Concentrations of fine particles in the stratosphere can influence the occurrence and severity of the Sahelian drought, according to work published online in Nature Climate Change this week. Analysis of historical observations, from 1900 to 2010, shows substantial Northern Hemisphere volcanic eruptions preceded three of the four driest summers.

Using this knowledge, Jim Haywood and colleagues modelled episodic volcanic eruptions, as well as continuous injection of particles into the stratosphere to mimic geoengineering. They show that heavy aerosol loadings in the Northern Hemisphere are a precursor to Sahelian drought, whereas Southern Hemisphere loading results in increased rainfall and greening.

These findings suggest that further study is needed to assess possible impacts before consensus on the global governance of any future aerosol geoengineering projects can be reached.