Aerosols directly impact the Earth’s radiative balance through scattering and absorption of (mostly) solar radiation. Scattering aerosols generally impart a radiative cooling impact on climate. Absorbing aerosols, such as black carbon, however, heat the atmosphere, and depending on the surface albedo, can radiatively warm or cool the climate system. Atmospheric heating by absorbing aerosols leads to the so-called thermodynamic “semi-direct” effect, in which clouds are decreased and relative radiative warming occurs. Regional-scale aerosol heating can also lead to circulation changes that may increase or decrease clouds.
We will examine the effects of aerosol absorption on climate using the NASA Goddard Observing System version 5 (GE0S-5) atmospheric circulation model coupled to the GOCART aerosol model. This model includes direct and semi-direct aerosol effects, but excludes aerosol interactions with cloud microphysics. First, we will compare and contrast the climate response to forcing from anthropogenic and biomass burning aerosols to forcing by natural (dust and sea salt) aerosols. We will show the opposite nature of the response to the more absorbing anthropogenic aerosol relative to the more scattering natural aerosol. Next, we will show how increasing dust aerosol absorption improves dust transport over the north Atlantic. Finally, we will show preliminary results from a study examining the effect of biomass burning aerosol absorption on temperature tendencies over southern Africa. In this work, we use the data assimilation capabilities of GEOS-5 to constrain aerosol distributions (by imposing assimilated meteorology) and evaluate their effect using the analysis update tendencies.