Study: Reduced Air Pollution Increases Hurricanes
A new NOAA study published in Science Advances, found that decreasing air pollution actually increased hurricanes.
Here is an excerpt:
“Air pollution is a big environmental risk to human health and we have made great strides in reducing health risks by reducing particulate air pollution,” said Hiroyuki Murakami, a physical scientist at NOAA’s Geophysical Fluid Dynamics Laboratory and study author. “But reducing air pollution does not always decrease the risk of hazards from tropical cyclones.”
Over the last 40 years, Europe and North America have been leaders in reducing particulate air pollution from industry, autos, energy and other sources. The increasing absence of human-caused air pollution in the Northern Hemisphere, estimated to be a 50-percent drop in concentration from 1980 to 2020, has led to surface warming over the tropical Atlantic Ocean, which contributes to more frequent tropical cyclones.
Without significant amounts of particulate pollution to reflect sunlight, the ocean absorbs more heat and warms faster. A warming Atlantic Ocean has been a key ingredient to a 33-percent increase in the number of tropical cyclones during this 40-year period, Murakami said.
The decrease in pollution has also led to a warming of the mid- and high-latitudes in the Northern Hemisphere. This warming of land and ocean is causing the steady poleward movement of the jet stream from the tropics toward the Arctic.
Here is an excerpt:
“Air pollution is a big environmental risk to human health and we have made great strides in reducing health risks by reducing particulate air pollution,” said Hiroyuki Murakami, a physical scientist at NOAA’s Geophysical Fluid Dynamics Laboratory and study author. “But reducing air pollution does not always decrease the risk of hazards from tropical cyclones.”
Over the last 40 years, Europe and North America have been leaders in reducing particulate air pollution from industry, autos, energy and other sources. The increasing absence of human-caused air pollution in the Northern Hemisphere, estimated to be a 50-percent drop in concentration from 1980 to 2020, has led to surface warming over the tropical Atlantic Ocean, which contributes to more frequent tropical cyclones.
Without significant amounts of particulate pollution to reflect sunlight, the ocean absorbs more heat and warms faster. A warming Atlantic Ocean has been a key ingredient to a 33-percent increase in the number of tropical cyclones during this 40-year period, Murakami said.
The decrease in pollution has also led to a warming of the mid- and high-latitudes in the Northern Hemisphere. This warming of land and ocean is causing the steady poleward movement of the jet stream from the tropics toward the Arctic.
The shift of the jet stream led to weakening westerly winds in the upper troposphere in the tropical Atlantic basin, an area of the atmosphere about 10 to 12 miles from the surface of the earth. Weaker winds, in turn, mean that there is less difference between the speed of winds in the lower and upper troposphere or less wind shear. With little wind shear, tropical cyclones are able to develop and grow in strength over the Atlantic Ocean.
The study also found that increased pollution in Asia could mean less hurricanes.
The earth system processes at work in the western North Pacific – an area where strong tropical cyclones are called typhoons - are the flip side of what’s happening in the Atlantic basin. The key ingredient for the decrease of tropical cyclones in the western North Pacific is also air pollution, according to the new research.
In this case, a 40-percent increase in the concentration of particulate air pollution has been one of several factors that has contributed to a 14-percent decrease in tropical cyclones, Murakami said. Other factors include natural variability and increased greenhouse gases.
The study also found that increased pollution in Asia could mean less hurricanes.
The earth system processes at work in the western North Pacific – an area where strong tropical cyclones are called typhoons - are the flip side of what’s happening in the Atlantic basin. The key ingredient for the decrease of tropical cyclones in the western North Pacific is also air pollution, according to the new research.
In this case, a 40-percent increase in the concentration of particulate air pollution has been one of several factors that has contributed to a 14-percent decrease in tropical cyclones, Murakami said. Other factors include natural variability and increased greenhouse gases.
How does reduced pollution in the Northern hemisphere lead to fewer tropical cyclones in the Southern Hemisphere?
The warming trend in the mid- and high-latitudes of the Northern Hemisphere has been changing largescale global circulation patterns, said Murakami. These changes have led to increased upward air flow in the Northern Hemisphere. This is causing a downward air flow in the Southern Hemisphere. This downward air flow comes with high pressure, which inhibits the formation of tropical cyclones.
The warming trend in the mid- and high-latitudes of the Northern Hemisphere has been changing largescale global circulation patterns, said Murakami. These changes have led to increased upward air flow in the Northern Hemisphere. This is causing a downward air flow in the Southern Hemisphere. This downward air flow comes with high pressure, which inhibits the formation of tropical cyclones.
What is the implication of the new research?
“This study indicates that decreasing air pollution leads to an increased risk of tropical cyclones, which is happening in the North Atlantic, and could also happen, if air pollution is rapidly reduced, in Asia,” said Murakami. “The ironic result suggests the necessity of careful policy decision-making in the future that considers the pros and cons of the multiple impacts.”
“This study indicates that decreasing air pollution leads to an increased risk of tropical cyclones, which is happening in the North Atlantic, and could also happen, if air pollution is rapidly reduced, in Asia,” said Murakami. “The ironic result suggests the necessity of careful policy decision-making in the future that considers the pros and cons of the multiple impacts.”