Scientists discovered an unexpected and problematic result of the US and Europe's decades-long efforts to reduce air pollution for the sake of public health and the environment: an increase in tropical storms in some areas.

According to a new study published in the journal Science Advances recently, a 50 per cent reduction in aerosols — tiny particles of air pollution — over North America and Europe over the past four decades has resulted in a 33 per cent increase in the number of tropical cyclones in the North Atlantic.

On the other hand, a 40 per cent rise in aerosol pollution in China and India during the same period resulted in a 14 per cent decrease in the number of tropical cyclones in the western North Pacific, the study said. Due to the countries' economic and industrial growth, air pollution in China and India increased significantly during that time.

Hiro Murakami, the lead author of the study and a scientist at the National Oceanic and Atmospheric Administration's Geophysical Fluid Dynamics Laboratory, said:

"Decreasing aerosol emissions is good for human health; but on the other hand, we found there are some bad effects when we reduce aerosol emissions — and that is hurricane activity."

Greenhouse gases aren't the same as aerosols. They are microscopic pollution particles that float in the air and, unlike carbon dioxide or methane, which absorb sunlight and cause warming, reflect sunlight to space, cooling the environment. Natural aerosols exist, but industrial smokestacks and car exhaust were major sources of pollution in the early to the mid-20th century.

Murakami discovered that as aerosol pollution dropped in the decades following the United States' Clean Air Act and similar European acts, the ocean was able to absorb more sunlight, resulting in warmer sea surface temperatures and more storms.

Murakami cautions that his findings do not imply that air pollution should be disregarded. He compared reducing aerosol emissions to stopping smoking. Giving up smoking improves one's health and reduces the risk of cancer. However, quitting smoking might have negative consequences, such as weight gain and stress.

He said, "Aerosol decreasing is similar. The aerosol decrease may lead to good health, but on the other hand, hurricane risk increases. This is where good things accompany bad things. It's kind of like pros and cons."

This study is crucial to help separate how storms respond to air pollution versus greenhouse gases, according to Jim Kossin, a senior hurricane scientist at the Climate Service who examined the data.

Kossin said, "Tropical cyclones are fairly random animals, and they respond to the random nature of the atmosphere at any given time. But certainly, this steady warming of the ocean that's been happening in the Atlantic because of the combination of greenhouse gas increases and the particulate pollution decreases has a profound effect — and the changes to the particulate pollution have a much more dramatic effect on the hurricanes."

Gabriel Vecchi, a professor of climate and geosciences at Princeton University, said:

"This study shows very nicely that the impact of aerosols is not isolated to the Atlantic, but involves a global shift in the distribution of tropical cyclones. Aerosols are among the most uncertain elements of the climate system, so I think that there should — and I predict there will — be follow-on studies that explore the sensitivity of the results to a range of aerosol-related uncertainties."

According to Murakami, aerosol pollution will remain stable, implying that greenhouse gas emissions will begin to exert influence on hurricanes over time, particularly on their strength.

Murakami said, "Climate science is very complex, and it's a work in progress, especially for hurricane activity. What we saw in the past 40 years may not be applied to the future, so we may see something much different."

Source: CNN