NOAA Study Shows Reduced Air Pollution Leads to Increase in Hurricanes

May 11, 2022

This afternoon I received an email from NOAA regarding some startling research in the area of ​​air pollution and tropical cyclones. This is a press release that is sure to spark conversation and maybe even controversy, as any discussion of the environment is often met with passion.

I want to share that with you in full below. But the simple conclusion is:

Less pollution in the northern hemisphere led to MORE tropical storms and hurricanes in the Atlantic.

Air pollution in North America and Europe is estimated to have dropped by 50% from 1980 to 2020. This is thought to have led to warmer ocean surface temperatures.

The opposite has been seen in Asia, where increased pollution has led to fewer tropical cyclones in the Pacific Northwest.

I know, that sounds crazy, and I think the researchers were surprised as well. This is by no means a suggestion to let air pollution get out of control again to calm the tropics. I’m fasting, there’s more I’d like to share. But note: the title of my article is very similar (just shorter) to the way they presented it.

Here’s the report as I received it, with an additional video embedded here for easy access.

Study: Reduced air pollution in North America and Europe yields unexpected result: more hurricanes
Research also finds that increasing pollution in Asia is reducing tropical cyclones

Contact
Monica Allen,
[email protected]202-379-6693

May 11, 2022

A new NOAA study published today in the journal Scientists progress about four decades of tropical cyclones reveals the surprising result that the reduction in 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. The study also found that the growth of particulate pollution in Asia has helped reduce the number of tropical cyclones in the western basin of the North Pacific.

“Air pollution is a significant environmental risk to human health, and we have made great strides in reducing health risks by reducing particulate air pollution,” said Hiroyuki Murakami, a physicist at the Dynamics of Dynamics Laboratory. NOAA Geophysical Fluids and author of the study. “But reducing air pollution doesn’t always reduce the risk of tropical cyclone hazards.”

A daylight composite of Earth from August 29, 2021 as seen by the NOAA-20 satellite. In this image, Hurricane Ida can be seen making landfall on the US Gulf Coast while Hurricane Nora orbits in the eastern Pacific Ocean. Credit: NOAA

While a number of recent studies have examined the impact of increasing greenhouse gas emissions on global tropical cyclone activity, Murakami addresses the less studied and highly complex area of ​​how the particulate pollution combined with climate change affects tropical cyclones in different regions of the planet. Murakami reaches these conclusions using the state-of-the-art climate model developed at NOAA GFDL.

How does less pollution in the northern hemisphere increase tropical storms in the Atlantic?

Over the past 40 years, Europe and North America have been leaders in reducing particulate air pollution from industry, automotive, energy and other sources. . The increasing absence of anthropogenic air pollution in the Northern Hemisphere, estimated to decline by 50% from 1980 to 2020, has led to a warming of the surface of 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. The warming Atlantic Ocean was a key ingredient in the 33% increase in the number of tropical cyclones over that 40-year period, Murakami said.

Decreasing pollution has also led to warming in mid and high latitudes in the northern hemisphere. This warming of land and oceans causes the constant poleward movement of the jet stream from the tropics to the Arctic. The shifting jet stream caused westerly winds to weaken in the upper troposphere of the Atlantic Tropical Basin, an area of ​​the atmosphere about 10 to 12 miles from the earth’s surface. Weaker winds, in turn, mean that there is less difference between the wind speeds in the lower and upper troposphere or less wind shear. With little wind shear, tropical cyclones can develop and strengthen over the Atlantic Ocean.

How does increased pollution in Asia reduce tropical storms in the western North Pacific?

Earth system processes at work in the western North Pacific — an area where powerful tropical cyclones are called typhoons — are the flip side of what’s happening in the Atlantic Basin. The key ingredient in diminishing 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 pollutant particles in the air was one of many factors that contributed to a 14% decrease in tropical cyclones, Murakami said. Other factors include natural variability and increased greenhouse gases.

Over the western North Pacific Ocean, increased air pollution from the rapidly developing economies of China and India has reduced the strength of Indian monsoon winds in summer . Increased pollution is cooling the land in East Asia, serving to reduce the difference between the temperature of the land and that of the ocean. Without this temperature contrast, monsoon winds become weaker. In general, tropical cyclones in Asia are born in the summer in what is called the monsoon trough, where the monsoon winds from the west of India converge with the trade winds from the west of the Pacific Ocean. . With weaker monsoon winds, there are fewer tropical cyclones.

How does reducing 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 altered large-scale global circulation patterns, Murakami said. These changes have resulted in increased updraft airflow in the northern hemisphere. This causes a downward airflow in the southern hemisphere. This downward airflow is accompanied by 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 occurs in the North Atlantic, and could also occur, if air pollution is rapidly reduced, in Asia,” Murakami said. “The ironic result suggests the need for careful policy decision-making going forward that considers the pros and cons of multiple impacts.”

Murakami added that the projection for the next few decades is that man-made particulate air pollution will remain stable in the North Atlantic and that increasing greenhouse gases will become a more significant influence on tropical cyclones. The projection is for fewer numbers of tropical cyclones, but those that do occur are likely to be more intense.

For more information:

Video

Also see the full report here: Highlights from NOAA’s Geophysical Fluid Dynamics Laboratory

Go online to read research in Science Advances, “Substantial Global Influence of Anthropogenic Aerosols on Tropical Cyclones Over the Past 40 Years.”

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