Could the planet's dirty air have been keeping hurricanes partially in check?
That's the startling conclusion of a new climate study, published in Nature Geoscience on Monday, that looked at the effects of man-made aerosols (particles suspended in atmosphere) on the North Atlantic's climate in the 20th Century.
Conducted by Britain's Meteorological Office, researchers used climate models to weigh pollutants against tropical storms.
"Researchers found that aerosols make clouds brighter, causing them to reflect more energy from the sun back into space," according to a release published by the Met Office. "This impacts ocean temperatures and tropical circulation patterns, effectively making conditions less favourable for hurricanes."
In other words, the study "raises the possibility that man-made particles may be linked to changing number of hurricanes" -- just not in the way many people might have assumed, climate scientist and lead study author Dr. Nick Dunstone told The Huffington Post in a phone interview.
While aerosols do occur naturally, the study focused on North America and Europe, where the particles were most likely to be man-made as a result of fossil fuel consumption, notes the Agence France-Presse.
Using a state-of-the-art Earth system climate model, the researchers studied historical data and noticed that there were fewer storms during periods of unfettered industrial activity (1930 to 1960), and an upswing in hurricane frequency in the 1990s, following the introduction of governmental clean-air initiatives.
Hurricanes are created when the right combination of warm ocean temperatures and circulation patterns result in a powerful rotating storm system that can grow to up to 600 miles across with winds reaching speeds of 200 mph. Because aerosols reflect the sun, they can change the amount of heat being projected to the ocean, and therefore how warm (or favorable to hurricanes) it is.
Dunstone acknowledged to HuffPost that the study may be controversial, but he stressed that the need to reduce aerosol particles far outweighs any effects on storm frequency. Aerosol reduction has many important and positive effects, including improving human health and decreasing severe droughts, he said.
In an effort to get a second opinion, The New York Times tracked down several scientists not involved with the British team. All the Times' sources said the Met Office's conclusions were "entirely plausible." However, the paper reported that there are several other theories that address the potential causes of tropical storms not linked to pollution, such as "large-scale natural oscillations in the ocean circulation".
It's worth noting that there continues to be some debate in the scientific community over the link between global warming and hurricanes, according to The Telegraph. While language approved by the Intergovernmental Panel on Climate Change in 2007 did claim that man-made greenhouse gasses were "more likely than not" making hurricanes stronger, this language did not specifically address hurricane frequency.
Ultimately, the Met Office's research proves the complexity of global climates, and the need for ongoing study of the ways greenhouse gasses and aerosols affect climate systems.
"It's not simple," Dunstone said. "This study really highlights that man may be having more of an influence on our regional climate than was previously thought."