Paleoclimate proxies suggest that modern droughts in North America pale in comparison to those of the Early to Mid-Holocene and the Medieval Warm Period. Modeling studies show that both tropical SSTs and local dust feedbacks modulate drought conditions over North America. We hypothesize that during the Early to Mid-Holocene, these effects combined to create severe droughts that are far larger than observed during the modern historical period. The NCAR Community Earth System Model (CESM) is used to examine the role of tropical North Atlantic (TNA) SSTs and dust changes over both North Africa and North America on North American rainfall variability. The atmospheric model (Community Atmosphere Model version 5) includes an interactive dust aerosol model with updated optics and size distributions and is capable of simulating both the dust direct effects on radiation and indirect effects on cloud properties. In our preliminary Preindustrial control simulations, though warming of the TNA results in drying over most of North America, dust enhances precipitation likely through the ‘elevated heat pump’ mechanism. This suggests, in contrast with earlier studies, that dust suppresses rather than amplifies past North American droughts.
Goes, L. M., Perlin, N., and Clement, A. C., “Evaluating the roles of tropical North Atlantic SSTs and local and remote dust impacts on North American drought”, vol. 2019, 2019.