The Lamont-Doherty group that has done so much to help our understanding of the factors that drive multi-decadal droughts has added a nice piece to our understanding of the issues.
In a paper in review (for which they’ve done a nice accessible writeup), Ben Cook and colleagues looked at a number of drivers for long-duration drought: sea surface temperature, warming caused when grasses die off and leave bare soil, and then the added role of increased aerosols from dust kicked up in the ensuing mess.
The addition of active dust sources led to dust emissions and significant aerosol loading that further decreased precipitation relative to the case with SST and bare soil forcing alone. Active dust emission from the dunes also increased the persistence of the megadroughts making them more in agreement with tree ring evidence of the character of the megadroughts. In the model dust aerosols suspended in the atmosphere reflect solar radiation reducing energy available at the surface increasing atmospheric stability and reducing upward motion and convection. This suppresses precipitation.