Air pollution causing stronger cyclones

Natural differences in wind speed and direction over different heights in the atmosphere, known as 'wind shear', normally keep cyclones in check by effectively tearing the storms apart before they reach a certain size.

But emissions from sources such as biomass burning and diesel vehicles have interfered with wind patterns, reducing wind shear and enabling cyclones to grow twice as intense.

Researchers compared cyclones that occurred between 1979 and 1996 with those between 1997 and 2010. They found that the more recent ones were up to 3 times more intense, with higher wind speeds and five of the strongest storms during the period occurred after 1998.

Aerosol emissions in the region have grown six-fold since the 1930s, creating a 3 km thick layer of pollution over the Indian Ocean, known as the South Asian atmospheric brown cloud, which absorbs sunlight, causing the ocean to cool and affecting wind circulation.

It was already known that soot pollution interferes with monsoons and even causes warming in the region.

"We are showing that pollution from human activity, as simple as burning wood or driving a vehicle with a diesel engine, can actually change these massive atmospheric phenomena in a significant way. It underscores the importance of getting a handle on emissions in the region," said Evan, author of the study and a researcher at the University of Virginia, United States.

The historical tropical cyclones in the Arabian Sea that were very intense made landfall in India, Pakistan, Oman, and Iran, in each case with tremendous destruction and loss of life.

Ainun Nishat, vice chancellor of BRAC University, Bangladesh, said that the number of disasters caused by cyclones outside the monsoon period in South Asia has increased significantly in recent years.

"The intensity of cyclonic wind in the Bay of Bengal has increased a lot, which we noticed in cyclones such as Sidr and Aila, both of which caused a lot of destruction."

Source: Scidev