(CN) — The recent uptick in major Atlantic hurricanes may reflect a rebound after a dip in tropical activity between the 1960s and 80s rather than a large-scale increase in frequency, according to new research analyzing major hurricane activity between 1851 and 2019.
But the findings, published Tuesday in the journal in Nature Communications, don’t necessarily mean that climate change is not affecting the frequency or intensity of tropical cyclones, which are expected to become more intense as sea surface temperatures increase.
Major hurricanes in the Atlantic Ocean have become more frequent since the 1980s, researchers note, but it’s not clear if this recent trend is a result of man-made greenhouse gas emissions or if it reflects the natural ebb and flow of Atlantic hurricane activity.
Researcher Gabriel Vecchi, professor of geosciences at Princeton University, and his colleagues on the study note one possibility is that the natural changes in climate, as well as cooling caused by aerosols, may have counteracted, or “masked,” the effects greenhouse gas-induced warming has on the frequency of North Atlantic hurricanes.
Aerosols are tiny particles in the air that are usually produced when different types of fossil fuels are burned, such as coal, petroleum or wood. Two of the major sources are cars and factories, but volcanoes and dust from deserts also create aerosol pollutants. These pollutants cool the Earth by reducing the amount of sunlight reaching its surface.
During the mid-20th century, there was a gradual increase in aerosol pollutants — fueled by an expansion in industrialization following World War II — that reached a peak in 1970, according to separate research by the National Oceanic and Atmospheric Administration, or NOAA. By the 1980s, oil embargos and environmental controls reduced aerosol pollution in North America, but greenhouse gas emissions continued to build up.
Vecchi’s research, supported by the NOAA, suggests the possibility that aerosol-induced cooling over the tropical Atlantic may have resulted in a decrease in tropical cyclone activity when compared to historical data.
But detailed satellite data only goes back to 1972, which means earlier data may be incomplete and earlier hurricane activity could be underestimated. So to study even older data, Vecchi and his team studied ship records from 1851 to 1971 and then used satellite records of hurricane tracks and characteristics to estimate the number of potentially missed storms.
"We find that recorded 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 study states. "After homogenization, 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."
But the researchers stopped short of saying climate change isn’t playing a role.
“Does this work provide evidence against the hypothesis that greenhouse-gas-induced warming may lead to an intensification of North Atlantic [hurricanes]? Not necessarily,” the paper states. “Substantial multi-decadal variability may obscure trends computed over the past century and recent studies suggest the possibility for an aerosol-driven reduction in [North Atlantic hurricane] and [major hurricane] activity over the 1960s–1980s which may have obscured any greenhouse induced [North Atlantic hurricane] and [major hurricane] intensification over the 20th century.”
The researchers behind Tuesday's paper did not respond to a request for comment on their findings.
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