Modeling Impacts of Dust Mineralogy on Earth’s Radiation and Climate

Mineralogical composition drives diverse dust impacts on Earth’s climate systems. However, most climate models still use fixed dust mineralogy, without accounting for its temporal and spatial variation. To quantify the radiative impact of resolving dust mineralogy on Earth’s climate, we implement and simulate the distribution of dust mineralogy (i.e., illite, kaolinite, smectite, hematite, calcite, feldspar, quartz, gypsum) in the GFDL AM4.0 model. Resolving dust mineralogy reduces dust absorption and achieves improved agreement with observation-based SSA, radiative fluxes from CERES (the Clouds and the Earth’s Radiant Energy System), and surface temperature from CRU (Climatic Research Unit). It also results in distinct radiative impacts on Earth’s climate over North Africa during the JJA (June-July-August). Over the 19-year (from 2001 to 2019) modeled results during JJA, it leads to a reduction of over 50% in net downward radiation across the Sahara and approximately 20% over the Sahel at top of atmosphere (TOA). The reduced dust absorption weakens the atmospheric warming effects of dust aerosols and leads to an alteration in land surface temperature, resulting in a decrease of 0.4K over the Sahara and an increase of 0.6K over the Sahel. The less warming in the atmosphere suppresses ascent motion and weakens the monsoon for the Gulf of Guinea. This brings less moisture to the Sahel, which combined with decreased ascent motion induces a reduction of precipitation. Interestingly, we found similar results by simply fixing the hematite content of dust to 0.9%, which is considerably more efficient than simulating all minerals. Nevertheless, incorporating dust mineralogy in models is likely to be important in other aspects, such as cloud properties, ocean biogeochemistry, air quality, and photochemistry. When incorporating dust mineralogy, we demonstrate that the number of mineral tracers can be reduced by combining clay minerals (i.e., illite, kaolinite, and smectite), excluding externally mixed hematite and gypsum. This reduction in degrees of freedom does not compromise the quality of comparison with observations.