If you think there are more hurricanes today than in your grandfather’s day, you are probably mistaken. But recent storms do tend to be stronger than they used to be.
That idea, which has been floating around for a decade or so, got a boost from a recently published study conducted by researchers connected with several U.S. universities and with the National Oceanic and Atmospheric Administration.
They studied the North Atlantic basin, which is a “minor contributor” to the total of hurricanes globally, the report notes, but which has been the subject of much research partly because there are records dating back further than in many other areas.
The researchers looked back at the history of Atlantic tropical cyclones recorded from 1851 through 2019. The sheer number of sightings increased dramatically, of course, because of changes in observation technology. In the mid-19th century, only storms that made landfall in a populated area or those that were sighted by a ship at sea made it onto the rolls. Since the late 20th century, satellites have revealed virtually every tropical disturbance.
After using a mathematical formula to compensate for the difference in observation methods, the researchers tracked the data. They concluded that while the number of named storms varies slightly from year to year and there may be brief periods of reduced or increased activity, there was no consistent trend over the past 168 years towards more hurricanes.
“We find that recorded (emphasis in the original) century-scale increases in Atlantic hurricane and major hurricane frequency, and associated decrease in USA hurricanes strike fraction, are consistent with changes in observing practices and not likely a true climate trend,” the report said
“Increases in basin-wide hurricane and major hurricane activity since the 1970s are not part of a century-scale increase, but a recovery from a deep minimum in the 1960s-1980s,” the researchers added.
The so-called “aerosol effect” is thought to be the cause of, or a major contributor to, that “deep minimum.” It is widely accepted that aerosols added to soot and sulfate particles in the air at the beginning of the second half of the 20th century, blocking and scattering sunlight and thus temporarily cooling the planet and – in the short term – counteracting the effects of global warming.
The researchers say that the aerosol-induced reduction in activity and regular climate variability “have probably masked century-scale greenhouse-gas warming contributions to North Atlantic major hurricane frequency.” But, their study of the historic record doesn’t prove that.
However, looking at satellite-based observations of storms since the early 1980s, the researchers did note a general increase in the intensity of storms during the last 30 years, which has been documented previously. The percentage of storms that become major hurricanes (that is, a Category 3 or above on the Saffir-Simpson scale) has increased both in the North Atlantic and globally, the report says. There also is a “documented” increase in the rapidity of a storm’s intensification.
“Changes in the Atlantic Major Hurricane Frequency Since the Late 19th century” was published July 13, 2021, in Nature Communicators. Gabriel A. Vecchi of Princeton University is the lead author. Others listed are Christopher Landsea, the National Hurricane Center at NOAA; Gabriele Villarini, University of Iowa; Wei Zhan, Utah State University; and Thomas Knutson, the NOAA laboratory at Princeton.