 1980 and 2020, there was an estimated 50% drop in human-caused air pollution in the Northern Hemisphere. With fewer pollutants to reflect incoming sunlight, the ocean absorbs more heat and warms up faster. Warm ocean water is key to the strength of tropical cyclones. In fact, experts state that the warmer Atlantic has led to a 33% jump in the number of hurricanes over the last four decades.

A reduction in these particulates also increased temperatures in the Northern Hemispheres’ mid and high latitudes. The warming trend of the water and land shifts the jet stream towards the North Pole and thus weakens westerly winds over the tropical Atlantic basin in the troposphere (about 10 to 12 miles above the planet’s surface). Weaker winds and less wind shear (change in wind speed and/or direction) allow hurricanes to blossom and grow in the Atlantic.

The atmosphere likes to be balanced. So, the rising air (associated with more storms) in the Northern Hemisphere correlates to sinking air in the Southern Hemisphere. That sinking air, which comes with high pressure, keeps tropical systems from forming south of the Equator.

A 2020 study found that a hurricane’s potential to become a Category 3 or higher storm has increased over the last 40 years. According to researchers, a hurricane is eight percent more likely to become a hurricane in this decade compared to the previous one.

Florida State University Professor James Elsner’s research found that one degree Fahrenheit rise in ocean temperature can increase a tropical cyclone’s wind speed by 15 to 20 miles per hour.

For a hurricane to form, the following is needed: a preexisting weather disturbance, low wind shear (change in wind speed or direction over a particular distance), sea surface temperatures at least 80° over a depth of 150 feet, and an area of thunderstorms. Once wind speeds reach 74 mph the storm, is officially a Category 1 hurricane on the Saffir-Simpson scale.

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