Increased air pollution over South Asia may be responsible for an increase in the intensity of pre-monsoon tropical cyclones over the Arabian Sea, research in this week’s Nature indicates. Most Arabian Sea tropical cyclones make landfall, causing considerable damage, so these results highlight a potential additional human health impact from regional air pollution.

Amato Evan and colleagues report an increase in the intensity of pre-monsoon Arabian Sea tropical cyclones over the past thirty years, and especially over the past decade. They show that this change is associated with a simultaneous increase in local emissions of black carbon and other aerosols. These emissions alter the atmospheric circulation over the Arabian Sea, decreasing the vertical wind shear and thereby creating an environment more favourable for tropical cyclone intensification. Strong vertical wind shear can limit the formation and intensity of tropical cyclones.

The authors suggest that reducing emissions could have a nearly immediate effect on the tendency of pre-monsoon tropical cyclones to reach their maximum potential intensity. However, the conclusions are based on the limited number of intense tropical cyclones that occurred over the study period. Further work will be required to confirm the proposed relationship between aerosols and cyclone intensity.