It's pretty well established that air pollution can influence local weather. Now a new study in Nature shows that recent increases in the intensity of tropical cyclones in the Indian Ocean may be a side-effect of increasing air pollution over South Asia.
These changing circulation patterns have been linked with increase aerosols in the atmosphere -- that is, more particulate pollution from coal burning, cooking fires, older diesel engines. The smog thus created, 1.9 miles thick in places, can weaken wind patterns and alter rainfall patterns.
Until recent decades, cyclones in the Arabian Sea tended to be relatively weak storms. This was attributed to a naturally occurring vertical wind shear over the sea, which tended to weaken and ultimately break up developing storms. But the study's investigators have found that wind circulation patterns over the Arabian Sea are changing, reducing vertical wind shear and allowing stronger storm development. (Science Daily)
Study lead author Amato Evan, from the University of Virginia, says the changes in circulation allowing the cyclones to intensify is a "fairly recent change." Evan notes, "The only thing that's been systematically changing in this part of the world is pollution. There's been a huge growth in pollution from human activity from the Indian subcontinent over the last 60 years or so, a six-fold increase in emissions of pollutions [sic] like black carbon and sulfates."
Important to note: Black carbon pollution and sulfate pollution have opposite effects on global warming. Black carbon pollution has been shown to increase warming, contributing significantly to glacier melting in the Himalayas. Sulfate pollution masks warming, scattering solar radiation.
Remember that along with that particulate pollution, greenhouse gas emissions have been rising as well. This too is having an impact on the weather of South Asia and the arrival and intensity of the monsoon -- something which is likely to increase as the planet continues to warm.