NOAA study finds reducing particulate air pollution in N America & Europe increases hurricanes in N Atlantic

The theme here is that aerosols have to some extent been having the opposite of the alleged effect of so-called greenhouse gases. This study, based on climate modelling, suggests at least some recent warming is linked to reductions in atmospheric aerosol content.
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A new NOAA study covering four decades of tropical cyclones found that reducing particulate air pollution in Europe and North America has contributed to an increase in the number of tropical cyclones in the North Atlantic basin and a decrease in the number of these storms in the Southern Hemisphere, says Green Car Congress.

The open-access study, published in Science Advances, also found that the growth of particulate pollution in Asia has contributed to fewer tropical cyclones in the western North Pacific basin.

While a number of recent studies have examined how increasing greenhouse gas emissions are impacting global tropical cyclone activity, Hiroyuki Murakami examined the less studied and highly complex area of how particulate pollution in combination with climate changes is affecting tropical cyclones in different areas of the planet.

Murakami reached these conclusions using the climate model developed at NOAA GFDL.

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% 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% 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 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% increase in the concentration of particulate air pollution has been one of several factors that has contributed to a 14% decrease in tropical cyclones, Murakami said. Other factors include natural variability and increased greenhouse gases.

Full article here.