Title: Between Smoke and Dust: How uncertainties in absorbing aerosols limit our understanding of global climate.
Abstract: Atmospheric aerosols are an important component of the Earth system. Because these aerosols interact with radiation and clouds, uncertainties in aerosol forcing remain a significant contributor to the uncertainties associated with climate change projections. Among all aerosols species, the light-absorbing aerosols are critical to understanding the aerosol forcing on climate, because they can warm the atmosphere and offset the cooling effects by non-absorbing aerosols. Despite the importance of absorbing aerosols, climate models fail to accurately represent their properties, their vertical distributions, and the associated environment in which they occur in the atmosphere. In this seminar, I will focus on dust and biomass-burning (smoke) aerosols because they account for the majority of the absorbing aerosols in the atmosphere. First, since the largest smoke loading overlying a major low-level cloud is over the southeast Atlantic, I will also explore how the large-scale environment complicates the attribution of aerosol impacts over this region. Specifically, I will discuss how the presence of mid-tropospheric moisture reduces the radiative warming of the above-cloud smoke, thus affecting the aerosol semi-direct effect over the region. Second, I will explore the representation of dust aerosol properties in global models and how newly-developed observational constraints on dust properties further expose the discrepancies in the models. For example, I will show that the atmosphere contains about four times more coarse dust than global models simulate, which indicates that these models substantially underestimate the coarse dust radiative warming at the top of the atmosphere. Overall, I will show that constraints on small-scale properties to large-scale environments of absorbing aerosols are necessary to reduce the uncertainties of aerosol impacts on the global climate.