Aerosol particles from human activities could have lowered the number of tropical storms over the Atlantic Ocean during the twentieth century.

Natural aerosols such as dust particles are thought to influence hurricane activity, but the effects of anthropogenic aerosols are unclear. A team led by Nick Dunstone at the Met Office Hadley Centre in Exeter, UK, modelled the frequency of North Atlantic tropical storms with simulations that either incorporated or excluded changes in man-made aerosols. The model suggests that as levels of anthropogenic aerosols increased in the earlier part of the century, tropical storm activity dropped; aerosol declines at the end of the century increased storms.

The authors attribute this to the effect of aerosols on clouds. By brightening clouds and causing them to stick around for longer, aerosols cool surface temperatures and shift circulation patterns in a way that suppresses hurricanes.

Nature Geosci. http://dx.doi.org/10.1038/ngeo1854 (2013)