Constraints on Desert Dust Impacts on Climate Obtained by Leveraging Understanding of the Physics of Dust Emission

Desert dust aerosols are the most prevalent aerosol specie by mass, and affect Earth’s energy balance through direct interactions with radiation and indirect interactions with clouds, ecosystems, and the cryosphere. However, the magnitudes of these effects are so uncertain that it remains unclear whether atmospheric dust has a net warming or cooling effect on global climate. Consequently, it is still uncertain whether large changes in atmospheric dust loading over the past century have slowed or accelerated anthropogenic climate change, or what the effects of potential future changes in dust loading will be. Much of this uncertainty in dust radiative effects arises from uncertainty in the balance between cooling interactions by fine dust and warming interactions by coarse dust. In this talk, I use the analogy of dust emission with the fragmentation of brittle materials such as glass to constrain the size distribution of atmospheric dust, finding that emitted dust is substantially coarser than represented in models. By further leveraging constraints on dust abundance from satellites and dust lifetime from global model simulations, I constrain the size and prevalence of atmospheric dust. These results indicate that atmospheric dust is substantially coarser than represented in current global climate models. This implies that the global dust direct radiative effect is likely less cooling than the ~-0.4 Wm^-2 estimated by models in a current global aerosol model ensemble. Instead, I constrain the dust direct radiative effect to a range between -0.48 and +0.20 Wm^-2, which includes the possibility that dust direct radiative effects net warm the planet.