Global warming can affect hurricanes, in part because a warmer ocean provides more energy to feed them. But that’s not the only factor at play: A study published Wednesday confirms that the effects of particulate air pollution are even greater for the frequency of hurricanes.
Over the past four decades, new research shows that declines in pollution in the form of small aerosol particles from transportation, power generation and industry in North America and Europe are responsible for an increased number of hurricanes and other tropical cyclones in the North Atlantic. .
During the same period, increased pollution from the growing economies of India and China had the opposite effect, reducing hurricane activity in the western North Pacific.
A growing body of research has shown links between tropical cyclones and global warming, which is the result of human-induced emissions of carbon dioxide and other greenhouse gases. A 2020 studyFor example, he has used observational data since the 1980s to show that hurricanes have become stronger and more destructive as the world warms and the oceans absorb more heat.
The new study looked at the number of such storms, not their strength. Its author, Hiroyuki Murakami, said it has shown that reducing or increasing anthropogenic aerosols is the “most important component” influencing frequency.
Scientist James P. Kossin of the Climate Service, who analyzes climate risks for companies and is an author of the 2020 study, told Dr. He said Murakami’s research is “consistent with other studies that show warming is much more effective by reducing regional pollution.” A profound effect on hurricane activity rather than warming of the ocean from increased greenhouse gases. The new study “attempts to provide a more global context in which regional climate changes occur,” he said.
study Published Wednesday in the journal Science Advances.
A physical scientist at the National Oceanic and Atmospheric Administration, Dr. Murakami Geophysical Fluid Dynamics Laboratory In Princeton, NJ, he used computer simulations to do what would be practically impossible in the real world: isolate the effects of pollutants like sulfur dioxide. These form aerosols, which are tiny particles that have been shown to be harmful to human health as a component of air pollution. They can also block some sunlight from reaching the Earth’s surface.
In recent years, aerosol pollution has decreased, maybe as much as 50 percent, as a result of laws and regulations reducing emissions from sources such as vehicles and power plants in North America and Europe. During roughly the same period in the North Atlantic, hurricane seasons have been more active with more storms than in previous decades.
Dr. Murakami found that the drop in aerosols in the North Atlantic led to warming, which had two effects on tropical cyclones. First, less pollution caused more ocean warming, which meant there was more energy for storms to form.
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The reduction in pollution also led to the warming of the soil, and the combined warming affected the atmospheric circulation, weakening the winds in the upper atmosphere. This in turn led to less wind shear, changes in wind speed and direction that could affect how cyclonic storms develop. Less wind shear meant that storms formed more easily.
Dr. Murakami’s simulations showed a different mechanism at work in the Pacific. There, he found that increased aerosol pollution, largely from China and India, was causing the land surface to cool. This reduced the temperature difference between land and ocean and weakened the monsoon winds that developed there. This, in turn, has led to fewer tropical cyclones, including typhoons, the Pacific equivalent of hurricanes.
Adam Sobel, a climate scientist at Columbia University, said the new study shows what other studies have shown, “aerosol cooling” in the western North Pacific. compensating for greenhouse gas warming” Just as in North America and Europe, this will likely change as governments in Asia take action to reduce pollution. effects on health.
Dr. Murakami said his work points to the challenges these governments will face as they act to reduce pollution, as this will likely lead to increased numbers of storms.